726
FXUS02 KWNH 110627
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Mon Aug 11 2025

Valid 12Z Thu Aug 14 2025 - 12Z Mon Aug 18 2025

...Overview...

Western troughing and eastern ridging will be the story for the
medium range period, with the jet stream mostly across southern
Canada. This will take the storm track into the Pacific Northwest
then through the northern tier of the Lower 48. Temperatures will
generally follow suit with cooler than normal readings for much of
the West but warmer than normal readings for most of the rest of
the CONUS. Rainfall will be favored in the Pacific Northwest, Upper
Midwest, Mid-South/Southeast, and increasingly in the Southwest as
the monsoon season finally shows some life.

...Guidance/Predictability Assessment...

Through the 12Z/18Z guidance, the deterministic runs offered
reasonable clustering with the ensemble means through the period.
Any differences within the runs were within expected tolerance
values for the lead time. By next weekend, trended toward a 1/3 to
2/3 ensemble/deterministic split to account for inherent
uncertainty, which also trended toward the ECMWF AIFS ensemble
mean.

...Weather/Hazards Highlights...

For Thursday and Friday, there are three areas with Marginal risks
for excessive rainfall/flash flooding -- the Upper Midwest, Mid-
South/Southeast, and Southwest. The first is due to an approaching
frontal system with another just to the south over the Plains --
showers/storms are likely ahead of the warm front. The second area
is due to increased moisture in the Southeast 1/4 of the CONUS,
coincident with daytime heating will spark mainly afternoon
showers/storms. The last area (Southwest) will see an increase in
moisture into the region out of Mexico Thursday with a nudge
eastward Friday. Potential exists for future upgrades to Slight
risks in each of these areas, but confidence is limited at this
range. Into the weekend and next Monday, rainfall may ease a bit in
the Southwest but increase over the Upper Midwest/Great Lakes and
eventually Northeast as the cold front moves eastward. The
Southeast will continue to see a daily chance of showers/storms in
typical summertime fashion.

Temperatures will be very warm/hot over the Plains Thursday
(approaching 100F) which will spread eastward into the weekend,
reaching the Midwest Friday and the Northeast/Mid-Atlantic this
coming weekend. Many areas will see temperatures into the 90s with
higher humidity. This will drive HeatRisk values into the the
Moderate (level 2) to perhaps Major (level 3 out of 4) category.
Over the Pacific Northwest into California, temperatures will be
cooler than normal as troughing digs into the West. Coastal areas
may only see highs into the 60s and low 70s with inland areas only
in the 80s to low 90s. Abundant cloud cover with elevated rain
chances over the Southwest will likely keep temperatures cooler
than normal as well -- 90s to low 100s for the desert cities.


Fracasso


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

$$