Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Wed Apr 02 2025

Valid 12Z Wed Apr 02 2025 - 12Z Fri Apr 04 2025

...Life-threatening, potentially historic flash flood event begins
Wednesday for the Lower Ohio Valley and Mid-South...

...Tornado outbreak expected Wednesday for the Mid-South with multiple
intense tornadoes possible...

...Late season winter storm continues Wednesday for portions of the
Northern Plains/Upper Midwest 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 Wednesday...

A powerful Spring storm system will bring a barrage of life-threatening
weather including flash flooding and strong tornadoes to portions of the
Lower Ohio Valley and Mid-South Wednesday, with the flash flood threat
only the beginning of a multi-day catastrophic and potentially historic
event. A deepening upper-level trough and accompanying strong low
pressure/frontal system over the Plains this morning will push eastward
through the Midwest, Mississippi Valley, and southern Plains Wednesday.
Extremely impressive dynamics given very strong upper-level and
lower-level wind fields, as well as a deep influx of boundary layer
moisture flowing northward from the Gulf, will help support a broad warm
sector featuring widespread, intense thunderstorms stretching from the
Great Lakes southwest through the Middle Mississippi/Lower Ohio Valleys,
Mid-South, ArkLaTex, and Southern Plains. The Storm Prediction Center
(SPC) has introduced a High Risk (level 5/5) of severe weather across
portions of the Mid-South where the most favorable overlap of strong
upper- and lower-level shear and instability may lead to an outbreak of
tornadoes, including multiple intense tornadoes, as well as very large
hail and significant damaging winds. A broader at least Enhanced level
(3/5) severe threat covers the rest of the region where a more scattered
but still significant threat of tornadoes, large hail, and damaging winds
exists. Unfortunately, this severe threat will be compounded by the
beginning of a life-threatening flash flood event. Strengthening
upper-level ridging to the east will help to slow the progression of the
cold front through the day Wednesday, increasing the chance of repeated
rounds of storms as they begin to move more parallel to the stalling
boundary. The blocked flow will also help to maintain a supply of
plentiful Gulf moisture helping to foster very-efficient, intense downpour
producing storms. There is a Moderate Risk of Excessive Rainfall (level
3/4) Wednesday overlapping much of the SPC High Risk from the Lower Ohio
Valley southwestward into the Mid-South where the greatest potential
exists for several inches of rainfall and scattered to numerous instances
of flash flooding through the evening and overnight hours. The front will
become nearly stationary across the region Thursday leading to an even
greater risk of significant heavy rainfall totals, with the probability of
more than 6" of rain over the two day period at 40-60%. The repeated
rounds of rainfall will lead to increasingly saturated soils, and could
bring additional rainfall over areas already experiencing flooding. For
these reasons, another Moderate Risk is in place Thursday for the Lower
Ohio Valley/Mid South to the ArkLaTex with an embedded High Risk (level
4/4) for western Kentucky, the Missouri Bootheel, northwestern Tennessee,
and extreme northeastern Arkansas where widespread, life-threatening flash
flooding is expected. The front will remain stalled into the weekend with
Moderate Risks already in place for Friday and Saturday. This event will
bring potentially historic amounts of rainfall, with some locations
possibly seeing as much as 10-15"+ of rain through the weekend.
Communities throughout the area should prepare now for the possibility of
long duration and severe disruptions to daily life given the expected
extreme rainfall and flood risk. Additional severe thunderstorms are also
expected on Thursday from the Mid-Atlantic southwest through the
Ohio/Tennessee Valleys and into the Southern Plains, with the SPC
maintaining a Slight Risk (level 2/5) for the threat of damaging winds,
large hail, and a few tornadoes.

Meanwhile, a winter storm continues Wednesday in the colder airmass north
of the system, with a band of heavy snow forecast along and to the north
of the surface low track from the eastern Dakotas into northern Minnesota.
Additional snowfall totals of 4-8", locally higher, are expected, with the
heaviest totals most likely along the northern shore of Lake Superior.
Gusty winds may lead to areas of blowing snow and very difficult travel
conditions. A wintry mix of snow, sleet, and freezing rain is expected
just to the southeast of the heavy snow from central Minnesota east into
northern Wisconsin and Michigan through at least Wednesday morning. These
areas of wintry precipitation are expected to transition over to rain and
even some thunderstorms as a warm front lifts northward during the day
Wednesday. A leading shortwave ahead of the system will also bring wintry
precipitation to areas of the interior Northeast/New England Wednesday,
with some light to moderate snow and ice accumulations possible for higher
mountain elevations and portions of northern Maine.

Wintry weather continues across much of the Interior West as embedded
perturbations round the broad upper-level trough over the region. Some
moderate snow totals will be possible for higher elevations of the
mountain ranges across the Pacific Northwest, Great Basin,
northern/central Rockies, and Four Corners region Wednesday. Western areas
will see the snow taper off into Thursday while the focus shifts to the
northern/central Rockies and Four Corners region. A frontal passage across
the northern Rockies and an area of low pressure east of the central
Rockies will help to enhance upslope flow and bring some heavier snow
totals to the mountains, with some snow also expected for adjacent
portions of the northern/central High Plains. Elsewhere, another day of
strong, gusty winds and low humidity across portions of the southern High
Plains and Southwest has prompted a Critical Risk of fire weather (level
2/3) from the SPC.

An amplifying pattern with mean ridging building over the eastern U.S. and
the noted troughing over the central/western U.S. will favor warmer, much
above average temperatures to the east and cooler, much below average
temperatures to the west through at least mid-week. Some of the greatest
anomalies will be from the Southern Plains eastward through the Southeast,
where highs into the 80s and low 90s may reach daily record-tying/breaking
levels. Well above average highs into the 70s to low 80s for the Midwest
Wednesday will fall into the 50s and 60s Thursday following a cold front
passage. Highs in the 50s and 60s for the Mid-Atlantic/Northeast on
Wednesday will warm into the mid-60s to low 80s on Thursday as the ridge
builds northward. Areas of the Central/Northern Plains will remain cooler
behind the cold front with highs ranging from the mid-30s to the mid-50s.
In the West, forecast highs generally range from the 40s in the Interior
West, the 50s in the Pacific Northwest, the 50s and 60s in California, and
the 60s to low 70s in the Desert Southwest.

Putnam

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Wed Apr 2 2025

Valid 12Z Sat Apr 05 2025 - 12Z Wed Apr 09 2025


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


...Overview...

A significant and potentially historic flooding and flash flooding
event will be ongoing as the period begins on Saturday along a
wavy frontal boundary from the Lower Mississippi Valley to the Ohio
Valley. This front is sandwiched between a strong Atlantic to Gulf
upper ridge and an amplified western U.S. trough. 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 the frontal boundary and rainfall
east with some heavy rainfall potential along the central Gulf
Coast and parts of the Southeast. A shortwave into the West on
Sunday-Monday could bring some light precipitation to parts of the
Northwest. After Monday, the medium range period should trend much
drier across the country as the overall pattern deamplifies.


...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 thae western trough do still show some 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 lasting through Saturday. Timing and aspects of the Great
Lakes to Northeast trough have also improved, but there is still
some uncertainty on how quickly southern stream energy finally
ejects east. Another shortwave into the Northwest shows some timing
uncertainties as well (CMC is slower than the ECMWF and GFS) with
bigger questions on how this evolves downstream mid next week and
how strong ridging is over the Southwest.

The WPC forecast for tonight utilized a deterministic model blend
the first half of the period amidst minimal model spread. By Day 5
and beyond, gradually increased the ensemble means to help mitigate
differences in the deterministic guidance, though still maintained
some operational models (anchored by the ECMWF) for added system
definition.

...Weather/Hazards Highlights...

A wavy and stuck frontal boundary will continue to focus moist and
unstable inflow leading 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 significant multi-day rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals on Saturday
alone in excess of 4-5 inches could be realized in some spots (and
this is on top of potentially 5-10 inches of rainfall in the short
range as well). A catastrophic and life-threatening flash flood
event is likely and the Day 4/Saturday ERO continues to show a
large moderate risk from northeast Arkansas into western
Kentucky/southern Indiana, with a likely high risk upgrade needed
once this moves into the short range period. 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. The Sunday ERO shows a
marginal risk for this region with an embedded slight risk farther
south across parts of southern Alabama and Mississippi where recent
heavy rainfall has primed soils and the greatest instability
should be located.

