Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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369 FXUS63 KARX 212023 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 323 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - Showers and storms into tonight, few could be strong to severe. Rain chances linger for parts of northeast IA/southern or west central WI into Sunday - Below normal temps into early next week. && .DISCUSSION... Issued at 315 PM CDT Sat Sep 21 2024 Overview: Water vapor satellite imagery, heights, and lightning show a trough over southern Canada with another area of closed 500mb low pressure approaching the Four Corners region with a ridge over the Southern Plains. Lightning was occurring with scattered convection over parts of central and eastern WI and along a cold front across MN as well as ahead of the storm system in the southwest U.S. With the warm front lifting north, we did have a few strong to severe storms move through parts of northeast Iowa and western WI. At 20Z...an outflow boundary was pushing through parts of southwest WI with the surface warm front between PDC and DBQ. The surface cold front had pushed to south central MN, however there were showers continuing west of this area. Rest of today through Sunday night: The Canadian trough will continue to swing through the Mississippi Valley through Sunday morning. The will drag a cold front through the forecast area. Meanwhile, the closed low over the Four Corners region will open up and shift eastward through the Central Plains. Moisture transport will continue through the evening hours across the forecast area with MUCAPE of 2000J/kg per the SPC Mesoscale page, however the SBCAPE is around 2500J/kg across northern Iowa. Scattered showers and thunderstorms will continue ahead of the cold front with strong to severe storms possible due to the CAPE and effective shear around 45kts. The convection and outflow boundary could temper the severe potential farther north, however the instability and downdraft CAPE of 1200J/kg or higher could lead to some strong to severe storms. The winds will veer with time, however the instability lingers into the evening. The CAMs were dry for the early day/early afternoon convection, thus not doing well with the pre-frontal storms. Hopefully, the RAP/HRRR has a handle on increasing convection through the afternoon with the showers/storms gradually pushing east through 07Z. The CAMs do hint at re-developing across the southern part of the forecast area for after 07Z into Sunday morning. Showers should gradually exit the area during the afternoon with cooler air for the area. Highs Sunday should top out in the mid 60s and lower 70s, more seasonable for this time of year. Monday through the week: Behind the weekend cold frontal system, cooler conditions look to continue for the start the week with highs in the upper 60s to low 70s and lows in the 40s to low 50s. Model guidance continues to suggest a shortwave trough in the northern flow while shortwave energy slides just south of the local area for the early part of the work week. There remain some differences between the individual GEFS/ECMWF ens solutions on precipitation potential. However, have noted a very slight trend towards a drier solution in the most recent blended model guidance, which currently keeps 15-20% chances in far southwest WI for late Monday night into Tuesday. Behind the upper level trough, guidance looks to favor upper level ridging building eastward. Still some variability, but GEFS/EPS ens solutions do not show a strong/definitive QPF signal through much of the rest of the week. Otherwise, temperatures are forecast to gradually increase back into the mid/upper 70s by the end of the week. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1255 PM CDT Sat Sep 21 2024 A warm front is lifting into the area today followed by a cold front tonight. These weather systems will bring scattered showers and thunderstorms to the area. The hi-res CAMs are going to have to catch of with the showers developing with the warm front at the models were dry. Will continue to refine the timing of showers/storms until the drier and cooler air arrives. It appears the showers/storms exit RST by around 06 or 07Z and 09Z at KLSE, however re-development will be possible until the mid-level trough pushes through Sunday morning. South to southeast surface winds 5 to 15kts with some stronger gusts at KRST shift to the southwest and northwest with the frontal passage this afternoon and early this evening. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...EMS/Zapotocny AVIATION...Zapotocny