Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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476 FXUS63 KLSX 041758 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1258 PM CDT Thu Jul 4 2024 .KEY MESSAGES... - A complex of thunderstorms will bring heavy rainfall and flash flooding before moving out of the area later this morning. - Another round of thunderstorms is expected to move across Missouri and Illinois late this afternoon and this evening. The primary threat will be damaging winds, with large hail, a brief tornado, and additional heavy rainfall also possible. - The combination of heat and humidity will allow heat index values to climb to around 105 degrees over parts of southeast Missouri where a Heat Advisory has been issued for this afternoon and evening. && .SHORT TERM... (Through Late Friday Afternoon) Issued at 431 AM CDT Thu Jul 4 2024 Latest regional radar is showing an east-west band of showers and thunderstorms extending from south central Illinois through the St. Louis metro area into west central Missouri. This area is occurring in a band of strong moisture convergence on the nose of a broad 30 knot LLJ. The setup of the LLJ with promote training through 12-14Z and PWATS and deep warm depths continue to be very favorable for heavy rainfall which all favor the risk for flash flooding to increase over the area the next few hours. The MCS will move out of the CWA from west to east from 13-16Z as the LLJ veers this morning. The 00Z HREF LPMM values are still pointing to pockets of an additional 3-5 inches of rainfall from this band before it moves out. While there will still be the low potential for showers and thunderstorms throughout the day, the best chance will be later this afternoon and this evening with the approach of a upper trough and attendant cold front. Showers and thunderstorms may also develop ahead along the remnant outflow boundary from this morning`s convection over southeast and central Missouri where I have kept the highest PoPs late this afternoon into the evening hours. The RAP is showing MLCAPES exceeding 3000 J/kg with deep layer shear of 30-40 knots suggesting the potential for organized multicells/ possible supercells with the primary threat being damaging winds, with large hail and a brief tornado also possible given the presence of boundaries. There will still be high PWATS and deep warm cloud depths, so the FFA will continue through 1 AM tonight. Highs today should be mainly modified by this mornings convection, though we should still see highs getting up into the lower 90s in the far south with dewpoints recovering well into the 70s. I have issued a Heat Advisory for this afternoon and early this evening for Reynolds, Iron, and Madison counties where heat index values should reach 105 degrees. The HREF is showing the front moving through the area tonight with the upper trough over the area tomorrow. Any showers should be moving out of the southeast counties in the early morning, otherwise Friday should be dry with temperatures on Friday in the lower to mid 80s. Britt && .LONG TERM... (Friday Night through Wednesday) Issued at 431 AM CDT Thu Jul 4 2024 Not much change in the thinking in the extended part of the forecast as high pressure will move across Missouri and Illinois keeping most of Friday night through Saturday night dry. Then the next storm system will move into the area early next week bringing the next chance of showers and thunderstorms Sunday into Tuesday. Temperatures will be at or just below normal. Britt && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1258 PM CDT Thu Jul 4 2024 MVFR ceilings will continue to scatter and lift generally from north to south this afternoon with improvement to VFR flight conditions at all terminals. Another round of showers and thunderstorms is expected this evening, but its northward extent from southern/southeastern MO and exact timing is uncertain. St. Louis metro terminals have the greatest chance of seeing showers and thunderstorms, with KUIN having the lowest chance (too low to mention). Thunderstorms will be capable of heavy rainfall, gusty winds, and MVFR to IFR flight conditions. Following showers and thunderstorms, a period of MVFR stratus is possible behind a passing weak cold front at all terminals. West- northwesterly winds with gusts of 20 to 25 kt are anticipated on Friday. Pfahler && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Flood Watch through late tonight for Boone MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO- Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO. Heat Advisory until 9 PM CDT this evening for Iron MO-Madison MO- Reynolds MO. IL...Flood Watch through late tonight for Monroe IL-Randolph IL-Saint Clair IL-Washington IL. && $$ WFO LSX