883
FXUS63 KLSX 150747
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
247 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 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