Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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145 FXUS63 KLSX 161757 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1257 PM CDT Thu May 16 2024 .KEY MESSAGES... - Showers and a few thunderstorms will fade over the area this morning. Additional showers and thunderstorms are possible this afternoon and evening with isolated hail and gusty winds. - Locally heavy rainfall could lead to localized nuisance flooding over extreme southern section of the forecast area Friday. - Temperatures will begin to warm this weekend and further into next week, becoming 10-15 degrees above normal. Next week`s warmth could be accompanied by another period of active weather. && .SHORT TERM... (Through Late Friday Afternoon) Issued at 344 AM CDT Thu May 16 2024 Regional satellite imagery shows a broad area of cloud cover over eastern Kansas and Oklahoma, streaming eastward into Missouri early this morning. Widespread rainfall and embedded thunderstorms can be seen over southwest Missouri, progressing almost due east. At far east fringes of this activity are isolated showers. Showers running ahead of the broader, more persistent rainfall have had little ground truth with radar trends showing them falling apart with eastward movement. Model soundings suggest that there may be enough dry air in the 700-850mb layer to inhibit at least the lighter activity from reaching the ground. Meanwhile, mid-level moisture is expected to continues advance northeast through the morning as rainfall moves into central and eastern Missouri. The main question then will be how long this area of rainfall hold together. Latest SPC mesoanalysis shows what thunderstorms do remain are riding along the northern fringes of MLCAPE that horseshoes from central Oklahoma into southwest Missouri and central Arkansas. This area of CAPE has greatly decreased in magnitude and area over the last several hours with essentially no CAPE over southeast Missouri. Additionally, mid-level lapse rates drop to 5.5-6C further east of the complex, which should lead to continued weakening through the morning as it approaches the Mississippi River. Though the area may not entirely collapse, scattered remnants will cross the CWA through early afternoon. All this leads to even great reservation with regard to severe thunderstorm potential given debris clouds that remain overhead. RAP guidance shows a mid-level vort reaching the Mississippi River around 19z this afternoon and approaching I-57 in southern Illinois by 23z. Simultaneously, MLCAPE only recovers to 500-1000 J/kg at any given location underneath the vort max. HREF guidance suggest only a 30-40% probability of reading 1000 J/kg and essentially 0% for reaching 2000 J/kg with that value being the absolute maximum possible and even that is localized. Shear values still only look to reach 30 knots at best. Model soundings don`t give much more excitement with long, thin CAPE profiles and deep saturation, both of which would not favor hail and gusty winds. All-in-all, while the severe threat isn`t zero, it`s not high either. If a strong storm develops, the window is extremely short (2pm-6pm) and has spatial limitations, too (far southeast MO and southwest IL). Activity today will play into Friday`s rainfall potential as cooler air is reinforces further south. A more vigorous surface low moves east out of Oklahoma underneath the left exit region of the upper jet and ahead of the upper level trough. While this provides plenty of support over a broad pool of high moisture content and leads to widespread rainfall along and south of I-70, the potential for locally heavy rain from thunderstorms has shifted slightly further south and further limits the spatial area previously concerning localized flood potential. Given the 14-30 day precipitation amounts have reached 150% to locally 300% of normal values, saturated ground layer would offer opportunity for nuisance flooding if locally heavy rain materialized over far southeast Missouri and southwest Illinois Friday. Maples && .LONG TERM... (Friday Night through Wednesday) Issued at 344 AM CDT Thu May 16 2024 (Friday Night through Thursday) The theme continues to be a trend toward warmer than normal temperatures beginning this weekend. Weekend warmth of 5-10 degrees above normal could inch to as much as 15 degrees above normal into the first half of next week. Signals show next week`s warmth could be accompanied by yet another period of active weather, which could have a play on temperatures, pending placement and timing of precipitation. A pronounced upper level trough will be gradually exiting to the east late Friday into early Saturday. A weak boundary/surface trough extending through the mid-Mississippi Valley will gradually become overtopped by an amplifying upper level ridge from the west later in the day Saturday. Surface high pressure begins to build in from the northern Plains, but may not occur quick enough to spare the region of isolated showers, especially over southeast sections of the CWA. A thunderstorm cannot be ruled out, but MLCAPE values peak between 500-1000 J/kg with weak bulk shear of 10-20 knots. Anything that develops will likely be slow-moving, relatively short-lived and fade after peak heating. Surface high pressure and upper ridging then take over to provide dry and warm conditions Sunday with temperatures running 5-10 degrees above normal through the weekend. Surface/mid-level ridging extending from north to south down the Atlantic seaboard will result in southerly return flow at the surface with strengthening southwesterly mid-level flow. Strong warm air advection Monday will boost temperatures even further with the potential that some areas could approach 90 degrees Monday and Tuesday. NBM spreads remain tightly clustered through Monday (5 degrees or less) with a little more spread introduced Tuesday. Beyond that, the gap continues to widen. The main culprit to the diverging solutions is the handling of broad upper trough that traversed the northern CONUS and shortwaves that eject northeast at the base of the trough. Where these features track, their surface inflections, and boundaries, will factor into precipitation chances and temperature trends. GEFS mean heights show very little spread, through Tuesday, placing us comfortably under the upper ridge and within the warm sector, while quickly spreading out Wednesday beyond. Additionally, CIPS analog threat guidance shows 70% probability for warmer than normal temperatures through days 6-8, but also signal potential for an increasingly wet pattern toward the end of the same period. Warm and mainly dry conditions have the potential to be tempered by an increasingly more active pattern next week. Maples && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1257 PM CDT Thu May 16 2024 Rain showers currently over the region are exiting the area with only light showers over the next few hours with MVFR ceilings possible. As these light showers exit the region, there is a chance of redevelopment of diurnal showers and isolated thunderstorms across the area this afternoon. Confidence if a shower/isolated thunderstorm directly impacts any given terminal is low, thus went with VCTS at this time. Reduced visibilities and flight conditions are possible if a shower/thunderstorm does directly impact a terminal. Overnight into early Friday morning, winds will become light and variable. As winds become light and variable, expect the development of fog and low stratus. It is possible that visibilities and ceilings could be lower (low MVFR to IFR) than what is currently forecast. Fog will dissipate after sunrise with ceilings generally between 3000-5000 ft clouds to persist through the day on Friday with southwesterly winds. MMG/Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX