985
FXUS63 KLSX 151111
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
611 AM CDT Tue Jul 15 2025

.KEY MESSAGES...

- This week is expected to be seasonably warm with frequent
  chances for afternoon thunderstorms.

- Heat and humidity build this weekend.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 245 AM CDT Tue Jul 15 2025

We`re finally seeing some rumblings of change in the upper air
pattern. A deeper trough moving into the Northern Rockies is helping
to erode the western US ridge while also strengthening ridging over
the southeast US. The last gasps of the persistent, weak, elongated
trough over the south central US will be with us again today,
providing yet another opportunity for afternoon showers and
thunderstorms, mainly across the southeast half of the forecast
area. But this trough is perhaps a bit weaker than previously
expected, and overall convective coverage today may be similar to
what was seen yesterday. With little to no shear, we`re expecting
pulse type thunderstorms which produce locally heavy downpours in a
moisture rich environment. But lack of storm organization and
persistence should limit the severe or flash flooding threat. Storms
should decrease in coverage through the evening.

As the southeast US ridge becomes a bit more dominant it finally
kicks out the lingering trough for Wednesday. The more pronounced
trough over the Upper Midwest moves east and develops a more
organized frontal boundary to our northwest. The result for us is we
see temperatures rise a few degrees with a much lower chance of
those afternoon pop up thunderstorms. With highs rising into the 90s
area wide, we`ll see heat index values topping 100 degrees in many
locations during the heat of the day.

Kimble

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 245 AM CDT Tue Jul 15 2025

While the trough moves into the Great Lakes, a cold front will push
southward behind it. Thunderstorms are expected to develop along
this front late Wednesday into Wednesday night. While this activity
develops to our north and west, there`s an increasing chance some of
this moves into our northern forecast area Wednesday night. Wind
shear does increase a bit, to about 20KT over northern MO. This will
be enough to provide at least some potential for storms to organize
into a convective cluster with a potential for damaging winds as
highlighted in the Day2 SPC outlook. There`s also the potential for
heavy rain and localized flash flooding as precipitable water values
maximize near 2 inches once again. With a slow moving boundary in
play, there`s a better chance that storms may be persistent in some
areas, leading to swaths of higher rain totals.

The front stalls in our area Thursday leading to a temperature
gradient across the forecast area. While where that front sets up is
uncertain, north of the front temperatures only reach the low to mid
80s, while south of the front it`s another hot and humid day in the
90s. The front will likely serve as a focus for shower and
thunderstorm activity in the afternoon and evening. While shear
decreases on Thursday, likely minimizing the severe weather risk,
precipitable water remains high with a boundary in the area to focus
potentially multiple rounds of storms, so we`ll still have at least
some risk for flash flooding. The front remains near our area on
Friday so we may see somewhat of a repeat performance with showers
and thunderstorms.

Ridging expands westward late this week, and by this weekend it will
be centered over the south central US. This signals a shift toward
warmer temperatures near the core of the ridge. While current
forecasts are only a few degrees above normal, in the low to mid 90s
for highs, the combination of heat and humidity will lead to heat
index values considerably higher, well over 100 degrees Saturday,
Sunday, and Monday. Northern areas will be near the periphery of the
ridge and more likely to be impacted by passing shortwave troughs.
These may bring periods of showers and thunderstorms and hold back
temperatures a bit. However, confidence in building heat and
humidity is greater across the southern and central portion of the
forecast area. We may eventually need Heat Advisories during this
time period.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 611 AM CDT Tue Jul 15 2025

Patchy morning fog burns off more quickly this morning than
yesterday, giving way to VFR conditions. Scattered thunderstorms
develop this afternoon, with the St Louis terminals the most
likely to be impacted. Even here, though, the chances remain
somewhat low, but just high enough for a Prob30 mention.

Kimble

&&

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

$$

WFO LSX