430
FXUS63 KLSX 041153
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
653 AM CDT Thu Jul 4 2024

.KEY MESSAGES...

- A complex of thunderstorms will bring heavy rainfall and flash
flooding before moving out of the area later this morning.

- Another round of thunderstorms is expected to move across Missouri
and Illinois late this afternoon and this evening.  The primary
threat will be damaging winds, with large hail, a brief tornado, and
additional heavy rainfall also possible.

- 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 has been issued for this afternoon and evening.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 431 AM CDT Thu Jul 4 2024

Latest regional radar is showing an east-west band of showers and
thunderstorms extending from south central Illinois through the St.
Louis metro area into west central Missouri.  This area is occurring
in a band of strong moisture convergence on the nose of a broad 30
knot LLJ.  The setup of the LLJ with promote training through 12-14Z
and PWATS and deep warm depths continue to be very favorable for
heavy rainfall which all favor the risk for flash flooding to
increase over the area the next few hours.  The MCS will move out of
the CWA from west to east from 13-16Z as the LLJ veers this morning.
The 00Z HREF LPMM values are still pointing to pockets of an
additional 3-5 inches of rainfall from this band before it moves out.

While there will still be the low potential for showers and
thunderstorms throughout the day, the best chance will be later this
afternoon and this evening with the approach of a upper trough and
attendant cold front.  Showers and thunderstorms may also develop
ahead along the remnant outflow boundary from this morning`s
convection over southeast and central Missouri where I have kept the
highest PoPs late this afternoon into the evening hours. The RAP is
showing MLCAPES exceeding 3000 J/kg with deep layer shear of 30-40
knots suggesting the potential for organized multicells/ possible
supercells with the primary threat being damaging winds, with large
hail and a brief tornado also possible given the presence of
boundaries.  There will still be high PWATS and deep warm cloud
depths, so the FFA will continue through 1 AM tonight.

Highs today should be mainly modified by this mornings convection,
though we should still see highs getting up into the lower 90s in
the far south with dewpoints recovering well into the 70s. I have
issued a Heat Advisory for this afternoon and early this evening
for Reynolds, Iron, and Madison counties where heat index values
should reach 105 degrees.

The HREF is showing the front moving through the area tonight with
the upper trough over the area tomorrow.  Any showers should be
moving out of the southeast counties in the early morning, otherwise
Friday should be dry with temperatures on Friday in the lower to mid
80s.


Britt

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 431 AM CDT Thu Jul 4 2024

Not much change in the thinking in the extended part of the forecast
as high pressure will move across Missouri and Illinois keeping most
of Friday night through Saturday night dry.  Then the next storm
system will move into the area early next week bringing the next
chance of showers and thunderstorms Sunday into Tuesday.
Temperatures will be at or just below normal.

Britt

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 642 AM CDT Thu Jul 4 2024

Showers and thunderstorms will continue to affect COU/JEF through
14Z and UIN/STL/SUS/CPS through 15Z with with MVFR/IFR
ceilings and visibilities in moderate-heavy rain at times. Then
the next chance will increase again after COU/JEF after 01Z and
at STL/SUS/CPS after 03Z. Once again, these storms will have will
have the potential to reduce ceilings and visibilities to MVFR or
IFR and as well as wind gusts over 35 knot and possible hail. MVFR
ceilings will be likely with winds from the northwest after this
round of storms.

Britt

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through late tonight for Boone MO-Callaway MO-Cole
     MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-Jefferson
     MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO-Reynolds
     MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO-
     Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

     Heat Advisory from noon today to 9 PM CDT this evening for Iron
     MO-Madison MO-Reynolds MO.

IL...Flood Watch through late tonight for Monroe IL-Randolph IL-Saint
     Clair IL-Washington IL.

&&

$$

WFO LSX