Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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405 FXUS63 KLSX 140845 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 345 AM CDT Fri Jun 14 2024 .KEY MESSAGES... - Above average temperatures are expected through next week with Sunday and Monday the warmest days as peak heat index values reach the upper 90s to 105 F. Although confidence in heat index values reaching dangerous levels is low, care should still be taken since this period will be the first wave of summer-like heat. - There are multiple opportunities with low (20 to 40 percent) chances of showers and thunderstorms, especially mid-next week. && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 344 AM CDT Fri Jun 14 2024 Multiple weakening clusters of showers and thunderstorms skirting central and southeastern MO will gradually dissipate early this morning as expanding cold pools and nocturnal cooling decrease instability in the absence of any strong forcing. The increasingly diffuse cold front originally responsible for these showers and thunderstorms will push southward through the CWA this morning as well. Although this front is anticipated to be south of the CWA by this afternoon and large-scale forcing within upper-level northwesterly flow will be negligible, CAMs indicate diurnally aided instability behind the front supporting a stray shower or thunderstorm during the afternoon across southeastern MO. Low-level CAA behind the front will be weak with high temperatures again reaching the upper 80s to low-90s F with infiltration of drier air/lower dewpoints a more noticeable change along and north of I-70. On Saturday, most short-term models depict weakening showers and thunderstorms across western MO tracking eastward during the morning and early afternoon while dissipating as a LLJ weakens and they outrun richer instability to the west. The latest HREF has highest probabilities of showers and thunderstorms to the west of the CWA but these probabilities reach around 20 percent across central and northeastern MO. Cloud debris from those showers and thunderstorms could have some impact on Saturday`s high temperatures; however, a decrease in these clouds through the day and onset of low-level WAA are expected to provide temperatures similar to today. Pfahler && .LONG TERM... (Saturday Night through Thursday) Issued at 344 AM CDT Fri Jun 14 2024 Late Saturday through the beginning of next week, global models are in good agreement that an anomalous upper-level ridge will blossom across the eastern CONUS, downstream of longwave troughing across the western CONUS. This upper-level wave pattern will leave the central CONUS, under the influence of weak, persistent southerly flow through much of the troposphere with a summer-like pattern in the CWA characterized by widespread temperatures in the 90s F (most days), increasing dewpoints/humidity, and chances of showers and thunderstorms at times. The NBM portrays the warmest, furthest above average temperatures of the period on Sunday and Monday owing to those days favored to have the least cloud cover, lowest probability of precip, and strongest southerly flow. The combination of temperatures well into the 90s F and increasing humidity will support peak afternoon heat index values reaching the upper 90s to 105 F. Although confidence is not high that heat index values will reach dangerous thresholds, care should still be taken, especially for vulnerable individuals, since this period will be the first wave of summer-like heat across the CWA. Late Monday onward, a series of low-amplitude mid-level shortwave troughs/potential MCVs are progged to drift northward in the aforementioned southerly flow, increasing the chance of showers and thunderstorms at times. It is impossible to glean further details of these features at this juncture, but associated showers/thunderstorms and cloud cover introduce some uncertainty in daily temperature forecasts after Monday. This uncertainty is encapsulated by NBM interquartile temperature ranges increasing to 5 to 8 F. With the 25th percentile remaining above average, however, confidence in above average temperatures persisting is still high. Pfahler && .AVIATION... (For the 06z TAFs through 06z Friday Night) Issued at 1107 PM CDT Thu Jun 13 2024 A weak frontal boundary is stalled north of the TAF sites at this hour, with the robust convection that plagued the region now far weaker as it moved into the I-70 corridor. The strongest thunderstorms are now in central Missouri and will threaten KJEF and KCOU for the next few hours. Weak, transient convection with a few lightning strikes will surround the St. Louis terminals for the next few hours, but by roughly 09Z the threat will shift south. Beyond this, dry and VFR conditions will persist through Friday night. MRB && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX