499
FXUS02 KWNH 150701
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sun Jun 15 2025

Valid 12Z Tue Jun 17 2025 - 12Z Sat Jun 21 2025


...Intensifying heat threat across portions of the
Plains/Midwest/Southeast to start the Summer late next
week/weekend...

...Continued threat for severe weather and heavy rainfall/flash
flooding into portions of the Midwest/Great Lakes mid-next week...

...General Overview...

Severe weather and heavy rainfall/possible flash flood threat will
continue across the Midwest/Great Lakes during the middle of next
week with enhanced pooled moisture and instability. Storms will
continue eastward into the Interior Northeast/New England southwest
through the Appalachians Thursday with some additional severe
weather and heavy rainfall possible. Also expect an
expanding/intensifying heat threat for the start of Summer across
portions of the Plains/Midwest/Southeast late next week/weekend as
a strong upper-ridge begins to build in. There is also some signal
for an increase in tropical moisture and rainfall into South Texas
and the western Gulf Coast by next weekend.

...Guidance/Predictability Assessment...

Guidance continues to indicate that a highly unsettled and active
zonal flow pattern will continue into to mid next week with
multiple short-wave trough energies traversing the central/eastern
U.S. keeping unsettled weather in the forecast, but with less
specificity in local details. Upstream, a deep upper-low anchored
over the northeastern Pacific looks to be the source for these
upper- waves including one that will traverse the CONUS mid week
helping to briefly dent upper-ridging over the southwestern to
south- central U.S. Then, into later next week, guidance also
continues to agree there will be a shift to a much more amplified
pattern following the progression of the noted upper-wave to the
East Coast, with upper-ridging returning and expanding northward
over the southwestern to central U.S. and eventually eastern U.S.
Meanwhile, guidance shows the upper-low over the northeastern
Pacific will begin to shift southward and overspread portions of
the northwestern U.S. and the West Coast, eventually leading to an
amplified upper-trough dug into the West next weekend. A northward
shift of the storm track should begin to trend down precipitation
chances over much of the central/eastern U.S. for this timeframe.
Main uncertainties with the latest guidance runs revolve around the
progression of both the East Coast upper-wave and deepening upper-
trough over the western U.S. late week and into the weekend. In
both cases, the ECMWF/CMC as well as their respective means are
faster and more progressive with bringing the upper-troughs and
associated surface low pressure/frontal system eastward compared to
the GFS, with the GEFS mean also slower but to a lesser degree. A
look at some of the EC AI guidance as well as the latest GFS
Graphcast support this faster evolution in both cases, particularly
for the East Coast. The updated WPC forecast began with a
composite blend of the deterministic guidance generally well
clustered with various smaller-scale differences. The GEFS mean was
substituted for the GFS in the mid- to late period given the noted
support for the ECMWF/CMC solutions, with increasing contributions
from the ECens and CMC ensemble means as uncertainty, particularly
with the western U.S. system and surface reflection in the
Plains/southern Canada, grows.

There is uncertainty regarding a potential influx of tropical
moisture/rainfall into South Texas and the West Gulf Coast next
weekend. The 12Z ECMWF/ECens mean show greater QPF totals compared
to the GFS/GEFS mean after the opposite was true in prior runs.
Have kept amounts generally tempered for late next week/next
weekend for now given collaboration with the NHC that does not
denote any organized features at this time.


...Weather/Hazards Highlights...

Unsettled weather will remain in the forecast across much of the
central/eastern U.S. through at least the middle of next week as an
upper-wave/associated surface frontal system pushes eastward with
seasonable moisture in place. On Wednesday (day 4), widespread
convection is expected along and ahead of surface low pressure and
a trailing cold front through the Great Lakes/Midwest southwest
through at least the Mississippi Valley and possibly into the
southern Plains. The storms, potentially organized, will be capable
of producing locally heavy rainfall with guidance QPF signals of
1-3"+. A Marginal Risk ERO has been expanded across the region and
it is likely a more focused corridor of higher risk will be needed
once there is more certainty in the areal placement. In addition to
heavy rainfall/flash flooding, the Storm Prediction Center has
also highlighted much of the same region for a severe weather risk
as moderate instability and sufficient shear will bring the threat
for large hail and damaging winds, particularly with any organized
convective lines. The focus for storms will shift eastward with the
system on Thursday (day 5) with another Marginal Risk ERO
stretching along the cold front from northern New England and the
Interior Northeast southwest through the Appalachians into portions
of the Tennessee Valley. Additional scattered storms will be
possible ahead of the cold front across the Mid- Atlantic and
through portions of the Southeast/Lower Mississippi Valley
Wednesday-Thursay. Storm/rainfall focus Friday- Sunday should shift
southward with the cold front to the Gulf Coast/Florida, as well
as along the northern tier from the Upper Midwest/Great Lakes to
the Interior Northeast as the storm track lifts northward. A signal
also remains for a multi-day enhanced tropical moisture feed from
the Gulf to northeast Mexico and South Texas/West Gulf Coast with
the potential for locally heavy rainfall. The approach of a deep
upper-trough/Pacific system look to bring increasing precipitation
chances to the Pacific Northwest by Friday and the northern Rockies
Saturday.

Expect a focus for above average temperatures across the
Intermountain West/Southwest early to mid-next week to shift into
the central Plains and the Middle/Upper Mississippi Valley by late
next week as a strong upper-ridge begins to build in bringing
heat/muggy conditions to start the Summer. The heat will also begin
to intensify across the Lower Mississippi Valley and Southeast as
well as the upper-ridge intensifies eastward. Forecast heat indices
late next week/weekend range from 95-100 across the central Plains
to Middle/Upper Mississippi Valley, 95-100 across the Southeast,
and 105-110+ for the Lower Mississippi Valley and Gulf
Coast/Florida. Hotter temperatures/muggy conditions are also
expected from the Ohio Valley east into the Mid-Atlanitc during the
middle of next week before a cold front passage brings relatively
more comfortable conditions late next week/weekend. Highs will
begin to trend cooler and below average by as much as 10-15 degrees
across portions of the Northwest by Friday and expand into the
Great Basin/northern Rockies by the weekend as an upper-trough and
associated surface cold front from the northeast Pacific begin to
overspread the region.

Putnam


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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