Gumbo, Missouri Weather Forecast Discussion

930
FXUS63 KLSX 181048
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
548 AM CDT Thu Sep 18 2025
.KEY MESSAGES...
- Temperatures will not be as hot starting on Friday, but will still
  be several degrees above normal into next week.
- There are multiple chances of thunderstorms starting this
  afternoon through early next week. The best chance (40-70%) will
  be tonight and again Sunday and Sunday night.
&&
.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 406 AM CDT Thu Sep 18 2025
Latest water vapor imagery over the Midwest is showing that the
prevalent upper ridge has shifted slightly east into the eastern
Great Lakes into the southern Plains early this morning.  Except for
a few isolated showers and thunderstorms, Missouri and Illinois is
mainly dry, but this will change as the ridge continues to move of
the east and the trough begins to slowly approach the area from the
Plains which will help break the capping over the western part of
the CWA by midday.  The RAP/NAM are showing MLCAPES in the 1000-2000
J/kg range this afternoon into the early evening over central and
northeast Missouri into west central Illinois with an outflow
boundary moving out of western Missouri and across the CWA. While
weak low level forcing will be enough to kick off some scattered
showers and thunderstorms earlier in the day, it still looks like
the best chance (40-60%) will be associated with the boundary during
the late afternoon and evening.  While overall low and deep level
shear will be relatively weak for organized severe weather, forecast
soundings are showing mixing into the 800-750mb layer this afternoon
so I couldn`t rule out one or two wind gusts over 50 mph with these
storms over central Missouri.
The trend for a slower progression with the Plains trough moving into
the area is still holding, so the initial surge of the showers and
thunderstorms shouldn`t make it much past eastern Missouri and west
central Illinois tonight.  This matches the latest CAMS which keeps
most of southwest Illinois and southeast Missouri dry through
tonight.
With another day of deep mixing, expect highs to reach into the low
to mid 90s across all but central and northeast Missouri.  Lows
tonight will be in the lower to mid 60s.
Britt
&&
.LONG TERM...  (Friday Night through Wednesday)
Issued at 406 AM CDT Thu Sep 18 2025
The NAM/GFS/ECMWF are in relatively good agreement with a pair of
troughs moving across the area Friday and again Saturday. This will
keep a chance (30-60%) of showers and thunderstorms going into the
weekend, however there will be plenty of dry time and not everyone
will see rain during this timeframe.  The chance will increase
Sunday into Monday as the LREF is showing the next upper trough
moving across the area with 40-70% of its members producing rain
over the area. Thereafter, there is increasing spread in the
individual models with the cluster analysis showing either a closed
low over the the central CONUS versus a large ridge by the middle of
next week. While both the NBM and LREF showing PoPS through this
timeframe, they gradually lower them to reflect the components with
drier solutions.   The greatest rainfall amounts still look to stay
across central and northeast Missouri where the LREF has a chance of
seeing >1" of rainfall around 60% through Tuesday.
Temperatures will fall back into the 80s starting on Friday and
Saturday, with locations staying in the 70s starting on Sunday. Lows
will mainly be in the 50s and 60s.
Britt
&&
.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 535 AM CDT Thu Sep 18 2025
The chances for showers and thunderstorms will increase later this
afternoon and tonight with the best timing at COU/JEF between
23-04Z and at UIN between 03-09Z tonight. While there is a low
chance for showers and thunderstorms at the St. Louis area
terminals, confidence is too low to include in those TAFs at this
time. Any of the heavier showers or thunderstorms will be capable
of producing MVFR or IFR ceilings and visibilities in heavy
downpours.
Britt
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion