Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Thu May 22 2025

Valid 00Z Fri May 23 2025 - 00Z Sun May 25 2025

...Severe weather and heavy rain threat migrates into the Heartland today;
rainy in the Northeast...

...Above average temperatures across southern tier states and West;
unusually cool weather persists from Northern Plains to
Northeast/Mid-Atlantic...

A relatively stagnant upper pattern with troughing along the coasts and
ridging over the Central U.S. will persist through the end of the week,
with cool and rainy weather forecast from the Ohio Valley to the
Northeast/Mid-Atlantic. Along the trailing end of the front, isolated to
scattered severe storms (some of which could produce intense hail and
wind) and heavy rainfall remain possible in the Southern Plains today.
Looking ahead through the first half of Memorial Day weekend (Saturday
evening), the threat of scattered severe and excessive rainfall is
expected to focus across this portion of the front as it slowly lifts into
the Ozarks and Central High Plains while a dryline sharpens.

Storms aside, the aforementioned upper-troughing over Great Lakes and
Northeast will facilitate cooler temperatures across the Northern Plains,
Midwest, Northeast and Mid-Atlantic through Saturday. High temperatures in
the 40s, 50s and low 60s will represent temperature anomalies between
20-35 degrees below average. Widespread low daily max temperature records
may be tied or broken from the Ohio Valley to the Northeast/Mid-Atlantic
today and tomorrow. In stark contrast to the cool conditions over the
Northeast, warm weather (daytime highs 10-15 degrees above average) will
continue across the Southern and Western U.S. Over portions of South and
West Texas, daytime highs creeping into the triple digits may translate to
Moderate to locally Major HeatRisk impacts through Saturday.

Asherman/Kebede


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

Extended Forecast Discussion...UPDATED
NWS Weather Prediction Center College Park MD
326 PM EDT Thu May 22 2025

Valid 12Z Sun May 25 2025 - 12Z Thu May 29 2025


...Heavy rain and flash flooding concerns continue in the Ozarks
and vicinity Sunday...


...Overview...

A pattern supporting heavy rain and thunderstorms will be in place
as the period begins Sunday, as an upper trough atop the Rockies
Sunday moves east with ample moisture and instability streaming
into a frontal system in the central U.S. ahead of it. Flash
flooding is expected in the Ozarks and vicinity as part of a
potentially significant multi-day heavy rainfall event. This trough
tracking east will combine with another trough stretching from the
East westward across the Great Lakes, causing the trough to dig
atop the east- central U.S. and finally press the front and the
resultant rainfall southeast across the southern tier into the
Appalachians and eventually the Eastern Seaboard. The rounds of
troughing aloft will cause cooler than normal temperatures in parts
of the central and eastern U.S., while upper ridging building in
the Intermountain West should allow for warmer than average
temperatures there.


...Guidance/Predictability Assessment...

The latest model guidance shows an initially blocky pattern
heading into the weekend with a lingering upper-low over the
northeastern U.S./Great Lakes, strong ridge anchored north into
south-central Canada, and another upper-low over the northeastern
Pacific. A lingering quasi-stationary frontal boundary from the
passage of this northeastern U.S. upper-low will be draped across
the Southeast west through the Mississippi Valley into the Southern
Plains, providing the focus for multiple days of widespread
shower/storm development. All of the guidance is in generally good
agreement depicting a somewhat complex evolution of southern stream
shortwave energy that will breakthrough under the prevailing
upper-ridge and slowly progress eastward from the western U.S. and
over the Plains Sunday into Monday, potentially combining with
additional lingering upper-energy from the upper-low over the
northeastern U.S. This should eventually lead to lee cyclogenesis
over the Plains and help to usher the frontal system eastward
through early to mid-next week. There is some discrepancy with the
exact evolution of this system as it lifts northeastward through
the Mississippi and into the Ohio Valley before approaching the
East Coast with regard to secondary coastal low development, though
the guidance tends to favor this development at some point mid-
next week which will have impacts on rainfall potential/amounts
extending into the Mid-Atlantic/Northeast.

There is greater disagreement in the pattern to the west early to
mid-next week as shortwave energy ejects from the northeastern
Pacific low. The 00Z ECMWF/CMC/UKMET (as well as the ensemble
means) generally agree that this wave will make slow progress as
the upper-ridge over south-central Canada and into the Interior
West remains entrenched to its east before eventually, potentially
weakening and lifting northeastward. The frontal system reflection
at the surface is expected to eventually dissipate given the
ridging to the east, with modest sensible weather impacts expected.
The lingering upper-energy may also eventually merge with
additional southern stream energy approaching from the Pacific. On
the other hand, the 00Z GFS was weaker with this upper
-ridge, and the 06Z had a much different solution depicting the
upper-wave helping to breakdown the ridging by merging with upper
energy from the lingering upper-troughing across the Great
Lakes/Northeast, and eventually moving eastward over the
northern/central Plains. This would lead to much more
precipitation across the north-central U.S. to Great Lakes. The
latest 12Z update for the GFS also shows upper-troughing lingering
longer westward over the north-central U.S., potentially
reinforced by additional energy from the west, that would lead to
more additional heavy precipitation chances over the
Plains/Mississippi Valley.

The updated WPC forecast blend includes a composite of the
available 00Z guidance (favoring the 00Z GFS given the noted
differences in the 06Z) given generally similar solutions. A
contribution from the means is included with a reduced contribution
from the 00Z GFS/CMC later in the period given naturally growing
differences, with larger differences specifically with the 00Z GFS.
This blend provides for good continuity with the prior WPC
forecast.

...Weather/Hazards Highlights...

A wavy west-east oriented front will be in place over the south-
central Plains and Mississippi Valley on Sunday. Moisture
(precipitable water) values likely over the 90th percentile and
ample instability will stream into the front, and the right
entrance region of the jet provides dynamical support. This will
lead to additional heavy rain, perhaps in multiple rounds, likely
centered in the Ozarks and vicinity on Sunday. This follows heavy
rainfall expected over almost the exact same region the prior two
days. A targeted Moderate Risk ERO has been introduced to cover the
third day of a potentially significant multi-day heavy rain and
flash flooding event given increasingly wet antecedent conditions.
A broader Slight Risk is in place from the south-central Plains
into parts of the Lower and Middle Mississippi Valley. Due to
models converging better on timing and placement of convection, the
size of a broader Marginal Risk has been reduced compared to the
previous couple of issuances.

By Memorial Day, the trough aloft should finally press the front
gradually south toward the southern tier and east toward the
Appalachians. Moisture and instability in place could still lead to
heavy rain rates across the south-central U.S. into the Tennessee
Valley and Lower Ohio Valley, but at least there should be
relatively less potential for training storms as the front moves.
For the Day 5/Monday ERO, show a Marginal Risk delineated across
these areas as a starting point. Embedded Slights may be needed in
future issuances but the details still need to be refined with
time, and much of this region will have been dry in the prior days
leading to high FFG values. On Tuesday, the eventual dominant low
on the frontal system should lift northeast and bring localized
heavy rain to the Eastern Seaboard, especially the Mid- Atlantic,
while the trailing front still lingers and causes showers and
storms across the southern tier Tuesday- Wednesday.

Farther north, the initial trough should produce some modest
precipitation in the central Rockies (even some snow in the highest
peaks) and the northern/central Plains early next week. The
frontal boundary curling back into the southern/central Rockies and
High Plains could help produce scattered convection there next
week as well. Meanwhile, rounds of fronts coming through the
Northwest could allow for light to moderate precipitation.
Summertime scattered storms are also likely across the Florida
Peninsula.

One more day of hot weather is likely for Texas across the
Southeast on Sunday. Temperatures well into the 90s to around 100
will support areas of Major HeatRisk in southern parts of Texas and
Louisiana. Meanwhile, cooler than normal temperatures by 5 to 15
degrees will take hold over the north-central to eastern U.S. into
early next week underneath upper troughing. The trough and front
pressing south will allow for temperatures to cool in the southern
tier Monday and Tuesday. The cooler temperatures should gradually
moderate closer to normal as next week progresses. But in the West,
a building upper ridge will lead to warmer than average
temperatures by 10 to 15 degrees for several days over the Great
Basin and northern/central Rockies.

Putnam/Tate


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
338 AM EDT Thu May 22 2025

Valid 00Z Fri 23 May 2025 - 00Z Fri 30 May 2025

An upper low/trough is forecast to set up over Hawaii Thursday
and Friday, allowing for some instability, while normal to above
normal moisture levels are in place. Meanwhile moderate to breezy
easterly trades are likely as midlatitude surface high pressure
systems track well north of Hawaii. This will add up to a wet
trade wind pattern with possibly heavy showers and a few
thunderstorms Thursday-Friday.

Then through the holiday weekend, moderate to breezy trades are
likely to persist. But model guidance continues to show moisture
levels gradually decreasing for fewer showers while the trough
aloft pulls away. Trade winds may weaken slightly to moderate
levels by Tuesday-Thursday as the drier pattern continues.


Tate

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu May 22 2025
Day 1
Valid 16Z Thu May 22 2025 - 12Z Fri May 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NEW ENGLAND, THE SOUTHERN PLAINS, AND SOUTHEAST FLORIDA...

...Southeastern New England...
Late season Nor'easter will strengthen and continue to move up the
coast just east of Massachusetts today, spreading significant
moisture onshore New England and eastern Long Island. Although
instability will be modest, generally less than 500 J/kg, and
highest right along the immediate coast, tremendous moisture flux
driven via 850mb U-wind below the 1st percentile (so easterly)
according to NAEFS will manifest as continuous moderate to heavy
rainfall today. Rain rates from the HREF are progged to generally
be around 0.5"/hr, although low probabilities (10-20%) for 1"/hr
exist across Southeast MA and the Cape/Islands. 0-6km mean winds of
10-20 kts will become increasingly anti-parallel to the Corfidi
vectors, and this suggests training of echoes will result in
repeating rounds of rainfall. Despite the overall modest rates,
this will cause as much as 3-5" of rain, especially across Rhode
Island, the Cape, and inside 495 around Boston. This could cause
localized flash flooding, especially in urban areas, and the MRGL
risk has been maintained with minimal changes.


...Southeast Florida...
Thunderstorms will blossom along the tail of a cold front that will
settle across the Florida Peninsula this aftn as it gets shunted
southward in response to an amplifying trough over the East. This
will impinge into a pool of anomalous moisture (PWs +1.5 sigma)
with SBCAPE above 2000 J/kg fueling thermodynamics that will
support heavy rain rates within thunderstorms. As convection
develops along the cold front this aftn, storms will track east on
0-6km mean winds of around 5-10 kts, so generally slow moving,
with aligned Corfidi vectors (and aligned to the front itself)
suggesting training/backbuilding cells across portions of South
Florida. The greatest risk for heavy rain will be near the Gold
Coast where the eastward advancing cells will interact with the
westward moving sea breeze to cause at least periods of nearly
stationary motion and redevelopment, enhancing both the rates to
above 3"/hr and duration of these rates. This will result in more
than 3" of rain in some areas as suggested by HREF probabilities
exceeding 90%, and locally as much as 5" of rain is possible. This
portion of Florida has been quite dry so FFG is elevated, but where
any storms stall over urban areas, instances of flash flooding are
possible.


...Southern Oklahoma/North Texas...
A trough amplifying over the Great Lakes/Northeast will yield
lowering heights over the Central Plains, with additional ascent
being forced through modest jet streak development and spokes of
energy via vort maxes rotating SE through the mean flow. At the
surface, this will leave a wavering boundary in place in the
vicinity of the Red River Valley of the South, which will serve as
a focus for convective development this aftn/eve, aided by
increasing return flow from the Gulf pushing PWs up to 1.5" and
forcing pronounced convergence of moisture transport vectors into
the boundary. The CAMs have become more robust with activity later
today, but there still exists considerable temporal and latitudinal
spread with development. What is more certain, however, is that
convection should grow upscale into clusters, especially this
evening, when moisture flux maximizes in the presence of 40-50 kts
of bulk shear. Storms that develop will feature rainfall rates for
which the HREF suggests have a 50% chance of exceeding 1"/hr, which
could produce 2-3" of rainfall where any short-term training can
occur. While this event does not appear to be exceptionally
significant, the highest probabilities for heavy rainfall
effectively overlap relatively wetter soils via NASA SPoRT,
suggesting at least isolated flash flooding instances are possible.
The inherited MRGL risk was expanded just slightly to account for
the continued spread in model guidance.


Weiss


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu May 22 2025
Day 2
Valid 12Z Fri May 23 2025 - 12Z Sat May 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEASTERN
KANSAS and NORTHEASTERN OKLAHOMA INTO THE OZARKS...

...Central Plains into the Ozarks...
Guidance continues to be confident in that development of a multi-
day heavy rainfall event which will commence Friday night.

The synoptic pattern becomes increasingly supportive of a heavy-
rainfall event as a closed low over the Northeast elongates NW to
SE, leaving NW flow across the Central Plains and into the
Southeast. Within this flow, a jet streak is progged to intensify,
leaving the favorably diffluent RRQ overhead the region, with weak
impulses embedded within the mid-level flow also producing ascent.
Although it is challenging to time/place these impulses even into
D2, which will limit confidence at this range, the overlap of the
diffluent jet portion with these impulses atop a warm front
lifting slowly northeast will create an environment that steadily
becomes more supportive of heavy rainfall. Friday night, as the LLJ
ramps up to 30-50 kts at 850mb and impinges into the front,
increasing isentropic ascent and moisture convergence will drive
the development of convection. Storms that fire will likely
produce impressive rain rates which the HREF suggests has a 70%
chance and 20% chance of exceeding 1"/hr and 2"/hr, respectively.
These rain rates will be supported by thermodynamic advection on
the LLJ, reflected by PWs surging above 1.75 inches and MUCAPE
rising towards 3000 J/kg.

As storms develop later Friday, they will intensify and organize
through pronounced bulk shear of 35-50 kts, indicating the
potential for clusters, supercells, and even an MCS. This
organization could at least briefly enhance rain rates even beyond
2"/hr, and with mean flow aligned to the warm front, with Corfidi
vectors becoming increasingly angled right into the moisture surge,
training of echoes from NW to SE appears likely. This has resulted
in an uptick in QPF probabilities, and the subtly modified SLGT
risk encompasses the area of greatest chance for 3+" of rain from
the HREF, ECENS, and GEFS clusters.


...Southeast Florida...
Another day of aftn showers and thunderstorms is expected to
develop across the Peninsula and track eastward through the
evening. The cold front leftover from D1 should wane, but any
residual low-level convergence will help focus thunderstorms, with
the persistent favorable thermodynamics supporting rainfall rates
of 2-3"/hr. Mean winds will be light on Friday, and as storms
approach the westward advancing sea breeze near the Gold Coast,
another day of convection stalling or moving erratically across the
urban corridor is expected. With heavy rain forecast during D1,
the footprint of this rainfall may overlap the same areas on D2,
and because of this a MRGL risk has been added.


Weiss


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu May 22 2025
Day 3
Valid 12Z Sat May 24 2025 - 12Z Sun May 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEASTERN
KANSAS and NORTHEASTERN OKLAHOMA INTO THE OZARKS...

Day 2 of what is becoming more certain to be a 3-day rainfall event
occurs Saturday across portions of the Central Plains and into the
Ozarks and Mid-Mississippi River Valley. A warm front wavering
near the OK/KS/MO/AR intersection will continue to be a focus for
convergence and ascent, while broad W/NW persists aloft between an
elongated trough over New England and a secondary trough over the
Great Basin. This fairly static flow will repeatedly shed weak
impulses atop the low-level front, providing additional forcing for
ascent through Saturday.

This forcing will occur within persistently favorable
thermodynamics, as return flow from the Gulf maintains elevated PWs
as high as 1.75 inches, with overlapping MUCAPE of 1000-2000 J/kg.
This will support efficient rainfall rates within convection, which
is likely to blossom each aftn/eve and then grow upscale in
clusters or an MCS training WNW to ESE across the region. While
there still remains some uncertainty into the latitudinal placement
of the heaviest rainfall, there is likely to be at least partial
overlap of the heavy rain footprint from D2 into D3. This is
reflected by NASA SPoRT 40cm soil moisture anomaly forecasts that
skyrocket to above the 98th% on D3, so soils will become much more
vulnerable to runoff/flash flooding D3. Considered an upgrade to a
MDT risk, but there remains just enough spread in the guidance,
including the AI models, to keep excessive rain probabilities below
40%, so a high-end SLGT risk remains at this time. It is possible a
MDT risk will be needed for some areas D3 with future updates,
however, helping to bridge the gap into the new D4 MDT risk issued
for these same areas on Sunday.


