Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Wed Jul 19 2023

Valid 12Z Wed Jul 19 2023 - 12Z Fri Jul 21 2023

...Lengthy & dangerous heat wave to continue across the Southern Tier this
week...

...Flash flooding & severe weather possible from the Nation's Heartland to
the Mid-Atlantic through Thursday, headlined by a Moderate Risk in western
Kentucky and northwest Tennessee today...

...Tropical Storm Calvin weakening on approach to Hawaii this morning, but
heavy rains and tropical storm force wind gusts still expected...

...Canadian wildfires/smoke responsible for Air Quality alerts over parts
of the Great Lakes, southern Mid-Atlantic, and Northeast today...

A prolonged and extremely dangerous heat wave continues for much of the
Southern Tier of the Lower 48 thanks to an expansive dome of high pressure
aloft, where over 80 million people are under either an Excessive Heat
Warning/Watch or Heat Advisory. Additional record breaking heat is
expected across the Four Corners states, Texas to the Lower Mississippi
Valley, and South Florida through the end of the work week. Daytime highs
will reside in the triple digits in the Desert Southwest and Southern
Plains today, while the Gulf Coast and Mid-South can expect daytime highs
in the upper 90s that coincide with oppressively high dew points through
Thursday, resulting in sweltering heat indices as high as 120 degrees in
some areas. Meanwhile, daily low temperatures will remain quite warm with
breaking record warm daily minimums expected. These exceptionally warm
overnight minimums limit relief from the heat overnight. Even parts of
South Florida will continue to contend with stifling heat thanks in large
part to well above normal sea surface temperatures and lighter than normal
winds across the Sunshine State. Please visit heat.gov for more
information on impacts from the heat wave. The Mid-Atlantic will continue
to see the usual hot and muggy conditions for mid-July while the Northeast
remains in the 80s but deals with less humid conditions compared to their
neighbors to the south. To the west, a pair of cold fronts will provide
the Upper Midwest and both the northern and central High Plains with
cooler than normal temperatures. Some locations in the northern and
central High Plains will struggle to get out of the 70s for through
midweek.

The aforementioned cold fronts that are ushering in cooler and more
refreshing temperatures into the north central U.S. are also to blame for
rounds to strong-to-severe storms from the central Rockies and Great
Plains to the Mid-Atlantic coast. This morning, ongoing rounds of
thunderstorms containing prolific rainfall rates are responsible for the
areas of significant flash flooding in parts of western Kentucky
overnight. The Weather Prediction Center maintains a Moderate Risk for
Excessive Rainfall from western Kentucky into northwest Tennessee. There
are also Slight Risks from central Missouri on south and east into the
heart of the Tennessee Valley, as well as southeast Virginia. Farther
north, the Storm Prediction Center (SPC) has issued a Slight Risk from
northern Kansas on north and west into the Upper Mississippi Valley.
Severe storms within the Slight Risk area could contain very large hail,
as well as damaging wind gusts and tornadoes. Both WPC and SPC have
Marginal Risk areas in the central High Plains and over the Mid-Atlantic.
By Thursday, the severe weather and Excessive Rainfall threat expands to
include the central High Plains, portions of the Great Lakes. the central
Appalachians, and the Carolinas. In these regions, thunderstorms could
produce any combination of damaging wind gusts, large hail, tornadoes, or
flash flooding. Farther west, the Rockies and Southwest will have enough
monsoon moisture to work with that, with the help of strong daytime
heating, scattered showers and thunderstorms are expected through the end
of the work-week.

In the north central Pacific Ocean, Tropical Storm Calvin is forecast to
continue weakening as it tracks just south of Hawaii's Big Island, where
Tropical Storm Warnings remain in place. The latest forecast from the
Central Pacific Hurricane Center shows the storm maintaining tropical
storm status as it tracks south of the Big Island tonight. The forecast is
still on track for Calvin to produce heavy rainfall, with as much as 4-8
inches and localized amounts up to 10 inches along the windward slopes of
the Big Island. A little farther north, 3-6 inches of rainfall are
possible along the windward slopes of Maui. Potential impacts include
localized flash flooding and mudslides. Calvin will also cause rough seas
and locally strong winds around "The Aloha State." See Central Pacific
Hurricane Center advisories on Calvin for more information on the storm.

Smoke from the Canadian wildfires are responsible for lingering Air
Quality alerts that are in place for portions of the Great Lakes, southern
Mid-Atlantic, and Northeast. Fortunately, short term forecasts show lesser
concentrations of Canadian wildfire smoke beyond this afternoon. This
should give most of the northern tier of the U.S. a break from the more
concentrated smoke plumes through at least Thursday.


Mullinax


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