Osage Bluff, Missouri Weather Forecast Discussion

690
FXUS63 KLSX 131841
AFDLSX
Area Forecast Discussion
National Weather Service Saint Louis MO
141 PM CDT Sat Sep 13 2025
.KEY MESSAGES...
- The ongoing heat will continue through at least the middle of next
  week.
- There is a slight chance (15 - 25%) of showers and
  thunderstorms each afternoon from today through Wednesday.
&&
.SHORT TERM...  (Through Late Sunday Night)
Issued at 132 PM CDT Sat Sep 13 2025
Upper level ridging remains entrenched across the central CONUS,
and the warmest temperatures of the month have arrived beneath it.
Early afternoon temperatures are already pushing into the low to
mid 90s, and most locations are expected to tick 4-5 degrees
warmer this afternoon. This heat has also allowed 1000-1500 J/kg
of MLCAPE to build into the region, and with limited capping
across our south, isolated thunderstorms have developed in SE MO.
Given very limited forcing, I expect storms to remain isolated
through the afternoon, tapering off as instability wanes. These
storms are not expected to be particularly strong given meager
wind shear.
The upper ridge across the Mississippi Valley responsible for the
weekend heat will get squeezed a bit on Sunday as a trough digs
across the Northern Plains. This will result in subtle height falls
across our region, which coupled with 1000-2000 J/kg of MLCAPE (HREF
mean), will allow for slightly greater cloud and thunderstorm
coverage compared to today. Storms are not expected to be severe
given weak deep layer wind shear beneath the decaying ridge. The
greater cloud coverage may help temperatures stay a degree or two
below today, but we`ll still see highs in the mid to upper 90s, or
15-20 degrees above normal for this time of year.
BSH
&&
.LONG TERM...  (Monday through Next Saturday)
Issued at 132 PM CDT Sat Sep 13 2025
On Monday, the Northern Plains trough mentioned above will zip north
into south-central Canada, allowing the upper ridge to build back
and remain in place through Tuesday. Beneath this, a weak cold front
associated with the upper trough will push into the Mid Mississippi
Valley on Monday, and will knock a few degrees off of high
temperatures on Monday and Tuesday. MLCAPE will remain in that
1000- 2000 J/kg range, and with little to no capping, I expect to
see isolated to perhaps scattered storms on both afternoons. Weak
wind shear will again keep these storms below severe levels.
As we look toward the middle of the week, the vast majority for
forecast guidance is dropping a trough into the north-central CONUS,
finally breaking down the ridge. This will bring a gradual cooldown
to the Mid Mississippi Valley, though there is a good chance (around
75%) that high temperature will remain above 90 for much of area on
Wednesday. Temps will begin to fall in earnest on Thursday as
shortwaves associated with the above trough ripple around its
southern flank, pushing cooler air into the region. We can expect
another round of diurnal, isolated showers and storms on Wednesday,
before more widespread/higher rain chances arrive on Thursday.
Unfortunately it does not look like this rain will do much to help
with the developing drought. In fact LREF probabilities of at
least 0.25" of rain in any 24 hour period remain below 30%, and
probabilities of at least 0.5" throughout the forecast period
remain below 50%.
BSH
&&
.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1221 PM CDT Sat Sep 13 2025
VFR conditions will persist through tomorrow. The primary aviation
concern will be diurnal thunderstorm chances both this afternoon
and tomorrow afternoon. For this afternoon, I can`t rule out an
isolated thunderstorm, high res forecast guidance has been coming
in drier with subsequent runs this morning, so the odds of these
storms impacting a terminal are quite low. For tomorrow, we may
see slightly greater storm coverage, but given forecast
uncertainty and that it would be at the end of the TAF period,
I`ve left any mention out of the TAFs.
BSH
&&
.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