Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
431 PM EDT Tue Mar 25 2025

Valid 00Z Wed Mar 26 2025 - 00Z Fri Mar 28 2025

...There is a Moderate Risk of excessive rainfall over Southern Texas on
Wednesday and Thursday...

...There is a Slight Risk of severe thunderstorms over parts of the
Pacific Northwest on Wednesday...

...Light snow from the Great Lakes to the Northeast on Wednesday into
Thursday...

Two weak fronts will move across the Great Lakes to the Northeast through
Thursday. The boundaries will produce light snow over parts of the Great
Lakes into the Northeast, with the light snow ending over the Great Lakes
by Wednesday night. The snow will continue over parts of Northern New
England through Thursday night. Overnight Wednesday, the second front will
move into the Upper Great Lakes, producing light snow over parts of the
Upper Great Lakes overnight Wednesday into Thursday evening. Furthermore,
light rain will develop over parts of the Lower Great Lakes on Thursday
evening.

Meanwhile, a third front extending from the southern Mid-Atlantic to the
Southern Plains will move eastward off the Southeast Coast by Wednesday
morning and southward to Florida and the Gulf Coast by Thursday. The
western end of the boundary will linger over/near the Western Gulf Coast
by Thursday evening. The boundary will produce light rain from the
Mid-Atlantic to the Ohio Valley early Tuesday night, with the rain ending
by early Wednesday morning. Light snow will develop over the Central
Appalachians by Wednesday morning, ending early Wednesday afternoon.

A weak moisture flow off the Gulf of America will stream northward over
the Southern Plains/Lower Mississippi Valley, producing showers and
thunderstorms over parts of the region overnight Tuesday. Upper-level
energy will develop an upper-level low over Texas on Wednesday night. The
developing upper-level low will pull move moisture off the Gulf of
America, producing showers and thunderstorms with heavy rain on Wednesday
into Thursday. Therefore, the WPC has issued a Moderate Risk (level 3/4)
of excessive rainfall over parts of southern Texas from Wednesday into
Thursday morning. Numerous flash flooding events are possible. Many
streams may flood, potentially affecting larger rivers.

The excessive rainfall threat will continue over the Western Gulf Coast on
Thursday. Therefore, the WPC has issued a Moderate Risk (level 3/4) of
excessive rainfall over parts of the Western Gulf Coast on Thursday.
Numerous flash flooding events are possible. Many streams may flood,
potentially affecting larger rivers.

Furthermore, the moisture over the Gulf Coast will continue northward into
Central Plains/Middle Mississippi Valley, producing showers and
thunderstorms over the region through Thursday evening.

In the meantime, a fourth front over the Eastern Pacific moves onshore
over the West Coast Wednesday afternoon into evening, continuing eastward
to the Northern Rockies to Southern California by Thursday evening. The
system will produce showers and thunderstorms over the Pacific Northwest
from Wednesday afternoon into Thursday. In addition, some of the
thunderstorms will be severe. Therefore, the SPC has issued a Slight Risk
(level 2/5) of severe thunderstorms over the Pacific Northwest from
Wednesday through Thursday morning. The hazards associated with these
thunderstorms are frequent lightning, severe thunderstorm wind gusts,
hail, and a few tornadoes. There is an added threat of hail, two inches or
greater over the region.

Showers and thunderstorms will continue over the Pacific Northwest into
the Northern Intermountain Region and Northern Rockies into Thursday
evening.

Overnight Wednesday, rain will develop over parts of Northern California
and by Thursday morning, after the front passes, snow levels will lower
over the Northwest and California. The storm will produce rain and highest
elevation snow over the Cascades Northern California and the Sierra Nevada
Mountains.


Ziegenfelder


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Wed Mar 26 2025

Valid 12Z Sat Mar 29 2025 - 12Z Wed Apr 02 2025

...Overview...

Continue to expect a moderately progressive pattern with active
weather across portions of the Lower 48. A southern stream
shortwave should bring a threat of locally heavy rain into the
east-central Gulf Coast early this weekend, but with less extreme
totals than expected farther west in the short range time frame.
Meanwhile emerging western dynamics will help to develop a wavy
frontal system pushing eastward from the Plains through the East
this weekend into next Monday. This system should produce some
wintry weather over northern latitudes with areas of enhanced
rainfall farther south. A system most likely to track northward
offshore the West coast should spread precipitation into the West
from late weekend into early next week. Additional precipitation
may reach the West into midweek, while leading moisture reaches the
east-central states, but guidance shows a lot of spread for flow
details by then so forecast confidence trends well below average.
Very warm temperatures will prevail ahead of the Plains/eastern
U.S. system while trailing cooler air will bring readings back down
to near or below normal.

...Guidance/Predictability Assessment...

Models are still working on resolving important finer details of
shortwave energy emerging from the West during the weekend and
continuing eastward thereafter. Shortwave differences have a
meaningful impact on surface wave specifics, with dynamical and
machine learning (ML) models still exhibiting a fairly wide
envelope by the time the system reaches the East. Among the 12Z/18Z
guidance, GFS runs and the UKMET were on the sharp/strong side
with the shortwave and the CMC on the weak/broad side. Ultimately
preferred a blend of the 18Z GFS/12Z ECMWF and their ensemble means
early in the period, trending to just 30 percent ECMWF and the
rest means by Day 5/Monday.

Farther west, guidance has also been quite diverse for low
pressure that may develop close to the West Coast around Sunday-
Monday. Some solutions like the 12Z CMC/UKMET merely brought a weak
wave into California while other solutions wrap it northward into
the mean low off the Pacific Northwest. ML models varied a lot as
well, thus providing little additional insight. The aforementioned
preference maintained good continuity with offshore development
lifting into the northern mean low.

Behind this system there is still remarkably wide divergence for
aspects of the blocky pattern over the Pacific and extending into
the Lower 48, with areas over the eastern Pacific and western U.S.
in particular showing ensemble members ranging between a ridge and
a trough--the GFS/GEFS tending to have more troughing over the
eastern Pacific and the ECMWF/CMC favoring a deeper trough over the
West. Adding to the confusion, some ML models actually develop a
decent ridge over the West while the AIFS tilts in the operational
ECMWF direction. Even with the differences aloft, by Wednesday
there is at least a common surface theme of high pressure over the
East and an axis of lower pressures over the Plains. At that time
favor a conservative forecast combining the GEFS/ECens means to
yield flat to broadly cyclonic flow aloft while waiting better
agreement in the dynamical and ML models.

...Weather/Hazards Highlights...

The Day 4/Saturday Excessive Rainfall Outlook maintains a Marginal
Risk area along and somewhat north of the central/east-central
Gulf Coast region, with only minor adjustments from continuity.
Guidance is consistent with the setup for locally heavy rainfall
(but trending somewhat lighter than across areas farther to the
west), as the supporting southern tier upper shortwave pushes
eastward. The distribution of solutions has remained similar as
well, with the ECMWF/UKMET and machine learning models clustered in
showing meaningful rainfall potential given sufficient moisture
and instability versus a more diffuse signal in other guidance. By
Day 5/Sunday expect a broad area of convection to develop over the
east-central U.S. ahead of the wavy front pushing eastward from the
Plains. Current guidance recommends a broad Marginal Risk area
from the Ohio Valley southwest into parts of the lower Mississippi
Valley. Improved guidance clustering especially from the Ohio
Valley southward where soils are on the damp side could eventually
lead to an embedded upgrade in risk level.

More broadly, the wavy frontal system affecting the central and
eastern U.S. will produce meaningful precipitation from the
northern Rockies/High Plains into the Northeast as well farther
south over the East, though the latter should be with lighter
totals than forecast over the area covered by the aforementioned
Day 5 Marginal Risk. In addition, the Storm Prediction Center is
monitoring the potential for severe weather from the east-central
U.S. to the Mid-Atlantic/Southeast during Sunday-Monday. Check
latest SPC outlooks for the latest info on severe threats. Some
snow will be possible across northern latitudes, with Rockies and
Plains totals dependent on elevation and/or time of day. There may
be a band of wintry mix separating the snow from rain from the
Upper Midwest into New England.

After a brief break, an area of rain and high elevation snow
should reach into the West by Sunday-Monday, most likely from
northern California into the Pacific Northwest and perhaps
extending into the northern Rockies by early next week. There is
still spread in the guidance for supporting low pressure but new
solutions are starting to cluster somewhat better for low pressure
wrapping up offshore the Pacific Northwest. Increasingly dramatic
guidance differences for the eastern Pacific/western U.S. pattern
early-mid week lead to low confidence for how much additional
precipitation may reach the West Coast. Initially preferred
ensemble-based guidance suggests a wetter trend focused along the
central West Coast into midweek, but there is a minority of
solutions with a drier forecast.

Very warm temperatures will prevail in the warm sector ahead of
the wavy frontal system evolving over the Plains and then pushing
eastward. During the weekend expect the warmest anomalies to extend
from the southern half of the Plains through the Midwest, Ohio
Valley, and Mid-Atlantic with readings 10-25F above normal (with
morning lows tending to be somewhat more anomalous than daytime
highs). Frontal progression will confine the warmth more toward the
East Coast by next Monday. Northern New England should remain a
lot colder though, as a sharp front stays just to the south. Near
to below normal readings will progress eastward behind the
Plains/eastern U.S. front, with precipitation keeping some
northern-central High Plains locations 10-15F below normal for
highs during the weekend. Periods of unsettled weather will keep
the diurnal spread over the West Coast states more narrow than
usual.

Rausch


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
340 AM EDT Tue Mar 25 2025

Valid 00Z Wed 26 Mar 2025 - 00Z Wed 02 Apr 2025

As an initial stalled front near the northern islands lifts back
to the north, expect multiple days of east/southeasterly trades
that should extend into at least part of the weekend. Today's
guidance continues to suggest that background flow will be
sufficient to support some windward focus for showers, but at
times it could be weak enough to allow for sea breeze influence.
Continuity looks good for the late week into early weekend time
frame providing the lightest rainfall as an upper ridge builds
into and settles over the area. The GFS/GEFS are still a little
weaker with this ridge than the majority cluster but have been
gradually trending stronger. From around late weekend into next
week the low level winds should turn more southerly and trend a
little stronger ahead of a developing system well to the
west/northwest of the state. The axis of heavier rainfall should
remain west of the main islands through Tuesday but some spread
develops for how close this axis reaches. Latest machine learning
models support a slower progression more like recent GFS runs
versus the farther east 00Z ECMWF/CMC and 12Z ECens mean.

Rausch

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Tue Mar 25 2025
Day 1
Valid 01Z Wed Mar 26 2025 - 12Z Wed Mar 26 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF NORTHEAST TEXAS INTO SOUTHERN OKLAHOMA AND OVER PORTIONS OF
SOUTHEAST FLORIDA...

...Florida...

Maintained the Marginal Risk area across the southeast Florida
peninsula after realigning it based on even trends in satellite and
radar imagery. Even though loss of daytime heating should result in
diminishing risk of excessive rainfall due to loss of daytime
heating by late evening...it was too early to entirely remove the
Marginal risk area as additional showers and thunderstorms capable
of producing downpours in a highly urbanized area...a few places
which had locally heavy rainfall earlier in the day. The
expectation is that the risk of excessive rainfall will diminish by
26/04Z.

...Texas/Oklahoma...

Convection has initiated across portions of southern OK near and
just north of a stationary front. Southerly flow should continue to
advect moisture northward and result in upwards of 1000-2000 j/kg
of CAPE with a base just above the boundary layer. This elevated
convection will track off to the southeast, generally parallel to
the low level convergence axis...which supports some training
potential. The 3km NAM remained the wettest model, but we have
seen elevated convective setups like this verify towards the higher
end of the model spread, and the 3km NAM has performed decently at
these events in the past. So while it depicts a lower probability
outcome based on all available guidance, and a swath of 1-3" is
most likely, can not rule out a localized swath of 3-6" of rain
across portions of northeast TX into southern OK late tonight into
Wednesday morning.

Overall the flash flood risk at any location is low given the dry
antecedent conditions and narrow nature of any heavy rainfall
swath. However intense rainfall rates and some training could allow
for a localized flash flood threat to evolve, particularly if the
heavy rain overlaps any more sensitive urban or low lying area. We
opted to maintain a focused Marginal risk area to account for this
isolated potential.

Chenard


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Tue Mar 25 2025
Day 2
Valid 12Z Wed Mar 26 2025 - 12Z Thu Mar 27 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH-CENTRAL AND SOUTH TEXAS...

Model guidance continues to speed up the timing of the onset of the
heavy rainfall event over southern TX. It now appears likely that
organized convection will begin growing upscale by later Wednesday
afternoon or evening. This area has been very dry and could use the
rain, unfortunately this setup looks good enough to be a case
where it's beneficial rain initially, but then quickly overwhelms
even the dry soil conditions. Model soundings by Wed
afternoon/evening show a deeply saturated profile with good
directional shear and moderate instability. This should support
some convective clusters with some weak mesocyclones and right
mover motions are very slow. Combine that with the front nearby and
anticipate upscale growth of slow moving convective clusters
through Wed night within an environment capable of 2-3" per hour
rainfall. Activity may eventually grow upscale enough that it
begins propagating east and possibly offshore, however even if that
eventually transpires, there will still be a prolonged period
where training convection is a possibility.

Overall there is above average model agreement on this overall
evolution, with only the 3km and 12km NAM really standing out as
outliers, and those are two of the less reliable models for
situations such as this. While confidence on the event happening
is above average, there is still uncertainty on the exact axis of
heaviest rainfall, which will probably be somewhat narrow in
nature. For now the MDT risk is centered around the highest HREF
probabilities, and generally on the southern gradient of the global
model QPF solutions. Flash flood coverage over this area is
expected to increase Wednesday night into Thursday morning, and
locally significant impacts are possible.

...Pacific Northwest...
A Marginal risk was added across portions of western OR and WA.
Convection is expected to develop over portions of southwest OR by
21z Wed and then track off to the north through the afternoon and
evening hours. An anomalous amounts of CAPE is forecast,
potentially upwards of 2000 j/kg, and PWs are forecast over the
climatological 90th percentile. This combination of CAPE and PWs
supports intense rainfall rates. These cells should be quick moving
and the bigger hazard is probably severe weather (as highlighted
by the SPC Slight risk), however the intense rainfall rates
producing over 1" in an hour may be enough for localized flash
flood concerns. Areas of terrain, urban areas, and low lying areas
will be most prone to localized flash flooding driven by these
short duration intense rainfall rates.

Chenard

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
853 PM EDT Tue Mar 25 2025
Day 3
Valid 12Z Thu Mar 27 2025 - 12Z Fri Mar 28 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTH-CENTRAL AND SOUTH TEXAS AND MUCH OF THE TEXAS GULF
COAST...

...South Texas...
The event described in the day 2 discussion over south TX will
continue into Thursday. There is a bit more uncertainty on the
details by this time as convective evolution will likely be
impacted by mesoscale influences of the day 2 convection. On the
synoptic scale, ingredients are likely even more favorable for
heavy rainfall on day 3 then they were on day 2. Large scale
forcing should reload and be even a bit stronger as the mid level
trough axis and associated shortwave energy moves across the area.
The CSU machine learning ERO is showing higher end MDT risk
probabilities (albeit probably a bit too far north), likely
indicating the favorable ingredients that will be in place for
excessive rainfall.

However, the extent of the excessive rainfall risk will likely be
at least partially dependent on mesoscale factors...such as the
outflow location form the day 2 convection and its impact on
instability. The expectation is that the outflow boundary will be
near the coast by this time, and so that is where the greatest
focus for training convection is expected on Thursday, and thus
where the MDT risk is in place. There is some chance this is
offshore by 12z Thursday, but the current consensus suggests it
may struggle to clear the coast, leaving coastal areas susceptible
to additional heavy rainfall and flash flooding. Even if
instability is eroded by Thursday, the increase in forcing and
southerly flow should be enough to destabilize portions of the area
again with time, and so do think at least some flash flood risk
exists even in a scenario where convection initially propagates
offshore.

Overall confidence is high in a flash flood event, but confidence
in the details by Thursday remains low. In a worst case scenario
outflow stalls near the coast allowing for repeat convection and a
significant flash flood event could evolve. In a best case
scenario convection propagates offshore, but redevelopment later in
the day still results in some flash flood threat, albeit probably
less significant. When combining day 2 and 3 it seems probable that
some areas receive 5-10" of rain over south TX, and localized
amounts of 10-15" are certainly possible. Confidence is increasing
in the coverage of flash flooding and the possibility of at least
localized significant impacts, warranting the Moderate risks on
both days 2 and 3.

...MS and OH Valley...
A Marginal risk was added across portions of northern MO, southern
IA, IL and central/southern IN. A stationary front draped across
this region will gradually lift north as a warm front through the
period. Southerly flow will result in an uptick in instability and
moisture, and at least scattered convection is expected Thursday
into Thursday night. There is at least some chance for organized
convective development near the front, which could briefly train
from west to east. Global model QPF is locally as high as 1-3"
along this corridor, and given the expected convective nature of
activity, this would suggest isolated amounts over 3" are probable.
A localized, and generally minor, flash flood risk could result.

...Pacific Northwest...
Another modest Atmospheric River (narrow ribbon of 500+ kg/m/s
IVTs) will result in pockets of 3-5+ inch 24 hour rainfall totals
along the West Coast from Northern CA northward through OR-WA.
Among the 00Z 3/25 models, the Regional GEM is by far the wettest,
with isolated totals of 6-8+ inches. Despite the lack of
instability, the wet antecedent soils along with the potential of
0.3-0.5 in/hr rainfall rates could lead to localized short-term
runoff issues, particularly along small streams and over burn
scars.

Chenard/Hurley


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 Tue Mar 25 2025


Latest guidance is consistent with the general theme of heavy rain
potential along and near the west-central into central Gulf Coast,
as an upper trough interacts with low level Gulf moisture and a
warm front. The Day 4/Friday Excessive Rainfall Outlook has
introduced a Slight Risk area covering parts of southeastern Texas
and southwestern Louisiana, with models/ensembles now clustering
better for this region seeing the best focus. By Day 5/Saturday,
guidance becomes much more diffuse with the rainfall signal. Recent
ECMWF/ECMWF AIFS/UKMET runs show the most agreeable theme of some
activity from Friday-Friday night continuing into Saturday, with
some instability, before trending lighter. Thus the Day 5 ERO
depicts a Marginal Risk area along and north of the central Gulf
Coast region.

Elsewhere, rain and high elevation snow will cross the northern
half of the West late this week, followed by an increasing area of
precipitation from the north-central Plains through Northeast and
extending southward through the Mississippi Valley and points east
during the weekend into early next week as one or more frontal
waves evolve and the overall frontal system eventually pushes
eastward. It may be cold enough to support wintry precipitation
types for a time from the northern Plains through the Upper Great
Lakes into northern New England. To the south, some rain could be
locally heavy over the north central Plains as well as from the
Mississippi Valley eastward. In addition, the Storm Prediction
Center is monitoring the potential for severe weather from parts of
the eastern Plains into a large part of the east- central U.S.
during the weekend. Check latest SPC outlooks for the latest info
on severe threats.

