964
FXUS63 KLSX 161810
AFDLSX

Area Forecast Discussion
National Weather Service St Louis MO
110 PM CDT Sun Aug 16 2026

.KEY MESSAGES...

- Showers and thunderstorms will produce pockets of heavy rain
  north of I-70 this morning, with some localized flooding
  possible. Another round of showers and thunderstorms is
  possible (30-50%) further south late this afternoon and
  evening, with a limited potential for damaging wind gusts,
  locally heavy rain, and a brief weak tornado or two.

- Dangerous heat continues in areas roughly along/south of I-70
  today, but widespread relief is expected tomorrow.

- Another round of showers and thunderstorms is increasingly
  likely (40-70%) Tuesday night through early Wednesday.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 333 AM CDT Sun Aug 16 2026

Much like the past few nights in a row, nocturnal convection is
beginning to develop across northern and central Missouri, largely
driven by a modest low level jet overriding a stalled surface front.
Once again, a corridor of very high moisture exists along this
boundary within an area of low level convergence (albeit slightly
less than yesterday), with storm motions parallel to the front.
While precipitable water values are slightly less extreme than
yesterday when they were near all-time records, there is still a
corridor of 2 to 2.25 inch PWATs, which is comfortably above the
95th percentile and supportive of very heavy rain rates. Meanwhile,
ample MUCAPE also exists (2000-2500 J/kg), although effective wind
shear is rather marginal (20-25kt). As the morning progresses,
showers and thunderstorms with 1-2+ inch rain rates will gradually
expand and move slowly eastward, producing streaks of soaking rain.
While we don`t quite expect enough coverage to result in widespread
Flash Flooding, there is at least the potential for localized issues
wherever multiple cells move over the same locations. This initial
activity is likely to persist into the mid-morning hours, when the
waning low level jet should limit surface convergence and new
updrafts.

During the day today, a cold front is finally set to start moving
slowly southward, driven by a a passing shortwave in the Great Lakes
and potentially remnant outflow. By mid/late afternoon, this
boundary should be approaching the I-44 corridor, and as a result,
some heat relief is expected slightly further south than has been
observed over the past few days. As such, we have opted to remove
Audrain/Ralls/Pike MO from the ongoing Heat Advisory, but in other
areas, one last day of dangerous heat and humidity can be expected.
This will almost certainly allow the remaining heat headlines to
expire on time today, with much more moderate temperatures expected
across most of the area tomorrow.

In addition to heat relief, this weak cold front may also provide a
loose focus for additional shower and thunderstorm development this
afternoon and evening, although it may be that that main driver of
new storms ends up being a remnant MCV arriving from the west around
this time. Latest high resolution model guidance has really latched
onto this feature, and it appears to be emanating from an ongoing
thunderstorm complex currently moving through north-central Kansas.
While ambient wind shear will be relatively meager still this
afternoon (~25kt of 0-6km bulk shear), MCVs tend to locally enhance
the shear profile, and it will also be arriving late in the
afternoon when instability is near its peak. As such, it wouldn`t be
out of the question to see resurgent thunderstorm activity driven by
the MCV, with at least some potential for damaging wind gusts or
even a brief tornado due to the aforementioned local shear
enhancement. Exactly where this would occur is highly uncertain, but
would be favored along and south of the advancing front, generally
from the I-70 corridor and points south from late this afternoon
through late evening. Even if this MCV fizzles out before it
arrives, scattered showers and thunderstorms may also simply develop
along/ahead of the cold front itself, also.

Overnight, this activity will push south and east out of the region.
As mentioned previously, this should spread near and even slightly
below average temperatures into the area, allowing the ongoing Heat
Advisory/Warning to expire on time. While we may still flirt with
100 degree heat indices across the Ozarks, this should not be enough
to maintain headlines in these areas another day. Meanwhile,
tomorrow should also be dry thanks to a modified post-frontal
airmass, leading to a pleasant day for most of the region.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Issued at 333 AM CDT Sun Aug 16 2026

On Tuesday, weak southerly low level flow is expected to resume as a
cold front slowly approaches from the north, driven by a more
substantial trough digging into the Great Lakes. While we don`t
expect strong warm-air advection and moisture return, this should be
enough for a modest northward rebound of warmer temperatures Tuesday
afternoon, although with the modified airmass still in place, we
don`t expect that this will be enough to reach Advisory level heat
locally. Instead, expect temperatures near or slightly above
average, the latter generally across the Ozarks, and dry conditions
during the day. While we don`t expect storms to develop during the
day, there has been a persistent signal for showers/thunderstorms to
develop along the advancing front across Iowa, which then advance
south southeastward into our area later in the evening and
overnight. This may pose at least a limited threat for strong or
severe thunderstorms Tuesday night/Wednesday morning, with a
preference for our northern areas given the late arrival of this
activity, although this will depend on how thunderstorms evolve as
they move further and further south after dark.

Chances for showers and thunderstorms also continue into Wednesday
and possibly even Thursday, although much will depend on how quickly
the passing cold front surges south and out of the area. Medium
range guidance does hint at additional shortwaves moving through the
area during this time frame, and if the boundary is on the slower
side, it wouldn`t be out of the question to see additional rounds of
showers and thunderstorms late Wednesday into Thursday, more likely
than not as elevated storms as the low level jet overrides a slowly
advancing or or stalled surface front. Meanwhile, confidence
continues to increase that even after a modest temperature rebound
Tuesday, this reinforcing front will drive milder temperatures back
into the area Wednesday through the end of the week.

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 103 PM CDT Sun Aug 16 2026

Outflow from earlier thunderstorms is sinking southward toward
KCOU and KJEF, potentially causing erratic light winds early in
the period. North of this outflow, a cold front is moving into
the region. Either the outflow or front will serve as a focus
for addition thunderstorms, some possibly strong, later this
afternoon and evening. KSUS, KSTL, and KCPS have the greatest
chance of seeing impacts, with strong winds, heavy rainfall, and
lightning all expected with direct impacts. The threat for
showers and thunderstorms will wind down late this evening into
the early overnight hours. Then, there is a low chance for low
stratus and fog. With the uncertainty of these hazards in
proximity to the local terminals, impacts have been left out of
the TAFs for now.

&&

.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...19
LONG TERM...19
AVIATION...Elmore