970
FXUS02 KWBC 211849
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
249 PM EDT Sat Jun 21 2025

Valid 12Z Tue Jun 24 2025 - 12Z Sat Jun 28 2025

...Significant and extremely dangerous heat wave continues across
the Midwest and Mid-Atlantic/Northeast next week...

...Multi-day heavy rain threat with potential for flash flooding
across the north-central Plains/Upper Midwest and the southern
Rockies/High Plains next week...


...Overview...

As the medium range period begins Tuesday, 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 and Mid-Atlantic. The
extreme, record-breaking heat should moderate slowly from 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 a mean
trough with embedded shortwaves in the West. This should lead to
potentially heavy rain focused initially around New Mexico, with
the moisture then reaching around the upper ridge (in a "ring of
fire" setup). This will interact with a wavy frontal boundary and
promote another area of potentially heavy rain and flash flooding
over the north-central Plains and Midwest/Corn Belt.


...Guidance/Predictability Assessment...

Model guidance remains in excellent agreement with the large scale
pattern especially through midweek. The 594+ dm upper ridge will
be most expansive at the start of the period Tuesday, stretching
across much of the eastern half of the Lower 48, before slowly
weakening and flattening midweek and beyond. Meanwhile farther
west, troughing across the Great Basin and vicinity will also
weaken as next 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
next 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 shows some timing differences by next
Saturday. A blend of the latest 00Z/06Z guidance was a sufficient
starting point for the fronts/pressure, trending toward more
ensemble mean inclusion. The 13Z NBM was utilized for many of the
sensible weather grids with slight modification. QPF
placement/amounts are a bit uncertain over the Midwest/Corn Belt
but hedged on the southern side of the guidance spread for now.


...Weather/Hazards Highlights...

Flash flooding threat will continue over New Mexico out of the
short range (Monday) and into the medium range (Tuesday) which has
the highest rainfall potential per the latest guidance. In
coordination with WFOs ABQ/EPZ, raised a Moderate risk in the
Excessive Rainfall Outlook over the Sacramento Mountains and nearby
areas where the influx of moisture and potential training of
rainfall atop wetted soils from the previous days may lead to more
widespread impacts (especially around burn scars and areas of steep
terrain). Rainfall will continue into Wednesday but likely
decrease, though the flash flooding threat will remain. Farther
north, the plume of subtropical/tropical moisture will arc
northeastward into the 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.
Maintained a Slight risk in the ERO for both Tues/Wed (noting some
high probabilities within that Slight outline as well). The
placement of the heavier rain remains more uncertain here rather
than farther south due to the sensitivity to day-to- day rainfall
patters and mesoscale boundaries. The heaviest rain and storms may
extend across Lower Michigan into NYS, and have looped this region
into the Marginal risk outline. This area of rainfall may shift
somewhat east into the Upper Great Lakes region by Thursday while
expanding into the Mid-Atlantic and Northeast mid to later 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.

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
through Tuesday. 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. 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 interior portions of the
West and High Plains into midweek, but should gradually warm closer
to or 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





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