After a brief break, another area of precipitation should spread
across the West from Sunday into early next week. There is still a
decent amount of uncertainty for the specifics of supporting
eastern Pacific low pressure, but currently expect highest totals
to be over the central West Coast/northern California.

Very warm temperatures will prevail in the warm sector ahead of
the wavy frontal system evolving over the Plains and then pushing
eastward. Some areas from the central High Plains into the Midwest
may see highs 20-30F above normal on Friday. The warmth will shift
south and east over the weekend with plus 20F or greater anomalies
for morning lows reaching from the Midwest into the Ohio Valley
while plus 10-20F anomalies for highs extend from the southern half
of the Plains into the Mid-Atlantic and Southeast. Continued
frontal progression will confine above normal readings to the East
Coast by Monday. However the Northeast will be on the cool side, to
the north of a front settling over or near the northern Mid-
Atlantic. Behind the main frontal system, modestly below normal
highs will progress from the West late this week into the Great
Lakes/Ohio Valley by next Tuesday.

Rausch

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Tue Mar 25 2025


Latest guidance is consistent with the general theme of heavy rain
potential along and near the west-central into central Gulf Coast,
as an upper trough interacts with low level Gulf moisture and a
warm front. The Day 4/Friday Excessive Rainfall Outlook has
introduced a Slight Risk area covering parts of southeastern Texas
and southwestern Louisiana, with models/ensembles now clustering
better for this region seeing the best focus. By Day 5/Saturday,
guidance becomes much more diffuse with the rainfall signal. Recent
ECMWF/ECMWF AIFS/UKMET runs show the most agreeable theme of some
activity from Friday-Friday night continuing into Saturday, with
some instability, before trending lighter. Thus the Day 5 ERO
depicts a Marginal Risk area along and north of the central Gulf
Coast region.

Elsewhere, rain and high elevation snow will cross the northern
half of the West late this week, followed by an increasing area of
precipitation from the north-central Plains through Northeast and
extending southward through the Mississippi Valley and points east
during the weekend into early next week as one or more frontal
waves evolve and the overall frontal system eventually pushes
eastward. It may be cold enough to support wintry precipitation
types for a time from the northern Plains through the Upper Great
Lakes into northern New England. To the south, some rain could be
locally heavy over the north central Plains as well as from the
Mississippi Valley eastward. In addition, the Storm Prediction
Center is monitoring the potential for severe weather from parts of
the eastern Plains into a large part of the east- central U.S.
during the weekend. Check latest SPC outlooks for the latest info
on severe threats.

After a brief break, another area of precipitation should spread
across the West from Sunday into early next week. There is still a
decent amount of uncertainty for the specifics of supporting
eastern Pacific low pressure, but currently expect highest totals
to be over the central West Coast/northern California.

Very warm temperatures will prevail in the warm sector ahead of
the wavy frontal system evolving over the Plains and then pushing
eastward. Some areas from the central High Plains into the Midwest
may see highs 20-30F above normal on Friday. The warmth will shift
south and east over the weekend with plus 20F or greater anomalies
for morning lows reaching from the Midwest into the Ohio Valley
while plus 10-20F anomalies for highs extend from the southern half
of the Plains into the Mid-Atlantic and Southeast. Continued
frontal progression will confine above normal readings to the East
Coast by Monday. However the Northeast will be on the cool side, to
the north of a front settling over or near the northern Mid-
Atlantic. Behind the main frontal system, modestly below normal
highs will progress from the West late this week into the Great
Lakes/Ohio Valley by next Tuesday.

Rausch

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
236 AM EDT Wed Mar 26 2025

Valid 12Z Wed Mar 26 2025 - 12Z Sat Mar 29 2025


...Northeast...
Day 1...

Compact upper low over southwestern Ontario this morning will move
across northern NY/VT midday and through Maine this evening. This
will spur some more light snow into the Tug Hill Plateau where 1-3"
is likely. Farther east, low probabilities (10-30%) are shown for
more than 4 inches of snow over the Green and White mountains via
upslope enhancement as the feature moves through.



