061
FXUS02 KWBC 051948
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Fri Dec 5 2025

Valid 12Z Mon Dec 08 2025 - 12Z Fri Dec 12 2025


...Multi-day heavy precipitation threat for the Pacific Northwest
early next week moisture fueled by a potent Atmospheric River...


...Overview...
A broad upper level trough with reinforcing shortwaves will
continue to dominate across the eastern two-thirds of the lower 48
during the medium range period, with broad ridging generally
preferred near the West Coast. Strong westerly flow over the broad
ridge will bring a wavering atmospheric river into the Northwest
with heavy rain and snow next week, along with potential for high
winds. Cold weather and clipper systems will be favored in this
pattern east of the Rockies.

...Guidance/Predictability Assessment...
Guidance continues to show general agreement with mid-larger scale
systems and the overall pattern evolution for much of this forecast
period, but there remains some uncertainty in the details of the
timing of flow embedded multiple shortwaves that will focus
sensible weather impacts locally. For the most part a multi-model
deterministic model blend works well for Monday-Wednesday, with
favored blend weighting toward the GEFS/Canadian and especially
the ECMWF ensemble means for later next week amid growing forecast
spread. The ECMWF ensemble mean offers more pronounced upper
ridge building into later time frames up through the West Coast.
This scenario seems to best match amplified flow upstream over the
Pacific and recent guidance trends including the latest 12 UTC
cycle. This would favor a northward shift and slowly waning
atmospheric river impact for the Pacific Northwest later next week.
Even so, the 13 UTC NBM seems to provide a solid forecast basis
for most mass fields through the period. However, NBM QPF was
modified upwards later next week over the Great Lakes later next
week given seemingly favorable surface low/system genesis and
trailing/cold lake effect pattern scenario expected to unfold.

...Weather/Hazards Highlights...
A shortwave moving into the Pacific Northwest late Monday looks
strong due to high IVTs, and looks to be impactful as a longer
duration event. Some significant multi-day totals are possible
both with coastal rain and higher elevation snows across the
Cascades. With strong IVT entering by Monday night, have let the
Slight/Marginal Risk areas from continuity for the Day 4/Monday
ERO ride. For Day 5/Tuesday, the front/atmospheric river waver
across portions of OR, so also mostly kept a Slight Risk area that
was coordinated with PQR/the Portland OR forecast office.
Additional rounds of heavy precipitation are likely into Thursday
in the Pacific Northwest and northern Rockies.

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 passage. Wavy and stalling
trailing fronts lingering down near southern Florida and into the
Gulf may also focus uncertain rain chances over/offshore next week.

Temperatures across the Upper Midwest Monday will be close to 20F
below average Monday, with low temperatures across the Northeast
Tuesday morning similarly below average. Otherwise, broad 10F
negative temperature anomalies will be experienced from the
Northern Plains, portions of the Midwest, Great Lakes, and
Northeast most days from Monday through next Friday. The West and
portions of the High Plains will experience 10-15F warmer than
average temperatures during the work week next week underneath
upper ridging.


Roth/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






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