522
FXUS02 KWBC 290750
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 AM EST Mon Dec 29 2025

Valid 12Z Thu Jan 1 2026 - 12Z Mon Jan 5 2026


...General Overview...

Broad cyclonic flow aloft will be in place across the eastern half
of the country for the end of this week, with a deep low pressure
system centered over James Bay, Canada keeping a cold airmass in
place. Meanwhile, an upper ridge will initially be in place across
the West, but this will flatten out as it gets shunted to the east
across the Plains by the weekend. An unsettled weather pattern
over the eastern Pacific will start affecting the West Coast by
Thursday and even more so by Friday with a potentially well
organized storm system reaching central and northern California
into Oregon Friday into early Saturday. Across the southern tier
states, a wave of low pressure develops along a frontal boundary
and brings higher rainfall chances from the Deep South to the
Southeast Coast on Friday.


...Guidance/Predictability Assessment...

The latest deterministic model guidance indicates solid overall
agreement with the synoptic pattern through the end of the week,
and a general blend of the guidance suffices for fronts and
pressures. Similar to yesterday, the best agreement is noted
across the eastern U.S. with the broad upper level trough pattern
in place.

More question marks arise with the eventual flattening of
the Western U.S. ridge as Pacific shortwave energy from both the
subtropics and the northeast Pacific moves towards the West Coast
towards the weekend. There is improved agreement in the overall
evolution near the West Coast compared to the past few model cycles
for a stronger system to affect northern California by early
Saturday, but the CMC is probably too fast in bringing the trough
inland compared to the more offshore ECMWF/GFS solutions. The
ensemble means account for about half of the fronts/pressures
forecast by next Sunday/Monday. In terms of the NBM, QPF/PoPs
values continue to be raised near the Great Lakes/Ohio Valley
through the end of the week with a likely low bias in the NBM
across this region.


...Weather/Hazards Highlights...

Lake effect snow is expected from Michigan to Upstate New York
with strong cold air advection across the Great Lakes through
Friday. Some heavy accumulations are likely over the course of
this multi-day event, particularly across portions of Upstate New
York where 1-2 feet is well within the realm of possibility
downwind of Lake Erie and Lake Ontario. Some upslope snows across
the central Appalachians is also likely on Thursday with strong
northwest flow.

In terms of heavy rainfall prospects, a weakening low pressure
system from the subtropics will head in the general direction of
southern California, bringing a modest surge of moisture from the
Pacific. This will bring another round of moderate rainfall to the
Transverse Ranges of southern California and also the Peninsular
Range for Thursday, and a Marginal Risk is valid for the Day
4/Thursday ERO as this area remains sensitive given recent heavy
rains. The risk for heavy rainfall will expand northward to include
northwestern California and the eastern slopes of the central and
northern Sierra by Thursday into Friday where Marginal Risk areas
are valid on both days, and heavy snowfall is also expected for
the higher terrain of the Sierra Nevada as precipitation becomes
heavier and more widespread as a stronger Pacific storm system
approaches the coast. Farther inland, some moderate snows will be
possible for the interior mountains of the Intermountain West.
Elsewhere, low pressure developing across the Deep South Friday
into Saturday will likely result in increasing rainfall coverage
and some thunderstorms to close out the week.

Temperatures will continue to be mild for this time of year across
much of the western half of the country through this forecast
period as a general upper ridge limits arctic airmass intrusions.
The warmest anomalies should be across the western High Plains and
western Texas, where highs could be 10 to 20+ degrees above
average. The opposite will hold true from the Upper Midwest to the
Northeast where the upper trough will tend to keeps readings about
5 to 15 degrees below normal, with perhaps some moderation going
into Sunday and Monday.

Hamrick




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














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