Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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186 FXUS63 KLSX 281201 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 701 AM CDT Sun Apr 28 2024 .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 12z TAFs through 12z Monday Morning) Issued at 650 AM CDT Sun Apr 28 2024 Metro terminals remain well east of decaying showers and thunderstorms that are tracking into section of central and northeast Missouri, as well as west-central Illinois. Given slow eastward movement and rate of weakening, metro terminals should remain VFR for much of the day with gusty southerly winds being the primary impact. Central Missouri terminals, along with KUIN, are on the edge of showers and isolated thunderstorms. Much of the lightning has decreased considerably in the couple of hour leading up to the 12z TAF package. Showers an intermittent lightning activity will move over KCOU/KJEF and KUIN through the morning hours with the potential to bounce between low VFR/high MVFR ceilings. Pockets of moderate shower activity and/or more persistent rainfall will also lead to marginal visibility reductions. Early morning activity could curb instability recovery for this afternoon through late this evening. There is uncertainty in how intense thunderstorms may get, but latest trends are favoring less in the way of stronger thunderstorms. Nonetheless, impacts will be similar to that of late night and this morning with weakening showers and thunderstorms move west to east. MVFR conditions are largely expected to accompany thunderstorms with pockets of IFR possible within isolated stronger cells. Much of the activity will move east of the terminals late in the TAF period. Maples && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX