562
FXUS02 KWBC 111804
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
104 PM EST Thu Dec 11 2025

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


...Bitterly cold, arctic air remains in place across the Midwest
Sunday/Monday, while spreading into the Southeast/Gulf Coast
Monday...

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

...Overview...

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. A series of upper-
energies in a split stream pattern will bring at least modest
precipitation chances across the northern tier as well as to the
Midwest/Mississippi Valley towards mid-next week. Bitterly cold
temperatures continue for much of the central/eastern U.S. before
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.


...Guidance/Predictability Assessment...

Updated 00/06Z guidance continues to remain generally well
clustered and depicts a pattern shift from more amplified mean
upper-troughing over the central to eastern U.S. and ridging over
the central to western U.S. to more zonal, progressive, split
stream flow. The pattern begins to change following the departure
of an upper-trough/surface frontal system along the East Coast this
weekend, with the flow upstream flattening and featuring multiple
upper-energies in a split northern/southern stream over the central
U.S. While there are some complexities with the smaller- scale
details, guidance has been in generally good agreement on the
broader pattern, which features a warm sector with moist Gulf
return flow ahead of more progressive system passages in the
northern stream over the Midwest, and a trailing frontal boundary
southwestward through the Mississippi Valley/southern Plains ahead
of a slower upper-wave in the southern stream. To the west, the
active northern stream will bring multiple systems through the
Pacific Northwest, with the greatest moisture surge/Atmospheric
River expected late this weekend and into early next week, with a
potential second surge mid-next week.

The generally good clustering in the guidance led to an updated
WPC forecast blend of the 00Z ECMWF/CMC/GFS for the early to mid-
period. More weight was given to the ECMWF as system progression
details in the CMC and GFS tended to waver a bit more compared to
the ECMWF as well as the ensemble means. The 00Z GFS was also
bettered clustered than the 06Z update. A contribution from the
ECens mean and GEFS mean is added for the late period as details
naturally begin to diverge in the deterministic guidance with
respect to individual upper-energies/surface systems, though still
remain relatively well clustered, ending with a 60%
deterministic/40% mean blend. For QPF, there is greater uncertainty
given the smaller-scale details in the northern/southern stream
flow over the central U.S. early to mid-next week, so a
contribution from the GEFS/Ecens means was used to compliment the
NBM to better indicate potential precipitation areas. Location and
amounts also begin to vary later into the period with respect to
precipitation in the west, and whether a secondary surge of
moisture may split and/or focus more into northern California than
the Pacific Northwest. For now, the NBM appears to best handle
coverage and amounts given the uncertainty.


...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 of the week over the
Norther Tier.

Zonal jet dynamics south of a 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 to start next week, though Gulf moisture is drawn back up in
return flow starting Tuesday/Wednesday, with at least modest
precipitation chances from Texas/the Lower Mississippi Valley
northeastward into the Midwest.

Bitterly cold Canadian air over the Midwest Sunday expands
southeastward into the Mid-Alantic/Southeast/Gulf Coast Monday,
with temperatures 25 to 35 degrees below normal. Wind chills may
dip as low as the teens as far south as the southeastern Atlantic
and Gulf Coasts Sunday night/Monday morning. 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.

Putnam/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




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