996
FXUS02 KWBC 161850
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
250 PM EDT Mon Jun 16 2025

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


...First significant heat wave of the season expected across much
of the central/eastern U.S. beginning late this week/weekend...

...Severe weather and locally heavy rainfall possible for the
Appalachians/Mid-Atlantic Thursday and Upper Midwest/Great Lakes
Friday...


...General Overview...

The risk for severe weather and locally heavy rainfall will
persist on Thursday 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. A significant heat wave
is set to kick off the start of summer across much of the
central/eastern U.S. late this week and into the weekend as a
strong upper level 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...

Model guidance remains in excellent agreement with the depiction
of the large scale pattern through the medium range period. A
qausi-zonal 500mb flow pattern late this week into the first half
of the weekend is forecast to become increasingly amplified through
early next week, setting the stage for a high confidence,
significant heat wave from the Plains to the Mid-Atlantic. Some
smaller scale differences in timing/depth remain with the
shortwaves lifting from the Great Lakes through the Northeast
early in the period, as well as with the shortwaves embedded within
the parent trough across the West later in the period; however,
these differences were generally minor and within the spread
typically seen at these time ranges.

The WPC forecast was constructed utilizing a composite blend of
the deterministic runs of the 00Z ECMWF, 00Z CMC, 00Z UKMET, and
the 06Z GFS. Slightly higher weighting was placed on the ECMWF and
GFS, given their similarities to the machine learning guidance,
particularly the EC AIFS. Beyond day 5, an increasing proportion
of EC and GEFS ensemble means up to 40 percent were included in
the blend, offering a desirable balance between stability,
continuity, and resolution of features.

...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.

The first significant heat wave of the season is expected across
the central Plains by Friday, the Middle/Upper Mississippi Valley
by Saturday, and the Lower Great Lakes/Ohio Valley/Mid-Atlantic by
Sunday thanks to anomalous upper level ridging building overhead.
The heat will also begin to intensify across the Lower Mississippi
Valley and Southeast as well as the 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 level trough and associated
surface cold front from the northeast Pacific begin to overspread
the region.

Miller/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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