140
FXUS02 KWBC 091943
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 PM EST Sun Nov 9 2025

Valid 12Z Wed Nov 12 2025 - 12Z Sun Nov 16 2025

...Atmospheric River to focus impact into California mid-late week
and bring a threat of heavy rains/mountain snows...

...Overview...

An upper trough over the east will begin to ease on Wednesday,
although some troughing will persist in the Great Lakes to
Northeast and lead to rounds of lake effect precipitation,
including some locally enhanced snows. Upper ridging in the West is
forecast to slowly move toward the central U.S., bringing much
warmer than average temperatures in stark contrast to some current
cold conditions. By mid-late week, upper troughing will move into
the West to direct an impactful atmospheric river into California.
This troughing subsequently moves and transitions with lingering
uncertainty to the Southwest/Rockies and Plains next weekend.

...Guidance/Predictability Assessment...

Model guidance is in fairly good agreement with the large scale
pattern through 12z Thursday, with subtle differences in the
embedded energy handled well with a multi model blend. Thereafter
we begin to see spread increase over the Eastern Pacific and
towards the West Coast as troughing moves east. While confidence is
high in large scale troughing moving into the West, there is a lot
of embedded shortwave energy within this trough, and exactly how
this energy interacts and evolves remains unclear.

00/06 UTC GFS runs are on the more progressive side of the model
spectrum...which leads to less overall QPF over the West, but a
quicker and stronger cold front eventually resulting in a more
significant rainfall threat over the Plains this coming weekend.
The 00z ECMWF has sped up compared to earlier runs, but is still
slower than those GFS runs and focused more shortwave energy at
the base of the trough forming a cutoff low that moves into
southern CA. The 00 UTC ECMWF keeps this cutoff low moving across
the Southwest Friday into Saturday...a much different solution than
the GFS. The 00z CMC and UKMET were in between the GFS and ECMWF,
and model trends would seem to suggest something in between the 00z
GFS and ECMWF is most likely. However, a look at the full ensemble
suite gives four pretty even clusters...ranging from a subset of
models looking more like the quick GFS, and some that are even
slower and stronger with the cutoff low than the ECMWF. Thus while
it may seem like models are starting to converge, there is still a
large amount of spread and think it is likely that additional model
jumps will occur over the next couple days. Interestingly, the 00z
AIFS (which verifies well at 500mb) trended slower with the cutoff
low...which is opposite the trend of most other models. This
emphasizes the point that the forecast evolution of the trough and
possible closed low is still unclear at this time. To add to the
uncertainty, the new 12 UTC GFS and ECMWF have flipped camps.

...Weather/Hazards Highlights...

It overall remains the case that shortwave energy moving into the
Great Lakes on Wednesday will reinforce the trough over the
Northeast, resulting in continued lake effect rain and snow into
Thursday. Temperatures are marginal, and thus while some snow is
likely, most of the accumulation should stay focused in areas of
higher terrain...mostly across upstate NY and the Tug Hill Plateau.

Most other areas of the lower 48 will see dry conditions until
precipitation chances increase along the West Coast Wednesday into
Thursday as a Pacific system approaches. High confidence that a
cold front and atmospheric river will likely move into northern CA
later Wednesday into Thursday bringing a heavy rainfall threat.
The model consensus at the moment would support moderate to strong
IVT values with this system, along with strong convergence along
the front and favorable upper support. Thus we should be able to
get some locally heavy rainfall rates (upwards 0.5"-0.75"/hr) as
the front moves into northern CA. The front looks progressive
through 12z Thursday, which will limit the duration of these higher
rates. Thus probably not looking at a significant flood risk with
this system on day 4, but rates could be high enough to result in a
minor flood threat, especially over any more sensitive burn scars
or sensitive terrain. Given a bit better agreement that this front
should move onshore prior to 12z Thursday, maintained a Marginal
risk in the day 4 ERO.

Greater uncertainty exists by day 5 (12z Thursday-12z Friday) as
this is when the model differences explained above take hold. A
stronger closed low moving into southern CA would help slow the
atmospheric river/front and enhance moisture transport/forcing
into it, likely resulting in a more significant rainfall event and
possible Slight risk level impacts. Meanwhile a more progressive
solution would result in less rain potential over southern CA and
a more limited flood threat. A middle ground preference would
likely bring enough a quick shot of heavy rainfall to support a
Marginal risk of excessive rainfall over central to southern CA,
including risk now expanded inland to lower Sierra terrain.
However, confidence on these details remain low and the eventual
outcome could realistically range anywhere from a more significant
flood risk to more limited rain to monitor with newer guidance.

Continued model differences and cycle to cycle flip-flopping offer
uncertainty to potentially significant sensible weather impacts
next weekend. The 00z GFS and CMC would bring a heavy rainfall
threat into the Plains by Saturday, with the 00z ECMWF keeping
activity focused over the Southwest, and the 00z AIFS and most
machine learning guidance even slower and bringing additional
heavy rainfall to southern CA. The 12z GFS and ECMWF have flipped
solutions, so no help there. Best bet still seems somewhere in
between for now, but cannot rule out the more extreme solutions.

Upper ridging in the West on Wednesday will result in above
average temperatures generally by around 10-20 degrees, spreading
into the Plains by Thursday and Friday and into the the MS and OH
Valley over the weekend. Temperatures should also moderate in the
East by Wednesday and beyond, with near to just slightly below
average temperatures...coolest over New England where troughing
will hang on strongest.

Chenard/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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