Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Sun Mar 30 2025

Valid 00Z Mon Mar 31 2025 - 00Z Wed Apr 02 2025

...Severe weather and heavy rainfall spread from the
Mississippi/Ohio/Tennessee Valleys on tonight to the East Coast Monday...

...Ice storm continues across parts of the Upper Midwest/Great Lakes and
Upstate New York/northern New England tonight...

...Unsettled weather arrives over the West Coast...

...Critical Fire Weather conditions likely for much of the Southern High
Plains into next week; much above average temperatures across the South
and East through Monday...

An energetic upper-level trough and accompanying surface low
pressure/frontal system moving through the central to eastern U.S. will
continue to bring the threat of severe weather, flash flooding, and an ice
storm along the northern tier the next couple of days. Another day of
moist return flow ahead of a trailing cold front progressing eastward
through the broader Mississippi Valley as a pair of upper-level shortwaves
pass overhead will encourage the development of numerous, intense
thunderstorms through tonight. This has prompted an Enhanced Risk of
severe weather (level 3/5) from the Storm Prediction Center over the
Ohio/Tennessee Valleys west through the Middle/Lower Mississippi Valley
and into the ArkLaTex. Very large hail, significant damaging winds
(especially into the evening hours), and tornadoes, a few of which could
be strong, can all be expected. In addition, more than sufficient moisture
for heavy downpours as well as increasing rainfall coverage as storms grow
upscale into an organized line into the evening hours will bring the risk
of some scattered instances of flash flooding. A Slight Risk of Excessive
Rainfall (level 2/4) is in place to cover this threat across portions of
the Tennessee and Lower Mississippi Valleys. The system will continue
eastward Monday with another round of storms expected ahead of the cold
front from the Mid-Atlantic southwestward through the Southeast to the
central Gulf Coast. Another Enhanced Risk of severe weather is in place
for the threat of large hail, damaging winds, and a few tornadoes. Some
isolated instances of flash flooding will also be possible, particularly
for northern portions of the Mid-Atlantic as well as for the Deep
South/central Gulf Coast.

To the north, a second round of wintry precipitation will continue an
ongoing ice storm across portions of the Upper Midwest/Great Lakes and
Upstate New York/northern New England as warmer air aloft overrides a
significantly colder airmass just north of a wavy quasi-stationary frontal
boundary. Significant, potentially destructive ice accumulations from
freezing rain upwards of 0.25-0.5", locally even higher, will be possible
through this evening, which is on top of an initial round of freezing rain
on Saturday. These totals are most likely from northern Wisconsin eastward
through the UP and northern LP of Michigan as well as for far Upstate New
York and northern New England. Tree damage and power outages will remain
possible. A band of moderate to locally heavy snowfall will also continue
just to the north of the freezing rain from far northern Wisconsin into
the UP of Michigan along Lake Superior, as well as in northern Maine. The
heaviest additional snowfall totals are most likely along Lake Superior in
the UP of Michigan, where another 4-6", locally higher, will be possible.
The wintry precipitation should wind down tonight, lingering longest
across northern Maine into early Monday.

A lower elevation rain/snow mix and higher elevation snow will begin to
wind down tonight for the Northern/Central Rockies and adjacent High
Plains as the upper-level trough passes overhead and in the presence of
upslope flow as a frontal boundary lingers through the region. To the
west, more significant precipitation chances will start to ramp up into
Monday for the West Coast as a Pacific system approaches the region.
Showers and even some thunderstorms are expected along the coast from
central California northward through the Pacific Northwest, with the
heaviest rainfall focused along the coastal ranges near the
California/Oregon border. Additionally, heavy snowfall is expected for
higher mountain elevations, particularly for the northern California
Ranges and Sierra Nevada as well as the southern Cascades. Snow totals of
1-2' will be possible, with higher totals as much as 4-5' for the Sierra.
Strong winds gusting up to 45-55 mph are also expected particularly for
portions of southern Oregon/northern California as well as southward
through the Sierra Nevada vicinity. Moisture will flow inland with the
system as it pushes into the Rockies Monday, bringing another round of
lower elevation rain/snow and higher elevation snow to the
Northern/Central Rockies and adjacent High Plains. Some areas of snow may
begin to push further east into the Northern Plains by early Tuesday
morning. Elsewhere, the Storm Prediction Center maintains a Critical Risk
of fire weather (level 2/3) across much of central/southern New Mexico
into far west Texas as conditions remain warm, very dry, and breezy. An
Elevated threat will continue into Monday, with another Critical Risk
expected Tuesday. Some intense downpours can be expected with
thunderstorms across the Florida Peninsula tonight, with an isolated
threat for flash flooding.

Much above average early Spring temperatures will continue for portions of
the eastern and southern U.S. ahead of the noted Central U.S. storm system
the next couple of days. Progression of the cold front will bring much
colder temperatures in the 40s and 50s to much of the Midwest/Ohio Valley
beginning Monday, while areas ahead of the front will remain warmer. Below
average, chilly temperatures will remain in place along the northern tier
with highs mainly in the 30s and 40s from the Northern Plains east into
the Upper Great Lakes and New England. A warm front lifting northward will
bring much warmer temperatures to New England on Monday as highs jump into
the 40s, 50s, and even some 60s. Highs will generally be closer to average
across the Pacific Northwest into the Interior West with 50s and some 60s
expected, as well as through the Desert Southwest with highs in the 70s
and 80s. Below average temperatures are expected for California as the
Pacific System impacts the region, with highs mainly in the 50s to low
60s.

Kebede/Putnam


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Sun Mar 30 2025

Valid 12Z Wed Apr 02 2025 - 12Z Sun Apr 06 2025


...Multi-day heavy rain/flooding and severe threat for
Lower/Middle Mississippi, Tennessee, and Ohio Valleys this week...


...Overview...

The medium range upper pattern will be amplified, blocky, and
active through the period. A surface low emerging into the Plains
by Wednesday will track towards the Great Lakes as a building upper
ridge over the western Atlantic into the Gulf should keep the
associated frontal boundary from making much progress on the
southern side, especially later in the week. This sets the stage
for a multi-day heavy rain and severe weather event from the Lower
Mississippi into the Ohio Valley, and significant flooding is
likely. Late-season snow is likely north of this system from the
northern Plains to Great Lakes and Interior Northeast for midweek,
and the Colorado Rockies are likely to see snow by late week. The
West should stay relatively cool underneath persistent troughing,
while above normal temperatures progress from the central U.S. and
Midwest, eventually settling late week across the Southeast and
into the Mid-Atlantic.


...Guidance/Predictability Assessment...

Model guidance is relatively agreeable on the large scale pattern
midweek into next weekend, but still uncertain with some of the
details, which could have sensible weather impacts. A building and
blocky ridge over the Atlantic to Gulf should help amplify
troughing over the West through the period. Shortwaves within that
trough show relatively more spread, but the first shortwave/compact
upper low and its associated surface low tracking from the Central
U.S. to Great Lakes into Thursday continues to show agreement. By
Friday and into the weekend, there is somewhat more uncertainty in
the details of another shortwave digging through the western side
of the trough. ECMWF runs in particular have been on the western
side with this energy compared to the larger consensus of other
models and even EC-based AI/ML models. The new 12Z ECMWF seems to
be coming into better alignment with the majority in the energy and
trough placement. Regardless there is still some spread in what
becomes of this energy next weekend, perhaps producing a closed
upper low within the trough becoming positively tilted while models
are converging on showing an upper ridge axis over the Northwest.

At the surface, a stationary frontal boundary will set up between
the Southeast ridge and Western trough that persists for several
days. There remain subtle differences still in the exact placement
of this front, which has notable implications on the exact
locations of heavy rainfall expected to accompany the front. Expect
these to vary a bit in future forecasts, though the general idea
of heavy rain leading to possibly significant flooding in parts of
the east-central U.S. is pretty locked in. A northern stream trough
may help to slowly nudge the stagnant east-central U.S. boundary
eastward a bit next weekend, though some typical spread remains
with the timing and depth of that trough.

The WPC forecast was able to utilize a deterministic model blend
through Day 4. By Day 5, began incorporating some ensemble mean
guidance to help temper the detail differences, while reducing the
proportion of operational models (especially the 00Z ECMWF) in
favor of over half means for Days 6-7. This approach maintained
relatively good agreement with the previous WPC forecast.


...Weather/Hazards Highlights...

Overall pattern amplification and a leading compact closed low
will support a surface low pressure system forming in the central
U.S. by Wednesday with widespread thunderstorms and heavy rainfall
across the east-central U.S. in its warm sector. Moist and unstable
inflow into the associated surface fronts along with the strong
upper level support will lead to widespread severe weather and
flash flooding concerns. SPC shows severe probabilities from the
south-central U.S. into the Midwest on Wednesday and Thursday. The
greatest concern for flash flooding on Wednesday and Thursday will
stretch across similar areas from the Ark-La-Tex northeast into the
Ohio Valley, as the front anchors storms for significant training
concerns. On Wednesday, precipitable water anomalies above the 95th
percentile with ample instability will be in place. Models are
indicating embedded rainfall totals of 5 to 8 inches during the 12Z
Wednesday to 12Z Thursday period alone, with the GFS already
explicitly forecasting hourly rain rates to 2", and certainly
expect the CAMs to show higher rates than that once we get into
their timeframe. Thus plan to upgrade the Day 4/Wednesday ERO to a
Moderate Risk from northeast Arkansas across the Ohio River Valley
to far southern Indiana. Much the same environmental pattern sets
up on Day 5/Thursday, with the added concern of very wet antecedent
conditions by then. The previously issued Moderate Risk for Day
5/Thursday was maintained, with a southwestward expansion per
coordination with the Little Rock local forecast office and
considering the higher instability there. Heavy rainfall is likely
to continue into late week, with perhaps a bit of a westward shift
into the southern Plains at times as the West trough pivots.
Through midweek into the weekend, significant flood impacts are
likely with the multiple rounds of heavy rain. High Risks are not
out of the question in future EROs as the event draws nearer and it
becomes clearer how the details could evolve, especially into the
timeframe of the CAMs.

Through Wednesday, some April snow is likely on the backside of
the initial low track, stretching across the Dakotas to Upper
Midwest and Interior Northeast. Snow amounts have typical
uncertainty, and an axis of freezing rain and/or sleet is possible
as well. Meanwhile as troughing sets up over the West with multiple
shortwaves moving through, rounds of precipitation are possible
from the West Coast into the Intermountain West and Rockies.
Generally lower elevation rain and higher elevation snow are
expected, with mainly light to modest amounts. Additionally, high
winds are possible for the central Rockies on Wednesday. Into late
week, a possible upper low in the Four Corners region could lead to
enhanced precipitation totals across the southern and central
Rockies and Plains. Snow is likely in higher elevations of the
Rockies in Colorado and northern New Mexico, with uncertainty at
this point in if/how much snow could spill into lower elevations of
the High Plains.

Above normal temperatures will be located across the south-central
U.S. to Midwest on Wednesday, and settle across much of the
southern and eastern U.S. Thursday and beyond. Daytime highs 10 to
20 degrees above normal are possible. Meanwhile, the West should
trend and stay cooler underneath upper troughing through Friday. By
next weekend, temperatures may moderate somewhat along the West
Coast while eastern Pacific upper ridging moves in. This shifts
cooler temperatures slightly east, and daytime highs across parts
of the southern Rockies could be 10 to 20 degrees below normal next
weekend.


Tate/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
322 AM EDT Sun Mar 30 2025

Valid 00Z Mon 31 Mar 2025 - 00Z Mon 07 Apr 2025

An upper ridge over Hawaii should linger into Sunday bringing
weaker trades and lighter rainfall. By Monday though, the ridge
should slowly shift eastward as a deep upper low develops north of
the state within an overall blocky pattern. The guidance has come
into much better agreement regarding the evolution of this upper
low compared to yesterday. The cold front for this system may
eventually reach close to the islands allowing for strengthening
southerly winds and some increased precipitation chances for
mainly the western islands. Guidance shows the heaviest
precipitation should remain west of the island chain though. As
the upper low lifts northward late next week, surface high
pressure may again 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
846 PM EDT Sun Mar 30 2025
Day 1
Valid 01Z Mon Mar 31 2025 - 12Z Mon Mar 31 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS AND CENTRAL GULF
COAST...

...Central Gulf Coast through the Ohio Valley...

01Z Update...
With diminishing convection along the immediate Upper Gulf
coast...removed the Slight risk area introduced earlier in the day.
Was not inclined to remove the Marginal risk area which surrounded
the Slight risk given how hydrologically sensitive the area became
as a result of prolific rain-makers earlier today. The latest model
guidance kept the bulk of QPF well to the north and west during the
overnight hours. Even so...any convection still lingering near the
coast of Alabama westward into southeast Louisiana could result in
additional excessive rainfall concerns. Also trimmed the Marginal
risk area from the western Florida peninsula based on trends in
radar imagery. The remainder of the previously-issued outlook still
covered the higher model QPF and any associated potential for
excessive rainfall.

Bann

Previous Excessive Rainfall Discussion...

A pair of shortwave troughs emerge from the Intermountain West
into the Central U.S. today, eventually partially phasing with an
associated longwave trough by later tonight. This complex
interaction is expected to result in a broad area of organized
convective activity across much of the eastern half of the CONUS,
including portions of the MS, TN, and OH Valleys.

Despite the continued complexity of the synoptic and mesoscale
details, models remain in fairly good agreement in indicating
convection breaking out across the broad warm sector today,
initially mostly discrete (and supportive of splitting supercells
and multicell clusters) and evolving into a QLCS/LEWP ahead of the
associated cold front by this evening. Broad inflow from the Gulf
will result in precipitable water values of 1.25-1.75" (at or above
the 90th percentile, per CFSR climatology) and SB CAPE of 2000-4000
J/kg, as deep layer (0-6 km) shear increases to 40-60 kts. Hourly
rainfall of up to 3"/hr are possible in this environment,
initially highly localized in association with established
supercells, then more numerous to widespread with the passage of
the QLCS/LEWP. Localized totals of 2-4" are generally expected
within the Slight for the whole of the event (with the majority
falling in a 3-6 hour period in association with the QLCS passage),
with totals near the upper-end of the range (~4") being possible
where storms train and/or where two or more mesocyclones align.
While there were some changes per the new guidance, in general,
continuity was maintained.

Ongoing organized convection midday in the general vicinity of
Mobile hadn't been disrupted by diurnal convection in its
vicinity, which threatened mergers as disorganized convection
moves more northward while organized convection moves more
eastward. Cold cloud tops continued to show expansion with the
convective area midday, which led to the introduction of a midday Slight
Risk from southern MS across southern AL into the FL Panhandle.
Hourly rain totals to 3" with additional local amounts to 6" remain
possible for as long as this convective mass can persist.

...Florida Peninsula/Southeasternmost Georgia...
A frontal boundary at 850 hPa slowly lifts through the state,
bringing precipitable water values to 1.5-1.75". ML CAPE should
maximize in the 2000-3000 J/kg, particularly in the southern
Florida peninsula. There appears to be enough effective bulk shear
for some degree of thunderstorm organization as well. The model
guidance --- mostly mesoscale -- indicates the potential for local
amounts in the 5-6" range. The Marginal risk was maintained with
minimal change.

Roth/Churchill


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sun Mar 30 2025
Day 2
Valid 12Z Mon Mar 31 2025 - 12Z Tue Apr 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL GULF COAST...

...Central Gulf Coast/Southeast... T
A pair of shortwave troughs are progged to fully separate, as the
northern stream shortwave continues to phase with the parent
longwave trough into the Mid-Atlantic and Northeast, while the
southern shortwave likely hangs back into the Mid-South and Lower
MS Valley. The best moisture and instability lies over portions of
the Southeast (where forcing from the secondary shortwave should
still be sufficient for organized convective activity). The
Marginal risk was generally maintained from continuity. However,
due to recent convective events along the Central Gulf Coast,
upgraded to a Slight Risk for portions of southernmost MS, AL, and
the western FL Panhandle which should have increased sensitivity/
soil saturation. Localized totals of 2-4" are generally expected.


...Northeast...
Thunderstorms with heavy rainfall are expected during the afternoon
and evening hours ahead of a northern stream shortwave as MU CAPE
peaks around 1000 J/kg and precipitable water values peak in the
1.25-1.5" range. Sufficient inflow and effective bulk shear is
available for organized convection for much of the period, with
activity expected to be in decline past Tuesday 06z. Hourly rain
totals up to 2" are possible where convection trains, which could
challenge the flash flood guidance across urban portions of the
Mid-Atlantic States. The inherited Marginal risk showed minimal
change.

Roth/Churchill


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sun Mar 30 2025
Day 3
Valid 12Z Tue Apr 01 2025 - 12Z Wed Apr 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS & MIDWEST...

A blocking pattern begins to emerge by Tuesday, as the
aforementioned shortwaves lift northeastward into Canada with
large-scale ridging quickly builds across the eastern United States
from the North Atlantic. Meanwhile, large-scale troughing becomes
amplified out West, with a potent upper-low expected to develop
over the Northern Rockies and Plains (translating across the
Rockies from the Pacific Northwest). While 12z global model suites
are in overall good agreement with the evolution of the synoptic
scale, the GFS/NAM are drier than the rest of the guidance with the
associated surface low (which is depicted as a sub 990 mb low from
the GFS, ECMWF, and CMC). Within the GFS/NAM guidance, the idea of
light QPF is internally inconsistent as the forecast precipitable
water values (1-1.25") combined with the 1000-500 hPa thickness
values near 5610 meters suggest a nearly saturated atmosphere, and
there appears to be sufficient instability in the vicinity and
effective bulk shear for convective organization, so the wetter
guidance was more believable. However, nearly as soon as the
necessary ingredients are in place, they take off to the east due
to system progression. Most deterministic solutions follow that
idea and depict localized totals of 2"+ (including the downscaled
ECMWF, the UKMET, and the CMC- reg) with remarkably good spatial
agreement for this range. The ingredients above suggest hourly
rainfall up to 1.75" with local amounts in the 3-4" where/when
cells have the opportunity train or backbuild, so the inherited
Marginal risk remains, though the area showed some expansion.

Roth/Churchill

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Sun Mar 30 2025


Overall pattern amplification and a leading compact closed low
will support a surface low pressure system forming in the central
U.S. by Wednesday with widespread thunderstorms and heavy rainfall
across the east-central U.S. in its warm sector. Moist and unstable
inflow into the associated surface fronts along with the strong
upper level support will lead to widespread severe weather and
flash flooding concerns. SPC shows severe probabilities from the
south-central U.S. into the Midwest on Wednesday and Thursday. The
greatest concern for flash flooding on Wednesday and Thursday will
stretch across similar areas from the Ark-La-Tex northeast into the
Ohio Valley, as the front anchors storms for significant training
concerns. On Wednesday, precipitable water anomalies above the 95th
percentile with ample instability will be in place. Models are
indicating embedded rainfall totals of 5 to 8 inches during the 12Z
Wednesday to 12Z Thursday period alone, with the GFS already
explicitly forecasting hourly rain rates to 2", and certainly
expect the CAMs to show higher rates than that once we get into
their timeframe. Thus plan to upgrade the Day 4/Wednesday ERO to a
Moderate Risk from northeast Arkansas across the Ohio River Valley
to far southern Indiana. Much the same environmental pattern sets
up on Day 5/Thursday, with the added concern of very wet antecedent
conditions by then. The previously issued Moderate Risk for Day
5/Thursday was maintained, with a southwestward expansion per
coordination with the Little Rock local forecast office and
considering the higher instability there. Heavy rainfall is likely
to continue into late week, with perhaps a bit of a westward shift
into the southern Plains at times as the West trough pivots.
Through midweek into the weekend, significant flood impacts are
likely with the multiple rounds of heavy rain. High Risks are not
out of the question in future EROs as the event draws nearer and it
becomes clearer how the details could evolve, especially into the
timeframe of the CAMs.

Through Wednesday, some April snow is likely on the backside of
the initial low track, stretching across the Dakotas to Upper
Midwest and Interior Northeast. Snow amounts have typical
uncertainty, and an axis of freezing rain and/or sleet is possible
as well. Meanwhile as troughing sets up over the West with multiple
shortwaves moving through, rounds of precipitation are possible
from the West Coast into the Intermountain West and Rockies.
Generally lower elevation rain and higher elevation snow are
expected, with mainly light to modest amounts. Additionally, high
winds are possible for the central Rockies on Wednesday. Into late
week, a possible upper low in the Four Corners region could lead to
enhanced precipitation totals across the southern and central
Rockies and Plains. Snow is likely in higher elevations of the
Rockies in Colorado and northern New Mexico, with uncertainty at
this point in if/how much snow could spill into lower elevations of
the High Plains.

Above normal temperatures will be located across the south-central
U.S. to Midwest on Wednesday, and settle across much of the
southern and eastern U.S. Thursday and beyond. Daytime highs 10 to
20 degrees above normal are possible. Meanwhile, the West should
trend and stay cooler underneath upper troughing through Friday. By
next weekend, temperatures may moderate somewhat along the West
Coast while eastern Pacific upper ridging moves in. This shifts
cooler temperatures slightly east, and daytime highs across parts
of the southern Rockies could be 10 to 20 degrees below normal next
weekend.


Tate/Santorelli

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Sun Mar 30 2025


Overall pattern amplification and a leading compact closed low
will support a surface low pressure system forming in the central
U.S. by Wednesday with widespread thunderstorms and heavy rainfall
across the east-central U.S. in its warm sector. Moist and unstable
inflow into the associated surface fronts along with the strong
upper level support will lead to widespread severe weather and
flash flooding concerns. SPC shows severe probabilities from the
south-central U.S. into the Midwest on Wednesday and Thursday. The
greatest concern for flash flooding on Wednesday and Thursday will
stretch across similar areas from the Ark-La-Tex northeast into the
Ohio Valley, as the front anchors storms for significant training
concerns. On Wednesday, precipitable water anomalies above the 95th
percentile with ample instability will be in place. Models are
indicating embedded rainfall totals of 5 to 8 inches during the 12Z
Wednesday to 12Z Thursday period alone, with the GFS already
explicitly forecasting hourly rain rates to 2", and certainly
expect the CAMs to show higher rates than that once we get into
their timeframe. Thus plan to upgrade the Day 4/Wednesday ERO to a
Moderate Risk from northeast Arkansas across the Ohio River Valley
to far southern Indiana. Much the same environmental pattern sets
up on Day 5/Thursday, with the added concern of very wet antecedent
conditions by then. The previously issued Moderate Risk for Day
5/Thursday was maintained, with a southwestward expansion per
coordination with the Little Rock local forecast office and
considering the higher instability there. Heavy rainfall is likely
to continue into late week, with perhaps a bit of a westward shift
into the southern Plains at times as the West trough pivots.
Through midweek into the weekend, significant flood impacts are
likely with the multiple rounds of heavy rain. High Risks are not
out of the question in future EROs as the event draws nearer and it
becomes clearer how the details could evolve, especially into the
timeframe of the CAMs.

Through Wednesday, some April snow is likely on the backside of
the initial low track, stretching across the Dakotas to Upper
Midwest and Interior Northeast. Snow amounts have typical
uncertainty, and an axis of freezing rain and/or sleet is possible
as well. Meanwhile as troughing sets up over the West with multiple
shortwaves moving through, rounds of precipitation are possible
from the West Coast into the Intermountain West and Rockies.
Generally lower elevation rain and higher elevation snow are
expected, with mainly light to modest amounts. Additionally, high
winds are possible for the central Rockies on Wednesday. Into late
week, a possible upper low in the Four Corners region could lead to
enhanced precipitation totals across the southern and central
Rockies and Plains. Snow is likely in higher elevations of the
Rockies in Colorado and northern New Mexico, with uncertainty at
this point in if/how much snow could spill into lower elevations of
the High Plains.

Above normal temperatures will be located across the south-central
U.S. to Midwest on Wednesday, and settle across much of the
southern and eastern U.S. Thursday and beyond. Daytime highs 10 to
20 degrees above normal are possible. Meanwhile, the West should
trend and stay cooler underneath upper troughing through Friday. By
next weekend, temperatures may moderate somewhat along the West
Coast while eastern Pacific upper ridging moves in. This shifts
cooler temperatures slightly east, and daytime highs across parts
of the southern Rockies could be 10 to 20 degrees below normal next
weekend.


Tate/Santorelli

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
618 PM EDT Sun Mar 30 2025

Valid 00Z Mon Mar 31 2025 - 00Z Thu Apr 03 2025


...Northern Great Lakes & Northeast...
Day 1...

The winter storm is in its final hours of producing hazardous
impacts across the northern Great Lakes and northern New England.
On the backside of the storm, periods of snow are ongoing from
northern Iowa and southern Minnesota to northwest Wisconsin and
the western Michigan U.P.. Freezing rain is ongoing in parts of
north-central Wisconsin, the eastern Michigan U.P., and from the
White Mountains of New Hampshire on north into Maine. As the storm
heads northeast towards Lake Huron tonight, freezing rain/sleet in
the eastern Michigan U.P. and north-central Wisconsin will
changeover to snow as the deformation zone moves in overhead. The
CAD signature over New England will linger over the White Mountains
and much of Maine (sans the coastal areas) to keep an icy wintry
mix into the early morning hours on Monday. By 12Z Monday, snow
will finally be coming to an end across the northern Great Lakes
while it may take until midday for far northern Maine to finally
see the wintry mix transition to a plain/cold rain.

WPC probabilities show moderate-to-high chances (40-70%) for an
additional >4" of snowfall for areas along the shore of Lake
Superior in the MI U.P, the Huron Mountains of the Michigan U.P.,
and into far northern Wisconsin. In terms of additional freezing
rain, WPC probabilities show low-to-moderate chances (20-50%) for
additional ice accumulations >0.25" in the eastern Michigan U.P.,
the White Mountains, and far western Maine bordering Quebec.
Hazardous
travel conditions will linger through Monday morning with the
potential for additional power outages in the areas that could see
an additional 0.25" of ice.


...The West...
Days 1-3...

An active stretch of wintry weather has begun from the West Coast
to the Front Range of the Rockies through Tuesday due to the
prolonged influence of a deep longwave trough over the western
U.S..

This afternoon, focus shifts to an exceptional closed upper low in
the northeast Pacific that slowly makes its way east towards the
Pacific Northwest by Monday night. Heavy high elevation mountain
snow (above 6,000ft in the northern CA ranges and above 5,000ft in
both the Cascade and Blue Mountains) will be underway, but as the
upper low inches closer to the Northwest U.S., falling heights and
colder temperatures aloft will force snow levels to lower into
Monday. By 12Z Monday, NAEFS shows just about all mandatory height
levels listed are bottoming out below the 2.5 climatological
percentile while IVT values >500 kg/m/s are aimed at southern
California. The northern extent of the IVT will sport values >90th
climatological percentile through the Sierra Nevada and into the
Great Basin by Monday afternoon. From northern California to the
northern Rockies, the divergent left-exit region of a 200mb jet
streak whose wind speeds (>130 kts) are above the 99th
climatological percentile will be placed directly overhead.

The best moisture advection and upslope enhancement will be seen
from California's Siskiyou and Salmon mountains on south and west
along the spine of the Sierra Nevada. On Monday afternoon and into
Monday night, the flood of Pacific moisture aloft will advance well
inland through much of the Intermountain West. Just about every
notable mountain range in the central and northern Rockies is
likely to see measurable snow Monday night into Tuesday. Meanwhile,
cyclonic flow around the upper low will still support ongoing
upslope snowfall in the central and northern California ranges
through Tuesday night. Then by early Tuesday the parent upper low
is expected to dive southeast across southwest OR and northern
California, proving a final surge of Pacific moisture within an
area of cold air aloft. The bulk of the Pacific moisture advection
will be finished Tuesday night and into Wednesday, but the core of
the longwave trough will be over the Rockies with NAEFS showing
500mb temps that are below the 10th climatological percentile from
the Sierra Nevada to the Front Range of the Colorado Rockies. With
the help of daytime heating, expect numerous snow showers to
envelope most of the western U.S. mountain ranges given the steep
lapse rates.

Through 00Z Thursday, WPC probabilities show the northern ranges
of California (Siskiyou, Salmon, Shasta) and the length of the
central and northern Sierra Nevada have high chances (>70%) for
snowfall totals >24". Most of these ranges above 6,000ft are
currently forecast to see localized amounts between 3-5 feet
through 00Z Thursday. Heavy snow also reaches into the Oregon
Cascades with high probabilities for at least 12". Farther inland,
many Intermountain West ranges (Sawtooth, Blue, Uinta, Bear River,
Wind River, Absaroka, Big Horn, and CO/WY central Rockies) are all
likely to see snowfall totals of 6-12" with locally higher amounts
in these ranges as well. Expect hazardous travel conditions for
many road ways that remain open in these mountain ranges.


...Northern Plains and Upper Midwest...
Day 3...

By Tuesday morning, the upper trough responsible for the barrage of
mountain snow in the West will position the 250mb jet streak's
divergent left-exit region over the Great Plains. Modest 500mb PVA
and strengthening WAA at low levels will give rise to lee
cyclogenesis east of the Rockies. Throughout the day Tuesday a
strengthening LLJ, (NAEFS shows 850mb winds reaching the 97.5
climatological percentile 18Z Tuesday from north Texas to eastern
Kansas), will deliver both increased moisture and increasing WAA
aloft. The upper trough to the west will also direct an IVT of
300-500 kg/m/s into the Upper Midwest, which is topping the 90th
climatological percentile Tuesday afternoon. There appears to be
sufficiently cold enough air present that precipitation will
transition over from rain to snow from the Black Hills on east
across South Dakota and as far east as central Minnesota Tuesday
afternoon that is largely due to strong 300K isentropic ascent and
850-700mb WAA resulting in FGEN at those mandatory height levels.

There are ongoing differences in the position and strength of this
winter storm. The GFS/CMC camps sports a deeper and more northerly
track storm system. The ECMWF and its AI counterpart (EC-AIFS) are
farther south and take a little longer to ramp up the storm system.
The GEFS is on the slower side of the upper trough's progression,
allowing it to be deeper and phase more effectively with nearby
shortwave troughs. The GEPS is more in between the ECENS, with the
latter being a little flatter and taking longer for the trough to
deepen, thus forcing the storm's more southerly track initially.

The ECMWF EFI continues to depict an increasing signal for a
potentially disruptive winter storm from the Dakotas on east across
northern Minnesota. This also aligns fairly well where WSO values
>50% exist on Days 3-4. Both snow amounts, along with snow load
and blowing snow, are likely to be hazards that the Northern Plains
and Upper Midwest contend with through Wednesday, with freezing
rain most likely on the eastern edge of the WAA across northern
Wisconsin and northern Michigan. Current WPC snowfall probabilities
(through 00Z Thursday) for >6" are moderate- to-high chance
(50-80%) across the eastern Dakotas and northern Minnesota. There
are also low-to-moderate chance probabilities (20-40%) for snowfall
totals >12" along the Minnesota Arrowhead. Residents and those
traveling to/from these regions should keep close eyes on the
forecast as additional changes in the types of impacts, the
severity of those impacts, and where/when these impacts occur are
likely to fluctuate for another day or so.

*Key Messages have been issued for this winter storm, and the link
to view them is posted below.


Mullinax



...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
300 PM EDT Sun Mar 30 2025

Valid 12Z Wed Apr 02 2025 - 12Z Sun Apr 06 2025


...Multi-day heavy rain/flooding and severe threat for
Lower/Middle Mississippi, Tennessee, and Ohio Valleys this week...


...Overview...

The medium range upper pattern will be amplified, blocky, and
active through the period. A surface low emerging into the Plains
by Wednesday will track towards the Great Lakes as a building upper
ridge over the western Atlantic into the Gulf should keep the
associated frontal boundary from making much progress on the
southern side, especially later in the week. This sets the stage
for a multi-day heavy rain and severe weather event from the Lower
Mississippi into the Ohio Valley, and significant flooding is
likely. Late-season snow is likely north of this system from the
northern Plains to Great Lakes and Interior Northeast for midweek,
and the Colorado Rockies are likely to see snow by late week. The
West should stay relatively cool underneath persistent troughing,
while above normal temperatures progress from the central U.S. and
Midwest, eventually settling late week across the Southeast and
into the Mid-Atlantic.


...Guidance/Predictability Assessment...

Model guidance is relatively agreeable on the large scale pattern
midweek into next weekend, but still uncertain with some of the
details, which could have sensible weather impacts. A building and
blocky ridge over the Atlantic to Gulf should help amplify
troughing over the West through the period. Shortwaves within that
trough show relatively more spread, but the first shortwave/compact
upper low and its associated surface low tracking from the Central
U.S. to Great Lakes into Thursday continues to show agreement. By
Friday and into the weekend, there is somewhat more uncertainty in
the details of another shortwave digging through the western side
of the trough. ECMWF runs in particular have been on the western
side with this energy compared to the larger consensus of other
models and even EC-based AI/ML models. The new 12Z ECMWF seems to
be coming into better alignment with the majority in the energy and
trough placement. Regardless there is still some spread in what
becomes of this energy next weekend, perhaps producing a closed
upper low within the trough becoming positively tilted while models
are converging on showing an upper ridge axis over the Northwest.

At the surface, a stationary frontal boundary will set up between
the Southeast ridge and Western trough that persists for several
days. There remain subtle differences still in the exact placement
of this front, which has notable implications on the exact
locations of heavy rainfall expected to accompany the front. Expect
these to vary a bit in future forecasts, though the general idea
of heavy rain leading to possibly significant flooding in parts of
the east-central U.S. is pretty locked in. A northern stream trough
may help to slowly nudge the stagnant east-central U.S. boundary
eastward a bit next weekend, though some typical spread remains
with the timing and depth of that trough.

The WPC forecast was able to utilize a deterministic model blend
through Day 4. By Day 5, began incorporating some ensemble mean
guidance to help temper the detail differences, while reducing the
proportion of operational models (especially the 00Z ECMWF) in
favor of over half means for Days 6-7. This approach maintained
relatively good agreement with the previous WPC forecast.


...Weather/Hazards Highlights...

Overall pattern amplification and a leading compact closed low
will support a surface low pressure system forming in the central
U.S. by Wednesday with widespread thunderstorms and heavy rainfall
across the east-central U.S. in its warm sector. Moist and unstable
inflow into the associated surface fronts along with the strong
upper level support will lead to widespread severe weather and
flash flooding concerns. SPC shows severe probabilities from the
south-central U.S. into the Midwest on Wednesday and Thursday. The
greatest concern for flash flooding on Wednesday and Thursday will
stretch across similar areas from the Ark-La-Tex northeast into the
Ohio Valley, as the front anchors storms for significant training
concerns. On Wednesday, precipitable water anomalies above the 95th
percentile with ample instability will be in place. Models are
indicating embedded rainfall totals of 5 to 8 inches during the 12Z
Wednesday to 12Z Thursday period alone, with the GFS already
explicitly forecasting hourly rain rates to 2", and certainly
expect the CAMs to show higher rates than that once we get into
their timeframe. Thus plan to upgrade the Day 4/Wednesday ERO to a
Moderate Risk from northeast Arkansas across the Ohio River Valley
to far southern Indiana. Much the same environmental pattern sets
up on Day 5/Thursday, with the added concern of very wet antecedent
conditions by then. The previously issued Moderate Risk for Day
5/Thursday was maintained, with a southwestward expansion per
coordination with the Little Rock local forecast office and
considering the higher instability there. Heavy rainfall is likely
to continue into late week, with perhaps a bit of a westward shift
into the southern Plains at times as the West trough pivots.
Through midweek into the weekend, significant flood impacts are
likely with the multiple rounds of heavy rain. High Risks are not
out of the question in future EROs as the event draws nearer and it
becomes clearer how the details could evolve, especially into the
timeframe of the CAMs.

Through Wednesday, some April snow is likely on the backside of
the initial low track, stretching across the Dakotas to Upper
Midwest and Interior Northeast. Snow amounts have typical
uncertainty, and an axis of freezing rain and/or sleet is possible
as well. Meanwhile as troughing sets up over the West with multiple
shortwaves moving through, rounds of precipitation are possible
from the West Coast into the Intermountain West and Rockies.
Generally lower elevation rain and higher elevation snow are
expected, with mainly light to modest amounts. Additionally, high
winds are possible for the central Rockies on Wednesday. Into late
week, a possible upper low in the Four Corners region could lead to
enhanced precipitation totals across the southern and central
Rockies and Plains. Snow is likely in higher elevations of the
Rockies in Colorado and northern New Mexico, with uncertainty at
this point in if/how much snow could spill into lower elevations of
the High Plains.

Above normal temperatures will be located across the south-central
U.S. to Midwest on Wednesday, and settle across much of the
southern and eastern U.S. Thursday and beyond. Daytime highs 10 to
20 degrees above normal are possible. Meanwhile, the West should
trend and stay cooler underneath upper troughing through Friday. By
next weekend, temperatures may moderate somewhat along the West
Coast while eastern Pacific upper ridging moves in. This shifts
cooler temperatures slightly east, and daytime highs across parts
of the southern Rockies could be 10 to 20 degrees below normal next
weekend.


Tate/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