881
FXUS02 KWNH 220639
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
239 AM 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 Central Rockies and
Southern/Central Plains next week...

...Overview...
For much of next week, the flow aloft will be amplified with
ridging present over the West and troughing over the East. This
pattern will continue to support a Heat Wave, shifting to the
interior Northwest. Meanwhile to the East, a series of shortwaves
will reinforce the trough which will bring substantial cooling for
areas east of the Continental Divide next week. 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.  Although there is
good agreement with the large scale pattern, differences with
various features among individual solutions remain in play that
will have direct implications on the sensible weather and QPF
amounts.

The preferred WPC blend for winds, pressures, fronts, and QPF began
with a general model compromise for the first half of the period.
Late period increased ensemble mean contribution to 40 percent of
the blend to help mitigate the larger scale late period
differences. Other grids were primarily 01z NBM based, with some
contribution from the 18z ECMWF AIFS. This maintained reasonable
continuity.


...Weather/Hazards Highlights...
Showers and thunderstorms are expected along and ahead of an
advancing strong cold front expected across the Northern
Appalachians Monday. An Marginal Risk of flash flooding/excessive
rainfall is expected with MU CAPE of 250+ J/kg and frontogenesis
possibly teaming up to lead to 1"+ an hour amounts at times. A
significant drop in daily temperatures expected in the wake of the
front, leading, or in some locations continuing, temperatures more
reminiscent of early fall than late summer. Record lows 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. Due to
the delightfully cool air moving across still mild to warm lakes,
guidance indicates that Lake Effect/enhanced showers and
thunderstorms are possible at times through the period.

Surges of moisture into the Southwest under the base of the Four
Corners ridge 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). Much of the Great Basin, Southwest, and
Rockies/Plains has been highlighted Monday and Tuesday as having
an elevated threat for locally excessive rainfall and isolated
flash flooding, where the broad Marginal Risk remains in place. An
intensification of rainfall is expected east of the Front Range
and spread out into the Plains as shortwave energy rounds the west
side of the Eastern trough and interacts with a front, bringing
precipitable water values to 1.75"+ and MU CAPE towards 1000 J/kg.
The best signal focuses the heavy rainfall parts of the Colorado
Rockies and into southern Kansas/portions of Oklahoma, & the Texas
Panhandle. The inherited Slight Risk was modified somewhat based on
the most recent guidance. This activity should continue through the
week to the north of a stationary front and lead to high
temperatures 20-25F below average for parts of KS.

The excessive heat prolongs over the Interior Pacific Northwest.
Major to locally extreme HeatRisk is forecast into next week for
portions of the Northwest, where high temperatures could exceed
100F. Some moderation anticipated Wednesday onward as a front
approaches from the Pacific.

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





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