Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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451 FXUS63 KLSX 281800 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 100 PM CDT Fri Jun 28 2024 .KEY MESSAGES... - Multiple rounds of showers and thunderstorms are expected today through Saturday evening. A few thunderstorms could be severe tonight and again Saturday afternoon into Saturday evening. The main threats will be damaging winds and large hail. These threats are highest over central Missouri tonight. The threats are relatively low otherwise. - Above normal temperatures are expect through Saturday. Cooler than normal temperatures Sunday and Monday will be bookended by above normal temperatures as warmer conditions return Tuesday. && .SHORT TERM... (Through Late Saturday) Issued at 351 AM CDT Fri Jun 28 2024 A broad view of the CONUS shows surface high pressure over the eastern Great Lakes early this morning. The eastward nudge in the surface ridge has resulted in southeasterly surface flow locally, progressively turning more southerly behind a warm front that is expected to slowly lift northward today. IR satellite shows much of the central sections of the U.S. covered by broken to overcast skies as a few clusters of thunderstorms are dispersed about the central section of the nation. While the aforementioned warm front resides at the surface, weak mid- level warm air advection at the back side of the ridge has resulted in a few showers grazing northern sections of Missouri. No lightning is associated with this activity with little or no CAPE over the area. Meanwhile, a more robust area of showers and thunderstorms line up from Oklahoma into the Upper Midwest. Resulting cloud cover will continue to stream east through the day. One feature to watch will be the potential for an MCV to track from the Plains into northern Missouri during the late morning and early afternoon. Showers and a few thunderstorms are likely to skim the northern, but the highest chances remain over north-central Missouri into southeast Iowa. Despite the warm front and southerly flow, cloud cover and any additional precipitation should hold temperature in the 80s north of I-70. It`ll be a touch warmer to the south with low- 90s. A broad trough traverses the Canadian/U.S. border through the day as the upper ridge flattens over the Midwest. The western periphery to the mid-level ridge also shifts slightly east with strong moisture advection driven into western sections of Missouri late this evening. An upper level shortwave approaches with signals that a rather compact LLJ takes aim at western sections of the state. A pool of higher MUCAPE in the 2500 to locally 4000 J/kg reside over eastern Kansas and western Missouri, along with 35-40 knots of 0-6km shear. This will be the initial area to focus for thunderstorm development late this evening into the overnight hours. While thunderstorms are more likely to be severe in their origin, CAPE and shear values quickly drop to the east. This should result in a weakening trend in the overnight period with limited support for severe potential with time. Thunderstorms shift southeast through Saturday morning, far less likely to be severe as they approach I-70. How quickly the area can recover will depend on how quickly activity decays and/or exits east Saturday morning. The front will then become the focus for additional convective potential Saturday afternoon and evening. The boundary lines up along or just south of I-70 and is largely supported by mid-level vorticity with the lack of upper level ascent. Guidance suggests surface instability could recover quickly with MLCAPE of 3500-4000 J/kg. The limiting factor is rather weak flow with shear only about 20-30 knots. Given better mid-level lapse rates of near 8C and thicker CAPE profiles on modeled soundings, large hail could be a threat with initial development, along with damaging winds with collapsing updrafts. Maples && .LONG TERM... (Sunday through Thursday) Issued at 351 AM CDT Fri Jun 28 2024 The cold front shifts south of the area Sunday as surface high pressure builds north to south from the Plain and upper level ridging begins to amplify over the central U.S. Northerly flow as the surface and northwest flow aloft will shunt higher dewpoints south with upper 60s to mid-70s being replaced by 50s to low-60s Sunday. 850mb temperatures in the mid-teens will make for a rather nice day relative to recent conditions. These conditions persist into Monday as the surface high slides east with easterly surface flow pushing dewpoints in toe the upper 40s to mid-50s. Highs ranging from the upper 70s to mid-80s may even feel refreshing. The surface high and upper ridge will stave off any precipitation potential as active weather curves around the area to the west and the north until at least midweek. Surface high pressure moves into the Atlantic Region with southerly return commencing Tuesday with warmer air advecting back into the area. The upper level ridge begins to flatten over the central U.S. in a similar fashion as is does late this week. Vorticity is ejected around the western periphery of the upper ridge once again as a broad upper trough moves west to east over the Canadian/U.S. border. This pushes a cold front into the Midwest Wednesday with the front showing a tendency to slow as it moves south. This introduces additional chances for showers and thunderstorms from mid to late week. Maples && .AVIATION... (For the 18z TAFs through 18z Saturday Afternoon) Issued at 1258 PM CDT Fri Jun 28 2024 Isolated showers and a few storms this afternoon for KCOU, KJEF and KUIN. Otherwise, VFR flight conditions until activity develops over western MO and slides east and southeast tonight. Showers and storms will move into KUIN, KCOU and KJEF between 04z and 06z Saturday, while not until 09z-10z Saturday for St. Louis metro area TAFs. Activity will then diminish and move out between 11z and 14z Saturday. As for winds, they will remain from the south for a majority of the forecast period. However, they will veer to the southwest to west at KUIN, KCOU and KJEF by 16z Saturday as cold front approaches area. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX