115
FXUS63 KLSX 141912
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
212 PM CDT Mon Jul 14 2025

.KEY MESSAGES...

- Seasonably warm temperatures are expected this week, with
  occasional 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 18z TAFs through 18z Tuesday Afternoon)
Issued at 1231 PM CDT Mon Jul 14 2025

Remaining MVFR ceilings along and east of the Mississippi River
should continue to rise to VFR over the next hour or two. VFR
flight conditions are expected to prevail for the remainder of the
afternoon and evening. Isolated to widely scattered showers and
thunderstorms are expected this afternoon into early evening,
primarily across the eastern Ozarks and southwest Illinois. A few
storms may stray as far north as the I-70 corridor this afternoon.
The strongest convection will be capable of reducing the
visibility to 2SM and below in heavy downpours. Convection will
diminish through the evening. Fog will likely develop after 06Z in
locations that receive rain this afternoon and evening.
Additionally, MVFR and possibly IFR ceilings are expected to
redevelop across parts of southeast and east central Missouri into
southwest and south central Illinois before sunrise Tuesday.
Ceilings/visibilities will improve through the morning after
sunrise.

Carney

&&

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

$$

WFO LSX