Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Mon Nov 10 2025

Valid 12Z Thu Nov 13 2025 - 12Z Mon Nov 17 2025

...Atmospheric River to move south across California on Thursday
bringing a threat of heavy rain and mountain snows...

...Overview...

Continued upper troughing in the Northeast will lead to additional
lake effect precipitation Thursday. Temperatures are marginal, but
some snow accumulation is likely in the higher terrain of upstate
NY and northern New England. Upper ridging in the West is forecast
to move into central U.S., bringing much warmer than average
temperatures Thursday into the weekend. By Thursday into Friday
troughing will move into the West directing an impactful
atmospheric river into California. This troughing subsequently
moves and transitions with lingering uncertainty to the
Southwest/Rockies and Plains over the weekend.

...Guidance/Predictability Assessment...

Confidence remains high in large scale troughing moving into the
West by late week, however there remains significant uncertainty
regarding the exact evolution of this troughing as it moves into
the Southwest and eventually the Plains. Essentially there are two
possible outcomes...one being a more phased/stronger trough that
ends up more progressive in pushing a front and eventual strong
low into the Plains...and the other more of a split trough, with
the southern stream energy cutting off resulting in a slower
eastward progression.

Walking into shift this evening the 18z GFS, 12z ECMWF and 12z
UKMET were actually in very good agreement, all favoring the more
progressive trough moving across the Intermountain West and
eventually developing a strong closed low over the mid MS Valley
by this weekend. However, the full 12z ensemble suite still
revealed 4 clusters of similar likelihood, suggesting that the
deterministic model agreement could be a coincidence and false
confidence. Seeing the 18z ECMWF trend slower and more split with
the energy added confidence in not jumping the forecast to the
18z/12z deterministic consensus (which would have been a big change
from continuity). Instead we favored something in between the
slower solutions offered by last nights old 00z ECMWF, WPC
continuity, 12z CMC and the quicker 12z/18z deterministic models.
Since then, the new 00z models are indeed coming in more split with
the energy and thus slower with the closed low moving across the
Southwest into the Plains. At this point we think confidence is
increasing a tad that this slower more closed low solution will pan
out, as most 00z models have trended this way and the AIFS has
consistently shown this evolution. However confidence is certainly
still not great, as ensemble data would indicate that the more
phased and progressive solution is still a possibility. Hopefully
model runs today will show a consistent trend, so we can finally
start gaining some confidence in a pattern that has been very hard
to predict thus far.


...Weather/Hazards Highlights...

A cold front and atmospheric river will continue pushing south
across CA on Thursday, with high confidence in this evolution
through Friday morning (although still some minor timing
uncertainty). The model consensus supports moderate to strong IVT
values with this system, along with strong convergence along the
front and favorable upper support. The setup looks favorable for a
quick shot of heavy rainfall into southern CA, with 1-3" probable
within the favored terrain. The combination of the strong front and
upper low moving across should support some weak instability and
low topped convective elements. Thus we would anticipate some
higher rainfall rate potential with this system which could drive
at least a localized flash flood risk. The main limiting factor
will be the progressive nature of the front, which should limit the
period of heavy rain to only a couple hours. Nonetheless, the
higher rates could still be enough to cause some flooding impacts,
especially over recent burn scars. Given some lingering uncertainty
regarding the trough/closed low evolution, and the progressive
nature of the front, we will stick with a Marginal risk in the ERO.
An eventual upgrade to a Slight risk is a possibility for the
favored terrain of southern CA, especially if confidence continues
to increase in the heavy rain rate potential. It should also be
noted that a more offshore and slower evolution of the closed low
is still a possibility (albeit seemingly a lower probability
outcome at the moment), with the AIFS showing this evolution pretty
consistently. This evolution would prolong the rainfall and
increase the flood risk, so will need to continue to monitor
trends.

Thereafter, continued model differences and cycle to cycle flip-
flopping offer uncertainty regarding potentially significant
sensible weather impacts over the weekend. The quicker 12z/18z
ECMWF/GFS would have supported a widespread convective threat from
the Plains into the MS Valley by Saturday, with rain spreading
into the OH valley and Mid-atlantic Sunday into Monday. The slower
and more closed off 00z runs focus the convective threat over the
Southern PLains into the lower MS Vally later Saturday into
Sunday. These latter solutions would also likely result in more of
a significant weather threat, as the closed low has impressive
large scale forcing and is able to tap into moisture from the
Gulf. Would expect a stronger thunderstorm threat to exist in this
scenario with flash flooding a risk. As described above, we are
slightly leaning towards this more closed off and slower solution
given trends and the AI guidance. However this is far from certain,
with possible solutions ranging from something more like the
earlier 12z ECMWF/18z GFS, to something even slower than the 00z
ECMWF/GFS/CMC (such as the solution shown by recent AIFS runs).
Thus the forecast over the central and eastern U.S this weekend has
a well below average confidence level, and while an increase in
active and possibly impactful weather is probable, the details
remain very unclear.

What we do have higher confidence on is the well above normal
temperatures from the Intermountain West into the Plains on
Thursday, spreading east across the Plains and into portions of
the MS and TN valley Friday into the weekend. Temperatures should
generally be 10-20 degrees above average. The timing of the cold
front bringing colder temperatures over the West and eventually the
Plains is of lower confidence and related to the uncertainty with
the troughing evolution.

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