Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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133 FXUS63 KLSX 151056 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 556 AM CDT Sat Jun 15 2024 .KEY MESSAGES... - Temperatures are expected to remain above average through next week. Summer-like heat will be most pronounced on Sunday and Monday with peak afternoon heat index values in the upper 90s to 105 F. - There is a low (20 to 40 percent) chance of showers and thunderstorms at times, primarily Monday onward and during each afternoon. && .SHORT TERM... (Through Late Tonight) Issued at 328 AM CDT Sat Jun 15 2024 An upper-level ridge will shift from the Mississippi River Valley to the Ohio Valley today, providing mostly dry conditions. In addition to a weakening MCS this morning passing well west/northwest of the CWA in the Central Plains, isolated to scattered showers and thunderstorms are anticipated to develop this afternoon near a weak warm front from west-central MO into southern MO. Instability should decrease with northeastward extent from this front into the CWA, with CAMs only indicating an isolated shower or weakening thunderstorm reaching central MO this afternoon. Upper-level cloud debris from any of these showers and thunderstorms is expected to be thin and transient, allowing insolation to accompany the onset of southerly low-level WAA and support high temperatures similar or slightly warmer than yesterday and in the upper 80s to low-90s F. Pfahler && .LONG TERM... (Sunday through Friday) Issued at 328 AM CDT Sat Jun 15 2024 Sunday through Monday, the upper-level ridge will amplify and expand over the eastern CONUS with deep, weak southerly flow becoming established throughout the troposphere in the lower to mid- Mississippi River Valley at the ridge`s western periphery. As a result, a period of summer-like heat is anticipated, especially on Sunday and Monday when ensemble model guidance depict the warmest 850-hPa temperatures above the 90th climatological percentile. Model guidance and the overall pattern (e.g., southwesterly component of low-level flow possibly downsloped off the Ozark Plateau) support the warmest temperatures occurring on Sunday with high temperatures in the low to upper 90s F, approaching daily records (see CLIMATE section). Moisture/dewpoints will also be increasing, yielding afternoon heat index values of 100 to 105 F in many locations. Although these values are just below hazardous thresholds, extra care should be taken since Sunday will be the hottest day of the year so far. As the axis of the upper-level ridge shifts northeast after Sunday, model guidance is in agreement that 850-hPa temperatures will cool slightly (1 to 2C)as low-level flow backs to the southeast. In addition, a series of mid-level perturbations/potential MCVs is progged to accentuate diurnal showers and thunderstorms Monday onward, communicated by low chances (20 to 40 percent) of showers and thunderstorms peaking during each afternoon. The exact impact of showers/thunderstorms and associated clouds on temperatures is unclear and captured by NBM temperature interquartile ranges spanning 5 to 8 F during that time. However, the vast majority of the ensemble model 850-hPa temperature distribution remains above average, increasing confidence in temperatures enduring above average across most of the CWA. Pfahler && .AVIATION... (For the 12z TAFs through 12z Sunday Morning) Issued at 556 AM CDT Sat Jun 15 2024 Predominantly dry and VFR flight conditions are expected through Sunday morning with the highest chances of showers and thunderstorms remaining west of all terminals this morning and afternoon. A stray shower or thunderstorm cannot be ruled out at KCOU and KJEF, but the probability of occurrence is too low to mention. Pfahler && .CLIMATE... Issued at 328 AM CDT Sat Jun 15 2024 Daily High Temperature Records: |=== June 16 ==|=== June 17 ==| St. Louis (KSTL) | 100 F (1952) | 99 F (1944) | Columbia (KCOU) | 99 F (2006) | 100 F (1936) | Quincy (KUIN) | 102 F (1936) | 103 F (1918) | && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX