661
FXUS63 KLSX 222018
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
318 PM CDT Wed May 22 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected mainly to the south
  of I-70 into the early evening hours. A few of these storms
  could produce hail and gusty winds. Additional storms are
  expected to develop late tonight into early Thursday morning.

- There will be chances for showers and thunderstorms throughout upcoming
  Memorial Day weekend, particularly on Friday and again late
  Saturday night into Sunday evening. It will not rain all of the
  time, and Sunday has the best chance for seeing strong storms in
  the area.

&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 316 PM CDT Wed May 22 2024

Latest surface analysis is showing that the front is well south of
the area over the Ohio Valley into northeast Arkansas.  There was a
surface high centered over west central Missouri.  We are seeing
some scattered thunderstorms to the north of the front this
afternoon which have produced some hail and gusty winds over the
area in a weak band of frontogenesis to the north of the front.
These storms will continue into the early evening and will continue
to pose a risk for hail/gusty winds before there will be a brief
waning in the activity this evening and early overnight hours as a
weak shortwave ridge moves across the area.  Then showers and
thunderstorms will pick up again late tonight into as the low level
jet picks up over the area.  There should be another lull during the
day on Thursday as another weak shortwave ridge moves across
Missouri and Illinois.  Expect another ramp up of showers and
thunderstorms on Thursday night as the low level jet will increases
at the same time the warm front moves back north over the region.
The CAMS are showing and increase in scattered convection by later
in the evening that increases in coverage through the night.

Britt

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 316 PM CDT Wed May 22 2024

Active pattern is expected through the upcoming holiday weekend with
several chances for showers and thunderstorms including the
potential for strong to severe thunderstorms.

It still looks like showers and thunderstorms will be likely on
Friday as there is good agreement in the model guidance that a weak
shortwave and an attendant cold front will move across Missouri and
Illinois.  MLCAPES are forecast to reach into the 1000-2000 J/kg
range by afternoon, though this could be held back by the extent of
morning convection.  Forecast deep layer shear is not impressive,
though could not rule a few of the stronger storms could produce
hail and gusty winds.

The front will drop south of the area on Friday night into early
Saturday which will limit rain chances to the southern parts of the
CWA during this time frame.  Later in the weekend a upper low will
move in the Midwest and we have two potential rounds of showers and
thunderstorms based on the global models.  The first will be late
Saturday night into Sunday morning associated with a lead shortwave
and as the front moves back north into the area as a warm front and
the second on Sunday afternoon and Sunday night with another upper
trough and a cold front.  There are differences in the speed and
timing of the upper trough that will be moving across the Midwest
which will ultimately affect the timing and intensity of the
thunderstorms this weekend which is reflected in the wide spread in
the NBM IQR temperatures seen at St. Louis on Saturday and Sunday.
The GEFS based CIPS and CSU guidance still suggests that there is
the potential for strong to severe thunderstorms with this activity
on Saturday night into Sunday night, but given the differences with
the individual models, will continue to hold on messaging this
risk at this point.

There will be a significant pattern change as we head into the
middle of next week as the HREF is showing the upper low moving into
the eastern CONUS and a upper ridge building over the Rockies.  This
will put Missouri and Illinois under northwest flow aloft with a
large surface high moving in which will lead to drier weather.

Britt

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1232 PM CDT Wed May 22 2024

Scattered showers and thunderstorms will affect COU/JEF and the
St. Louis area terminals through 23Z. Expect mainly VFR
conditions, though cannot rule out that a heavier shower or
thunderstorm wouldn`t move directly over the terminal and reduce
ceilings and visibilities briefly to MVFR or IFR. There is some
potential for additional shower and thunderstorm development after
06Z tonight at the St. Louis terminals, and have kept the mention
of VCSH at the St. Louis terminals. Otherwise westerly winds will
turn out of the east to southeast by the end of the period.

Britt

&&

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

$$

WFO LSX