653
FXUS02 KWBC 040716
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 AM EDT Mon Aug 4 2025

Valid 12Z Thu Aug 07 2025 - 12Z Mon Aug 11 2025

...Major to Extreme heat threat for the Southwest to south-
central Plains spreads to Upper Midwest/Great Lakes later week...

...Southeast U.S. Coastal Low in the wake of exiting Tropical
Storm Dexter being monitored by the NHC...


...Overview...

A pesky and cooling mean 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 all 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 into later this week, but as
a Bermuda High begins to build westward, wet weather is also forecast
to spread gradually up the eastern U.S. later week/next weekend,
albeit with uncertainty of lift/expansion given variance with
vorts/impulses embedded in the upper trough and uncertain
interactions with a potential Southeast U.S. coastal wave/tropical
development and track. Meanwhile, a series of amplified upper
troughs/frontal systems progressing out from the Northwest to the
north-central U.S. will fire multiple rounds of thunderstorms.

...Guidance/Predictability Assessment...

The synoptic pattern will feature a dominant area of upper ridging
from the Southwest to south/central U.S. with a main storm track
shifted north/overtop along the U.S./Canadian border. Expect a
series of amplified shortwave troughs will translate out through
the northwestern U.S. over the next week. This pattern will keep
precipitation chances generally limited to the northern tier of the
U.S. along frontal waves ahead of the upper-troughs, as well as
east of the upper-high over the southeastern U.S. to Mid- Atlantic
where a lingering trailing frontal boundary remains under the
influence of an upper-level weakness. There is one specific area of
uncertainty with regards to the potential for development of a
coastal wave/low pressure off the coast of the Southeast mid-late
next week with significant impacts on precipitation chances. The
National Hurricane Center has now included low probabilities for
tropical development as well. Recent ECMWF/CMC and ECens mean runs
offer potential for possibly more significant heavy rainfall along
the central Appalachians, with the GFS trending significantly less
robustly with coastal low development and track. Recent EC AI
guidance/GFS Graphcast showed more QPF along the southern
Appalachians with coverage varyingly more northward along the
coastal Mid-Atlantic in a pattern with an elevated ceiling.

Heading into the weekend, guidance still also tends to agree that
additional upper-energy over the northeastern Pacific will help to
strengthen the upper-trough over an unsettled Northwest and then
bring this feature eastward as the upper-high over Southwest to
south/central U.S. slowly weakens. However, there is disagreement
in the progression, with recent GFS runs in particular more
progressive over the north-central U.S. to south-central Canada.
Most other deterministic and machine learning guidance remain
slower. Accordingly, a growing contribution from the ensemble means
was included by the weekend, partially at the expense of the GFS.

...Weather/Hazards Highlights...

A rather expansive cool high pressure airmass will linger over the
eastern U.S. over the next week. 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 so far for Day 4/Thursday and Day
5/Friday from portions of the Southeast to south-central areas of
the Appalachians/Mid-Atlantic given upper trough position and
uncertain coastal wave/tropical development in addition to moist
onshore flow from the Carolinas to 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. Into late week, expect the northern
Plains/Upper Midwest/Great Lakes to see periodic rain and storms.
WPC Day 4/5 Marginal Risk ERO areas are depicted for Thursday and
Friday given likely moisture/instability pooling with shortwave
passages. 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 so far. Elsewhere, some
moderate rainfall chances may develop and slowly progress this
weekend from over the Pacific Northwest under the influence of a
cooling and unsettling upper-level trough.

Cooler than average temperatures will continue on the cool side of
the main frontal system for the central to eastern U.S.. 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 and offers some major HeatRisk
areas over the southern and central Plains as the upper ridge
expands, with pre-frontal heat spreading into the Upper
Midwest/Great Lakes later week. Some record high temperatures there
could be challenged and eclipsed into late 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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