Clarence, Missouri Weather Forecast Discussion

346
FXUS63 KLSX 121645
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1145 AM CDT Fri Sep 12 2025
.KEY MESSAGES...
- Seasonally hot temperatures will continue through at least the middle
  of next week. The hottest temperatures are expected this
  weekend.
- There is a slight chance (10 - 20%) of showers and thunderstorms each
  day from Sunday through Wednesday.
&&
.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 337 AM CDT Fri Sep 12 2025
Continued mid-level ridging, plenty of sun, and warm air advection
along low-level southwest winds will boost temperatures into the low
to mid-90s this afternoon. Tomorrow, the ridge will be almost
directly overhead and 850 mb temperatures will climb into the low
20s C, translating to mid-90s at the surface. Thankfully, the lack
of high humidity will keep heat index values within a couple of
degrees of the actual temperature, making triple digit heat index
values an uncommon occurrence across the area.
Jaja
&&
.LONG TERM...  (Saturday Night through Thursday)
Issued at 337 AM CDT Fri Sep 12 2025
On Sunday the mid-level ridge axis will be directly overhead with
troughing over the central and northern Plains. The temperature
forecast will be on par with Saturday, though there will be a slight
gradient increasing from west to east due to incoming high clouds.
The continued influence of the ridge will keep temperatures in the
90s through at least the middle of next week. This is corroborated
by a tight NBM interquartile temperature spread of 2 - 3 degrees
each day.
There is a slight chance (10 - 20%) of diurnally driven isolated
showers and thunderstorms from Sunday through Wednesday as
instability increases. The mid-levels won`t see the same degree of
warming as the low-levels. This removes capping as a hindrance
for convection, but a lack of significant forcing will keep
coverage low.
A pattern change is in store late in the week as mid-level ridging
breaks down ahead of an incoming shortwave. Ensemble and
deterministic guidance agree in the existence of this feature, but
details vary which directly impacts how long the heat will last. The
NBM interquartile range expresses confidence in Thursday being
another hot day, with a spread of 4 degrees at KSTL and 5 degrees at
KIRK, slightly closer to the influence of the shortwave. This is
consistent with most members in the WPC cluster analysis favoring a
less amplified shortwave and suggests that a return to seasonally
average temperatures (77-80) may come more gradually than most of us
would prefer.
Jaja
&&
.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1143 AM CDT Fri Sep 12 2025
VFR flight conditions will continue through the period under
largely dry conditions. Isolated afternoon showers and perhaps
even a thunderstorm are expected Saturday afternoon area wide,
though confidence in where these pop up is far too low to include
a mention in the TAFs at this time (15% chance). Winds will shift
from southeasterly to southwesterly by tomorrow morning.
Delia
&&
.CLIMATE...
Issued at 218 PM CDT Wed Sep 10 2025
Record daily highs Friday 9/12 through Monday 9/15:
9/12 | 9/13 | 9/14 | 9/15
STL   98    100    101    101
COU  100     99    104    101
UIN   99    100     99    100
Delia
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion