Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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501 FXUS63 KLSX 171135 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 635 AM CDT Mon Jun 17 2024 .KEY MESSAGES... - Today will be another hot day with heat index values ranging from 95-103. There is a chance for isolated to scattered afternoon showers and thunderstorms along and south of the I-44 corridor (20- 40%). - Summer-like temperatures will continue Tuesday through the weekend with periodic shower and thunderstorm chances (20-30%). && .SHORT TERM... (Through Late Tuesday Afternoon) Issued at 349 AM CDT Mon Jun 17 2024 Water vapor imagery shows that mid-level ridging and high pressure has begun to dominate the eastern CONUS with southerly low level flow into the Mid-Mississippi River Valley. This deep southerly flow favors warm and moist air to be transported into the Mid-Mississippi River Valley through at least midweek. There is agreement in the deterministic guidance that a weak mid- level vorticity maximum, currently seen in water vapor imagery over northeast Louisiana, will round the mid-level high and traverse across far southeast Missouri and southern Illinois this afternoon. With the abundant available low-level moisture, this area will be the focus of diurnally-driven scattered showers and thunderstorms this afternoon and evening. Deterministic model soundings are indicating DCAPE values 1000+ J/kg, SBCAPE values between 2000-3000 J/kg, and mid-level lapse rates around 6 C/km. This favors pulse thunderstorms capable of gusty winds and heavy downpours. Today will be another hot and humid day amidst deep southerly flow, however not as hot as yesterday. Dewpoints across the area are forecast to be in the upper 60s - low 70s. These high dewpoints combined with highs in the upper 80s - mid 90s will keep heat index values between 95-103 degrees area wide. The main factor for temperatures not being as hot as yesterday is that guidance is hinting at increased mid-level cloud cover with the passing vorticity maximum. Another factor that would keep high temperatures on the "cooler" side is the shower and thunderstorm potential across southeast Missouri and southern Illinois. Should an area see a shower and thunderstorm, expect for high temperatures to be suppressed. Despite the slightly less warm temperatures today, it is important to still take necessary heat precautions such as taking frequent breaks if outside and drinking plenty of water. Tuesday will be another hot day with highs in the mid 80s - low 90s in the persistent deep southerly flow. Deterministic guidance is in agreement that additional weak vorticity maxima will round the mid- level high Tuesday afternoon and evening and be the focus for another chance (20-30%) of diurnal showers and thunderstorms. Similar to today, areas that see a shower or thunderstorm could see highs on the "cooler" side. MMG/Glass && .LONG TERM... (Tuesday Night through Sunday) Issued at 349 AM CDT Mon Jun 17 2024 There is agreement among guidance that hot temperatures will continue Wednesday onward as the mid-level high retrogrades westward through Saturday. As it shifts westward, there will be periodic chances (20-30%) of afternoon showers and thunderstorms associated with the rounding of additional vorticity maxima around the high. The areas that will see these chances for convection will be across north-central and northeast Missouri on Wednesday. Shower and thunderstorm chances diminish even more on Thursday and Friday as surface high pressure dominates the Mid-Mississippi River Valley and favors dry conditions. Dewpoints will remain in the 60s through the end of the work week and with convection chances decreasing Thursday and Friday, temperatures will rebound into mid to upper 90s area wide. By late Saturday, ensemble guidance is in consensus that a mid-level trough will traverse across the Upper Mississippi River Valley. As it propagates east-southeastward into Sunday, a surface cold front will move across the region and be the focus for showers and thunderstorms. There is uncertainty in the exact timing of convection as there are timing and amplitude differences amongst deterministic guidances of the trough and thus the cold frontage passage. MMG/Glass && .AVIATION... (For the 12z TAFs through 12z Tuesday Morning) Issued at 634 AM CDT Mon Jun 17 2024 VFR flight conditions are forecast through the TAF period. Southerly winds will continue to increase through the day today with gusts in excess of 20 knots. Cumulus cloud cover will increase during the late morning and afternoon hours and diminish shortly after sun down at all terminals. There is a chance for isolated to scattered afternoon showers and thunderstorms across southeast Missouri today, however, confidence is too low in the northern extent of the shower/thunderstorm activity so there is no mention in the St. Louis Metropolitan TAFs. MMG/Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX