Flash Flood Warning 19, NWS St. Louis, MO

063 
WGUS73 KLSX 190057
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
757 PM CDT Mon May 18 2026

MOC071-073-219-190107-
/O.EXP.KLSX.FF.W.0019.000000T0000Z-260519T0100Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Franklin MO-Gasconade MO-Warren MO-
757 PM CDT Mon May 18 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 8 PM CDT THIS EVENING FOR
NORTHWESTERN FRANKLIN, NORTHERN GASCONADE AND WARREN COUNTIES...

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 100 PM CDT Tuesday for portions
of southwest Illinois central Missouri and east central Missouri.

&&

LAT...LON 3858 9164 3871 9142 3885 9142 3884 9127
      3887 9127 3888 9111 3887 9096 3854 9096
      3856 9101 3861 9107 3859 9113 3862 9123
      3865 9123 3844 9164

$$

Jaja

Area Forecast Discussion
National Weather Service Saint Louis MO
410 PM CDT Mon May 18 2026

.KEY MESSAGES...

- Widespread showers and thunderstorms are expected to continue
  into the evening with heavy rainfall in some locations
  potentially leading to flash flooding.

- A few strong to severe thunderstorms are possible through the
  early morning hours of Tuesday with the main hazards being
  damaging winds, large hail, and a brief tornado or two.

- Another round of thunderstorms are possible along a cold front
  Tuesday afternoon/evening. Damaging wind gusts and large hail
  are the primary threats.

&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 251 PM CDT Mon May 18 2026

Showers and thunderstorms from this morning laid out west to east
on the upwind portion of the MCS. The outflow made it to a
Crawford to Washington to Randolph County line before stalling.
The 850 mb flow was out of the southwest this morning and has
started to back from the south this afternoon. Simultaneously, a
low level MCV ejected northeast out of Arkansas this afternoon. As
this occurred, convection has begun to intensify on the northern
side of the old outflow. Highest convective rates are currently
just east of Columbia. Rainfall totals are already averaging 1 to
2 inches across the Flood Watch with isolated totals of 3 to 4
inches.

This afternoon into evening, as the LLJ (or 850 mb flow) starts to
slightly back and the the MCV ejects northeast convection will
finally start to exit the region to the east. The break will be
short lived though as another line of showers and thunderstorms
will approach the region from the northwest this evening into
early Tuesday morning. This line of storms will likely start to
dissipate across central Missouri, but how quickly and exactly
where matters regarding flood potential. The current thinking is
for the line to weaken and dissipate near or just north of the St.
Louis metro.

However, a cold front will then approach the area from the
northwest and cross the region Tuesday afternoon into evening.
As this occurs, another round of showers and thunderstorms will
develop. Damaging wind gusts and large hail appear to be the
primary threat.

After the final round of showers and thunderstorms moves across
the area Tuesday evening, storm total rainfall amounts (from
Monday morning to Tuesday evening) of 3 to 5 inches with isolated
amounts of 6 to 8 inches appear likely.

These amounts of rainfall will result in some flash flooding.
Residents should monitor the latest forecasts and be prepared to
seek higher ground if a Flash Flood Warning is issued for your
area.

BAH

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 251 PM CDT Mon May 18 2026

A surface cold front will be located across southern Missouri
Wednesday with most of the region expected to be seasonably cool
and dry. The one exception to this is across Reynolds, Iron and
Madison counties were another round of thunderstorms will be
possible close to the frontal boundary.

Thursday into Friday, another mid-level wave will be located over
the Mountain West with low level flow out of the southwest. As
this occurs, the cold front will wash out with temperatures rising
along with a return of showers and thunderstorms.

The warm up will then persist into the weekend and early next week
as another wave approaches from the west. This warming trend is
supported by both the LREF and NBM IQRs. Looking at global
ensemble guidance, a general building of mid-level heights is
forecast to start this weekend across the Eastern United States
and then retrograde west next week.

