Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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656 FXUS63 KLSX 222322 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 622 PM CDT Wed May 22 2024 .KEY MESSAGES... - Scattered showers and thunderstorms are expected mainly to the south of I-70 into the early evening hours. A few of these storms could produce hail and gusty winds. Additional storms are expected to develop late tonight into early Thursday morning. - There will be chances for showers and thunderstorms throughout upcoming Memorial Day weekend, particularly on Friday and again late Saturday night into Sunday evening. It will not rain all of the time, and Sunday has the best chance for seeing strong storms in the area. && .SHORT TERM... (Through Late Thursday Night) Issued at 316 PM CDT Wed May 22 2024 Latest surface analysis is showing that the front is well south of the area over the Ohio Valley into northeast Arkansas. There was a surface high centered over west central Missouri. We are seeing some scattered thunderstorms to the north of the front this afternoon which have produced some hail and gusty winds over the area in a weak band of frontogenesis to the north of the front. These storms will continue into the early evening and will continue to pose a risk for hail/gusty winds before there will be a brief waning in the activity this evening and early overnight hours as a weak shortwave ridge moves across the area. Then showers and thunderstorms will pick up again late tonight into as the low level jet picks up over the area. There should be another lull during the day on Thursday as another weak shortwave ridge moves across Missouri and Illinois. Expect another ramp up of showers and thunderstorms on Thursday night as the low level jet will increases at the same time the warm front moves back north over the region. The CAMS are showing and increase in scattered convection by later in the evening that increases in coverage through the night. Britt && .LONG TERM... (Friday through Next Wednesday) Issued at 316 PM CDT Wed May 22 2024 Active pattern is expected through the upcoming holiday weekend with several chances for showers and thunderstorms including the potential for strong to severe thunderstorms. It still looks like showers and thunderstorms will be likely on Friday as there is good agreement in the model guidance that a weak shortwave and an attendant cold front will move across Missouri and Illinois. MLCAPES are forecast to reach into the 1000-2000 J/kg range by afternoon, though this could be held back by the extent of morning convection. Forecast deep layer shear is not impressive, though could not rule a few of the stronger storms could produce hail and gusty winds. The front will drop south of the area on Friday night into early Saturday which will limit rain chances to the southern parts of the CWA during this time frame. Later in the weekend a upper low will move in the Midwest and we have two potential rounds of showers and thunderstorms based on the global models. The first will be late Saturday night into Sunday morning associated with a lead shortwave and as the front moves back north into the area as a warm front and the second on Sunday afternoon and Sunday night with another upper trough and a cold front. There are differences in the speed and timing of the upper trough that will be moving across the Midwest which will ultimately affect the timing and intensity of the thunderstorms this weekend which is reflected in the wide spread in the NBM IQR temperatures seen at St. Louis on Saturday and Sunday. The GEFS based CIPS and CSU guidance still suggests that there is the potential for strong to severe thunderstorms with this activity on Saturday night into Sunday night, but given the differences with the individual models, will continue to hold on messaging this risk at this point. There will be a significant pattern change as we head into the middle of next week as the HREF is showing the upper low moving into the eastern CONUS and a upper ridge building over the Rockies. This will put Missouri and Illinois under northwest flow aloft with a large surface high moving in which will lead to drier weather. Britt && .AVIATION... (For the 00z TAFs through 00z Thursday Evening) Issued at 606 PM CDT Wed May 22 2024 Showers and thunderstorms will pass south of I-70 very early Thursday morning. Confidence is low in a direct hit by a thunderstorm to any given terminal, so maintained VCTS at the St. Louis metropolitan terminals and added it at KJEF. If a site does receive a direct impact, brief reduced visibilities are expected. MVFR ceilings will push into southeast Missouri for a few hours after sunrise, but there is uncertainty in how far north they get. For this reason, only included them at KJEF where confidence is highest and will update as needed. Otherwise, light and variable winds tonight will increase from the southeast tomorrow morning. Jaja && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX