427 FXUS63 KARX 261919 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 219 PM CDT Sat Aug 26 2023 .DISCUSSION...(This evening through Saturday) Issued at 219 PM CDT Sat Aug 26 2023 Key Messages: - Cooler temperatures continue Sunday. Temperatures rebound late in the week with highs back into the 80s. - Low end rain chances with the possibility of a few storms Monday afternoon into Monday night. Then..mainly dry weather through the end of the week Tonight into Sunday Per GOES visible imagery trends and surface observations, pesky clouds in cold advective northeast flow providing a very fall-like feel for much of the area sans northeast IA, with highs in the lower 70s for many. Clouds do continue to lift and are becoming, generally, more cellular and slowly decreasing in coverage for much of the area per GOES visible loops. There remains some suggestions in the shorter term guidance that clouds (NAM/NAM3km) or at least some low-level moisture /850 mb/ will remain. Thus, while the clearing this evening should occur with the loss of diurnal heating, some morning cloud or fog may be around the area with I-90 and south a bit more favored with higher lingering moisture. River valley fog looks like a surety for the WI river (90%), but may also occur in the Miss river tribs and mainstem (35%). This will need to be monitored this evening as the deep wind layer and moisture profiles above 800 mb suggest radiative cooling may be pretty favorable. With lower dewpoint spreads heading into the evening after a bit cooler day, everything could line up. Sunday should be a sunnier day with temperatures in the 70s. Sunday night through Tuesday Upper level trough will continue to dig over the Upper Great Lakes Region Sunday night through Tuesday. A couple of impulses embedded in the northerly flow aloft will move over the Upper Great Lakes Region Sunday night into Monday night. The better lift/moisture convergence with the first impulse will be north/east of the forecast area Sunday night. This will allow the forecast area Sunday night to remain mainly dry. A stronger impulse will track over northern Wisconsin Monday afternoon/evening. With better moisture convergence/lift in association with the impulse...there is the possibility of showers or a few storms across northern parts of the forecast area...albeit small chance 20-30 percent. Instability is limited with this impulse and coverage of storms will be isolated. Severe weather is not expected with any of the storms. High temperatures will climb into the middle 70s to middle 80s out ahead of the stronger impulse Monday afternoon. Behind the impulse...cooler airmass will advect into the forecast area and high temperatures Tuesday will mainly be in the 70s across the forecast area. Tuesday night into Saturday Main forecast concerns Tuesday night through Saturday are temperatures through the period. Upper level ridge builds into the central/southern United States through the period. The main issue is the strength of the upper level ridge/timing of shortwave trough into the Upper Great Lakes region late in the period. The GEFS ensemble members are all over the place on the strength of the upper level ridge/timing of the shortwave trough with the deterministic models of the 26.12z GFS/ECMWF differ on the strength of upper level ridge/timing of shortwave trough. This will have impacts on how warm temperatures will be late in the period. The deterministic models of the 26.12z GFS/ECMWF indicate 925mb temperatures warming to plus 25 degrees celsius over the forecast area Friday and potentially into Saturday. Expect high temperatures to climb well into the 80s Friday and potentially on Saturday...depending on timing of shortwave trough. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1242 PM CDT Sat Aug 26 2023 MVFR clouds remain at KLSE and KRST per observations. GOES satellite imagery suggesting some break up to more cellular cloud is occurring which should allow ceilings to 1) continue to lift to VFR and 2) decrease to SCT clouds as the afternoon progresses. This trend has been slowed in the forecast all morning based on satellite trends in cooler northeast flow. There will be clearing this evening but lingering moisture could cause morning clouds to form. It would appear south of I-90 is highest probability (30%) where lingering moisture is highest, but confidence in the Sunday morning forecast is low overall for aviation. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ DISCUSSION...Baumgardt/DTJ AVIATION...Baumgardt