201
FXUS63 KLSX 030924
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
424 AM CDT Wed Jul 3 2024

.KEY MESSAGES...

- The combination of heat and humidity will allow heat index
  values to climb to around 105 degrees over parts of southeast
  Missouri where a Heat Advisory is in effect this afternoon into
  early this evening.

- There will be additional rounds of thunderstorms through
  Thursday night. A few of the storms could be severe this
  afternoon and this evening and again on Thursday afternoon and
  evening.

- In addition to the severe weather potential, locally heavy
  rainfall is possible with these thunderstorms.


&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 422 AM CDT Wed Jul 3 2024

Highs will reach the lower 90s over southeast Missouri and dewpoints
are forecast to be in the mid to upper 70s over much of the area.
Peak heat index readings will reach around 105 over parts of
southeast Missouri, so I have issued a Heat Advisory for Reynolds,
Iron, and Madison counties from 11 am through 8 pm today.

I have gone ahead and canceled the flood watch early as the heavy
rainfall threat has ended over the northern CWA.  We are continuing
to see showers and thunderstorms over the central part of the CWA
early this morning.  These were occurring on the nose of the LLJ and
they should gradually weaken and move east over the next few hours
as the LLJ veers and weakens.  The associated outflow boundary will
move south into the southern part of the CWA this afternoon.  The
most likely time for additional thunderstorm development today will
be this afternoon over southeast Missouri into southwest Illinois
along this effective front where MLCAPES will be 2500+ J/kg with
deep layer shear of 30+ knots.  This could is favorable for
producing a few organized multicell clusters that could produce
damaging winds through early this evening.

The coverage of showers and thunderstorms will increase across the
area late this evening and overnight as a shortwave trough
approaches the area and the low level jet kicks back warranting 60-
90% PoPs.  We are still looking at PWATS between 2-2.5" and very
high warm cloud depths, and the HREF LPMM has some small spots with
with totals exceeding 3" tonight into tomorrow morning.  Will
continue to look at the potential for locally heavy rainfall tonight
into early Thursday.

Then there will be another risk for severe thunderstorms Thursday
afternoon and evening as yet another shortwave trough move across
the area where the warm front will intersect the incoming cold
front.  The combination of CAPE/shear favors a few supercells/
organized multicells capable of producing damaging winds and large
hail.

Britt

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 422 AM CDT Wed Jul 3 2024

Available guidance is still favoring the front moving through the
area on Thursday night with showers and thunderstorms moving out of
the southeastern part of the CWA on Friday.  Friday night into
Saturday look dry as large surface high moves across the area.  The
next upper trough moves through the area early next week bringing a
chance of showers and thunderstorms as early as Sunday.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1223 AM CDT Wed Jul 3 2024

A line of showers and thunderstorms will affect UIN/JEF/COU
through 10Z, but will decrease in intensity with mainly showers
and just isolated thunderstorms affecting STL/CPS/SUS between
10-15Z. Additional scattered and thunderstorms will develop over
Missouri and Illinois later in the day into the evening, but
coverage is not expected to be great enough to include in the TAFs
at this time. Have included a VCTS at STL after 06Z on Wednesday
night as the coverage of thunderstorms is expected to be greater
then. Any thunderstorms will be capable of reducing the ceilings
and visibilities to MVFR and possible IFR conditions in heavy
rain.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from 11 AM this morning to 8 PM CDT this evening
     for Iron MO-Madison MO-Reynolds MO.

IL...None.
&&

$$

WFO LSX