210
FXUS63 KLSX 122337
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
637 PM CDT Thu Jun 12 2025

.KEY MESSAGES...

- Widespread showers and a few thunderstorms will plague much of
  the region tonight through the first half of the weekend,
  bringing some locally heavy rainfall.

- Our first run of temperatures in the 90s looks likely for the
  middle of next week.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 1242 PM CDT Thu Jun 12 2025

A slow-moving upper level low will be the main focus of the short
term period. Latest satellite and radar imagery show widespread
cloudiness, with a few showers affecting central MO. Forcing for
ascent ahead of a northward moving vorticity lobe rounding the
upper-level low will keep the best threat of showers in central
and northeast MO through the rest of the day into this evening.
Instability has been limited due to the widespread cloudiness, but
can`t completely rule out an isolated storm in central/northeast
MO through this evening.

Attention turns to the southwest overnight as the main upper-level
low meanders over the region. A weak surface reflection will
bring enhanced low-level convergence, coupled with the forcing
from the low aloft, resulting in fairly widespread showers
overnight into early Friday. Therefore, I have upped pops from
the previous forecast.

Coverage of showers will wane a bit late Friday morning, which
might allow for some limited diurnal heating by early Friday
afternoon (through a thick cirrus shield and a broken lower cloud
deck). Even with the limited heating, we should realize around
500-1000 J/kg of MLCAPE which should be just enough to promote a
few more robust showers and some scattered storms. With fairly
deep warm cloud depths, these showers will be pretty efficient
rain makers. In fact, the HREF LPMM suggests some isolated
locations may see up to two inches of rain. That being said, they
should be moving enough to not cause too many widespread concerns
for flooding. Nothing severe is expected given very poor lapse
rates and weak deep-layer shear.

Coverage should wane a bit from west to east Friday night as the
upper level low continues to meander to the east and the loss of
diurnal instability should limit thunderstorm chances, but showers
will likely persist especially in IL.

Deitsch

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 1242 PM CDT Thu Jun 12 2025

The pesky upper-level low will finally begin to rotate off to the
east by Saturday. That being said, lobes of vorticity will continue
to rotate around the backside of the low, keeping enough upper-level
ascent in place to foster showers in our Illinois counties, with
less coverage expected the further west you go into Missouri
(especially by the afternoon/evening). Given the deep, saturated
soundings, lapse rates are quite poor thus instability is limited.
That being said, a few lightning strikes are possible here and there
as showers bubble just deep enough to initiate ice and charge
separation. Given deep warm cloud depths, any shower will be
efficient rain makers but I think there will be enough breaks in
between rounds of showers to limit any flood potential.

The upper-level low will finally push well to the east by Sunday. As
it stands now, Sunday looks like a generally dry day. However, with
temperatures warming back into the mid 80s, enough instability will
be around and there are some hints of a subtle wave moving around
the backside of the departing low which could be just enough to
spark a few isolated showers/storms in a generally uncapped
environment.

The pattern turns more zonal, and then more southwesterly aloft
through midweek next week. This will allow for generally warming
temperatures, along with at least some threat of shower/storm
complexes. The most favored times for these complexes look to be
late Sunday/Monday morning, and then again Tuesday night into
Wednesday. That being said, timing out these threats in a zonal flow
pattern are notoriously challenging, so these windows are likely to
change. The severe threat looks fairly low through Monday, but the
mid/upper level flow does increase a bit by midweek thus I think the
potential for some more organized convection exists Tuesday night
and beyond. This increasing threat is supported by the NCAR/CSU ML
guidance.

I also think our run at dodging the heat is likely to come to an end
next week. The latest ensemble guidance suggests highs likely to
exceed 90 degrees (70-80% chance) by Tuesday into Wednesday of next
week. This will push heat index values well into the 90s, perhaps
approaching 100 degrees at times next week (depending on storm
timing).

Deitsch

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 634 PM CDT Thu Jun 12 2025

A slow moving area of low pressure will gradually track toward the
region from the southwest spreading showers and perhaps a few
thunderstorms across the area. These showers become more numerous
overnight and into the day on Friday with ceilings gradually
lowering to MVFR or perhaps even IFR through the morning. While
showers are expected, confidence in thunderstorms is considerably
lower. If any breaks in the clouds can form on Friday, then better
instability will develop and lead to more thunderstorms in the
afternoon.

Kimble

&&

.CLIMATE...
Issued at 620 PM CDT Wed Jun 11 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 around June 17.

Kimble


&&

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

$$

WFO LSX