Gamma, Missouri Weather Forecast Discussion

097
FXUS63 KLSX 110944
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
444 AM CDT Thu Sep 11 2025
.KEY MESSAGES...
- A period of summer-like temperatures will extend into the mid-
  next week.
- Mainly dry conditions are expected into mid-next week, but
  isolated afternoon showers and thunderstorms are possible (20
  percent chance) Sunday onward.
&&
.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 315 AM CDT Thu Sep 11 2025
An upper-level ridge will begin to build into the Mid-Mississippi
River Valley late today into Friday as the flow pattern across the
CONUS as a whole becomes configured into a pseudo-Omega Block
pattern. Low-level flow will be weak today with continued warming
mainly from greater insolation, including high temperatures in the
upper 80s and low-90s F. However, weak low-level southwesterly
flow/WAA will become established by Friday with 850-hPa temperatures
warming above the 90th climatological percentile with high
temperatures in the low to mid-90s F.
Pfahler
&&
.LONG TERM...  (Friday Night through Wednesday)
Issued at 315 AM CDT Thu Sep 11 2025
The upper-level ridge will remain over the Mid-Mississippi River
Valley into early next week thanks to the blocking pattern,
contributing to the extended period of summer-like temperatures.
Model guidance is in agreement that Saturday will be the hottest day
for most of the CWA with 850-hPa temperatures peaking around the
99th climatological percentile. Diurnal cumulus and varying upper-
level clouds will be present through Saturday, however, which limits
confidence in whether or not high temperatures will reach the upper
90s and threaten daily records. There are indications that there
will be enough upper-level moisture for a decent amount of upper-
level clouds on Sunday, which could limit high temperatures from
being as hot as Saturday in most areas. Fortunately, the antecedent
dry conditions/drought and lack of direct access to Gulf of Mexico
moisture will keep dewpoints from supporting heat index values much
above air temperatures.
After Sunday, global model guidance is coming into better agreement
on the evolution of the upper-level flow pattern with only around 24
percent of total ensemble membership depicting an upper-level trough
in the Great Lakes that forces a backdoor cold front into the
region. Instead, the growing consensus is that temperatures will
very gradually cool next week as the upper-level ridge looses
amplitude and 850-hPa temperatures cool, translating to high
temperatures in the 90s becoming less common and 80s becoming more
common. Daytime instability and little convective inhibition also
poses a threat of mainly diurnal showers and thunderstorms,
especially Sunday onward as moisture peaks and weakening of the
ridge ensues. During that time, 6-hour ensemble model probabilities
of measurable rainfall are around 15 to 30 percent, highest in the
18 to 00z timeframes. Shower and thunderstorm coverage is hard to
decipher at this point with nebulous forcing suggesting isolated to
perhaps scattered coverage at most. The bottom line is that
widespread beneficial rainfall is not expected.
Pfahler
&&
.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 444 AM CDT Thu Sep 11 2025
Aside from a potential brief period of river valley fog at KSUS
around sunrise, dry and VFR flight conditions are expected at all
terminals through Friday morning. Winds will remain light but will
become more prevalently easterly to southeasterly tonight.
Pfahler
&&
.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