570 
FXUS63 KLSX 100725
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
225 AM CDT Wed Jun 10 2026

.KEY MESSAGES...

- Hot and humid conditions are expected through Thursday. 

- Strong to severe thunderstorms are expected this evening, with 
  the main threats being damaging wind gusts and large hail. 

- Another round of strong to severe thunderstorms will occur 
  along a cold front Thursday afternoon and evening. These storms 
  will be capable of damaging wind gusts, large hail, and 
  tornadoes.


&&

.SHORT TERM... (Through Thursday Night) 
Issued at 223 AM CDT Wed Jun 10 2026

Water vapor imagery shows an upper-level trough broadening across 
the Northern and Central Plains this morning. This trough will mute 
the upper-level ridge over the Middle Mississippi Valley today, with 
guidance consensus showing 850 mb temperatures cooling by a degree 
or two compared to yesterday. While this favors slightly cooler 
temperatures at the surface, southwesterly surface flow will provide 
a boost to temperatures via downsloping and adiabatic warming off 
the Ozarks. This will produce air temperatures a degree or two 
warmer than yesterday; however, the same process will also lower dew 
points. In the end, this will result in heat index values similar to 
if not a few degrees below what was experienced yesterday and below 
Heat Advisory criteria. 

Another heat-mitigating factor is the potential for convection prior 
to and during peak heating. As the trough draws closer to the CWA, a 
subtle disturbance within the southwesterly flow aloft will move 
northeastward across Missouri into northern Illinois from mid 
morning into the afternoon. Despite this being prior to peak heating 
and when instability will be maximized, there will be at least 2,500 
J/kg of SBCAPE per guidance consensus. Deep layer shear is expected 
to be around 30 kts, but updrafts may be slightly elevated with 
lower effective shear. The instability will be sufficient for at 
least small hail production in the strongest cores, and if the 
degree of forecasted shear is realized, there will be a threat for 
isolated large hail and damaging wind gusts across northeastern 
Missouri and west-central Illinois. Convective debris and/or outflow 
from this convection will reduce temperatures across this part of 
the area. 

The main concern for strong to severe storms will come later this 
evening as a cold front sinks south-southeastward into the region. 
There is some concern that the early-day convection may reduce 
instability and the atmosphere not be able to fully recover prior to 
late afternoon/early evening CI; however, there is a strong 
consensus among guidance that recovery will not be an issue and the 
environment will be plenty unstable. Around 4pm when CI is expected 
roughly across north-central Missouri and southern Iowa, 3,000-4,000 
J/kg of SBCAPE is forecast within the warm sector among 30-35 kts of 
deep-layer shear. The shear vectors will be nearly parallel to the 
front, leading to quick upscale growth as storms move into the CWA 
this evening. Clusters of multi-cells with embedded supercells will 
pose mainly a damaging wind and large hail threat. Low-level shear 
will be sufficient for tornadoes, though storm interactions and any 
supercells being short-lived limit this threat to bowing segments 
that can develop mesovortices. The area most favorable for these 
threats is northeastern Missouri and west-central Illinois along and 
north of Highway 36 and I-72. Convection is expected to drift east 
of the CWA by around midnight as the low-level jet veers, with a 
relative lull in activity then expected through Thursday morning. 

The aforementioned cold front will not make much progress south until 
a shortwave induces cyclogenesis along the boundary over the Central 
Plains during the day Thursday; swinging it through the Middle 
Mississippi Valley during the late afternoon and evening. With that 
frontal timing, there is a low to medium chance for dangerous heat 
across portions of the CWA, with potential cloud cover and 
uncertainty in FROPA specifics leading these confidence levels. 
Nevertheless, upwards of 3,000 J/kg of SBCAPE is expected ahead of 
the front with deep-layer shear once again being around 30kts. An 
inversion/capping around 700mb within the warm sector is expected to 
keep convection tied to the front, with the deep-layer shear vectors 
becoming increasingly parallel to the boundary as proximity to it 
increases. Both factors will favor clusters and/or a linear storm 
mode, with steep low-level lapse rates and DCAPE over 1,000 J/kg 
supporting primarily a damaging wind threat. Low-level shear of 20-
30 kts is favorable for a tornado threat, but a limiting factor may 
be slightly elevated LCLs. Convection will gradually weaken with 
southeastward extent as instability and shear decrease through the 
evening, with the front clearing the CWA as early as late evening to 
just after midnight.

Elmore

&&

.LONG TERM... (Friday through Tuesday) 
Issued at 223 AM CDT Wed Jun 10 2026

The consensus among guidance continues to be that zonal flow will 
persist over the Middle Mississippi Valley in the wake of Thursday's 
front. This flow and a weekend FROPA will keep temperatures at or 
below climatological normals through this portion of the period. 
This cold front will drift southward through the region Saturday 
into Sunday and serve as the focus for periodic rounds of rain 
through the weekend. Guidance diverges on how far south it makes it 
relative to the CWA before a shortwave enhances rain chances along 
it early next week. If the front is further south from the CWA, 
little to no rain can be expected. If it stalls just south of the 
CWA, rain chances will continue into early next week.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1039 PM CDT Tue Jun 9 2026

Dry and VFR flight conditions will continue under elevated
southwesterly winds through most of the TAF period. Winds will
become gusty Wednesday afternoon through the early evening before
diminishing with sunset.

Showers and thunderstorms will approach northern Missouri and
west-central Illinois tomorrow afternoon, with the best chance 
for rain at KUIN. However, there is a great deal of uncertainty in
when they will approach the region. Some guidance has an early 
round of rain as early as 17Z, though there is a lot of 
uncertainty in the location of this complex, which could miss KUIN
entirely. Most guidance has the main thrust of showers and 
thunderstorms moving through between roughly 00-05Z, and I've 
currently outlined the best chance in the TAF with a PROB30 group
for 00-03Z. Where thunderstorms form, brief MVFR visibility is 
expected.

Confidence is low in whether showers and thunderstorms will be
strong enough further south to impact the mid-Missouri (KJEF,
KCOU) and St. Louis metro (KSTL, KCPS, KSUS) terminals, I have
left the mention of TSRA out of these TAFs for now.

Delia

&&

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

$$

WFO LSX