209
FXUS02 KWNH 110812
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
311 AM EST Thu Dec 11 2025

Valid 12Z Sun Dec 14 2025 - 12Z Thu Dec 18 2025


...Hazardous wind chills continue for portions of the Northern
Plains and Upper Midwest Sunday morning...

...Further atmospheric rivers to impact the Pacific Northwest for
much of next week...


...Overview...
Broad ridging over the West this weekend expands across the lower
48, spreading above normal temperatures before flattening out
through the middle of the week into zonal flow. Further low
pressure development over the Gulf of Alaska directs atmospheric
rivers into the Pacific Northwest for much of next week with
renewed heavy rain and mountain snow through the Northern
Continental Divide. Low pressure crossing the Northeast Sunday
will have following lake effect snow into Monday with a series of
shortwave trough passages then for the northern tier east of the
Rockies given the zonal flow.


...Guidance/Predictability Assessment...
The most pronounced feature of next week is the low shifting from
the St. Lawrence across the Northeast Sunday and Atlantic Canada
Monday. Decent global deterministic guidance agreement persists
with this feature. A southern stream shortwave over the Four
Corners states Monday and its vector from there is the next feature
of note. The 12Z and now 00Z ECMWF are closest to ECAIFS
solutions that are slower and farther south into north Mexico. The
00Z CMC remains the second slowest which was part of the reason to
prefer the EC/CMC through much of the forecast cycle. However, the
00Z CMC is quicker with a potent shortwave trough into the Pacific
Northwest Tuesday than all other global deterministics, so some
caution should be used there. Modifications were made to the QPF
from the 01Z NBM across the board with the 12Z ECMWF/CMC with
targeted inclusions of output from the 18Z ECAIFS which led to less
PacNW QPF midweek due to less influence in the more meridional GFS.
However, this blend increased QPF over the lower MS Valley to the
TN Valley midweek.


...Weather/Hazards Highlights...
Snow is expected over the Northeast urban corridor Sunday as low
pressure shifts east to Atlantic Canada. Lake effect snow follows
this system into Monday with clipper like systems bringing brief
rounds of snow then for much of the remainder over the week over
the Norther Tier.

Zonal jet dynamics south of Gulf of Alaska low pressure directs
tropically-sourced moisture into the Pacific Northwest starting
Monday. A Day 5 Marginal Risk ERO has been introduced. The PW
anomaly is nearly 4 sigma above normal, though the low level inflow
is much more SSWly, not orthogonal to terrain during the highest
moisture influx which should limit duration of the heaviest
rainfall. That said, multiple days of continued rain next week
could lead to additional significant impacts given the moderate to
major flooding ongoing at present.

High pressure keeps much of the central portions of the country dry
for the first half of next week, though Gulf moisture is drawn back
up in return flow starting Thursday.

Bitterly cold Canadian air shifts east from the Midwest/Mid-South
Sunday and offshore early next week with temperatures 25 to 35
degrees below normal into Monday. However, upper level high
pressure expands over the country from the West allowing
temperatures to reach 15F to 25F above seasonal average over the
West early next week with above normal temperatures for much of
the Lower 48 for midweek creating a December thaw.

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


$$