818
FXUS02 KWNH 090759
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EST Sun Nov 9 2025

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

...An Atmospheric River will likely impact portions of California
by mid to late week bringing a threat of heavy rainfall...

...Overview...

The depth of the 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 snow. Upper ridging in the West is forecast to
slowly move toward the central U.S. bringing much warmer than
average temperatures. By mid to late week, upper troughing will
move into the West and should direct an atmospheric river into
California. This troughing moves into the Rockies and Plains over
the 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.

Recent 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 the GFS and focuses more shortwave energy at the base
of the trough forming a cutoff low that moves into southern CA. The
ECMWF keeps this cutoff low moving across the Southwest Friday
into Saturday...a much different solution than the GFS. The 00z CMC
and UKMET are 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 12z 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.


...Weather/Hazards Highlights...

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 we went ahead and added
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 like the GFS would result in very little rain over
southern CA and no 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 southern CA. However,
confidence on these details remain low...and the eventual outcome
could realistically range anywhere from a more significant flood
risk to almost no rain at all...so we will have to continue to
monitor trends.

These model differences lead to even bigger sensible weather
impacts over the 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
even slower and bringing additional heavy rainfall to southern CA.
Best bet at the moment would be somewhere in between the 00z GFS
and ECMWF, but realistically can not rule out the more extreme
solutions either, as run to run model variability remains high.

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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