Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
234 PM EST Mon Dec 22 2025

Valid 00Z Tue Dec 23 2025 - 00Z Thu Dec 25 2025

...High Risk of excessive rainfall for portions of southern
California on Wednesday/Wednesday night...

...Very heavy snow for the Sierra Nevada with falling snow
levels...

...Widespread anomalous warmth across most of the country leading
up to Christmas...

The main thing making weather headlines leading up to Christmas
Eve will be the continued onslaught of heavy rain and heavy
mountain snow from atmospheric rivers across much of California.
There is expected to be a brief abatement in the precipitation
intensity on Tuesday compared to yesterday, with areas north of
San Francisco mainly being impacted with moderate rainfall and
heaviest across the western slopes of the northern Sierra Nevada.
A much stronger storm system arrives Tuesday night into Wednesday
with much of central and then southern California affected, with a
steady stream of deep moisture from the Pacific oriented directly
towards the terrain. Moisture anomalies are quite elevated with
this atmospheric river event, and this will likely lead to many of
the heavily populated areas of southern California getting a few
inches of rainfall, and perhaps six inches or more in the elevated
terrain of the Transverse Ranges. This will likely result in
serious flooding and potential mudslides, and the Weather
Prediction Center has a High Risk of excessive rainfall for
Wednesday/Christmas Eve. Another area of concentrated
precipitation will be over the Sierra Nevada, with snow levels
falling compared to recent days. This will equate to several feet
of snow, leading to severe travel disruptions for the higher
mountain passes, so having an alternate travel plan is prudent
should road closures happen.

Across the Eastern U.S., a low pressure system currently over the
Midwest states will quickly cross the Great Lakes and then reach
the Northeast U.S. by late Tuesday. A swath of snow and mixed
wintry precipitation is likely well ahead of the surface warm
front across the northern Mid-Atlantic into New England, with the
heaviest snow likely to be across Maine as the low develops
further upon exiting the East Coast. A few inches of accumulation
will be possible across mainly inland portions of the region, and
winter weather advisories are now in effect for those areas. Light
showers are likely to the south from the Ohio Valley to the
central Mid-Atlantic through early Tuesday. Improving conditions
arrive in time for Christmas Eve.

Elsewhere across the country, expect mainly dry conditions from
the Rockies eastward to the Midwest states, and most of the
southern Plains to the Deep South, with a few isolated showers
possible across the south-central U.S. through mid-week.
Temperatures will continue to be well above normal for this time
of year across most of the country, and highs are expected to
reach well into the 70s from Texas to South Carolina, and near 80
degrees across southern Texas.  Widespread 50s and 60s are likely
from the central Plains to the Ohio Valley. Multiple record high
temperatures are within the realm of possibility. The only
portions that will closer to seasonal averages will be near the
Canadian border and New England.

Hamrick



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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
131 PM EST Mon Dec 22 2025

Valid 12Z Thu Dec 25 2025 - 12Z Mon Dec 29 2025


...An atmospheric river will continue to bring heavy to
significant rainfall to parts of California through about
Thursday...


...Overview...

A quite amplified and warming upper ridge will shift through the
east-central U.S. late this week, as deep troughing off the West
Coast shifts inland by the weekend to finally bring an end to the
atmospheric river (AR) impacting California. Heavy to significant
rainfall though will continue through at least Thursday/Christmas
Day for southern California with rainfall coverage and intensity
weakening by Friday and especially the weekend. West Coast activity
will also continue, in moderated form, for the Intermountain West
and Rockies. Across the middle part of the nation, the big story
will be unseasonable warmth and possible record warm temperatures
from the Southwest into the Plains and east-central states. The
colder northern tier may see plowable snow chances from the Upper
Great Lakes to the Northeast as shortwaves and frontal systems pass
through.

...Guidance/Predictability Assessment...

The guidance shows good agreement in the beginning of the period,
but uncertainty really grows by the weekend, especially as it
pertains to the evolution of the trough as it moves into the West.
Models generally show this trough to split, sending a deepened
shortwave into the north- central U.S. and cutoff energy/closed low
development over the Southwest. By Sunday, the GFS is faster with
the northern stream shortwave which allows for a quicker cutoff of
the upper low and it holds a very strong low over California into
early next week. There may be slightly better consensus (with
support from the ECMWF and CMC and ensemble means) for something a
bit slower, allowing for a later and more westward upper low over
the eastern Pacific. The AI guidance is mixed, with some support
for the GFS as well. So with uncertainty high and all solutions
still in play, opted to stick fairly close to WPC Continuity and
the ensemble means for the later period forecast. Based on
continuity though, models have trended quite a bit stronger with a
surface low through the Great Lakes and Northeast in what seems to
be a trend towards a more amplified pattern overall mid to late
period. The 13z NBM served as a good starting point for the medium
range sensible weather grids, with minimal editing needed given
high uncertainty in the details.

...Weather/Hazards Highlights...

Eastern Pacific amplified upper troughing and system genesis will
work toward the West Coast with lead deep onshore flow continuing
to direct Pacific moisture into the West Coast into late this week
with considerable flood impacts expected, especially for parts of
Southern California over the Christmas period. This impactful event
will steadily lose influence by Friday and especially into the
weekend as the surface low/frontal system works inland with upper
trough progression. Marginal and embedded Slight Risk ERO threats
continue to be depicted for Thursday/Friday, from central to
southern California and the southern Great Basin. Higher elevations
of the Sierra should see an extended heavy snow event. To the
north, the Pacific Northwest can also expect organized
precipitation this week, but with lesser amounts. Additionally,
moisture is forecast to spill over the Cascades to the
Intermountain West and northern/central Rockies to produce heavy
snow at higher elevations. Some precipitation may continue across
parts of the Southwest into next week, but highly dependent on
evolution of the lingering cutoff low near/off California.

Elsewhere, leading shallow shortwaves moving through the northern
tier and associated surface system reflection and possible flow
amplification with the digging of northern stream upper troughing
into the lower 48 may bring generally light precipitation from the
north-central U.S. to the Great Lakes and Ohio Valley and
Northeast. This may include chances for some enhanced snows with
main focus from the Upper Great Lakes to increasingly southward
across the Northeast to monitor.

Temperatures will continue to be anomalously warm from the central
to east-central U.S. Thursday to Saturday. Daytime highs 25-30+
degrees above normal may set daytime and warm morning low records.
The airmass moves east with time, moderating as it reaches the East
on Sunday. An amplified shortwave into the Northeast will bring
temperatures back below normal by next Monday. Out West,
temperatures should moderate towards normal this weekend, with
another warmup possible early next week as upper ridging builds in.


Santorelli/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
756 PM EST Mon Dec 22 2025
Day 1
Valid 01Z Tue Dec 23 2025 - 12Z Tue Dec 23 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF NORTHERN CALIFORNIA...

...01Z Update...

The atmospheric river impacting California continues to weaken this
evening as it drift northward through the northern Sacramento
Valley. Rainfall rates in excess of 0.25"/hr are rather sparse, but
earlier heavier rain has left much of the area saturated. HI-res
models show a lull in the QPF overnight through 12Z, with
additional QPF generally under 0.50" in most places and only near
1" in the northern Sierra. Have removed the Slight Risk area in
response to the diminished threat overnight. The next surge in
moisture/rainfall is expected after 12Z Tuesday.

Fracasso

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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
756 PM EST Mon Dec 22 2025
Day 2
Valid 12Z Tue Dec 23 2025 - 12Z Wed Dec 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CALIFORNIA...

2100 UTC update: No changes made to the previous

Previous discussion...

The trajectory of the atmospheric river will become more S/SW to
N/NE as it shifts southward during this period as the trough
offshore in the Pacific also digs to the south. In contrast to
the air mass containing the atmospheric river, which will be warm
and moisture-laden, this contrast will support cyclogenesis along
the greatest gradient/boundary between the cold air mass within the
trough and the much warmer air mass in the ridge/atmospheric
river. As the low deepens the onshore flow will align parallel to
the coastline thus significantly increasing the areal extent heavy
rainfall and the higher terrain snow accumulations. The onshore
flow associated with the low itself will continue very heavy rain
and mountain snow across northern California, while the trailing
cold front moves into southern California starting Tuesday night.

The areas of greatest impact will be into the northern Coastal
Ranges and the Transverse Ranges. Both these ranges are
sufficiently aligned perpendicular to the south-southwesterly flow
to have a significant local upslope contribution to rainfall rates.
In the Transverse Ranges, local burn scars will also worsen impacts
from resultant flooding over and downstream of any burn scars north
and west of the Los Angeles Basin. The renewed round of heavy rain
will be in areas getting hard hit by the current atmospheric river
and will continue with the deepening low offshore into the
northern coastal ranges. A Slight Risk was maintained for the
Oregon border down through Los Angeles.

Campbell/Wegman


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
756 PM EST Mon Dec 22 2025
Day 3
Valid 12Z Wed Dec 24 2025 - 12Z Thu Dec 25 2025

...THERE IS A HIGH RISK FOR EXCESSIVE RAINFALL ACROSS SOUTHERN
CALIFORNIA...

2100 UTC UPDATE:

The primary change to the previous day 3 Excessive Rainfall Outlook
was to add a high risk area along the west to east Transverse
Range region of Southern California after collaboration with WFO
LOX. Anomalous 850-700 mb moisture flux...5+ standard deviations
above the mean...will impact Southern CA late day 2 into day 3
ahead of the amplifying mid to upper level trof off the CA coast.
The heavy rainfall totals for Southern CA will likely occur over an
18 hour period, with widespread 4-7 inch totals, with isolated max
amounts of 9"+. Expect a well defined south to north precip band
in this anomalous moisture flux axis with hourly rainfall rates of
.50-1.5"+ likely. The potential for high hourly rainfall totals
will accentuate runoff over soil that is relatively dry and or over
recent burn scar areas. This will pose a significant threat of
flash flooding, landslides, rock falls and mud slides. The greater
than normal travel during the Christmas Holiday will likely expose
a potentially larger number of people to these lift threatening
hazards and was taken into consideration with the upgrade to high
risk.

Oravec


Previous discussion...Widespread heavy rainfall will ramp up even
further across the Transverse Range and surrounding locations of
southern California. Areal average of 3 to 5 inches are expected
but isolated local maximums may reach as much as 9 inches. A
Moderate Risk is in effect for a majority of Santa Barbara,
Ventura, Los Angeles, range, San Bernardino, Riverside and San
Diego Counties. Although snow levels will be lowering across the
Sierra Nevada and adjacent locations and much of the highest
elevations will have significant snow, some of the lower elevations
could receive additional rainfall of 1 to 4 inches, which is
covered by a sprawling Slight Risk area. Deep-layered moisture will
also track eastward across eastern California, southern Nevada and
into southern Utah and western Arizona where areal averages up to
1 to 2+ are forecast. A new Slight Risk area was raised for much of
southern Nevada, along the California/Nevada border and for
western Arizona. Rainfall rates will easily surpass 0.5-1.0 inch/hr
rates, particularly for California.


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

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
358 PM EST Mon Dec 22 2025

Valid 00Z Tue Dec 23 2025 - 00Z Fri Dec 26 2025

*** Strong Atmospheric River followed by low pressure systems to
impact California and the Sierra Nevada through Friday ***


...Northeast...
Days 1-2... Maximum impact level from WSSI: Moderate

A shortwave trough crosses northern Ontario Tuesday and New England
Tuesday night on a potent 150+kt NWly jet below a deep and
sprawling vortex centered north of Hudson Bay. Precip blossoms
late tonight in warm air advection over the upper Ohio Valley and
the Northeast Tuesday. Day 1 snow probs for >4" are 30-60% for the
Catskills west toward the Finger Lakes and the southern slopes of
the Adirondacks. Light freezing rain (a few hundredths accretion)
on the southern edge of the precipitation shield (from central PA
to central WV) is possible late tonight into Tuesday morning.

The surface low crosses New England Tuesday evening with continued
snow for Tuesday night in terrain including the Whites, Greens and
Adirondacks as the WAA pivots to deformation banding with
topographic enhancement (which should boost snow rates into the
1"/hr range) on the back side of the low. Day 1.5 snow probs for
>6" are 30-80% over this terrain with 50% probs for over 8" in the
highest terrain.

Most of Maine is north of the surface low track which will have
ocean enhanced snow Tuesday night before the back side banding
shifts down the coast to produce ocean enhanced snow for eastern
Mass Wednesday morning. Day 2 probs for >6" are 40-70% for much of
the central Maine coast west well into the remote interior
portions of the state.


...California/Sierra Nevada...
Days 2-3... Maximum impact level from WSSI: Extreme

Atmospheric River (AR) over northern CA this afternoon pivots north
to OR and the northern Rockies tonight. High snow levels over
8000ft lift north with the core of highest precip from the
northern Sierra Nevada through the CA Cascades/Trinity Alps keeping
Day 1 quiet in CA from a snow perspective.

However, the now north-south oriented AR pushes across the CA coast
late Tuesday, reaching the full extent of the Sierra Nevada with
heavy precip and snow levels around 7000ft Tuesday evening with
particularly heavy snow starting roughly after midnight (with rates
exceeding 3"/hr per the 12Z HREF) above the snow level. Snow
levels drop under height falls from the approach trough through the
day Wednesday, though precip rates decrease on the Sierra Nevada
as the AR focuses over southern CA with 9000ft snow levels for the
SoCal ranges. Day 2 snow probs for >18" are 40% for the higher
central Sierra and 70-100% for the southern Sierra and the highest
White Mtns along the border with NV.

Expect a lull in Sierra Nevada snow Wednesday night as the dry
slot works its way across. However, by Thursday rates increase
again ahead of the upper trough axis. This time snow levels are
around 6000ft on the Sierra Nevada under the lower heights of an
upper low centered off northern CA. Snow rates of 2"/hr or more can
be expected for much of Thursday. Broader coverage of the >18"
snow probs are depicted for Day 3 with 50-90% values along the full
length of the Sierra Nevada as well as the CA Cascades including
Donner Pass on I-80.


Key Messages for the CA atmospheric river and subsequent low that
maintains impacts through Friday are linked below. CPC has further
KMs for next week.


...Pacific Northwest, Great Basin and Rockies...
Days 1-3... Maximum impact level from WSSI: Major

Upper low that is directing AR into CA is centered over the Queen
Charlotte Sound (BC) and a reinforcing shortwave trough crosses
Vancouver Island by this evening bringing a round of moderate
precip to the WA Cascades this evening. Snow levels already down
around 2500ft drop to around 1800ft before rates decrease overnight
providing impactful snow well below pass level. Day 1 snow probs
for >6" are 40-60% roughly at pass level in western WA, but it's
really all for this evening.

AR across northern CA to western WY this afternoon pivots
north to southern OR to the Bitterroots through Tuesday. Snow
levels rise in this moisture axis to around 7000ft keeping Day 1
snow probs for >6" limited to the highest Sawtooths, Tetons, and
Absarokas. The AR continues to pivot north-south along the West
Coast through Tuesday night with snow levels rising above 4000ft on
the WA Cascades by Wednesday. Day 2 snow probs for >4" are 40-60%
in the WA Cascades.

The focus for precip shifts interior on Wednesday as the AR
extending the length of CA shifts east over the Great Basin and the
Rockies for Wednesday night/Thursday. Snow levels are generally
high, 8000-9000ft with this moisture shield shifting inland. Day 3
snow probs for >6" are limited to the highest Great Basin ranges,
the Sawtooths, Uinta, Wind River, and San Juans where values are
40-70% (80% or greater for the higher Wind Rivers).


Jackson



...Atmospheric River/Winter Storm Key Messages are in effect for
California as linked below...

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
131 PM EST Mon Dec 22 2025

Valid 12Z Thu Dec 25 2025 - 12Z Mon Dec 29 2025


...An atmospheric river will continue to bring heavy to
significant rainfall to parts of California through about
Thursday...


...Overview...

A quite amplified and warming upper ridge will shift through the
east-central U.S. late this week, as deep troughing off the West
Coast shifts inland by the weekend to finally bring an end to the
atmospheric river (AR) impacting California. Heavy to significant
rainfall though will continue through at least Thursday/Christmas
Day for southern California with rainfall coverage and intensity
weakening by Friday and especially the weekend. West Coast activity
will also continue, in moderated form, for the Intermountain West
and Rockies. Across the middle part of the nation, the big story
will be unseasonable warmth and possible record warm temperatures
from the Southwest into the Plains and east-central states. The
colder northern tier may see plowable snow chances from the Upper
Great Lakes to the Northeast as shortwaves and frontal systems pass
through.

...Guidance/Predictability Assessment...

The guidance shows good agreement in the beginning of the period,
but uncertainty really grows by the weekend, especially as it
pertains to the evolution of the trough as it moves into the West.
Models generally show this trough to split, sending a deepened
shortwave into the north- central U.S. and cutoff energy/closed low
development over the Southwest. By Sunday, the GFS is faster with
the northern stream shortwave which allows for a quicker cutoff of
the upper low and it holds a very strong low over California into
early next week. There may be slightly better consensus (with
support from the ECMWF and CMC and ensemble means) for something a
bit slower, allowing for a later and more westward upper low over
the eastern Pacific. The AI guidance is mixed, with some support
for the GFS as well. So with uncertainty high and all solutions
still in play, opted to stick fairly close to WPC Continuity and
the ensemble means for the later period forecast. Based on
continuity though, models have trended quite a bit stronger with a
surface low through the Great Lakes and Northeast in what seems to
be a trend towards a more amplified pattern overall mid to late
period. The 13z NBM served as a good starting point for the medium
range sensible weather grids, with minimal editing needed given
high uncertainty in the details.

...Weather/Hazards Highlights...

Eastern Pacific amplified upper troughing and system genesis will
work toward the West Coast with lead deep onshore flow continuing
to direct Pacific moisture into the West Coast into late this week
with considerable flood impacts expected, especially for parts of
Southern California over the Christmas period. This impactful event
will steadily lose influence by Friday and especially into the
weekend as the surface low/frontal system works inland with upper
trough progression. Marginal and embedded Slight Risk ERO threats
continue to be depicted for Thursday/Friday, from central to
southern California and the southern Great Basin. Higher elevations
of the Sierra should see an extended heavy snow event. To the
north, the Pacific Northwest can also expect organized
precipitation this week, but with lesser amounts. Additionally,
moisture is forecast to spill over the Cascades to the
Intermountain West and northern/central Rockies to produce heavy
snow at higher elevations. Some precipitation may continue across
parts of the Southwest into next week, but highly dependent on
evolution of the lingering cutoff low near/off California.

Elsewhere, leading shallow shortwaves moving through the northern
tier and associated surface system reflection and possible flow
amplification with the digging of northern stream upper troughing
into the lower 48 may bring generally light precipitation from the
north-central U.S. to the Great Lakes and Ohio Valley and
Northeast. This may include chances for some enhanced snows with
main focus from the Upper Great Lakes to increasingly southward
across the Northeast to monitor.

Temperatures will continue to be anomalously warm from the central
to east-central U.S. Thursday to Saturday. Daytime highs 25-30+
degrees above normal may set daytime and warm morning low records.
The airmass moves east with time, moderating as it reaches the East
on Sunday. An amplified shortwave into the Northeast will bring
temperatures back below normal by next Monday. Out West,
temperatures should moderate towards normal this weekend, with
another warmup possible early next week as upper ridging builds in.


Santorelli/Schichtel


Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw