024
FXUS63 KLSX 130337
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1037 PM CDT Fri Jun 12 2026

.KEY MESSAGES...

- Thunderstorms are possible Saturday morning across portions of the
region. The severe weather threat with these is low.

- Additional thunderstorms are expected along a cold front Saturday
evening. These will have a greater threat for damaging winds.

- Below normal temperatures and dry conditions are expected Sunday
into early next week.


&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 224 PM CDT Fri Jun 12 2026

A weak area of high pressure is currently situated across eastern
Missouri and will quickly slide eastward into the Ohio Valley
tonight. Low-level winds will turn out of the south/southwest,
with increasing mid/high level clouds ahead of a midlevel
disturbance moving eastward out of the south-central Plains.
Surface winds turning out of the south along with the
aforementioned increase in clouds are expected to stunt the
temperature drop overnight, with lows mainly in the low to mid 60s
(close to seasonal averages). Dry conditions are forecast for the
most part overnight, though some low chances (20-40%) of showers
and thunderstorms return to parts of central/southeast Missouri
toward daybreak Saturday as low-level moisture convergence
increases.

Better chances (40-60%) for showers and thunderstorms hold off until
after sunrise Saturday morning as storms are likely to move in from
the west. There is some uncertainty on the timing as some CAMs have
pretty high coverage early in the morning whereas others actually
move an MCV in later in the day toward southeast Missouri. Any
activity early in the morning should be elevated, at least
initially, with hail to the size of quarters possible in the
strongest cores. The low-level jet does not abate at all during the
day, so the expectation is for any ongoing showers and thunderstorms
Saturday morning to at the very least percolate into the early
afternoon hours. In fact, moisture convergence actually strengthens
throughout the day on deterministic models, with the nose of the jet
focused on southwest/south central Missouri. Storms may try and get
more surface-based with time, which would also increase the risk for
damaging winds in a multicellular clusters/line segments that manage
to get a consolidated, balanced cold pool. This threat likely would
be higher in the scenario where an MCV moves toward southeast
Missouri more toward midday/early afternoon. The best chances for
severe weather (and thunderstorms in general) are a bit further to
our southwest where the low-level moisture convergence should be
stronger and where higher instability is likely to be located. In
addition to the possible strong to severe thunderstorms, locally
heavy rainfall may be a threat. There is some concern for training
of thunderstorms in an environment with increasingly deep warm cloud
depths and high precipitable water values (~1.80"; >95th percentile
of climatology). This area of the CWA has largely missed out on the
rainfall over the past 72 hours. In fact, MRMS pass 2 72-hour totals
are largely in the 0.10-0.50" range. Therefore, while antecedent
conditions are not exactly "dry", they aren`t nearly as susceptible
as parts of northeast Missouri/west central Illinois where 4-8" of
rain has fallen. With the best threat for sustained, robust
convection staying to our southwest, will hold off on a flash flood
watch. The LPMM from the 12Z HREF only shows some isolated pockets
of 1-2" of rain through Saturday afternoon across central/southeast
Missouri. While I could not rule out some higher totals if there is
sustained training, even 2-3" over a 3-hour period is largely less
than the latest flash-flood guidance.

Attention heading toward the early evening will shift northwestward
toward an approaching surface cold front. At least scattered showers
and thunderstorms should develop along the boundary across northwest
Missouri into southeastern Iowa. The higher coverage (and likely
better chance of severe) of thunderstorms may stay to our west where
surface convergence is greatest. How much instability will reside
across our northern counties is a bit uncertain for early Saturday
evening, not so much due to the earlier convection (which should
stay well to the south), but due to spread with respect to the
moisture return ahead of the boundary. The IQR spread for
instability in northeast Missouri/west central Illinois is around
1000-2000 J/kg on the 12Z HREF centered on 7PM Saturday evening. So,
while there is high confidence in sufficient deep-layer shear (35-
40+ knots) for organized strong-severe convection, there is a lot
less confidence in instability. In addition, as alluded to above,
the stronger surface convergence is very likely to reside well to
our west moreso across eastern Kansas. While there is still likely
enough surface convergence for at least some convective initiation,
as we saw yesterday, weaker surface convergence does lead the
severity of the storms more into question. Storms may tend to be
more outflow dominant once again, which may tend to keep winds more
on the subsevere side. Speaking of winds, that does look to be the
primary threat for most of the area, though large hail is certainly
possible through early evening across portions of northeast Missouri
and west-central Illinois. Those locations also may have a brief
flash flood threat given the susceptibility, but overall storms
should be quite progressive. Initial storms should be supercells
given the mostly orthogonal component of the deep-layer shear vector
to the cold front. Storms should tend to grow more upscale due to
the moderately strong linear forcing along the front. With time,
storms should tend to weaken through the night as deep-layer shear
weakens and storms are likely to head into a more hostile (i.e.,
less instability) environment. Parts of east central and southeast
Missouri as well as southwest Illinois are more likely to be
impacted by earlier convective activity.


Gosselin

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 224 PM CDT Fri Jun 12 2026

(Sunday - Monday Night)

Behind Saturday night`s cold front, much cooler and drier air will
infiltrate the mid-Mississippi Valley. The incoming air mass looks
particularly strong for this time of year, characterized by 850-hPa
temperatures below +10C (~5th percentile), anomalous surface high
pressure (~1020 hPa; >90th percentile), and low dewpoints (50s;
~10th percentile). Not surprisingly, a period of well-below normal
temperatures is expected with this air mass along with dry weather.
Highs in the 70s with lows in the 50s are forecast. These values
would be about 10 degrees below normal for the middle of June.


(Tuesday - Next Friday)

Ensemble guidance is in fairly good agreement with respect to the
synoptic pattern across the CONUS through much of next week.
Mid/upper level northwest flow will remain entrenched across the
eastern two-thirds of the US, with multiple midlevel shortwave
troughs moving quickly across the Upper Midwest. This means multiple
cold frontal passages for our neck of the woods, and timing these
features is a bit difficult this far out. That being said, the first
one is likely late Tuesday, with another for Wednesday night. Each
of these fronts may bring showers and thunderstorms to the region,
with the better signal for Wednesday night (50-70% chance). That
front will have to be watched, as there will be ample deep-layer
shear (40-50+ knots). Moisture return/instability will again be the
question mark along where surface convergence is strongest.

Temperatures are expected to moderate through Wednesday ahead of the
second and stronger cold front back closer to normal. At least
slightly cooler readings are expected to end the week, but there is
still a lot of spread with both the timing of that second cold front
and with respect to how cool the incoming air mass will be for late
week.


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1033 PM CDT Fri Jun 12 2026

The primary concern in the 06Z TAF period remains the potential
for multiple rounds of showers and thunderstorms. The first round
is most likely to impact COU/JEF early this morning, and remnants
may move as far east as St. Louis and impact terminals there later
in the morning. This activity may be capable of bursts of heavy
rain and mostly small hail at COU/JEF. After a lull in the early
afternoon, another round of showers and thunderstorms is likely to
impact terminals sometime between late afternoon and late evening,
although the timing and coverage of these storms is somewhat
uncertain. Still, these storms have the highest potential for
strong winds, larger hail, and heavier rain.

A cold front will sweep storms out of the area near the end of the
period, but low clouds and ceiling category reductions may follow
the cold front into the early morning tomorrow.

BRC

&&

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

$$

WFO LSX