Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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612 FXUS63 KARX 280819 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 319 AM CDT Sun Apr 28 2024 .KEY MESSAGES... - Heavy rain axis has shifted south of the area. A more widespread rain of 0.5-1" is expected through Monday, with most falling during the afternoon and evening today. The risk of storms being severe is low. - An active week is expected with periodic rain and storm chances with the next chance coming Tuesday/Tuesday night. && .DISCUSSION... Issued at 318 AM CDT Sun Apr 28 2024 Widespread Storms Today into early Monday: As the surface low moves northeast towards the Upper Midwest region, dewpoints and lift will increase. Dewpoints increase as the warm sector pushes northward, while lift increases due to waves of energy originating from the surface low passing through the area. Current CAM guidance has a swath of widespread showers and storms moving into northeast Iowa and southern Wisconsin by mid-morning today and pushing northward through the afternoon. As this band moves northward during the afternoon, moisture advection increases from the south, resulting in PWAT values between 1" and 1.4". These values are in the NAEFS 90th to 99th percentiles for PWATS. The highest PWATs will be along the stationary boundary in far southern Wisconsin, northern Illinois and eastern Iowa. Not much is in the way for instability, as the boundary stays to our southeast for most of the day, at least with this first round of storms. Instability will increase a little as the surface low pushes northeastward. SBCAPE and MUCAPE will be around 500J/kg heading into the late afternoon and lasting through the evening. This appears to be the most likely time for any severe weather to occur. Not much is expected given the lack of instability and daytime convection, however with the surface low close by and good amounts of shear, there remains a marginal risk for severe weather along and south of I-94. As far as precipitation goes, most areas look to have 0.5 to 1" of rain from today into Monday. The latest HREF probabilities have between a 20 and 40% for at least an 1" of rain to occur. Active Pattern Next Week: Next week is looking like another active period as the region ends up being in a predominant zonal flow. This flow pattern will result in periodic shortwave disturbances to bring more precipitation chances throughout the week. The first wave to move through is expected on Tuesday. Current guidance has a compact shortwave moving through the area. This will be accompanied by good moisture advection from the Gulf of Mexico ahead of a cold front Tuesday afternoon/evening. By Tuesday afternoon, the cold front will be near I-35, where the greatest lift and instability will be at, due to being in close proximity to the shortwave. MLCAPE values of around 500J/kg are expected across southern Minnesota at this time as well. Given these dynamics, SPC has gone with a Marginal for portions of southeast Minnesota. CSU severe probabilities also have a 5 to 15% chance of severe weather occurring late Tuesday. There is a lot of uncertainty with what happens after Tuesday. Zonal flow will continue. Ensemble guidance has differing solutions with a slight lean into a trough moving through the region on Thursday and another on Saturday. Confidence is not low, however the week will remain active with multiple chances of precipitation. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1112 PM CDT Sat Apr 27 2024 Conditions will deteriorate with MVFR/IFR cigs by morning as a low pressure system begins to track northwest of our region. As it progresses, showers will envelope the region during the morning Sunday. A few storms are possible later into the day on Sunday, however confidence is very low in how they may manifest at this time so will opt to keep any mention of VCTS out of the TAF for now. CAMs try to reduce coverage of shower activity close to 06z but will hold onto shower mention through the evening. Winds will begin the TAF period under 10 kts before increasing during the morning as the surface pressure gradient tightens with wind speeds of around 15 kts by the afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Cecava AVIATION...Naylor