892
FXUS63 KLSX 230003
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
703 PM CDT Wed Jul 22 2026

.KEY MESSAGES...

- Cooler temperatures will continue through Friday before
heat/humidity returns by late this weekend.

- Widespread rain showers along with a few thunderstorms are
forecast across central and southeast Missouri Friday - Friday night.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 218 PM CDT Wed Jul 22 2026

Seasonably strong (~1020 hPa; >90th percentile) surface high
pressure across the Upper Midwest will remain in control of our
sensible weather over the next 24-36 hours. Dry weather along
with cooler than normal temperatures and low humidity is
expected to continue through Thursday. Lows tonight are forecast
to drop down into the low to mid 60s, or roughly 6-8 degrees
below normal for the date and the coolest night for most
locations in a month. Mid/high level clouds are forecast to
increase from the west/northwest on Thursday. These clouds
should help keep temperatures in check, with highs only in the
upper 70s to low 80s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 218 PM CDT Wed Jul 22 2026

(Thursday Night - Saturday)

As the surface high slides more into the eastern Great Lakes/Upper
Ohio Valley, our low-level winds will turn more out of the south. By
late Thursday night, scattered to widespread shower activity is
expected to move into central Missouri ahead of an approaching
midlevel shortwave trough. This activity will try and move
east/southeast during the day, but the combination of little/no
instability downstream and a slight weakening of the low-level jet
suggests any rain that continues on Friday may tend to stay on the
light side. Thicker cloud cover should limit daytime highs on
Friday, though exactly how much is not certain. Some deterministic
model guidance that has more widespread/heavier rain only has highs
in some areas near 70 degrees. Given the lack of even elevated
instability and modest low-level jet, it is hard to envision really
widespread rainfall on Friday limiting temperatures that much.
Therefore, the expectation is for most areas to top out in the mid
70s to near 80 degrees.

The coverage of rain showers, along with some thunderstorms, should
increase Friday night as the low-level jet strengthens. Showers and
thunderstorms should tend to focus across southeast Missouri, though
the exact location is not certain due to timing/track differences of
a midlevel shortwave trough. Given increasing instability and better
chances for convection, we will have to keep an eye on the potential
for heavy rainfall. Precipitable water values are forecast to
approach 2" (>90th percentile of climatology), and thunderstorms
could train over the same areas. River/stream levels are still
elevated from 2 weeks ago, though soils (especially the top soil)
have dried out a bit. At this point in time, there looks to be
several critical differences compared to the event 2 weeks ago: 1) a
weaker low-level jet, which is also more transient with its
associated moisture convergence, 2) lower PWAT values, and 3) much
less instability. These factors point toward a lower end, more
typical summer isolated flash flood threat, if any threat develops
in our local area at all. Probabilities for at least 1" of rainfall
on the LREF through Saturday morning are at most 20-30% in parts of
central Missouri. Those chances may be a bit low given the coarser
resolution of the LREF, but do buttress the point that the overall
threat for flash flooding is low.


(Saturday Night - Next Wednesday)

Models are in good agreement that the mid/upper level ridge will
amplify and shift a bit eastward by late this weekend into early
next week. With 850-hPa temperatures expected to climb into the +22
to +26C range (~99th percentile of climatology) and seasonably high
humidity, we may have at least a 2-day period (Sunday-Monday) of
heat index values near or above 105 degrees.

Forecast uncertainty increases Tuesday and beyond, as ensemble
guidance suggests the mid/upper level ridge to weaken a bit and
shift back to the south and west. This should enable at least
chances for showers and thunderstorms to return to the region, and
possibly, a cold frontal passage.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 702 PM CDT Wed Jul 22 2026

Some high level clouds have overspread the area, but conditions
remain VFR with a light NNE wind. Winds may vary and slowly turn
toward the SE on Thursday but remain light.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.

&&

$$

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...Kimble