Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
358 PM EDT Tue Apr 01 2025

Valid 00Z Wed Apr 02 2025 - 00Z Fri Apr 04 2025

...Significant, life-threatening, and potentially catastrophic flash flood
event begins Wednesday for the Lower Ohio Valley and Mid-South...

...Severe weather threat shifts from the central/southern Plains this
evening to the Midwest and Middle/Lower Mississippi Valley Wednesday...

...Another late season winter storm for the Northern Plains into the Upper
Midwest/Great Lakes through Wednesday with heavy snowfall expected...

...Unsettled weather continues over the West as an upper-level trough
passes over the region...

...Critical Risk of fire weather for portions of the central/southern High
Plains and Southwest through Wednesday...

A potent Spring storm will bring the threat of significant,
life-threatening, and potentially catastrophic flash flooding, widespread
severe weather, and impactful winter weather to portions of the
Plains/Mississippi Valley/Midwest this week. An energetic upper-level
trough will deepen over the Intermountain West as an accompanying surface
low and frontal system strengthens in the lee of the Rockies through this
afternoon and evening. As the developing surface cyclone ejects into the
central Plains, moist southerly return flow will intensify and bring
increasingly unstable air into the region. Combined with strong
atmospheric dynamics and wind fields associated with the trough and
surface low, the risk of thunderstorms and severe weather will steadily
increase across the central/southern Plains. The Storm Prediction Center
has maintained an Enhanced Risk (level 3/5) for the threat of very large
hail, damaging winds, and several tornadoes, some of which could be
strong, especially during the late evening hours. In addition, expanding
storm coverage and the potential for heavy downpours may also lead to some
isolated instances of flash flooding through tonight. Then, on Wednesday,
the progression of the system will begin to slow heading into the
Midwest/Mississippi Valley, especially with southward extent, as an
upper-level ridge builds over the southeastern U.S. More widespread storms
are expected in the warm sector ahead of the cold front with an increasing
tendency for storms to cluster/repeat over the same regions by Wednesday
evening as the progress of the cold front slows. This is most likely to
occur along an axis from the Lower Ohio Valley southwestward through the
Mid-South. Increasing moisture pooling ahead of the cold front will also
lead to more intense downpours following another day of return flow on
Thursday. A Moderate Risk of Excessive Rainfall (level 3/4) remains in
effect for the region as this will be the beginning of a multi-day
significant, life-threatening flash flood event. On Thursday, the existing
Moderate Risk was upgraded to a High Risk (level 4/4) for portions of
southeast Missouri, southern Illinois, western Kentucky, and northwest
Tennessee given increasing confidence of potentially catastrophic impacts
from flash flooding and river flooding. While the placement of the cold
front and exact axis of heaviest rainfall is likely to change somewhat as
the event nears, several inches of heavy rain are probable, with some
locations potentially seeing amounts in excess of 10" over the next 7
days. Widespread severe weather is also expected Wednesday across much of
the Midwest/Ohio Valley southwest through the Mid-South, ArkLaTex, and
North Texas. A broad Enhanced Risk covers the region for the growing
potential of very large hail, significant damaging winds, and strong
tornadoes, but the greatest threat lies from the Lower Ohio Valley to the
Middle Mississippi Valley where the Storm Prediction Center has upgraded
to a Moderate Risk (level 4/5).

Beyond the flash flood and severe weather threat, a late-season winter
storm is also forecast in the colder air to the north of the system across
portions of the Northern Plains and Upper Midwest. Snow has already begun
and will continue to increase in coverage and intensity through this
evening, lasting through Wednesday night, as the system intensifies and
lifts northeastward through the region. An axis of heavy snow is forecast
along and to the north of the surface low track from the eastern Dakotas
east through central/northern Minnesota and into northern Wisconsin. Storm
total snowfall of 4-8 inches, locally higher, is expected. Gusty winds may
lead to areas of blowing snow and difficult travel conditions. A wintry
mix of sleet and freezing rain is expected just to the southeast of the
heavy snow from central Minnesota/Wisconsin east into the LP of Michigan.
A leading shortwave ahead of the system will also bring wintry mix to the
interior Northeast/New England on Wednesday with precipitation beginning
as snow/freezing rain before changing over to mostly rain as warmer air
reaches the region. Some light to moderate snow and ice accumulations are
possible for higher elevations and portions of northern Maine.

In the West, coastal rain, an interior lower elevation wintry mix, and
heavy higher elevation snow continue as the noted upper-level trough
slowly pivots over the region. Moderate to locally heavy rainfall will
continue along portions of the West Coast, especially along the coastal
ranges of northern California into far southern Oregon. Precipitation
across lower elevations of the interior from the Great Basin east into the
northern/central Rockies should remain very light with little to no snow
accumulations. Very heavy snowfall continues across the regional mountain
ranges, especially for the Sierra Nevada and the northern/central Rockies.
Additional snowfall totals of over foot are expected, with 1-4 feet
possible for the Sierra Nevada. Snowfall should come to an end for
California and western areas of the Great Basin by Wednesday while
lingering for the eastern Great Basin and northern/central Rockies. The
potent upper-jet accompanying the trough as it dives south and eastward
over the West and into the central U.S. will also bring very strong winds
with gusts upwards of 50-60 mph from southern California and the Southwest
east into the southern Rockies and the Plains. Warm temperatures and very
dry antecedent conditions on top of the high winds have prompted the Storm
Prediction Center to highlight a Critical Risk of fire weather conditions
for portions of the central/southern High Plains and Southwest through
Wednesday. Dust storms will also be possible.

An amplifying pattern will bring increasingly warmer/above average
conditions across the south-central and eastern U.S. while temperatures
remain cooler and below average under the upper-level trough over the
West. High temperatures in the 70s and 80s across the Southeast and
central/southern Plains this afternoon will spread into the Midwest by
Wednesday, followed by the Eastern U.S. on Thursday. Prior to the arrival
of the unseasonable warmth, highs in the Mid-Atlantic and Northeast will
generally be near to below normal, especially with northward extent. North
of the surface low track, high temperatures will remain quite cool across
the northern Plains and Upper Great Lakes through Thursday. With respect
to seasonal averages, the coldest departures from normal across the U.S.
will generally reside along and west of the Continental Divide given
plentiful clouds and precipitation chances the next few days.


Miller/Putnam


Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 1 2025

Valid 12Z Fri Apr 04 2025 - 12Z Tue Apr 08 2025


...Multi-day and potentially catastrophic heavy rain/flooding and
severe threat likely for Lower/Middle Mississippi, Tennessee, and
Ohio Valleys through next Saturday...


...Overview...

The medium range upper pattern will be amplified and quite stormy
this week. A wavy frontal boundary settling from the Ohio Valley
to Southern Plains, holding in between an amplified western trough
and strong Atlantic to Gulf upper ridge, will continue to be the
focus for an ongoing multi-day heavy rain and severe weather event
from the Lower Mississippi Valley to the Ohio Valley, which starts
during the short range period. Significant to catastrophic
flooding and flash flooding is increasingly likely for portions of
this area. A gradually amplifying Canada into northern U.S. upper
trough nearing the East into Monday and eventual southern stream
energy ejection and phasing will finally help to push out the
frontal boundary. Most of the West this week should stay relatively
cool underneath persistent troughing with some progression
eastward early next week into the Central U.S., while upper ridging
brings a warming trend to the Northwest during the weekend. The
East will see above normal temperatures late this week and then a
cooler trend that moves in from the north and west. Detailed WPC
forecasts are linked below.

...Guidance/Predictability Assessment...

Latest model guidance agrees fairly well on the main aspects of
the forecast through medium range time scales and have good
ensemble and machine learning model support. There are
differences still with some embedded lower predictability details,
which would have sensible weather impacts. Shortwaves and energy
perturbations exiting that trough show more spread, and will play a
role in exactly where the heaviest rainfall occurs. Either way,
models have been extremely consistent in showing a significant
flooding event from the lower Mississippi Valley to the Ohio
Valley. One aspect of the machine learning models to consider is
their depiction of a slightly narrower axis of heaviest rainfall on
a given day, albeit with locally higher amount potential daily
compared
to the NBM. WPC QPF was trended in this manner.

Energy digging through the western trough heading into the weekend
should with lingering uncertainty eventually interact with a more
amplifying northern stream upper trough into next weekend to
eventually help push the wavy front and heavy rain threat eastward.
This shortwave should amplify over the East by early next week.
There are some differences in the weekend interactions between this
shortwave and western U.S. energy and then timing of surface low
pressure/cold front through the East next week. Any leftover
troughing over the West should weaken and shift east as an upper
ridge moves into the Northwest next Monday-Tuesday.

Overall reasonable GFS/ECMWF/UKMET/Canadian guidance clustering
and continuity aspects allowed for usage of a composite model blend
through medium range timescales to produce a solid starting
forecast basis in line with the NBM. This solution plan maintains
good WPC product continuity and consistent hazards messaging.

...Weather/Hazards Highlights...

It generally still remains the case that by Friday, a wavy frontal
boundary will be stuck between a strong upper ridge to the east
and amplified troughing over the West. Moist and unstable inflow
pooling along the front will lead to widespread flash flooding
concerns which should begin during the short range period and
continue through about Saturday. For several days now, models have
been indicating several inch rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals in excess of
5-8 inches could be realized in some spots (and this is on top of
multiple inches of rainfall in the short range as well). For
Friday, the heaviest rainfall axis looks to be from eastern
Oklahoma northeastward into the Ohio Valley, with some slight shift
to the east by Saturday, but there has been some wobble in exactly
where the heaviest rain sets up. Regardless, the potential for
high impact and life-threatening flash flooding is there. As such,
moderate risks are in place for this general region for both the
Day 4/Friday and Day 5/Saturday ERO periods. High Risks upgrades
may well occur in future EROs as details become clearer, especially
into the timeframe of the CAMs. This would be consistent with
highly anomalous and protracted IVT/ARI values and training risks.
By Sunday, the heavy rain threat should finally begin to shift
eastward with moderate to heavy rains possible across the Gulf
Coast states into the Tennessee Valley/Southeast, and rainfall
farther north into the Mid-Atlantic and Northeast near the front.

Out West, an upper low dug into the Southwest into Friday/Saturday
is expected to lead to enhanced precipitation totals across the
southern and central Rockies and Plains. Snow is likely in higher
elevations of the Rockies in Colorado and northern New Mexico, with
uncertainty on how much snow could spill into lower elevations of
the High Plains as enhanced by cooled post-frontal upslope flow.
Elsewhere by Monday, a cold upper trough reaching the Great Lakes
should lead to unsettled weather over the region with rain or snow.

Meanwhile upstream, upper shortwave/front expected to reach the
West Coast into early next week offers seemingly modest moisture
transport, but will likely bring some light to terrain enhanced
moderate activity to western Washington/Oregon and northwestern
California, with decreasing amounts inland over the Northwest.

Above normal temperatures will linger across much of the East
through the weekend with daytime highs 10 to 20 degrees above
normal. Best potential for daily records will be across the
South/Southeast into southern Mid-Atlantic. Temperatures should
moderate early next week as the upper ridge shifts eastward and
troughing moves into the East. Meanwhile, the West should stay
cooler underneath upper troughing through Friday. By next weekend,
temperatures may moderate somewhat along the West Coast while
eastern Pacific upper ridging moves in. Parts of the Northwest
could see highs reach up to 10 to 15 degrees above normal which
eventually expands into the northern Plains next week. This shifts
cooler temperatures eastward, and daytime highs across parts of the
southern Rockies and High Plains could be 10 to 25 degrees below
normal next weekend. Below normal temperatures also shift into the
central U.S. and Midwest by next Monday, including highs as low as
10 to 15 degrees below normal over the Great Lakes/Ohio Valley.

Santorelli/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
324 AM EDT Tue Apr 1 2025

Valid 00Z Wed 02 Apr 2025 - 00Z Wed 09 Apr 2025

An upper low to the north and west of Hawaii will linger for a
day or two before beginning to lift away. The cold front for this
system will approach and swing through the northern islands
allowing for strengthening southerly winds and some increased
precipitation chances. Guidance shows the heaviest precipitation
should remain west of the island chain though. By later in the
week and next weekend, surface high pressure should move in north
of the state allowing for a more typical trade wind pattern.


Santorelli

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Apr 1 2025
Day 1
Valid 01Z Wed Apr 02 2025 - 12Z Wed Apr 02 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL PLAINS...

01Z Update: Minor modifications were made to the Day 1 ERO, based
on the latest observational/mesoanalysis trends and more recent
HRRR and WoFS guidance. The Slight continues with minor adjustments
across across northeast KS, far southeast NE, and northern MO. Recent
RAP runs continue to show the nose of 2000+ J/Kg nudging into the
Slight Risk area after 03Z, coinciding with the highest HREF 1-3hr
rainfall exceedance probabilities.

Hurley

16Z Update: Upon examination of the 12Z CAM guidance suite and in
consultation with the affected WFOs, a Slight Risk is now in effect
across extreme northeast Kansas, extreme southeast Nebraska, and
portions of northwest Missouri. A nocturnal MCS is likely to
develop to the northeast of the main surface low across central
Kansas, with the CAM guidance in agreement on indicating a band of
heavy convection with short term training potential, mainly during
the 3Z to 12Z time period. Three-hourly HREF neighborhood
probabilities of flash flood guidance exceedance are on the order
of 15-30 percent across portions of this region, with rainfall
totals up to 3 inches possible by 12Z and 1-2 inch per hour rates
possible. The MCS should weaken and become more progressive after
12Z Wednesday. Otherwise, the forecast remains on track and the
previous discussion is appended below for reference. /Hamrick

Hamrick

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Apr 1 2025
Day 2
Valid 12Z Wed Apr 02 2025 - 12Z Thu Apr 03 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM EASTERN
ARKANSAS TO SOUTHERN INDIANA...

19Z Update: The overall forecast remains in good shape compared to
the overnight issuance with only some minor adjustments needed. The
12Z CAM guidance generally has the heaviest QPF signal on the
southern edge of the MCS events that will develop along the stalled
out frontal boundary, and combining this fact along with historical
trends for max QPF to occur slightly south of the multi-model
consensus in many cases, the updated Marginal Risk area was
adjusted to the southeast by about a row of counties across western
Tennessee, western Kentucky, and eastern Arkansas. The HREF flash
flood guidance exceedance probabilities are generally highest
during the 00Z to 9Z time period Thursday, when multiple rounds of
training convection are expected to produce widespread 2 to 4 inch
rainfall totals, with isolated 4 to 6 inch totals possible. It
appears more likely the 3-hourly guidance values will be exceeded
compared to the 1-hourly guidance, so this will likely be more of
a prolonged duration event. This will also saturate the soils and
elevate stream and river flows ahead of the additional heavy
rainfall expected during the Day 3 period 12Z Thursday to 12Z
Friday, with a major flooding event looking more likely. The
previous forecast discussion from overnight is appended below for
reference. /Hamrick
-------------------


The D2 period will represent the initial stages of a prolonged
heavy rain event that will reside over the Lower Mississippi and
Ohio Valleys with a multitude of frontal waves riding along a
persistent quasi-stationary front that will undulate at times when
interacting with the aforementioned surface waves. The general
longwave pattern will become increasingly favorable for a "highway"
of moisture and mid-level impulses to eject northeastward out of
the southern Rockies/Plains and up through the Mississippi and Ohio
Valleys beginning Wednesday afternoon, onward. The consensus among
all ensembles and much of the deterministic fields are the first
wave of the pattern to maneuver over the mid-Mississippi Valley
around the base of a broad trough located over the Plains/Midwest
creating ample surface-based ascent to couple with the powerful
upper jet component situated over the Central CONUS in response to
the evolving pattern the day prior.

