680
FXUS63 KLSX 201740
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1240 PM CDT Fri Sep 20 2024

.KEY MESSAGES...

-Scattered showers and thunderstorms (20 to 30% chance) are
 possible through this evening. An isolated strong to severe storm
 over southeast Missouri and southwest Missouri is possible this
 afternoon and this evening.

-Several rounds of showers and thunderstorms (50-90% chance) and
 locally heavy rainfall are expected between Saturday and Monday night,
 with the best chance north I-70 between Saturday night and
 Monday morning. Isolated strong to possibly severe storms and
 locally will be possible on Sunday.

-Temperatures are expected to be above normal through tomorrow,
 but then back to near normal starting on Monday.


&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 405 AM CDT Fri Sep 20 2024

The latest surface analysis is showing a front extending from
central Iowa through northwest Missouri into northwest Oklahoma.
Thunderstorms that had earlier developed across Iowa have shown a
gradual weakening trend as they have moved southeast into less
instability early this morning.  I have continued with lows PoPs (20-
30%) through today as the front will continue to move east across
the CWA including early this morning when convergence increases on
the nose of the low level jet.  Chances will continue this afternoon
into this evening over southwest Illinois into southeast Missouri
when MLCAPES are expected to climb into the 2000-3000 J/kg range
with deep layer shear up to 30 knots.  This would support one or two
strong to severe storms capable of producing downburst and perhaps
some large hail.

There will be a better chance (40-70%) on Saturday morning when
showers and thunderstorms develop along a warm front that will move
through the area during the day.  Both the NAM/GFS are showing a 35
knot low level jet developing over the Plains late Friday night that
will bring the best chance for showers and thunderstorms into
central Missouri on Saturday morning.

High today will once again be around 90 degrees with 850mb
temperatures around 20C and sufficient sunshine.  Highs tomorrow
will be mainly 80s and with the coolest reading where there be the
most clouds and rain.

Britt

&&

.LONG TERM...  (Saturday Night through Thursday)
Issued at 405 AM CDT Fri Sep 20 2024

The unsettled weather pattern will continue into early next week as
the medium range models are showing the upper ridge that has been
over the central CONUS shifting to the east and the low in the
Southwest lifting out and moving across the Midwest.  The highest
PoPS (70-90%) will be Saturday night into Sunday when a initial
shortwave trough will move out across the area as cold front moves
back southeast across the area.  There will be a few strong to
possibly severe storms given CAPE/shear parameter space and some
locally heavy rainfall is also possible as PWATS will be near 2".
There will also be likely PoPs (60-70%) going Sunday night into
Monday night as the main upper trough and attendant cold front moves
across the area.  Chances for rain the rest of the week are low as
the LREF is showing a large area of high pressure moving across the
area with most members (<15%) not producing any precipitation after
Monday night.

Temperatures will fall back closer to normal behind the cold front
beginning on Sunday and staying there most of next week.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1240 PM CDT Fri Sep 20 2024

The largest changes to the TAFs this issuance are the removal of
thunderstorms at the St. Louis metro terminals this afternoon and
the addition of rain at all terminals tomorrow morning. This
afternoon`s/evening`s thunderstorm potential has fallen, and any
thunderstorms that do develop are expected to remain further south
and east than previously forecast. Showers will ramp up overnight,
with the Mid-Missouri terminals having the highest likelihood at
seeing precipitation. Elsewhere confidence decreases in whether a
terminal will see rain and when exactly it will occur. Therefore,
the 4 hour VCSH window is a best estimate. Rain may start sooner
and/or end later, but rain will not be falling during the entire
duration. Otherwise, winds will be variable during most of the TAF
period as a cold front sinks south today and buckles back northward
overnight and into tomorrow.

Jaja

&&

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

$$

WFO LSX