782 FXUS63 KLSX 020315 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1015 PM CDT Sun Jun 1 2025 .KEY MESSAGES... - The warmest days of the week will be Monday and Tuesday when afternoon temperatures approach 90 degrees. - An active stretch of weather kicks off on Tuesday and continues through the weekend, with multiple rounds of showers and thunderstorms capable of heavy rainfall expected. && .SHORT TERM... (Through Late Monday Night) Issued at 235 PM CDT Sun Jun 1 2025 Afternoon water vapor imagery shows northwesterly flow over the CWA, with upper-level troughing over the eastern CONUS and a ridge building over the Intermountain west. This northwesterly flow continues to advect Canadian wildfire smoke into the region aloft, which has been thick enough today to slightly mute the diurnal temperature trend for several areas. Most locations in the CWA will still see highs in the upper 70s to low/mid 80s, with the relatively cooler temperatures being in Illinois behind the backdoor cold front. This front is still expected to serve as the focus for isolated to scattered convection across far southeastern Missouri this afternoon and early evening, and cumulus has developed in this area recently per visible satellite. Tall, skinny CAPE, poor low- level lapse rates, and 0-6 km shear of 25 kts or less will keep any updrafts that develop weaker and short lived. The upper-level ridge will quickly build into the Midwest tomorrow, with mid-level ridging proceeding it. This will turn mid-level flow south-southwesterly and ramp up warm air advection, giving temperatures a boost for tomorrow afternoon compared to today. Then, most locations are forecast to reach the upper 80s. With the ridge shifting eastward, steering flow will begin to push the wild fire smoke further eastward, but not locally noticeably until Monday night. Therefore, another day of milky skies can be expected tomorrow, but smoke is still not forecast to reach the surface. Elmore && .LONG TERM... (Tuesday through Next Sunday) Issued at 235 PM CDT Sun Jun 1 2025 For Tuesday, guidance consensus is that an upper-level trough over the western CONUS will slowly edge eastward as a shortwave rounds its base across the Central Plains. Deep southerly to southwesterly flow over the Middle Mississippi Valley will continue advecting warm, moist air into the region ahead of an approaching front. This will lead to one more day of temperatures in the upper 80s to around 90s for many locations, though specifics are still uncertain due to variability in forecasted cloud cover and frontal timing. The general timing of this front among guidance has quickened, with rain chances associated with the low-level jet ahead of the front ramping up across portions of central and northeastern Missouri already Tuesday morning. The prefrontal environment Tuesday afternoon and evening will be characterized by 30-35 kts of 0-6 km shear, though there is quite a spread in SBCAPE, with a majority of ensemble guidance having approximately 1,000 J/kg or less, though some outliers and deterministic guidance have as much as 3,000 J/kg. This leads to at least a low concern for strong to severe thunderstorms, though mean flow and deep-layer shear parallel to the front and weak CIN will lead to numerous updrafts interfering with each other, limiting a severe thunderstorm threat. Though, given the slow-moving nature of the front and the aforementioned wind profile, there is a low concern for locally heavy rainfall late Tuesday into Wednesday. For Wednesday through the weekend, guidance consensus breaks down on the phasing of the trough, though some degree of quazi-zonal flow is expected over the Middle Mississippi Valley. As long as the front can remain in the vicinity of the CWA, this will lead to regular chances of convection through the weekend as disturbances within the flow ripple overhead. Given the lack of prolonged warm air advection and frequent rain/cloud chances, the 75th percentile of ensemble guidance struggles to break 80 degrees for much of the CWA through Sunday. Elmore && .AVIATION... (For the 06z TAFs through 06z Monday Night) Issued at 1012 PM CDT Sun Jun 1 2025 No significant changes made to the 06Z TAF cycle, as VFR conditions remain most likely to prevail throughout the period. There is a low probability potential for shallow fog to impact river valley sites late tonight and early tomorrow morning, particularly JEF/SUS. However, the chance of visibility reductions and terminal impacts remains too low for explicit mention in the TAFS at this time. Otherwise, light and variable winds will become southerly tomorrow morning, and may be occasionally gusty at COU/JEF/UIN in the afternoon. BRC && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX