109
FXUS02 KWBC 061850
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
150 PM 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-mid next week with 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 an 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 along with enhanced northern
tier wind/snow chances to include to the lee of the Great Lakes.

...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 of the GFS/ECMWF/Canadian/UKMET seems to
work well for Tuesday-Wednesday, with favored blend of the overall
compatible GEFS/Canadian/ECMWF ensemble means for later next week
amid growing forecast spread. 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 to the lee of
the Great Lakes given cold flow pattern with system passages.

...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, but an overall slow northward shift
across western WA and western OR with gradual upper ridge building
up the West Coast over time. Precipitable water values approaching
1.5" not far offshore with 50+ kts of low-level inflow from the
Pacific promises days of heavy rains. Significant multi-day
precipitation totals are possible both with coastal rain and higher
elevation snows across the Cascades. The Slight Risk was
maintained for day 4/9-10th as well as a Slight Risk area for day
5/10-11th per recent coordinations with the PDX/Portland OR and
SEW/Seattle WA forecast offices. Meanwhile, dynamic energies
working progressively inland to drive enhanced periods of snow
with max focus into favored northern Rocky mountain states terrain.

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 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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