Out West, an upper low dug into the Southwest into 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
some snow possibly spilling 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. Meanwhile, well below
normal temperatures will be in place across parts of the southern
Rockies and High Plains where daytime highs 10 to 25 degrees below
normal are possible this weekend. Moderated below normal
temperatures also shift into the central U.S. and Midwest Monday
and the East mid next week. Warmer than average temperatures
initially over the Northwest this weekend should expand into the
remainder of the West and the northern/central Plains by next week.

Santorelli


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
412 AM EDT Wed Apr 2 2025

Valid 00Z Thu 03 Apr 2025 - 00Z Thu 10 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
339 AM EDT Wed Apr 2 2025
Day 1
Valid 12Z Wed Apr 02 2025 - 12Z Thu Apr 03 2025

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

..A PROLONGED LIFE-THREATENING FLASH FLOOD EVENT WILL BEGIN TODAY
WITH SEVERAL DAYS OF HEAVY RAINFALL IMPACTING A LARGE PORTION OF
THE LOWER MISSISSIPPI AND OHIO VALLEY'S..

The setup for the D1 period is already underway with a broad upper
trough pattern across the Central and Western CONUS taking shape
and interacting with a building Western Atlantic ridge that's
already flexing its muscle in the overall longwave pattern. A
deepening surface low over the Plains will migrate in-of the Upper
Midwest with a cold front advancement towards the Mississippi
Valley as we move into the first half of the period. The issue
becomes two-fold by later this afternoon as the frontal boundary
slows its forward momentum due to the surface reflection over the
Midwest becoming vertically stacked and losing its vigor in
progressing the pattern. Meanwhile, the ridge over the Atlantic
will continue to strengthen leading to a stout western edge of the
surface ridge pattern acting as a "wall" to prevent much more
motion of the surface front migrating out of the Plains. By the
evening, the front will likely be deemed quasi-stationary, meaning
the overall advancement of the boundary will be limited and will
only move based on subtle surface wave propagations that ride along
the boundary, or from well-defined cold pools that originate from
organized convective clusters that form within the vicinity. In
this case, both of these outcomes are likely to play a significant
role in location of the frontal positioning, as well as an
inflection point for daily organized convection across the Lower
Mississippi Valley up through the western half of the Ohio Valley
for D1.

Assessment of the 500mb vorticity field based off the past several
deterministic outputs indicates the first in a set of 3 distinct
surface waves that will originate out of the Southern Rockies and
Plains that will eject northeastward out of the base of the mean
trough and migrate right up the stationary boundary in place. This
is a textbook signal for enhanced convective development with a
sharp low to mid-level moisture advection regime along and ahead of
the surface amplification, much of which is aided by a budding LLJ
presence within the eastern flank of the surface wave. The latest
CAMs and global deterministic are in agreement on a large areal
extent of southwest to northeast oriented convection that will
likely spawn between 18-00z this afternoon and evening, mainly once
the primary mid-level perturbation enters the picture and provides
sufficient ascent to trigger convection along the surface front.
00z HREF probabilities for >2" PWATs are generally modest between
25-50% across the Lower Mississippi Valley with the primary axis
located across southern and eastern AR. >1.5" PWATs is very high,
however across the same areas with a northern expansion all the
way beyond the Ohio River near IL/IN/KY/OH by later in the evening.
This is thanks to the strengthening nocturnal LLJ pattern that will
transpire ~00z, maintaining a nearly steady state as we move
through the overnight hours Wednesday into Thursday.

Considering the variables above, a significant precip core is
anticipated extending from the ArklaTex, north into the north-
central Ohio Valley with a sharp eastern edge defined by the
greater subsidence provided by the western fringes of the low to
mid-level ridge anchored over and off the Southeast U.S. coast.
This sharp delineation is typically an artifact of strong surface
based convergence present just upstream, especially within a primed
upper pattern fighting against the ridge itself. Across AR up
through western TN and KY, a well-defined axis of heavy precip is
progged across all major NWP, a testament to the agreement on the
placement of the primary convective cell motions, but also where
there is an expectation for the future cell mergers and forward
propagation to occur leading to repeated rainfall threats during
the course of Wednesday evening to Thursday morning. HREF
neighborhood probabilities for >3" of rainfall indicate a large
corridor of 70-90+% probs located across south-central and eastern
AR, extending northeast up through western TN and the far
southwestern KY area to the south of PAH. The >5" probs are also
elevated within that same zone running 25-50% across that corridor
leading to general continuity in what has been forecast the past
several cycles. EAS probabilities are also very impressive for >2"
over much of the above area with 60-80% located over almost all of
western TN, including the Memphis metro. These types of outputs
from the prob fields are historically aligned with higher-end risk
days, especially over regions that have already primed soils or
exhibit large scale urban footprints privy to runoff potential.
This setup is shifting towards the significant category in terms of
expectation for the first day of a long-lasting period of enhanced
rainfall concerns thanks to the pattern hitting a "longwave
roadblock".

Totals for the D1 period are likely to reach 2-4" across a large
domain with localized totals of 5-8" plausible in areas that see
greater training and focused cell mergers once the storm mode
shifts from supercellular to more of a multi-cell cluster after
cold pool mergers late in the evening. The previous Moderate Risk
was relatively maintained, but did extend the risk a bit further
east due to CAMs output signaling a greater risk of outflow
dominant regimes pushing the eastern extent of the heavier precip
further into northern MS and western TN. A high-end Moderate is
most likely from the Pine Bluff, AR up through the southwestern KY,
northwest TN border south of Paducah. The Memphis, TN metro and
the eastern side of Little Rock, AR is the most likely large metro
corridors under the greatest threat for significant flash flood
prospects when assessing the latest probabilities and general QPF
output. Further north into KY and IN, a Moderate Risk still exists
for most of western KY up into southern IN as guidance indicates a
secondary maxima of QPF due to cell initiation late Wednesday into
early Thursday along the leading edge of the surface wave as it
migrates northeast. Some guidance is very aggressive with precip
outputs >2" over a short time scale, enough to cause flash flood
concerns within any urban corridors and valleys located within the
river flood plane. Considering the signals for >1" at the very
least, the Moderate Risk was drawn north to account for the
potential with a general expectation this setup will evolve into
that area as we work into the D2.

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Wed Apr 2 2025
Day 2
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...

..A PROLONGED LIFE-THREATENING FLASH FLOOD EVENT WILL BEGIN TODAY
WITH SEVERAL DAYS OF HEAVY RAINFALL IMPACTING A LARGE PORTION OF
THE LOWER MISSISSIPPI AND OHIO VALLEY'S..

The D2 period will be an ongoing atmospheric evolution with the
first half of the time frame being a continuation of the
significant rainfall from the D1 as the succession of cold pool
mergers and convective clusters propagate across the Ohio and
Tennessee Valleys before finally fading as they lose steam moving
into the wall of subsidence to the east. Scattered showers and
storms will still be ongoing within the confines of the quasi-
stationary front just due to continued low-level convergence and
smaller mid-level perturbations ripping through the "atmospheric
speedway" setup from southwest to northeast across the Southern
Plains up through the Ohio Valley. Despite the expectation for
lower rates during the early to mid-afternoon period on Thursday,
any additional rainfall will act as a priming mechanism for what
will transpire later in the evening as the second of 3 major
surface waves takes shape across the Lower Mississippi to Ohio
Valleys.

