668
FXUS63 KLSX 030739
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
239 AM CDT Sun May 3 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected this evening
  mainly along the I-70 corridor.

- Additional scattered showers and thunderstorms are forecast Monday
  night, with periods of rain expected then through Tuesday
  night.


&&

.SHORT TERM... (Through Monday Night)
Issued at 237 AM CDT Sun May 3 2026

The main focus for the short term forecast period is a series of
cold fronts sagging southward toward the CWA. The first front will
drift toward the CWA tonight. Ahead of it, low-level southwesterly
flow will have boosted temperatures through the day compared to as
of late, and provided very limited moisture return. This will yield
upwards of 1,000 J/kg of SBCAPE by mid evening per the REFS and HREF
means among robust deep-layer shear (50-60 kts). Then, weak forcing
via the front and lift from a subtle shortwave and the low-level jet
will allow for isolated to scattered showers and thunderstorms to
develop. Given the timing, instability will be quickly waning,
leading to a very narrow window for strong updrafts to develop. A
still relatively dry boundary layer decreases confidence in robust
updrafts, and a majority of what instability is available is
elevated. This limits effective bulk shear to around 30 kts. All
that to say that confidence remains very low in storms becoming
strong to severe. If a storm does reach severe criteria, hail up to
1" in diameter is the greatest hazard, followed by an isolated
occurrence of damaging wind gusts. Given this threat is highly
conditional, we will continue not to message the SPC Day 1 Marginal.

Tonight`s front will wash out early Monday morning, with our local
airmass experiencing no impact from it. This will keep the door open
for warm, moist air to continue advecting into the CWA, keeping our
warming trend going and allowing for better moisture return on
Monday. The result will be upwards of 2,000 J/kg of SBCAPE per the
HREF and REFS ahead of a deepening upper-level trough sending
another cold front through the Midwest. Deterministic soundings show
capping within the warm sector through the afternoon into the
evening, supported by a dearth of convection in the CAMs. Better
forcing that will allow for scattered convection is expected along
the front, though the front`s timing relative to CI is uncertain. If
the front is closer to the CWA Monday evening when storms form,
storms will have a greater chance of being discrete and capable
mainly of large hail and secondarily damaging wind gusts. If the
front is further north of the CWA when storms form Monday evening,
then upscale growth prior to storms entering the CWA and little to
no severe threat is expected due to destructive interactions thanks
to the low-level jet oriented nearly parallel to the front and
forcing being tied mainly to the front itself. The low-level jet
will continue to feed moisture to the front, leading to widespread
rainfall along and behind the front Monday night.

Elmore

&&

.LONG TERM... (Tuesday through Saturday)
Issued at 237 AM CDT Sun May 3 2026

The cold front will continue sinking southward on Tuesday, as the
low-level jet and deepening trough aloft force continuing rain
chances through the day. To what extent through the day depends on the
speed of the front, with a faster front supporting rain chances
ending sooner in the day, while a slower front would yield rain
chances lingering into Tuesday night. Given the spread in solutions,
confidence in either scenario is low.

As the trough deepens further aloft, an embedded shortwave digs into
the Plains as a cutoff drifts eastward across the Southwest.
Guidance has unsurprisingly varied in the phasing of this cutoff
with the aforementioned shortwave, and how this phasing occurs will
impact the strength of the shortwave as it passes through the
Midwest Wednesday into Thursday. There is a low chance (30%) that
this wave is potent enough to briefly induce cyclogenesis over the
Plains and provide additional rainfall to portions of the
CWA Wednesday night.

Both deterministic guidance and ensemble clusters show the upper-
level trough remaining over the eastern CONUS through Saturday,
maintaining northwesterly flow over the Middle Mississippi Valley.
This will keep temperatures around seasonal normals through
Saturday, supported by ensemble means.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1038 PM CDT Sat May 2 2026

Light winds and a clear sky is expected overnight, with winds
turning southerly by morning. A few showers and thunderstorms are
expected Sunday evening. Although there`s at least some chance of
this occurring anywhere, the most likely area to be affected
includes the St Louis metro late Sunday evening.

Kimble

&&

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

$$

WFO LSX