Sullivan, Missouri Weather Forecast Discussion

757
FXUS63 KLSX 281913 CCA
AFDLSX
Area Forecast Discussion...CORRECTED
National Weather Service Saint Louis MO
213 PM CDT Sun Sep 28 2025
.KEY MESSAGES...
- Warm conditions will persist for the next week. The warmest
  days will be tomorrow and Tuesday, with highs in the mid to
  upper 80s. Fortunately, morning lows will remain cool.
- Rain chances remain nearly zero for the next week.
&&
.SHORT TERM... (Through Late Tuesday Night)
Issued at 138 PM CDT Sun Sep 28 2025
Very little has changed in the forecast for this iteration, both in
the short and long term. Warm and dry conditions can once again be
expected today, and will likely continue for the next week.
As expected, temperatures so far this afternoon are running about 1
to 4 degrees ahead of yesterday`s values at the same time, and we
are on pace to reach the mid 80s to near 90 degrees in the next 1 to
3 hours. The warmest readings are generally being observed east of
the Mississippi River, but overall temperatures are fairly uniform
and only vary by about 5 degrees total across the entire area.
Meanwhile, surface high pressure and subsidence aloft has settled
in, resulting in light winds and clear skies.
Once again, a combination of valley fog and steam fog were
observed in many local river valleys early this morning, as has
been the case for the last few days in a row. We have seen a very
slight decrease in the time window for this fog and coverage has
also shrunk slightly, but in spite of this, fog has remained
generally reliable in these areas. As afternoon temperatures reach
their peak values today through Tuesday, eventually we should see
a slow reduction in fog coverage each night just due to the
slight increase in overnight temperatures, but considering that
winds will remain light and skies clear for the next few nights,
it`s possible that this will just be a routine occurrence until
we can get some nocturnal cloud cover.
Very little change in the overall pattern can be expected tomorrow
and Tuesday, and as a result, each day will be reminiscent of the
last with afternoon temperatures in the mid to upper 80s and
overnight lows in the upper 50s to low 60s. Clear skies and light
winds are also expected to persist throughout this window.
BRC
&&
.LONG TERM... (Wednesday through Next Sunday)
Issued at 138 PM CDT Sun Sep 28 2025
The primary question in the long term forecast period to be "exactly
when will this stagnant pattern finally shake loose". In spite of
the best efforts from some tropical moisture from the Atlantic, this
likely won`t occur until near the end of the week or possibly
beyond.
The primary driver of this warm and dry pattern will be a large
upper level ridge, which will overlay an equally large area of
surface high pressure and dry air. These two features are both
expected to be remarkably persistent for the next week, perhaps only
being interrupted by an intrusion of mid/upper level moisture
emanating from Tropical Depression 9 currently across the Bahamas.
This has been alluded to in previous forecasts, and model
ensembles continue to predict that this system will not make
landfall, and only a very small portion of its moisture will be
advected in this direction. As such, we can expect to see an
increase in cloud cover around mid week and a very slight drop
(1-5 degrees) in temperatures, but its effect will be hardly
noticeable.
The next best hope for any meaningful weather changes will be for
a trough to finally break down this stubborn ridge, which is not
likely to occur until sometime next weekend or possibly even
farther. We do see a persistent signal for a trough inching
eastward and at least suppressing upper level heights during this
time period, but in spite of this, the overall pattern does not
appear to be particularly progressive and overall this trough has
slowed in recent runs. If this trend holds and we maintain mean
ridging across the central and eastern CONUS into the weekend, the
best chance for additional rain may come in the form of tropical
moisture moving into the area from the Gulf. While a reasonable
minority of ensemble members to hint at this sometime over the
weekend, it is far from a given, and as a result the official
forecast remains dry for the next week.
BRC
&&
.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1240 PM CDT Sun Sep 28 2025
Clear skies, light winds, and VFR conditions are expected for a
majority of the TAF period. Once again, patchy river valley fog
may impact JEF/SUS/CPS to varying degrees overnight and early
tomorrow morning, but should quickly dissipate within 1-2 hours
after sunrise.
BRC
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion