465
FXUS02 KWBC 160642
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
242 AM EDT Sat Aug 16 2025

Valid 12Z Tue Aug 19 2025 - 12Z Sat Aug 23 2025

...Overview...

An expansive ridge across the southern tier states into Tuesday
will retrograde and focus across the Four Corners region by
Wednesday and beyond. Significant heat across the Midwest early on
in the period will ease while temperatures across parts of the
Intermountain West and Southwest gradually ramp up. Troughing will
amplify over the Eastern U.S. helping to steer Hurricane Erin away
from the East Coast. An additional shortwave through south-central
Canada will reinforce troughing across the East to continue into at
least next weekend. Rainfall for the period will focus over the
Midwest- Northeast/Mid-Atlantic and eventually into the Southeast
and back into the Southern Plains.


...Guidance/Predictability Assessment...

The large scale pattern continues to show above average agreement
through the medium range period, with a blend of the deterministic
models offering a good starting point to the forecast. By later in
the week, there are some notable differences with a south-central
compact upper low/shortwave which will help to eventually reinforce
the Eastern U.S. troughing. The GFS was displaced south of the
better consensus with this feature and not used in the blend for
the latter half of the period. The day 6 and 7 forecast from WPC
was based on the ECMWF and CMC with 40-60 percent of the ensemble
means.

Regarding Erin, models are consistent with showing the East Coast
trough helping to pull Erin poleward with time before another
upstream system pushes Erin quickly in a more northeasterly
direction away from the East Coast. Despite above average
confidence in this scenario, the strength of a ridge over the
Atlantic, and the Eastern U.S. shortwave timing and the depth of
the trough will ultimately determine how far west Erin reaches
before turning northward and away from the U.S. coastline. Please
consult the NHC website for the latest information.


...Weather/Hazards Highlights...

A generally east-west oriented frontal boundary will be the focus
for heavy rainfall much of next week. Above normal PW values and
ample instability will support at least isolated instances of
excessive rainfall. On Tuesday/Day 4, a broad marginal risk is in
place from the central U.S., through the Midwest, and into the
interior Northeast. By Day 5/Wednesday, the marginal risk shifts
southward and extends from Texas northeastward into the central
Appalachians/Ohio Valley. It is possible for both days, embedded
slight risks may eventually be needed if/when models converge on
exactly where the heavier rains may set up. The front will continue
to sag into the Southeast and weaken by later in the week with
increased convection continuing from the Southern Plains to the
Southeast later in the week.

Elsewhere, surges of moisture into the Southwest combined with
diurnal heating may trigger storms capable of producing heavier
rainfall over more sensitive areas (steep terrain, in/around burn
scars, etc.). A Marginal Risk ERO continues to be depicted for both
Days 4-5. Rainfall should decrease in coverage by the second half
of the week as the ridge shifts more into the region. While the
heaviest rain and wind from Erin should remain well offshore, Erin
will likely bring high waves and and increased threat for Rip
Currents along much of the East Coast next week.

Above normal temperatures and Major to Extreme HeatRisk will
continue through Tuesday for much of the Midwest, but is expected
to moderate by mid week with lower heights aloft and a westward
shift in the upper ridge. Heat threats will increase across much of
the interior West, with major to localized extreme HeatRisk by
late week across much of the Southwest with daytime temperatures
exceeding 110F in some locations.

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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