501
FXUS02 KWNH 080827
PREEPD

Preliminary Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Sat Nov 8 2025

Valid 12Z Tue Nov 11 2025 - 12Z Sat Nov 15 2025

...First winter-like chill and lake effect snow event of the
season for much of the central and eastern U.S. into early next
week...

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

...Overview...

An anomalously deep upper trough will still be over the eastern
U.S. Tuesday, bringing another day of well below average
temperatures and freezing temperatures as far south as the Gulf
Coast. The depth of the trough will ease by Wednesday, but some
troughing will persist in the Great Lakes to Northeast and lead to
rounds of lake effect precipitation, including 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 next
week, upper troughing will edge toward the West and could direct
an atmospheric river towards portions of California.


...Guidance/Predictability Assessment...

Model guidance begins the period in rather good agreement with the
synoptic scale pattern, including the deep trough with its axis
over the east-central U.S.. There is some typical spread with
embedded energies within the trough, but a multi-model blend
handled the differences fine. The trough is forecast to lift as it
moves east, but additional shortwave energy moving over top the
ridge in south-central Canada should reach the Great Lakes by
midweek and maintain troughing aloft that lasts through late week,
with good model agreement.

Model consensus is also good with an upper ridge over the West
early to mid next week, with this ridge pushing eastward into the
Plains as the week progresses. The main uncertainty with this
forecast package is the evolution of troughing over the Pacific and
the timing and depth of this feature as it moves into the West
Coast. Model guidance has been bouncing around considerably, with
some runs showing a weakening and more progressive trough moving
into the West Coast by late week, and others showing a stronger and
slower closed low embedded within the larger scale trough. For
example, the 12z ECMWF was on the slower/stronger side of the full
ensemble spread, and now the 00z run is one of the faster models.
Even the AIFS is showing significant run to run variability. This
all suggests this is a low predictability pattern, and without a
clear trend at the moment, we can not really rule out any
particular solution. Thus taking a multi model consensus approach
is likely the best course of action for now.


...Weather/Hazards Highlights...

Troughing over the Great lakes into the Northeast will periodically
be reinforced by additional shortwave energy resulting in
continued lake effect rain and snow. Light snow accumulation are
likely Tuesday through Thursday from northwest PA into
central/western NY and into northern New England. More significant
snowfall appears probable across the Tug Hill Plateau.

Most other areas of the lower 48 will see dry conditions next
week, until precipitation chances increase along the West Coast mid
to late week as a Pacific system approaches. As mentioned above,
significant uncertainty remains with this feature, especially by
later in the week. It does seem likely that an atmospheric river
will move into northern CA either later Wednesday or on Thursday.
There will be pretty strong convergence and upper support with
this atmospheric River, and thus some higher rainfall rates are
probable. At the moment the system looks progressive enough to
limit the duration of heavier rainfall, but nonetheless the setup
would seem to support a Marginal risk of excessive rainfall.
However, given the timing uncertainty, we will hold off on
introducing any risk area on day 5 (ending 12z Thu), as it remains
unclear whether the heaviest rainfall will occur before or after
this time frame.

Even greater uncertainty exists for day 6 and 7 over southern CA
as this will depend on the evolution/timing of the trough and
possible embedded closed low. The 12z ECMWF was a very strong
solution and would likely result in a significant heavy rain risk
to southern CA...however the 00z ECMWF is much more progressive
and weaker. Similar run to run variability can be seen in most
other global models, including the AIFS. Thus confidence on these
details remain low and plausible outcomes next weekend range from
a quick shot of locally heavy rain as the trough moves through to
a more prolonged period of significant rainfall. Thus we will need
to continue to closely monitor trends over the coming days.

One more cold day is expected across the East on Tuesday, with
highs 10-20 degrees below average and lows Tuesday morning below
freezing as far south as the Gulf Coast. In fact, with a high
pressure overhead resulting in light winds and clear skies, low
temperatures over portions of the Southeast could end up a bit
below NBM values Tuesday and Wednesday morning, as should be ideal
radiational cooling resulting in a widespread freeze.

Meanwhile strong upper ridging in the West will result in above
average temperatures generally by around 10-15 degrees Tuesday into
Wednesday. These warmer than average temperatures are forecast to
spread east into the Plains and eventually the Mississippi Valley
as the week progresses as the ridge shifts east. By Thursday into
Saturday highs in the 60s and 70s over portions of the Plains and
MS Valley will be approaching 20 degrees above average in spots.
Temperatures should also moderate in the East by Wednesday and
beyond, with near to just slightly below average temperatures.

Chenard/Tate


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







$$