909
FXUS63 KLSX 152242
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
542 PM CDT Wed May 15 2024

.KEY MESSAGES...

- Unsettled weather returns to the region late tonight through
  Friday. Isolated strong to severe thunderstorms are possible
  Thursday afternoon and evening.

- Portions of southeast Missouri and southwest Illinois could see locally
  heavy rainfall that could produce minor flooding on Friday.

- Warmer weather returns to the region late in the weekend and
  through next week. Temperatures will be around 10 degrees above
  normal by Monday and Tuesday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 237 PM CDT Wed May 15 2024

A weak surface ridge will continue to slide off to the southeast
tonight as the next system over the Northern/Central Plains moves
into western MO by 06z Thursday. A warm front will develop along the
MO/AR border this evening and lift northward as an upper level
shortwave associated with the system lifts northeastward out of the
Southern Plains. Still some uncertainty on the exact location of the
warm front through the period and where the main axis of showers and
storms will develop. The latest deterministic model runs range from
across northern MO (NAM) to across southern MO (GFS), while the
majority of the HREF ensembles have the main axis along and south of
I-70 tonight through Thursday. So kept the highest POPs along and
south of I-70. Since the activity will take awhile to reach the
region, still have high confidence that it will be weakening as it
moves into the area due to weakening instability and veering low
level jet. There is still some uncertainty on how much the
atmosphere will recover by Thursday afternoon due to the morning
rain and cloud cover. However, as a remnant MCV, associated with the
morning activity, slides along the MO/AR border Thursday afternoon
combined with MU CAPEs between 1000-2000 J/kg and 0 to 6km bulk
shear of 30 to 40 kts, could see isolated severe storms develop over
southeast Missouri and southwest Illinois, as well as a small
portion of east-central Missouri. The main threats will be damaging
winds and large hail between 2 pm and 8 pm Thursday.

The activity will taper off by late evening Thursday with the
boundary stalling out along the MO/AR border. This boundary will be
the focus for additional activity developing after 06z Friday as the
main shortwave/trough over the TX panhandle slowly slides east
northeast towards the region.

Byrd
&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 237 PM CDT Wed May 15 2024

The shortwave with associated surface low will continue to slide
east northeast on Friday towards the forecast area. With the
surface boundary lingering across southern Missouri, the
combination of a southerly low level jet (25 to 35 kts), PWATS in
excess of 1.5 inches and deep layer ascent at the left exit region
of the upper jet will generate widespread showers and storms.
Thus portions of southeast Missouri and southwest Illinois could
see locally heavy rainfall that could produce minor flooding on
Friday.

The latest ensembles as well as deterministic models still have
differences in timing, strength and location of the system as moves
through the region this weekend. For now still expect low chances
(20-40%) of showers and a few storms Friday night through Saturday,
especially across portions of east-central/southeast Missouri and
southwest/south-central Illinois. Otherwise, a majority of the
region will be dry this weekend.

Beyond the weekend, warmer weather is expected with above normal
temperatures by Monday and Tuesday. Otherwise, there is the
potential for another active period as multiple shortwaves move
across the region.

Byrd

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 536 PM CDT Wed May 15 2024

While there will be plenty of cloud cover around area terminals at
the start of the period, VFR ceilings are expected for the most
part through the overnight hours. Some scattered cumulus may dip
briefly to MVFR levels at times before dissipating later this
evening. Scattered showers are expected to impact most terminals
between early morning and mid afternoon, with a few thunderstorms
possible as well. I-70 corridor terminals (COU/JEF/STL/SUS/CPS)
will see greater shower coverage than UIN, and are more likely to
observe thunderstorms. Additional, potentially stronger
thunderstorms may redevelop after this initial round near the end
of the TAF period, but most of this activity is likely to remain
south of area terminals. However, confidence in the location of
these storms remains somewhat low, and we can`t rule out
thunderstorms developing as far north as I-70.

BRC

&&

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

$$

WFO LSX