047
FXUS02 KWBC 222000
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Fri Aug 22 2025

Valid 12Z Mon Aug 25 2025 - 12Z Fri Aug 29 2025

...Hot 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 pattern will be in place for much of next week, with an
amplified pattern consisting of 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 like boundary placement (fronts and outflows)
will affect sensible weather parameters like QPF, but with low
predictability out into the medium range. The primary relatively
larger scale model diagnostic concern is with an upper low that
approaches the Northwest by the latter part of next week. This will
influence the timing of the Northwest heat wave ending. Models
show spread in this upper low`s timing, with the 00Z CMC on the
west/slow side and the 00Z GFS on the fast/east side by Wednesday-
Thursday. The 00Z ECMWF and 06Z GFS showed pretty similar timing in
between, so these along with the ensemble means seemed the best
way to lean. AI/ML models were mixed with the low`s timing and
depiction, but at least the 06Z AIFS was slow like the CMC,
lowering confidence. The newer 12Z GFS and ECMWF runs have slowed
down a tad compared to their previous runs, while the 12Z CMC sped
up, for somewhat better agreement overall through Thursday, but by
next Friday models still differ with how much energy could remain
over/near the Northwest or shear east.

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, especially in the Northwest. 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) in the vicinity of a meandering front. Slight Risks are
in place for both Day 4/Monday and Day 5/Tuesday for the flash
flooding threat, somewhat modified from the previous issuance based
on latest guidance. More broadly, monsoonal moisture will be in
place across much of the West under the base of 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 Monday and
Tuesday 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.

Farther east, showers and thunderstorms are expected along and
ahead of an advancing strong cold front in the Northern
Appalachians Monday. An Marginal Risk of flash flooding/excessive
rainfall is expected with MUCAPE of 500-1000 J/kg and frontogenesis
possibly teaming up to lead to 1"+ an hour amounts at times. Lake
effect/enhanced precipitation is possible at times through the rest
of next week. Meanwhile 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 perhaps
for isolated locations in the Southeast, southern Appalachians, and
Mid-Atlantic States on Thursday.

Meanwhile, the excessive heat prolongs over the Interior Northwest.
Major to locally Extreme HeatRisk is forecast into 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.


Tate/Roth


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



$$