Monkey Run, Missouri Weather Forecast Discussion

398
FXUS63 KLSX 221731
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1231 PM CDT Mon Sep 22 2025
.KEY MESSAGES...
- Southeastern Missouri and southwestern Illinois will be the
  focus for rounds of showers and thunderstorms through the day
  today. Strong thunderstorms are not anticipated, but frequent
  lightning and heavy rainfall are still threats.
- Another round of widespread rainfall is forecast from the
  latter half of Tuesday through Wednesday.
&&
.SHORT TERM... (Through Wednesday Night)
Issued at 245 AM CDT Mon Sep 22 2025
The area of rain with embedded convective elements that is ongoing
across southeastern Missouri and southwestern Illinois this morning
is being aided by subtle disturbances rounding the base of an upper-
level trough and lift from the low-level jet. As the main
disturbance moves eastward and the jet veers, this rain will exit
the CWA eastward through the morning hours. There is a low chance
(30-40%) that isolated to scattered convection will linger through
the daylight hours across far southeastern Missouri and southwestern
Illinois thanks to continuous weak warm air advection and subtle
disturbances moving through the flow aloft. Also in this part of the
CWA, more continuous cloud cover will aid in keeping temperatures
cooler this afternoon (mid to upper 70s) compared to elsewhere in
the CWA (around 80 degrees).
The chance for rain will increase yet again through the day on
Tuesday as a shortwave moves into the Central Plains and lift
increases over the Middle Mississippi Valley. A low-level jet will
ramp up and nose into the CWA through the day, supporting widespread
rainfall expanding across the CWA through the afternoon and evening.
The shortwave will induce surface cyclogenesis over the Southern
Plains, with the low tracking east-northeastward through the Mid
South or Middle Mississippi Valley through Wednesday. The track of
this low will dictate where the best chances for another round of
soaking rain will peak. Despite the fluctuations in guidance,
ensemble-based probabilities for higher thresholds of rainfall have
remained focused generally across far southeastern Missouri and
southern Illinois. For areas south of I-70, as much as an inch of
additional rain may fall (40-50% chance), while areas north of I-70
could see up to around 0.5" (40-50% chance).
Elmore
&&
.LONG TERM... (Thursday through Sunday)
Issued at 245 AM CDT Mon Sep 22 2025
The evolution of the upper-level pattern from the middle of the week
through the weekend continues to fluctuate notably among guidance
sources and initializations. The recent trend has been for a slower
cutoff/fracturing of Wednesday`s trough/shortwave over the Midwest
into the weekend. Despite this trend, the impact on our sensible
weather from previous forecasts will be mostly negligible.
As the core of the trough pulls eastward through Thursday, the
surface low will depart the area, with deep northerly flow setting
up over the Middle Mississippi Valley as a portion of the trough
cuts off somewhere over the center of the CONUS. This flow will
support our temperatures running around seasonal normals through
Thursday night, and moisture wrapping around the backside of the low
will keep a low chance (20-40%) of rain going through then. A
majority of guidance keeps this cutoff meandering over the eastern
half of the CONUS through Friday, with guidance then diverging
significantly in the phasing of the upper-level pattern. Even with
the spread in solutions, a majority of global ensemble members
support calm weather into the weekend with temperatures warming to
just above average.
Elmore
&&
.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1228 PM CDT Mon Sep 22 2025
Stratus/stratocumulus should rise and scatter out a bit by late
afternoon, with VFR conditions then forecast through the late
evening/early overnight hours. Primary concern late tonight into
Tuesday morning is on fog development. Fog should be most
prevalent in south-central Illinois and east central/southeast
Missouri river valleys. IFR visibilities are expected, with the
lowest most likely at KSUS. Visibilities should gradually improve
Tuesday morning as mid/upper level clouds increase ahead of the
next disturbance. Chances of showers/thunderstorms should hold off
until later Tuesday.
Gosselin
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion