Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
409 PM EDT Mon Mar 10 2025

Valid 00Z Tue Mar 11 2025 - 00Z Thu Mar 13 2025

...Widespread record high temperatures possible across portions of the
Upper Midwest and Northern/Central Plains...

...Critical Fire Weather Risk over parts of the Northern Plains today then
Southern High Plains through the rest of the week...

Scattered showers and thunderstorms persist this afternoon across portions
of the Southeast and Florida peninsula as a low pressure system tracks
further offshore. Meanwhile over the Northern Plains strong, gusty winds
associated with a potent low pressure system and cold front dropping south
are increasing the risk for the development and spreading of wildfires.
The Storm Prediction Center has highlighted an area from eastern
Montana/Wyoming to the western Minnesota border with critical fire weather
conditions. Ahead of this system, warm southerly flow will support
anomalously high maximum temperatures in the 50s and 60s with some
isolated areas possibly exceeding 70 degrees. These anomalous maximum
temperatures will represent 20-40 degree departures from average for much
of the Northern/Central Plains and Upper Midwest, where widespread records
may be tied or broken.

Dry downslope flow can be expected Tuesday from the Southern Rockies to
the Southern High Plains as an upper trough moves through the Southwest.
These dry gusty winds (15 to 25 mph) will support Critical Risk for fire
weather conditions for southeast Arizona, southern New Mexico and far
western Texas. Fire danger will likely remain elevated for this region for
the remainder of the week. An amplified upper trough will bring unsettled
weather to the West Coast Tuesday night into Wednesday.

Campbell/Kebede


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 Mon Mar 10 2025

Valid 12Z Thu Mar 13 2025 - 12Z Mon Mar 17 2025


...Potent system brings precipitation to the West into Thursday,
the central U.S. Friday, and toward the east-central/eastern U.S.
next weekend...


...Overview...

The primary weather feature of concern later this week will be a
deep and phased upper trough near the West Coast by early Thursday
that closes off an embedded upper low over the Plains on Friday
while spinning up a strong surface low. The upper trough will bring
widespread rain and higher elevation snow across the West on
Thursday. Then hazards associated with the surface low pressure
system will include heavy rain and severe thunderstorms in the
Mississippi Valley beginning Friday and into the Southeast and
Tennessee/Lower Ohio Valleys Saturday. Convection should reach the
Eastern Seaboard Sunday. Snow is possible on the backside of the
low in the northern half of the Plains into the Upper Midwest
Friday-Saturday. Meanwhile areas of strong winds are likely, which
could cause fire danger especially in the southern Plains. Behind
that system, another upper trough is forecast to approach the West
this weekend and spread additional precipitation there. The leading
Pacific trough crossing the West will bring below normal highs to
that region while the leading ridge (and possibly a weaker one
farther east) should promote above normal temperatures over the
central/eastern U.S., gradually lessening in scope with time.


...Guidance/Predictability Assessment...

Most dynamical guidance agrees reasonably well for the large scale
pattern evolution, with modest spread for the deep Plains/Upper
Midwest storm and associated upper trough along with acceptable
clustering for the next upper trough nearing the West Coast by next
Monday. Some guidance guidance differs more significantly for
smaller scale frontal wave details over the eastern half of the
country during the weekend as well as for specifics of the surface
system nearing the West Coast around Sunday ahead of the second
upper trough. The early-mid part of the forecast maintained good
continuity by way of a 06Z/00Z model composite with more GFS/ECMWF
emphasis relative to the UKMET/CMC. Days 6-7 Sunday-Monday
introduced 20-40 percent total weight of the 06Z GEFS/00Z ECens
means, leading to modest detail adjustments within the more
persistent general evolution of forecast systems.

For the central High Plains through Upper Midwest storm Friday-
Saturday, guidance as a whole has been fairly steady over the past
day with some lingering typical spread for depth/track/timing. As
of early Friday over the High Plains, the members from most
ensemble systems favor a depth in the 980s mb (some GEFS members
leaning a bit deeper). Then by Saturday ensemble members
concentrate in the 970s mb. Operational models generally fit within
this envelope. Ahead of this system by early Saturday, there is
some divergence in guidance for how quickly the front near the East
Coast may return north as a warm front. In particular there are
some machine learning (ML) models that suggest potential for
surface ridging to be more persistent north of the front than seen
in the dynamical guidance, delaying northward progress.

Then by Saturday into Sunday latest guidance is showing more of a
signal today that the front anchored by the central U.S. storm may
contain a western Gulf Coast into Great Lakes wave. Thus far the
dynamical models say that the parent low will continue northeast
into Canada with the frontal wave lagging, but a number of recent
ML models have been showing slow enough progression of the main low
for the frontal wave to merge with it over the Great Lakes by
early Sunday. Will monitor for any dynamical model trends, but for
now the forecast does not account for the alternative ML model
scenario. Heading into next Monday there is also spread for frontal
timing and possible additional embedded waviness due to
differences in how energy is distributed within the overall upper
trough. This leads to significant differences for
existence/magnitude of rainfall along the East Coast. Possibly due
in part to that alternative ML evolution, ML frontal timing leans
slower than the dynamical consensus by Monday, though the 00Z/06Z
average has nudged a bit slower versus continuity. The 12Z ECMWF
has trended slower as well.

For the system that may approach the Pacific Northwest/Vancouver
Island by next Sunday, there was still a lot of spread for system
specifics through the 00Z/06Z cycle given dependence on small-scale
evolution of supporting dynamics. This spread includes a broad
envelope for track and depth among ensemble members and separate
clusters depicted by the ML models. However there was very little
support for the suppressed structure in the past couple ECMWF runs.
Thus preference favored the depiction non- ECMWF models and the
ensemble means, still leaning on the weaker side due to depth
uncertainty (though a few mb deeper than continuity). Incoming 12Z
guidance suggests growing confidence in a stronger system, with the
new ECMWF now looking more similar in shape to other dynamical
models. An average of guidance looks good for resolving
timing/detail differences with the upper trough and associated
surface reflection over the West by next Monday.


...Weather/Hazards Highlights...

On Thursday, the tail end of a weak atmospheric river (with
precipitable water values briefly around 2-3 standard deviations
above normal very early in the day) and possible convective showers
behind it could bring moderate to heavy precipitation to southern
California, and a Marginal Risk remains in place in the Day 4 ERO
with latest guidance maintaining support. More broadly, areas of
rain and higher elevation snow are forecast across much of the West
into Thursday. Higher elevation snow could be heavy across the
Sierra Nevada and into the terrain of the central Great Basin and
Mogollon Rim. Widespread high winds will also be a concern in the
West on Thursday.

Ahead of this system, an initial shortwave will produce some light
to moderate rain across the Southeast on Thursday. Precipitation
remains more questionable farther north, with latest guidance
becoming lighter and more scattered with any Great Lakes/Ohio
Valley into Northeast activity that does occur.

As the primary upper trough moves into the central U.S., there is
high confidence in surface low development/consolidation in the
central Plains by Friday with strong fronts and northeastward
progression of the system thereafter. Potential exists for this low
to challenge some sea level pressure records for March from
eastern Nebraska into parts of Minnesota/Wisconsin. On the backside
of the low, snow could spread across the central High Plains and
into the Dakotas on Friday and into the Upper Midwest on Saturday.
Some of these areas may initially see rain in the warm sector, and
a transition zone of ice is also possible. Best potential of
meaningful snow waits until Saturday, when probabilities for 0.25
inch liquid in the form of snow maximize in the 30 to slightly more
than 50 percent range over western Minnesota and eastern Dakotas.

Rain and thunderstorm chances will emerge ahead of the cold front
across the Mississippi Valley on Friday. The Storm Prediction
Center is highlighting the best severe potential from parts of the
Midwest southward almost to the west-central Gulf Coast on Friday.
Most guidance (minus the GFS/GEFS) shows heavy rain rates beginning
late Friday into Friday night that could cause flooding concerns.
The updated Day 5 ERO for Friday maintains a Marginal Risk for the
Lower/Middle Mississippi Valley and Mid- South with minimal
adjustment from continuity. Rain totals are forecast to become even
heavier by Saturday centered in the Tennessee Valley, and SPC
indicates severe potential for the Tennessee Valley and Southeast.
During Friday-Saturday SPC shows a relatively greater severe threat
from parts of Missouri/Arkansas into Mississippi and Alabama. As
the upper trough and surface fronts move east, rain and
thunderstorms will overspread the East on Sunday. Winds are another
possible concern near the deep low track, as well as in the Plains
behind the cold front. Currently the guidance shows the potential
for highest wind speeds over the southern Rockies/High Plains
around Friday, likely producing fire weather concerns. In addition
southerly winds in the warm sector could get fairly strong
over/near the Appalachians and East Coast next weekend.

Additional rounds of precipitation are likely in the West late
this week into the weekend, with one frontal system forecast to
arrive around Friday-Saturday and another storm/frontal system
likely arriving by Sunday. Rain amounts in the Pacific Northwest to
northern California look to stay below thresholds for any
excessive rainfall risk through Friday, but chances for heavy
precipitation (lower elevation rain and higher elevation snow)
could increase by the weekend for the Pacific Northwest into
California. The upper trough supporting the latter system should
reach at least as far east as the West Coast by Monday, leading to
a decrease in precipitation intensity near the coast and eastward
expansion of the moisture shield over parts of the Interior West
and Rockies.

Above average temperatures are likely over most areas east of the
Rockies to start the period. Temperature anomalies of 20 to as much
as 35 degrees above normal are forecast Thursday for the northern
Plains to Midwest as highs reach the 60s and 70s. Farther south,
temperatures in Texas and Louisiana could reach the 80s while
localized areas like far South Texas can expect 90s, even
approaching 100F. Warmer than normal temperatures will gradually
shrink in area late week into the weekend as possibly multiple cold
fronts track east. The Midwest and Great Lakes can expect plus
20-30F anomalies on Friday but more limited to the Great Lakes on
Saturday, and warmer than normal temperatures by 10-20F are likely
in the Northeast over the weekend. Daily record highs look fairly
isolated across the central to eastern U.S., but there could be
more widespread record warm lows from the Midwest through the East
Friday-Sunday if the morning mins hold for the calendar day. In the
West, the upper troughing along with clouds and precipitation will
promote below normal temperatures spreading across the region mid-
late week. Highs are forecast to be generally below average by
15-20 degrees for the central Great Basin and Southwest, while lows
of 5-15 degrees below normal are likely. Temperatures should
moderate somewhat over the weekend as the trough pulls away, but
another trough approaching could lead to another bout of cool
temperatures there early next week.


Rausch/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
356 AM EDT Mon Mar 10 2025

Valid 00Z Tue Mar 11 2025 - 00Z Tue Mar 18 2025

Surface high pressure in place to the north of Hawaii will promote
continued breezy to windy trades for the next several days. On
Monday, a weakening frontal boundary will push slowly south and
allow for rainfall to focus over the Big Island before shifting
farther south and dissipating by Tuesday. The HREF shows focused
rainfall over eastern slopes of the Big Island given the trades,
but with some rain possibly reaching leeward areas. A reasonably
moist pattern with showers favoring windward/mauka areas should
persist as the week progresses.

Late this week into the weekend, the surface high is forecast to
drift southeastward, and meanwhile an upper trough pushing a cold
front will approach west of the state. This combination should
allow winds to weaken gradually from breezy to more moderate
levels, while veering some and reorienting best rain chances on
the southeastern sides of the islands. Model guidance shows
moisture levels increasing by early next week ahead of the front,
so will continue to monitor for possible increases in rain amounts
by that time.


Tate

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Mon Mar 10 2025
Day 1
Valid 16Z Mon Mar 10 2025 - 12Z Tue Mar 11 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Churchill/Chenard

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Mon Mar 10 2025
Day 2
Valid 12Z Tue Mar 11 2025 - 12Z Wed Mar 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN CALIFORNIA...

...2030z Update...

Introduced a Marginal risk area for portions of Southern CA, as a
deep layer cut-off low looks to bring a risk of moderate to heavy
showers to the San Diego metro area (and possibly as far north as
portions of greater LA metro area). While the bulk of the IVT in
association with the low will likely remain just offshore and to
the south of populated areas, PWATs will be near 0.75" (about the
90th percentile at NKX, per SPC sounding climatology) with the 12z
HREF indicating 20-30% probabilities for hourly 0.5" exceedance
(using a 40-km neighborhood method, though these probabilities are
likely a bit overdone due to the high biased NAM-nest members).
While the flash flood risk is conditionally dependent on the
development of stronger showers, the risk appears high enough to
necessitate a Marginal risk for the potential for localized flash
flooding (particularly so if these heavier showers are co-located
with more sensitive terrain, such as burn scars).

Churchill


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Mon Mar 10 2025
Day 3
Valid 12Z Wed Mar 12 2025 - 12Z Thu Mar 13 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHERN CALIFORNIA...

...2030z Update...

Very little adjustment to the inherited outlook, as thinking is
unchanged from the prior discussion regarding the upcoming trough
and associated atmospheric river. While the expected timeframe for
peak rates (00z-12z Thurs) remains just outside of CAM range, the
odds for 0.5"/hr (or locally even higher) rates are relatively high
based on the strong ensemble signal for 1-2" QPF combined with IVT
peaking around 500 kg/m/s. Only needed to expand the Slight and
Marginal risks a tad to the east based on very minor timing
differences in the new guidance.

Churchill


...Previous Discussion...

