Area Forecast Discussion

395
FXUS63 KLSX 152322
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
622 PM CDT Sun Jun 15 2025

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are expected through
  Wednesday, with some of the thunderstorms Tuesday night and
  Wednesday capable of becoming strong to severe.

- Confidence is high (90% or greater) that most, if not all, of
  the area will see afternoon temperatures reach 90 degree or
  greater by the end of next Sunday.


&&

.SHORT TERM...  (Through Late Monday Night)
Issued at 216 PM CDT Sun Jun 15 2025

The CWA is beneath weak northwesterly flow aloft as a shortwave
noted in water vapor imagery digs into the Mid-South. This wave`s
surface reflection can be seen in regional radar and satellite
imagery spinning over southwestern Missouri. As this surface
reflection drifts east-southeastward through the remainder of the
day, SBCAPE of around 1,500-2,000 J/kg ahead of it across
southeastern Missouri will allow for isolated showers and weak
thunderstorms where updrafts can overcome an inversion in the mid-
levels. Deterministic guidance varies in the strength and erosion
of this inversion through the remainder of the afternoon, so
confidence is medium in convection (40% chance or less). The better
chances (60%) for showers and thunderstorms comes overnight as
forcing from the shortwave and its surface reflection glance
southeastern Missouri and southwestern Illinois. Some deterministic
soundings show subtle hints at patchy fog across portions of the CWA
late tonight and early tomorrow morning, though cloud cover from the
passing wave is expected to limit sufficient surface cooling for
widespread fog development like the last couple of nights.

Tomorrow, the northern portion of the shortwave will drift eastward
into the Ohio Valley as it becomes sheared out. Enough lift will be
present over southeastern Missouri and southwestern Illinois to keep
the chance (50-70%) for scattered showers and thunderstorms going
through the afternoon. Cloud cover over this portion of the CWA will
keep temperatures in the low to mid-80s, with upper 80s expected
elsewhere in the CWA.

Elmore

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 216 PM CDT Sun Jun 15 2025

The extended forecast period will start out fairly active, with
multiple potential rounds of storms Tuesday through Wednesday. On
Tuesday, the aforementioned shortwave will become increasingly
elongated over the Southeast, as subtle upper-level ridging builds
into the Middle Mississippi Valley in its wake and ahead of a trough
digging across the Plains. Deep southerly to southwesterly flow will
boost temperatures and push afternoon highs to around 90 degrees for
much of the CWA for possibly the first time this year, with NBM
probabilities for 90 degrees or greater topping out around 90% for
portions of Missouri south of I-70. These temperatures will pair
with dew points forecast to reach the low 70s to produce SBCAPE
values of at least 2,500 J/kg during the afternoon per guidance
consensus. While this instability will wane somewhat during the
evening with the setting sun, confidence is high that the atmosphere
will remain sufficiently unstable as convection develops across the
Central Plains, congeals into a MCS, and tracks eastward toward
the CWA. The timing and track of this MCS is highly variable among
guidance, with faster solutions supporting it impacting the CWA as
early as Tuesday evening, and slower solutions not showing it moving
into the area until Wednesday morning. When the storms enter the CWA
will determine their ability to be strong to severe, with earlier
solutions having a greater potential to be severe thanks to higher
instability and shear earlier in the night.

What happens with this Tuesday evening to Wednesday morning MCS
dictates the parameter space present across the CWA when the
aforementioned trough pivots into the Upper Midwest and Great Lakes,
sending a cold front through the Middle Mississippi Valley. Along
and immediately ahead of the front during the afternoon, guidance
consensus is that deep-layer shear will be plentiful, with generally
40-45 kts shown. This is more than sufficient for rotating updrafts,
though the occurrence of such storm structures will hinge on if the
atmosphere can destabilize after the overnight or early morning
convection. If it can not, then the severe threat will be locally
lower and/or confined to small portions of the CWA. If instability
can build, the forecasted shear profile supports initially discrete
supercells that would quickly grow upscale into clusters or line
segments given deep-layer shear is roughly parallel to the cold
front. Hail would be the main concern, followed by damaging wind
gusts given relatively dry low-levels, though poor low-level lapse
rates may limit this threat to some degree. These lapse rates and
LCLs forecast to be at or just above 1 kft will limit a tornado
threat, and weak 0-3 km shear (20 kts) will restrict mesovortex
development in any line segments.

In the wake of the front on Thursday, deep northwesterly flow on the
backside of the trough will keep temperatures seasonable for the
last day in the foreseeable future. Friday into early next week,
guidance consensus is that an expansive ridge will build across
central and eastern portions of the CONUS, supporting sustained
warm air advection and pushing temperatures above 90 degrees (90%
chance or greater) this weekend.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 620 PM CDT Sun Jun 15 2025

A complex of thunderstorms and remnant showers will continue to
track east across southern Missouri overnight. This is spreading
rather thick high level clouds across much of the region. This
cloud cover, while well within VFR range, should be enough to
prevent strong surface cooling and any fog formation overnight.
Rain from this activity is expected to stay south of any of our
TAF sites. Some guidance suggests MVFR ceilings may spread into
the St Louis metro by morning, but confidence is low that this
will occur. Additional shower and thunderstorm development is
expected again tomorrow afternoon across southeast Missouri but
will remain south of the TAF sites.

Kimble

&&

.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.

Kimble/Pfahler


&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion