Flash Flood Warning 31, NWS St. Louis, MO

760 
WGUS73 KLSX 102113
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
413 PM CDT Wed Jun 10 2026

MOC205-102123-
/O.EXP.KLSX.FF.W.0031.000000T0000Z-260610T2115Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Shelby MO-
413 PM CDT Wed Jun 10 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 415 PM CDT THIS AFTERNOON FOR
SHELBY COUNTY...

The heavy rain has ended. Flooding is no longer expected to pose a
threat. Please continue to heed remaining road closures.

A Flood Watch remains in effect until 700 AM CDT Thursday for
portions of west central Illinois and northeast Missouri.

&&

LAT...LON 3985 9184 3966 9209 3966 9219 3960 9219
      3961 9230 3979 9229 3995 9229 3995 9184

$$

MRB

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1217 PM CDT Wed Jun 10 2026

.KEY MESSAGES...

- Hot and humid conditions are expected through Thursday.

- Strong to severe thunderstorms are expected this evening, with
  the main threats being damaging wind gusts and large hail.

- Another round of strong to severe thunderstorms will occur
  along a cold front Thursday afternoon and evening. These storms
  will be capable of damaging wind gusts, large hail, and
  tornadoes.

&&

.SHORT TERM... (Through Thursday Night)
Issued at 223 AM CDT Wed Jun 10 2026

Water vapor imagery shows an upper-level trough broadening across
the Northern and Central Plains this morning. This trough will mute
the upper-level ridge over the Middle Mississippi Valley today, with
guidance consensus showing 850 mb temperatures cooling by a degree
or two compared to yesterday. While this favors slightly cooler
temperatures at the surface, southwesterly surface flow will provide
a boost to temperatures via downsloping and adiabatic warming off
the Ozarks. This will produce air temperatures a degree or two
warmer than yesterday; however, the same process will also lower dew
points. In the end, this will result in heat index values similar to
if not a few degrees below what was experienced yesterday and below
Heat Advisory criteria.

Another heat-mitigating factor is the potential for convection prior
to and during peak heating. As the trough draws closer to the CWA, a
subtle disturbance within the southwesterly flow aloft will move
northeastward across Missouri into northern Illinois from mid
morning into the afternoon. Despite this being prior to peak heating
and when instability will be maximized, there will be at least 2,500
J/kg of SBCAPE per guidance consensus. Deep layer shear is expected
to be around 30 kts, but updrafts may be slightly elevated with
lower effective shear. The instability will be sufficient for at
least small hail production in the strongest cores, and if the
degree of forecasted shear is realized, there will be a threat for
isolated large hail and damaging wind gusts across northeastern
Missouri and west-central Illinois. Convective debris and/or outflow
from this convection will reduce temperatures across this part of
the area.

The main concern for strong to severe storms will come later this
evening as a cold front sinks south-southeastward into the region.
There is some concern that the early-day convection may reduce
instability and the atmosphere not be able to fully recover prior to
late afternoon/early evening CI; however, there is a strong
consensus among guidance that recovery will not be an issue and the
environment will be plenty unstable. Around 4pm when CI is expected
roughly across north-central Missouri and southern Iowa, 3,000-4,000
J/kg of SBCAPE is forecast within the warm sector among 30-35 kts of
deep-layer shear. The shear vectors will be nearly parallel to the
front, leading to quick upscale growth as storms move into the CWA
this evening. Clusters of multi-cells with embedded supercells will
pose mainly a damaging wind and large hail threat. Low-level shear
will be sufficient for tornadoes, though storm interactions and any
supercells being short-lived limit this threat to bowing segments
that can develop mesovortices. The area most favorable for these
threats is northeastern Missouri and west-central Illinois along and
north of Highway 36 and I-72. Convection is expected to drift east
of the CWA by around midnight as the low-level jet veers, with a
relative lull in activity then expected through Thursday morning.

The aforementioned cold front will not make much progress south until
a shortwave induces cyclogenesis along the boundary over the Central
Plains during the day Thursday; swinging it through the Middle
Mississippi Valley during the late afternoon and evening. With that
frontal timing, there is a low to medium chance for dangerous heat
across portions of the CWA, with potential cloud cover and
uncertainty in FROPA specifics leading these confidence levels.
Nevertheless, upwards of 3,000 J/kg of SBCAPE is expected ahead of
the front with deep-layer shear once again being around 30kts. An
inversion/capping around 700mb within the warm sector is expected to
keep convection tied to the front, with the deep-layer shear vectors
becoming increasingly parallel to the boundary as proximity to it
increases. Both factors will favor clusters and/or a linear storm
mode, with steep low-level lapse rates and DCAPE over 1,000 J/kg
supporting primarily a damaging wind threat. Low-level shear of 20-
30 kts is favorable for a tornado threat, but a limiting factor may
be slightly elevated LCLs. Convection will gradually weaken with
southeastward extent as instability and shear decrease through the
evening, with the front clearing the CWA as early as late evening to
just after midnight.

Elmore

&&

.LONG TERM... (Friday through Tuesday)
Issued at 223 AM CDT Wed Jun 10 2026

The consensus among guidance continues to be that zonal flow will
persist over the Middle Mississippi Valley in the wake of Thursday's
front. This flow and a weekend FROPA will keep temperatures at or
below climatological normals through this portion of the period.
This cold front will drift southward through the region Saturday
into Sunday and serve as the focus for periodic rounds of rain
through the weekend. Guidance diverges on how far south it makes it
relative to the CWA before a shortwave enhances rain chances along
it early next week. If the front is further south from the CWA,
little to no rain can be expected. If it stalls just south of the
CWA, rain chances will continue into early next week.

Elmore

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1212 PM CDT Wed Jun 10 2026

The primary concern during the 18Z TAF period will be multiple
opportunities for thunderstorms, particularly at UIN, and to a
lesser extent along I-70 corridor terminals. UIN is likely to see
multiple rounds of storms, first early this afternoon and the
second again this evening, and these storms may feature bursts of
heavy rain and strong, erratic winds. The latter round of storms
are more likely to feature higher wind speeds.

Overnight, decaying storms may drift as far south as I-70,
potentially impacting the remainder of our local terminals as
well. Confidence is relatively low that this will occur.

Otherwise, breezy ambient southwesterly winds can be expected even
outside of thunderstorm activity this afternoon.

BRC

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Thursday morning for Knox MO-Lewis MO-Marion
     MO-Shelby MO.

IL...Flood Watch through Thursday morning for Adams IL-Brown IL-Pike
     IL.

&&

WFO LSX