Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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341 FXUS63 KLSX 160856 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 356 AM CDT Sun Jun 16 2024 .KEY MESSAGES... - Above average temperatures will persist through the upcoming week with today and Monday expected to be the warmest days including peak afternoon heat index values in the upper 90s to 105 F. - Isolated to scattered showers and thunderstorms are forecast at times through the upcoming week as well, with the greatest chances (20 to 40 percent) on Monday and Tuesday during the afternoon. && .SHORT TERM... (Through Late Monday Afternoon) Issued at 355 AM CDT Sun Jun 16 2024 An upper-level ridge centered over the southern Appalachian Mountains and Ohio Valley will begin amplifying and expanding today increasing low-level southerly flow in the Mid-Mississippi River Valley at the ridge`s western periphery. After a much milder night tonight (5 to 15 F warmer than 24 hours ago), ingredients will come together for the warmest day of the year thus far today, including 850-hPa temperatures warming above the 90th climatological percentile, a slight southwesterly component of low-level flow downsloped off the Ozark Mountains, and strong insolation. The result will be widespread high temperatures in the low to upper 90s F. Additionally, moisture/dewpoints will be increasing, but compensated to some degree by deep mixing and slight downsloping, contributing to peak heat index values reaching the upper 90s to 105 F this afternoon. These values fall just short of conventional hazardous thresholds; however, care should be taken by individuals spending time outdoors today. Lastly, recent CAMs are advertising that a remnant MCV from an MCS currently tracking in eastern KS will have the potential to produce a few showers and thunderstorms in northeastern MO and west-central IL this afternoon. Otherwise, dry conditions are anticipated. On Monday, the first of a series of mid-level perturbations rotating northward around the upper-level ridge will arrive to the Mid- Mississippi River Valley, acting to enhance development of diurnal isolated to scattered showers and thunderstorms during the afternoon and evening as instability peaks and convective inhibition is at a minimum. The presence of these showers/thunderstorms and greater cloud cover along with a slight cooling of 850-hPa temperatures will lead to slightly cooler temperatures on Monday mainly along and south of I-70, but greater moisture/higher dewpoints will again promote peak afternoon heat index values reaching the upper 90s to 105 F across most of the CWA. Pfahler && .LONG TERM... (Monday Night through Saturday) Issued at 355 AM CDT Sun Jun 16 2024 The center of the upper-level ridge will shift more northeastward into the Mid-Atlantic and Northeast on Tuesday and Wednesday, allowing low-level flow to back slightly with a brief cooling of 850- hPa temperatures. Additional opportunities for diurnal isolated to scattered showers and thunderstorms are also expected Tuesday and Wednesday with the help of additional passing mid-level perturbations, leading to some uncertainty in exact temperatures each day. As a result, NBM temperature interquartile ranges still span 5 to 8 F but remain largely above average. After Wednesday, global models are in agreement that there will be a period of time that the upper-level ridge retrogrades westward slightly, which is indicated by ensemble models to support another increase in temperatures further above average and lower chances of showers and thunderstorms. Pfahler && .AVIATION... (For the 06z TAFs through 06z Sunday Night) Issued at 1059 PM CDT Sat Jun 15 2024 Dry and VFR flight conditions are expected throughout the TAF period with southeasterly winds becoming southerly and strengthening on Sunday. 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