Heat in Alabama, July 18, 2020

Area Forecast Discussion
National Weather Service Huntsville AL
1248 PM CDT Sat Jul 18 2020

.UPDATE...
For 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 1136 AM CDT Sat Jul 18 2020

The synoptic scale regime across the TN Valley will continue to be
dominated by a strong subtropical ridge in the mid-levels, extending
from the southern Rockies to the southern Mid-Atlantic coast.
Although there is effectively no support for the development of
convection aloft, light southwesterly flow around the rim of a
Bermuda High sitting over the western North Atlantic will interact
with both terrain features and subtle mesoscale boundaries from
convection yesterday evening to force the development of isolated-
scattered showers and thunderstorms through the remainder of the
afternoon. Latest models suggest that the greatest coverage of this
activity will occur across northeast AL, but based on recent trends
in reflectivity data from KHTX, we have included a slight chance POP
for the remainder of the forecast area, as well. A consensus of
forecast soundings indicate MLCAPE values in the 1500-2000 J/kg
range, with roughly 1000-1500 J/kg DCAPE, and this should translate
to a marginal threat for outflow gusts in the 40-50 MPH range with
the strongest cells.

Aside from the updates to POP/weather grids mentioned above, we have
raised high temperatures by a degree or so based on current surface
observations. This will boost HI values into the 100-105 degree range
for all valley locations and 95-100 degree range in elevated
terrain.

.SHORT TERM...(Tonight through Monday)
Issued at 326 AM CDT Sat Jul 18 2020

More of the same of Sunday and Monday as the aforementioned 594 dm
ridge remains generally centered across the Tennessee Valley region.
Strong subsidence from this ridge will limit opportunities for
diurnally driven convection for the most part, save for a few
isolated storms on Sunday and some isolated to widely scattered
activity on Monday. The main story will continue to be the heat an
humidity as highs in the low to mid 90s will be common, with heat
index values peaking between 100 to 105 degrees once again.

.LONG TERM...(Monday night through Friday)
Issued at 326 AM CDT Sat Jul 18 2020

An upper-trough over the Northern Plains will shift into the Great
Lakes on Tuesday, and dig ever so slightly into the Ohio Valley by
Wednesday. While no fronts will make it this far south, this will
serve to nudge the center of the ridge just to the west of the area
during the middle to later part of the upcoming work week. With
plenty of moisture present underneath this ridge, this will serve to
generate more scattered to potentially numerous showers and
thunderstorms each afternoon, thanks to a weaker cap and lower
convective temperatures. Additionally, depending on the position of
the ridge, there may be an opportunity for the remnants of a
convective complex to drop into the region should we enter more of a
northwest flow regime by Thursday and Friday. Model solutions differ
on this, however, with the GFS being the wetter of the two solutions
and ECMWF bringing back a 594 dm ridge by next weekend. Regardless,
the main headlines for the extended will be some better rain chances
by the middle of next week, but also continued hot and humid
conditions, with highs in the lower 90s and heat index values near
100 degrees each day.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1248 PM CDT Sat Jul 18 2020

Isolated-scattered SHRA and TSRA will continue to develop throughout
the aftn in the vicinity of several mesoscale and outflow boundaries
located in the region. We have included VCSH in the forecast at both
terminals thru 19/00Z, but TAF amendments and AWWs may be required
if it appears that a storm will directly impact either HSV or MSL.
Otherwise, little change in the synoptic weather pattern is
anticipated for the upcoming 24-hr forecast period, with a large
ridge aloft remaining in place across the TN Valley. Thus, we expect
sct-occasionally broken mid and high-lvl clouds and lgt/vrbl to lgt
SW flow. Conditions will be favorable for the development of patchy
BR/FG between 09-13Z, but confidence in vsby reductions at the
airports is too low to include in the forecast attm.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.

&&

NEAR TERM...70/DD
SHORT TERM...AMP.24
LONG TERM...AMP.24
AVIATION...70/DD

For more information please visit our website
at weather.gov/huntsville.

Hazardous Weather Outlook
National Weather Service Huntsville AL
329 AM CDT Sat Jul 18 2020

ALZ001>010-016-TNZ076-096-097-182330-
Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan-
Marshall-Jackson-DeKalb-Cullman-Moore-Lincoln-Franklin TN-
329 AM CDT Sat Jul 18 2020

This Hazardous Weather Outlook is for north Alabama and portions of
southern middle Tennessee.

.DAY ONE...Today and Tonight...

Hot temperatures are expected again today, with heat index values
rising into the 100-104 degree range. Isolated thunderstorms are
also possible. Primary threats posed by the stronger storms will be
lightning, gusty winds, and brief heavy rainfall.

.DAYS TWO THROUGH SEVEN...Sunday through Friday...

Hot temperatures continue through at least midweek next week, with
daily heat index values warming to around 100 degrees over most of
the Tennessee Valley through Thursday.

Isolated to widely scattered afternoon thunderstorms are possible
Sunday and Monday. However, thunderstorms are expected to increase in
coverage from Tuesday through Friday during the afternoons. Some
thunderstorms during this period may be capable of producing strong,
gusty winds.

.SPOTTER CALL TO ACTION STATEMENT...

Activation of storm spotters and emergency management personnel is
not anticipated at this time.