416
FXUS63 KLSX 030531
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1231 AM CDT Fri May 3 2024

.UPDATE...
Issued at 742 PM CDT Thu May 2 2024

Increased PoPs to categorical tonight as nearly the entire CWA is
covered by showers and thunderstorms ahead of a slow moving cold
front. Threat of severe weather is over.

CVKING

&&

.KEY MESSAGES...

- Showers and thunderstorms will continue through the afternoon
  and evening. There is potential for an isolated severe
  thunderstorm across central through northeast Missouri and west-
  central Illinois between 2-8pm. Should a thunderstorm become
  severe, the hazards will be damaging winds up to 60 mph and
  quarter sized hail.

- An active weather pattern will continue through at least mid-
  week, with strong to severe thunderstorms possible at points
  between Saturday and next Wednesday.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 239 PM CDT Thu May 2 2024

Radar imagery is showing two areas of shower and thunderstorm
activity, one across southwest Missouri and another ahead of a cold
front extending from west-central Missouri through northeast
Missouri. Current water vapor imagery and surface analysis shows the
Mid-Mississippi River Valley in deep southwesterly flow.

Amidst southwesterly flow is a shortwave trough that is pushing
its way into southwest Missouri and is the current focus of the
convection in that area. Ahead of this shortwave, from central
Missouri through northeast Missouri, is a region of vorticity
advection. With increased deep moisture convergence and ample mid-
day heating due to a decrease in cloud cover this morning, these
areas are the prime location for shower and thunderstorm
development and intensification over the next few hours.

It is possible that a few of these thunderstorms could become strong
to severe with the primary threat being damaging winds however
quarter sized hail cannot be ruled out. 18Z environmental analysis
indicates SBCAPE values between 1500-2000 J/kg and deep-layer shear
values maximized between 20-25 kts across the aforementioned areas.
This low shear environment will help keep thunderstorms
disorganized and further limit the severe chances. The most likely
time for isolated severe thunderstorms will be between 2 - 8 pm.
The strong to severe thunderstorm potential will diminish quickly
after sunset with the loss of instability and weaker shear further
to the east.

These showers and thunderstorms will continue to move east-northeast
through the afternoon and evening hours as the shortwave treks to
the northeast and the cold front shifts east. Showers with a few
rumbles of thunder are expected overnight and will diminish on
Friday. Despite the passage of the cold front and northeasterly
flow, high temperatures on Friday will remain near to slightly above
normal for early May.

MMG/Jaja

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 239 PM CDT Thu May 2 2024

Our ongoing active pattern will continue this weekend and into the
middle of next week as multiple shortwaves pass through the Mid-
Mississippi Valley. The first of these shortwaves will arrive
Saturday afternoon into evening, bringing with it the potential for
strong to severe thunderstorms. At the surface, a cold front will be
approaching the region from the northwest with abundant moisture
return ahead of it. Deterministic guidance is quite uniform in
depicting mid-60s dewpoints across most of the CWA on Saturday, with
70-90% of ensembles corroborating this. If this comes to fruition,
dewpoints on Saturday will be above the 90th percentile of
climatology and jeopardizing records at KSTL/KCOU/KUIN. Despite
anomalous moisture, there is uncertainty regarding the amount of
instability we`ll have on Saturday. Ensembles range from 500-1000
J/kg, but incoming cloud cover, warmer or cooler temperatures, and
timing of the frontal passage could all sway these values higher or
lower. With upper level ascent, abundant moisture and instability,
and a surface trigger all present, confidence is high that we will
see convection on Saturday. What`s uncertain is the strength of
thunderstorms that do develop.

Another shortwave is forecast to pass over the region sometime
Sunday into Monday as a surface low and warm front push north
through the CWA. This will bring more precipitation to the area, but
the potential for severe will be much lower than on Saturday.
Anomalous moisture and heat will be wiped clean from the area by
Saturday`s cold front and deep layer shear will be unimpressive.
Anything that initiates along the warm front would be elevated in
nature and quite shallow according to model soundings. With guidance
trending later into the evening on the arrival of the shortwave,
this only dampens the potential for severe.

A deep mid-level trough will swing through the Intermountain West
and into the Plains early next week. This feature will be the point
of focus for severe weather next week as it enhances upper level
ascent and deep layer shear, and at the surface advects warmer air
and more abundant moisture back into the Plains and Midwest,
increasing instability. There are still too many differences among
guidance (as highlighted in very different WPC clusters for next
week) to discuss specifics, but this is a set-up conducive for
severe weather. Just when and where that happens is unclear as of
yet.

Jaja

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1221 AM CDT Fri May 3 2024

Showers along and ahead of a cold front are gradually winding down
across the area, with impacts from rainfall departing the
terminals through the early morning hours. The front will slowly
sag across the local terminals, leading to a period of variable
winds until the front clears the sites with winds becoming
northerly to northeasterly in its wake. Additionally, a relatively
narrow band of low stratus is expected along the front brining
MVFR to IFR ceilings to the area. Given the slow moving nature of
the front and it pivoting across the region as it moves through,
low stratus may hang around KCOU, KJEF, KSUS, KSTL, and KCPS
longer than indicated into the mid to late morning.

Elmore

&&

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

$$

WFO LSX