998
FXUS63 KLSX 142254
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
554 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 00z TAFs through 00z Tuesday Evening)
Issued at 547 PM CDT Mon Jul 14 2025

The primary concerns during the 00Z TAF period will once again be
the potential for fog overnight and early tomorrow morning,
followed by afternoon showers and thunderstorms. Regarding the
former, fog and low clouds do not appear likely to be as
widespread as they were last night, but patchy radiation fog will
remain possible in river valleys. This will be most likely at
fog-prone terminals like SUS/JEF/CPS, but confidence is low that
prolonged dense fog will recur.

Fog should diminish early tomorrow morning, with VFR conditions
likely until another round of scattered showers and thunderstorms
develops in the afternoon. This is most likely at St. Louis area
terminals, but because storms will be scattered and slow moving,
it`s possible that not all terminals will be directly impacted. If
a storm does move overhead, heavy rain and lightning can be
expected, with visibility and ceiling reductions as well. Some
erratic gusty winds will also be possible with the stronger cells.

&&

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

$$

WFO LSX