A deep mid level trough and cold front will move across CA
Wednesday into Wednesday night bringing widespread rain and
mountain snow to the region. The IVT axis is rather narrow and
quick moving and only forecast to peak around 400-600
kg/m/s. When combining this modest strength and lack of longevity
of these higher values...this event will likely only reach weak
atmospheric river levels. This limitation will be partially offset
by the strength of the cold front and deep layer forcing
associated with the synoptic scale trough and upper jet. Even so,
rainfall totals over much of the state are unlikely to be enough to
cause much of a flood concern. Mainly looking at a beneficial
rainfall, although some locally higher rates near the front could
be enough to result in generally minor and localized flooding
within urban and other prone low lying areas.

More flood impacts are possible over southern CA, specifically
portions of Santa Barbara, Ventura and Los Angeles counties. South
to southwesterly upslope flow into the Transverse range will likely
help enhance rainfall over this area late Wednesday night into
Thursday morning. Also will likely have a bit better large scale
forcing overrunning the front at the base of the mid level trough,
helping steepen lapse rates and increasing rainfall rate potential.
Most of the weak instability is currently forecast to be post-
frontal, but could see just enough destabilization work into the
front to produce some localized convective elements within the
southward shifting rainfall axis. It does seem probable that some
0.5"/hr rainfall will accompany this front, and while any heavy
rates will only last for an hour or two, this could be enough to
locally increase the flash flood threat over the more sensitive
burn scars and any flood prone urban areas. The quick shot of
potential high rainfall rates, combined with the sensitive burn
scars over this area, warrants a Slight risk upgrade, and localized
significant impacts are possible.

Chenard

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 Mon Mar 10 2025


On Thursday, the tail end of a weak atmospheric river (with
precipitable water values briefly around 2-3 standard deviations
above normal very early in the day) and possible convective showers
behind it could bring moderate to heavy precipitation to southern
California, and a Marginal Risk remains in place in the Day 4 ERO
with latest guidance maintaining support. More broadly, areas of
rain and higher elevation snow are forecast across much of the West
into Thursday. Higher elevation snow could be heavy across the
Sierra Nevada and into the terrain of the central Great Basin and
Mogollon Rim. Widespread high winds will also be a concern in the
West on Thursday.

Ahead of this system, an initial shortwave will produce some light
to moderate rain across the Southeast on Thursday. Precipitation
remains more questionable farther north, with latest guidance
becoming lighter and more scattered with any Great Lakes/Ohio
Valley into Northeast activity that does occur.

As the primary upper trough moves into the central U.S., there is
high confidence in surface low development/consolidation in the
central Plains by Friday with strong fronts and northeastward
progression of the system thereafter. Potential exists for this low
to challenge some sea level pressure records for March from
eastern Nebraska into parts of Minnesota/Wisconsin. On the backside
of the low, snow could spread across the central High Plains and
into the Dakotas on Friday and into the Upper Midwest on Saturday.
Some of these areas may initially see rain in the warm sector, and
a transition zone of ice is also possible. Best potential of
meaningful snow waits until Saturday, when probabilities for 0.25
inch liquid in the form of snow maximize in the 30 to slightly more
than 50 percent range over western Minnesota and eastern Dakotas.

Rain and thunderstorm chances will emerge ahead of the cold front
across the Mississippi Valley on Friday. The Storm Prediction
Center is highlighting the best severe potential from parts of the
Midwest southward almost to the west-central Gulf Coast on Friday.
Most guidance (minus the GFS/GEFS) shows heavy rain rates beginning
late Friday into Friday night that could cause flooding concerns.
The updated Day 5 ERO for Friday maintains a Marginal Risk for the
Lower/Middle Mississippi Valley and Mid- South with minimal
adjustment from continuity. Rain totals are forecast to become even
heavier by Saturday centered in the Tennessee Valley, and SPC
indicates severe potential for the Tennessee Valley and Southeast.
During Friday-Saturday SPC shows a relatively greater severe threat
from parts of Missouri/Arkansas into Mississippi and Alabama. As
the upper trough and surface fronts move east, rain and
thunderstorms will overspread the East on Sunday. Winds are another
possible concern near the deep low track, as well as in the Plains
behind the cold front. Currently the guidance shows the potential
for highest wind speeds over the southern Rockies/High Plains
around Friday, likely producing fire weather concerns. In addition
southerly winds in the warm sector could get fairly strong
over/near the Appalachians and East Coast next weekend.

Additional rounds of precipitation are likely in the West late
this week into the weekend, with one frontal system forecast to
arrive around Friday-Saturday and another storm/frontal system
likely arriving by Sunday. Rain amounts in the Pacific Northwest to
northern California look to stay below thresholds for any
excessive rainfall risk through Friday, but chances for heavy
precipitation (lower elevation rain and higher elevation snow)
could increase by the weekend for the Pacific Northwest into
California. The upper trough supporting the latter system should
reach at least as far east as the West Coast by Monday, leading to
a decrease in precipitation intensity near the coast and eastward
expansion of the moisture shield over parts of the Interior West
and Rockies.

Above average temperatures are likely over most areas east of the
Rockies to start the period. Temperature anomalies of 20 to as much
as 35 degrees above normal are forecast Thursday for the northern
Plains to Midwest as highs reach the 60s and 70s. Farther south,
temperatures in Texas and Louisiana could reach the 80s while
localized areas like far South Texas can expect 90s, even
approaching 100F. Warmer than normal temperatures will gradually
shrink in area late week into the weekend as possibly multiple cold
fronts track east. The Midwest and Great Lakes can expect plus
20-30F anomalies on Friday but more limited to the Great Lakes on
Saturday, and warmer than normal temperatures by 10-20F are likely
in the Northeast over the weekend. Daily record highs look fairly
isolated across the central to eastern U.S., but there could be
more widespread record warm lows from the Midwest through the East
Friday-Sunday if the morning mins hold for the calendar day. In the
West, the upper troughing along with clouds and precipitation will
promote below normal temperatures spreading across the region mid-
late week. Highs are forecast to be generally below average by
15-20 degrees for the central Great Basin and Southwest, while lows
of 5-15 degrees below normal are likely. Temperatures should
moderate somewhat over the weekend as the trough pulls away, but
another trough approaching could lead to another bout of cool
temperatures there early next week.


Rausch/Tate

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Mon Mar 10 2025


On Thursday, the tail end of a weak atmospheric river (with
precipitable water values briefly around 2-3 standard deviations
above normal very early in the day) and possible convective showers
behind it could bring moderate to heavy precipitation to southern
California, and a Marginal Risk remains in place in the Day 4 ERO
with latest guidance maintaining support. More broadly, areas of
rain and higher elevation snow are forecast across much of the West
into Thursday. Higher elevation snow could be heavy across the
Sierra Nevada and into the terrain of the central Great Basin and
Mogollon Rim. Widespread high winds will also be a concern in the
West on Thursday.

Ahead of this system, an initial shortwave will produce some light
to moderate rain across the Southeast on Thursday. Precipitation
remains more questionable farther north, with latest guidance
becoming lighter and more scattered with any Great Lakes/Ohio
Valley into Northeast activity that does occur.

As the primary upper trough moves into the central U.S., there is
high confidence in surface low development/consolidation in the
central Plains by Friday with strong fronts and northeastward
progression of the system thereafter. Potential exists for this low
to challenge some sea level pressure records for March from
eastern Nebraska into parts of Minnesota/Wisconsin. On the backside
of the low, snow could spread across the central High Plains and
into the Dakotas on Friday and into the Upper Midwest on Saturday.
Some of these areas may initially see rain in the warm sector, and
a transition zone of ice is also possible. Best potential of
meaningful snow waits until Saturday, when probabilities for 0.25
inch liquid in the form of snow maximize in the 30 to slightly more
than 50 percent range over western Minnesota and eastern Dakotas.

Rain and thunderstorm chances will emerge ahead of the cold front
across the Mississippi Valley on Friday. The Storm Prediction
Center is highlighting the best severe potential from parts of the
Midwest southward almost to the west-central Gulf Coast on Friday.
Most guidance (minus the GFS/GEFS) shows heavy rain rates beginning
late Friday into Friday night that could cause flooding concerns.
The updated Day 5 ERO for Friday maintains a Marginal Risk for the
Lower/Middle Mississippi Valley and Mid- South with minimal
adjustment from continuity. Rain totals are forecast to become even
heavier by Saturday centered in the Tennessee Valley, and SPC
indicates severe potential for the Tennessee Valley and Southeast.
During Friday-Saturday SPC shows a relatively greater severe threat
from parts of Missouri/Arkansas into Mississippi and Alabama. As
the upper trough and surface fronts move east, rain and
thunderstorms will overspread the East on Sunday. Winds are another
possible concern near the deep low track, as well as in the Plains
behind the cold front. Currently the guidance shows the potential
for highest wind speeds over the southern Rockies/High Plains
around Friday, likely producing fire weather concerns. In addition
southerly winds in the warm sector could get fairly strong
over/near the Appalachians and East Coast next weekend.

Additional rounds of precipitation are likely in the West late
this week into the weekend, with one frontal system forecast to
arrive around Friday-Saturday and another storm/frontal system
likely arriving by Sunday. Rain amounts in the Pacific Northwest to
northern California look to stay below thresholds for any
excessive rainfall risk through Friday, but chances for heavy
precipitation (lower elevation rain and higher elevation snow)
could increase by the weekend for the Pacific Northwest into
California. The upper trough supporting the latter system should
reach at least as far east as the West Coast by Monday, leading to
a decrease in precipitation intensity near the coast and eastward
expansion of the moisture shield over parts of the Interior West
and Rockies.

Above average temperatures are likely over most areas east of the
Rockies to start the period. Temperature anomalies of 20 to as much
as 35 degrees above normal are forecast Thursday for the northern
Plains to Midwest as highs reach the 60s and 70s. Farther south,
temperatures in Texas and Louisiana could reach the 80s while
localized areas like far South Texas can expect 90s, even
approaching 100F. Warmer than normal temperatures will gradually
shrink in area late week into the weekend as possibly multiple cold
fronts track east. The Midwest and Great Lakes can expect plus
20-30F anomalies on Friday but more limited to the Great Lakes on
Saturday, and warmer than normal temperatures by 10-20F are likely
in the Northeast over the weekend. Daily record highs look fairly
isolated across the central to eastern U.S., but there could be
more widespread record warm lows from the Midwest through the East
Friday-Sunday if the morning mins hold for the calendar day. In the
West, the upper troughing along with clouds and precipitation will
promote below normal temperatures spreading across the region mid-
late week. Highs are forecast to be generally below average by
15-20 degrees for the central Great Basin and Southwest, while lows
of 5-15 degrees below normal are likely. Temperatures should
moderate somewhat over the weekend as the trough pulls away, but
another trough approaching could lead to another bout of cool
temperatures there early next week.


Rausch/Tate

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
302 PM EDT Mon Mar 10 2025

Valid 00Z Tue Mar 11 2025 - 00Z Fri Mar 14 2025


...The West...
Days 2-3...

...Impactful heavy snow from the California mountain ranges
Wednesday to the Intermoutnain West late week. Please see current
Key Messages below...

An upper-level trough in the northeast Pacific will direct an
atmospheric river at California starting Tuesday night and
continuing through Wednesday. Mountain snow begins Tuesday night
from
the Cascade Range on south to the Siskiyou/Shasta and northern
Sierra Nevada. By 18Z Wednesday, ECMWF SATs shows a SWrly >400
kg/m/s IVT that surpasses the 97.5 climatological percentile over
central California. This enhanced moisture transport combined with
a cold frontal passage and falling heights aloft will result if
plummeting snow levels Wednesday night along the Sierra Nevada
with heavy snow as low as 5,000ft in elevation. Hourly snowfall
rates between 2-3"/hr are expected in these ranges, with the
combination of heavy/wet snow also posing a potential risk for
scattered areas of power outages and tree damage. Snow will also
unfold into the Southern California ranges north and east of Los
Angeles and San Diego Wednesday night and into Thursday morning.
Minor snow accumulations are possible as low as 4,000ft in the San
Rafael, San Gabriel, and San Bernadino Mountains through the day on
Thursday. WPC probabilities between 00Z Wed - 00Z Fri show high
chances (>70%) for snowfall totals >24" along the entire length of
the Sierra Nevada above 6,000ft. Some areas above 8,000ft could see
as much as 4-5 feet of snowfall by the time a break in the snow
arrives Thursday night. The WSSI is depicting Major to Extreme
Impacts in the Sierra Nevada that is driven due to the Snow Amount
algorithm, as well as some inclusion of the Snow Load and Blowing
Snow elements as well. Note that the Cascades above 4,000ft and
Olympics above 3,000ft have high chances (>70%) for snowfall
accumulations >6" through Thursday afternoon.

East of the Pacific Mountain ranges, the expansive swath of
Pacific moisture will expand well inland Wednesday night and into
the second half of the week. The heaviest snowfall is likely to
occur on Thursday as the cold front sweeps across the Intermountain
West and the diffluent left-exit region of a 250mb jet streak
positions itself overhead. Snow is likely to continue a little
longer into Tuesday night and Friday, so for more on those
potential snowfall details, please refer to our medium range
discussion. WPC probabilities through 00Z Friday depict high
chances (>70%) for snowfall >8" in parts of the Blue, Sawtooth,
central and southern Nevada terrain, portions of the Wasatch, and
the tallest peaks of the Mogollon Rim.

Mullinax

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Mon Mar 10 2025

Valid 12Z Thu Mar 13 2025 - 12Z Mon Mar 17 2025


...Potent system brings precipitation to the West into Thursday,
the central U.S. Friday, and toward the east-central/eastern U.S.
next weekend...


...Overview...

The primary weather feature of concern later this week will be a
deep and phased upper trough near the West Coast by early Thursday
that closes off an embedded upper low over the Plains on Friday
while spinning up a strong surface low. The upper trough will bring
widespread rain and higher elevation snow across the West on
Thursday. Then hazards associated with the surface low pressure
system will include heavy rain and severe thunderstorms in the
Mississippi Valley beginning Friday and into the Southeast and
Tennessee/Lower Ohio Valleys Saturday. Convection should reach the
Eastern Seaboard Sunday. Snow is possible on the backside of the
low in the northern half of the Plains into the Upper Midwest
Friday-Saturday. Meanwhile areas of strong winds are likely, which
could cause fire danger especially in the southern Plains. Behind
that system, another upper trough is forecast to approach the West
this weekend and spread additional precipitation there. The leading
Pacific trough crossing the West will bring below normal highs to
that region while the leading ridge (and possibly a weaker one
farther east) should promote above normal temperatures over the
central/eastern U.S., gradually lessening in scope with time.


...Guidance/Predictability Assessment...

Most dynamical guidance agrees reasonably well for the large scale
pattern evolution, with modest spread for the deep Plains/Upper
Midwest storm and associated upper trough along with acceptable
clustering for the next upper trough nearing the West Coast by next
Monday. Some guidance guidance differs more significantly for
smaller scale frontal wave details over the eastern half of the
country during the weekend as well as for specifics of the surface
system nearing the West Coast around Sunday ahead of the second
upper trough. The early-mid part of the forecast maintained good
continuity by way of a 06Z/00Z model composite with more GFS/ECMWF
emphasis relative to the UKMET/CMC. Days 6-7 Sunday-Monday
introduced 20-40 percent total weight of the 06Z GEFS/00Z ECens
means, leading to modest detail adjustments within the more
persistent general evolution of forecast systems.

For the central High Plains through Upper Midwest storm Friday-
Saturday, guidance as a whole has been fairly steady over the past
day with some lingering typical spread for depth/track/timing. As
of early Friday over the High Plains, the members from most
ensemble systems favor a depth in the 980s mb (some GEFS members
leaning a bit deeper). Then by Saturday ensemble members
concentrate in the 970s mb. Operational models generally fit within
this envelope. Ahead of this system by early Saturday, there is
some divergence in guidance for how quickly the front near the East
Coast may return north as a warm front. In particular there are
some machine learning (ML) models that suggest potential for
surface ridging to be more persistent north of the front than seen
in the dynamical guidance, delaying northward progress.

Then by Saturday into Sunday latest guidance is showing more of a
signal today that the front anchored by the central U.S. storm may
contain a western Gulf Coast into Great Lakes wave. Thus far the
dynamical models say that the parent low will continue northeast
into Canada with the frontal wave lagging, but a number of recent
ML models have been showing slow enough progression of the main low
for the frontal wave to merge with it over the Great Lakes by
early Sunday. Will monitor for any dynamical model trends, but for
now the forecast does not account for the alternative ML model
scenario. Heading into next Monday there is also spread for frontal
timing and possible additional embedded waviness due to
differences in how energy is distributed within the overall upper
trough. This leads to significant differences for
existence/magnitude of rainfall along the East Coast. Possibly due
in part to that alternative ML evolution, ML frontal timing leans
slower than the dynamical consensus by Monday, though the 00Z/06Z
average has nudged a bit slower versus continuity. The 12Z ECMWF
has trended slower as well.

For the system that may approach the Pacific Northwest/Vancouver
Island by next Sunday, there was still a lot of spread for system
specifics through the 00Z/06Z cycle given dependence on small-scale
evolution of supporting dynamics. This spread includes a broad
envelope for track and depth among ensemble members and separate
clusters depicted by the ML models. However there was very little
support for the suppressed structure in the past couple ECMWF runs.
Thus preference favored the depiction non- ECMWF models and the
ensemble means, still leaning on the weaker side due to depth
uncertainty (though a few mb deeper than continuity). Incoming 12Z
guidance suggests growing confidence in a stronger system, with the
new ECMWF now looking more similar in shape to other dynamical
models. An average of guidance looks good for resolving
timing/detail differences with the upper trough and associated
surface reflection over the West by next Monday.


...Weather/Hazards Highlights...

On Thursday, the tail end of a weak atmospheric river (with
precipitable water values briefly around 2-3 standard deviations
above normal very early in the day) and possible convective showers
behind it could bring moderate to heavy precipitation to southern
California, and a Marginal Risk remains in place in the Day 4 ERO
with latest guidance maintaining support. More broadly, areas of
rain and higher elevation snow are forecast across much of the West
into Thursday. Higher elevation snow could be heavy across the
Sierra Nevada and into the terrain of the central Great Basin and
Mogollon Rim. Widespread high winds will also be a concern in the
West on Thursday.

Ahead of this system, an initial shortwave will produce some light
to moderate rain across the Southeast on Thursday. Precipitation
remains more questionable farther north, with latest guidance
becoming lighter and more scattered with any Great Lakes/Ohio
Valley into Northeast activity that does occur.

As the primary upper trough moves into the central U.S., there is
high confidence in surface low development/consolidation in the
central Plains by Friday with strong fronts and northeastward
progression of the system thereafter. Potential exists for this low
to challenge some sea level pressure records for March from
eastern Nebraska into parts of Minnesota/Wisconsin. On the backside
of the low, snow could spread across the central High Plains and
into the Dakotas on Friday and into the Upper Midwest on Saturday.
Some of these areas may initially see rain in the warm sector, and
a transition zone of ice is also possible. Best potential of
meaningful snow waits until Saturday, when probabilities for 0.25
inch liquid in the form of snow maximize in the 30 to slightly more
than 50 percent range over western Minnesota and eastern Dakotas.

Rain and thunderstorm chances will emerge ahead of the cold front
across the Mississippi Valley on Friday. The Storm Prediction
Center is highlighting the best severe potential from parts of the
Midwest southward almost to the west-central Gulf Coast on Friday.
Most guidance (minus the GFS/GEFS) shows heavy rain rates beginning
late Friday into Friday night that could cause flooding concerns.
The updated Day 5 ERO for Friday maintains a Marginal Risk for the
Lower/Middle Mississippi Valley and Mid- South with minimal
adjustment from continuity. Rain totals are forecast to become even
heavier by Saturday centered in the Tennessee Valley, and SPC
indicates severe potential for the Tennessee Valley and Southeast.
During Friday-Saturday SPC shows a relatively greater severe threat
from parts of Missouri/Arkansas into Mississippi and Alabama. As
the upper trough and surface fronts move east, rain and
thunderstorms will overspread the East on Sunday. Winds are another
possible concern near the deep low track, as well as in the Plains
behind the cold front. Currently the guidance shows the potential
for highest wind speeds over the southern Rockies/High Plains
around Friday, likely producing fire weather concerns. In addition
southerly winds in the warm sector could get fairly strong
over/near the Appalachians and East Coast next weekend.

Additional rounds of precipitation are likely in the West late
this week into the weekend, with one frontal system forecast to
arrive around Friday-Saturday and another storm/frontal system
likely arriving by Sunday. Rain amounts in the Pacific Northwest to
northern California look to stay below thresholds for any
excessive rainfall risk through Friday, but chances for heavy
precipitation (lower elevation rain and higher elevation snow)
could increase by the weekend for the Pacific Northwest into
California. The upper trough supporting the latter system should
reach at least as far east as the West Coast by Monday, leading to
a decrease in precipitation intensity near the coast and eastward
expansion of the moisture shield over parts of the Interior West
and Rockies.

Above average temperatures are likely over most areas east of the
Rockies to start the period. Temperature anomalies of 20 to as much
as 35 degrees above normal are forecast Thursday for the northern
Plains to Midwest as highs reach the 60s and 70s. Farther south,
temperatures in Texas and Louisiana could reach the 80s while
localized areas like far South Texas can expect 90s, even
approaching 100F. Warmer than normal temperatures will gradually
shrink in area late week into the weekend as possibly multiple cold
fronts track east. The Midwest and Great Lakes can expect plus
20-30F anomalies on Friday but more limited to the Great Lakes on
Saturday, and warmer than normal temperatures by 10-20F are likely
in the Northeast over the weekend. Daily record highs look fairly
isolated across the central to eastern U.S., but there could be
more widespread record warm lows from the Midwest through the East
Friday-Sunday if the morning mins hold for the calendar day. In the
West, the upper troughing along with clouds and precipitation will
promote below normal temperatures spreading across the region mid-
late week. Highs are forecast to be generally below average by
15-20 degrees for the central Great Basin and Southwest, while lows
of 5-15 degrees below normal are likely. Temperatures should
moderate somewhat over the weekend as the trough pulls away, but
another trough approaching could lead to another bout of cool
temperatures there early next week.


Rausch/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