Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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818 FXUS63 KLSX 261738 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1238 PM CDT Sun May 26 2024 .KEY MESSAGES... -The evolution of today`s severe thunderstorms remains uncertain, but in both scenarios the best chance for significant severe thunderstorms remains across southeast Missouri and southern Illinois. With the strongest storms 80 mph winds, large hail, and a few strong tornadoes will be possible. Elsewhere severe thunderstorms will be less intense, though 60 mph winds, quarter sized hail, and a weak tornado are still possible. -Locally heavy rainfall, up to 2-5 inches, is possible with both rounds of thunderstorms on Sunday. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 312 AM CDT Sun May 26 2024 A strong dynamic environment is establishing across the mid- Mississippi Valley this morning. An upper-level jet is nosing eastward into the region while in the mid-levels a trough is swinging through the central Plains, approaching the mid-Mississippi Valley. The low level jet is edging into western Missouri. The result is convection that has spawned across eastern Kansas and western Missouri, tracking eastward over the early morning hours in an unstable environment with 1500-3000 J/kg of MUCAPE. Convection is currently a mix of discrete supercells across southwest MO and northern AR and linear convection across eastern KS. The evolution of this convection has been messy and further complicates today`s forecast. A few scenarios are still possible: 1. If the linear convection over KS is able to organize into an MCS, it will push into the forecast area this morning, using up much of our instability and throwing the potential for afternoon convection into doubt. If an MCS forms, it will push eastward across Missouri and into Illinois by mid-morning. Within the MCS multicell clusters and bowing line segments will be capable of strong damaging winds up to 70 mph. QLCS tornadoes are also a concern, particularly where segments are oriented with a strong north-south component. The MCS would effectively stabilize the environment through which is moves, as well as lay out an outflow boundary to it`s south. Destabilization during the day will be stunted, despite the likely partly sunny sky in this wake of this convection. In this scenario, the best chance for afternoon/evening convection would be along and south of the outflow boundary, with the potential for this to occur south of our forecast area. The northern extent remains uncertain as the outflow hasn`t developed yet, but the current location and movement of convection suggests that the outflow will remain south of the I-70 corridor. Storms in this environment will have access to robust instability and strong deep layer shear. All hazards will be possible with these severe thunderstorms, with the potential for large hail, 80 mph winds, and a few strong tornadoes. North of the outflow boundary thunderstorms are still possible, but how much destabilization occurs will impact the strength and coverage of severe thunderstorms north of the outflow boundary. 2. If this convection diminishes as it moves into more stable air in western Missouri, and our forecast area remains largely unaffected by significant convection, then our chances for significant severe weather during the afternoon and evening would increase. In this scenario the 1500-2000 J/kg of MUCAPE currently across our forecast area would remain largely untapped as we moved into the day and instability would continue to increase with southerly flow and some sunshine. As the broad, mid to upper level ascent pushed over the forecast area this afternoon, convection would fire off of lingering outflow boundaries from this morning`s convection. In this scenario, the entire forecast area would be ripe for severe thunderstorms. North of I-70 the intensity of severe thunderstorms would be weaker, and 60 mph winds, quarter sized hail, and a tornado would be possible. Across far southeast Missouri and southern Illinois where shear is more robust, all hazards will be possible with these severe thunderstorms, with the potential for large hail, 80 mph winds, and a few strong tornadoes. In either scenario, heavy rain and flash flooding is a concern with storms today. This is particularly true with training storms, which are possible with west-east shear parallel to the expected outflow boundary. The HREF probability matched mean continue to show the potential for rainfall on the order of 2" over 3 hrs. Areas that have already seen modest rainfall in the past two days will be at higher risk for flash flooding today. MRM && .LONG TERM... (Monday Night through Saturday) Issued at 312 AM CDT Sun May 26 2024 The focus of this forecast was on today`s severe weather potential. Little has changed in the long term forecast. Dry weather with near normal temperatures will persist through most of the work week under northwesterly mid-level flow. A mid-level ridge will shift east over the forecast area into the weekend, bringing southwesterly flow back to the area and increasing the chance for above normal temperatures and rain. MRM && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1234 PM CDT Sun May 26 2024 Morning activity now well east of TAF sites. Still expect another round of showers and storms will develop, mainly along and south of I-70. So kept KUIN dry and VFR. Otherwise, for TAF sites along I-70 have vicinity thunderstorm mention. For KCOU and KJEF it will be between 18z Sunday and 01z Monday, then for St. Louis metro area TAFs between 21z Sunday and 03z Monday, tapering off once cold front moves through region. As for the winds, gusty south to southwest winds will veer to the northwest behind the cold front and diminish. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch through late tonight for Audrain MO-Boone MO- Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO- Iron MO-Jefferson MO-Lincoln MO-Madison MO-Moniteau MO- Monroe MO-Montgomery MO-Osage MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO- Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO. IL...Flood Watch through late tonight for Bond IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-Madison IL- Marion IL-Monroe IL-Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-Washington IL. && $$ WFO LSX