Flash Flood Warning 59, NWS St. Louis, MO

366 
WGUS73 KLSX 061118
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
618 AM CDT Thu Aug 6 2026

MOC071-061315-
/O.CON.KLSX.FF.W.0059.000000T0000Z-260806T1315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MO-
618 AM CDT Thu Aug 6 2026

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 815 AM CDT THIS
MORNING FOR FRANKLIN COUNTY...

At 618 AM CDT, the heaviest rain had come to an end. However, flash
flooding was ongoing. Emergency management reported flash flooding
causing road closures. Flash flooding will continue even as the rain
has decreased in intensity.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Emergency management reported.

IMPACT...Flash flooding of small creeks and streams, urban areas,
         highways, streets and underpasses as well as other poor
         drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Washington, Union, Sullivan, Pacific, St. Clair, Villa Ridge, Gray
  Summit, Parkway, Miramiguoa Park, Lonedell, Moselle, Piney Park,
  Robertsville, Catawissa, Stanton and Lyon.

This includes the following State Parks...
Robertsville State Park and Meramec State Park.

This includes Interstate 44 in Missouri between exits 225 and 257.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.

In hilly terrain there are hundreds of low water crossings which are
potentially dangerous in heavy rain. Do not attempt to cross flooded
roads. Find an alternate route.

&&

LAT...LON 3820 9118 3860 9118 3860 9112 3861 9106
      3860 9104 3856 9101 3853 9092 3858 9082
      3859 9078 3864 9073 3842 9074 3821 9078

FLASH FLOOD...OBSERVED
EXPECTED RAINFALL RATE...1-3 INCHES IN 1 HOUR AND 30 MINUTES

$$

Kimble

883 
WGUS73 KLSX 061310
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
810 AM CDT Thu Aug 6 2026

MOC071-061320-
/O.EXP.KLSX.FF.W.0059.000000T0000Z-260806T1315Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MO-
810 AM CDT Thu Aug 6 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 815 AM CDT THIS MORNING FOR
FRANKLIN COUNTY...

Flood waters have receded. Flooding is no longer expected to pose a
threat. Please continue to heed remaining road closures.

A Flood Watch remains in effect until 100 PM CDT for portions of
Illinois and Missouri.

A Flood Watch remains in effect until 1000 AM CDT for portions of
central, east central, and northeast Missouri.

&&

LAT...LON 3820 9118 3860 9118 3860 9112 3861 9106
      3860 9104 3856 9101 3853 9092 3858 9082
      3859 9078 3864 9073 3842 9074 3821 9078

$$

Elmore

Area Forecast Discussion
National Weather Service St Louis MO
302 AM CDT Thu Aug 6 2026

.KEY MESSAGES...

- Showers and thunderstorms are expected to continue through
  this morning, particularly along the I-70 corridor. Localized
  flash flooding is possible.

- Additional rounds of showers and thunderstorms are possible
  through Saturday night before heat and humidity builds back
  into the region this weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 301 AM CDT Thu Aug 6 2026

Widespread showers and thunderstorms have entered central
Missouri on the nose of a southerly 30+ knot low-level jet. RAP
short-term forecasts have this jet veering with time this
morning, which should lead to continued development of new cells
on the western flank. This should increase the threat of
training, though lesser MUCAPE in our area suggests rates may
not be too terribly high. Usually in these cases, the flash
flood threat is highest closer to the genesis region (western
Missouri), where there is also higher MUCAPE per latest SPC
mesoanalysis. All that being said, the flash flood threat in our
area looks a bit lower than it did 12-24 hours ago. The best
chance for isolated flash flooding will be through mid-late
morning in central Missouri near I-70. This is the part of the
CWA that will be closer to the genesis region this morning and
where the REFS/HREF LPMM shows some pockets of 2-3+" of rain
through midday today.

The low-level jet is slow to weaken through the day today, with some
modest moisture convergence near or just east of the Mississippi
River even at 1800 UTC. While much of the convection should be lost
by midday, I do think lingering showers and weak thunderstorms will
continue into early this afternoon. At the very least, widespread
thick cloud cover looks likely to linger through much of the day.
Therefore, have made a couple of changes: 1) extended the flash
flood watch in time until 1800 UTC for far eastern Missouri into
western Illinois, while trimming the far north which will miss the
heavier rains, and 2) cooled high temperatures today on average
nearly 5 degrees from the previous forecast.