At the surface, a cold front will run into a stout western ridge
extension from a surface high located over the Western Atlantic
into the Canadian Maritimes. The pattern essentially comes to a
stalemate thanks to an expected +2 to +3 standard deviation height
anomaly centered over the Western Atlantic. This ridge will counter
the deepening trough over the Central U.S. creating a funneling
affect for deep moisture advection through the Mississippi and Ohio
Valley's, along with ample mid-level impulses that will be preside
over the same areas. The gridlocked setup will create a formidable
moderate to heavy rain event across the above areas with
depictions from guidance indicating a widespread 2-4" with some
areas exceeding 5" increasingly likely within the corridor impacted
by the multitude of convective elements spawning southwest to
northeast in proxy to the quasi- stationary front.

Latest prob fields based within the NBM blend and relevant EC/GEFS
ensembles signal a high likelihood of totals >3" over the span of
18z Wed to 12z Thu with more rain continuing beyond the D2 period.
The maxima is focused within a narrow corridor from central and
northeast AR up through the mid-Mississippi Valley encompassing far
southeastern MO, western KY, and southern IN with the probability
for >2" running between 60-80% and >3" settling between 40-60%
without a full implementation of the CAMs into the blend. Rainfall
rates will be generally between 1-2"/hr at peak intensity when
assessing the current HREF/NBM outputs, however, there's a chance
for higher rates located within the southwestern flank of the
stationary boundary (Much of Arkansas up into western KY) as
assessment of the PWAT advection regime signals potential for
localized PWATs exceeding 2" at times during organized convection.
Historically, this tends to lead to locally higher rates with
prospects of 2-3"/hr possible, especially when accounting for
intra-hour rates during maturing convection. In all, the setup is
very much conducive for substantial rainfall totals in a span of
12-hrs that will allow for high flash flood concerns within urban
zones and an increasing potential for significant flash and river
flooding outside those areas just due to the overall QPF footprint
anticipated.

This is an increasingly significant setup approaching with
potential for high impacts and life-threatening flash flooding
spanning the course of several days. Be sure to prepare if you live
in a flood zone anywhere from Arkansas, northeast through the
Ohio/Tennessee Valley's. Anyone surrounding will want to monitor
this setup closely as small changes could have heightened impacts
given the forecasted setup.

Kleebauer

Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Tue Apr 1 2025
Day 3
Valid 12Z Thu Apr 03 2025 - 12Z Fri Apr 04 2025

...THERE IS A HIGH RISK OF EXCESSIVE RAINFALL FOR EXTREME SOUTHEAST
MISSOURI TO WESTERN KENTUCKY WITH MAJOR FLOODING EXPECTED...

20Z Update: Major and potentially catastrophic flooding is
becoming more likely across portions of the Mid-South from
northeastern Arkansas to western Kentucky, including portions of
northwestern Tennessee and southeastern Missouri. Very heavy
rainfall in the 12 hours preceding this time period will greatly
saturate the soils over the region and thus dramatically reduce
flash flood guidance, which will easily be exceeded Thursday into
Thursday night. There is strong model consensus for several inches
of additional rainfall during the Day 3 period over many of the
same areas. Additional shortwave energy tracking along the stalled
out frontal boundary will serve as forcing mechanisms for more MCS
activity with multiple rounds of convective training likely, with
rainfall rates exceeding an inch per hour for potentially multiple
consecutive hours. Major rises on area creeks and streams are
expected. After consultation with the affected field offices, river
forecast centers, and the National Water Center, a High Risk area
has been introduced for this update. The previous forecast
discussion is appended below for reference. /Hamrick
------------------


The D3 period is a general extension of the D2 time frame with the
synoptic scale pattern yielding very little difference in what is
driving the setup. The biggest change from day to day with the
positioning of the quasi-stationary front will be the northern
extent becoming a bit more elongated from west-southwest to east-
northeast as we move through KY leading to a better push of
moisture and surface based ascent focused across more of the
western 1/3rd of KY up through the Ohio River basin. This will
encompass areas like Louisville to Cincinnati that might be on the
edge of the heavier QPF footprint on D2, but will be within the
northern periphery of the heavier precip come D3. The key to the
extent of the significant flood prospects will be where the D2 and
D3 overlap in the overall QPF distribution. There is a considerable
probabilistic output within the 01z NBM for D3 totals to exceed 2"
with a wide swath of 60-80% probs for the threshold situated from
southwest AR all the way up through southern OH, an area that will
experience significant rainfall the period prior. The 72-hr
probability for >6" of total rainfall is between 30-60% across
northeast AR up through northwest TN and western KY with the max
prob field positioned between Paducah, KY down to Jonesboro, AR.
This corridor is located within a notorious flood plane thanks to a
litany of streams and river channels with the Mississippi River the
main stem that bisects the region.

The forecasted surface wave in question is well-defined when
assessing the global deterministic 500mb vorticity pattern. A
developing 250mb jet coupling is also being orchestrated by some
of the global deterministic with, at minimum a substantial right-
entrance region jet dynamic well- positioned over much of the
Mississippi Valley. This setup is textbook for a continuation of
the "meteorological highway" of moisture and mid-level vorticity
advection that historically has caused significant flash flood
issues over the Lower Mississippi and Ohio Valley's. This is only
day 2 of the forecasted 4 day event, so the priming of soils will
have been underway and only getting worse as time moves on.

The previous MDT risk inherited from the D4 was relatively
maintained, however there was some expansion of the MDT to the
northwest to account for a small trend within the forecasted
alignment of the quasi-stationary front and amplitude of expected
surface wave ejecting out of the southern plains. This period is
considered to be a higher-end Moderate, meaning the prospects for a
targeted high risk are within reason pending the previous period's
QPF outcome and the convective expectation as we get closer to the
D3 time frame. The area of vested interest for a potential upgrade
includes that corridor of northeast Arkansas up through western
Tennessee, far southeast Missouri, western Kentucky, and slivers of
both southern Illinois and Indiana.

This setup is shaping up to be a more extreme flooding scenario
considering the multi-day prospects and forecasted 72 to 96 hr
rainfall totals reaching 10-15+ inches in the hardest hit
locations. Be sure to prepare if you live in a flood zone anywhere
from Arkansas, northeast through the Ohio/Tennessee Valley's.
Anyone surrounding will want to monitor this setup closely as small
changes could have heightened impacts given the forecasted setup.

Kleebauer

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 1 2025


It generally still remains the case that by Friday, a wavy frontal
boundary will be stuck between a strong upper ridge to the east
and amplified troughing over the West. Moist and unstable inflow
pooling along the front will lead to widespread flash flooding
concerns which should begin during the short range period and
continue through about Saturday. For several days now, models have
been indicating several inch rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals in excess of
5-8 inches could be realized in some spots (and this is on top of
multiple inches of rainfall in the short range as well). For
Friday, the heaviest rainfall axis looks to be from eastern
Oklahoma northeastward into the Ohio Valley, with some slight shift
to the east by Saturday, but there has been some wobble in exactly
where the heaviest rain sets up. Regardless, the potential for
high impact and life-threatening flash flooding is there. As such,
moderate risks are in place for this general region for both the
Day 4/Friday and Day 5/Saturday ERO periods. High Risks upgrades
may well occur in future EROs as details become clearer, especially
into the timeframe of the CAMs. This would be consistent with
highly anomalous and protracted IVT/ARI values and training risks.
By Sunday, the heavy rain threat should finally begin to shift
eastward with moderate to heavy rains possible across the Gulf
Coast states into the Tennessee Valley/Southeast, and rainfall
farther north into the Mid-Atlantic and Northeast near the front.

Out West, an upper low dug into the Southwest into Friday/Saturday
is expected to lead to enhanced precipitation totals across the
southern and central Rockies and Plains. Snow is likely in higher
elevations of the Rockies in Colorado and northern New Mexico, with
uncertainty on how much snow could spill into lower elevations of
the High Plains as enhanced by cooled post-frontal upslope flow.
Elsewhere by Monday, a cold upper trough reaching the Great Lakes
should lead to unsettled weather over the region with rain or snow.

Meanwhile upstream, upper shortwave/front expected to reach the
West Coast into early next week offers seemingly modest moisture
transport, but will likely bring some light to terrain enhanced
moderate activity to western Washington/Oregon and northwestern
California, with decreasing amounts inland over the Northwest.

Above normal temperatures will linger across much of the East
through the weekend with daytime highs 10 to 20 degrees above
normal. Best potential for daily records will be across the
South/Southeast into southern Mid-Atlantic. Temperatures should
moderate early next week as the upper ridge shifts eastward and
troughing moves into the East. Meanwhile, the West should stay
cooler underneath upper troughing through Friday. By next weekend,
temperatures may moderate somewhat along the West Coast while
eastern Pacific upper ridging moves in. Parts of the Northwest
could see highs reach up to 10 to 15 degrees above normal which
eventually expands into the northern Plains next week. This shifts
cooler temperatures eastward, and daytime highs across parts of the
southern Rockies and High Plains could be 10 to 25 degrees below
normal next weekend. Below normal temperatures also shift into the
central U.S. and Midwest by next Monday, including highs as low as
10 to 15 degrees below normal over the Great Lakes/Ohio Valley.

Santorelli/Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 1 2025


It generally still remains the case that by Friday, a wavy frontal
boundary will be stuck between a strong upper ridge to the east
and amplified troughing over the West. Moist and unstable inflow
pooling along the front will lead to widespread flash flooding
concerns which should begin during the short range period and
continue through about Saturday. For several days now, models have
been indicating several inch rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals in excess of
5-8 inches could be realized in some spots (and this is on top of
multiple inches of rainfall in the short range as well). For
Friday, the heaviest rainfall axis looks to be from eastern
Oklahoma northeastward into the Ohio Valley, with some slight shift
to the east by Saturday, but there has been some wobble in exactly
where the heaviest rain sets up. Regardless, the potential for
high impact and life-threatening flash flooding is there. As such,
moderate risks are in place for this general region for both the
Day 4/Friday and Day 5/Saturday ERO periods. High Risks upgrades
may well occur in future EROs as details become clearer, especially
into the timeframe of the CAMs. This would be consistent with
highly anomalous and protracted IVT/ARI values and training risks.
By Sunday, the heavy rain threat should finally begin to shift
eastward with moderate to heavy rains possible across the Gulf
Coast states into the Tennessee Valley/Southeast, and rainfall
farther north into the Mid-Atlantic and Northeast near the front.

Out West, an upper low dug into the Southwest into Friday/Saturday
is expected to lead to enhanced precipitation totals across the
southern and central Rockies and Plains. Snow is likely in higher
elevations of the Rockies in Colorado and northern New Mexico, with
uncertainty on how much snow could spill into lower elevations of
the High Plains as enhanced by cooled post-frontal upslope flow.
Elsewhere by Monday, a cold upper trough reaching the Great Lakes
should lead to unsettled weather over the region with rain or snow.

Meanwhile upstream, upper shortwave/front expected to reach the
West Coast into early next week offers seemingly modest moisture
transport, but will likely bring some light to terrain enhanced
moderate activity to western Washington/Oregon and northwestern
California, with decreasing amounts inland over the Northwest.

Above normal temperatures will linger across much of the East
through the weekend with daytime highs 10 to 20 degrees above
normal. Best potential for daily records will be across the
South/Southeast into southern Mid-Atlantic. Temperatures should
moderate early next week as the upper ridge shifts eastward and
troughing moves into the East. Meanwhile, the West should stay
cooler underneath upper troughing through Friday. By next weekend,
temperatures may moderate somewhat along the West Coast while
eastern Pacific upper ridging moves in. Parts of the Northwest
could see highs reach up to 10 to 15 degrees above normal which
eventually expands into the northern Plains next week. This shifts
cooler temperatures eastward, and daytime highs across parts of the
southern Rockies and High Plains could be 10 to 25 degrees below
normal next weekend. Below normal temperatures also shift into the
central U.S. and Midwest by next Monday, including highs as low as
10 to 15 degrees below normal over the Great Lakes/Ohio Valley.

Santorelli/Schichtel

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
240 PM EDT Tue Apr 1 2025

Valid 12Z Tue Apr 01 2025 - 12Z Fri Apr 04 2025


...Northern Plains & Upper Midwest...
Days 1-2...

...Major winter storm to bring heavy snow and gusty winds to
portions of the Dakotas and Minnesota. Key Messages have been
issued for this system and are linked below...

This is no April Fool's joke - a major winter storm will develop
late tonight and then expand and intensify into Minnesota late
Wednesday. The trough responsible for this evolution will be
elongated across the western CONUS at the start of the forecast
period, with an embedded shortwave trough sharpening and digging
across the Northern Plains by Wednesday morning. As shortwave
amplifies, it will close off over SD Wednesday, and the continue
to deepen, with 850-500mb heights dropping to below the 1st
percentile within the NAEFS CFSR climatology. This indicates a
strong system, and as the strongest height falls and PVA from the
mid-level evolution overlap with the increasingly intense
diffluence within the LFQ of a pivoting jet streak, a strong and
intensifying surface cyclone will develop and track from eastern
Nebraska through the Arrowhead of MN before exiting into Canada
Thursday aftn.

There continues to be some latitudinal spread amongst the various
global model systems, leading to a bit lower confidence in the
exact track of the low and subsequent placement of the greatest
impacts. The GEFS/CMCE systems are more aligned with each other
with the surface low track, and are both a bit north of the ECE
ensembles. The key difference appears to be with the dominant
surface, as the ECMWF wants to keep the southern edge of the
elongated low the dominant feature, whereas the GFS and CMC make
the northern low the primary feature. The GFS/CMC also are more
aligned with the now available high-res guidance, so the northern
track seems a bit more supported. Additionally, looking at the D3
clusters (from yesterday), the EC cluster is heavily influenced by
its own ensembles (74%) so it may be a bit under-dispersive as
well. This indicates that a more northern low track is probable
which will allow for warm air to flood farther north, leading to
a mixed precipitation axis from both a warm nose and a subsequent
dry slot, from far northeast SD to potentially across the
Arrowhead.

Northwest of this, however, significant snow accumulations with
heavy snow rates and gusty winds are likely. Despite the now
early-April sun, a potent deformation axis overlapped with an
increasingly impressive TROWAL, especially across northern MN, will
cause heavy snow rates for which the WPC prototype snowband tool
and the HREF probabilities suggest will reach 1-2"/hr. Even these
kinds of rates could overwhelm the warmth due to April sun, leading
to rapid snow accumulations. The heaviest snow amounts are likely
from eastern ND through northern/central MN where the potent
deformation axis will pivot and then translate northeast. Here, WPC
probabilities are high for 6+ inches of snow, with locally 8-12
inches possible. The Arrowhead of MN will also be a focus for
locally heavier snowfall as reflected by a 70-90% chance for 8
inches here, but there remains some uncertainty into how
effectively lake enhancement can occur.

South of this axis of heavy snow, a swath of mixed precipitation,
including freezing rain, is likely. The heaviest icing is expected
across the Coteau of SD, and parts of lower MI, where WPC
probabilities for 0.1" of ice or more range from 10-50%.


...Northeast...
Day 2...

The same system that will bring the major winter storm to the
Northern Plains/Upper Midwest will bring some wintry weather to the
Northeast as well. As the primary surface low over MN occludes to
the east into the Great Lakes, an attendant warm front will begin
to lift northeast downstream of this secondary low pressure. As
this warm front lifts into the Northeast, it will spread increasing
moisture across Upstate NY and northern New England, especially
after 00Z Thursday. The accompanying lift through WAA will ascend
isentropically, especially along the 290K-295K surfaces, which
will push PWs to above the 99th climatological percentile according
to NAEFS, while at the same time driving a warm nose above 0C
northward. The impressive ascent along this warm front will result
in axis of heavy precipitation, but with p-type gradually changing
from snow to a mix to rain, even into northern Maine. The fast
progression of this event, combined with heavy precipitation rates,
and the transitioning p-type will limit overall amounts, but
impacts will still be notable due to snow, sleet, and freezing
rain. WPC probabilities for more than 4 inches of snow are modest
at just 30-50% in the higher terrain of NH and ME, but more than
0.5" of sleet is possible across a larger portion of those areas.
Additionally, freezing rain has a 50-70% chance of accreting to
more than 0.1" of ice across the Adirondacks, southern Greens, the
Northeast Kingdom of VT, and northern NH.


...California...
Day 1...

A shortwave trough embedded within the much larger trough
encompassing much of the West will advect onshore central CA at the
start of the period and then continue to traverse southeast into
the Great Basin Wednesday aftn. Confluent flow south of this
feature combined with a slowly departing jet streak will maintain
steady moisture advection onshore, characterized by IVT that will
continue above 250 kg/m/s the first half of D1. This moisture will
be forced efficiently into the Sierra, with upslope flow wringing
out moderate to heavy snow above generally 3000 feet. While the
heaviest accumulations are likely before this forecast period,
additional snowfall will still be significant as snow rates remain
above 1"/hr at times, and many of the area passes will experience
impacts to travel. WPC probabilities for more than 6 inches of
additional snowfall after 00Z tonight are as high as 70% across the
higher terrain of the Sierra.


...Rockies...
Days 1-3...

Widespread light to moderate snow D1-D2 potentially becomes more
significant across the Southern/Central Rockies late D3.

For D1 and D2 /00Z Wednesday through 00Z Friday/, the entire region
will be covered by large but diffuse troughing extending from the
Pacific Coast through the High Plains. Beneath this large and slow
moving trough, waves of vorticity will rotate through, leading to
periods of enhanced ascent within steep low level lapse rates and
aided by upslope flow. In general, this forcing will be modest
across the region, but an exception is likely across southern
Montana into Wyoming on D1, where a stalled cold front and
accompanying weak wave of low pressure will drive more pronounced
ascent through fgen leading to areas of heavy snow. The heaviest
accumulations D1 are likely above 3500 ft in this region, where WPC
probabilities indicate a high risk (>70%) for more than 4 inches of
snow in the Absarokas, Wind Rivers, and into the Black Hills of
SD.
Elsewhere on D1, light to moderate snowfall across much of the
terrain from the Four Corners and Great Basin Northward has a less
than 30% chance of exceeding 4 inches.

Then through much of D2 forcing again remains modest but widespread
across the Rockies, leading to areas of light to moderate snow in
most of the terrain. A local exception will again exist, this time
across the Northern Rockies and maybe as far south as Yellowstone
NP as a cold front digs out of Canada leading to some increased
fgen and enhanced upslope flow in its wake. This will cause
heavier snow rates and at lower snow levels (falling to 2000-3000
ft) leading to accumulations that have a high risk (>70% chance) of
exceeding 6 inches around Glacier NP, and 10-30% chance around
Yellowstone. Some locally heavier snow is also expected D3 in the
vicinity of the Four Corners, especially across UT and CO as a
shortwave pivots northeast, and WPC probabilities indicate a
moderate risk (30-50%) for more than 6 inches in the southern
Wasatch and San Juans.

Then during D3, more impressive and consolidated ascent begins to
manifest across the central and southern Rockies, generally from WY
through CO and into NM as the tail shortwave within this larger
trough begins to amplify. There is good agreement that this
shortwave will close off and dig south into the Deserts of AZ,
leading to increasingly impressive mid-level divergence downstream.
At the same time, a subtropical jet streak will intensify and
rotate around the base of this amplifying closed low to place
favorable LFQ ascent into the eastern Rockies, while additionally
the cold front from D2 across the northern Rockies drops south
across WY and CO. The overlap of this baroclinic gradient with the
increasing synoptic ascent could result in an impressive area of
expanding precipitation D3 and even moreso into D4. There is still
uncertainty into the exact evolution of this event, and current WPC
probabilities are modest (10-30%) for more than 6 inches of snow,
but during D4 these could increase and expand more impressively.

Weiss




...Winter Storm Key Messages are in effect. Please see current
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 1 2025

Valid 12Z Fri Apr 04 2025 - 12Z Tue Apr 08 2025


...Multi-day and potentially catastrophic heavy rain/flooding and
severe threat likely for Lower/Middle Mississippi, Tennessee, and
Ohio Valleys through next Saturday...


...Overview...

