743
FXUS63 KLSX 270657
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
157 AM CDT Mon Apr 27 2026

.KEY MESSAGES...

- While periods of storms are expected through Monday morning, the most
  potent thunderstorms will occur this afternoon and evening.

- Thunderstorms this afternoon and evening will be capable of
  damaging wind gusts, large hail, and strong tornadoes.

- A period of cool, calm weather is expected mid-week through the
  weekend.

&&

.SHORT TERM... (Through Tuesday Night)
Issued at 155 AM CDT Mon Apr 27 2026

Storms across southeastern Missouri continue to butt up against an
instability gradient draped from north to south across Missouri.
The warm air advection feeding these storms will also push greater
instability slowly northeastward through this morning, though
propagation vectors will favor convection continuing to move east-
southeastward generally away from the CWA or into an unfavorable
environment. Additionally, the low-level jet refocusing across
Kansas will continue to support the downward trend in convection
across southeastern Missouri early this morning. Any linger storms
over the next couple of hours will be capable mainly of large hail,
though there is also a very low damaging wind and tornado threat for
storms that remain surface based.

Our attention turns to the storms over eastern Kansas that are
propagating eastward with the nose of the low-level jet. With the
nose of this low-level jet edging into northeastern Missouri later
this morning, the focus for these storms will spread into portions
of the CWA north of I-70. Vertical thermal profiles suggest that this
convection will be elevated, mitigating a threat of damaging wind
gusts and/or tornadoes. However, with around 40 kts of effective
shear and building MUCAPE, there is a low chance for isolated
instances of large hail.

How long this convection lingers is uncertain, although guidance
trends have been toward a lull in convective activity in the wake of
this convection and that associated with a cold front during the
late afternoon and evening. Ahead of the front, the warm sector
remains capped through much of the afternoon per a majority of
deterministic soundings. Although, any remnant outflow or
differential heating boundary from early day convection may serve as
enough of a forcing mechanism to spawn discrete convection during
the afternoon as lift from an approaching shortwave increases over
the region. If this convection does form, it will be in an
environment characterized by 2,000-2,500 J/kg of SBCAPE and roughly
50 kts of deep-layer shear. This will favor supercells capable of
all hazards, with long curved hodographs favoring strong tornadoes,
especially if storms are able to latch on to any remnant boundaries
across the CWA.

Where the environment isn`t contaminated from earlier rounds of
convection, additional updrafts are expected along the cold front as
it enters the area 4-5pm. Forcing from the front paired with lift
from the shortwave will lead to numerous updrafts along the front.
While this will be occurring within a similar environment detailed
prior, the number of updrafts paired with them occurring along the
front may lead to destructive interactions and congealing into line
segments and/or clusters. While this will tend to limit a strong
tornado threat, storms will still be capable of all severe hazards.
Convection is expected to depart the CWA with the front by 9-10pm.

Even with the FROPA Monday evening, the threat for convection will
continue on Tuesday. Guidance consensus has the front stalling just
south of the CWA early Tuesday and then buckling northward as a
shortwave moves through the Central Plains and into the Midwest
through the day. This shortwave will send a subtle surface
reflection through the Mid South along the front, with a brief
period of warm air advection that will help force elevated
convection for areas mainly along and south of I-70. If the front
can move northward enough, shear profiles and instability amounts
favor supercells capable primarily of large hail across far
southeastern Missouri during the afternoon. Waning instability and
the front continuing southward will bring an end to rain chances
during the evening.

Elmore

&&

.LONG TERM... (Tuesday Night through Sunday)
Issued at 155 AM CDT Mon Apr 27 2026

Both deterministic guidance and ensemble clusters keep upper-level
troughing slowly moving eastward over the eastern CONUS through the
long range forecast period. This will maintain northwesterly flow
over the Middle Mississippi Valley through Saturday as several
rounds of high pressure pass through the region. As a result,
temperatures will run at or below climatological normals into the
weekend and mostly dry weather is expected.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1231 AM CDT Mon Apr 27 2026

Light to moderate rainfall with occasional lightning strikes are
expected at the local terminals through the first several hours of
the TAF period. Thunderstorms currently over Kansas will continue
eastward overnight and through the early morning hours, impacting
KCOU, KJEF, and KUIN during the mid morning hours. There is a low
chance that these storms also impact KSUS, KSTL, and KCPS too,
but confidence is currently greater that they will stay north of
these sites. Yet another round of storms is expected during the
late afternoon and evening along a cold front. These storms will
have the potential to produce hail, erratic strong winds, and
tornadoes. They will be moving quickly, and their window of impact
be much more narrow than the current forecast, which is wider due
to timing uncertainty.

Elmore

&&

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

$$

WFO LSX