516
FXUS02 KWNH 120704
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
203 AM EST Tue Nov 12 2024

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

...Overview...

Shortwave energy will exit the East coast by Friday, and combine
with an upper low near Maine that lingers for a few days. 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 into early next week. This should increase
precipitation chances across parts of 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.


...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 plenty of 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 a lot of variability by
Monday on how quickly this progresses east. The 12z CMC was much
quicker to eject the shortwave east, but the GFS and ECMWF are
deeper and slower and the 00z CMC tonight did trend towards the GFS
and ECMWF. The exact evolution of this feature though will have
implications for heavy rainfall potential next week across the
central US. Some timing uncertainties with the next shortwave into
the Pacific Northwest early next week, with potential deepening
again mid week over the West. The WPC progs for tonight used a
blend of the ECMWF, GFS, and UKMET for the first couple of days,
and then trended quickly towards the ensemble means which were a
nice middle ground and helped to mitigate the smaller scale
differences. Overall, stayed close to WPC continuity for days 3-6.


...Weather/Hazards Highlights...

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 light rain or snow to the north of the
surface low across the northern Plains/Upper Midwest into Saturday.
Excessive Rainfall is not expected anywhere Friday-Saturday, so
the Days 4-5 EROs are blank. Precipitation should increase in
intensity and coverage across parts of the Four Corners region into
the south- central Plains/Mississippi Valley Sunday into Monday,
though exact amounts and impacts remain very uncertain given model
differences. 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, with lesser
amounts farther inland.

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


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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