421
FXUS63 KLSX 232320
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 PM CDT Thu May 23 2024

.KEY MESSAGES...

- Thunderstorms are expected to move across the area on Friday
  ahead of a cold front. A few of these thunderstorms could
  become severe with damaging winds and large hail being the
  primary threats.

- After a dry Saturday, two potential rounds of showers and
  thunderstorms are possible Saturday night and Sunday. Both
  rounds could bring strong to severe thunderstorms will locally
  heavy rainfall.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 245 PM CDT Thu May 23 2024

Scattered showers and thunderstorms have been locally strong earlier
today over southeast Missouri.  This activity will diminish as
another shortwave ridge will build over Missouri and Illinois late
this afternoon into this evening.  This ridge will keep most of the
area dry tonight before we see rain return to the area tomorrow.
There better chances for showers and thunderstorms during the day on
Friday as the latest GFS/NAM is showing a cold front moving
southeast across CWA during the afternoon.  The majority of the CAMS
including the HRRR show thunderstorms moving into the CWA by late
morning and progressing southeast during the afternoon into the
early evening hours.  MLCAPES ahead of the line tomorrow afternoon
will be in the 2000-3000 J/kg range with 0-6km shear only around 30-
40 knots which favors some organized multicells and a few
supercells.  The primary threats will be a few storms capable of
producing large hail and damaging winds and perhaps a brief tornado.
The chance for showers and thunderstorms will end from west to east
by late tomorrow evening as the front moves east of the area.

Highs tomorrow will climb into the mid 80s ahead of the front.  Lows
tomorrow night will begin to cool down a bit behind the front.

Britt

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 245 PM CDT Thu May 23 2024

Saturday still looks like the most quiet day of the holiday weekend
as a large surface anticyclone moves across Missouri and Illinois.
The focus then turns toward Saturday night into Sunday when the
deterministic model suite is showing a trough moving out of the
Rockies into the Midwest. There is fairly good agreement that the
lead shortwave will move across the area on Saturday night which
will bring a warm front north through the area.  Given the strength
of the forcing, will keep likely/categorical PoPs late Saturday
night into Sunday morning. Consensus of available model guidance is
showing MLCAPES over 1500 J/kg with deep layer shear >40 knots
suggesting the potential for strong to severe storms on Saturday
night and Sunday morning.  The bigger question is whether there will
be a second round in the afternoon and evening.  This will be
dependent on how quickly the morning convection will clear out of
the area allowing recovery of instability.  There is also some
uncertainty between the models with the timing of the secondary
shortwave that will move across the area during evening that will
determine how quickly the cold front moves through the area during
the afternoon.  Models are showing varying timing on the front
moving across the area during the afternoon with weak convergence
along it.  Will maintain likely PoPs for showers and thunderstorms
with the potential for the an additional round for strong to severe
thunderstorms.  There could also be some areas with locally heavy
rainfall as the LREF is showing PWATS near 1.5".

The LREF continues to shows a pattern shift into early-mid next week
with a trough deepening over the eastern CONUS and a ridge building
over the Rockies which will lead to northwest flow aloft.  There
will still be a few shortwaves moving southeast through the area
which will bring a chance of showers and thunderstorms on Memorial
Day, but we look dry as we head into Wednesday as the upper ridge
moves east into the Midwest.

There will be quite a variety in temperatures over the weekend with
highs in the 70s and 80s on Saturday and then some question on just
how warm will it be on Sunday depending on how quickly the morning
convection and clouds moves out and how quickly the cold front moves
through the area.  Highs could climb well into the 80s over the
southern half of the CWA in the warm sector on Sunday ahead of the
cold front if we clear out.  Then temperatures looks to be closer to
late May normals behind the cold front next week.

Britt

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 614 PM CDT Thu May 23 2024

Dry and VFR conditions will persist through tomorrow morning before
a cold front passes through the forecast area. This front will bring
brief MVFR ceilings as well as showers and thunderstorms as it
passes. There is still uncertainty regarding the timing and
evolution of thunderstorms tomorrow, so introduced VCTS at each
terminal during this issuance and will hone it with further forecast
packages. Southeast winds will become gusty (15-20 kts) for most
locations ahead of the cold front tomorrow morning.

Jaja

&&

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

$$

WFO LSX