704
FXUS02 KWNH 030708
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 AM EDT Sun Aug 3 2025

Valid 12Z Wed Aug 06 2025 - 12Z Sun Aug 10 2025

...Major to Extreme heat threat focus for the Southwest mid-late
week to expand through the south-central High Plains...


...Overview...
A cooling upper trough into the eastern third of the nation will
be periodically reinforced by disturbances digging from the
Plains/Midwest to the South/Southeast. This is to the lee of an
upper ridge anchoring over the Southwest and spread to the south-
central High Plains. A wavy stalled front will support heavy rain
threats over the Southeast past midweek, but as a Bermuda High
begins to build westward, wet weather is forecast to spread
gradually up the eastern U.S. later week/next weekend, albeit with
uncertainty of lift/expansion given variance with vorts/impusles
embedded in the upper trough and uncertain interactions with any
downstream coastal wave development and track. Meanwhile, upper
troughing will progress eastward over the north- central U.S. to
fire northern Plains to Midwest thunderstorms with heavy downpours.

...Guidance/Predictability Assessment...
This pattern will keep much of the heavy precipitation chances
this period to the north-central U.S. ahead of the upper-trough,
and from the Southeastern U.S./Gulf Coast under an upper-level
weakness between main highs and as a lingering frontal boundary
from the passage of this week`s strong cold front over the East
remains. Guidance does show more uncertainty with coverage and
especially range in potential rain amounts in both regions. Opted
to again bring up QPF values compared to the latest NBM, but there
remains an even higher ceiling given slow translation and deep
moisture pooling along with an uncertain coastal wave affect. Both
the deterministic and mean guidance suggest the pattern will begin
to change heading into next weekend as upper-level energy over the
northeastern Pacific helps to dig the upper-trough southward, with
some moderation of the Southwest upper-high. This should lead to
increasingly heavier and more widespread precipitation chances over
the northern tier as the Southwest to south/central Plains heatwave
may lessen and eyes monitor any new low offshore the Southeast.

The WPC medium range product suite was mainly made from a blend
of best clustered ECMWF/UKMET/Canadian and GEFS/ECMWF/Canadian
ensemble guidance along with the National Blend of Models and
machine learning guidance. The 18 UTC GFS deep low up off the East
Coast did not match latest NHC guidance. Otherwise, the blend
process aimed to mitigate numerous lingering smaller scale/timing
variiances as consistent with individual predictability. This plan
maintains decent WPC product continuity in a pattern with overall
average to above normal predictability.

...Weather/Hazards Highlights...

It generally still remains the case that a rather expansive cool
airmass will settle into the eastern U.S. for the first week of
August. High moisture content and instability near a front on the
leading edge of this airmass will focus some localized heavy rain
to raise flash flooding risks given wet antecedent conditions. WPC
Excessive Rainfall Outlook (ERO) Marginal Risk areas are depicted
for Day 4/Wednesday and Day 5/Thursday for the Southeast through
south-central portions of the Appalachians/Mid-Atlantic.

Farther west, shortwaves rounding into the eastern edge of the
upper ridge from the Rockies/Plains are forecast to interact with a
downstream frontal zone. By early-midweek, there is a trend for
the northern Plains/Upper Midwest/Great Lakes to see increasing
rain and storms. WPC Day 4/5 Marginal Risk ERO areas are depicted
for Wednesday and Thursday given likely moisture/instability
pooling with shortwave passage. Activity will spread more across
the Great Lakes and Midwest later in the week. Meanwhile, the Four
Corners states could see some increasing monsoon showers underneath
the broad ridge, amid the relatively dry monsoon season especially
across Utah/Arizona. Some moderate rainfall chances may eminate
later period from over the Pacific Northwest under the influence
of a cooling upper-level trough given amplifying flow trends.

Cooler than average temperatures will continue on the cool side of
the main frontal system for the central to eastern U.S. and slowly
moderate through the week. Meanwhile across the Southwest,
dangerous heat will build throughout the week with some location
high temperatures as high as 110-115F, equating to major to extreme
HeatRisk. Some relative relief may come next weekend as the upper-
high begins to weaken. Temperatures will also be warming to above
normal into the southern and central High Plains as the upper ridge
expands. Some record high temperatures there could be challenged
and eclipsed through mid-later week over the Southwest. Florida is
forecast to see seasonable temperatures in the 90s, but with ample
humidity allowing for some areas of Major HeatRisk there as well.


Schichtel


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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