437
FXUS02 KWNH 160700
PREEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Mon Jun 16 2025

Valid 12Z Thu Jun 19 2025 - 12Z Mon Jun 23 2025


...Intensifying heat threat across much of the central/eastern
U.S. beginning late this week/weekend...

...Severe weather and heavy rainfall/flash flooding threats for
the Appalachians/Mid-Atlantic Thursday and Upper Midwest/Great
Lakes Friday...


...General Overview...

Severe weather and heavy rainfall/flash flood threats will persist
Thursday with storms from the Northeast down through the
Appalachians/Mid- Atlantic. Expect the focus for storms to shift
northward to the Upper Midwest/Great Lakes Friday with another
heavy rainfall/flash flood threat possible. An
expanding/intensifying heat threat for the start of Summer will
unfold across much of the central/eastern U.S. into late week/next
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 into next weekend.

...Guidance/Predictability Assessment...

Guidance has remained in good agreement for several days now that
a pattern change will begin by late next week (Thursday June 19) as
unsettled, zonal flow over the central/eastern U.S. will
transition to a much more amplified pattern. The last of a series
of upper- level waves and leading surface frontal system will pass
from the Midwest to the East Coast mid- to late week. The latest
12/18Z runs of the GFS remain a bit slower with the progression of
this system compared to the other standard deterministic/mean
guidance, but there is further support for this solution from the
latest run of the ECMWF AIFS. In the wake of this wave, an upper-
level ridge over the southwestern U.S. will begin to expand and
strengthen as it shifts over the central and then towards the
eastern U.S. late week/this weekend. At the same time, a deep
upper-low anchored over the northeastern Pacific for several days
will begin to shift southward first over the Pacific Northwest, and
eventually leading to a deepening upper-trough more broadly across
the western U.S. Slow eastward progression of the upper- trough as
it deepens over the West brings some uncertainty to the leading
surface frontal system, with at least a couple rounds of
cyclogenesis on the Plains possible, but all 12Z guidance generally
remains well clustered on the the larger-scale details. The 18Z
GFS was more active in eastward progression with leading
upper/surface energy into the Midwest. Otherwise, all guidance is
supportive of this pattern with an eastern upper-ridge, western
upper-trough being locked in through at least early next week, with
the main ramification being a start of Summer heat wave for much
of the central/eastern U.S.

The updated WPC forecast used a composite blend of the
deterministic guidance for the early part of the period/late this
week with the guidance generally well clustered overall with GFS/AI
model support for a bit slower progression of the eastern U.S.
system. A growing contribution from the means is introduced for
later in the period this weekend/early next week as uncertainty
with respect to the details of leading frontal system evolution
over the Plains increases, but with both deterministic and ensemble
guidance in support of eastern upper-ridge/western upper- trough
pattern. The 12Z GFS was used over the 18Z given noted outlier
nature of additional leading upper-wave/surface energy.

...Weather/Hazards Highlights...

One more day of unsettled weather is forecast broadly across the
eastern U.S. Thursday (day 4) with the approach of another upper-
level wave and leading surface frontal system. Scattered to
widespread showers and storms are expected ahead of a cold front
stretching from the Northeast southwest through the Mid-
Atlantic/Appalachians and into the Tennessee/Lower Mississippi
Valleys. Seasonably high precipitable water values will bring the
threat for some locally heavier rainfall and have maintained a
Marginal Risk ERO for isolated flash flooding along the front over
lower FFGs/terrain sensitive areas from the Interior
Northeast/northern New England southwest through the Appalachians.
Moderate instability with daytime heating ahead of the front along
with sufficient shear as the upper-wave approaches will bring the
threat of some severe storms to the central Appalachians through
Mid- Atlantic as well, with the Storm Prediction Center noting the
risk for mainly damaging winds. Storm potential will focus
southward with the front along the Gulf Coast and northward across
the Great Lakes/Northeast with the lifting upper-jet Friday into
the weekend. Embedded impulses withing the growing upper-ridge over
the central U.S. will trigger convection, potentially organized,
across the Upper Midwest/Great Lakes Friday (day 5) with a Marginal
Risk ERO in place as a strong low level jet and high precipitable
water values (2 standard deviations above the mean) support the
threat of heavy rainfall/isolated flash flooding. Additional but
uncertain influx of tropical moisture into south Texas may bring
locally heavy downpours, with a Marginal Risk for days 4/5 focused
along the Rio Grande Valley for now, but further adjustment/higher
probabilities may be needed as confidence in this scenario grows.
This influx of moisture also looks to bring precipitation chances
further northwest into western Texas and the southern high Plains
by late weekend/early next week. Upstream, the energetic approach
of a deep upper-trough/Pacific system and northern stream into the
West will bring increasing precipitation chances to the Pacific
Northwest and northern Rockies/Plains Friday through the weekend in
unsettled flow with moderate rainfall potential. Eventual lead
frontal system development over the Plains may bring a return of
thunderstorm chances to portions of the northern/central Plains and
Midwest Sunday-Monday.

Expect a gradually shifting focus for hot, above average
temperatures across the Intermountain West/Southwest mid-next week
to expand into the central Plains by Friday, the Middle/Upper
Mississippi Valley by Saturday, and the Lower Great Lakes/Ohio
Valley/Mid-Atlantic by Sunday as a strong upper- ridge begins to
build in bringing a heat wave to start the Summer. The heat will
also begin to intensify across the Lower Mississippi Valley and
Southeast as well as the upper- ridge expands eastward. Widespread
Major Heat Risk (level 3/4) is forecast, indicating an intensity of
heat that effects anyone without adequate cooling or hydration, as
heat indices climb to 95-105, 105-110+ for the Lower Mississippi
Valley and Gulf Coast/Florida. In addition, muggy overnight lows in
the mid- to upper 70s will bring little overnight relief from the
heat. Unfortunately, this heat wave looks to persist into next
week. 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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