BAH

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 101 PM CDT Mon May 18 2026

A complex of showers and thunderstorms continues across central
Missouri this afternoon. This round of thunderstorms has persisted
since the overnight hours with almost continuous thunder at the
TAF sites (except KUIN) since 12z. The line of thunderstorms has
stalled just south of KCPS this afternoon with a shortwave wave
currently near the Arkansas/ Missouri border. The shortwave is
causing additional thunderstorm development just north of the
boundary (or close to Columbia, MO). This means that all
terminals will likely (>90% chance) observe thunderstorms through
the remainder of the afternoon into the early evening.

As the shortwave moves northeast of the region, showers and
thunderstorms will begin to finally move east of the terminals
with thunder temporarily ending from west to east. This break will
be brief though. Another line of showers and thunderstorms will
approach the terminals from the northwest Tuesday morning between
4 and 7 AM. This line of storms will likely weaken as they
progress southeast, but the question is how quickly will they
weaken. As of current, the thinking is the line of thunderstorms
will hold together long enough to make it to KUIN, KCOU, and KJEF.
It is unclear if there will be thunder at the St. Louis terminals.
For now have only added SHRA (no thunder) for KSTL, KSUS, and
KCPS.

A cold front will then cross the terminals Tuesday afternoon with
MVFR/ IFR cigs behind.

BAH

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Flood Watch through Tuesday afternoon for Audrain MO-Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Jefferson MO-Lincoln MO-Moniteau MO-Monroe MO-Montgomery MO-
     Osage MO-Pike MO-Ralls MO-Saint Charles MO-Saint Louis City
     MO-Saint Louis MO-Warren MO-Washington MO.

IL...Flood Watch through Tuesday afternoon for Bond IL-Calhoun IL-
     Clinton IL-Fayette IL-Jersey IL-Madison IL-Marion IL-Monroe
     IL-Saint Clair IL-Washington IL.

&&

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
355 PM CDT Mon May 18 2026

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-192100-
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL-
Calhoun IL-Jersey IL-Madison IL-Saint Clair IL-Monroe IL-Knox MO-
Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO-
Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO-
Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO-
Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO-
Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
355 PM CDT Mon May 18 2026

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAYS ONE THROUGH SEVEN...This afternoon through Sunday.

More detailed information can be accessed at:
https://www.weather.gov/media/lsx/DssPacket.pdf

The Area Forecast Discussion is available at:
https://forecast.weather.gov/
product.php?issuedby=LSX&product=AFD&site=lsx

.KEY MESSAGES...

- Widespread showers and thunderstorms are expected throughout the
  day with heavy rainfall in some locations potentially leading to
  flash flooding.

- A few strong to severe thunderstorms are possible this afternoon
  and evening with the main hazards being hail and damaging wind
  gusts.

- Additional thunderstorms are forecast late tonight and early
  Tuesday morning with another round possible along a cold front
  Tuesday afternoon/evening.

NOTE: Starting May 29, 2026, this outlook product will be
discontinued. Please see the above products for more detailed
forecast information.

WFO LSX

Preliminary Local Storm Report
National Weather Service St Louis MO
413 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0208 PM     Flood            Salem                   38.63N 88.95W
05/18/2026                   Marion             IL   Emergency Mngr

            Pictures confirm street flooding in Salem,
            IL.

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
422 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0256 PM     Rain             1 WSW Truesdale         38.80N 91.14W
05/18/2026  M1.70 Inch       Warren             MO   Emergency Mngr

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
428 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0319 PM     Rain             Hannibal                39.71N 91.39W
05/18/2026  M1.80 Inch       Marion             MO   Emergency Mngr

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
447 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0440 PM     Rain             Ferguson                38.74N 90.30W
05/18/2026  M2.03 Inch       St. Louis          MO   Public

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
451 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0215 PM     Rain             Catawissa               38.42N 90.78W
05/18/2026  M1.52 Inch       Franklin           MO   Public

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
456 PM CDT Mon May 18 2026

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0315 PM     Rain             1 SW Holts Summit       38.63N 92.13W
05/18/2026  M1.64 Inch       Callaway           MO   Public

            South side of Holts Summit.

&&

MCF