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FXUS63 KLSX 241107
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
607 AM CDT Fri Apr 24 2026

.KEY MESSAGES...

-Showers and thunderstorms will exit the forecast area this morning,
and largely dry conditions are expected through Saturday.

-Next best chance for showers and thunderstorms will be Monday,
 with a 30% chance for severe thunderstorms during the afternoon
 and evening.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 409 AM CDT Fri Apr 24 2026

Showers and thunderstorms continue across much of the area ahead of
a cold front slowly moving through the mid-Mississippi Valley. The
showers and thunderstorms will largely exit the forecast area this
morning, though the cold front will be a bit slower as it is driven
by a shortwave within the leading edge of a mid-level trough
currently across south-central Canada. The shortwave will push the
cold front through the forecast area later today, and while an
isolated shower or thunderstorm is possible along the front this
afternoon, increasingly dry mid-level air will prevent more
significant re-development.

A surface high will push into the Great Lakes region Saturday behind
the cold front, keeping conditions dry with temperatures peaking 5
or so degrees above normal.

Delia

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 409 AM CDT Fri Apr 24 2026

Saturday into Sunday the mid-level flow will start setting the stage
for our next chance for active weather. The mid-level trough will
remain stationary over south-central Canada, while the southern
stream flow will spit several shortwaves out of the Four Corners
region. The most robust of these shortwaves will progress northeast
into the Central Plains Sunday afternoon, forming a surface low in
the lee of the southern Rockies at the same time. Strong moisture
return ahead of the surface low, building instability, strong shear,
and strong forcing along the associated dryline is expected to
produce some severe thunderstorms to our west across Kansas and
Oklahoma near the surface low Sunday afternoon and evening. As the
system progresses eastward into the forecast area during the
overnight hours, waning instability and moisture will limit the
potential for thunderstorms, let alone severe thunderstorms, but how
much so remains uncertain. As with the past several rounds of severe
weather, central and northeast Missouri will have the greatest of
this limited risk, reflected in the Day 3 severe weather marginal
risk.

The surface low will track eastward overnight, bringing a warm front
northward into the mid-Mississippi Valley during the morning on
Monday. Bolstered by an increasing low-level jet, moisture and
temperatures will increase across the forecast area. The cold front
associated with the low will push through the area during the
afternoon into the early evening. Thunderstorms are expected to form
ahead of and along the front as it moves through thanks to forcing
from the mid-level shortwave and the nose of the upper level jet.
While plenty of shear will exist to organize these thunderstorms (40-
50kts), instability remains the limiting factor. Showers and
thunderstorms from overnight Sunday may be ongoing Monday morning,
and how long they and their associated cloud cover linger will
impact how well we destable during the afternoon. The interquartile
spread of SBCAPE illustrates this well with a range from 500-2500
J/kg across much of the forecast area, and up to -150 J/kg of SBCIN.
Less cloud cover will result in greater destabilization and a higher
severe risk. We will continue to monitor these chances for severe
weather, but if the severe threat materializes all hazards will be
possible across the forecast area.

The system will exit the area Monday night, and a surface high will
push into the mid-Mississippi Valley in its wake. Through the
remainder of the work week a few features will dominate the pattern,
though with increasing uncertainty. The mid-level trough over
southern Canada will gradually shift eastward, though the mid-
Mississippi Valley will remain within the flow and reach of
disturbances. These will bring multiple chances for showers and
thunderstorms to the central CONUS. At the surface, high pressure
systems will flit around the region, and guidance shows several
different scenarios with regards to strength and location of these
highs. All this means that while there are additional chances for
showers and thunderstorms through the late week period, there is no
strong signal to latch onto at this time. Temperatures will remain
largely above normal through this period, though the potential for
rain and cloud cover introduces uncertainty into exactly how warm we
will get.

Delia

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 554 AM CDT Fri Apr 24 2026

Showers and thunderstorms are exiting the region with only
KSTL/KSUS/KCPS impacted by rain. KSUS and KCPS may be briefly
impacted by MVFR visibility as the heaviest showers move out of
the terminals, but confidence in them prevailing through the end
of the rain is low, so have relegated this mention to a TEMPO
group. Once this rain exits, dry conditions are expected to
prevail through the end of the period. There is only a 15-20%
chance of an afternoon shower or thunderstorm, but confidence in
this occurring, let alone at a specific terminal, is very low.

Across central Missouri patchy IFR/low MVFR ceilings are eroding,
and confidence is lowering that these lower ceilings will make it
into KCOU and KJEF before day time mixing lifts and breaks the low
cloud cover. Therefore, have kept the mention of low MVFR ceilings
largely out of the TAF.

As daytime mixing picks up and the cold front to our north pushes
through the area today the sky will lift and clear and winds will
become northerly. The front will move through the terminals
between the afternoon (KUIN/KCOU/KJEF) and the early evening
(KSTL/KSUS/KCPS).

Delia

&&

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

$$

WFO LSX