858
FXUS63 KLSX 031918
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
218 PM CDT Sun Aug 3 2025

.KEY MESSAGES...

- Pleasant summer temperatures continue for the next few days, but
  summer heat returns later this week.

- The best chance of rain this week is Monday and Tuesday
  afternoon when scattered showers and storms are expected.


&&

.SHORT TERM... (Through Tuesday)
Issued at 217 PM CDT Sun Aug 3 2025

Cool high pressure remains in control of our weather at the
moment, but it is gradually retreating toward the Great Lakes and
we will soon lose our refreshing northeasterly breeze. Beginning
tonight, winds die off and we get one more very cool night for
summer standards, with widespread 50s expected. Dewpoints slightly
higher than yesterday and winds likely to be calm lead to a
greater chance of fog in the valleys so long as the sky remains
otherwise clear.

While ridging builds over the Southwest US over the next couple
of days, downstream troughing develops over the Mississippi
valley. This will slowly pull in a remnant wave currently over
Tennessee along with its accompanying moisture. As it moves toward
our area from the southeast it will bring increasing humidity,
instability, and pockets of lift to produce showers and
thunderstorms. This will be most widespread in the afternoon, but
the presence of the trough aloft will keep at least low chances
for a shower through the night as well. Some guidance has this
activity occurring as far west as the St Louis area, but the
greater chance remains on the eastern side of the trough in
Illinois. Weak shear means storms should be of the pulse variety
with little if any severe weather threat. Moisture, while higher
than we`ve had in recent days, remains modest by summer standards,
so precipitation rates will not be particularly excessive.
However, if some areas can see more persistent storms then locally
heavy rainfall could result. The lack of a clear forcing
mechanism to produce training storms limits any flash flooding
threat.

The broader trough remains overhead on Tuesday with the embedded
shortwave trough gradually lifting northward. As such, we`ll
continue to see the potential for afternoon thunderstorms on
Tuesday, but perhaps not as widespread as Monday.

Kimble

&&

.LONG TERM... (Wednesday through Next Sunday)
Issued at 217 PM CDT Sun Aug 3 2025

Ridging aloft becomes more dominant across our region beginning
Wednesday and through the end of the week, spreading more typical
summer temperatures back into the region. However, a larger scale
trough moving into the Pacific Northwest and out into the
Northern Plains will push the core of the ridge back to the
southwest, limiting the extent of the heat development further
east into our area. We`ll see a return of the 90s, but heat likely
peaks in the mid 90s.

Surface high pressure moves east and lee troughing develops over
the High Plains, allowing a broader southerly flow to develop
through the middle of the country. Each day of this southerly
flow will bring gradually increasing humidity from the Gulf to the
point where dewpoints in the low 70s become increasingly likely
by this weekend. This isn`t as extreme as our recent heat wave,
but it`s enough to potentially push the heat index up to 100 for a
few days. The increased humidity also leads to more instability
developing, but the lack of forcing in a primarily subsident
regime on the eastern side of the ridge will limit the chances of
daily thunderstorms through at least Friday.

The trough over the Northern Plains eventually wraps up into an
upper low over the Canadian prairies. Shortwave troughs rotating
around this low will eventually push back the broader scale
ridging and even bring a surface front toward our area. Guidance
varies considerably on these embedded waves and when the first one
might bring us some heat relief and a better chance of rain.
However, the chances that broader sale troughing takes over
increase through the weekend and into next week. So our total
duration of this period of hotter weather is limited.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1228 PM CDT Sun Aug 3 2025

Light northeast winds continue today with just some diurnal
cumulus around. Winds go light or calm tonight and there may be
some valley fog. The most likely terminal impacted is KSUS.
Conditions remain VFR Monday as well with continued light winds.

Kimble

&&

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

$$

WFO LSX