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

Extended Forecast Discussion...UPDATED
NWS Weather Prediction Center College Park MD
326 PM EDT Thu May 22 2025


A wavy west-east oriented front will be in place over the south-
central Plains and Mississippi Valley on Sunday. Moisture
(precipitable water) values likely over the 90th percentile and
ample instability will stream into the front, and the right
entrance region of the jet provides dynamical support. This will
lead to additional heavy rain, perhaps in multiple rounds, likely
centered in the Ozarks and vicinity on Sunday. This follows heavy
rainfall expected over almost the exact same region the prior two
days. A targeted Moderate Risk ERO has been introduced to cover the
third day of a potentially significant multi-day heavy rain and
flash flooding event given increasingly wet antecedent conditions.
A broader Slight Risk is in place from the south-central Plains
into parts of the Lower and Middle Mississippi Valley. Due to
models converging better on timing and placement of convection, the
size of a broader Marginal Risk has been reduced compared to the
previous couple of issuances.

By Memorial Day, the trough aloft should finally press the front
gradually south toward the southern tier and east toward the
Appalachians. Moisture and instability in place could still lead to
heavy rain rates across the south-central U.S. into the Tennessee
Valley and Lower Ohio Valley, but at least there should be
relatively less potential for training storms as the front moves.
For the Day 5/Monday ERO, show a Marginal Risk delineated across
these areas as a starting point. Embedded Slights may be needed in
future issuances but the details still need to be refined with
time, and much of this region will have been dry in the prior days
leading to high FFG values. On Tuesday, the eventual dominant low
on the frontal system should lift northeast and bring localized
heavy rain to the Eastern Seaboard, especially the Mid- Atlantic,
while the trailing front still lingers and causes showers and
storms across the southern tier Tuesday- Wednesday.

Farther north, the initial trough should produce some modest
precipitation in the central Rockies (even some snow in the highest
peaks) and the northern/central Plains early next week. The
frontal boundary curling back into the southern/central Rockies and
High Plains could help produce scattered convection there next
week as well. Meanwhile, rounds of fronts coming through the
Northwest could allow for light to moderate precipitation.
Summertime scattered storms are also likely across the Florida
Peninsula.

One more day of hot weather is likely for Texas across the
Southeast on Sunday. Temperatures well into the 90s to around 100
will support areas of Major HeatRisk in southern parts of Texas and
Louisiana. Meanwhile, cooler than normal temperatures by 5 to 15
degrees will take hold over the north-central to eastern U.S. into
early next week underneath upper troughing. The trough and front
pressing south will allow for temperatures to cool in the southern
tier Monday and Tuesday. The cooler temperatures should gradually
moderate closer to normal as next week progresses. But in the West,
a building upper ridge will lead to warmer than average
temperatures by 10 to 15 degrees for several days over the Great
Basin and northern/central Rockies.

Putnam/Tate

Extended Forecast Discussion...UPDATED
NWS Weather Prediction Center College Park MD
326 PM EDT Thu May 22 2025


A wavy west-east oriented front will be in place over the south-
central Plains and Mississippi Valley on Sunday. Moisture
(precipitable water) values likely over the 90th percentile and
ample instability will stream into the front, and the right
entrance region of the jet provides dynamical support. This will
lead to additional heavy rain, perhaps in multiple rounds, likely
centered in the Ozarks and vicinity on Sunday. This follows heavy
rainfall expected over almost the exact same region the prior two
days. A targeted Moderate Risk ERO has been introduced to cover the
third day of a potentially significant multi-day heavy rain and
flash flooding event given increasingly wet antecedent conditions.
A broader Slight Risk is in place from the south-central Plains
into parts of the Lower and Middle Mississippi Valley. Due to
models converging better on timing and placement of convection, the
size of a broader Marginal Risk has been reduced compared to the
previous couple of issuances.

By Memorial Day, the trough aloft should finally press the front
gradually south toward the southern tier and east toward the
Appalachians. Moisture and instability in place could still lead to
heavy rain rates across the south-central U.S. into the Tennessee
Valley and Lower Ohio Valley, but at least there should be
relatively less potential for training storms as the front moves.
For the Day 5/Monday ERO, show a Marginal Risk delineated across
these areas as a starting point. Embedded Slights may be needed in
future issuances but the details still need to be refined with
time, and much of this region will have been dry in the prior days
leading to high FFG values. On Tuesday, the eventual dominant low
on the frontal system should lift northeast and bring localized
heavy rain to the Eastern Seaboard, especially the Mid- Atlantic,
while the trailing front still lingers and causes showers and
storms across the southern tier Tuesday- Wednesday.

Farther north, the initial trough should produce some modest
precipitation in the central Rockies (even some snow in the highest
peaks) and the northern/central Plains early next week. The
frontal boundary curling back into the southern/central Rockies and
High Plains could help produce scattered convection there next
week as well. Meanwhile, rounds of fronts coming through the
Northwest could allow for light to moderate precipitation.
Summertime scattered storms are also likely across the Florida
Peninsula.

One more day of hot weather is likely for Texas across the
Southeast on Sunday. Temperatures well into the 90s to around 100
will support areas of Major HeatRisk in southern parts of Texas and
Louisiana. Meanwhile, cooler than normal temperatures by 5 to 15
degrees will take hold over the north-central to eastern U.S. into
early next week underneath upper troughing. The trough and front
pressing south will allow for temperatures to cool in the southern
tier Monday and Tuesday. The cooler temperatures should gradually
moderate closer to normal as next week progresses. But in the West,
a building upper ridge will lead to warmer than average
temperatures by 10 to 15 degrees for several days over the Great
Basin and northern/central Rockies.

Putnam/Tate

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
214 PM EDT Wed May 7 2025

Valid 00Z Thu May 08 2025 - 00Z Sun May 11 2025


...Colorado...
Day 1...

Lingering vorticity on the western side of the departing upper low
will still trigger some light snow over the San Juans this evening
before tapering off tonight/early Thursday. WPC probabilities for
at least an additional 4 inches of snow after 00Z are low (10-40%)
above 11,000ft.

For days 2-3, the probability of at least 4 inches of snow is less
than 10%.

The probability of significant freezing rain across the CONUS is
less than 10%.

Note - this is the last regularly scheduled discussion (QPFHSD)
for the 2024-2025 winter season. Unless a significant winter
weather threat emerges, this discussion will next be updated on or
about September 25, 2025.


Fracasso

Extended Forecast Discussion...UPDATED
NWS Weather Prediction Center College Park MD
326 PM EDT Thu May 22 2025

Valid 12Z Sun May 25 2025 - 12Z Thu May 29 2025


...Heavy rain and flash flooding concerns continue in the Ozarks
and vicinity Sunday...


...Overview...

A pattern supporting heavy rain and thunderstorms will be in place
as the period begins Sunday, as an upper trough atop the Rockies
Sunday moves east with ample moisture and instability streaming
into a frontal system in the central U.S. ahead of it. Flash
flooding is expected in the Ozarks and vicinity as part of a
potentially significant multi-day heavy rainfall event. This trough
tracking east will combine with another trough stretching from the
East westward across the Great Lakes, causing the trough to dig
atop the east- central U.S. and finally press the front and the
resultant rainfall southeast across the southern tier into the
Appalachians and eventually the Eastern Seaboard. The rounds of
troughing aloft will cause cooler than normal temperatures in parts
of the central and eastern U.S., while upper ridging building in
the Intermountain West should allow for warmer than average
temperatures there.


...Guidance/Predictability Assessment...

The latest model guidance shows an initially blocky pattern
heading into the weekend with a lingering upper-low over the
northeastern U.S./Great Lakes, strong ridge anchored north into
south-central Canada, and another upper-low over the northeastern
Pacific. A lingering quasi-stationary frontal boundary from the
passage of this northeastern U.S. upper-low will be draped across
the Southeast west through the Mississippi Valley into the Southern
Plains, providing the focus for multiple days of widespread
shower/storm development. All of the guidance is in generally good
agreement depicting a somewhat complex evolution of southern stream
shortwave energy that will breakthrough under the prevailing
upper-ridge and slowly progress eastward from the western U.S. and
over the Plains Sunday into Monday, potentially combining with
additional lingering upper-energy from the upper-low over the
northeastern U.S. This should eventually lead to lee cyclogenesis
over the Plains and help to usher the frontal system eastward
through early to mid-next week. There is some discrepancy with the
exact evolution of this system as it lifts northeastward through
the Mississippi and into the Ohio Valley before approaching the
East Coast with regard to secondary coastal low development, though
the guidance tends to favor this development at some point mid-
next week which will have impacts on rainfall potential/amounts
extending into the Mid-Atlantic/Northeast.

There is greater disagreement in the pattern to the west early to
mid-next week as shortwave energy ejects from the northeastern
Pacific low. The 00Z ECMWF/CMC/UKMET (as well as the ensemble
means) generally agree that this wave will make slow progress as
the upper-ridge over south-central Canada and into the Interior
West remains entrenched to its east before eventually, potentially
weakening and lifting northeastward. The frontal system reflection
at the surface is expected to eventually dissipate given the
ridging to the east, with modest sensible weather impacts expected.
The lingering upper-energy may also eventually merge with
additional southern stream energy approaching from the Pacific. On
the other hand, the 00Z GFS was weaker with this upper
-ridge, and the 06Z had a much different solution depicting the
upper-wave helping to breakdown the ridging by merging with upper
energy from the lingering upper-troughing across the Great
Lakes/Northeast, and eventually moving eastward over the
northern/central Plains. This would lead to much more
precipitation across the north-central U.S. to Great Lakes. The
latest 12Z update for the GFS also shows upper-troughing lingering
longer westward over the north-central U.S., potentially
reinforced by additional energy from the west, that would lead to
more additional heavy precipitation chances over the
Plains/Mississippi Valley.

The updated WPC forecast blend includes a composite of the
available 00Z guidance (favoring the 00Z GFS given the noted
differences in the 06Z) given generally similar solutions. A
contribution from the means is included with a reduced contribution
from the 00Z GFS/CMC later in the period given naturally growing
differences, with larger differences specifically with the 00Z GFS.
This blend provides for good continuity with the prior WPC
forecast.

...Weather/Hazards Highlights...

A wavy west-east oriented front will be in place over the south-
central Plains and Mississippi Valley on Sunday. Moisture
(precipitable water) values likely over the 90th percentile and
ample instability will stream into the front, and the right
entrance region of the jet provides dynamical support. This will
lead to additional heavy rain, perhaps in multiple rounds, likely
centered in the Ozarks and vicinity on Sunday. This follows heavy
rainfall expected over almost the exact same region the prior two
days. A targeted Moderate Risk ERO has been introduced to cover the
third day of a potentially significant multi-day heavy rain and
flash flooding event given increasingly wet antecedent conditions.
A broader Slight Risk is in place from the south-central Plains
into parts of the Lower and Middle Mississippi Valley. Due to
models converging better on timing and placement of convection, the
size of a broader Marginal Risk has been reduced compared to the
previous couple of issuances.

By Memorial Day, the trough aloft should finally press the front
gradually south toward the southern tier and east toward the
Appalachians. Moisture and instability in place could still lead to
heavy rain rates across the south-central U.S. into the Tennessee
Valley and Lower Ohio Valley, but at least there should be
relatively less potential for training storms as the front moves.
For the Day 5/Monday ERO, show a Marginal Risk delineated across
these areas as a starting point. Embedded Slights may be needed in
future issuances but the details still need to be refined with
time, and much of this region will have been dry in the prior days
leading to high FFG values. On Tuesday, the eventual dominant low
on the frontal system should lift northeast and bring localized
heavy rain to the Eastern Seaboard, especially the Mid- Atlantic,
while the trailing front still lingers and causes showers and
storms across the southern tier Tuesday- Wednesday.

Farther north, the initial trough should produce some modest
precipitation in the central Rockies (even some snow in the highest
peaks) and the northern/central Plains early next week. The
frontal boundary curling back into the southern/central Rockies and
High Plains could help produce scattered convection there next
week as well. Meanwhile, rounds of fronts coming through the
Northwest could allow for light to moderate precipitation.
Summertime scattered storms are also likely across the Florida
Peninsula.

One more day of hot weather is likely for Texas across the
Southeast on Sunday. Temperatures well into the 90s to around 100
will support areas of Major HeatRisk in southern parts of Texas and
Louisiana. Meanwhile, cooler than normal temperatures by 5 to 15
degrees will take hold over the north-central to eastern U.S. into
early next week underneath upper troughing. The trough and front
pressing south will allow for temperatures to cool in the southern
tier Monday and Tuesday. The cooler temperatures should gradually
moderate closer to normal as next week progresses. But in the West,
a building upper ridge will lead to warmer than average
temperatures by 10 to 15 degrees for several days over the Great
Basin and northern/central Rockies.

Putnam/Tate


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