Sunrise 6:06 AM   Sunset 7:54 PM Moonrise 12:00 AM   Moonset 8:02 AM

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FXUS63 KLSX 281735 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1235 PM CDT Sun Apr 28 2024

UPDATE
Issued at 835 AM CDT Sun Apr 28 2024

Regional radar mosaic depicts a decaying convective linear structure tracking into eastern Missouri, with a stratiform rain shield to its west behind the storm motion. Satellite imagery paints widespread clouds across the region, and objective surface analysis shows limited low-level moisture within the open warm sector of a sluggish surface low.

All of the above factors are leading to a rather drastic decrease in the threat for severe convection across the bi-state area today. Instability is being drastically overestimated by high- resolution guidance, and there is little to no support in the real atmosphere for a significant recovery in this energy. Behind the weakening showers, we may be able to destabilize enough ahead of the approaching cold front to support marginally-severe thunderstorms at the worst this afternoon and evening. This potential will continue to be monitored through the day, but it is entirely possible that no severe weather occurs.

MRB

KEY MESSAGES

- A line of showers and thunderstorms will move east out of west/southwest Missouri this morning and is expected to weaken in time.

- Additional showers and thunderstorms are expected along a cold front this afternoon into late this evening. A few thunderstorms could be severe with marginally severe hail, damaging winds and an isolated tornado or two.

- The front will stall over the region Monday with showers and sub-severe thunderstorms over sections of southeast Missouri and southwest Illinois. The front returns north with warmer than normal conditions continuing through the upcoming week.



SHORT TERM
(Through Late Monday Afternoon)
Issued at 413 AM CDT Sun Apr 28 2024

Key Messages:

- A line of showers and weakening thunderstorms will move east out of western Missouri this morning and continue to decay as the line approaches the Mississippi River.

- Additional thunderstorms are expected along a cold front this afternoon into late this evening. A few thunderstorms could be severe with marginally severe hail, damaging winds and an isolated tornado or two.

- The front will stall over the region Monday with showers and sub- severe thunderstorms over sections of southeast Missouri and southwest Illinois. The front returns north with warmer than normal conditions continuing through the upcoming week.

Radar trends show precipitation over northeast Missouri and west- central Illinois, remnant of overnight convection that quickly decayed as it encountered a less favorable environment over eastern sections of Missouri. In fact, very little lightning is being detected within this area and what thunderstorms remain are further west with the next round of approaching precipitation.

The the focus shifts to western Missouri where another line of weakening thunderstorms are progressing eastward early this morning.
Given the diurnal minimum and thunderstorms that preceded the incoming activity, further decay is expected as the line departs the origin of instability and moves into air that has been largely stabilized by preceding thunderstorms. Though this activity is expected to be sub-severe as it enters the CWA this morning, rainfall and cloud cover could eat into potential for instability to recover this afternoon, when redevelopment is possible along the approaching cold front.

This afternoon's thunderstorm potential could very well be to be conditional upon the survival and geographic spread of the lingering rainfall that is ejecting out of western Missouri. The upper level low continues to track into the northern Plains with the surface low slightly to the southeast over western Iowa. The trailing cold front begins to slow, presenting less of a convergent focus as it moves into central Missouri. Upper ascent becomes more fragmented in the vicinity of the surface front, along with marginal MUCAPE values around 1000 J/kg encompassing much of the state of Missouri. Mid- level lapse rates of around 7C are more respectable than in previous days, but highest values reside over south-central Missouri around the time convective initiation is favored between early and mid- afternoon. RAP model sounding show skinny CAPE profiles closer to the Mississippi River, suggesting hail may not be much of a threat, if any at all, as thunderstorms approach the St. Louis Metro area.
The one favorable parameter are 0-6km shear values that are at 40-50 kts ahead of the front, along with a strengthening LLJ.

All of this suggests that redevelopment will once again be focused to our west, closer to the slowing front. This leaves a limited window of opportunity to organize behind the preceding rainfall and prior to waning diurnal maximums with much of the surface air already being rain-cooled over central Missouri. Should strong to severe thunderstorms develop this afternoon, their peak intensity may be over western portions of the CWA Should hail be a concern, it will be with initial discrete development, which then transitions to a damaging wind threat as convection become linear. An isolated tornado or two may be embedded in the line with backed winds ahead of the approaching line. Confidence in severe weather is low given all of the potential caveats ahead of the redevelopment.

Guidance has been consistent in stalling the front over southern sections of the forecast area Monday. This becomes the focus for scattered, sub-severe thunderstorms over sections of southeast Missouri and southwest Illinois Monday afternoon.

Maples

LONG TERM
(Monday Night through Saturday)
Issued at 441 AM CDT Sun Apr 28 2024

The pattern continues to look warm and active over the upcoming week. Surface high pressure quasi-zonal flow lends potential for one quiet and dry day Tuesday before mid and upper level amplification commences through midweek. The initial topic will be the warming temperatures as southerly return flow leads to well above normal conditions Tuesday into Wednesday. NBM spread continues to point at temperatures that could inch within a few degrees of record highs Wednesday. The key will be the evolution of a broad upper trough over the Intermountain West, which becomes a slingshot for multiple shortwaves that eject out of the southwest into the central U.S. The consequence is what looks to be an increasingly active week over the Plains and Midwest. A cold front begins to approach the region from the northwest late Tuesday or Wednesday. While the front initially hangs up at the northwest periphery of the southeast ridge, thunderstorm potential increases as the front draws near. Guidance then begins to spread as there is less agreement on the progress of the front and evolution of the synoptic setup through the later half of the week.

Maples

AVIATION
(For the 18z TAFs through 18z Monday Afternoon)
Issued at 1218 PM CDT Sun Apr 28 2024

Widespread cloud cover of varying heights are currently impacting the regional terminals, with CIGs as low as 2kft and as high as 10kft observed. The region is well-within the warm sector of a surface low that is slowly moving northeast in the central Great Plains. A few weak showers are all that's left from overnight convection, and are slowly eroding.

The potential for stronger thunderstorms late this evening into tonight is diminishing quickly, owing to the abundant cloud cover limiting instability. The catalyst for convection will be the cold front, currently far from the region in east-central Kansas and eastern Nebraska. The boundary will eventually track east, leading to showers and a few thunderstorms from west to east tonight.
Winds gradually shift out of the west behind the front, with a period of MVFR CIGs forecast overnight into the early morning Monday. However, drier air and diurnal heating will help erode the lower CIGs and allow for VFR conditions to resume.

MRB

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

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