Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
419 AM EDT Mon Aug 14 2023

Valid 12Z Mon Aug 14 2023 - 12Z Wed Aug 16 2023

...Flash flooding and severe thunderstorms possible for the Great
Lakes/Ohio Valley/Mid-Atlantic Monday, lingering along the coast into
Tuesday...

...Portions of the South to see a brief reprieve from the heat mid-week as
a heat wave intensifies across the Pacific Northwest into the Northern
Rockies...

...Monsoonal showers continue across the Four Corners region with some
locally heavy downpours possible...

A consolidating/organizing frontal system will push eastward from the
Mississippi Valley towards the East Coast today aided in part by an
unseasonably strong upper-level wave dropping south from Canada. Strong
lift as well as very moist, southerly flow ahead of and around the system
will trigger scattered to widespread showers and thunderstorms Monday
stretching from the Great Lakes south into the Upper Ohio/Tennessee
Valleys eastward through the Appalachians and into the Mid-Atlantic. Two
areas of concern have arisen for flash flooding with Slight Risks of
Excessive Rainfall (level 2/4) in place. The first covers areas around
southern Lake Michigan where slow moving, widespread storms may lead to
long duration, heavy rainfall totals. The second stretches from the Upper
Tennessee/Ohio Valleys east through the Appalachians into the Mid-Atlantic
where some organized lines as well as individual storms will both have the
potential to produce very heavy downpours with anomalously high moisture
in the region. In addition to flash flooding, the Storm Prediction Center
has outlined this region for a Slight Risk (level 2/5) of severe weather
as strengthening upper-level flow with the approaching wave will provide
enough shear for more robust, organized storms which may produce some
instances of damaging winds as well as a few tornadoes. The cold front
will slow as it approaches the East Coast Monday night, allowing for
renewed storm development Tuesday ahead of the front from the DelMarVa
south through the eastern Carolinas, where Slight Risks for Excessive
Rainfall and severe weather are in place. Highs ahead of the front in the
Mid-Atlantic will remain seasonably warm and in the mid-80s to mid-90s,
while locations to the north of the system into New England and behind the
front into the Great Lakes/Midwest will be unseasonably cooler and mainly
in the 70s. 

To the south, dangerous heat will continue Monday thanks to a well
anchored upper-level ridge with widespread heat-related advisories and
warnings spanning from Florida north to the Carolinas and west to
Texas/Oklahoma. High temperatures once again are forecast to range from
the mid-90s in Florida and the Carolinas, the upper 90s to low 100s for
the Southeast into the Lower Mississippi Valley, and as high as the
mid-100s into portions of Texas. These temperatures when combined with
high humidity will allow for heat indices as high as 110 to 120F for many
locations. Numerous record-tying/breaking highs are forecast, with
similarly record-level warm low temperatures in the upper 70s to low 80s
providing little relief from the heat overnight. Fortunately, the noted
strong upper-level wave/cold front pushing southeastward will bring a
brief reprieve to northern portions of the region by Tuesday. Highs from
northern Georgia west through north Texas will drop to much more
seasonable values in the mid-80s to low 90s, and even upper 70s for
portions of the Mid-South. The heat will remain oppressive Tuesday to the
south of the front from south Texas east along the Gulf Coast to Florida
and northeastward into the Carolinas, but even some of these locations may
see a bit of relief into mid-week as well. 

Another major heatwave will continue to build today over the Pacific
Northwest/Northern Rockies in relation to a strengthening ridge of high
pressure overhead. High temperatures will range from the low 90s around
Puget Sound, the upper 90s to low 100s for the interior Northwest and
Northern Rockies, and the mid-100s to potentially over 110 degrees for the
interior valleys west of the Cascades in Oregon. Numerous near
record-tying/breaking highs are possible here as well. These temperatures
combined with the duration of heat, expected to continue through this
week, will increasingly pose a heightened health risk, especially for
those without adequate air conditioning.  

Daily rounds of thunderstorm activity can be expected across the Four
Corners region northwestward into the Great Basin and portions of the
Sierra thanks in part to Monsoonal moisture and a lingering frontal
boundary near the region. Any of these storms may have the potential to
produce heavy downpours with an isolated threat for flash flooding. Daily
highs will be near seasonal averages with 70s in proximity of the
California Coast, low to mid-90s for the Great Basin, and 100s for the
Desert Southwest. Highs in the interior California valleys will trend a
bit hotter with mid-100s expected and Heat Advisories in place. With
cooler, post-frontal air filtering south into the central U.S., portions
of the Central/Southern High Plains/Rockies will have some cooler highs
than points west on Monday; mainly in the upper 70s to low 80s.
Temperatures will begin to rapidly rebound Tuesday as conditions moderate
following the frontal passage, with highs jumping back into the upper 80s
to low 90s.

Putnam

Graphics available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php