515
FXUS02 KWBC 191905
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
305 PM EDT Tue Aug 19 2025

Valid 12Z Fri Aug 22 2025 - 12Z Tue Aug 26 2025

...High waves and rip currents may continue along the Mid-Atlantic
coast through Friday associated with Dangerous Hurricane Erin...

...Heat wave builds over the Southwest late this week and lingers
into the weekend...

...Overview...

An anomalously strong ridge of high pressure centered over the
Four Corners states will lead to a significant heat wave across
much of the Southwest through the weekend. Downstream of the ridge,
an amplifying trough across the eastern half of the U.S. will help
to steer Erin away from the Mid-Atlantic coast, though high surf
and rip currents may continue to be a threat through at least
Friday. A strong cold front will accompany the eastern trough,
bringing a substantial cool down east of the Continental Divide
next week. Rainfall through the period will mainly focus across the
South and East, with surges of monsoonal showers and storms over
the Southwest/Rockies and eventually into the central Plains.


...Guidance/Predictability Assessment...

Model guidance continues to advertise above average agreement and
predictability for most of the medium range period. The synoptics
favor an increasingly amplified 500mb flow pattern, with a ridge
shifting about in the west and a developing trough deepening in the
east. The 00Z and 06Z runs of the deterministic models handled the
driving Canadian shortwaves of the eastern troughing fairly
similarly, with only minor spatial and temporal differences that
did not impact the overall big picture noted. By the end of the
period, models are hinting at the development of a Rex block along
the West Coast of the U.S., along with a closed mid-level low well
off the coast of British Columbia. This block is likely to keep the
closed low farther offshore. The 00Z CMC was too progressive and
too close to the coast compared to consensus, so opted to remove
its contribution by Day 6. With greater confidence of more ridging
over the Pacific Northwest next week, a focus for more significant
heat over the region becomes more likely.

The WPC forecast started with a compromise of the deterministic
guidance, gradually increasing to include half of the ensemble
means and removing the 00Z CMC by the end of the forecast period.


...Weather/Hazards Highlights...

Hurricane Erin should be well off the coast by Friday, but high
surf and rip current threats may continue, mainly along the beaches
of the Mid-Atlantic. This risk should gradually wane through the
weekend into early next week as Erin moves farther out to sea.

Heavy rainfall will focus along a lingering frontal boundary over
the southern states through the weekend with above normal PW values
and instability. Marginal risks remain in place on the Day
4/Friday and Day 5/Saturday Excessive Rainfall Outlooks, with only
minor adjustments made for most areas with the latest forecast
package. That being said, the signal for higher QPF was a bit more
pronounced for the southern Appalachians, and given terrain
sensitivities, decided to add that area for Day 4 and especially on
Day 5.

A strong shortwave and amplifying trough will send a cold front
through the Midwest and the East this weekend. Showers and
thunderstorms will likely accompany this front as it moves through
the Midwest/Ohio Valley and eventually into the East this weekend.
With the exception of maybe Florida, rainfall should clear the East
Coast by early next week. In the wake of the front, a significant
cool down is expected, sending temperatures well below climatology
for late August.

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). A Marginal Risk ERO continues to be depicted for both
Days 4/5 valid for Friday and Saturday. Favorable flow/shortwave
energy may also spread activity into the central Rockies/Plains
early next week.

Heat will mainly focus across the Western U.S. into the weekend,
with major to localized extreme HeatRisk likely across the
Southwest and daytime temperatures exceeding 110F in some
locations. Farther north into the interior West and California
valley, moderate to locally major HeatRisk is forecast. Heat may
abate across the Southwest late Sunday into Monday, but ramp up
across the Pacific Northwest into the middle of next week.

Miller/Santorelli


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















$$