Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Wed Aug 16 2023

Valid 12Z Wed Aug 16 2023 - 12Z Fri Aug 18 2023

...Dangerous Heat Wave continues over the Pacific Northwest/Northern
Rockies as heat builds back in over Texas Thursday...

...Severe thunderstorms possible for the Upper Midwest Wednesday...

...Showers, thunderstorms, and isolated flash flooding will continue
across the Four Corners region...

An expansive upper-level ridge will remain in place over the Pacific
Northwest/Northern Rockies the next couple of days allowing for a
dangerous heat wave to continue. Forecast high temperatures will be in the
low to mid-100s for interior locations with low 90s around Puget Sound.
The heat will expand further into the Northern Rockies and adjacent
Northern High Plains on Thursday. Numerous near record-tying/breaking
highs are possible, with overnight lows remaining warm and at similarly
high record-tying/breaking levels. The duration and intensity of the heat
is leading to a more significant health risk to the region than typical
summer heat, particularly for those without adequate air conditioning. A
Pacific system moving in from the northwest may begin to provide some
relief for western portions of Washington and Oregon on Thursday, before a
more expansive cool down is expected Friday just beyond the current
forecast period.

Meanwhile, much of the South will continue to see a brief reprieve from
the recent oppressive heat thanks to a lingering frontal boundary
stretching from the Carolinas southwest along the Gulf Coast and into
Texas. Highs will be near or even a bit below more reasonable summer-time
averages, with low to mid 90s for Florida and the central Gulf Coast and
mid-80s further north into the Southeast. Areas south of the boundary
along the western Gulf Coast and south Texas will remain very hot, with
low to mid-100s expected. Portions of west Texas will also see
temperatures return into the low 100s as an upper-level ridge begins to
expand eastward. Unfortunately, with this eastward ridge expansion, most
of Texas will soar back into the mid- to upper 100s on Thursday, with
numerous record-tying/breaking highs possible. This heat wave is expected
to expand across much of the central and southern U.S. in the coming days.
Please see WPC's Heat Key Messages for more information on these heat
waves. 

Beyond the heat headlines, scattered showers and thunderstorms are
expected Wednesday to the southeast of the stationary boundary along
portions of the coastal Carolinas southward through Florida. Deep moisture
residing over the region may contribute to some locally heavy downpours
and an isolated instance or two of flash flooding. Storm chances should
continue in Florida through Thursday. To the north, a strengthening low
pressure system over south-central Canada/the Northern Plains will sweep
eastward across the Upper Midwest Wednesday. Moist return flow ahead of
the system as well as strengthening flow aloft as an upper-level shortwave
drops south over the region will provide the necessary ingredients for
robust, organized storm development along the cold front. The Storm
Prediction Center has outlined a Slight Risk (level 2/5) of severe weather
for the threat of some damaging winds and large hail. Storm chances will
continue through the overnight hours late Wednesday/early Thursday over
the Great Lakes as the system moves eastward and then into the Northeast
for Thursday. An isolated chance will remain for a severe thunderstorm
and/or locally heavy rainfall. High temperatures will be near average for
much of the Northeast and Mid-Atlantic, with 80s and low 90s forecast.
Highs will be below average in New England (70s) and portions of the
Ohio/Middle Mississippi Valley (low to mid-80s). Ahead of the storm
system, highs will range from the mid-80s in the Upper Midwest to the
upper 90s for portions of the Central Plains and Upper Missouri Valley.
Cooler temperatures will follow the cold front passage for much of this
region on Thursday, with highs dropping into the mid-70s to low 80s.

Anomalously high moisture in place over the Four Corners region and Great
Basin will continue to lead to daily, scattered thunderstorm chances. Some
locally heavy downpours are possible with an isolated risk of flash
flooding, particularly for more sensitive locations such as urban areas,
burn scars, dry washes, and slot canyons. High temperatures broadly across
the southern tier of the West will range from the 70s along coastal
California, the mid-80s in the precipitation cooled Four Corners region,
and low to mid-90s for the Central/Southern Rockies and Great Basin. More
anomalous temperatures are expected for the interior California Valleys,
with Heat Advisories in place for highs in the mid-100s. High temperatures
will also climb back into the 110s for the Desert Southwest, with
heat-related advisories and warnings in place as record-tying/breaking
level heat is possible by Thursday. 

Putnam


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