069
FXUS63 KLSX 210906
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
406 AM CDT Sat Sep 21 2024

.KEY MESSAGES...

-Several rounds of showers and thunderstorms are expected through Monday
 night will bring some beneficial rainfall to some areas. The
 best chance (70-90%) will be late tonight into Sunday morning.

-There is the potential for some locally heavy rainfall late
 tonight into Monday. Isolated strong to severe storms are also
 possible over parts of central and southeast Missouri on Sunday
 afternoon and evening.

&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 405 AM CDT Sat Sep 21 2024

Latest radar mosaic was showing a complex of showers and
thunderstorms over western Missouri on the nose of the low level jet
early this morning.  The latest runs of the CAMS continue to show
that this complex will weaken as it moves east into the CWA early
this morning as the LLJ veers and weakens.  Have lowered PoPs to 40-
60% over southeast and central MO early this morning based on the
recent trends.  Chances for showers and thunderstorms the rest of
the day into the evening will be dependent on developing along a
warm front moving over the area or any residual outflow boundaries
underneath an upper level ridge.   Will keep chances in the 20-40%
range for now.

Better chance is still late tonight into Sunday as the axis of the
aforementioned upper ridge will begin to shift to the east and an
upper low currently over the southwestern CONUS will lift out and
move into the Plains.   Lift associated with an initial shortwave
trough will move into the area late tonight at the same time that a
cold front will move southeast out of Iowa.  The increase in the low
level jet will bring added moisture with PWATS around 2".   Will
continue with high PoPs (70-90%) late tonight into Sunday morning as
the front will move slowly southeast as it will be aligned with
southwesterly flow aloft.  There may be an isolated strong to severe
storms capable of producing damaging wind gusts on Sunday afternoon
and evening ahead of the slow moving front.   MLCAPES will be in the
1000-2000 J/kg range with deep layer shear range ahead of the front
before it moves south of the area early on Sunday evening.

Highs will be in the 80s to near 90 where the clouds can clear out.
There will be a contrast in temperatures from north to south based
on the front moving through with 70s in the north and 80s in the
south.

Britt

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 405 AM CDT Sat Sep 21 2024

Will continue with the high PoPs Sunday night into Monday night (50-
80%) as all of the available guidance is showing one or two
additional troughs moving through the area along with an attendant
cold front, though with different timing and strength.  The LREF
does match these high PoPs, with some lower chances on Tuesday
before going dry Tuesday night into Wednesday night as a surface
high  moves through the Midwest.  Will continue with slight chances
for showers at the end of the week as some of the guidance is
showing an upper low over the central CONUS.

Temperatures will be below normal to start next week, with Monday
having highs in the 60s over northwest half of the CWA where there
will clouds, rain, and CAA. Temperatures will gradually climb back
to near normal Wednesday into Friday.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1043 PM CDT Fri Sep 20 2024

VFR conditions will continue through much of the overnight period
with the focus shifting westward to eastern Kansas. A decaying
complex of showers and thunderstorms continue to move east into
western Missouri with broken/overcast mid to high clouds reaching
as far east as the Mississippi River. The main question heading
into Saturday morning will be how much of this complex survives as
it approaches KCOU/KJEF/KUIN. The stalling surface front lifts
northeastward with scattered showers and a few thunderstorms
expected along the boundary. This northward shift is limited with
precipitation generally expected to track northwest to southeast,
also leaving in question just how far east activity makes it
before total decay. Therefore, much of the prevailing groups
maintained VCSH/SHRA mention with VCTS over central Missouri
terminal and VCSH near metro terminals. While VFR is favored
through much of the period, isolated and intermittent MVFR
cigs/vsby cannot be entirely ruled out if a lingering thunderstorm
directly impacts a terminal.

There could be a lull Saturday late morning into the afternoon
with isolated showers/thunderstorms. The better potential holds
off until late in the period when a more vigorous shortwave
support more widespread showers and thunderstorms late Saturday
night into Sunday. Much of this lies in the tail end or beyond the
period, which will be addressed in later updates.


Maples

&&

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

$$

WFO LSX