Severe Thunderstorm Warning 156, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1118 PM CDT Sun May 31 2026

.KEY MESSAGES...

- Thunderstorms are forecast across much of the region overnight
  tonight through early Monday morning. A few storms may be
  strong to severe with damaging winds, large hail, and locally
  heavy rainfall.

- Dry weather is expected Tuesday through Thursday along with near
  normal temperatures.

&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 300 PM CDT Sun May 31 2026

Showers and thunderstorms in southeast Missouri continue to move
southeast along/behind a composite outflow boundary. The
environment downstream is characterized by moderate to high
instability (>2000 J/kg SBCAPE), but less than 20 knots of
effective shear. Not surprisingly, individual updrafts have ebbed
and flowed with most of the activity staying subsevere. Individual
cores are having a difficult time staying tied to their outflow
boundaries. Once they get well behind the outflow, the updraft
weakens and the storm gradually diminishes with time. That being
said, one or two may produce wind gusts to 60 mph or hail to the
size of quarters over the next few hours, but organized severe
thunderstorms are not expected. Further north, mostly dry weather
is favored for the remainder of the afternoon and most of the
evening.

Isolated to scattered showers and thunderstorms may form within a
couple hours after dusk as the nocturnal low-level jet strengthens.
However, more numerous storms should develop near the Missouri-
Kansas border and move east/southeast with time overnight tonight
into early Monday morning. The low-level jet itself (and its
associated moisture convergence) is not particularly strong, only on
the order of about 20-25 knots. This should be enough to ramp up the
coverage of showers and thunderstorms, but probably does lessen the
overall threat for heavy rainfall/flash flood potential. The short-
fused hydrological threat should stay confined to areas that have
seen significant rainfall over the past 48+ hours (mainly
Moniteau/Boone counties), and if these areas likely would need to
see at least some training. The low-level jet does veer more to the
west, so that is possible, but uncertain where that would occur.
Therefore, have elected to not issue a flash flood watch for
portions of central Missouri at this time, but that will be an area
we will have to watch overnight given the wet antecedent conditions.
There is also a marginal severe threat overnight with 2000+ J/kg of
MUCAPE and 20-30 knots of effective shear. Hail up to the size of
quarters and gusts to 60 mph will be the main threats, though hail
may become more of the predominant threat late tonight as model
soundings show a deepening inversion. Elevated convection can
certainly produce wind damage, but it does get tougher the deeper
your stable boundary layer becomes.

Storms will be ongoing Monday morning, most likely across southeast
Missouri. They should exit quickly off to the southeast. The rest of
the day is expected to be dry, assuming we do get fairly widespread
showers and thunderstorms that move through the area and exit Monday
morning. That should help push the effective front to our south,
with additional development in an area of weak surface convergence
more likely closer to the Missouri-Arkansas border. Did keep 20-30%
PoPs in southeast Missouri however for Monday afternoon in case the
aforementioned preceding round of convection is not as widespread as
forecast.

Gosselin

&&

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 300 PM CDT Sun May 31 2026

(Monday Night - Thursday)

A backdoor low-level cold front will finish pushing through the mid-
Mississippi Monday night, with a real air mass change expected.
Seasonably cool nights (lows in 50s) along with near normal highs
(low 80s) are forecast along with plenty of sunshine.

(Thursday Night - Next Sunday)

Moderating temperatures are forecast late this week as low-level
winds turn out of the southwest behind a departing surface ridge
axis. Ensemble guidance is in fairly good agreement that the
mid/upper level ridge axis will weaken and shift slightly east
Friday into Saturday, which may allow a cold front to drop into
portions of the area and bring a chance (30-50%) of showers and
thunderstorms. Given the southwest flow aloft across the
southeastern CONUS, this front is more likely than not to stall out
as well and prolong the threat for showers and thunderstorms
at least through the remainder of next weekend.

Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1106 PM CDT Sun May 31 2026

The focus for impacts this period continues to be showers and
thunderstorms through this morning. The main corridor for these
showers and thunderstorms will stretch from near KCOU and KJEF
east-southeastward through KSUS, KSTL, and KCPS. KUIN has a low
chance of being grazed by this activity, though confidence in this
occurring is dwindling. Storms will be capable of heavy rainfall
that will reduce visibilities to MVFR and even IFR flight
categories, and there is a very low chance for gusty, erratic
winds and small hail at KCOU and KJEF. Showers and thunderstorms
will move south of the local terminals by mid morning, with
confidence high in VFR flight conditions through the remainder of
the day.

Elmore

&&

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

WFO LSX