Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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878 FXUS63 KLSX 231946 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 246 PM CDT Thu May 23 2024 .KEY MESSAGES... - Thunderstorms are expected to move across the area on Friday ahead of a cold front. A few of these thunderstorms could become severe with damaging winds and large hail being the primary threats. - After a dry Saturday, two potential rounds of showers and thunderstorms are possible Saturday night and Sunday. Both rounds could bring strong to severe thunderstorms will locally heavy rainfall. && .SHORT TERM... (Through Late Friday Night) Issued at 245 PM CDT Thu May 23 2024 Scattered showers and thunderstorms have been locally strong earlier today over southeast Missouri. This activity will diminish as another shortwave ridge will build over Missouri and Illinois late this afternoon into this evening. This ridge will keep most of the area dry tonight before we see rain return to the area tomorrow. There better chances for showers and thunderstorms during the day on Friday as the latest GFS/NAM is showing a cold front moving southeast across CWA during the afternoon. The majority of the CAMS including the HRRR show thunderstorms moving into the CWA by late morning and progressing southeast during the afternoon into the early evening hours. MLCAPES ahead of the line tomorrow afternoon will be in the 2000-3000 J/kg range with 0-6km shear only around 30- 40 knots which favors some organized multicells and a few supercells. The primary threats will be a few storms capable of producing large hail and damaging winds and perhaps a brief tornado. The chance for showers and thunderstorms will end from west to east by late tomorrow evening as the front moves east of the area. Highs tomorrow will climb into the mid 80s ahead of the front. Lows tomorrow night will begin to cool down a bit behind the front. Britt && .LONG TERM... (Saturday through Next Thursday) Issued at 245 PM CDT Thu May 23 2024 Saturday still looks like the most quiet day of the holiday weekend as a large surface anticyclone moves across Missouri and Illinois. The focus then turns toward Saturday night into Sunday when the deterministic model suite is showing a trough moving out of the Rockies into the Midwest. There is fairly good agreement that the lead shortwave will move across the area on Saturday night which will bring a warm front north through the area. Given the strength of the forcing, will keep likely/categorical PoPs late Saturday night into Sunday morning. Consensus of available model guidance is showing MLCAPES over 1500 J/kg with deep layer shear >40 knots suggesting the potential for strong to severe storms on Saturday night and Sunday morning. The bigger question is whether there will be a second round in the afternoon and evening. This will be dependent on how quickly the morning convection will clear out of the area allowing recovery of instability. There is also some uncertainty between the models with the timing of the secondary shortwave that will move across the area during evening that will determine how quickly the cold front moves through the area during the afternoon. Models are showing varying timing on the front moving across the area during the afternoon with weak convergence along it. Will maintain likely PoPs for showers and thunderstorms with the potential for the an additional round for strong to severe thunderstorms. There could also be some areas with locally heavy rainfall as the LREF is showing PWATS near 1.5". The LREF continues to shows a pattern shift into early-mid next week with a trough deepening over the eastern CONUS and a ridge building over the Rockies which will lead to northwest flow aloft. There will still be a few shortwaves moving southeast through the area which will bring a chance of showers and thunderstorms on Memorial Day, but we look dry as we head into Wednesday as the upper ridge moves east into the Midwest. There will be quite a variety in temperatures over the weekend with highs in the 70s and 80s on Saturday and then some question on just how warm will it be on Sunday depending on how quickly the morning convection and clouds moves out and how quickly the cold front moves through the area. Highs could climb well into the 80s over the southern half of the CWA in the warm sector on Sunday ahead of the cold front if we clear out. Then temperatures looks to be closer to late May normals behind the cold front next week. Britt && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1250 PM CDT Thu May 23 2024 Lingering high MVFR and low VFR ceilings will affect terminals over central Missouri and the St. Louis area terminals through this afternoon. Then mainly dry and VFR conditions are expected through tonight before a cold moves into the area on Friday. There will be an increasing chance for thunderstorms at UIN/COU/JEF by late morning at STL after 18Z. Winds will remain out of the southeast to south at 10 knots or less. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX