230
FXUS02 KWNH 190700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM 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...


...Overview...

A Four Corners subtropical ridge will remain in place through much
of the medium range period, with upper troughing favored
downstream over the East. Erin will be moving away from the Mid-
Atlantic coast by Friday morning; however high surf and rip
currents may continue to be a threat. At the same time, a shortwave
moving over Canada will help to reinforce and amplify troughing
over the East next weekend. Shortwave troughing into the Northwest
around next Monday may help weaken the western ridge some. Heat
will be continue to be a threat across the Southwest through at
least the weekend, while rainfall focuses mainly across the South
and East along with monsoonal activity over the Southwest/Rockies
and eventually into the central Plains.


...Guidance/Predictability Assessment...

The mid-large scale pattern continues to show above average
agreement and predictability for the much of the extended period.
By Friday, Erin should be racing away from the Mid-Atlantic coast,
though the guidance still struggles with how quickly it will get
picked and absorbed by initial troughing exiting the Northeast.
Specifics with an upper low through Canada late week has improved,
but guidance does all strongly agree this will act to amplify
troughing over the East by the weekend. Some minor timing
differences late period with reinforcing shortwaves through the
flow still though. Otherwise, the western ridge should begin to
weaken somewhat by early next week as some shortwave energy tries
to make its way into the Northwest. Guidance seem to be trending
towards an upper low off the British Columbia coast which may limit
progression of energy inland, but plenty of uncertainty on the
placement of that.

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


...Weather/Hazards Highlights...

Hurricane Erin should be well off the Northeast Coast by Friday,
but high surf and rip current threats may continue, mainly along
the Mid-Atlantic coast beaches.

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. There is
some signal for maybe a focus along and east of the southern
Appalachians but not enough agreement yet for any ERO risk beyond a
marginal yet.

A strong shortwave and eventual amplifying trough will send a cold
front through the Midwest and the East this weekend. Showers and
thunderstorms may 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.

Surges of moisture into the Southwest under the base of the Four
Corners ridge combined with diurnal heating may 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 by next weekend as the ridge weakens.

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











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