Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
219 PM EDT Mon Jul 17 2023

Valid 00Z Tue Jul 18 2023 - 00Z Thu Jul 20 2023

...Lengthy heat wave to continue in the Southwest, South Central U.S., and
South Florida...

...Tropical Storm Calvin weakening on approach to Hawai'i...heavy rains
expected...

...Canadian wildfires/smoke responsible for Air Quality alerts over parts
of the Northern High Plains, Midwest, Great Lakes, and Northeast...

The upper level ridge of high pressure responsible for the heat wave in
the West will expand across the Southwest and Gulf Coast states through
mid-week. Record breaking heat is expected in the Four Corners states,
Texas to the Lower Mississippi Valley, and South Florida each day. 
Daytime highs will routinely reside in the triple digits in the Desert
Southwest and Texas. The Gulf Coast and Mid-South can expect daytime highs
in the mid-upper 90s that coincide with oppressively high dew points,
resulting in sweltering heat indices between 105-115F.  Daily low
temperatures will remain quite warm, breaking record warm daily minimums
in some areas, allowing for minimal relief from the heat overnight.  An
expansive area of Excessive Heat Warnings and Heat Advisories remains in
the Southwest, Southern Plains, western Gulf Coast, and even parts of
South Florida where the air-sea interaction is leading to a feedback loop
between the air and water temperatures due to the lighter than average
wind flow. Please visit heat.gov for more information on impacts from the
heat wave.  The Northeast and Mid-Atlantic will continue to see hot and
humid conditions through Tuesday, despite the recent passage of a weak
cold front.  To the west, a stronger cold front will provide the Midwest
and Great Lakes with cooler than normal temperatures. Some locations in
the Upper Midwest will struggle to get out of the 70s for highs on
Tuesday.

In the north-central Pacific ocean, Tropical Storm Calvin will continue to
weaken as it approaches the island of Hawai'i, where tropical storm
watches are in effect -- late Tuesday into Wednesday, with the system
becoming a tropical depression later on Wednesday.  The system should lead
to locally heavy rainfall, as much as 4-7 inches on windward slopes, as it
passes by the 50th state.  Rough seas are also possible.  See Central
Pacific Hurricane Center advisories on Calvin for more information on the
storm.

Back in the Lower 48, numerous showers and thunderstorms will engulf
portions of the Midwest and much of the East on Tuesday and Wednesday. On
Tuesday, the threat for heavy and excessive rainfall become heightened
over the Northeast as a cold front approaches from the west.  On Tuesday
and Wednesday, portions of the Ohio Valley have heightened risks of
excessive rainfall, with the best chance of severe weather near the
Illinois/Missouri border on Tuesday per Storm Prediction Center outlooks,
with lower chances in the Plains and Ohio Valley on Wednesday.  For exact
threat levels and related discussions, see WPC excessive rainfall outlooks
and SPC Convective Outlooks. 

Canada's has witnessed their most extensive wildfires on record in 2023
based on area burned; an area approaching the size of Kentucky.  Smoke
from the Canadian wildfires will remain in the picture through Tuesday as
northwesterly winds aloft that originate from Canada continue to direct
smoke into the Lower 48. There are Air Quality alerts issued for areas the
include the northern High Plains, the Midwest, Great Lakes, central
Tennessee and North Carolina, and into the Northeast where higher
concentrations of smoke will result in unhealthy air quality for sensitive
groups. Smoke concentrations should diminish over parts of the Heartland
on Tuesday, but may still cause poor air quality along the East Coast.

Roth/Mullinax


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