129
FXUS02 KWBC 171858
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
258 PM EDT Thu Jul 17 2025

Valid 12Z Sun Jul 20 2025 - 12Z Thu Jul 24 2025

...Heavy rain and flash flooding threat from portions of the
Midwest to the central Appalachians continues into Sunday...

...Possibly dangerous Heat Wave building from the Southeast into
parts of the Central U.S. next week and beyond...


...Overview...

The medium range period will feature an expansive and building
upper ridge from the southeast to the Central Plains. This will
promote a persistent and potentially dangerous heat wave, which
looks to last even past the medium range period. Elsewhere, a west
to east oriented nearly stationary frontal boundary draped from the
Midwest to the central Appalachians this weekend will provide
focus for potentially heavy rainfall and strong thunderstorms.
Monsoonal moisture across the Southwest may briefly lessen early
week, but could pick up again by mid to late week.


...Guidance/Predictability Assessment...

Model guidance continues to show good overall agreement with its
depiction of the large scale pattern during the medium range
period, dominated mostly by a strengthening subtropical ridge
across the South and Central states and persistent troughing across
the Northwest U.S. Several shortwaves moving through the northern
stream flow continue to show some uncertainty, which is
particularly important for QPF distribution and amounts along a
nearly stationary frontal boundary Sunday into Monday. In the
Northwest, guidance shows persistent troughing wedged in between
the CONUS ridge and an upper high over the northeast Pacific the
first half of the period, with the potential for some energy to
pinch off into a closed low in the vicinity of northern California
by the middle of next week. The latest runs of the GFS seemed to be
much too progressive with this feature, with non-NCEP models
favoring a solution that holds the trough back and develops a much
stronger and larger closed low. The latest runs of the machine
learning EC-AIFS also favor this outcome, lending increased
confidence. As a result, the WPC forecast used a blend of the
deterministic guidance with higher weighting on non-NCEP models for
the first half of the period, transitioning to 50 percent ensemble
means (EC/GEFS) by day 7.


...Weather/Hazards Highlights...

A series of shortwaves and associated surface fronts through the
northern tier will continue to support showers and thunderstorms
from the northern Plains eastward to the Mid-Atlantic/Southeast.
This entire area is encompassed by broad marginal risks on the
Excessive Rainfall Outlooks (EROs) with the warm and very moist
airmass in place. There continues to be a good signal for heavy
rain and the potential for flash flooding from portions of the
Midwest to the Central Appalachians beginning this weekend at the
end of the short range and lasting into Sunday. For the Day
4/Sunday ERO graphic, a higher-end slight risk remains in place
where thunderstorms could train along a nearly stationary frontal
boundary. It is possible a moderate risk may be needed in future
updates depending on convective evolution and potential interaction
with sensitive terrain. In addition, a fairly decent signal for
heavy rainfall is beginning to gain traction across a portion of
the northern Plains on Sunday, given increasing instability and
anomalous moisture. Despite some lingering uncertainties, decided
to go ahead and introduce a slight risk for a part of North Dakota
and far northwest Minnesota.

Elsewhere, the heavy rainfall threat lessens by Monday onward as
this whole system shifts eastward, but have maintained a broad
marginal risk on the Day 5/Monday ERO from the northern Plains to
the Southeast. In the Southwest, monsoonal moisture will be in
place into early next week. Marginal Risks remain across much of
Arizona and New Mexico for Sunday/Monday EROs. Areas like burn
scars and urban areas would be of greatest concern for flash
flooding. A brief break in the moisture flow may be possible before
picking up again later next week.

There is growing concern for a persistent and potentially
dangerous heat wave across portions of the Southeast this weekend
and expanding into the Tennessee Valley and Midwest next week.
Record setting temperatures are possible, with hot and humid days
and little relief overnight leading to widespread areas of Major
HeatRisk, with localized extreme values. See Key Messages being
issued by WPC for the latest on this Heat Wave, which may persist
beyond the medium range period as well, per Climate Prediction
Center Outlooks.


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






















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