065
FXUS63 KLSX 241620
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1120 AM CDT Mon Jun 24 2024

.KEY MESSAGES...

- Heat Advisory looks on track for central Missouri today. Heat will
  expand across much of the area along and south of I-70 for
  Tuesday so the Heat Advisory in central Missouri has been
  extended, and expanded east.

- A cold front is expected to move through late Tuesday night. Widespread
  showers and thunderstorms are expected ahead of the front
  Tuesday night. Current indications are that some parts of the
  are could get an inch or more of rain. Additionally, some of the
  storms could be severe with damaging winds and large hail.


&&

.SHORT TERM... (Through Tuesday Night)
Issued at 353 AM CDT Mon Jun 24 2024

High pressure centered over the Midwest this morning will drift
eastward causing the wind to swing around to the south today.  This
will bring warmer and more humid air back into the area, particularly
into parts of central Missouri.  High temperatures across the area
should be between 2 and 7 degrees warmer than yesterday, with a
corresponding increase in dew point.  This pushes heat index values
in central Missouri up to right around 105, so the Heat Advisory
continues to look on track for today.  There could be one fly in the
ointment though.  Widely scattered convection has developed over
Iowa and is pushing into north central Missouri.  While most
guidance shows this convection dissipating before it reaches our
area, there are some CAMs that show weak showers persisting past 17Z
across parts of central and northeast Missouri.  If this happens,
the clouds and precip would likely suppress temperatures enough to
spoil the advisory. However, the low level jet that`s forcing this
convection weakens and backs slightly this morning according to the
RAP and GFS, so I don`t think that scenario is very likely.

Attention turns to Tuesday as persistent southwest flow continues
the warm/moist advection into Missouri and Illinois.  Some guidance
numbers have come in a little cooler than previous runs, but
widespread mid to upper 90s continues to look likely, and St. Louis
may still hit 100.  Afternoon heat index values rise rise into the
105+ range generally along and south of I-70, so we`ve extended the
central Missouri heat advisory, and expanded it eastward through
east central and southeast Missouri into southwest Illinois.  There
continues to be a chance for afternoon showers and thunderstorms,
which could suppress temperatures, however low level forcing to
trigger convection looks weak to non-existent so the chance for
storms looks very low at this time.

That will not be the case on Tuesday night as a cold front drops
south from Iowa across Missouri and Illinois.  The CAMs that go out
that far show a complex of thunderstorms developing along the front,
and then moving south into Missouri and Illinois as a linear MCS.
Both the GFS and RAP shows some pretty beefy CAPE values in excess of
4000 J/Kg across northern Missouri and Iowa.  The GFS loses a lot of
that instability between 03-06Z Wednesday, but the RAP hangs on to
3500+ J/Kg through 6Z when the run ends.  Luckily the deep-layer
shear isn`t that strong across our area at only 15-20kts.  However
with that amount of instability the storms could certainly be
capable of producing damaging wind gusts and large hail, most likely
across northern portions of the forecast area during the late
evening, possibly extending past 06Z and farther south.  The other
big story with these storms is the potential for substantial
rainfall.  Latest WPC QPF shows most of the area getting between
0.50 and 1.10 inches of rain which is more than most of the area has
seen in several weeks.

Carney

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 353 AM CDT Mon Jun 24 2024

The remainder of the forecast looks relatively quiet.  The short
wave which is driving the front is forecast to move relatively
slowly into the Mid-Mississippi Valley, which will cause the front
to move slowly as well. This changes late Tuesday night as another
wave which will be moving across the Upper Midwest phases up with
southern wave.  This amplifies the pattern and finally gives the
front a shove south Wednesday morning.  This will bring cooler
temperatures in the mid to upper 80s to the area for Wednesday and
Thursday.  There will probably be some lingering showers and storms
on Wednesday in the vicinity of the front, primarily across southern
Missouri as the the two waves come into phase.  Thursday looks dry
as high pressure moves across the Midwest into the Great Lakes
region.  Heat and humidity return Friday as the high moves farther
east and low level flow swings back to the south, although current
indications are that it won`t be as hot as this recent stretch. LREF
mean temperatures are in the low 90s Friday and Saturday, and even
the 75th percentile doesn`t break the mid 90s either day.  Medium
range deterministic guidance is advertising another FROPA Saturday
night/Sunday morning, and the LREF seems to agree with temperatures
falling back into the low to mid 80s Sunday afternoon.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1116 AM CDT Mon Jun 24 2024

VFR flight conditions will prevail through the remainder of the
TAF period under southerly winds that will gradually become
westerly by the end of the TAF period.

There is a 20-40% chance for showers and thunderstorms early
Tuesday morning through the remainder of the period. The best
chances are across northeast Missouri and west-central Illinois
early Tuesday morning through the afternoon hours as an existing
complex of thunderstorms could move southeast into the area.
Confidence is low in the complex holding together and pushing into
the forecast area, so have left mention of this out of the KUIN
TAF for now.

Additional shower and thunderstorm development is possible Tuesday
afternoon associated with daytime heating. The development of
these thunderstorms remains uncertain, as do their locations, so
have also left a mention of this out of the TAFs for now.

MRM

&&

.CLIMATE...
Issued at 353 AM CDT Mon Jun 24 2024

With hot temperatures forecast, here are some of the daily high
temperature records:

            MON JUN 24     TUE JUN 25
ST LOUIS    102 in 1988    102 in 1954
COLUMBIA    103 in 1988    102 in 1988
QUINCY       99 in 1988    102 in 1931


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory from noon to 8 PM CDT Tuesday for Audrain MO-
     Callaway MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Jefferson MO-Lincoln MO-Madison 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 until 8 PM CDT Tuesday for Boone MO-Cole MO-
     Moniteau MO.

IL...Heat Advisory from noon to 8 PM CDT Tuesday for Bond IL-Clinton
     IL-Madison IL-Monroe IL-Randolph IL-Saint Clair IL-
     Washington IL.

&&

$$

WFO LSX