Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
243 PM EDT Sun Jun 22 2025

Valid 12Z Wed Jun 25 2025 - 12Z Sun Jun 29 2025

...Record heat gradually lessens but dangerous heat continues for
the Ohio/Tennessee Valleys and Mid-Atlantic/Southeast mid to late
week...

...Heavy rain and flash flooding concerns continue for the north-
central Plains/Upper Midwest Wednesday and Thursday, and lingering
in New Mexico Wednesday...


...Overview...

As the medium range period begins Wednesday, a significant and
extremely dangerous heat wave will be ongoing across the Midwest,
Ohio Valley, and eastern U.S. as a notably strong upper high is
centered from the Ohio/Tennessee Valleys into the Mid-Atlantic. The
extreme, record-breaking heat should moderate slowly midweek and
beyond, but temperatures will remain quite hot across those areas,
and the long duration of the heat wave could cause exacerbated
impacts. Meanwhile strong southerly inflow with deep tropical
moisture will set up between the upper high and an initial mean
trough with embedded shortwaves in the West. Moisture will
initially reach New Mexico and lead to additional heavy rain there
(extending from the short range into the medium range), with the
moisture then reaching around the upper ridge (in a "ring of fire"
setup). This should interact with a wavy frontal boundary and
promote another area of potentially heavy rain and flash flooding
over the north-central Plains, Corn Belt/Midwest, and Great
Lakes/Northeast region.


...Guidance/Predictability Assessment...

The large scale pattern remains in excellent agreement for
midweek, as models for several days have shown a 594+ dm upper
ridge lasting through Wednesday, and weakening and flattening after
that. Meanwhile farther west, troughing across the Great Basin and
vicinity will also weaken as the week progresses. This, combined
with a wave train of northern stream shortwaves, will trend the 500
mb flow pattern toward more zonal and less amplified flow for the
latter half of the week. The slight differences in speed and
amplitude of multiple shortwaves streaming from the West to the
Upper Midwest introduces a bit more uncertainty for the mid to late
medium range period, but nothing out of the ordinary at that time
range. Somewhat broader scale troughing moving into the Northwest
late week and progressing eastward into the weekend shows some
timing and amplitude differences. The 06Z GFS was a bit offset from
the larger cluster of solutions around the 00Z ECMWF with
shortwaves out of the northeastern Pacific, so it was excluded from
the blend by next weekend.

The WPC forecast for mass fields was based on a general multi-
model blend early in the period before sunsetting the GFS in favor
of the ensemble means and continuity. The NBM was sufficient for
most sensible weather grids. For QPF, main challenge was with the
placement and downstream extension of heavier rainfall from NE/IA
up and over the ridge into the Great Lakes and possible
Northeast/Mid-Atlantic. This was encapsulated within the Excessive
Rainfall Outlooks for days 4-5.


...Weather/Hazards Highlights...

On Wednesday, the upper trough in the Interior West will be
gradually weakening, lessening upper jet right entrance region
support and slightly lessening moisture anomalies in the southern
Rockies/High Plains compared to what's now the short range period.
However, some heavy rain could still be a concern centered around
New Mexico, especially considering the wet antecedent conditions by
then. A Slight Risk is delineated in the Sacramento Mountains and
vicinity for the Day 4/Wednesday ERO, where orographic support
could enhance rainfall totals and where burn scars and steep
terrain make the area sensitive to heavy rain. Rain amounts should
continue to gradually decrease there into later week. Maintained a
Marginal Risk on Day 5/Thursday for southern portions of New Mexico
including the Sacramento Mountains for another potential round of
moderate to locally heavy rain.

The plume of subtropical/tropical moisture will arc northeastward
into the north-central Plains and Upper Midwest/Corn Belt where the
additional lift around the frontal boundary and potential training
will favor areas of heavier rainfall and some flash flooding
potential. For the Day 4/Wednesday ERO, continue to show a Slight
Risk (with embedded probabilities on the higher end of the Slight
range) for these areas. The Slight generally covers some model
spread from an eastern Nebraska/northwestern Iowa focus to areas
farther northeast (southern MN to northern/central WI). The details
in the heavy rainfall placement remain uncertain due to the
sensitivity of day-to-day rainfall patterns and mesoscale
boundaries. A weak surface low embedded along the front may track
somewhat east by Thursday, pushing the heaviest rain totals across
much of Wisconsin and possibly the U.P. of Michigan. Thus for the
initial Day 5/Thursday ERO, will show a Slight Risk there, given
potential for 2 to 4 inches to accumulate despite continued spread
in the exact positioning. Nudged the focus area southward a bit due
to a shift southward with the frontal placement. For both
Wednesday and Thursday, some convection with locally heavy rain
could traverse the northern side of the ridge farther east into New
York State and the northern Mid- Atlantic, and have captured these
areas within the Marginal Risk as well. The Northeast may see
increasing rain amounts by Friday, while another round of rain is
possible in the north- central U.S. late week as well.

Farther south, there is some uncertainty with how much convection
may occur under the upper ridge across the Gulf Coast and
southeastern U.S. as surface-based instability likely battles with
subsidence aloft. In general, scattered thunderstorms may increase
in coverage as the week progresses as the upper high gradually
weakens. For now, will leave this area out of any Marginal Risk in
the ERO.

The strong upper high/ridge stretching across the south-central to
eastern U.S. will allow for well above average temperatures that
could approach or exceed daily records at a few dozen locations
early in the week (short range) but fewer by Wednesday. Record warm
morning lows are possible if those numbers hold through the
calendar day. This translates into highs well into the 90s into the
low 100s, with heat indices to near 110F as dew points will be in
the 60s to low/mid-70s. Overnight lows will only drop into the
low/mid 70s for many areas, and even may stay around 80-83F in the
urban centers like Washington, D.C., Baltimore, Philadelphia, and
New York City Wednesday morning. This will bring little relief from
the heat and exacerbate potential impacts. Thus, HeatRisk values
will be Major to Extreme for portions of the Midwest and Ohio
Valley to Eastern states -- levels 3 and 4 on a scale from 1 to 4
(4 being Extreme). This indicates an intensity and duration of heat
that is extremely dangerous to anyone without adequate cooling or
hydration. Extreme heat is the number 1 weather-related killer --
please take precautions if you are outside during the hottest part
of the day and seek cooling if you are without adequate means.
Temperatures will remain above average, though a few degrees lower
and with fewer records possible, across much of the Ohio
Valley/Mid- Atlantic/Southeast into the latter part of next week.
But the Northeast should see moderating temperatures after a cold
frontal passage. Meanwhile, temperatures (particularly highs) are
forecast to be below average by a few degrees in the High Plains
into midweek, but the West should gradually warm to a bit above
average as the week progresses.


Fracasso/Tate


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