359
FXUS02 KWBC 240645
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
245 AM EDT Sun Aug 24 2025

Valid 12Z Wed Aug 27 2025 - 12Z Sun Aug 31 2025

...Mild across much of the Plains, Midwest & East...

...Heavy rainfall for parts of the southern and central High
Plains and Plains into the ArkLaTex...


...Overview...
The amplified pattern near the Lower 48 (eastern Pacific and
Eastern troughing) slowly weakens towards the end of August.
Ridging in between meanders between the Southern Rockies and Great
Basin. The main shower and thunderstorm foci will be across the
Great Basin, Southern/Central Rockies and Plains, and into the
Lower Mississippi Valley with locally heavy rainfall possible.


...Guidance/Predictability Assessment...
Model guidance remains in generally good agreement with the
pattern described above. What is less certain is the location of
the eastern Pacific trough/closed low as we move into next weekend.
Generally, the guidance has been slowly speeding up the progression
of Pacific systems towards the West Coast. In general, the 23/12z
ECMWF control run and its ensemble mean are slower than the
remainder of the guidance, which fits typical ECMWF, GFS, and
Canadian biases, arguing for an intermediate solution.

The WPC forecast blend for the pressures, fronts, 500 hPa height
pattern, winds, and QPF/PoPs was based on a general model
compromise during the early period. Gradually increased the
proportion of ensemble means as the period progressed to 40% by
next weekend as individual model differences increased. This
maintained reasonable continuity, all things considered. The
remainder of the grids were primarily the 01z NBM with some 18z
ECMWF AIFS sprinkled in.


...Weather/Hazards Highlights...
Flash flooding concerns from the short range period spill over
into the medium range time frame for portions of the High Plains
and Plains through much of the week. Shortwave energy will round
the western side of the trough and provide ample lift from the jet
stream in a broadly moist and unstable environment (precipitable
water values of 1.75-2" and MUCAPE towards 1000 J/kg) in the
vicinity of a meandering front. A Slight Risk remains in place for
Day 4/Wednesday for Kansas and vicinity which shifts east towards
the MO/KS/AR/OK irregular border intersection on Day 5/Thursday
with portions of CO and NM also gaining a Slight Risk area due to
expected rainfall and anticipated soil saturation between now and
then. Heavy rain concerns continue in and near eastern OK/the
ArkLaTex on Friday and Saturday.

Monsoonal moisture will remain in place across much of the West
around the meandering ridge to the east of approaching upper level
troughing. The moisture combined with diurnal heating will likely
trigger storms capable of producing heavier rainfall, which could
cause localized flash flooding especially 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 Wednesday and
Thursday for the isolated flash flood potential. The West should
start begin to dry out across portions of CA, OR, and NV on
Thursday and be mostly dry by Saturday outside of NM and southeast
AZ.

Within the fall-like cold sector, cooler than normal temperatures
overnight as well as drier than normal dewpoints for August along with
resplendent sunshine during the day for many areas across the Midwest,
Ohio Valley, and the Mid-Atlantic States. Lake effect/enhanced showers,
with thunderstorms possible at times, are expected from the short range
period into Friday within the post-frontal cool air mass near the Great
Lakes before relaxing by this weekend. Down south, the front stalling
over Florida may provide a focus for locally heavy rain there, a risk
that appears to increase Thursday through Saturday across the
Southern Peninsula.

In the vicinity of Kansas and eventually Oklahoma, it should be
especially mild/cool for high temperatures (15-25F below normal,
only reaching the 60s and 70s) within the moderate to heavy rain
shield poleward of the front; record cool high temperatures are
possible in some locations. Below average temperatures are likely
through most of the country from the Rockies eastward. Record low
maximum and minimum temperatures are also possible in the Midwest
and Ohio Valley Wednesday, and for widely scattered locations in
the Southeast, southern Appalachians, and Mid-Atlantic States on
Thursday. The excessive heat footprint/magnitude should be fading
early on across the Northwest, as moderation of the heat wave in
the short range period is anticipated Wednesday onward as upper
lows/troughing and fronts approach 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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