019
FXUS02 KWBC 121834
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
134 PM EST Tue Nov 12 2024

Valid 12Z Fri Nov 15 2024 - 12Z Tue Nov 19 2024


...Overview...

Overall, shortwave energy will exit the East coast by Friday, and
combine with an upper low near Maine that lingers for a few days to
support a maritime low over the western Atlantic. Upper ridging
will progress from the Central to Eastern U.S. bringing a return to
seasonably warm temperatures. Meanwhile, a trough over the West by
Friday will deepen as it slowly shifts east over the weekend and
downstream into early next week. This should increase
precipitation chances across parts of the Southwest/southern
Rockies and with cyclogensis/frontogenesis over the Central U.S.
early next week. Another shortwave into the Pacific Northwest will
bring a chance for enhanced precipitation to that region as well,
digging southeastward and inland over a cooled/windy West/Rockies
that will lead to some enhanced mountain snows next week as well.

...Guidance/Predictability Assessment...

The guidance continues to show good agreement on the overall large
scale pattern across the CONUS for the upcoming medium range
period, but with some uncertainty in the details and evolution of
individual systems. The main area of uncertainty lies out West with
the deepening shortwave which may briefly close off a low
in/around northwest Mexico. Guidance shows variability by Monday
on how quickly this progresses east. The exact evolution of this
feature though will have implications for heavy rainfall potential
next week across the Rockies andcentral US. There is also lingering
timing uncertainty with the next potent shortwave into a wet
Pacific Northwest early next week, with potential deepening again
into next midweek over the West to a snowy Rockies.

WPC progs for today used a composite blend of the ECMWF, GFS,
Canadian and UKMET for Friday and the weekend, and then trended
quickly towards mainly the ECMWF ensemble mean whose overall more
amplified ensemble solution seemed to best fit over longwave trends
of guidance at mid-latitudes and also latest guidance from NHC for
an emerging late season tropical threat out from the Caribbean.

...Weather/Hazards Highlights...

It generally remains the case that troughing over the West on
Friday will bring some light to moderate rain and mountain snows to
parts of the Great Basin and northern Rockies with some rain or
snow to the north of the surface low across the northern
Plains/Upper Midwest into Saturday. Excessive Rainfall is not
expected over most of the lower 48 Friday-Saturday, but added a
small Marginal Risk area for western Washington for the weekend
given moisture feed ahead of the next main system. Precipitation
should increase in intensity and coverage across parts of the Four
Corners region into the south-central Rockies/Central U.S. Sunday
into Monday, though exact amounts and impacts remain very uncertain
given model differences but trending westward from overnight
guidance. But models are showing a signal for the potential. The
next shortwave into the Pacific Northwest will bring another AR and
modest precipitation Sunday into Monday as well, along with an
emerging chance for widespread enhanced heavy snow/winds inland
across a cooled West to the Rockies early-mid next week to monitor.

Above normal temperatures will progress eastward with time from
the northern Plains/Midwest Friday-Saturday, enveloping the East by
Sunday into Monday. Daytime highs could be 10-15 degrees above
normal in some spots. Out West, temperatures will trend much cooler
with time as upper troughing amplifies over the region and
persists into next week.

Santorelli/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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