FXUS63 KLSX 150807
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
307 AM CDT Wed Apr 15 2026

.KEY MESSAGES...

- Warm spring weather continues through the end of the week with a
  sharp cool down behind a front this weekend.

- Thunderstorms, some potentially severe, are expected today and
  again late Friday.

&&

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 301 AM CDT Wed Apr 15 2026

Our area remains in an axis of moist, unstable air within
southwesterly flow around high pressure off the southeast US coast.
Yesterday's thunderstorm activity played out about as expected, with
the primary focus being at the boundaries of this unstable air near
the front to the north and the dryline to the west. Remnants of this
activity may bring some rain to parts of the area this morning. A
dying MCS over southwest Missouri will likely bring some light rain
to central Missouri over the next few hours, but will likely be
drying up by the time it reaches the St Louis metro around dawn.
The activity on the front to our north continues to send outflow
southward into northern Missouri but is showing signs of lessening
convective development on its outflow and may not make it much
into our area this morning.

As this morning's showers dissipate we'll see temperatures warm well
above normal again today. If we get more breaks in the clouds it
could warm even further into the 80s, providing more fuel for
thunderstorms later in the day, while more extensive cloud cover
taking longer to dissipate would hold temperatures down and limit
instability. Meanwhile, a subtle wave currently entering Texas
will translate quickly northeast today embedded in the broader
southeasterly mid level jet. This wave will bring more lift into
our area today than we've seen in the last several days, giving us
greater confidence that thunderstorms will develop locally during
the afternoon and evening hours. A steadily weakening cap through
the day will also allow access to surface based instability
during the time around peak heating this afternoon, setting the
stage for the most widespread thunderstorm threat locally in this
air mass. The strong flow aloft in the jet will contribute to
strong deep layer shear across the area today, so any storms that
form are expected to take the form of supercells, potentially
splitting supercells, with primarily a threat for large hail and
locally damaging winds. Storms may eventually merge into clusters
with a greater wind threat.

This warm sector activity fades after peak heating this evening, but
another round of storms is likely along the front to our northwest
as it makes its way southeast through our region during the evening
hours. This will be driven in part by low level convergence on the
front supported by the passage of the primary shortwave trough aloft
which helps to finally drive this front southeast through our area.
This front doesn't offer much of a change in wind direction, but we
do see a modest drop in dewpoints behind it, from the mid 60s today
to the mid 50s tomorrow. That's enough to reduce our rain chances on
Thursday behind the front, though some showers may linger mainly in
the morning in southeast Missouri into southern Illinois. The severe
weather threat for Thursday afternoon similarly shifts southeast
toward the Ohio Valley. Despite the passage of the weak cold front,
more sun on Thursday allows us to warm into the 80s again across
most of the region.

Kimble

&&

.LONG TERM...  (Thursday Night through Tuesday)
Issued at 301 AM CDT Wed Apr 15 2026

The next trough to affect our weather is currently near British
Columbia making its presence felt across the Pacific Northwest. It
will track through the Northern Rockies on Thursday before emerging
out into the Plains on Friday. This trough is much more amplified
than the last one and will set up a much stronger frontal system
stretching from Minnesota to Texas on Friday. Moisture return ahead
of the front re-establishes an unstable air mass beneath strong
southwesterly flow aloft setting up the potential for another round
of severe weather through the middle of the country. Latest guidance
is in good agreement on the timing of this front with the focus for
severe thunderstorm development to our northwest from eastern Kansas
to northern Iowa. Although initially supercells, wind flow parallel
to the boundary suggests storms will rapidly coalesce into a line
with this line pushing east through the evening along or ahead of
the front. This doesn't look to arrive into our area until later in
the evening when instability will be decreasing. Thus the threat in
our area takes on a strong northwest to southeast gradient as the
line of storms eventually runs out of good instability. The primary
threats with this line will be damaging winds, although QLCS
tornadoes will also be possible if portions of the line can surge
forward and become better aligned with the low level shear.

The air mass behind this front will be much cooler than we've seen
lately as it has its origins in the Arctic. Dewpoints drop from
the 60s to the 20s and daytime highs within this air mass likely
only top out in the 50s to low 60s (5 to 10 degrees below normal).
Uncertainty on how quickly this front moves through Saturday
morning leads to a wide spread in guidance for high temperatures
on Saturday, but the warmer end highs (near 70) will likely be in
the morning with cooler air blowing in through the day. Nighttime
lows drop into the 30s, but persistent winds likely keep us just
above frost or freeze levels. A sunny Sunday will begin to
moderate the air mass further with highs more likely to reach 60
area wide. The warm up continues further Monday into Tuesday as
southerly winds return and temperatures push back into the 70s
beneath a ridge aloft arriving from the west. Rain chances remain
low until the middle to end of next week as the ridge shifts east
and exposes us to more potential troughing influences.

Kimble

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1045 PM CDT Tue Apr 14 2026

There is increasing confidence of dry weather initially, though
chances of showers and thunderstorms should come up in central
Missouri closer to 10 UTC. However, at least some weakening of the
convection in northeast Oklahoma should occur, and this area may
also just stay southeast of KCOU/KJEF. At least scattered showers
and thunderstorms should impact northeast Missouri/west central
Illinois Wednesday morning, so did add a TEMPO group for that.
Further south, additional storms are expected to refire Wednesday
early afternoon. The best chances are across the metro terminals
across into Illinois. PROB30 groups continue for these sites.
Finally, convection should develop along a remnant cold front in
western Missouri by late afternoon and progress eastward during
the evening hours. This activity may impact all terminals from
west to east toward the end of the valid TAF. In any convection,
visibilities may briefly go MVFR/IFR. Gusty winds are also
possible, particularly during the evening on Wednesday.

Gosselin

&&

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

$$

WFO LSX