River Flood Warning 88, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
607 AM CDT Sat Jun 13 2026

.KEY MESSAGES...

-There are multiple chances for severe thunderstorms today, though
the best chance will be this evening along the cold front.

-Cool and dry conditions expected on Sunday and Monday before
 showers and thunderstorms return to the region Tuesday and
 beyond.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 305 AM CDT Sat Jun 13 2026

Today's forecast will have many moving parts with several
opportunities for thunderstorms to develop. The best chance for
thunderstorms, as well as severe thunderstorms, remains this evening
along a cold front. Each chance is outlined below:

1. Morning convection: Showers and a few thunderstorms have formed
across eastern Kansas and west-central Missouri this morning, aided
by a weak low-level jet and warm air advection. Previous rounds of
guidance have shown this convection becoming more widespread,
developing into an MCS and pushing east across the forecast area
this morning. Confidence has started to decrease in this solution as
the latest CAM guidance keeps convection weak and disorganized
before it dissipates over the western forecast area this morning.

In the absence of a robust MCS cold pool, convection will indeed
weaken as it pushes east through the forecast area, outside the
influence of the low-level jet. Roughly 500-1500 J/kg of MLCAPE will
be available during the mid-morning, with decreasing values east of
the Mississippi River. So if an MCS does develop and instability is
on the higher end of the spectrum, the system would be able to
maintain itself at least to the Mississippi River before starting to
diminish. Severe chances are low with the morning convection given
all the above caveats, but if an MCS does become rooted in the
boundary layer, damaging wind gusts would be the main concern. Any
isolated severe thunderstorms will bring a risk for quarter-sized
hail.

2. Afternoon warm air advection convection:

Warm air advection will continue across the region this afternoon,
aided by a low-level jet that will only continue to strengthen
through the day. This will promote the development of isolated to
small clusters of showers and thunderstorms across the region.
Increasing instability to around 1000-2000 J/kg of MLCAPE area wide,
depending on how much the morning convection stunts
destabilization, plus 30-40 kts of 0-6 km shear will encourage at
least a few cells to become severe. Quarter-sized hail and
damaging wind gusts are possible with any storms that become
severe. While I cannot rule out a tornado at this point, the
hodographs are not as favorable as they will be along the front
during the evening.

3. Evening convection along cold front:

The best chance for severe thunderstorms today will be along a cold
front that will drop into the region this evening, with enhanced
lift from a mid-level shortwave. Initial development will be
isolated supercells across southern Iowa and northwest Missouri
where the best instability, shear, and lapse rates will be. As the
front and associated convection progress southeast into the forecast
area convection is expected to become so widespread that clusters
and bowing segments develop, though embedded supercells are still
possible. The main threat with any severe thunderstorms during this
period will be damaging winds, though quarter-sized hail and a
tornado cannot be ruled out within embedded supercells near the
front as hodographs become more curved. Instability will wane over
the evening and further southeast from the front, though there is
uncertainty in how quickly this will happen. Thus, confidence in
severe thunderstorm development across southeast Missouri and
southern Illinois is lower than over central and northeast Missouri.

4. Flash flood potential

Confidence is high that convection will be progressive enough in our
forecast area to preclude any widespread flash flood threat. The
best chance for any flash flooding would result front multiple
thunderstorms moving across the same area through the course of the
day. Where this happens, 2-3 inches of rain is possible, with
localized amounts up to 5" (via the HREF 24 hour LPMM), though 5"
amounts are representative of the worst case scenario. Northeast
Missouri is at the greatest risk for flash flooding, all other
things being equal, given the very wet antecedent conditions. Over
the past 72 hours portions of this area have been between 4-7" of
rain (MRMS Multi-Sensor Pass 2), while the remainder of the CWA has
seen generally less than 2".

Delia

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 305 AM CDT Sat Jun 13 2026

In the wake of Saturday's cold front, cold air advection will drop
850 mb temperatures to around 10C by Sunday afternoon. The result
will be high temperatures nearly 10 degrees below normal for this
time of year, in the 70s. Monday likewise will be cooler than normal
for mid June. Starting Tuesday, however, low-level flow will become
westerly then southwesterly, advecting warm, moist air back into the
region and giving high temperatures a boost. At the same time, mid-
level disturbances will propagate through the northwest mid-level
flow on the western side of an amplified mid-level trough. This
will bring a return of showers and thunderstorms to the region
Tuesday.

The best chance for showers and thunderstorms will be Wednesday into
Thursday ahead of and along a cold front that will push through the
forecast area. Uncertainty remains in the details of the timing of
the frontal passage, the favorability of the environment, and the
subsequent severe chances.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Sunday Morning)
Issued at 554 AM CDT Sat Jun 13 2026

Showers and thunderstorms are blooming across central Missouri
this morning and are expected to dissipate within a few hours.
They are already impacting the mid-Missouri terminals (KJEF,
KCOU), where brief reductions in visibility to MVFR flight
conditions are possible. Confidence is low in if this round of
showers and thunderstorms will impact the St. Louis metro
terminals (KSTL, KCPS, KSUS).

Additional showers and thunderstorms are possible this afternoon
across the area, though confidence is low in where these will
form. The best chance for showers and thunderstorms at all
terminals today will be this evening as thunderstorms form along a
cold front and move southeast through the region. MVFR to IFR
visibilities are expected underneath any thunderstorms, and MVFR
stratus is expected to trail the front for a few hours before dry
air erodes this layer. Southerly winds will become variable during
the afternoon ahead of the front, and eventually northwesterly
behind the front.

Delia

&&

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

WFO LSX

Preliminary Local Storm Report
National Weather Service St Louis MO
1126 AM CDT Sat Jun 13 2026

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

0903 PM     Tstm Wnd Dmg     2 NNW Mount Olive       39.10N 89.75W
06/11/2026                   Macoupin           IL   Broadcast Media

            Pictures from Facebook were shared by local
            media of large trees down damaging buildings
            in Lake Ka-ho. Time is estimated.

&&