Severe Thunderstorm Warning 146, NWS St. Louis, MO

818 
WWUS53 KLSX 162058
SVSLSX

Severe Weather Statement
National Weather Service St Louis MO
358 PM CDT Sat May 16 2026

ILC121-162115-
/O.CON.KLSX.SV.W.0146.000000T0000Z-260516T2115Z/
Marion IL-
358 PM CDT Sat May 16 2026

...SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 415 PM CDT FOR
NORTHWESTERN MARION COUNTY IN SOUTH CENTRAL ILLINOIS...

At 358 PM CDT, a severe thunderstorm was located 6 miles east of
Patoka, or 11 miles north of Salem, moving east at 15 mph.

HAZARD...60 mph wind gusts and quarter size hail.

SOURCE...Radar indicated.

IMPACT...Hail damage to vehicles is expected. Expect wind damage to
         roofs, siding, and trees.

This severe thunderstorm will be near...
  Patoka around 400 PM CDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Seek shelter inside a well-built structure and stay away from
windows. This storm is capable of producing damaging winds and large
hail.

Tornadoes can develop quickly from severe thunderstorms. Seek shelter
immediately in an interior room on the lowest floor of a well-built
structure.

&&

LAT...LON 3882 8891 3870 8895 3871 8914 3874 8914
      3882 8902
TIME...MOT...LOC 2036Z 266DEG 11KT 3877 8908

TORNADO...POSSIBLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...1.00 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

BRC

Area Forecast Discussion
National Weather Service Saint Louis MO
121 PM CDT Sat May 16 2026

.KEY MESSAGES...

- Additional scattered thunderstorms are possible (20-30%) this
  afternoon and evening. The main risk is large hail and damaging
  winds.

- Additional thunderstorm chances return early this week with a
  more widespread severe weather threat possible along a slow
  moving cold front Monday night into Tuesday.

&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 112 PM CDT Sat May 16 2026

An upper level trough has moved onshore over the western CONUS,
with a surface low over the Central High Plains and a warm front
extending into Iowa. There was a secondary warm front/convergence
zone draped along the I-70 corridor this morning, and this is
what kicked off this morning's storms. These storms have reinforced
a baroclinic zone across the CWA, with temps in the upper 60s
across our north and pushing 80 in our south.

As we move through the afternoon and into the evening, additional
thunderstorm development will be largely focused to the north and
west of the area, near the primary warm front. However, the above
baroclinic zone may serve as a secondary focus for convection this
afternoon, and a few of the most recent runs of the HRRR are hinting
at that possibility. Given the weak forcing along this feature and
lack of deep forcing, I don't expect widespread convection, but a
few additional thunderstorms remain a possibility. If these storms
do develop, MUCAPE around 2,500 J/kg and effective bulk shear around
30 kts may allow few of these storms to become strong enough the
support large hail or damaging winds.

The stronger convection expected to develop near NW MO should
grow upscale and track to the ENE through the night. While
previous runs of high-res guidance has largely kept these storms
to our north, a few of the CAMs have begun pushing them a bit
further south into our area. These storms may also pose a marginal
threat for damaging winds and large hail as they diminish and
move across NE MO and west-central IL this evening.

Tomorrow, longwave troughing will amplify over the western CONUS,
reinforcing deep southwesterly flow over the Mid-Mississippi Valley.
Given the lack of any focused forcing for ascent, it appears likely
that we'll see little to no precipitation and notably less cloud
coverage than today. The increased insolation, coupled with the
above deep southerly flow, should push temperatures quite a bit
higher tomorrow.

BSH

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 112 PM CDT Sat May 16 2026

A compact shortwave will eject from the western CONUS trough on
Monday, spurring cyclogenesis over the Central Plains. The resultant
forcing for ascent from central KS through Iowa and into the Great
Lakes will force another round of thunderstorms, largely to the north
and west of our forecast area. These areas will also feature strong
dynamics, which coupled with a very unstable airmass, will result
in scattered/numerous strong to severe thunderstorms. The atmosphere
will also be rather unstable over the Mid-Mississippi Valley, but
without any focused forcing, anything more than widely scattered
thunderstorms appear unlikely. Additionally, much more modest
wind shear on our CWA will limit storm organization and severe
potential. Our best chance for severe weather through Tuesday
morning will be tied to whether the storms that develop to our
northwest are able to grow upscale and persist as they advance
into our forecast area.

A cold front associated with Monday's surface low is expected to
push through the region on Tuesday. Ahead of the front, instability
should build into the 1000-2000 J/kg range, which coupled with the
front, will result in the best chance for thunderstorms in the
extended forecast. While the SPC convective outlook continues to
highlight our area on Tuesday, I do see a couple of factors that may
limit the potential for severe thunderstorms. First of all, the best
deep layer dynamics are expected to remain well to the north of our
forecast area, limiting deep layer shear to around 30kts ahead of
the front. Secondly, it's unclear how storms from Monday night and
Tuesday morning will unfold across the area and whether the
atmosphere can recover before the frontal passage. Even if we do
recover, the above wind shear would be only marginally supportive
for severe thunderstorms. With that, the 15% contour from SPC seems
appropriate, but I would not expect that to increase much, barring a
notable change in the models.

The above cold front should push the deep moisture our of our
region, with the vast majority of guidance keeping dewpoints below
60 through the end of the week. Persistent weak zonal flow aloft
may open the door for a few weak shortwaves to move through the
region, but the lack of moisture will keep precipitation chances
limited.

BSH

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1216 PM CDT Sat May 16 2026

The primary aviation concern are the ongoing storms near the STL
metro and over NE MO and west-central IL. The storms near STL are
rapidly decaying, but are still hanging onto some lightning. With
that, I've just included an hour of -TSRA to cover the lightning
threat, but no notable visby reduction as precipitation should be
relative light.

Further north, more robust convection has persisted generally just
to the south and west of KUIN. Those storms should move over that
terminal at some point in the first few hours of the TAF before
gradually tapering off this afternoon.

There will be a low (<30% chance) for storms through the
afternoon, especially toward NE MO and west-central IL, before
falling further this evening. Otherwise, VFR conditions should
persist with southerly winds, becoming a bit gusty tomorrow.

BSH

&&

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

WFO LSX

Hazardous Weather Outlook
National Weather Service St Louis MO
555 AM CDT Sat May 16 2026

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-171100-
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-
555 AM CDT Sat May 16 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...Today through Friday.

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...

- Showers and scattered thunderstorms are expected this morning
  with coverage forecast to gradually fade by this afternoon. The
  strongest storms could produce hail up to 1" and damaging wind
  gusts.

- Thunderstorms are possible (20-30%) this afternoon and evening.
  The main risk is large hail with a lower potential for damaging
  winds.

- Additional thunderstorm chances return early this week with a
  more widespread severe weather threat possible along a slow
  moving cold front Monday night into Tuesday.

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

WFO LSX