375
FXUS02 KWBC 060617
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
117 AM EST Sat Dec 6 2025

Valid 12Z Tue Dec 09 2025 - 12Z Sat Dec 13 2025


...Multi-day heavy precipitation threat for the Pacific Northwest
early to mid next week due to a potent & persistent 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 high elevation 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 Tuesday-Wednesday, with
favored blend including some of the 05/12z NAEFS the ECMWF
ensemble means for later next week amid growing forecast spread,
particularly across the southern Plains and Southeast. The 01z 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 and Northwest midweek given
the then available guidance early in the medium range period.


...Weather/Hazards Highlights...
The incoming atmospheric river across the Northwest looks strong
and relatively persistent from the 8th possibly into the 11th, with
some wavering in the axis across western WA and western OR.
Precipitable water values approaching 1.5" not far offshore with
50+ kts of low- level inflow from the Pacific promises days of
heavy rains, potentially 5"+ locally per day. Significant multi-
day precipitation totals are possible both with coastal rain and
high elevation snows across the Cascades. The Slight Risk was
maintained for day 4/9-10th with a new Slight Risk area added for
day 5/10-11th per coordination with the PDX/Portland OR and
SEW/Seattle WA forecast offices.

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 near southern Florida and into the
Gulf may also focus uncertain rain chances over/offshore next week.

Tuesday will be cold across the East, with 10-15F cold anomalies at
that point. While a general thaw is noted Wednesday, the beginning
of a colder air mass invades the northern Plains with 10F cold
anomalies noted, before intensifying and expanding from the
northern Plains southeast across the Midwest and towards the
Southern Appalachians with 15F+ cold anomalies across a broader
swath east of the Rockies Thursday into next Saturday. The West
and portions of the High Plains will experience 15-20F warm
anomalies 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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