Weather Prediction Center

National Oceanic and Atmospheric Administration

Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
237 AM EST Sat Dec 20 2025

Valid 12Z Sat Dec 20 2025 - 12Z Mon Dec 22 2025

...There is a Moderate Risk of excessive rainfall over parts of Northern
California on Sunday...

...Heavy snow over parts of the Upper Peninsula of Michigan...

...Heavy snow for the Cascades and Northern Rockies...

A front extending from the Upper Great Lakes to the Central Plain will
move eastward off the East Coast by Sunday evening. On Saturday, the
system will produce heavy snow over parts of the UP of Michigan and light
to moderate snow over the Lower Great Lakes/Northeast on Sunday. See the
WPC Heavy Snow Discussion for details and amounts.

Meanwhile, moisture from the Gulf will stream northward over the Lower
Mississippi Valley, intersecting the boundary there, producing rain over
the area from early Sunday into Monday. In addition, moisture from the
Pacific will stream into Northern California, producing light rain on
Saturday, increasing to heavy rain on Sunday. Therefore, the WPC has
issued a Moderate Risk (level 3/4) of excessive rainfall over parts of
Northern California on Sunday into Monday morning. Numerous flash flooding
events are possible. In addition, many streams may flood, potentially
affecting larger rivers. The flooding may include debris flows in or near
recently burned areas. Moreover, rain and highest-elevation snow will
develop over parts of the Great Basin, the Central Rockies, the Pacific
Northwest, and the Northern Intermountain Region through Monday.


Ziegenfelder


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Dec 20 2025

Valid 12Z Tue Dec 23 2025 - 12Z Sat Dec 27 2025


...Major series of atmospheric rivers to fuel rounds of heavy
rainfall to impact the West Coast, but especially California
through the holidays...


...Overview...

An amplified upper ridge will shift from the interior West/Rockies
through the east-central U.S. next week and develop a south-
central U.S. upper high. This will occur in response to a slow but
steady eastward translation of a deepened upper trough from the
eastern Pacific into the West Coast. In this impactful pattern,
onshore flow will continue to direct leading atmospheric rivers
(ARs) to fuel rounds of heavy precipitation affecting California in
particular, but with widespread activity from the West Coast to
the Intermountain West/Rockies. Temperature-wise, unseasonably to
potentially record-breaking warm temperatures are forecast to
spread next week from the West/Southwest through the south-central
Rockies/Plains to the east-central U.S., though the northern tier
states out through northern New England can expect cooler periods
with some snow chances as shortwaves/frontal systems work through.

...Guidance/Predictability Assessment...

Model and ensemble solutions are mainly on the same page for
Christmas Eve and Christmas and a favored composite of best
clustered guidance of the 18 UTC GFS and 12 UTC ECMWF/UKMET seems
to produce a solid forecast basis. A more uncertain and continued
impactful part of this pattern is with upper troughing that
deepens off the eastern Pacific as it moves towards California and
possibly onshore by Friday. The models do agree that this will
occur, but the details of energies within the trough and vort maxes
towards the coast will create considerable impacts to sensible
weather aspects. There continues to be a signal for a couple of ARs
during the period and heavy rainfall shifting southward along the
California coast, but there is some distribution/exact amounts
uncertainty. Impactful timing differences emerge by Friday, with
recent model runs including the latest 00 UTC cycle slower to bring
trough energies onshore and show closed low develoment back near
southern California even a week from now. This trend may be
reasonable given the increasingly separated stream flows signal.

...Weather/Hazards Highlights...

It remains the case that the biggest story during the period will
focus out West with amplifying upper troughing and system genesis
working toward the West Coast and persistent lead onshore flow
directing Pacific moisture into the West Coast through next week.
High moisture anomalies expected with atmospheric rivers impacting
northern/central California early in the week and eventually
central/southern California through Christmas Eve/Christmas.

Atmospheric rivers will fuel a continued wet period for
especially California during the upcoming busy holiday week. The
guidance signal is growing in support of a renewed deep moisture
feed early-mid next week for northern-central California, with
high rain rates (1+ inch per 3 hours) and areal averaged rainfall
of 3"+ toward coastal areas and 5"+ towards the Sierra Nevada. WPC
Excessive Rainfall Outlook Marginal risk threat areas with embedded
Slight Risk areas are depicted as precipitation may prove slow to
shift from areas already with wet conditions. By about midweek and
into mid-later next week, some connection to tropical Pacific
moisture is likely to stream in and increasingly impact southern
California as a surface low approaches the coast. Marginal and
Slight Risk EROs have been introduced. Higher elevations of the
Sierra should see an extended heavy snow event. To the north, the
Pacific Northwest can also expect organized precipitation into
early next week, but with lesser amounts and intensities.
Additionally, moisture is forecast to spill over the Cascades and
into the Intermountain West and northern/central Rockies next week
to produce heavy snow at higher elevations.

Shallow shortwaves moving through the northern tier and associated
surface system reflection focus will bring light precipitation
across the north-central and northeastern U.S. through the early
part of next week, including some light-moderate snows. Farther
south, some weak to moderate Gulf moisture may stream into trailing
frontal systems across the south and east-central U.S. and lead to
precipitation (mostly rain) chances across the Lower Mississippi,
Tennessee, and Ohio Valleys for early to mid next week.

Warmer than average temperatures are forecast across the interior
West and central U.S. through much of the period. The highest
anomalies will likely be across the interior West into the Plains,
with widespread temperature anomalies upwards to 20-30 degrees
above normal. Highs into the 80s across parts of the Southwest to
Texas could set daily records. Unseasonable warmth is likely to
spread east across the mid-latitudes to the Mississippi, Ohio, and
Tennessee Valleys over the Christmas holiday period.

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

Hawaii Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Sat Dec 20 2025

Valid 00Z Sun 21 Dec 2025 - 00Z Sun 28 Dec 2025

An upper-level ridge is forecast to build over the islands by the
start of the period and remain in place through mid-week. A
stable pattern, supported by surface high pressure building north
of the islands, will maintain easterly trades across the island
chain through at least Wednesday. Global models indicate positive
precipitable water anomalies will persist through mid-week,
supporting passing showers along the windward slopes. By late in
the week, the upper ridge and surface high are expected to shift
east, allowing the local pressure gradient to relax and low-level
winds to veer toward a more southeasterly direction. Drier air is
forecast to filter in from the east during the latter half of the
period. There is some minor model divergence regarding the arrival
of this drier airmass, as the GFS remains slower to progress the
dry air compared to the more progressive ECMWF and Canadian
solutions.

Pereira

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
701 PM EST Fri Dec 19 2025
Day 1
Valid 01Z Sat Dec 20 2025 - 12Z Sat Dec 20 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Kleebauer


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

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Sat Dec 20 2025
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Sat Dec 20 2025
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
309 AM EST Sat Dec 20 2025
Day 3
Valid 12Z Mon Dec 22 2025 - 12Z Tue Dec 23 2025

...THERE IS A MODERATE RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
PORTIONS OF THE SIERRA NEVADA IN NORTHERN CALIFORNIA...

The ongoing atmospheric river will persist while sinking a bit southward
toward central California, spreading rainfall further down the
Sierra Nevada Range and along the coastline. With the reduction of
rain on the northern periphery the threat for excessive rainfall
will remain at a Marginal level. A Moderate Risk was raised again
for much of the area identified during the day 2 period and for
locations a touch to the south. This part of the state is expected
to pick up another 3+ inches which will tip the 3 day accumulations
over 12 inches for some areas. Any additional rainfall will lead to
runoff and increase the potential for sloughing and debris flow
along the foothills/adjacent locations.


Campbell


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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Dec 20 2025


It remains the case that the biggest story during the period will
focus out West with amplifying upper troughing and system genesis
working toward the West Coast and persistent lead onshore flow
directing Pacific moisture into the West Coast through next week.
High moisture anomalies expected with atmospheric rivers impacting
northern/central California early in the week and eventually
central/southern California through Christmas Eve/Christmas.

Atmospheric rivers will fuel a continued wet period for
especially California during the upcoming busy holiday week. The
guidance signal is growing in support of a renewed deep moisture
feed early-mid next week for northern-central California, with
high rain rates (1+ inch per 3 hours) and areal averaged rainfall
of 3"+ toward coastal areas and 5"+ towards the Sierra Nevada. WPC
Excessive Rainfall Outlook Marginal risk threat areas with embedded
Slight Risk areas are depicted as precipitation may prove slow to
shift from areas already with wet conditions. By about midweek and
into mid-later next week, some connection to tropical Pacific
moisture is likely to stream in and increasingly impact southern
California as a surface low approaches the coast. Marginal and
Slight Risk EROs have been introduced. Higher elevations of the
Sierra should see an extended heavy snow event. To the north, the
Pacific Northwest can also expect organized precipitation into
early next week, but with lesser amounts and intensities.
Additionally, moisture is forecast to spill over the Cascades and
into the Intermountain West and northern/central Rockies next week
to produce heavy snow at higher elevations.

Shallow shortwaves moving through the northern tier and associated
surface system reflection focus will bring light precipitation
across the north-central and northeastern U.S. through the early
part of next week, including some light-moderate snows. Farther
south, some weak to moderate Gulf moisture may stream into trailing
frontal systems across the south and east-central U.S. and lead to
precipitation (mostly rain) chances across the Lower Mississippi,
Tennessee, and Ohio Valleys for early to mid next week.

Warmer than average temperatures are forecast across the interior
West and central U.S. through much of the period. The highest
anomalies will likely be across the interior West into the Plains,
with widespread temperature anomalies upwards to 20-30 degrees
above normal. Highs into the 80s across parts of the Southwest to
Texas could set daily records. Unseasonable warmth is likely to
spread east across the mid-latitudes to the Mississippi, Ohio, and
Tennessee Valleys over the Christmas holiday period.

Schichtel

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Dec 20 2025


It remains the case that the biggest story during the period will
focus out West with amplifying upper troughing and system genesis
working toward the West Coast and persistent lead onshore flow
directing Pacific moisture into the West Coast through next week.
High moisture anomalies expected with atmospheric rivers impacting
northern/central California early in the week and eventually
central/southern California through Christmas Eve/Christmas.

Atmospheric rivers will fuel a continued wet period for
especially California during the upcoming busy holiday week. The
guidance signal is growing in support of a renewed deep moisture
feed early-mid next week for northern-central California, with
high rain rates (1+ inch per 3 hours) and areal averaged rainfall
of 3"+ toward coastal areas and 5"+ towards the Sierra Nevada. WPC
Excessive Rainfall Outlook Marginal risk threat areas with embedded
Slight Risk areas are depicted as precipitation may prove slow to
shift from areas already with wet conditions. By about midweek and
into mid-later next week, some connection to tropical Pacific
moisture is likely to stream in and increasingly impact southern
California as a surface low approaches the coast. Marginal and
Slight Risk EROs have been introduced. Higher elevations of the
Sierra should see an extended heavy snow event. To the north, the
Pacific Northwest can also expect organized precipitation into
early next week, but with lesser amounts and intensities.
Additionally, moisture is forecast to spill over the Cascades and
into the Intermountain West and northern/central Rockies next week
to produce heavy snow at higher elevations.

Shallow shortwaves moving through the northern tier and associated
surface system reflection focus will bring light precipitation
across the north-central and northeastern U.S. through the early
part of next week, including some light-moderate snows. Farther
south, some weak to moderate Gulf moisture may stream into trailing
frontal systems across the south and east-central U.S. and lead to
precipitation (mostly rain) chances across the Lower Mississippi,
Tennessee, and Ohio Valleys for early to mid next week.

Warmer than average temperatures are forecast across the interior
West and central U.S. through much of the period. The highest
anomalies will likely be across the interior West into the Plains,
with widespread temperature anomalies upwards to 20-30 degrees
above normal. Highs into the 80s across parts of the Southwest to
Texas could set daily records. Unseasonable warmth is likely to
spread east across the mid-latitudes to the Mississippi, Ohio, and
Tennessee Valleys over the Christmas holiday period.

Schichtel

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Sat Dec 20 2025

Valid 12Z Sat Dec 20 2025 - 12Z Tue Dec 23 2025


...Great Lakes...
Days 1-2...
Maximum impact level from WSSI: Minor

Weather pattern across the Great Lakes quickly shifts away from
strong cold air advection as a shortwave crosses over the region
with an associated surface low tracking north of Lake Superior
towards southern Quebec by Sunday morning. This allows for some
moderate warm air advection snow across the Upper Great Lakes
followed by lake effect snow overnight behind a potent cold front.
This west-northwest flow returns to Lake Ontario and Lake Erie by
Sunday as well. All in all snowfall amounts from this system don't
appear that impressive given it's progressive nature. WPC
probabilities for at least 6 inches of snowfall are highest across
the eastern U.P. of MI and between 40-70%. Chances for at least 4
inches of snow downwind of Lake Ontario are low (20-40%) along its
southern shore and the Tug Hill through Day 2.


...Cascades, Northern Rockies, & Northern California...
Days 1-3...
Maximum impact level from WSSI: Major to Extreme

Deep upper troughing in eastern Pacific below the 10th
climatological percentile through at least early next week
continues to allow for an influx of westerly flow and Pacific
moisture into the western U.S. along with increasing IVT within a
wavering Atmospheric River. As moisture flux wanes across the
northern Rockies on Day 1 the next surge enters the region by the
start of Day 2 with snow levels starting around 5000ft across the
Sawtooths before steadily increasing throughout the region,
including the Absarokas, Tetons, and Wind River Range, up to
around 8000ft within the core of the moisture plume extending all
the way back to the central Pacific. Moisture will be plentiful as
PWs increasing to above the 99th climatological percentile over
northern UT and into WY. The heaviest snowfall is expected
throughout the ranges of central ID and western WY. WPC
probabilities for at least 18 inches of snowfall through Tuesday
morning are high (70-90%) across the Sawtooths of ID and Wind
River/Teton/Absaroka ranges of WY above 8000ft. Snowfall totals in
this region could top 2 to 3 feet.

Farther north and away from the immediate AR plume, persistent
westerly flow and lower snow levels are forecast to impact the
Pacific Northwest. Snow levels across the Cascades are expected to
start the forecast period around 2000ft and only briefly rise to
around 3000ft tonight before falling yet again to 2000ft on Monday.
This places all major passes at risk of heavy accumulating snowfall
and treacherous driving conditions. Snoqualmie (3022ft) and
Stevens Pass (4061ft) of particular note could see total snow
accumulations between 1 to 2 feet. WPC probabilities for at least 2
feet of snowfall are high (70-90%) across the WA Cascades above
4000ft, with high chances for at least 12 inches of snow above
3000ft. Moisture also continues to stream into the northern ID and
northwest MT ranges, where elevations above 5000ft have high
chances for at least 8 inches of snowfall over a 72-hr period.


*** Strong Atmospheric River to impact California and the Sierra
Nevada through next week ***

...Sierra Nevada...
Days 1-3...
Maximum impact level from WSSI: Major to Extreme

Multiple AR impulses through Tuesday are expected with snow levels
potentially dropping down to around 7500ft as these moisture
plumes are aimed at the northern/central Sierra Nevada, with the
strongest surge forecast on Sunday ahead of a strong shortwave.
This may impact some of the passes across the crest (e.g., Donner
Pass at 7239ft) as snow levels dip/oscillate. The AR event will
continue beyond this forecast period into the medium range. WPC
probabilities for at least 12 inches of snowfall on days 1-3
(ending 12Z Tuesday) are between 70-90% and primarily above 8500ft
elevation. Snow levels will trend a bit lower into Monday and
Tuesday as WPC probabilities for at least 4 inches of snow are >30%
to elevations around 7500ft. This is possibly the start of a very
active and impactful weather pattern across California, with
additional high elevation heavy snow likely through the middle to
end of next week. See our latest Key Messages that cover the event
through the end of next week, and CPC's Key Messages into week 2.


The probability of significant icing is less than 10 percent.


Snell



...Atmospheric River Key Messages are in effect. Please see
current Key Messages below...

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

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Dec 20 2025

Valid 12Z Tue Dec 23 2025 - 12Z Sat Dec 27 2025


...Major series of atmospheric rivers to fuel rounds of heavy
rainfall to impact the West Coast, but especially California
through the holidays...


...Overview...

An amplified upper ridge will shift from the interior West/Rockies
through the east-central U.S. next week and develop a south-
central U.S. upper high. This will occur in response to a slow but
steady eastward translation of a deepened upper trough from the
eastern Pacific into the West Coast. In this impactful pattern,
onshore flow will continue to direct leading atmospheric rivers
(ARs) to fuel rounds of heavy precipitation affecting California in
particular, but with widespread activity from the West Coast to
the Intermountain West/Rockies. Temperature-wise, unseasonably to
potentially record-breaking warm temperatures are forecast to
spread next week from the West/Southwest through the south-central
Rockies/Plains to the east-central U.S., though the northern tier
states out through northern New England can expect cooler periods
with some snow chances as shortwaves/frontal systems work through.

...Guidance/Predictability Assessment...

Model and ensemble solutions are mainly on the same page for
Christmas Eve and Christmas and a favored composite of best
clustered guidance of the 18 UTC GFS and 12 UTC ECMWF/UKMET seems
to produce a solid forecast basis. A more uncertain and continued
impactful part of this pattern is with upper troughing that
deepens off the eastern Pacific as it moves towards California and
possibly onshore by Friday. The models do agree that this will
occur, but the details of energies within the trough and vort maxes
towards the coast will create considerable impacts to sensible
weather aspects. There continues to be a signal for a couple of ARs
during the period and heavy rainfall shifting southward along the
California coast, but there is some distribution/exact amounts
uncertainty. Impactful timing differences emerge by Friday, with
recent model runs including the latest 00 UTC cycle slower to bring
trough energies onshore and show closed low develoment back near
southern California even a week from now. This trend may be
reasonable given the increasingly separated stream flows signal.

...Weather/Hazards Highlights...

It remains the case that the biggest story during the period will
focus out West with amplifying upper troughing and system genesis
working toward the West Coast and persistent lead onshore flow
directing Pacific moisture into the West Coast through next week.
High moisture anomalies expected with atmospheric rivers impacting
northern/central California early in the week and eventually
central/southern California through Christmas Eve/Christmas.

Atmospheric rivers will fuel a continued wet period for
especially California during the upcoming busy holiday week. The
guidance signal is growing in support of a renewed deep moisture
feed early-mid next week for northern-central California, with
high rain rates (1+ inch per 3 hours) and areal averaged rainfall
of 3"+ toward coastal areas and 5"+ towards the Sierra Nevada. WPC
Excessive Rainfall Outlook Marginal risk threat areas with embedded
Slight Risk areas are depicted as precipitation may prove slow to
shift from areas already with wet conditions. By about midweek and
into mid-later next week, some connection to tropical Pacific
moisture is likely to stream in and increasingly impact southern
California as a surface low approaches the coast. Marginal and
Slight Risk EROs have been introduced. Higher elevations of the
Sierra should see an extended heavy snow event. To the north, the
Pacific Northwest can also expect organized precipitation into
early next week, but with lesser amounts and intensities.
Additionally, moisture is forecast to spill over the Cascades and
into the Intermountain West and northern/central Rockies next week
to produce heavy snow at higher elevations.

Shallow shortwaves moving through the northern tier and associated
surface system reflection focus will bring light precipitation
across the north-central and northeastern U.S. through the early
part of next week, including some light-moderate snows. Farther
south, some weak to moderate Gulf moisture may stream into trailing
frontal systems across the south and east-central U.S. and lead to
precipitation (mostly rain) chances across the Lower Mississippi,
Tennessee, and Ohio Valleys for early to mid next week.

Warmer than average temperatures are forecast across the interior
West and central U.S. through much of the period. The highest
anomalies will likely be across the interior West into the Plains,
with widespread temperature anomalies upwards to 20-30 degrees
above normal. Highs into the 80s across parts of the Southwest to
Texas could set daily records. Unseasonable warmth is likely to
spread east across the mid-latitudes to the Mississippi, Ohio, and
Tennessee Valleys over the Christmas holiday period.

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