747
FXUS63 KLSX 150310
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1010 PM CDT Mon Jul 14 2025

.KEY MESSAGES...

- Showers and thunderstorms are expected again Tuesday afternoon.
  A few strong storms with gusty winds are possible. Some storms
  may also produce locally heavy rain and localized flooding.

- Temperatures are expected to remain within a few degrees of
  normal through the rest of the week with a chance for mainly
  afternoon thunderstorms.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 211 PM CDT Mon Jul 14 2025

Widely scattered showers and thunderstorms along and south of I-44
in Missouri into parts of southern Illinois will persist into
early evening before dissipating with the loss of daytime heating.
The RAP is showing around 1500-1700 J/Kg in these areas this
afternoon, but very little deep-layer shear, so severe storms are
unlikely. The storms aren`t moving very fast though, and will have
to be monitored for potential localized flooding through the
evening. Areas that receive rain this afternoon and evening will
be susceptible to fog development again late tonight, so another
Dense Fog Advisory may be needed, though confidence is not high
enough to issue at this time.

The upper trough which was stretching from the Upper Midwest into
the southeast Plains has moved east into the Ohio Valley today.  The
southern end of this trough has fractured into a vorticity chain
stretching from southwest Texas up into southwest Missouri and
sandwiched between ridges over the Southeastern and Southwestern
U.S.  The vort chain will drift northeast across Missouri and
Illinois through Tuesday as the two ridges slowly close ranks over
the lower Mississippi Valley. The general effect on sensible weather
on Tuesday will be more widespread afternoon and evening convection,
mostly along and south of the I-70 corridor.  Short range guidance
suggests there will be more instability with MLCAPE in excess of
2000 J/Kg, as well as more 0-6km shear up to around 25kts.  This
would be good enough for convection to get more organized into
marginally severe clusters and possibly some linear structures with
gusty winds up to around 60 mph, much like what happened Sunday
afternoon. The potential for locally heavy rain will continue as
P-wat values are forecast to be around 2 inches, and forecast
soundings show the warm cloud depth in excess of 14,000 ft. Storms
should diminish in strength and coverage during the evening with
the loss of diurnal heating.

Carney

&&

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 211 PM CDT Mon Jul 14 2025

The forecast for the long term remains virtually unchanged.  The
flow aloft becomes quasi-zonal across the Mid Mississippi Valley
Wednesday and remains that way at least through the end of the week.
The deterministic GFS and NAM show a compact short wave (most likely
enhanced by an MCV) moving across Minnesota and Iowa on Wednesday
which begins dragging a cold front into the Upper Midwest.  Another
wave moves across the Upper Midwest and southern Canada in the
Thursday-Friday time frame which attempts to push the front farther
south into central Missouri and southern Illinois.  The second short
wave looks fairly weak, so the extent of the effective front`s
southward progression may be controlled more by convection and
outflow boundaries than synoptic scale forcing. This puts a good
deal of uncertainty in frontal position for the end of the week. The
interquartile range if high temperatures in the LREF increases from
2-4 degrees on Tuesday and Wednesday to 5 to 9 degrees for Thursday
and Friday with the front draped (somewhere) across our forecast
area. The front will also be a focusing mechanism for afternoon and
evening convection, further increasing the uncertainty in the
afternoon temperature forecast.

Models have been consistently showing the Southeast U.S. ridge
building westward into the Mississippi Valley late Friday into
Saturday. This will bring a persistent south to southwesterly low
level flow back to Missouri and Illinois which will push the front
back into Iowa and northern Illinois for the weekend. The
interquartile range of temperatures remains fairly wide, most likely
due to differences in how strong the ridge becomes over the
Mississippi Valley. However, the overall range increases a few
degrees each day Saturday through Monday indicating a warming trend
during that period.

Carney

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1005 PM CDT Mon Jul 14 2025

VFR conditions are expected at the start of the period, but patchy
fog will be possible overnight through early tomorrow morning in
river valley locations. While we do not expect fog to be as
widespread or as dense as the previous night, some visibility
reductions will be possible, with best chances at fog-prone
terminals like SUS/JEF/CPS. Any fog that does develop tonight is
likely to dissipate quickly tomorrow morning.

While VFR conditions are expected through the rest of the morning,
another round of scattered showers and thunderstorms is likely
tomorrow, with best chances at St. Louis area terminals. While
this activity will be scattered and some terminals may not be
directly impacted, those terminals that do see a thunderstorm
overhead will likely observe bursts of heavy rain, lightning, and
occasionally gusty wind. Reduced visibility and ceiling categories
would also be likely in that scenario.

BRC

&&

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

$$

WFO LSX