Sunrise 6:01 AM   Sunset 8:03 PM Moonrise 2:40 AM   Moonset 1:55 PM

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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.

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