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

Valid 00Z Thu Jul 20 2023 - 00Z Sat Jul 22 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...

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

Little change to the overall message regarding a prolonged and extremely
dangerous heat wave ongoing over much of the Southern Tier of the Lower
48, where around 80 million people remain under a Excessive Heat
Warning/Watch or Heat Advisory. Dozens of high temperature records could
fall 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, which will 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, and the Key Messages issued by the Weather
Prediction Center and Climate Prediction Center 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. In fact, 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. Since this morning, catastrophic
flooding occurred across portions of Western Kentucky where preliminary
reports show over 10" of rainfall since midnight across far western
portions of the state from a persistent band of training thunderstorms.
Fortunately, the prolific rainfall event is generally on a downward trend,
although a Moderate Risk of Excessive Rainfall remains as any additional
rainfall will quickly translate to runoff over areas hit hard earlier
today. Meanwhile, a Slight Risk of Excessive Rainfall also extends into
eastern Tennessee, with a separate area also highlighted across southeast
Virginia/northeast North Carolina. Heavy rain aside, the Storm Prediction
Center (SPC) has issued a Slight Risk of severe weather today across the
Central Plains into the Upper Midwest, and over southeast
Virginia/northeast North Carolina for some tornadoes, hail, and wind. 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 Tennessee Valley. 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
also have enough monsoon moisture to work with to fuel scattered showers
and thunderstorms through the end of the work-week.

In the north central Pacific Ocean, Tropical Storm Calvin will continue to
weaken as it drifts west of the Hawaiian Islands today and tonight,
although some peripheral impacts (including dangerous surf and damaging
winds) will remain. Through tomorrow, rainfall amounts upwards of 4-8"
(locally up to 10") are possible along the windward slopes of the Big
Island of Hawaii, which could lead to localized flash flooding and
mudslides. See Central Pacific Hurricane Center advisories on Calvin for
more information on the storm.


Asherman/Mullinax


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