Flash Flood Warning 4, NWS St. Louis, MO

667 
WGUS73 KLSX 271836
FFSLSX

Flash Flood Statement
National Weather Service St Louis MO
136 PM CDT Mon Apr 27 2026

MOC019-051-135-271846-
/O.EXP.KLSX.FF.W.0004.000000T0000Z-260427T1845Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boone MO-Cole MO-Moniteau MO-
136 PM CDT Mon Apr 27 2026

...FLASH FLOOD WARNING WILL EXPIRE AT 145 PM CDT THIS AFTERNOON FOR
CENTRAL BOONE, NORTHWESTERN COLE AND MONITEAU 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 900 PM CDT Monday for portions
of Illinois and Missouri.

&&

LAT...LON 3892 9250 3894 9251 3896 9255 3917 9211
      3906 9211 3906 9213 3903 9214 3902 9213
      3890 9217 3889 9215 3887 9216 3887 9215
      3885 9215 3885 9214 3883 9215 3881 9214
      3851 9273 3860 9284 3868 9284 3868 9262

$$

Britt

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
647 AM CDT Mon Apr 27 2026

.KEY MESSAGES...

- While periods of storms are expected through Monday morning, the most
  potent thunderstorms will occur this afternoon and evening.

- Thunderstorms this afternoon and evening will be capable of
  damaging wind gusts, large hail, and strong tornadoes.

- A period of cool, calm weather is expected mid-week through the
  weekend.

&&

.SHORT TERM... (Through Tuesday Night)
Issued at 155 AM CDT Mon Apr 27 2026

Storms across southeastern Missouri continue to butt up against an
instability gradient draped from north to south across Missouri.
The warm air advection feeding these storms will also push greater
instability slowly northeastward through this morning, though
propagation vectors will favor convection continuing to move east-
southeastward generally away from the CWA or into an unfavorable
environment. Additionally, the low-level jet refocusing across
Kansas will continue to support the downward trend in convection
across southeastern Missouri early this morning. Any linger storms
over the next couple of hours will be capable mainly of large hail,
though there is also a very low damaging wind and tornado threat for
storms that remain surface based.

Our attention turns to the storms over eastern Kansas that are
propagating eastward with the nose of the low-level jet. With the
nose of this low-level jet edging into northeastern Missouri later
this morning, the focus for these storms will spread into portions
of the CWA north of I-70. Vertical thermal profiles suggest that this
convection will be elevated, mitigating a threat of damaging wind
gusts and/or tornadoes. However, with around 40 kts of effective
shear and building MUCAPE, there is a low chance for isolated
instances of large hail.

How long this convection lingers is uncertain, although guidance
trends have been toward a lull in convective activity in the wake of
this convection and that associated with a cold front during the
late afternoon and evening. Ahead of the front, the warm sector
remains capped through much of the afternoon per a majority of
deterministic soundings. Although, any remnant outflow or
differential heating boundary from early day convection may serve as
enough of a forcing mechanism to spawn discrete convection during
the afternoon as lift from an approaching shortwave increases over
the region. If this convection does form, it will be in an
environment characterized by 2,000-2,500 J/kg of SBCAPE and roughly
50 kts of deep-layer shear. This will favor supercells capable of
all hazards, with long curved hodographs favoring strong tornadoes,
especially if storms are able to latch on to any remnant boundaries
across the CWA.

Where the environment isn't contaminated from earlier rounds of
convection, additional updrafts are expected along the cold front as
it enters the area 4-5pm. Forcing from the front paired with lift
from the shortwave will lead to numerous updrafts along the front.
While this will be occurring within a similar environment detailed
prior, the number of updrafts paired with them occurring along the
front may lead to destructive interactions and congealing into line
segments and/or clusters. While this will tend to limit a strong
tornado threat, storms will still be capable of all severe hazards.
Convection is expected to depart the CWA with the front by 9-10pm.

Even with the FROPA Monday evening, the threat for convection will
continue on Tuesday. Guidance consensus has the front stalling just
south of the CWA early Tuesday and then buckling northward as a
shortwave moves through the Central Plains and into the Midwest
through the day. This shortwave will send a subtle surface
reflection through the Mid South along the front, with a brief
period of warm air advection that will help force elevated
convection for areas mainly along and south of I-70. If the front
can move northward enough, shear profiles and instability amounts
favor supercells capable primarily of large hail across far
southeastern Missouri during the afternoon. Waning instability and
the front continuing southward will bring an end to rain chances
during the evening.

Elmore

&&

.LONG TERM... (Tuesday Night through Sunday)
Issued at 155 AM CDT Mon Apr 27 2026

Both deterministic guidance and ensemble clusters keep upper-level
troughing slowly moving eastward over the eastern CONUS through the
long range forecast period. This will maintain northwesterly flow
over the Middle Mississippi Valley through Saturday as several
rounds of high pressure pass through the region. As a result,
temperatures will run at or below climatological normals into the
weekend and mostly dry weather is expected.

Elmore

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 647 AM CDT Mon Apr 27 2026

Thunderstorms are expected at times throughout the day, impacting
all terminals. The greatest coverage of thunderstorms this morning
is expected to be across central, northeastern MO into west-central
IL impacting KCOU, KJEF, and KUIN, with lower confidence in
thunderstorms reaching the St. Louis metro terminals through early
afternoon. Another round of redevelopment will take place this
afternoon and evening with the greatest chance of severe
thunderstorms as well. These thunderstorms will be capable of hail,
strong winds, and some tornadoes. Trends will need to be monitored
for more significant terminal impacts beyond MVFR to IFR flight
conditions.

A cold front will pass through the region this evening, veering
southerly winds to northwesterly with drier conditions prevailing.
There is the potential for some post-frontal MVFR ceilings late
tonight into Tuesday morning, with the highest chance of impacts at
KUIN. However, given that confidence is low in impacts before the
end of the TAF period, VFR flight conditions are maintained for
now.

Pfahler

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
202 AM CDT Mon Apr 27 2026

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-280715-
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-
202 AM CDT Mon Apr 27 2026

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

.DAY ONE...Today and tonight.

Periods of thunderstorms are expected through the day into this
evening. Thunderstorms this afternoon and evening will be capable of
large hail, damaging wind gusts, and tornadoes.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

There is a chance of thunderstorms Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report wind damage, hail occurrence and
size, and tornado occurrence to NWS St. Louis.

Elmore

Preliminary Local Storm Report
National Weather Service St Louis MO
506 AM CDT Mon Apr 27 2026

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

0333 AM     Hail             Farmington              37.78N 90.42W
04/27/2026  M2.00 Inch       St. Francois       MO   Emergency Mngr

            Photo of multiple large hail stones, largest
            is measured at 2 inches. Time estimated from
            radar.

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
548 AM CDT Mon Apr 27 2026

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

0541 AM     Hail             2 S Belleville          38.50N 90.00W
04/27/2026  E1.00 Inch       St. Clair          IL   Amateur Radio

            Pea to quarter sized hail. Time estimate
            from radar.

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
629 AM CDT Mon Apr 27 2026

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

0616 AM     Hail             University City         38.67N 90.33W
04/27/2026  E1.50 Inch       St. Louis          MO   Public

            Estimated ping pong sized hail with photo
            and US quarter. Time estimated from radar.

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
631 AM CDT Mon Apr 27 2026

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

0620 AM     Hail             2 ENE Maplewood         38.63N 90.30W
04/27/2026  E1.00 Inch       St. Louis City     MO   County Official

&&

Delia

Preliminary Local Storm Report
National Weather Service St Louis MO
816 AM CDT Mon Apr 27 2026

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

0751 AM     Tstm Wnd Gst     3 W Granville           39.56N 92.15W
04/27/2026  M65 MPH          Monroe             MO   Public

&&

MCF

Preliminary Local Storm Report
National Weather Service St Louis MO
1030 AM CDT Mon Apr 27 2026

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

1024 AM     Tstm Wnd Dmg     Modesto                 39.48N 89.98W
04/27/2026                   Macoupin           IL   Emergency Mngr

&&

MCF