191
FXUS02 KWNH 230644
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 AM EDT Sat Aug 23 2025

Valid 12Z Tue Aug 26 2025 - 12Z Sat Aug 30 2025

...Waning heat in the Northwest; mild across the Northern Plains,
Midwest & East...

...Heavy rainfall possible for parts of the South-Central Rockies
and Plains next week...


...Overview...
A stagnant/amplified pattern will be in place for much of
next week, with a ridge in the West supporting a heat wave
shifting to the interior Northwest and a cool trough east of the
Continental Divide with reinforcing shortwaves. The main rainfall
focus next week will be across the Great Basin, Central Rockies,
and into the southern & central Plains into Arkansas with locally
heavy rainfall possible.


...Guidance/Predictability Assessment...
The latest model and ensemble guidance continues to show
reasonable agreement for much of the medium range period. Smaller
scale differences are seen as usual, but with low predictability
at this time range.

The preferred WPC blend for winds, pressures, fronts, and QPF
began with a general model compromise for the first half of the
period. Gradually increased the proportion of ensemble means as the
period progressed to half by Day 6 and more by Day 7 as individual
model differences increased. This maintained reasonable
continuity.


...Weather/Hazards Highlights...
Multiple days of flash flooding concerns are expected for south-
central portions of the Rockies and Plains through much of next
week. Shortwave energy will round the western side of the trough
and provide ample lift in the form of the right entrance region of
the jet (at least on Monday) in a broadly moist and unstable
environment (precipitable water values to 1.75"+ and MUCAPE towards
1000 J/kg particularly in the CO Front Range) in the vicinity of a
meandering front. A Slight Risk remains in place for Day 4/Tuesday
for portions of the southern High Plains. Even though most guidance
is trying to converge on higher amounts in KS day 5/Wednesday, the
GFS
remains light so have left the the threat level as Marginal for
now. Monsoonal moisture will be in place across much of the West
around the Four Corners ridge after a relatively dry monsoon season
in most places. The moisture combined with diurnal heating will
likely trigger storms capable of producing heavier rainfall over
more sensitive areas (steep terrain, in/around burn scars, dry
washes/arroyos, urban areas). Broad Marginal Risks remain
highlighted for much of the Great Basin, Southwest, and
Rockies/Plains for both Tuesday and Wednesday for locally excessive
rainfall and isolated flash flooding. Rain and thunderstorm
chances continue through much of next week in similar areas to the
north of a stationary front.

Lake effect/enhanced showers and thunderstorms possible at times
through the rest of next week within the cool air mass near the
Great Lakes. Down south, the front may stall over Florida for some
locally heavy rain there.

Behind these fronts, cooler than normal temperatures are likely.
The Central Plains should be particularly cool for highs (15-25F
below normal, only reaching the 60s and 70s) just behind the front
and where there is rain. Below average temperatures are likely
through most of the country from the Rockies eastward, with
temperatures more reminiscent of early fall than late summer.
Record low maximum and minimum temperatures are possible from the
central Plains into the Midwest Tuesday and Wednesday, and for
widely scattered locations in the Southeast, southern
Appalachians, and Mid-Atlantic States on Thursday.

Meanwhile, the excessive heat prolongs over the Interior Northwest
though its footprint/magnitude shrinks each day. Major to locally
Extreme HeatRisk is forecast early next week for portions of the
Northwest, where high temperatures could exceed 100F. Some
moderation is anticipated Wednesday onward as an upper low and
resulting front approaches from the Pacific.


Roth/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





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