419
FXUS02 KWBC 021856
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Wed Jul 2 2025

Valid 12Z Sat Jul 5 2025 - 12Z Wed Jul 9 2025


...Heavy Rain/Flash flooding threat for Florida as well as from
the north-central Plains to the Midwest this holiday weekend...

...Hazardous heat and humidity to spread from the Midwest this
holiday weekend to the Mid-Atlantic/Northeast early next week as
sweltering heat lingers for the South and builds over the West...

19Z Update: Not much has changed in the overall forecast philosophy
for the medium range period. There has been a modest increase in
overall rainfall totals across the central and northern Plains
compared to the previous forecast. The 12Z model guidance is in
reasonably good agreement for the beginning of the period Saturday,
although the CMC is stronger with the trough across the Pacific
Northwest. By next Wednesday, the GFS becomes stronger with the
trough crossing the northern Great Lakes, but in decent agreement
elsewhere. At the time of fronts/pressures preparation, the
previous CMC was out of phase across the north-central U.S. for
early-mid next week, so it was phased out of the forecast blend by
that time. The ensemble means were gradually increased to about
half by Wednesday amid increasing mesoscale uncertainties. The
previous forecast discussion is appended below. /Hamrick
-------------------

...Pattern Overview...

Upper troughing over the Northeast will eject into the Canadian
Maritimes over the holiday weekend as multiple Pacific shortwaves
dig into a West Coast mean upper trough which will help to keep it
in place heading into next week. In between, a building upper ridge
will spread a threat of hazardous heat and humidity from the
Midwest this holiday weekend to the Mid-Atlantic/Northeast early
next week as a hot summer airmass lingers over the South and builds
over the Southwest/West. Meanwhile, a series of strong to severe
convection forcing and heavy rain fueling impulses will progress
atop the ridge from the north-central U.S. to the Midwest and into
the Northeast. Meanwhile, tropical moisture will fuel some heavy
downpours along/south of a slowly weakening Florida front over the
weekend in a region with local precursor heavy rains and tropical
moisture, with any organization being monitored by the NHC.

...Guidance/Predictability Assessment

The WPC medium range product suite was derived from a composite
blend of compatible GEFS/ECMWF/Canadian ensemble mean guidance
along with WPC continuity and the National Blend of Models.
Forecast spread increases over time within average seasonal norms,
but ensemble mean usage mutes individual system depictions given
uncertainty, especially in the Gulf and offshore the Southeast
U.S. given slowly growing but limited NHC support. Recent model
have been less than stellar run to run with the handling of this,
but latest 00 UTC runs trended to the AIFS with main focus now
just offshore the Southeast coast this weekend/early next week.

...Weather/Hazards Highlights...

Tropical moisture and instability will support heavy convective
downpours along/south of a lingering front across Florida through
the upcoming holiday weekend. WPC Excessive Rainfall Outlook (ERO)
Marginal Risk areas are shown for Day 4/Saturday and Day 5/Sunday
for west-central Florida as preceded by heavy rainfall.
Additionally, a Marginal Risk has been added for portions of the
South Carolina Low Country and into the greater Savannah metro area
for Day 4 given the increased moisture and rainfall potential
associated with the low pressure area that NHC is monitoring.

Periodic strong to severe storms/MCSs will offer periodic heavy
rain/runoff threats to focus from the north-central U.S. to the
Midwest this weekend as upper trough/impulse energies work on the
northern periphery of the main central U.S. upper ridge where
moisture/instability tends to be lifted near a wavy draping front.
WPC ERO Marginal Risk areas are depicted for Day 4/Saturday and
downstream for Day 5/Sunday. Into early-mid next week, showers and
embedded thunderstorms will focus near the slow moving front into
the Northeast/Mid-Atlantic, but also refire back across the north-
central states where ejecting upper-level waves will interact with
moisture and instability pooling frontal zones.

Meanwhile, a broadening upper ridge will spread a hazardous heat
and humidity threat from the Midwest this holiday weekend to the
Mid-Atlantic/Northeast into next week as a hot summer airmass
lingers broadly over the South and builds up across the West.


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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