Sparta, Illinois Weather Forecast Discussion

221
FXUS63 KLSX 162252
AFDLSX
Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
552 PM CDT Tue Sep 16 2025
.KEY MESSAGES...
- Hot weather is expected through Thursday with some relief expected
  beginning Friday.
- There are multiple chances of thunderstorms starting on Thursday
  afternoon through early next week. The best chances (30-60%)
  across much of the area are Thursday night through Friday.
&&
.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 219 PM CDT Tue Sep 16 2025
The 1900 UTC surface analysis shows predominantly light northeast
winds, helping to usher in drier and more stable air into the
mid-Mississippi Valley. Isolated to widely scattered convection
is expected to develop once again this afternoon, but this time
some 50-100 miles further to the west given the advection of
drier, more stable air into the region. Kept any mentionable PoPs
out of the forecast for central/northeast Missouri, but cannot
completely rule out a brief isolated shower or weak thunderstorm
late this afternoon/early this evening. The better
chances/coverage are definitely west (and well south) of the area
however over the next 6-9 hours.
A mostly clear sky with light winds are forecast tonight. Lows
should be able to drop back into the upper 50s to mid 60s, or a
couple of degrees cooler than last night. This change is mainly due
to the drier air mass in place tonight compared to last night.
Favored river valleys may even see a few spotty mid 50s.
Persistence looks like a very good forecast for tomorrow with
little/no change in the ambient air mass. Dry weather is once again
forecast areawide, though a few isolated showers/thunderstorms could
threaten to move into far western sections of the forecast area late
Wednesday afternoon. Better chances however are in western Missouri
so left the forecast dry. High temperatures should reach into the
low 90s areawide, which would be some 10-12 degrees above normal for
the date.
Gosselin
&&
.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 219 PM CDT Tue Sep 16 2025
The persistent mid/upper level ridge across the area will begin to
break down on Thursday as a closed mid/upper level low develops over
the Dakotas. A lobe of vorticity is expected to rotate cyclonically
around this low Thursday afternoon/evening. Forcing for ascent ahead
of this feature along with weakening convective inhibition should
allow for the return of showers and thunderstorms to parts of
central/northeast Missouri Thursday afternoon. This activity should
spread eastward overnight toward the Mississippi River as moisture
convergence increases on the nose of a 20-25 knot low-level jet.
There probably will be some type of lull in activity Friday morning
before another vorticity maxima moves through during the afternoon.
Convective coverage should tend to maximize along/near a weak cold
front where surface convergence is strongest. This subtle boundary
should move through much of the CWA Friday night before washing out.
All in all, this is still when the best chances of measurable
rainfall are across the area. Highest chances are in
central/northeast Missouri Thursday night (50-60%), with chances
lowering gradually with eastward extent.
Ensemble guidance generally shows quasi-zonal flow aloft to end the
weekend into early next week, with some type of midlevel troughing
remaining near the US-Canadian border. Another cold front (or two)
should move toward our region in this time frame, providing
additional chances for showers and thunderstorms. Uncertainty with
any specifics however is low with respect to timing/area with where
the best chances of showers/storms will be.
Temperature wise, there remains high confidence in continued mild
overnight lows. For high temperatures, readings will cool back
mostly into the 80s. The confidence is lower on Friday compared to
the weekend due to the potential for more widespread showers/storms
to limit heating. The spread between the 25th/75th percentile from
the NBM is in the 6-8 degree range for most locations. Thereafter,
even the 25th percentile from the NBM has highs at or above normal.
While "cooler" temperatures are expected through early next week,
they should remain warmer than normal and nothing like the cool
weather observed early this month (or even during parts of August).
Gosselin
&&
.AVIATION...  (For the 00z TAFs through 00z Wednesday Evening)
Issued at 547 PM CDT Tue Sep 16 2025
Dry and VFR flight conditions are expected at a majority of the
local terminals through the TAF period. Similar to last night,
confidence is high in another round of fog at KJEF late tonight
and early tomorrow morning. Any fog that develops is expected to
dissipate with the rising sun tomorrow morning.
Elmore
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion