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Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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818 FXUS63 KLSX 161919 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 219 PM CDT Fri Aug 16 2024 .KEY MESSAGES... - A few chances for isolated, weak showers and thunderstorms across portions of the area through tomorrow afternoon, but the majority of the area will be dry. - Sunday and beyond will be largely dry with below normal temperatures. && .SHORT TERM... (Through Late Saturday Night) Issued at 219 PM CDT Fri Aug 16 2024 A weak cold front is slowly making its way southeastward through the forecast area, with little modification to our sensible weather behind the front. Meanwhile, aloft a trough is churning over the Great Lakes region, with a ridge centered over New Mexico/west- Texas, leaving the mid-Mississippi Valley in northwesterly flow. Despite the weak moisture convergence along the front, a small mid- level disturbance moving across the region has a 20% chance of generating a few showers or isolated thunderstorm along and south of the front through the early evening. The weakness of the synoptic features increases confidence that if anything does develop, it will be short lived. Tonight, an MCS (ongoing across central Kansas) will strengthen and organize, sliding into southwest Missouri overnight along the northwesterly Corfidi vectors. While this area of showers and thunderstorms is expected to stay largely outside of our forecast area, I cannot rule out portions of our central Missouri counties getting clipped by a few showers and isolated thunderstorms overnight. As this MCS passes by, a secondary cold front will start sliding through the forecast area tomorrow morning. While forcing for ascent aloft and at the surface will be weak, I cannot rule out a weak diurnal shower or thunderstorm across southeast Missouri and southern Illinois ahead of the front during the afternoon. This airmass south of the front will be moist and unstable with 1000-2000 J/kg of MLCAPE during the afternoon, favorable for thunderstorm development if enough lift can force one. The secondary front will usher in the expected shift in sensible weather, bringing seasonally cool and dry conditions back to the region. MRM && .LONG TERM... (Sunday through Next Friday) Issued at 219 PM CDT Fri Aug 16 2024 The mid-level trough will end the weekend over the Great Lakes region, but shift eastward through the first half of next week. At the same time the ridge over the southern Rockies will expand. The resulting northwest flow over the mid-Mississippi Valley, combined with a large surface high, will advect a cooler, drier airmass into the region through much of next week. 850mb temperatures will drop about 5-6 degrees with the post-frontal airmass from where they are now. Confidence is high in this occurrence, with the ensemble spread in 850 mb temperatures only 1-2 degrees into next week. Surface temperatures will respond in kind, topping out about 5 degrees below average for this time of year through mid-week. Into the second half of next week the surface the high will shift east, throwing the region back into southerly surface flow. This will start a gentle warming trend that we will see through the remainder of the period. MRM && .AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1219 PM CDT Fri Aug 16 2024 Dry and VFR flight conditions will continue through the TAF period, expect for a short period of VCSH at the mid-Missouri terminals tonight. There is a 20% chance for showers along the northern edge of a complex of thunderstorms moving through SW Missouri that could impact the terminals (KCOU, KJEF). Confidence isn`t yet high enough to include more than a VCSH at this point. A cold front will move through the terminals tomorrow, turning winds to the northwest. MRM && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX