395
FXUS63 KLSX 152002
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
302 PM CDT Tue Jul 15 2025

.KEY MESSAGES...

- Warm and humid weather will continue this week with a chance for
  thunderstorms each day. A few strong to severe storms are
  possible Wednesday evening, though confidence in severe storms
  is low at this time.

- Temperatures are expected to get warmer this weekend into early
  next week.

&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 259 PM CDT Tue Jul 15 2025

Widely scattered showers and thunderstorms have developed again this
afternoon.  The convection has spread farther north this afternoon
in response to a chain of vorticity maxima which are drifting
northeast across Missouri and Illinois this afternoon.  SPC meso
analysis is showing a lithe more instability than yesterday with
MLCAPE in excess of 2500 J/Kg and the RAP is showing a little more
shear in the 20-25kt range across the eastern Ozarks.  Have already
seen some downburst signatures on RADAR this afternoon, and with the
greater shear across southeast Missouri into southern Illinois,
would not be surprised if convection can get semi-organized into a
marginally severe cluster or two in those locations.  Farther to the
northwest, expect isolated-widely scattered "airmass" thunderstorms
to continue for the rest of the afternoon with occasional downburst
winds likely not exceeding 40-50 mph even in the strongest storms.
Convection should diminish through the evening with loss of daytime
heating.

Short range guidance is showing some weak to moderate low level
moisture convergence developing during the pre-dawn hours of
Wednesday morning.  The RAP, GFS, NAM, and a few CAMs develop weak
convection in response to this moisture convergence.  This is a
telltale sign of early morning elevated convection, so have added in
a slight chance for showers Wednesday morning.  A short wave will
move across the Upper Midwest Wednesday which will help convection
develop along a cold front which will push through Iowa into
northern Missouri Wednesday night.  There are significant timing
differences with when convection will move into northeast Missouri
and west central Illinois Wednesday night, with some models hinting
at a line of thunderstorms entering in the evening, and others
holding off until after 06Z.  If the front and attendant
thunderstorms move into the area earlier in the evening, then there
will be a higher chance for severe wind gusts due to greater
available instability.  However the slower solutions would give
storms much lower instability to work with in addition to a
nocturnal inversion which would tend to block severe wind gusts from
mixing down to the surface.  Unfortunately I don`t see any reason to
prefer one solution over the other at this time, so confidence in
the thunderstorm/severe forecast is low.


Carney

&&

.LONG TERM...  (Thursday through Next Tuesday)
Issued at 259 PM CDT Tue Jul 15 2025

The forecast for Thursday through Sunday remains on track.  Global
deterministic guidance is in pretty good agreement with the position
of the cold front on Thursday morning, extending from central
Illinois southwest into central Missouri.  Models show the front
continuing to the southeast, although this appears to be more driven
by convection rather than synoptic scale forcing as 850mb flow
remains from the west-southwest or southwest.  The LREF mean tracks
pretty well with the deterministic guidance, which lends confidence
to the more southward progression of the front along with cooler
temperatures for Thursday and Friday and higher PoPs.

The front spends Saturday moving north into Iowa in response to low
pressure developing over the Great Plains, but another round of
convection develops along it on Saturday night.  The convection
pushes the effective front back to the south Saturday night, but
there`s some disagreement in how far south it will get, which makes
Sunday`s temperatures and precip chances fairly uncertain.  Current
thinking is that the front won`t make it very far into the forecast
area, if at all, so low chance PoPs and warmer temperatures look
reasonable at this time.  Temperatures continue to warm early next
week as the upper level ridge over the southeastern U.S. builds
westward into the Mid Mississippi Valley.  If the current forecast
pans out, we could be issuing Heat Advisories in the Monday/Tuesday
timeframe.


Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1236 PM CDT Tue Jul 15 2025

Widely scattered showers and thunderstorms are expected to
continue this afternoon. The convection will be capable of
reducing the visibility to 2SM or less in locally heavy rain. Some
gusty winds to 40kts and higher are also possible in downbursts.
Storms should diminish after sunset this evening. There is another
chance for showers Wednesday morning, mainly along and west of the
Mississippi River. If these showers occur, they should be fairly
light, with high bases. Visibility impacts at the surface are
unlikely, tho there`s a small chance of MVFR visibilities if the
showers are stronger than anticipated. Otherwise, VFR flight
conditions are expected to prevail across most of the area, with a
small area of MVFR ceilings persisting across parts of the eastern
Ozarks at least into the early evening.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX