Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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738 FXUS63 KARX 100841 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 341 AM CDT Mon Jun 10 2024 .KEY MESSAGES... - Scattered showers and thunderstorms Tuesday. Marginal risk (level 1 of 5) for severe weather with gusty winds and hail as the main threats. - Thunderstorm chances return Wednesday night. Higher severe risk compared to Tuesday with more focus over Minnesota and west central Wisconsin (level 2 of 5). - Below normal temperatures for Monday/Tuesday, but a warming trend into the weekend with temperatures trending normal to above normal with highs in the 80s. && .DISCUSSION... Issued at 341 AM CDT Mon Jun 10 2024 Tue: Marginal Risk (level 1 of 5) for Severe Weather A ridge will be over the area for the beginning of the week. Heading into Tuesday, a shortwave trough dips down from Canada and brings the area its next chance of precipitation. Moisture transport increases Tuesday afternoon just as dewpoints approach the upper 50s to near 60F. Guidance continues to show some showers moving out ahead of the main trough in the morning to early afternoon. As the trough gets closer, instability increases with MLCAPE values potentially getting as high as 1000 J/kg and bulk shear, 0-6km, ranging from 40 to 50kts. The key for these storms is sufficient daytime heating. Depending on how the timing of the showers that move through and how long they stick around will help in determining on unstable the atmosphere can get. Another thing to aid in increasing instability is the warm southwest flow that will increase as 850hPa flow increases during the day. After the early showers move through, isolated to scattered thunderstorms are expected to form and CAMS have shown this occurring in the late afternoon to early evening on Tuesday. With these ingredients in place, SPC has gone ahead and placed a marginal risk (level 1/5) for severe weather to occur. Wed into Thu: Thunderstorm Chances and Severe Weather The ridge flattens out for mid-week allowing for a couple of shortwave troughs to pass through the region. The first disturbance has deeper moisture and stronger southwest flow allowing for moisture transport to increase as a result. If this convergent zone ends up maintaining its strength, there could be a risk of heavy rainfall across the area. Westerly flow is in place for the mid levels while southwest flow will be in place for the lower levels. The area will also be in the exit region of a jet that will be moving into the area. Strong instability and high lapse rates are expected across South Dakota and Minnesota. Bulk shear across this area is forecasted to be in the 40 to 50kt range. Storms are expected to fire up in this area during the afternoon and move eastward into the overnight period. Given these stronger ingredients compared to Tuesday, current SPC outlook has a slight risk (level 2 of 5) for portions of southeast Minnesota and west central Wisconsin, with a marginal risk (level 1 of 5) for the rest of the forecast area. Temperatures will be a bit warmer with the stronger southwest flow, with highs generally between 5 to 8F above normal. This means high temperatures around the area are forecasted to be in the upper 70s to mid 80s. Current NBM probabilities have between a 20 to 30% chance for parts of northeast Iowa and river valley locations to hit 90F both days. Fri through the Weekend: More Storm Chances? As the weekend approaches, the ridge strengthens and drier conditions are expected for Friday and Saturday. There is something else to watch however, as ensemble and deterministic guidance continue to show a closed low over the Intermountain West. This low is forecast to move into the Upper Mississippi River Valley later this coming weekend. This will be another potential to watch as the weekend gets closer. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1045 PM CDT Sun Jun 9 2024 High pressure will provide light and variable winds for the 10.06Z TAF period. Narrow cloud bank at TAF issuance seen sagging south through Wisconsin and southeast Minnesota on satellite imagery. While MVFR ceilings observed at select upstream sites, have continued VFR at local TAF sites (KRST & KLSE). With the drier air eroding bases, expect slight lifting to result in VFR. Will be the main forecast challenge over the next couple of hours. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Cecava AVIATION...JAR