878
FXUS63 KLSX 162351
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
Issued by National Weather Service Kansas City/Pleasant Hill MO
651 PM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected late this
  afternoon and evening mainly along and south of I-70. A
  couple of storms will be capable of mainly damaging wind
  gusts.

- Rain chances return Tuesday night into Wednesday and then
  Wednesday night into Thursday.

- Seasonable temperatures are expected for a majority of the
  area through this week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 314 PM CDT Sun Aug 16 2026

An MCV can be seen on visible satellite imagery and in surface obs
moving across northern Missouri and southern Iowa this afternoon. A
cluster of thunderstorms associated with this MCV raced through
northeastern Missouri and west-central Illinois earlier today,
producing a cold pool and outflow boundary that is moving toward I-
70. The outflow is becoming increasingly diffuse in satellite
imagery, though broken cloud cover has kept the cold pool in place
and kept instability from rebuilding in this portion of the CWA.

A cold front is currently edging into northeastern Missouri and will
continue south-southeastward through this evening. As it does so, it
will encounter an air mass characterized by 3,000 J/kg of
MLCAPE along and south of I-70. Forcing from the front and
passing MCV will initiate scattered convection in this part of
the CWA starting around 5-6pm. Effective shear may be as high as
30-35 kts, allowing for organized multicell clusters capable of
damaging wind gusts. Much of this shear is going to be
associated with the MCV and behind the front, so the potential
for strong to severe storms will be confined to along the front;
therefore, right along the I-70 corridor. Additionally, LCLs
along the front may be low enough to allow for a threat of brief
tornadoes in bowing segments thanks to about 30 kts of 0-3km
shear.

Convection is expected to depart the CWA eastward shortly after
midnight, with the front clearing the area through the early
morning hours. A much more comfortable air mass will then settle
into the region, with highs tomorrow expected to only top out
in the low to mid 80s for most locations.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 314 PM CDT Sun Aug 16 2026

Portions of the CWA will only have a brief break from the heat, as
guidance consensus is that as Monday`s post-frontal air mass shifts
east, low-level ridging will nose into the region. However, there is
not a consensus as to how far north the crest of the ridge will
build, and therefore, how warm temperatures at the surface will get.
The overall trend over the last 24 hours has been for a less
aggressive ridge, with NBM probabilities for highs reaching and
exceeding 90 degrees are at most 50-70% over southeastern Missouri
Tuesday and south of I-70 on Wednesday.

Wednesday`s temperatures will have to contend with a cold front
dropping southward through the CWA. While guidance consensus is that
much of the CWA will not see FROPA prior to peak heating, associated
rainfall and cloud cover will produce an effective boundary further
south across the area. This will produce a strong temperature
gradient bisecting the CWA west to east, with low to mid 80s to the
north and low to mid 90s to the south. Once the front pushes south
of the area on Thursday, near normal to below normal temperatures
are expected through the weekend.

As the front slowly sinks through the area, guidance consensus is
that two shortwaves will ripple through the Midwest; one early
Wednesday, and one early Thursday. The location of the front during
the passage of the waves is where rainfall will be focused, and this
is currently north of I-70 Wednesday morning and south of I-70
Thursday morning. The front appears to be progressive enough to
mitigate a threat for flooding. However, ensemble guidance supports
PWAT of 1.5-2", and given upper-level flow parallel to the southward-
moving front, training convection capable of locally heavy rainfall
may be a concern.

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 635 PM CDT Sun Aug 16 2026

Scattered thunderstorms are developing along a composite cold
front/outflow boundary currently stretching from near KI63 to
near KJEF. Expect this activity to increase in coverage and
intensity somewhat as it moves east this evening. Thunderstorms
will be capable of producing IFR flight conditions in heavy
rain, and wind gusts to 40-50kts are also possible.
Thunderstorms should be through the eastern portions of our area
in south central Illinois by 06-08Z. There may be some
lingering showers behind the main area of precipitation, but
most guidance is dry after the initial wave of storms. There is
also the possibility of low stratus behind the cold front
tonight. Initial thoughts are that the eastern Ozarks and south
central/southwest Illinois will have the highest chance for low
ceilings before sunrise Monday, however parts of east central
Missouri, and possibly central Missouri may also see low MVFR
ceilings before sunrise tomorrow. Any low ceilings that do
develop should lift and scatter by 17-18Z Monday and VFR
conditions are expected to prevail after that.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Heat Advisory until 9 PM CDT this evening for MOZ035-036-042-
     052.
     Extreme Heat Warning until 9 PM CDT this evening for MOZ041-
     047>051-059>065-072>075-084-085-099.
IL...Heat Advisory until 9 PM CDT this evening for ILZ058>060-064-
     065-098-099.
     Extreme Heat Warning until 9 PM CDT this evening for ILZ069-
     070-074-079-100>102.

&&

$$

SHORT TERM...Elmore
LONG TERM...Elmore
AVIATION...Carney