439
FXUS63 KLSX 081838
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
138 PM CDT Tue Jul 8 2025

.KEY MESSAGES...

- Scattered thunderstorms are expected to track southeast through
  the region today. A few thunderstorms could be strong, including
  the potential for isolated severe thunderstorms with winds gusts
  to 60 mph and locally heavy rain.

- Warm, seasonable temperatures will persist through the next
  several days along with periodic chances for thunderstorms
  impact the region.


&&

.SHORT TERM...  (Through Late Wednesday Night)
Issued at 138 PM CDT Tue Jul 8 2025

Thunderstorm potential will be the primary focus this afternoon
into this evening as an upper level trough and MCV (mesoscale
convective vortex) rotate southeastward through late this evening.
IR satellite shows a broad expanse of broken/overcast clouds
extending from northern MO through portions of IA/IL/WI. Clouds
are associated with the MCV, remnant of a convective complex that
developed over SD/NE last evening. Another area of clouds and
convection extend from eastern OK into southern IN. In between the
two areas, skies have remained mostly clear, allowing instability
to build ahead of the approaching MCV.

As of 18z, SPC mesoanalysis shows a what little CIN that exists
extending from Kansas City roughly just west of Quincy, IL. Where
skies have remained mostly clear, surface instability has climbed
with 2500 J/kg of SBCAPE roughly along and north of the I-44
corridor into southwestern IL along I-70. This not only jives
pretty well with guidance from prior runs, including this morning,
and maybe even on the higher end. HREF means showed SBCAPE of
2-2.2k with deterministic hi-rese guidance (RAP/HRRR) plotting
2.5-3k this afternoon. Moisture is no question with dewpoints in
the upper 60s to low-70s and PWATs around 1.7" per SPC
mesoanalysis. Thunderstorms will certainly have the moisture to
produce efficient rainfall with locally heavy rain, resulting in
ponding/nuisance flood in areas impacted by multiple cells. Though
soundings aren`t showing a particularly classic inverted-V,
50-100mb dewpoint depressions in the realm of 10-13C suggest
localized downbursts with marginally severe wind gusts (60 mph)
are possible. Hail cannot be entirely ruled out, but what does
fall is likely sub-severe with mid-level lapse rates at 5.5-6C and
competing updrafts as scattered convection become more numerous
in time.

Despite some slight spatial/temporal variability between
deterministic hi-res models, paintball plots (simulated reflectivity
>40 dBZ) show a general consensus that the best timeframe for
development runs from near KCOU to just south of KPPQ. IR satellite
is showing a notable uptick in development in this region,
increasing confidence that this will be the region for focused
initiation. Thunderstorms then move southeast through approximately
8-9 p.m. as thunderstorms progress southeast and weaken after
sunset.

Once thunderstorms clear to the southeast and dissipate late this
evening, clouds likely hang on for some time tonight before partial
clearing works into northeast MO. There is some hint at patchy fog
development running from central to northeast MO, but cloud cover
may not clear quick enough before sunrise, limiting fog potential.
This will be something to monitor through tonight, but even if fog
develops, it is not expected to be anything significant with the
limited time to take advantage of clearing.

By Wednesday, mostly dry conditions are expected with the low chance
that an isolated shower may develop. However, much of the potential
will reside outside the CWA. Should anything develop, the best
chance (30-40%) will line up along the southeast portion of the CWA
with chances quickly tapering to the north and dropping through the
day as surface high pressure builds in from the northwest.

Maples

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 336 AM CDT Tue Jul 8 2025

The LREF is showing that the upper pattern from mid week into early
next week will be highlighted by a large high over the southwest
CONUS with Missouri and Illinois on the southern edge of the active
westerlies.   While there will be on and off chance of showers and
thunderstorms over the Midwest as troughs move through the
aforementioned westerlies, the best chance (40-60%) over our area
will be Friday night into Saturday when there is good agreement in
the global models that a upper trough and attendant cold front will
move across Missouri and Illinois.  While the weekend does not look
like a washout, I can`t rule out heavy downpours with some of the
thunderstorms given PWATS around 2".

Temperatures through the period will be close to July normals
ranging from the mid 80s to around 90 degrees.  The NBM is showing
the warmest day on Friday when most areas will see highs in the low
90s and heat indexes near 100 degrees ahead of the front.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1232 PM CDT Tue Jul 8 2025

The primary focus will be the potential for showers and
thunderstorms this afternoon into this evening, a few of which
could be strong to marginally severe. The primary threats will be
locally heavy rain and gust winds, including isolated gusts
approaching 60 mph in the strongest thunderstorms. A few showers
have already developed around KUIN with potential trending
southward as more robust convection initialized across central and
east-central Missouri into southwestern Illinois. Considering the
slight difference in hi-resoultion guidance and scattered nature
of convection, TEMPO groups were utilized to convey the period of
greatest impact. This may be adjusted in later amendments should
initialization of activity be departed from current thoughts. The
strongest cells are likely to result in MVFR ceilings/visibility
for brief periods.

Outside of the thunderstorm potential, VFR conditions are
expected. A few showers and thunderstorms may linger into this
evening, but generally speaking, thunderstorms will move south of
the terminals and weaken after sunset. Light/variable surface
winds will persist into Wednesday.

Maples

&&

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

$$

WFO LSX