River Flood Warning 90, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
623 PM CDT Sat Jun 13 2026

.KEY MESSAGES...

- A few strong to severe thunderstorms are possible through the
  early overnight hours with damaging winds the main threat.

- Cool and dry conditions are forecast behind the cold front
  before chances of showers and thunderstorms return midweek.

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 233 PM CDT Sat Jun 13 2026

Ongoing showers and thunderstorms have continued all day, thanks
in large part to a very persistent 25+ knot southwesterly low-
level jet. This activity along with the thicker debris clouds have
helped keep our entire area quite a bit cooler (and more stable)
than expected this time yesterday. More importantly, two separate
complexes of showers and thunderstorms have each sent out
composite outflow boundaries. One is currently just south of the
Missouri-Arkansas border and moving southeast with time. Another
outflow boundary is draped across northeast Kansas and northwest
Missouri. Initial convective initiation has just started along
this boundary as it has stalled over the past hour. As these
thunderstorms develop and push southeast, they may tend to weaken
by early this evening as they enter a less unstable air mass
across central (and northeast) Missouri. These locations have seen
at least some rain and plenty of cloud cover. Latest SPC
mesoanalysis shows 500-1000 J/kg of MLCAPE, but upstream
satellite/radar imagery shows either thicker clouds (in C MO) or
thunderstorms (NE MO). Therefore, it seems doubtful there will be
too substantial air mass recovery over the coming hours. CAMs
have struggled much of the day with scattered
showers/thunderstorms north of southeast Missouri. Therefore, it
seems quite unlikely that the 2500+ J/kg of MLCAPE by 0Z forecast
from the RAP/HRRR will actually come to fruition given their poor
initializations. Finally, the synoptic cold front is still located
well to the northwest across southeast Nebraska and southwest
Iowa. Both the HRRR and WoFs suggest some development along the
front near the Nebraska-Kansas border by ~22 UTC. This makes sense
conceptually given that this is where the strongest low-level
convergence resides. Those initial storms are likely to be
supercells with large hail the primary threat. Damaging winds will
become a bigger concern as storms head into eastern Kansas/far
western Missouri. This may sound like a theme, but similar to
earlier foci for (severe) thunderstorms, these too should stay to
our west, though I cannot completely rule out a strong/severe
storm clipping parts of central Missouri very late this evening.
Our main region of interest will be further northeast along the
front. I do think at least some scattered thunderstorms will
develop along the front upstream of northeast Missouri by early
this evening, but the coverage should be less due to weaker
surface convergence along the boundary. In addition, storms as
they head southeast may have a tendency to weaken as they enter
our region due to poor timing (late evening/early overnight) and
an overall more hostile environment due to the antecedent
showers/storms mitigating diurnal instability. Summing all of this
up, the confidence in severe weather in our area overall has
decreased quite a bit. A few of the storms in our area may be
strong to severe, but the chances of widespread severe weather
have decreased substantially. The main threats with any
thunderstorms through the early overnight hours would be damaging
winds and locally heavy rainfall. Regarding the rainfall threat,
areas that have been heavily impacted over the past several days
(i.e., parts of northeast Missouri and west-central Illinois)
would be the main areas of concern.

Gosselin

&&

.LONG TERM...  (Sunday through Next Saturday)
Issued at 233 PM CDT Sat Jun 13 2026

(Sunday - Monday Night)

Behind tonight's synoptic cold front, much cooler and less humid air
will infiltrate the mid-Mississippi Valley. Temperatures are still
forecast to run about 10 degrees below normal day and night, with
highs in the mid to upper 70s and lows in the 50s.

(Tuesday - Next Saturday)

After a day ~60 hours across the region, we are still on track for a
return of chances for showers and thunderstorms starting as early as
Tuesday. This is when the first of two cold fronts is expected to
move across the bi-state area. With this first front, surface
convergence is fairly weak along the boundary with the stronger
mid/upper level forcing for ascent residing farther to the northeast
across the Great Lakes. In addition, moisture return ahead of this
front looks modest. Probabilities for 1500+ J/kg of SBCAPE from the
GEFS/GEPS only top out around 10-20% for parts of the area.

The following frontal passage will be of more concern. There remains
some timing/track differences with the midlevel shortwave trough
coming through the Upper Midwest and its corresponding surface low
track. The most likely scenario is for a warm front to be draped
just to our north, with widespread showers/thunderstorms near this
feature during the day on Wednesday. The trailing cold front is then
expected to move through our neck of the woods Wednesday night
through Thursday and provide our best chances (60-80%) of showers
and thunderstorms. Given the anomalous deep-layer shear, this should
yield another chance of organized convection via strong/severe
thunderstorms. However, as we have seen a few times now the past
several days, everything is nuanced and mesoscale features are key.
These cannot be predicted several days in advance. One main concern
this far out is the instability/moisture return. There is a large
degree of spread (~2000 J/kg) in the IQR of SBCAPE from the
GEFS/GEPS. Higher instability along with a quicker frontal timing
could yield a high threat for widespread severe weather while the
lower instability scenario and/or a later frontal timing may yield
more in the way of typical summertime thunderstorms.

The frontal speed is quite slow, not likely clearing the southern
CWA until sometime late Thursday. This means that high chances (40-
70%) of showers and thunderstorms continue through much of the day
Thursday, and only gradually shift out from northwest to southeast.
A slow moving front and a prolonged period of showers and
thunderstorms may also portend to a flash flood threat. The good
news is (at least at this time) that model precipitable water values
are expected to be not too high above normal (~1.4-1.7"; ~75th
percentile). A welcome 2-3 day break from any rain also will help
the soils at least dry out slightly and smaller tributaries to
recede.

Behind Wednesday night/Thursday's cold front, ensemble spread has
decreased slightly with respect to the incoming air mass later in
the week. Temperatures should return back to near, or even slightly
below, normal. Dry weather is also favored to end the work week.

Gosselin

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 620 PM CDT Sat Jun 13 2026

VFR conditions are expected at the start of the period, but
terminals are likely to be impacted by showers and thunderstorms
late this evening and overnight for a brief period. This is most
likely at COU/JEF/UIN, with lower confidence at St. Louis area
terminals although there will likely be at least some rain.
Visibility reductions due to heavy rain and erratic, gusty winds
will be the main hazards. Low ceilings are also possible during
storms, and a few hours of MVFR to briefly IFR stratus may follow
these storms as a cold front passes through the area overnight.

Skies are expected to clear quickly in the morning, and breezy
northwest winds are expected to persist the remainder of the
period.

BRC

&&

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

WFO LSX