...Upper Midwest/Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary astride the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through Canada and into the Northeast with
an influx of moisture from the southwest, reaching into NY Fri
evening then into New England overnight into early Saturday.
Temperatures are marginal for most areas, confining wintry
precipitation to areas closer to the Canadian border. However, that
sub-freezing surface layer will be overrun from the S/SW with
warmer air aloft, promoting a rather large area of sleet/freezing
rain from northern MN eastward across the U.P. of Michigan and
northern WI across Ontario and into the Adirondacks. Ptype from the
models (and NBM) show a strong signal for freezing rain
(impressive for late March), but this may be modulated my afternoon
insolation. Nevertheless, WPC probabilities for at least 0.10"
icing are moderate (30-70%) over northeastern MN, the U.P./northern
WI, and the northern part of Lower Michigan. Snow amounts may be
limited, with the highest amounts of a couple inches over northern
MN where WPC probabilities for at least 4 inches are barely 10%.


...Cascades into the northern Sierra Nevada...
Days 2-3...

An anomalously deep, cold core low in the northeast Pacific will
curl up toward Vancouver Island as its wound up occlude front moves
inland tonight. High snow levels (>8000ft) this afternoon will
steadily drop to around 4000-5000ft tomorrow, then to around 4000ft
Friday with the passage of the upper trough. Snow will eventually
get to some of the passes but much of this will fall over the
higher terrain. Two-day probabilities of at least 8 inches of snow
are highest above 5000ft or so along the Cascades southward to the
NorCal ranges and northern Sierra. Moisture will continue inland to
the northern Rockies with a few to several inches of snow for the
Blue Mountains and into SW MT as a frontal boundary in the area
acts as another focus for forcing. There, WPC probabilities for at
least 8 inches of snow are low (10-30%).


Fracasso

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Wed Mar 26 2025

Valid 12Z Sat Mar 29 2025 - 12Z Wed Apr 02 2025

...Overview...

Continue to expect a moderately progressive pattern with active
weather across portions of the Lower 48. A southern stream
shortwave should bring a threat of locally heavy rain into the
east-central Gulf Coast early this weekend, but with less extreme
totals than expected farther west in the short range time frame.
Meanwhile emerging western dynamics will help to develop a wavy
frontal system pushing eastward from the Plains through the East
this weekend into next Monday. This system should produce some
wintry weather over northern latitudes with areas of enhanced
rainfall farther south. A system most likely to track northward
offshore the West coast should spread precipitation into the West
from late weekend into early next week. Additional precipitation
may reach the West into midweek, while leading moisture reaches the
east-central states, but guidance shows a lot of spread for flow
details by then so forecast confidence trends well below average.
Very warm temperatures will prevail ahead of the Plains/eastern
U.S. system while trailing cooler air will bring readings back down
to near or below normal.

...Guidance/Predictability Assessment...

Models are still working on resolving important finer details of
shortwave energy emerging from the West during the weekend and
continuing eastward thereafter. Shortwave differences have a
meaningful impact on surface wave specifics, with dynamical and
machine learning (ML) models still exhibiting a fairly wide
envelope by the time the system reaches the East. Among the 12Z/18Z
guidance, GFS runs and the UKMET were on the sharp/strong side
with the shortwave and the CMC on the weak/broad side. Ultimately
preferred a blend of the 18Z GFS/12Z ECMWF and their ensemble means
early in the period, trending to just 30 percent ECMWF and the
rest means by Day 5/Monday.

Farther west, guidance has also been quite diverse for low
pressure that may develop close to the West Coast around Sunday-
Monday. Some solutions like the 12Z CMC/UKMET merely brought a weak
wave into California while other solutions wrap it northward into
the mean low off the Pacific Northwest. ML models varied a lot as
well, thus providing little additional insight. The aforementioned
preference maintained good continuity with offshore development
lifting into the northern mean low.

Behind this system there is still remarkably wide divergence for
aspects of the blocky pattern over the Pacific and extending into
the Lower 48, with areas over the eastern Pacific and western U.S.
in particular showing ensemble members ranging between a ridge and
a trough--the GFS/GEFS tending to have more troughing over the
eastern Pacific and the ECMWF/CMC favoring a deeper trough over the
West. Adding to the confusion, some ML models actually develop a
decent ridge over the West while the AIFS tilts in the operational
ECMWF direction. Even with the differences aloft, by Wednesday
there is at least a common surface theme of high pressure over the
East and an axis of lower pressures over the Plains. At that time
favor a conservative forecast combining the GEFS/ECens means to
yield flat to broadly cyclonic flow aloft while waiting better
agreement in the dynamical and ML models.

...Weather/Hazards Highlights...

The Day 4/Saturday Excessive Rainfall Outlook maintains a Marginal
Risk area along and somewhat north of the central/east-central
Gulf Coast region, with only minor adjustments from continuity.
Guidance is consistent with the setup for locally heavy rainfall
(but trending somewhat lighter than across areas farther to the
west), as the supporting southern tier upper shortwave pushes
eastward. The distribution of solutions has remained similar as
well, with the ECMWF/UKMET and machine learning models clustered in
showing meaningful rainfall potential given sufficient moisture
and instability versus a more diffuse signal in other guidance. By
Day 5/Sunday expect a broad area of convection to develop over the
east-central U.S. ahead of the wavy front pushing eastward from the
Plains. Current guidance recommends a broad Marginal Risk area
from the Ohio Valley southwest into parts of the lower Mississippi
Valley. Improved guidance clustering especially from the Ohio
Valley southward where soils are on the damp side could eventually
lead to an embedded upgrade in risk level.

More broadly, the wavy frontal system affecting the central and
eastern U.S. will produce meaningful precipitation from the
northern Rockies/High Plains into the Northeast as well farther
south over the East, though the latter should be with lighter
totals than forecast over the area covered by the aforementioned
Day 5 Marginal Risk. In addition, the Storm Prediction Center is
monitoring the potential for severe weather from the east-central
U.S. to the Mid-Atlantic/Southeast during Sunday-Monday. Check
latest SPC outlooks for the latest info on severe threats. Some
snow will be possible across northern latitudes, with Rockies and
Plains totals dependent on elevation and/or time of day. There may
be a band of wintry mix separating the snow from rain from the
Upper Midwest into New England.

After a brief break, an area of rain and high elevation snow
should reach into the West by Sunday-Monday, most likely from
northern California into the Pacific Northwest and perhaps
extending into the northern Rockies by early next week. There is
still spread in the guidance for supporting low pressure but new
solutions are starting to cluster somewhat better for low pressure
wrapping up offshore the Pacific Northwest. Increasingly dramatic
guidance differences for the eastern Pacific/western U.S. pattern
early-mid week lead to low confidence for how much additional
precipitation may reach the West Coast. Initially preferred
ensemble-based guidance suggests a wetter trend focused along the
central West Coast into midweek, but there is a minority of
solutions with a drier forecast.

Very warm temperatures will prevail in the warm sector ahead of
the wavy frontal system evolving over the Plains and then pushing
eastward. During the weekend expect the warmest anomalies to extend
from the southern half of the Plains through the Midwest, Ohio
Valley, and Mid-Atlantic with readings 10-25F above normal (with
morning lows tending to be somewhat more anomalous than daytime
highs). Frontal progression will confine the warmth more toward the
East Coast by next Monday. Northern New England should remain a
lot colder though, as a sharp front stays just to the south. Near
to below normal readings will progress eastward behind the
Plains/eastern U.S. front, with precipitation keeping some
northern-central High Plains locations 10-15F below normal for
highs during the weekend. Periods of unsettled weather will keep
the diurnal spread over the West Coast states more narrow than
usual.

Rausch


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