Sunrise 6:02 AM   Sunset 7:51 PM Moonrise 12:02 AM   Moonset 9:01 AM

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FXUS63 KLSX 290520 AFDLSX

Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1220 AM CDT Mon Apr 29 2024

KEY MESSAGES

- The threat for severe thunderstorms this evening is greatly diminished due to a lack of appreciable instability. If a stronger storm can develop, marginally-severe wind and hail is still an outside possibility. A tornado cannot be ruled out as well, but is very unlikely.

- Heavy rain has a 30% chance in causing nuisance flooding overnight in southeast Missouri and southwest Illinois. More dramatic impacts are not forecast given the general lack of rainfall and progressive nature of the storms.

- Temperatures remain above-normal into the work week, with sporadic rain chances through the week. The highest chance for rain will accompany a cold front near the end of the week.



SHORT TERM
(Through Late Monday Night)
Issued at 235 PM CDT Sun Apr 28 2024

Abundant cloud cover plagues the Mid-Mississippi Valley, per latest GOES-East satellite imagery. A sluggish surface low is tracking northeast out of the central Great PLains into Iowa, leaving our region in the open warm sector ahead of a cold front extending south from the low. Despite this, the clouds and persistent showers are drastically hindering diurnal heating, keeping temperatures far more moderated than forecast. Aloft, heights have either remained steady or risen slightly in the amplified southwest flow of a closed shortwave over the northern Great Plains. The limited cooling aloft and stunted diurnal surface heating is keeping destabilization in the warm sector to a minimum.

The cold front will advance east this afternoon into the evening, serving as the catalyst for another round of showers and isolated thunderstorms. Despite nearly every CAM's poor attempt at modeling the instability, the mitigating factors listed above will likely win the day and hamper any threat for strong to severe thunderstorms in the forecast area. While isolated instances of marginally-severe convection can't be ruled out along the front itself, posing a damaging wind and brief, weak tornado threat, most showers and/or thunderstorms will not pose a severe weather threat. Ahead of the front, a low-level jet across southeast Missouri and southern Illinois will intensify nearly parallel to the boundary, leading to more widespread rain in that area. Given PWATs exceeding the 90th climatological percentile, deep warm cloud depths, and skinny CAPE profiles in southeast Missouri and southwest Illinois, rainfall will be rather efficient and there's a 30% chance for some degree of nuisance flooding. That said, the front will keep things progressive enough to preclude any noteworthy flash flooding. The rain will also fall in an area that's largely missed out on the heavy rain that the rest of the region saw over the last few days.

The front will gradually exit the region to the southeast tomorrow and become more diffuse. While low (15-25%) PoPs linger in our far southeast region, most of the bi-state will be dry. Little to no cold air advection will be present aloft, so temperatures will stay warm to start the work week. High pressure builds into the region more prominently on Monday night amidst weak ridging aloft, sending temperatures into more comfortable low/mid-50s overnight.

MRB

LONG TERM
(Tuesday through Next Sunday)
Issued at 235 PM CDT Sun Apr 28 2024

The unsettled weather pattern will continue through most of this week into next weekend. The LREF supports most of the global models in showing quasi-zonal flow on Tuesday becoming more southwesterly by Thursday when a deeper trough moves into the Plains with the GEFS/Canadian showing a deeper and slightly slower solution than the ECWMF. At the surface, a surface front will move north of the area on Tuesday leaving the area dry before it moves down into northern parts of the CWA Tuesday night into Wednesday night bringing a chance for showers and thunderstorms. The aforementioned trough will bring increased ascent over the area Thursday into Thursday night along with the front, so will keep the NBM's likely/categorical PoPs as it moves across the area. Depending on the timing of the trough, chances will decrease on Friday with just slight chances currently next weekend as some of the ensemble members (10-20%) have rain chances in the zonal flow aloft. The amount of CAPE/shear seen in the LREF and the global models do not support any widespread risk for organized severe thunderstorms over the area this week which go along with the CIPS/CSU probabilities.

Temperatures Tuesday through Thursday look like they will be 10-15 degrees above normal as 850mb temperatures climb to around +15C in the warm sector. Temperatures will drop back closer to normal over the weekend behind the cold front, though the NBM IQR shows a larger spread which reflects the uncertainty associated with the zonal flow.

Britt

AVIATION
(For the 06z TAFs through 06z Monday Night)
Issued at 1209 AM CDT Mon Apr 29 2024

Widespread rain with some embedded thunderstorms will continue to move eastward through the area over the next several hours. The rain has moved out of KCOU/KJEF and shoud exit KUIN by 0700-0800 UTC. For the metro terminals, the rain should cease around 1000-1100 UTC. Some brief IFR visibilities are possible in thunderstorms over the next few hours for the metro terminals.
Some lower ceilings are expected to impact the terminals late tonight into early Monday morning, but confidence is low. The stratus may be scattered in nature, with ceilings ranging from IFR to high MVFR. Any stratus should lift and then scatter out quickly from west to east Monday morning, with dry/VFR conditions forecast thereafter with light winds.

Gosselin

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

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