198
FXUS63 KLSX 161928
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
228 PM CDT Mon Jun 16 2025

.KEY MESSAGES...

-Training showers across southeast Missouri and southern Illinois
may produce flooding conditions this afternoon.

-There are conditional threats for severe weather early Wednesday
morning and again Wednesday afternoon and evening across the area.
All hazards are possible at this point.

-Weekend highs will peak in the 90s and may be harmful to some
groups.



&&

.SHORT TERM... (Through Wednesday Night)
Issued at 227 PM CDT Mon Jun 16 2025

Showers and a few thunderstorms will persist through the afternoon,
mainly across southeast Missouri and southern Illinois where a
stationary front has been parked. The environment across this area
is characterized by high instability (1500-2500 J/kg), warm cloud
depths, and well distributed instability (tall, skinny CAPE). This
favors efficient showers and thunderstorms, so as coverage expands,
training cells will be able to produce as much as 2-3 inches of rain
in localized spots. This will lead to flooding of roadways and
culverts, particularly in areas of poor drainage. Convection will
diminish this evening and leave a largely dry night as a mid-level
shortwave kicks east out of the region and we lose day time
instability.

A mid-level disturbance will push through the region Tuesday
afternoon, and a complex of showers and thunderstorms will develop
in response, mainly over Iowa. Some hi-res guidance sources produce
a robust outflow from these storms that stretches down into the CWA
Tuesday afternoon and evening, becoming a focus for showers and
thunderstorms. Confidence is low in this occurrence given the
uncertainty in the location of the complex, strength and location of
the outflow, and the presence of modest CIN. 15-25 kts of 0-6 km
shear will help prevent widespread organization of thunderstorms,
and if thunderstorms develop they are generally expected to be non-
severe. Like today, any showers and thunderstorms along this outflow
are expected to diminish into the evening as the boundary layer
becomes increasingly stable and the shortwave kicks east.

Meanwhile, an MCS will be forming across eastern Kansas out ahead of
a surface low developing in the lee of the Rockies. Confidence is
much higher that this convection will track eastward overnight and
move into central and northeast Missouri during the early morning
hours Wednesday. While guidance shows convection weakening as it
moves east, it`s also possible that it remains organized from
sufficient MUCAPE (1000-2000 J/kg) and the dynamics from the surface
low. Severe thunderstorms are expected with this complex before it
reaches the LSX CWA, and if it`s able to hold together, damaging
winds will be the main threat, though I cannot rule out large hail
and a brief tornado.

The MCS will push eastward through the day, putting out an outflow
somewhere across the forecast area. The surface low will push
northeastward in lockstep with a mid-level trough, and slide into
the upper Mississippi Valley, dragging a cold front through the
forecast area Wednesday afternoon and evening. To the north of this
outflow stable conditions will stunt the environment from
destabilizing later in the day and significantly lower the severe
threat. South of the boundary the environment will have access to
moist, unstable air with SBCAPE values 3000+ J/kg, modest lapse
rates, and 30-40kts of 0-6km shear. Where the cold front interacts
with the environment south of the outflow boundary severe
thunderstorms are possible with the potential for all hazards. The
cold front will be progressive, and exit the forecast area during
the evening Wednesday. A majority of both low-res and hi-res
guidance keeps areas south of I-70 within this favorable
environment, though details on exactly where the outflow boundary
sets up won`t be clear until Tuesday-Wednesday.

Delia

&&

.LONG TERM... (Thursday through Next Monday)
Issued at 227 PM CDT Mon Jun 16 2025

The mid-level trough associated with Wednesday`s cold front will
move east out of the region, leaving northwesterly mid-level flow
across the mid-Mississippi Valley Thursday as a ridge builds into
the area. At the surface, dry conditions and temperatures in the 80s
will make for a pleasant day. The aforementioned mid-level ridge
will continue to push into the area and by Friday low-level flow
will become southwesterly and warm air advection will kick off. Once
southwesterly flow becomes established on the western side of the
mid- and low-level ridges, the pattern is not expected to change
very much through the end of the period. Conditions will be largely
dry as we stay south of the favorable zone for ridge runners.

Temperatures will be the main concern going into the weekend as 850
mb temperatures climb into the low 20s, resulting in high
temperatures pushing well into the 90s area wide over the weekend.
This will be the first longer stretch of warm temperatures this
season. In places like St. Louis City where it hasn`t reached 90
degrees yet this year and folks aren`t used to these temperatures,
certain groups may be particularly at risk for heat related
illnesses. We`ll continue to monitor the forecast regarding the high
temperatures, but even if temperatures do not hit Advisory criteria,
conditions will be harmful for some groups.

Delia

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1234 PM CDT Mon Jun 16 2025

A stationary front is sneaking northward just south of the St.
Louis metro and showers are expected to develop along and north of
the boundary through the afternoon. Confidence in where these
showers will pop up across the metro is low, so have kept a
mention at PROB30. This threat will diminish through the
afternoon/evening and dry conditions will prevail for the
remainder of the period.

The front will continue to linger overnight and MVFR to IFR
stratus is expected along the front. Some guidance sources are
also hinting at visibility reductions from fog, but conditions are
not favorable for widespread fog. I expect we`ll see some fog in
the river valleys and low lying areas, but confidence in this
happening is not high enough to include a mention in the TAFs for
now.

Delia

&&

.CLIMATE...
Issued at 320 AM CDT Sun Jun 15 2025

St Louis still hasn`t reached 90 yet in 2025. This puts 2025 in
the Top 20 all time latest dates of the first 90 degree
temperature, and the latest in at least 30 years (Jun 19, 1995).
The all time latest first 90 degrees was July 4 in both 1961 and
1912. Records began in St Louis in 1874.

Columbia has also not yet seen a 90 degree reading in 2025. The
latest date of first 90 degrees on record was July 14, 1904.
Records began in Columbia in 1890.

Quincy reached 90 degrees on May 15 of this year.

Based on the current forecast, our next best chance to see 90
degrees is Tuesday, June 17.

Kimble/Pfahler


&&

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

$$

WFO LSX