Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Apr 29 2025

Valid 00Z Wed Apr 30 2025 - 00Z Fri May 02 2025

...Strong to severe thunderstorms expected from the interior Northeast, to
the Ohio Valley, to the southern Plains through this evening...

...Another round of strong to severe thunderstorms possible across
portions of Oklahoma, Arkansas, and Texas on Wednesday...

...Episodes of heavy rain will bring flash flooding concerns across the
south-central U.S. through early Thursday...

An elongated low pressure system and its trailing cold front continues to
track eastward across the upper Great Lakes this afternoon. Daytime
heating under a warm southwesterly flow ahead of the front will promote
the development of strong to severe thunderstorms across portions of the
interior Northeast and Ohio Valley through this evening. The Storm
Prediction Center continues to maintain an Enhanced Risk (level 3/5) of
severe weather with high winds and hail being the primary threats. The
front is expected to clear the entire Northeast by Wednesday morning,
ending the threat of severe weather as gusty westerly winds usher much
cooler and drier air from the Great Lakes into the Northeast ahead of a
high pressure system. The high pressure system will continue to settle
into the Northeast, bringing a chilly and dry morning into the region by
Thursday morning.

In addition to the severe threat across the interior Northeast and Ohio
Valley, severe storms will also be possible farther south and west across
portions of western Texas and southwest Oklahoma through this evening.
Here, the Storm Prediction Center highlights an Enhanced Risk (level 3/5)
of severe weather, with very large hail and damaging winds the greatest
threats. An isolated tornado or two is not ruled out as well. Then on
Wednesday, the threat for strong to severe thunderstorms shifts to
portions of the Lower Mississippi Valley and the southern Plains. The
Storm Prediction Center outlines a Slight Risk (level 2/5) across parts of
Oklahoma, Arkansas, and Texas. Large hail, damaging wind gusts, and the
potential for a couple tornadoes are the primary concerns. Meanwhile, the
trailing portion of the aforementioned cold front is forecast to stall
across the southern Plains through tonight before beginning to lift
northeastward on Wednesday as a warm front. An episode of heavy rain is
expected to impact areas from northern Texas into a large portion of
Oklahoma toward the mid-Mississippi Valley as the front remains nearly
stationary. Given the already saturated grounds from recent heavy
rainfall, and the potential for an additional 2 to 4+ inches of rain, the
Weather Prediction Center maintains a Moderate Risk (level 3/4) of
excessive rainfall for portions of the aforementioned areas through
Wednesday. Numerous instances of flash flooding are possible, some of
which could potentially be significant. On Wednesday, the focus for
significant heavy rain and flash flooding shifts only slightly east from
the southern Plains toward the western Ozarks of Arkansas where another
Moderate Risk highlights the concern for numerous instances of flash
flooding due to repeated training of strong thunderstorms for these areas.
By later Wednesday into Thursday, another frontal system and strong cold
front descending out of the Intermountain West and the northern/central
Rockies will sweep to the south and east, ending the severe and flooding
threats and bringing cooler air into the region.

The aforementioned frontal system that brings an end to the severe weather
and flooding concerns across the southern Plains will first push across
the Pacific Northwest before digging southward through the Intermountain
West and Rockies the next couple of days. This system will bring unsettled
weather to the region through midweek, with areas of rain falling in the
lower elevations, and accumulating wet snow in the mountains. In the wake
of the system and cold front, drier weather works in later Wednesday into
Thursday as high pressure takes control.

A strong ridge of high pressure extending across much of the eastern U.S.
will bring well above average warmth to much of the region through mid to
late week. Forecast highs in the 70s and 80s will be common, including for
more northern locations like the Midwest and Northeast this afternoon
ahead of the cold front. Behind the front, portions of the Great Lakes and
Northeast cool down briefly Wednesday before warming back up on Thursday.
Overall near average temperatures are in store for the Western and central
U.S. Wednesday into Thursday before warming up some across the Pacific
Northwest heading into the latter half of the week.

Miller/Kong


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 29 2025

Valid 12Z Fri May 02 2025 - 12Z Tue May 06 2025


...Overview...

Behind a system tracking across southeastern Canada on Friday with
some rain and thunderstorms across the East/South, guidance
continues to show a more blocky pattern settling over the Lower 48.
With only moderate detail differences/adjustments, most solutions
have been fairly well behaved as an upper trough approaches the
West Coast by Saturday and closes off an upper low that should
drift into the southwestern U.S. early next week, spreading rain
and high elevation snow across the West. This system may start to
generate heavier southern High Plains rainfall toward the end of
the period. A leading ridge should settle over the Plains into the
Mississippi Valley. In contrast to the western consensus,
individual models and ensembles continue to show remarkably
different ideas for the ultimate evolution of energy within an
upper trough reaching the East during the weekend into early next
week. This spread keeps confidence much lower than average for
details of eastern U.S. sensible weather.

...Guidance/Predictability Assessment...

Guidance is clustered better than normal through med-range time
scales with the development and slow progression of a significant
upper trough/closed low and mid-larger scale features working
into/across the West, eventually affecting the central portion of
the nation. A model composite seems to provide a reasonable
forecast basis with good continuity and ensemble support.

However over the East, individual models and ensemble members and
recent machine learning models continue to diverge considerably
from the weekend into early next week with depiction and diggy
nature of a potential closed upper trough/low. Given well clustered
guidance showing ample flow amplitude upstream, favor a solution
over the East somewhere on the more amplified/closed side of the
full envelope of model and ensemble solutions. Accordingly, the
WPC product suite incorporated best clustered guidance in this vein
from the 00 UTC ECMWF/Canadian ensemble means that offer better
cycle to cycle continuity than individual models. Recent GFS and
GEFS runs seem too progressive given upstream amplitude. Latest 12
UTC model guidance remains mixed and uncertain.

...Weather/Hazards Highlights...

Expect some showers and thunderstorms ahead of a cold front
pushing through the East on Friday. Latest guidance signals have
become a little more diffuse regarding how much flash flood
potential there may be over the central and northern Appalachians
where ground conditions are on the wetter side, but enough
instability may exist to promote rain rates that could cause
localized runoff issues. Models are starting to develop some
clustering for the idea of frontal waviness producing a band of
enhanced rainfall over parts of the Northeast on Saturday. This is
an emerging trend and there is a question of how much instability
may exist in this rain band, so initially opted for no risk area in
the Day 5 ERO for this activity. Will continue to monitor this
aspect of the forecast in future runs. Precipitation coverage and
amounts over the East become increasingly uncertain after Saturday,
depending on evolution of upper troughing and possible closed low.
Latest guidance preferences suggest more likely closed low
development and settling over the East into early next week that
would support protracted unsettled conditions including wrapback
western Atlantic low moisture to fuel light to moderate rain
potential, possibly with focus into the northern Mid-Atlantic.

Multiple days of low level flow coming in from the Gulf, along
with some weak shortwave energy approaching from the Southwest and
eventually height falls ahead of the deeper western upper low, will
support multiple episodes of rainfall over portions of the
southern and eventually also central Plains. With a fair amount of
variance in the details, guidance continues to maintain support in
principle for the existing Marginal Risk area from southeastern New
Mexico into Texas on Day 4/Friday. Latest solutions are increasing
potential for impactful rain to extend farther east along a
surface front, now favoring extension of the Marginal Risk area
into parts of Louisiana. Moisture/instability and pattern
persistence should lead to additional pockets of enhanced rainfall
over the southwestern half of Texas into Saturday, meriting a
Marginal Risk over that region on Day 5. The Southwest upper low
still looks to drift far enough eastward to start generating
heavier rainfall over the southern half of the High Plains during
the first half of next week.

The Pacific system moving into the West will bring rain and high
elevation snow into the Northwest around Friday, with precipitation
then continuing across the Sierra Nevada/Great Basin/northern
parts of the Southwest and into the northern-central Rockies.
Highest totals will be dependent on the exact tract of the forecast
evolving upper low, and are currently most likely to be over the
Great Basin and north-central Rockies. Latest guidance is keying on
potential for a band of locally heavy rainfall over Nevada on Day
5/Saturday as the upper low closes off over California, with
anomalous moisture and some instability. The Day 5 ERO depicts a
Marginal Risk area to reflect this possible threat. Leading weak
shortwave/upper low energy may produce lighter precipitation from
the Sierra Nevada east into the Rockies on Friday.

Well above normal temperatures should migrate from the northern
half or so of the West on Friday into the northern Plains by the
weekend and early next week. Plus 15-25F anomalies should be most
common over far northern areas during Friday-Sunday. In contrast,
the upper low tracking into the Southwest will bring much cooler
temperatures to the region. Highs should be 10-20F below normal on
Sunday-Monday, with some record cold highs possible near the upper
low's path. Persistent clouds and precipitation should keep the
southern High Plains highs below normal as well. Locations near the
East Coast will see a warm day on Friday ahead of a cold front,
followed by a trend to near or slightly below normal readings.
However confidence in specifics from Sunday onward is lower than
average due to very uncertain upper level flow details.

Rausch/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
335 AM EDT Tue Apr 29 2025

Valid 00Z Wed 30 Apr 2025 - 00Z Wed 07 May 2025

An unsettled pattern will continue through Tuesday. A surface
trough and band of enhanced moisture will persist over the state
while an upper low tracking just northeast of the main islands may
provide enough instability to support some thunder in locally
heavy showers that should have a land/sea breeze focus due to
light prevailing winds. Guidance consensus maintains the idea of
the pattern returning to a trade regime Wednesday onward as the
upper low contiues eastward and opens. Windward/mountain-focused
showers should trend lighter as precipitable water values settle
to near or slightly below climatological levels. One surface high
passing by to the north around Friday and another next Tuesday
will likely support brisk winds from Friday onward.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
900 PM EDT Tue Apr 29 2025
Day 1
Valid 01Z Wed Apr 30 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...


...Southern Plains to the Mid Mississippi Valley...
01Z Update...

Continued the southern adjustment, especially on the northern edge,
of the outlook areas extending from western Texas northeastward
across Oklahoma. Recent runs of the HRRR, as well as the 18Z HREF,
indicate multiple convective rounds training northeastward across
the region, producing several inches of rain, with numerous flash
floods likely across portions of the region. The latest guidance
shows the greatest threat extending from Northwest Texas across the
Wichita Falls area into southwestern and south-central Oklahoma --
brushing the southern extent of the OKC metro. Deterministic runs
of the HRRR show accumulations of 7+ inches, while the HREF shows
high neighborhood probabilities for accumulations of 5 inches or
more through the overnight across this region. The Slight and
Moderate Risk areas were shifted a bit farther south across the
southern Texas Panhandle and western Oklahoma, where limited
instability in the most recent analysis supports guidance
indicating a lesser threat for heavy rainfall rates and flash
flooding.

Further to the east, pulled the Marginal and the Slight Risk areas
back west of the Mississippi. Relatively drier and more stable air
is expected to persist until showers and storms now developing
back to the southwest spread into the region late in the period,
with the general model consensus showing relatively lighter amounts
and a lesser flooding threat.

...Ohio Valley to the Central Appalachians...
01Z Update...

In addition to brief heavy downpours across sensitive areas, some
training along the southwest flank of the storms currently moving
across the region may raise the threat for locally heavy rains and
flash flooding. But overall, storms are expected to move
progressively across the area, limiting the potential for
widespread heavy rainfall and flash flooding concerns.

Pereira

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
900 PM EDT Tue Apr 29 2025
Day 2
Valid 12Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL AND SOUTHEAST OKLAHOMA, NORTH TEXAS, AND WESTERN
ARKANSAS...

The primary change for this updated ERO for Wednesday was to
recenter the Moderate Risk further south (approx. 50 mi). This was
due to a corresponding shift in guidance, especially hi-res
guidance, but also the UKMET, CMC, and ECMWF AIFS. It also fits
with the updated expectations for the current Day 1 period, as
guidance has signaled the potential for relatively strong cold
pools reinforcing the effective front and gradually pushing it
further south. This would center it more squarely near the Red
River (OK-TX border region) or perhaps fully into N TX. There is
still some uncertainty associated with the exact convective
evolution over the 12-18 hours immediately prior to the start of
the Day 2 period, so the Moderate Risk and Slight Risk were kept
fairly broad to account for different scenarios. Nevertheless,
there was a clear enough shift in the guidance to warrant an
adjustment in the overall risk contours.

A significant flash flooding event could be ongoing at the start of
the period (~12Z Wednesday) over western North Texas and/or south-
central and southwest Oklahoma. Late tonight the southward drift of
the effective front and the associated zone of active convection
may begin to slow or stall as the low-level jet (LLJ) begins to
ramp up considerably over Texas. Where the nose of the LLJ sets up
relative to ongoing convection will go a long way to determining
the primary area of concern for Wednesday. Most hi-res models show
the convective cluster(s) propagating east through the morning
toward AR and N LA, with renewed development upstream over N TX by
the afternoon and another training and backbuilding configuration.

This same guidance generally supports the idea of a 24-hour
rainfall maximum in excess of 7 inches somewhere in the new
Moderate Risk area, but there is lingering uncertainty as to
precisely where that will occur. Although the probability is
currently highest in the vicinity of the Red River near where SE OK
borders N TX, it's conceivable it could occur closer to or inside
the DFW metro area. The metro area is now fully in the Moderate
Risk area with this latest update.

Some significant flash flooding will be possible as much of the
rain will likely fall in 6-12 hours and the high end amounts
produced by some of the guidance would approach or exceed a 100
year ARI for those durations. Neighborhood probabilities of
100 year ARI exceedance are not particularly high, reflecting both
the uncertainty of the exact placement of the heaviest amounts, and
that amounts well in excess of those thresholds are not currently
supported by guidance. Significant and life-threatening flash
flooding would be most likely in two scenarios:

(1) In western North Texas or south-central Oklahoma at the
beginning of the period, as a continuation from the previous night.
These areas have been quite wet over the past week or so, so there
is existing vulnerability to extreme rainfall. (This is more
likely.)

(2) In the Dallas-Ft. Worth metro area, as the rainfall in question
would cause serious issues in a highly urbanized area. (This is
also possible, but not certain, and highly dependent on the exact
convective evolution.)

Further north, a broad Marginal and Slight Risk area was maintained
for the Mid Mississippi Valley and Central Plains. There is some
signal for organized convection and localized heavy rainfall,
including a scattering of low probabilities of FFG exceedance, but
confidence in any specific scenario is lacking.

Lamers

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
900 PM EDT Tue Apr 29 2025
Day 3
Valid 12Z Thu May 01 2025 - 12Z Fri May 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A BROAD AREA
FROM THE GREAT LAKES TO MID MISSISSIPPI VALLEY TO WESTERN GULF
COAST...

An expansive plume of instability is expected to support scattered
to numerous areas of thunderstorms during the day 3 period ahead of
a surface low and trailing cold front. Machine learning
probabilities from Colorado State support the idea of a broad
Marginal Risk; this is what was inherited and it was generally
maintained. The biggest change was to extend the area southwest
through portions of Louisiana and south and southeast Texas.
Confidence in specifics is low, and the overall flash flood threat
should be limited by the fairly progressive nature of the
convection. Precipitable water values are more anomalous in the
Great Lakes region (above the 90th percentile; above 1.3 inches),
but that is also where thunderstorms should be moving the fastest.
Meanwhile, available moisture will be less anomalous further south,
in TX and LA, but thunderstorms will be moving slower. Therefore,
heavy rainfall ingredients will generally be offset across the
whole region. Hi-res models that extend out beyond 48 hours show
more significant localized rainfall maxima in TX and LA, which
makes sense given stronger instability and slower overall storm
motions. This may be where a targeted upgrade to a Slight Risk is
eventually needed.

Lamers

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 29 2025


Expect some showers and thunderstorms ahead of a cold front
pushing through the East on Friday. Latest guidance signals have
become a little more diffuse regarding how much flash flood
potential there may be over the central and northern Appalachians
where ground conditions are on the wetter side, but enough
instability may exist to promote rain rates that could cause
localized runoff issues. Models are starting to develop some
clustering for the idea of frontal waviness producing a band of
enhanced rainfall over parts of the Northeast on Saturday. This is
an emerging trend and there is a question of how much instability
may exist in this rain band, so initially opted for no risk area in
the Day 5 ERO for this activity. Will continue to monitor this
aspect of the forecast in future runs. Precipitation coverage and
amounts over the East become increasingly uncertain after Saturday,
depending on evolution of upper troughing and possible closed low.
Latest guidance preferences suggest more likely closed low
development and settling over the East into early next week that
would support protracted unsettled conditions including wrapback
western Atlantic low moisture to fuel light to moderate rain
potential, possibly with focus into the northern Mid-Atlantic.

Multiple days of low level flow coming in from the Gulf, along
with some weak shortwave energy approaching from the Southwest and
eventually height falls ahead of the deeper western upper low, will
support multiple episodes of rainfall over portions of the
southern and eventually also central Plains. With a fair amount of
variance in the details, guidance continues to maintain support in
principle for the existing Marginal Risk area from southeastern New
Mexico into Texas on Day 4/Friday. Latest solutions are increasing
potential for impactful rain to extend farther east along a
surface front, now favoring extension of the Marginal Risk area
into parts of Louisiana. Moisture/instability and pattern
persistence should lead to additional pockets of enhanced rainfall
over the southwestern half of Texas into Saturday, meriting a
Marginal Risk over that region on Day 5. The Southwest upper low
still looks to drift far enough eastward to start generating
heavier rainfall over the southern half of the High Plains during
the first half of next week.

The Pacific system moving into the West will bring rain and high
elevation snow into the Northwest around Friday, with precipitation
then continuing across the Sierra Nevada/Great Basin/northern
parts of the Southwest and into the northern-central Rockies.
Highest totals will be dependent on the exact tract of the forecast
evolving upper low, and are currently most likely to be over the
Great Basin and north-central Rockies. Latest guidance is keying on
potential for a band of locally heavy rainfall over Nevada on Day
5/Saturday as the upper low closes off over California, with
anomalous moisture and some instability. The Day 5 ERO depicts a
Marginal Risk area to reflect this possible threat. Leading weak
shortwave/upper low energy may produce lighter precipitation from
the Sierra Nevada east into the Rockies on Friday.

Well above normal temperatures should migrate from the northern
half or so of the West on Friday into the northern Plains by the
weekend and early next week. Plus 15-25F anomalies should be most
common over far northern areas during Friday-Sunday. In contrast,
the upper low tracking into the Southwest will bring much cooler
temperatures to the region. Highs should be 10-20F below normal on
Sunday-Monday, with some record cold highs possible near the upper
low's path. Persistent clouds and precipitation should keep the
southern High Plains highs below normal as well. Locations near the
East Coast will see a warm day on Friday ahead of a cold front,
followed by a trend to near or slightly below normal readings.
However confidence in specifics from Sunday onward is lower than
average due to very uncertain upper level flow details.

Rausch/Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 29 2025


Expect some showers and thunderstorms ahead of a cold front
pushing through the East on Friday. Latest guidance signals have
become a little more diffuse regarding how much flash flood
potential there may be over the central and northern Appalachians
where ground conditions are on the wetter side, but enough
instability may exist to promote rain rates that could cause
localized runoff issues. Models are starting to develop some
clustering for the idea of frontal waviness producing a band of
enhanced rainfall over parts of the Northeast on Saturday. This is
an emerging trend and there is a question of how much instability
may exist in this rain band, so initially opted for no risk area in
the Day 5 ERO for this activity. Will continue to monitor this
aspect of the forecast in future runs. Precipitation coverage and
amounts over the East become increasingly uncertain after Saturday,
depending on evolution of upper troughing and possible closed low.
Latest guidance preferences suggest more likely closed low
development and settling over the East into early next week that
would support protracted unsettled conditions including wrapback
western Atlantic low moisture to fuel light to moderate rain
potential, possibly with focus into the northern Mid-Atlantic.

Multiple days of low level flow coming in from the Gulf, along
with some weak shortwave energy approaching from the Southwest and
eventually height falls ahead of the deeper western upper low, will
support multiple episodes of rainfall over portions of the
southern and eventually also central Plains. With a fair amount of
variance in the details, guidance continues to maintain support in
principle for the existing Marginal Risk area from southeastern New
Mexico into Texas on Day 4/Friday. Latest solutions are increasing
potential for impactful rain to extend farther east along a
surface front, now favoring extension of the Marginal Risk area
into parts of Louisiana. Moisture/instability and pattern
persistence should lead to additional pockets of enhanced rainfall
over the southwestern half of Texas into Saturday, meriting a
Marginal Risk over that region on Day 5. The Southwest upper low
still looks to drift far enough eastward to start generating
heavier rainfall over the southern half of the High Plains during
the first half of next week.

The Pacific system moving into the West will bring rain and high
elevation snow into the Northwest around Friday, with precipitation
then continuing across the Sierra Nevada/Great Basin/northern
parts of the Southwest and into the northern-central Rockies.
Highest totals will be dependent on the exact tract of the forecast
evolving upper low, and are currently most likely to be over the
Great Basin and north-central Rockies. Latest guidance is keying on
potential for a band of locally heavy rainfall over Nevada on Day
5/Saturday as the upper low closes off over California, with
anomalous moisture and some instability. The Day 5 ERO depicts a
Marginal Risk area to reflect this possible threat. Leading weak
shortwave/upper low energy may produce lighter precipitation from
the Sierra Nevada east into the Rockies on Friday.

Well above normal temperatures should migrate from the northern
half or so of the West on Friday into the northern Plains by the
weekend and early next week. Plus 15-25F anomalies should be most
common over far northern areas during Friday-Sunday. In contrast,
the upper low tracking into the Southwest will bring much cooler
temperatures to the region. Highs should be 10-20F below normal on
Sunday-Monday, with some record cold highs possible near the upper
low's path. Persistent clouds and precipitation should keep the
southern High Plains highs below normal as well. Locations near the
East Coast will see a warm day on Friday ahead of a cold front,
followed by a trend to near or slightly below normal readings.
However confidence in specifics from Sunday onward is lower than
average due to very uncertain upper level flow details.

Rausch/Schichtel

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
201 PM EDT Tue Apr 29 2025

Valid 00Z Wed Apr 30 2025 - 00Z Sat May 03 2025


...Northern/Central Rockies...
Days 1-2...

Positively-tilted trough over southwestern Canada/northern Divide
this evening will carry a cold front through the region with colder
air in its wake and lowering snow levels. Precipitation will
translate from northwest to southeast Days 1-2 from southwestern MT
through Wyoming then into the CO Rockies. By Wednesday evening,
the trough will moving into the High Plains as heights rebound into
Day 3, ending any snowfall over the region. Snow levels will start
around 8000ft near/ahead of the cold front then drop to
6500-7000ft during the morning hours behind the front, only to rise
again over 7000ft during the day. This will confine the most snow
to the mountain ranges like the Absarokas, Tetons/Wind River,
Bighorns, and CO Rockies. WPC probabilities for at least 8 inches
of snow for this period are at least 50% above 10,000ft or so.

The probability of at least 4 inches of snow on Day 3 is less than
10%.

The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
255 PM EDT Tue Apr 29 2025

Valid 12Z Fri May 02 2025 - 12Z Tue May 06 2025


...Overview...

Behind a system tracking across southeastern Canada on Friday with
some rain and thunderstorms across the East/South, guidance
continues to show a more blocky pattern settling over the Lower 48.
With only moderate detail differences/adjustments, most solutions
have been fairly well behaved as an upper trough approaches the
West Coast by Saturday and closes off an upper low that should
drift into the southwestern U.S. early next week, spreading rain
and high elevation snow across the West. This system may start to
generate heavier southern High Plains rainfall toward the end of
the period. A leading ridge should settle over the Plains into the
Mississippi Valley. In contrast to the western consensus,
individual models and ensembles continue to show remarkably
different ideas for the ultimate evolution of energy within an
upper trough reaching the East during the weekend into early next
week. This spread keeps confidence much lower than average for
details of eastern U.S. sensible weather.

...Guidance/Predictability Assessment...

Guidance is clustered better than normal through med-range time
scales with the development and slow progression of a significant
upper trough/closed low and mid-larger scale features working
into/across the West, eventually affecting the central portion of
the nation. A model composite seems to provide a reasonable
forecast basis with good continuity and ensemble support.

However over the East, individual models and ensemble members and
recent machine learning models continue to diverge considerably
from the weekend into early next week with depiction and diggy
nature of a potential closed upper trough/low. Given well clustered
guidance showing ample flow amplitude upstream, favor a solution
over the East somewhere on the more amplified/closed side of the
full envelope of model and ensemble solutions. Accordingly, the
WPC product suite incorporated best clustered guidance in this vein
from the 00 UTC ECMWF/Canadian ensemble means that offer better
cycle to cycle continuity than individual models. Recent GFS and
GEFS runs seem too progressive given upstream amplitude. Latest 12
UTC model guidance remains mixed and uncertain.

...Weather/Hazards Highlights...

Expect some showers and thunderstorms ahead of a cold front
pushing through the East on Friday. Latest guidance signals have
become a little more diffuse regarding how much flash flood
potential there may be over the central and northern Appalachians
where ground conditions are on the wetter side, but enough
instability may exist to promote rain rates that could cause
localized runoff issues. Models are starting to develop some
clustering for the idea of frontal waviness producing a band of
enhanced rainfall over parts of the Northeast on Saturday. This is
an emerging trend and there is a question of how much instability
may exist in this rain band, so initially opted for no risk area in
the Day 5 ERO for this activity. Will continue to monitor this
aspect of the forecast in future runs. Precipitation coverage and
amounts over the East become increasingly uncertain after Saturday,
depending on evolution of upper troughing and possible closed low.
Latest guidance preferences suggest more likely closed low
development and settling over the East into early next week that
would support protracted unsettled conditions including wrapback
western Atlantic low moisture to fuel light to moderate rain
potential, possibly with focus into the northern Mid-Atlantic.

Multiple days of low level flow coming in from the Gulf, along
with some weak shortwave energy approaching from the Southwest and
eventually height falls ahead of the deeper western upper low, will
support multiple episodes of rainfall over portions of the
southern and eventually also central Plains. With a fair amount of
variance in the details, guidance continues to maintain support in
principle for the existing Marginal Risk area from southeastern New
Mexico into Texas on Day 4/Friday. Latest solutions are increasing
potential for impactful rain to extend farther east along a
surface front, now favoring extension of the Marginal Risk area
into parts of Louisiana. Moisture/instability and pattern
persistence should lead to additional pockets of enhanced rainfall
over the southwestern half of Texas into Saturday, meriting a
Marginal Risk over that region on Day 5. The Southwest upper low
still looks to drift far enough eastward to start generating
heavier rainfall over the southern half of the High Plains during
the first half of next week.

The Pacific system moving into the West will bring rain and high
elevation snow into the Northwest around Friday, with precipitation
then continuing across the Sierra Nevada/Great Basin/northern
parts of the Southwest and into the northern-central Rockies.
Highest totals will be dependent on the exact tract of the forecast
evolving upper low, and are currently most likely to be over the
Great Basin and north-central Rockies. Latest guidance is keying on
potential for a band of locally heavy rainfall over Nevada on Day
5/Saturday as the upper low closes off over California, with
anomalous moisture and some instability. The Day 5 ERO depicts a
Marginal Risk area to reflect this possible threat. Leading weak
shortwave/upper low energy may produce lighter precipitation from
the Sierra Nevada east into the Rockies on Friday.

Well above normal temperatures should migrate from the northern
half or so of the West on Friday into the northern Plains by the
weekend and early next week. Plus 15-25F anomalies should be most
common over far northern areas during Friday-Sunday. In contrast,
the upper low tracking into the Southwest will bring much cooler
temperatures to the region. Highs should be 10-20F below normal on
Sunday-Monday, with some record cold highs possible near the upper
low's path. Persistent clouds and precipitation should keep the
southern High Plains highs below normal as well. Locations near the
East Coast will see a warm day on Friday ahead of a cold front,
followed by a trend to near or slightly below normal readings.
However confidence in specifics from Sunday onward is lower than
average due to very uncertain upper level flow details.

Rausch/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