426
FXUS63 KLSX 020759
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
259 AM CDT Sat May 2 2026

.KEY MESSAGES...

- Multiple rounds of showers and thunderstorms are expected across the
  area Monday-Wednesday.

- The chance for strong to severe thunderstorms and heavy
  rainfall Monday-Wednesday is very low.


&&

.SHORT TERM... (Through Sunday Night)
Issued at 250 AM CDT Sat May 2 2026

Water vapor imagery this morning shows the axis of a shortwave
moving into the Middle Mississippi Valley. Its associated weak
surface reflection and associated scattered, light rainfall is
moving into the Ohio Vally, dragging a subtle cold front with it.
In the wake of this front, high pressure will settle into the
region providing yet another day of relatively calm weather and
below normal temperatures. The high will scoot eastward this
evening and tonight, with weak southerly flow returning to the
region. This will help overnight lows from dropping as cool as
this morning`s, limiting a low chance for frost to protected,
low-lying areas in the Ozarks.

With southerly low-level flow in place, warm air will advect into
the CWA on Sunday, providing about a ten-degree bump in
temperatures compared to those expected today. The southerly flow
will provide limited moisture return ahead of a weak cold front
sagging southward into the Middle Mississippi Valley during the
afternoon and evening. Both REFS and HREF means support
1,000-1,500 J/kg of SBCAPE ahead of this front, with pockets of as
much as 2,000 J/kg. However, a majority of deterministic
soundings show a strong inversion/capping across the warm sector,
with a majority of these hi-res ensemble membership remaining
convection free during the daylight hours. Those members that do
produce convection do so as a subtle shortwave moves overhead
during the late evening, which is when instability is expected to
be quickly diminishing. Therefore, the chance of strong
thunderstorms forming, let alone showers and weak thunderstorms,
is very low. We will continue not to message the Day 2 SPC
Marginal Risk.

Elmore

&&

.LONG TERM... (Monday through Friday)
Issued at 250 AM CDT Sat May 2 2026

To start the workweek, an upper-level trough will be nearly
stationary and stretching from the Northern Plains, through the
Midwest, and into the Northeast. This will place the Middle
Mississippi Valley beneath subtle northwesterly flow in which
another cold front will slowly sag southward toward the region
through the day. Ahead of the front, strong southwesterly low-
level flow will advect warm air into the region, boosted by
downsloping from the Ozarks. This favors above normal
temperatures, with ensembles clustering in the upper 70s to around
80 degrees during the afternoon.

Meager moisture return will combine with this warmth to yield 1,000-
2,000 J/kg of SBCAPE per guidance consensus; however, confidence in
this magnitude of instability is low. Models typically don`t handle
the degree of warmth and dryness the CWA experiences beneath
southwesterly low-level flow, and if that is the case on Monday,
then forecasted instability may be too high. Regardless, guidance
is converging on an evening or overnight FROPA, which will serve
as the main forcing mechanism for convection. There is a low
chance that WAA could yield convective initiation during the
afternoon, but deterministic soundings show capping and varying
degrees of lift. Even during the evening, some degree of capping
remains in place over the warm sector.

As the front slowly sags through the region Monday night through
Wednesday, a series of upper-level disturbances will ripple along
it, producing multiple rounds of rainfall. As a shortwave digging
equatorward along the western periphery of the trough phases with
a cutoff moving eastward off the California Baja, the front will
be shunted far enough south-southeastward to bring an end to rain
chances late Wednesday. The orientation of the front, its
progression, and the involvement of a cutoff all introduce a lot
of uncertainty in specifics on rainfall timing and amounts despite
guidance consensus, which is likely underdispersive. Even so, the
general pattern is not favorable for widespread severe weather,
supported by ML/AI guidance, and is also not ideal for heavy
rainfall. Even so, any rainfall in key river basins may exacerbate
ongoing minor flood conditions on local rivers and streams.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1049 PM CDT Fri May 1 2026

Light winds overnight increase a bit out of the NNW tomorrow
morning. Another round of afternoon cumulus is expected. Conditions
remain VFR through the entire forecast period.

Kimble

&&

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

$$

WFO LSX