The medium range upper pattern will be amplified and quite stormy
this week. A wavy frontal boundary settling from the Ohio Valley
to Southern Plains, holding in between an amplified western trough
and strong Atlantic to Gulf upper ridge, will continue to be the
focus for an ongoing multi-day heavy rain and severe weather event
from the Lower Mississippi Valley to the Ohio Valley, which starts
during the short range period. Significant to catastrophic
flooding and flash flooding is increasingly likely for portions of
this area. A gradually amplifying Canada into northern U.S. upper
trough nearing the East into Monday and eventual southern stream
energy ejection and phasing will finally help to push out the
frontal boundary. Most of the West this week should stay relatively
cool underneath persistent troughing with some progression
eastward early next week into the Central U.S., while upper ridging
brings a warming trend to the Northwest during the weekend. The
East will see above normal temperatures late this week and then a
cooler trend that moves in from the north and west. Detailed WPC
forecasts are linked below.

...Guidance/Predictability Assessment...

Latest model guidance agrees fairly well on the main aspects of
the forecast through medium range time scales and have good
ensemble and machine learning model support. There are
differences still with some embedded lower predictability details,
which would have sensible weather impacts. Shortwaves and energy
perturbations exiting that trough show more spread, and will play a
role in exactly where the heaviest rainfall occurs. Either way,
models have been extremely consistent in showing a significant
flooding event from the lower Mississippi Valley to the Ohio
Valley. One aspect of the machine learning models to consider is
their depiction of a slightly narrower axis of heaviest rainfall on
a given day, albeit with locally higher amount potential daily
compared
to the NBM. WPC QPF was trended in this manner.

Energy digging through the western trough heading into the weekend
should with lingering uncertainty eventually interact with a more
amplifying northern stream upper trough into next weekend to
eventually help push the wavy front and heavy rain threat eastward.
This shortwave should amplify over the East by early next week.
There are some differences in the weekend interactions between this
shortwave and western U.S. energy and then timing of surface low
pressure/cold front through the East next week. Any leftover
troughing over the West should weaken and shift east as an upper
ridge moves into the Northwest next Monday-Tuesday.

Overall reasonable GFS/ECMWF/UKMET/Canadian guidance clustering
and continuity aspects allowed for usage of a composite model blend
through medium range timescales to produce a solid starting
forecast basis in line with the NBM. This solution plan maintains
good WPC product continuity and consistent hazards messaging.

...Weather/Hazards Highlights...

It generally still remains the case that by Friday, a wavy frontal
boundary will be stuck between a strong upper ridge to the east
and amplified troughing over the West. Moist and unstable inflow
pooling along the front will lead to widespread flash flooding
concerns which should begin during the short range period and
continue through about Saturday. For several days now, models have
been indicating several inch rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals in excess of
5-8 inches could be realized in some spots (and this is on top of
multiple inches of rainfall in the short range as well). For
Friday, the heaviest rainfall axis looks to be from eastern
Oklahoma northeastward into the Ohio Valley, with some slight shift
to the east by Saturday, but there has been some wobble in exactly
where the heaviest rain sets up. Regardless, the potential for
high impact and life-threatening flash flooding is there. As such,
moderate risks are in place for this general region for both the
Day 4/Friday and Day 5/Saturday ERO periods. High Risks upgrades
may well occur in future EROs as details become clearer, especially
into the timeframe of the CAMs. This would be consistent with
highly anomalous and protracted IVT/ARI values and training risks.
By Sunday, the heavy rain threat should finally begin to shift
eastward with moderate to heavy rains possible across the Gulf
Coast states into the Tennessee Valley/Southeast, and rainfall
farther north into the Mid-Atlantic and Northeast near the front.

Out West, an upper low dug into the Southwest into Friday/Saturday
is expected to lead to enhanced precipitation totals across the
southern and central Rockies and Plains. Snow is likely in higher
elevations of the Rockies in Colorado and northern New Mexico, with
uncertainty on how much snow could spill into lower elevations of
the High Plains as enhanced by cooled post-frontal upslope flow.
Elsewhere by Monday, a cold upper trough reaching the Great Lakes
should lead to unsettled weather over the region with rain or snow.

Meanwhile upstream, upper shortwave/front expected to reach the
West Coast into early next week offers seemingly modest moisture
transport, but will likely bring some light to terrain enhanced
moderate activity to western Washington/Oregon and northwestern
California, with decreasing amounts inland over the Northwest.

Above normal temperatures will linger across much of the East
through the weekend with daytime highs 10 to 20 degrees above
normal. Best potential for daily records will be across the
South/Southeast into southern Mid-Atlantic. Temperatures should
moderate early next week as the upper ridge shifts eastward and
troughing moves into the East. Meanwhile, the West should stay
cooler underneath upper troughing through Friday. By next weekend,
temperatures may moderate somewhat along the West Coast while
eastern Pacific upper ridging moves in. Parts of the Northwest
could see highs reach up to 10 to 15 degrees above normal which
eventually expands into the northern Plains next week. This shifts
cooler temperatures eastward, and daytime highs across parts of the
southern Rockies and High Plains could be 10 to 25 degrees below
normal next weekend. Below normal temperatures also shift into the
central U.S. and Midwest by next Monday, including highs as low as
10 to 15 degrees below normal over the Great Lakes/Ohio Valley.

Santorelli/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw