625
FXUS63 KLSX 021927
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
227 PM CDT Sat Aug 2 2025

.KEY MESSAGES...

- Mild weather and exceptionally pleasant humidity continue this
  weekend into early next week before a gradual warm up begins.
  Summer heat returns by the end of the week.

&&

.SHORT TERM... (Through Sunday)
Issued at 225 PM CDT Sat Aug 2 2025

Surface high pressure continues to sit over Wisconsin this
afternoon, driving a dry and cool northwest flow into our region.
The northwest flow which drove this high into position is
gradually weakening, and as such the surface high will weaken and
broaden in place through Sunday. Winds tomorrow will be lighter as
a result, allowing for the early August sun to more effectively
warm us up with local evapotranspiration gradually increasing the
humidity, though it will remain at noticeably pleasant levels. The
primary source of uncertainty in the near term is whether morning
fog can develop in the valleys. Mid afternoon dewpoints in the low
50s suggest we`ll have to get quite cool for that to happen
tonight, so for now the forecast leans against it.

Kimble

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 225 PM CDT Sat Aug 2 2025

Ridging building over the Southwest US gradually expands eastward
with time, so eventually we`ll see a warm up. But a trough
currently over the southeast US will gradually retrograde westward
over the next several days, helping to delay the onset of the
higher temperatures. A related inverted trough at the surface
also pushes westward and brings a little better humidity. This
feature represents our best chance of precipitation this week,
mainly Monday into Tuesday. At the moment, NBM continues to be
quite pessimistic with its PoP forecast only peaking around 25
percent in the southeastern forecast area. However, long range
ensemble guidance is more optimistic about the rain chances. 70
percent or more of ensemble members produce measurable rain over
the southeastern forecast area in the 24 hour period ending
Tuesday afternoon. Even at lower time thresholds (6 hour period)
these chances are over 50 percent Tuesday afternoon. This suggests
other factors beyond just timing uncertainty are keeping NBM PoP
lower. At this point confidence is fairly high that there will be
showers and thunderstorms around Tuesday afternoon, the
uncertainty is more on coverage and location.

The weak trough gradually weakens and moves away by Wednesday,
with the ridge taking greater hold of our weather later in the
week. This will lead to warmer temperatures, back into the 90s,
though a lack of a strong or persistent flow from the Gulf will
keep humidity from getting as oppressive as it was in late July.

The ridge won`t be as long lasting as we saw in late July either.
There`s pretty good agreement that a trough via the Pacific
Northwest will eventually push back this ridge and keep it from
developing into something much hotter. There is some uncertainty
on when that will happen, though, and to what extent. This is
reflected in an increasing interquartile range in NBM high
temperature forecasts next weekend. If the ridge stays dominant
for longer, we could see those temperatures approaching the mid
90s for highs, with heat index values back over 100.

Kimble

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1251 PM CDT Sat Aug 2 2025

VFR conditions continue with a light northeast wind. Winds may go
calm tonight which could result in some localized fog or smoke in
valley locations, but otherwise VFR continues into Sunday.

Kimble

&&

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

$$

WFO LSX