The introduction of yet another stout LLJ pattern and attendant
low-level moisture flux will yield another round of widespread
convection within proxy to the surface front that will modestly
undulate north to south within the confines of the aforementioned
areas. The positioning of the front will make all the difference in
the inevitable convective cell motions and subsequent QPF
distribution, something that will be important when assessing where
the worst flooding will occur as the grounds around much of the Low
to Mid-Mississippi Valley and western Ohio Valley will be flood
prone from the previous convective impacts. As of this time, there
is ample agreement from global deterministic, as well as the
relevant ensemble packages for an axis of heavy precipitation to
impact a zone spanning central and northeastern Arkansas up through
western Tennessee and Kentucky with the northern edge of the
heavier precip aligned with the KY/OH border near the Ohio River
basin. Additional amounts of 2-4" with locally up to 7" will
impact those above zones, overlapping several areas that will have
seen significant rainfall the previous 24 hrs. 01z NBM
probabilities for rainfall amounts >6" over the D1-2 period are now
upwards of 40-60% located from Pine Bluff, AR up through western
KY between Paducah and Bowling Green. The area with the highest
probabilities is across western TN, just north of the Memphis
metro, but very close by the major metro center. Considering the
elevated theta_e alignment and +2 to +3 deviation PWATs present,
rainfall rates within matured convective cores will likely breach
1"/hr with 2-3"/hr within reason, especially in the early evening
when instability is highest and the LLJ is at peak intensity. The
deep moist convergence regime will be well-established and cell
motions will remain generally parallel to the frontal boundary
thanks to the stagnant synoptic scale pattern in place. This will
lead to significant, life-threatening flash flooding to impact a
large area where FFG's will likely lean critically low.

Considering all the above variables, there was no reason to remove
the High Risk. Instead, the risk area was expanded to account for
the latest probabilities and relevant run to run continuity from
the pertinent NWP. A Moderate Risk spans from southwestern Arkansas
to the northeast, just outside Cincinnati on the Kentucky side of
the Ohio River. Memphis, Little Rock, Pine Bluff, Bowling Green,
Louisville, and Evansville are all major urban corridors within the
Moderate Risk with areas like Paducah and Union City the larger
towns/metros embedded within the High Risk. The travel routes most
susceptible to flash flooding will be along the I-69 and I-55
interstates within western KY, western TN, and northeastern AR.

Kleebauer


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
339 AM EDT Wed Apr 2 2025
Day 3
Valid 12Z Fri Apr 04 2025 - 12Z Sat Apr 05 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR A LARGE
PORTION OF THE LOWER AND MID-MISSISSIPPI VALLEYS...

The final surface wave within the atmospheric parade across the
Southern Plains to Mississippi Valley will show itself by late-
Friday morning through the remainder of the period. This wave will
likely be the strongest of the 3 allowing a much more amplified
surface evolution that will shift the focus of heavier precip
further northwest while also providing some vigor in the overall
QPF distribution. The trend the past 24 hrs is for a zone of
significant (3-6+") totals to be recognized across portions of the
Southern Plains up through the Ozarks and Mid-Mississippi Valley
of Missouri, spanning as far north as south-central Illinois. When
assessing the theta_e environment, there is a noticeable push north
of more modestly unstable air with the most pertinent area of
available instability situated across southern MO down through AR,
southeastern OK, and even northeastern TX. A sharp uptick in
regional PWATs with deviations between +2.5-3.5 anomaly-wise are
forecast within that zone correlating with a substantial rise in
area convection blossoming late Friday afternoon, onward. This
setup is fortunately further west compared to the previous periods,
so the overlap of the heaviest rainfall is not anticipated to be
as problematic as the previous period.

Having said that, the pattern will yield high precip totals due to
widespread convective schema, falling over some areas that will
have seen appreciable rain, and over other areas that are more
prone to flooding due to complex terrain situated over the Ozarks.
The pattern is such that several areas from northeast of DFW up
through IL will see rainfall amounts of 3-6" with locally higher
beginning Friday afternoon with the heaviest rainfall likely to
occur by the evening with the implementation of yet another LLJ
structure thanks to the surface wave mentioned previously. Further
to the west, another closed upper reflection across the Southwest
U.S. will only entice greater upper forcing within a broad axis of
difluence situated over the Plains. This setup is more privy to
convection forming as far west as the Western Rolling Plains of TX
to points east and northeast. Even there, modest 1-2" with locally
higher totals are forecast in-of those zones. As a result, there
was a general expansion of the Slight Risk further southwest into
Central TX, an expansion of the Moderate Risk to include the
eastern Red River Basin up through the southeast half of Missouri
into southern Illinois, and a high-end Moderate impacting
southeastern OK up through western AR and much of southern and
southeast MO. The threat of widespread flash flooding is
increasing for areas within the Moderate risk and aforementioned
higher-end Moderate designation. Be sure to stay up to date for the
latest changes as we move through the remainder of the week as this
pattern remains very active and prone to significant life-
threatening flash flood concerns.

Kleebauer

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Wed Apr 2 2025


A wavy and stuck frontal boundary will continue to focus moist and
unstable inflow leading 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 significant multi-day rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals on Saturday
alone in excess of 4-5 inches could be realized in some spots (and
this is on top of potentially 5-10 inches of rainfall in the short
range as well). A catastrophic and life-threatening flash flood
event is likely and the Day 4/Saturday ERO continues to show a
large moderate risk from northeast Arkansas into western
Kentucky/southern Indiana, with a likely high risk upgrade needed
once this moves into the short range period. 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. The Sunday ERO shows a
marginal risk for this region with an embedded slight risk farther
south across parts of southern Alabama and Mississippi where recent
heavy rainfall has primed soils and the greatest instability
should be located.

Out West, an upper low dug into the Southwest into 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
some snow possibly spilling 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. Meanwhile, well below
normal temperatures will be in place across parts of the southern
Rockies and High Plains where daytime highs 10 to 25 degrees below
normal are possible this weekend. Moderated below normal
temperatures also shift into the central U.S. and Midwest Monday
and the East mid next week. Warmer than average temperatures
initially over the Northwest this weekend should expand into the
remainder of the West and the northern/central Plains by next week.

Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
257 AM EDT Wed Apr 2 2025


A wavy and stuck frontal boundary will continue to focus moist and
unstable inflow leading 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 significant multi-day rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals on Saturday
alone in excess of 4-5 inches could be realized in some spots (and
this is on top of potentially 5-10 inches of rainfall in the short
range as well). A catastrophic and life-threatening flash flood
event is likely and the Day 4/Saturday ERO continues to show a
large moderate risk from northeast Arkansas into western
Kentucky/southern Indiana, with a likely high risk upgrade needed
once this moves into the short range period. 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. The Sunday ERO shows a
marginal risk for this region with an embedded slight risk farther
south across parts of southern Alabama and Mississippi where recent
heavy rainfall has primed soils and the greatest instability
should be located.

Out West, an upper low dug into the Southwest into 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
some snow possibly spilling 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. Meanwhile, well below
normal temperatures will be in place across parts of the southern
Rockies and High Plains where daytime highs 10 to 25 degrees below
normal are possible this weekend. Moderated below normal
temperatures also shift into the central U.S. and Midwest Monday
and the East mid next week. Warmer than average temperatures
initially over the Northwest this weekend should expand into the
remainder of the West and the northern/central Plains by next week.

Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Wed Apr 2 2025

Valid 12Z Wed Apr 02 2025 - 12Z Sat Apr 05 2025


...Northern Plains & Upper Midwest...
Day 1...

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

The storm system responsible for today's heavy April snow is
currently organizing across the central Plains early this morning
with an initial impulse of WAA snow showers lifting northward
across the Dakotas and Upper Midwest. At the start of the forecast
period, broad and deep upper troughing will be situated over the
Intermountain West as an ejecting shortwave lifts northward in
conjunction with a ridge building over the East Coast. As this
shortwave amplifies, it will close off over eastern SD this
afternoon and then continue to deepen while sliding northeast
across northern MN this evening. For context, the 850-700mb heights
associated with this low pressure system are forecast to drop
below the 0.5 percentile and even near the 18Z record minimum
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 track from eastern Nebraska through the Arrowhead of
MN before exiting into Canada Thursday aftn. With this track, the
heaviest snowfall will occur just to the north and northwest of the
low center.

Two main areas most likely to experience heavy snowfall rates
>1"/hr and accumulating snow despite the early-April sun are along
the MN Arrowhead and north shores of Lakes Superior, as well as a
corridor from the SD/ND/MN border intersection through northern MN.
The latter region will fall with a potent deformation axis
overlapped with an increasingly impressive TROWAL, especially
across from west-central through northern MN, causing 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. These impressive snowfall rates may also occur for
several hours (roughly 14Z-21Z per the 00Z HREF) as the upper low
crosses overhead and pivots the TROWAL over west-central MN and
the eastern Dakotas, which led to an increase in snowfall here
compared to the prior forecast. Here, WPC probabilities are
moderate (50-70%) for 6+ inches of snow, with locally 8-10 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 and parts of lower MI, where WPC probabilities for 0.1" of
ice or more range from 10-30%.


...Northeast...
Days 1-2...

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 into neighboring ME.


...Rockies into the CO Front Range...
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 /12Z Wednesday through 12Z 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 a local exception will exist 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 by the end of D1 into D2. 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 and northern
Absarokas.
Elsewhere on D1 and D2, moderate to locally heavy snowfall across
much of the terrain from the Four Corners and UT ranges into the CO
Rockies has 30-50% chances of exceeding 6 inches, primarily above
8000 ft. This is in response to a shortwave rounding the base of
the trough in the Southwest pivoting over the Four Corners.

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 bleeding into D4, with snow levels
starting around 6000 ft and dropping below 4000 ft and snow into
the High Plains. There is still uncertainty into the exact
evolution of this event and how far heavy snow extends into the CO
Front Range. Current WPC probabilities on D3 are high (60-90%) for
more than 8 inches of snow in the Sangre de Cristos and eastern San
Juans, with slightly lower into the central and northern CO Mts.


Snell/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
257 AM EDT Wed Apr 2 2025

Valid 12Z Sat Apr 05 2025 - 12Z Wed Apr 09 2025


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


...Overview...

A significant and potentially historic flooding and flash flooding
event will be ongoing as the period begins on Saturday along a
wavy frontal boundary from the Lower Mississippi Valley to the Ohio
Valley. This front is sandwiched between a strong Atlantic to Gulf
upper ridge and an amplified western U.S. trough. 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 the frontal boundary and rainfall
east with some heavy rainfall potential along the central Gulf
Coast and parts of the Southeast. A shortwave into the West on
Sunday-Monday could bring some light precipitation to parts of the
Northwest. After Monday, the medium range period should trend much
drier across the country as the overall pattern deamplifies.


...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 thae western trough do still show some 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 lasting through Saturday. Timing and aspects of the Great
Lakes to Northeast trough have also improved, but there is still
some uncertainty on how quickly southern stream energy finally
ejects east. Another shortwave into the Northwest shows some timing
uncertainties as well (CMC is slower than the ECMWF and GFS) with
bigger questions on how this evolves downstream mid next week and
how strong ridging is over the Southwest.

The WPC forecast for tonight utilized a deterministic model blend
the first half of the period amidst minimal model spread. By Day 5
and beyond, gradually increased the ensemble means to help mitigate
differences in the deterministic guidance, though still maintained
some operational models (anchored by the ECMWF) for added system
definition.

...Weather/Hazards Highlights...

A wavy and stuck frontal boundary will continue to focus moist and
unstable inflow leading 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 significant multi-day rainfall totals, especially across
Arkansas into western Kentucky where 24-hour totals on Saturday
alone in excess of 4-5 inches could be realized in some spots (and
this is on top of potentially 5-10 inches of rainfall in the short
range as well). A catastrophic and life-threatening flash flood
event is likely and the Day 4/Saturday ERO continues to show a
large moderate risk from northeast Arkansas into western
Kentucky/southern Indiana, with a likely high risk upgrade needed
once this moves into the short range period. 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. The Sunday ERO shows a
marginal risk for this region with an embedded slight risk farther
south across parts of southern Alabama and Mississippi where recent
heavy rainfall has primed soils and the greatest instability
should be located.

Out West, an upper low dug into the Southwest into 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
some snow possibly spilling 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. Meanwhile, well below
normal temperatures will be in place across parts of the southern
Rockies and High Plains where daytime highs 10 to 25 degrees below
normal are possible this weekend. Moderated below normal
temperatures also shift into the central U.S. and Midwest Monday
and the East mid next week. Warmer than average temperatures
initially over the Northwest this weekend should expand into the
remainder of the West and the northern/central Plains by next week.

Santorelli


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