Flash Flood Warning 24, NWS St. Louis, MO

891 
WGUS73 KLSX 080556
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
1256 AM CDT Mon Jun 8 2026

MOC019-027-051-135-080606-
/O.CAN.KLSX.FF.W.0024.000000T0000Z-260608T0830Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boone MO-Callaway MO-Cole MO-Moniteau MO-
1256 AM CDT Mon Jun 8 2026

...FLASH FLOOD WARNING FOR SOUTHEASTERN BOONE, WEST CENTRAL CALLAWAY,
WESTERN COLE AND EASTERN MONITEAU COUNTIES HAS BEEN REPLACED WITH A
FLOOD WARNING...

&&

LAT...LON 3844 9264 3884 9254 3882 9202 3835 9240
      3835 9241 3842 9240 3843 9240 3843 9262

$$

Delia

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
603 PM CDT Sun Jun 7 2026

.KEY MESSAGES...

- Waves of showers and thunderstorms are expected through at
  least Monday afternoon/evening with lower chances extending into
  Tuesday morning.

- Locally heavy rainfall is possible through Tuesday morning, but
  confidence relatively higher in flash flooding across central
  MO tonight into Monday morning. An isolated severe thunderstorm
  with damaging winds and/or brief, weak tornado is also possible
  this evening and again Monday afternoon and evening.

- Heat and humidity will build Tuesday into Thursday with high
  temperatures reaching the 90s F and afternoon heat index values
  exceeding 100 F in some locations.

&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 257 PM CDT Sun Jun 7 2026

An upper-level low will continue to slowly migrate northeastward
across the Mid-Mississippi River Valley through late Monday,
providing episodic showers and thunderstorms across the CWA as lobes
of associated mid-level vorticity and/or MCVs rotate cyclonically
around the parent low. Due to the broad/ill-defined large-scale
forcing and influence of previous rounds of showers and
thunderstorms, CAMs and model guidance as a whole have struggled to
come into agreement on the exact evolution of the upper-level low
and resulting timing and coverage of showers and thunderstorms. On
Monday afternoon/evening, HREF membership has the greatest coverage
shifting to along/east of the Mississippi River or beneath and
downstream of the upper-level low. Although mid-level heights will
be unfavorably rising Monday night, a lingering diffuse boundary has
been indicated by some model guidance to exist Monday night along
with potential interaction from a LLJ in addition to an upstream MCS
or MCV tracking along that boundary early Tuesday morning. This
evolution results in an increasingly uncertain forecast in terms of
showers and thunderstorms, especially Monday night through Tuesday
morning with a wide range of scenarios possible include those with
very little or only isolated showers and thunderstorms.

With precipitable water flirting with 2" (99th climatological
percentile) and deep warm cloud depths combined with kinematic
profiles favorable for some organization of thunderstorms into
clusters or small MCSs with training and backbuilding, locally heavy
rainfall continues to be a concern through Monday night. Confidence
in the threat of flash flooding has increased sufficiently to issue
a Flood Watch for portions of central MO where multiple rounds of
heavy rainfall are likely on top of 1 to 3" of rain that fell and
has moistened soils. Elsewhere, we are missing this preconditioning
of soils, lowering confidence in flash flooding at this point,
especially considering a lack of coherent or consistent high-QPF
signal in CAMs.

In addition to heavy rainfall there is also a low threat of severe
thunderstorms this afternoon/evening and again on Monday. The latest
SPC mesoanalysis depicts 1000 to 1500 J/kg MLCAPE including 100+
J/kg 0-3 km CAPE and 20 to 25 kt effective wind shear along with
just enough low-level hodograph curvature to support a low, brief
tornado or isolated damaging wind threat with a potential low-
topped, transient supercell. However, the more favorable environment
is across southwestern and southern MO. On Monday, the environment
is significantly more variable with wind shear magnitude and
hodograph structure sensitive to both the presence of a potential
remnant MCV from overnight thunderstorms in southwestern
MO/southeastern KS and arrival of a mid-level jet streak on the heel
of the upper-level low. HREF joint probabilities of 1000+ J/kg
SBCAPE and 25+ kt deep-layer wind shear are greatest (50 to 70
percent) late Monday afternoon along/west of the Mississippi River,
but the best overlap with stronger large-scale forcing appears to be
across southeastern MO. However, confidence is low in the placement.
At least isolated damaging winds are possible, with a low tornado
threat possible if wind shear sufficient for supercells is realized.

With regards to temperatures, early day cloud cover and showers and
thunderstorms at times are expected to keep high temperatures on
Monday in the 80s F. On Tuesday, there could be some morning cloud
debris or lingering showers or thunderstorms, but an upper-level
ridge axis shifting overhead will favor increasingly dry conditions
and scattering of any cloud cover. With low-level southerly flow
will also act to warm 850-hPa temperatures to near the 99th
climatological percentile, supporting high temperatures in the upper
80s to low-90s F. With dewpoints well into the 70s F, ensemble model
guidance has 30 percent probabilities of 100+ F heat index values
during the afternoon and evening.

Pfahler

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 257 PM CDT Sun Jun 7 2026

Global model guidance is trending toward a slightly quicker eastward
shift/break down of the ridge as upper-level troughing takes place
across the Northern Plains. This evolution has led to slightly
cooler temperatures on Wednesday, but confidence is still high that
it will be the warmest day of the week with much of the CWA seeing
high temperatures in the 90s F given an approaching 850-hPa thermal
ridge and potential downsloping of low-level southwesterly flow off
the Ozark Plateau. Despite being warmer on Wednesday, dewpoints may
tend to diurnally lower during peak heating, decreasing confidence
that heat index values will be much higher than Tuesday. Model
guidance is consensus that a shortwave trough rounding the broader
longwave trough will force a cold front into the CWA sometime
Thursday, providing another opportunity for showers and
thunderstorms along with cooling temperatures closer to average.
However, this front may waver across the Mid-Mississippi River
Valley into the upcoming weekend, prolonging chances of showers and
thunderstorms.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 551 PM CDT Sun Jun 7 2026

Ongoing showers and thunderstorms across central Missouri are
expected to begin moving more to the east over the first several
hours of the TAF period. This will bring thunderstorm chances into
the mid-Missouri terminals, though how long the terminals are
impacted remains uncertain at this time. Showers and thunderstorms
will continue to form and move northeast to east across Missouri,
impacting the St. Louis metro and Quincy terminals overnight.
There is uncertainty with where exactly thunderstorms will move,
though confidence is high that thunderstorms will continue to
impact the broader region overnight. With any thunderstorms MVFR
ceilings and brief reductions in visibility are expected.

MVFR ceilings are expected to build into the region overnight from
increased near surface moisture, and linger into the late morning
before mixing is able to raising ceilings to VFR after noon.

Delia

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Monday afternoon for Boone MO-Callaway MO-
     Cole MO-Moniteau MO-Osage MO.

IL...None.
&&

WFO LSX