Additional showers and thunderstorms are expected to develop late
this afternoon, likely in parts of southwest Missouri near the
surface front, which may be enhanced by differential heating. These
storms may become strong to severe, but should move east/southeast
and stay to our southwest. More showers and storms should develop
late this evening/early overnight as the southwesterly low-level jet
strengthens. The location of the strongest moisture convergence
varies quite a bit, but may be centered over southwest Missouri. Our
best chances (30-50%) are in southeast Missouri and southwest
Illinois. Even if those areas are impacted tonight, the flash flood
threat looks relatively low for a few reasons: 1) weaker low-level
jet forecast tonight, 2) lower PWAT values, and 3) drier antecedent
conditions in SE MO/SW IL and higher FFG values.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 301 AM CDT Thu Aug 6 2026

(Friday - Friday Night)

The position of the quasi-stationary front Friday morning is
uncertain, but should tend to push northward during the day.
Convergence near this feature though looks very modest, so it is
uncertain if it will be strong enough to help promote any convective
initiation during peak heating. There is an even weaker low-level
jet forecast for Friday night (~15-20 knots), but weak moisture
convergence may interact with the surface boundary to yield at least
scattered showers and thunderstorms along/poleward of the boundary.

(Saturday - Monday Night)

Deterministic models are in good agreement that the front will shift
north of the area as a warm front by Saturday. This should leave at
least most of our area dry, but with increasing heat and humidity
beginning this weekend. Peak heat index values Saturday afternoon
may crest the century mark roughly along/south of I-70, and
potentially over the entire area Sunday and Monday. Magnitude heat
advisory criteria (105+) is also possible, especially Sunday and
Monday. There is a fly in the ointment for Sunday (and maybe even
Monday), at least in our northern counties. With the heart of the
mid/upper level anticyclone centered well to our west, we may be
susceptible to seeing the southern end of an MCS either or both
Sunday/Monday mornings. If this occurs, that could provide enough
clouds and/or an outflow boundary, which could limit the heat
threat.

(Tuesday - Wednesday)

There is still plenty of spread with the strength of a mid/upper
level trough crossing the Great Lakes/southeast Canada early next
week. Clusters of the 500-hPa height pattern show this quite well,
with roughly half of LREF members showing a stronger trough whereas
the other half is weaker. The stronger trough solution would be much
more likely to send some type of backdoor cold front through the
region and help end the hot/humid pattern. The weaker trough
scenario likely would keep the same air mass in place, which likely
would mean a more prolonged period of heat/humidity.

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1045 PM CDT Wed Aug 5 2026

The primary focus of the 06Z TAF period continues to be the
potential for showers and thunderstorms at all terminals
overnight through the morning, with heavy rain and
visibility/ceiling reductions very likely to varying degrees.
The heaviest storms are slightly favored at COU/JEF, but
thunderstorm impacts will be possible at STL/SUS/CPS/UIN as
well. In addition to period of very heavy rain, gusty winds are
possible at times, but less likely overall. MVFR categories are
expected at times, with the potential to reach IFR or lower
within the heaviest rain cores.

Showers and storms should move east-southeast of local terminals
sometime between mid/late morning tomorrow, with perhaps some
lingering low clouds possible. We may also see some fog at
times, with best chances at UIN, although with the uncertain
end time of the rain in the morning, we opted to exclude
significant fog mention for the time being. VFR conditions are
likely tomorrow afternoon, with some redeveloping showers
possible near the end of the period near St. Louis terminals.

BRC

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 10 AM CDT Thursday for MOZ018-019-026-027-
     034>036-041-042-047>052-059>065-072-073.
IL...Flood Watch until 10 AM CDT Thursday for ILZ058-095>102.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch until 1 PM CDT this afternoon for MOZ036-052-
     060>065-073.
     Flood Watch until 10 AM CDT this morning for MOZ026-027-034-
     035-041-042-047>051-059-072.
IL...Flood Watch until 1 PM CDT this afternoon for ILZ058-097>102.

&&

SHORT TERM...Gosselin
LONG TERM...Gosselin
AVIATION...19