390
FXUS02 KWBC 072005
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 PM EST Sun Dec 7 2025

Valid 12Z Wed Dec 10 2025 - 12Z Sun Dec 14 2025


...Potent/Persistent Atmospheric River continues to bring heavy
rain and high mountain snow to the Pacific Northwest into
Thursday...


...Overview...
A broad upper level trough with reinforcing shortwaves will
continue to dominate areas east of the Rockies with broad ridging
persisting along the West Coast through this weekend. Strong
westerly flow over the western ridge will continue to bring an
atmospheric river through the Northwest and Northern Rockies with
heavy rain and high elevation snow into Thursday, along with high
winds. Cold weather and clipper systems will be favored in this
pattern east of the Rockies with enhanced northern tier wind/snow
chances and following lake effect snow in the lee of the Great
Lakes.


...Guidance/Predictability Assessment...
Positioning of the remaining/lingering deep cold core lows is a
main question for the Wednesday to Friday timeframe. Global
deterministics, especially the 00Z ECMWF/06Z GFS have been farther
north near James Bay while the 06Z ECAIFS and the 00Z CMC were
farther south was near Georgian Bay. Given the valuable insights
the ECAIFS has made for large scale positioning, the WPC forecast
from this morning was heavily weighed toward the 06Z ECAIFS and the
00Z CMC. However, there has been a bit of a shift toward a
consensus solution between James and Georgian Bays with the 12Z
suite. Timing of shortwave troughs around this gyre remain
uncertain given the transient nature of these shortwaves and
impulses. QPF wise, the 13Z NBM was blended with the 00Z CMC/EC
with some enhancements from the 06Z ECAIFS. Of note is a northward
trend in the atmospheric river, more into WA than OR, on Day 4.


...Weather/Hazards Highlights...
Persistent AR into Thursday. Precipitable water values approaching
1.5" not far offshore with 50+ kts of low-level inflow from the
Pacific plenty of heavy rain and high snow levels. The Day 4 Slight
Risk was shifted north a bit to include more of the WA Cascades and
less OR per consensus of the 12Z guidance.

Elsewhere, clipper systems will bring rounds of precipitation,
mainly snow, over a cold northern Plains and Midwest, Great
Lakes/Appalachians, and the Northeast next week. Aforementioned
surface cyclo/fronto genesis will act to enhance wrapping activity
and especially Lake Effect with system passages. Wavy and stalling
trailing fronts lingering down off southern Florida and into the
Gulf may also focus uncertain rain chances near the Coast by Friday.

Strong temperature gradient forecast along the Rockies Thursday
into this weekend areas west 15-25F above normal with a polar front
shifting from Canada starting on Thursday. Max temps 20 to 30
degrees below normal over the northern Plains Friday spread across
the Midwest Saturday, reaching the Eastern Seaboard Sunday.


Jackson


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


$$