633
FXUS02 KWNH 150700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
159 AM EST Fri Nov 15 2024

Valid 12Z Mon Nov 18 2024 - 12Z Fri Nov 22 2024

***Heavy rain and potential severe storms for portions of the
 Plains early next week***


...Overview...

A rather active weather pattern is expected to be in place across
the Continental U.S. next week with an upper trough over the
Western U.S. amplifying the flow pattern. Shortwave energy within
the trough will induce surface cyclogenesis across the Plains
Sunday and continuing into Monday, and this will likely produce a
wide swath of moderate to heavy rainfall from Texas to the Upper
Midwest. A large cut-off upper low is likely to develop over the
Great Lakes and Ohio Valley region by the second half of the week,
with colder weather moving in across this region. In terms of the
Tropics, although Tropical Storm Sara will likely remain well to
the south across Central America and the far southern Gulf, a plume
of enhanced moisture is likely to advect northward across the Gulf
and bring the potential for heavy rain ahead of an approaching
cold front for portions of the central Gulf Coast and the Florida
Peninsula. Meanwhile, rain and mountain snow returns to the Pacific
Northwest by midweek as a Pacific storm system approaches the
region.

...Guidance/Predictability Assessment...

The models have been divergent on the handling of multiple
shortwaves crossing the Western U.S. that will eventually
consolidate into the formation of a broad and deep upper
trough/closed low over the north-central U.S. There has been a
notable eastward trend with the evolution and placement of the
closed low that develops near the Great Lakes in the latest 00Z
model guidance suite, so there has been poor run-to-run model
continuity and therefore reduced forecast confidence for the
Wednesday-Friday time period. The ensemble means accounted for
about half of the forecast blend by Thursday, and then two-thirds
by Friday.

...Weather/Hazards Highlights...

There has been a slightly faster trend in the latest model guidance
with the QPF associated with the developing low pressure system
over the Plains early in the week, although the forecasted amounts
remain similar with QPF maxima likely on the order of 1-2 inches
from Oklahoma to Iowa. For the time being, a broad Marginal Risk
area is planned from north Texas to southern Minnesota, with most
rainfall rates likely remaining under an inch per hour in regions
with convection. However, there is a good chance that a Slight Risk
area could eventually be needed once more of the mesoscale details
come into better focus. There will also be a separate area of
enhanced rainfall near the central Gulf Coast and extending
eastward to portions of Florida. Even though the main circulation
from Tropical Storm Sara should remain well to the south based on
the latest NHC forecasts, some of the moisture from it will likely
be advected northward ahead of the approaching cold front. A
Marginal Risk area is planned for this region.

Some strong to severe thunderstorms are likely to develop in the
warm sector of the Plains low pressure system on Monday, mainly
across portions of north Texas and into central Oklahoma, where the
most favorable wind shear and instability parameters are likely to
be in place. This is something that the Storm Prediction Center is
monitoring closely in the days ahead. There may also be some snow
on the northwestern edge of the precipitation shield across
portions of the Dakotas as the surface low occludes and a
deformation zone likely develops.

Temperatures are expected to be quite chilly across the Rockies and
adjacent portions of the Intermountain West and western High Plains
in the wake of the cold front, with a strong surface high building
in. Some overnight lows could be near or even below zero for
portions of the central and northern Rockies. Meanwhile, warm and
humid conditions are likely for the Gulf Coast and to the Southeast
U.S. with deep southerly flow from the Tropics through midweek,
followed by a return to more fall-like conditions to close out the
work week.

Hamrick


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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