681
FXUS63 KLSX 300018
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
718 PM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Isolated strong to severe storms possible late this afternoon through
  this evening, mainly along and south of I-70. The primary
  threat is damaging winds. Though brief bursts of heavier rain
  and occasional large hail are possible as well.

- Despite slightly cooler temperatures this afternoon, the
  humidity remains high with heat index values between 100-105
  degrees over sections of southeast Missouri. So heat advisory
  will remain in effect until 7PM today.

- Next chance of showers and thunderstorms will be Wednesday
  through Thursday.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 312 PM CDT Sat Jun 29 2024

The atmosphere is beginning to recover across the area this
afternoon since the cloud cover continues to diminish from the
earlier activity. Also, the latest HREF ensemble indicates that
CIN will continue to weaken and mean surface based CAPE is
expected to increase to between 2500-3500 J/kg by 21z along and
ahead of the cold front. The cold front has been a bit slower in
it`s movement to the south today and as of 19z it extends from
northeastern IL southwestward into northeast MO (just north of
Quincy) to just south of Kansas City. The front as well as outflow
boundaries across southern Missouri will be the focusing
mechanisms for storms to develop late this afternoon through this
evening. So could see one area of activity just north of the St.
Louis metro and another area south of the St. Louis metro area
initially. Latest CAMs indicate that the best chances of strong to
severe storms will be south of I- 70. The main threat will be
damaging winds, though brief bursts of heavier rain and occasional
large hail are possible as well.

Another issue to deal with late this afternoon is the heat advisory
for portions of southeast Missouri. Even though temperatures have
been slow to recover, should still see them warm up into the low 90s
with heat index values between 100 and 105, so heat advisory will
remain in effect until 7PM this evening.

The cold front will continue to sink south through the region,
exiting the forecast area early on Sunday. So precipitation will
taper off by daybreak. Then strong surface high pressure ridge will
build over the area beginning on Sunday. Much cooler and drier air
will filter in Sunday into Monday with below normal temperatures.

Byrd
&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 312 PM CDT Sat Jun 29 2024

While enjoying the cooler than normal weather through Monday, upper
level ridge will begin to build in from the Plains. By Tuesday,
surface flow will become southerly once again with highs back in the
90s. However, low level moisture return will be a bit slower, with
the main axis of higher dewpoints just to our west, though dewpoints
will be near 70 degrees in portions of central Missouri, so could
see heat index values around 100 Tuesday afternoon. By Wednesday,
dewpoints will be in the 70s across the entire area with heat index
values between 100 and 105 along and south of I-70.

In the meantime, the next system will be approaching the central
CONUS. The pattern will be similar to what we are currently
experiencing with a system sliding east along the US/Canadian border
and cold front approaching the region by Wednesday. There is better
agreement among the deterministic as well as ensembles on timing,
location and strength of the system, so have likely POPs Wednesday
night into Thursday. Still some uncertainty on coverage of the
activity, so don`t want to say that the Fourth of July holiday will
be a washout at this time, but will need to keep an eye out on model
trends over the next several days. With the chances of precipitation
for the last half of the work week, temperatures will be a tad
cooler, in the 80s.

Byrd

&&

.AVIATION...  (For the 00z TAFs through 00z Sunday Evening)
Issued at 715 PM CDT Sat Jun 29 2024

UPDATE: Some MVFR stratocumulus has developed in the vicinity of
JEF and COU, and may persist for 1-2 hours this evening before
diminishing. Otherwise, the remainder of the previous discussion
is valid.

Previous discussion:

Primary concern during the 00Z TAF period will be the potential
for lingering showers and thunderstorms near I-70 terminals. For
the most part, convective activity is likely to be southeast of
these terminals by 00Z, but a few may persist in the vicinity of
STL/SUS/CPS for an hour or so. If this is the case, bursts of
heavy rain with visibility reductions, along with erratic wind
gusts, will be the most likely hazards. These impacts have a low
probability of occurring. Afterward, VFR conditions are expected,
with persistent light north-northeast winds.

&&

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

$$

WFO LSX