Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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131 FXUS63 KLSX 241910 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 210 PM CDT Mon Jun 24 2024 .KEY MESSAGES... - The Heat Advisory remains in effect, and has been expanded into south-central Illinois on Tuesday. -There remains a slight risk for strong to severe thunderstorms Tuesday evening and overnight, largely north of I-70. The main hazards will be damaging winds and large hail. This is the best chance for a soaking rain for the next week. && .SHORT TERM... (Through Late Tuesday Night) Issued at 209 PM CDT Mon Jun 24 2024 The region remains on the northeastern side of a mid-level ridge that is centered over the southern CONUS, while in the lower levels southwesterly flow continues warm air advection into the region. Combined with a clear sky, temperatures are rocketing into the 90s across the region today. Across central Missouri, where the nose of the warm air advection is, heat index values have jumped above 100. Overnight a shortwave will move through the quasi-zonal flow across the Great Lakes region, producing an MCS that will march through the Upper Mississippi Valley. How far south this convection, and any additional isolated convection that forms along the southwest end of the MCS, extends remains uncertain at this point. Weak forcing across the area is not favorable for widespread thunderstorm development. However, I cannot rule out an isolated shower or thunderstorms moving into far northeast Missouri and west-central Illinois tomorrow morning around sunrise. Plenty of instability will be present (1000-3000 J/kg of MUCAPE), but shear will be weak (10-15 kts) so the stronger storms that linger across the northern CWA will be capable of small hail. Tuesday will be the hottest day of the week with another day of robust warm air advection and sunshine. After warm overnight lows in the mid to upper 70s, temperatures will warm into the mid 90s to 100, with the hottest temperatures within the St. Louis metro. The Heat Advisory has been expanded into south central Illinois to account for the increased temperatures and heat index values in this area. Instability will likewise rocket tomorrow with deterministic guidance indicating 2000-4000+ J/kg of SBCAPE will be available tomorrow afternoon. Air mass thunderstorms will be possible across the forecast area during the afternoon, though short-lived under a weak flow regime with only 10-15 kts of 0-6 km shear. The better chance for rain is overnight ahead of an approaching cold front. An MCS is expected to develop across the Upper Mississippi Valley and push southeastward into Missouri and Illinois overnight, driven aloft by a shortwave embedded within the northern periphery of the mid-level ridge. This MCS will bring much needed rain to some parts of the mid-Mississippi Valley, while others will remain dry. The location of the MCS and beneficial rainfall remains uncertain with hi-res CAMs split on whether the MCS moves through our forecast area, or moves largely to our west. Where any outflow boundaries from tonight linger will influence where convection forms and congeals. Instability will remain high into the overnight hours (1500-3000 J/kg of MUCAPE), and 10-30 kts of 0-6 km shear will be able to bolster organization and maintenance of the MCS overnight. Any thunderstorms that become strong to severe will be capable of damaging winds and quarter sized hail. The best location for strong to severe thunderstorms Tuesday night will be along and north of I-70 where the best shear will be. Uncertainty remains in how strong that shear will be, so doubt remains that any thunderstorms will be able to strengthen to that extent. Rainfall rates underneath thunderstorms could reach 1-2 inches over a 3 hourly period, providing a much needed soaking rain for some. MRM && .LONG TERM... (Wednesday through Next Monday) Issued at 209 PM CDT Mon Jun 24 2024 A cold front will follow behind the MCS, it`s attendant surface low moving east of the Great Lakes region by Wednesday morning. This front will slowly drag southward until another mid- level shortwave moves through the northern stream of the westerlies and phases with the overnight shortwave described above. This will kick the cold front through the remainder of the forecast area Wednesday morning. Low-level cold air advection in its wake will bring sweet relief to the forecast area, dropping high temperatures to near normal (mid to upper 80s) for Wednesday and Thursday. As the low-level high shifts eastward towards the end of the work week, southwesterly flow and associated warm air advection will reestablish. Temperatures will warm Friday back above normal, but this shot of hot air will be short lived. From Friday into the weekend the region will remain on the southern edge of the westerlies with a broad ridge stretching across the southern CONUS. A mid-level trough will slide along the US-Canada border Friday into Saturday, it`s surface reflection taking a similar path. An attendant cold front is expected to move through the area during the weekend, bringing the next best chance of showers and thunderstorms to the area. Uncertainty remains as to the timing and strength of this system, so who receives rain and how much remains uncertain. Behind this system another shot of cold air advection will help cool the region back to near normal. MRM && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1116 AM CDT Mon Jun 24 2024 VFR flight conditions will prevail through the remainder of the TAF period under southerly winds that will gradually become westerly by the end of the TAF period. There is a 20-40% chance for showers and thunderstorms early Tuesday morning through the remainder of the period. The best chances are across northeast Missouri and west-central Illinois early Tuesday morning through the afternoon hours as an existing complex of thunderstorms could move southeast into the area. Confidence is low in the complex holding together and pushing into the forecast area, so have left mention of this out of the KUIN TAF for now. Additional shower and thunderstorm development is possible Tuesday afternoon associated with daytime heating. The development of these thunderstorms remains uncertain, as do their locations, so have also left a mention of this out of the TAFs for now. MRM && .CLIMATE... Issued at 353 AM CDT Mon Jun 24 2024 With hot temperatures forecast, here are some of the daily high temperature records: MON JUN 24 TUE JUN 25 ST LOUIS 102 in 1988 102 in 1954 COLUMBIA 103 in 1988 102 in 1988 QUINCY 99 in 1988 102 in 1931 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Heat Advisory from noon to 8 PM CDT Tuesday for Audrain MO- Callaway MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO- Jefferson MO-Lincoln MO-Madison 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 8 PM CDT Tuesday for Boone MO-Cole MO- Moniteau MO. IL...Heat Advisory from noon to 8 PM CDT Tuesday for Bond IL-Clinton IL-Fayette IL-Madison IL-Marion IL-Monroe IL-Randolph IL- Saint Clair IL-Washington IL. && $$ WFO LSX