Sunrise 6:06 AM   Sunset 7:50 PM Moonrise 10:06 PM   Moonset 6:22 AM

  Print   HELP   Reset   Save   Recall

FXUS63 KLSX 261055 AFDLSX

Area Forecast Discussion National Weather Service Saint Louis MO 555 AM CDT Fri Apr 26 2024

KEY MESSAGES

- An active weather pattern over the central U.S. will introduce multiple days with severe thunderstorm potential, including marginally severe hail, damaging winds and an isolated tornado.
Much of the threat will remain over western portions of the forecast area until Sunday.

- Sunday remains the highest threat for severe thunderstorms ahead of an approaching cold front. Large hail, damaging wind, and tornadoes will all be a concern. Any thunderstorm will be capable of producing heavy rain with a localized flash flood threat.

SHORT TERM
(Through Late Saturday Afternoon)
Issued at 553 AM CDT Fri Apr 26 2024

A wing of mid-level warm air advection currently bisects the state of Missouri with a strong 50-60 knot low level jet pointed into western sections of the state. IR satellite shows robust cloud development in this region with regional radar mosaics mapping showers and thunderstorms from northwest Missouri to just west of Columbia as of 09z this morning. While the CAMs have all had some version of this activity, the HRRR seems to be handling this the best so far. Activity is expected to to move northeast through mid- morning underneath an area of upper level vorticity that advects northeast. Thunderstorms are elevated and while MUCAPE values creep up over eastern Missouri and western Illinois this morning, they are substantially lower than the 1500+ J/kg values that exist over the central Plains. This morning's thunderstorms are expected to remain sub-severe with small hail accompanying the strongest thunderstorms.

Severe weather potential this afternoon into tonight will rely on development that takes shape over sections of western and southwestern Missouri. Some of the potential activity is already developing over northern Texas and Oklahoma, where yet another mid/upper level disturbance continue to drive east-northeast around the parent upper level trough. CAMs all show some version of a broad mess of showers and thunderstorms moving into central Missouri by mid-afternoon. The question then is the coverage and intensity of thunderstorm activity as it runs into weaker instability (less than 1000 J/kg). Mid-level lapse rates of 6-7.5C edge into western sections of the CWA but drop dramatically to the east will little, if any, support along and east of the Mississippi River. It is likely convection will weaken over eastern sections of the forecast area. HRRR could be overselling thunderstorm intensity after 00z with no surface forcing mechanism to support such. However, stronger thunderstorms could produce marginally severe hail, damaging winds and/or an isolated tornado. The main focus remains west, where yet another round of surface based, discrete convection fires along the front over eastern Kansas and moves into western Missouri. How this activity impacts the region will largely depend on the preceding round of convection, should it keep conditions cooler and more stable east of the more discrete development to the west. It is more plausible that the later development further west will weaken as it approach central Missouri, if not die out entirely.

Trends are making Saturday look more tame than previously thought.
While high MUCAPE values cover the region, the warm front lifts to the north with warm air aloft keeping the environment capped much of the time. The upper low moves to the northeast with a void between it and the next upper low that drive into the Plains for the later half of the weekend. Warmer air aloft also keep the environment capped with the absence of a strong surface forcing mechanism. Aside from an isolate to widely scattered shower/thunderstorm along remnant boundaries produced by prior convection, much of the daytime period seems quite tame in comparison.

Maples

LONG TERM
(Saturday Night through Thursday)
Issued at 553 AM CDT Fri Apr 26 2024

The main concern in the long term period is late Saturday into Sunday morning and again late Sunday afternoon into Sunday evening.
However, there are some trends that may be signaling a slowing cold front and much later arrival than previously anticipated. This could lend some challenges to thunderstorm potential as we get into the late weekend and early next week.

This pattern makes the forecast sound more like a broken record with repeated waves of showers and thunderstorms developing from the west and tracking east into the local area. The difference by Saturday is the broader area of greater instability that encompasses the region as MUCAPES climb to around 3000 J/kg over central and northeast Missouri. A more vigorous upper low closes off over the Four Corners Region before taking a negative tilt and turning northeast later in the weekend. The cold front remains well to the west, once again triggering showers and thunderstorms over the Plains.
Deterministic guidance is not entirely aligned on the eastward extent of convective potential late Saturday into Sunday with varying strength in disturbances that eject northeast ahead of the upper low. NAM is far weaker with next to nothing, while the GFS is more aggressive and stronger with the leading shortwave providing ascent over a broad region of instability. Even considering the more aggressive GFS, thunderstorms edge into central and northeast Missouri before decaying late Saturday night into Sunday morning.
Should this slightly westward trend continue, it may be enough to keep most of the severe potential west of the forecast area. For now, the far western extent of the CWA could see a strong to severe thunderstorm late Saturday night into early Sunday, but confidence is not high.

Sunday afternoon into Sunday evening has been the primary timeframe when severe potential increases as the upper low tracks northeast and gives some eastward push in the overall pattern. However, there are now questions arising there, too. While the surface boundary does edge closer to the area, there isn't a real push of cold air and the boundary itself doesn't seem to clear the area entirely, if at all. In fact, southerly flow persists into early Monday with surface temperatures in the mid-50s to near 60 degrees and a brief westerly component to surface flow

Maples

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1115 PM CDT Thu Apr 25 2024

A broad area of MVFR ceilings will overspread the area through the overnight hours ahead of a warm front. Some IFR is possible, however ensemble guidance is showing IFR probabilities mostly below 50 percent, so confidence in IFR is low and will therefore not go lower than 1000ft in the 06Z TAFs. Winds will increase from the southeast and become gusty through the early morning.
Widely scattered showers and likely a few thunderstorms are expected to develop near the Mississippi River between 09-12Z and move northeast through the morning. Another, more widespread area of showers and thunderstorms is expected to develop over central or west central Missouri between 12-15Z, and this area will move east to affect much of the area through 18-20Z. Ceilings behind this second area of convection should rise to between 2500-4000ft.

SPECIFICS FOR KSTL:

Latest indications are that widely scattered showers will develop in the vicinity of the terminal between 10-13Z. I do not expect much thunder in this first batch of convection, although it's not a zero chance at Lambert. The second batch of convection looks likely to affect the terminal between 18Z-21Z. This looks more organized and should have more coverage as it moves in from the west.

Carney

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

Full Color Weather Map

Link to Loop


Other links: GEOS-West     Contential US     Full GOES-East

St. Louis, MO,