116 FXUS63 KARX 170356 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1056 PM CDT Wed Apr 16 2025 .KEY MESSAGES... - Widespread rain with a risk for strong to severe storms (risk level 2/5 west of the Mississippi River and level 1/5 to the east) especially Thursday evening into Friday morning. large hail would be the primary concern however cannot rule out damaging winds or an isolated tornado. - General amounts of .25 to .85" of rainfall Thursday into Friday morning. Some low probabilities of 1" per hour rates (10-20%) Thursday evening, thus higher amounts possible with the storms. && .DISCUSSION... Issued at 329 PM CDT Wed Apr 16 2025 Overview: At midday, water vapor satellite imagery and heights revealed a 500mb ridge over the Upper Mississippi Valley into the Plains with a trough over New England and a closed 500mb low pressure system off the southern California coast. In addition there was a trough over southwest Canada. High clouds were noted across the region. Surface high pressure was over the local area with a warm front located over southwest Iowa. Locally, temperatures were mostly in the 50s early this afternoon with surface dewpoints in the 20s. Southeast winds 10 to 20 mph. Regionally, temperatures were quite mild south of the warm front in the 70s, however dewpoints remain quite dry with 20s and 30s dewpoints still across all of Missouri. Tonight into Friday The trough over southern Canada and the trough off the California coast will merge through Thursday. Meanwhile surface low pressure organizes over the Plains. Although much of the region is quite dry (850mb dewpoints of less than 2 deg. C), strengthening low level flow with increasing 900-850mb winds are progged to result in the axis of 10 deg. C dewpoints over OK spreading northeast across Iowa tonight and reaching northeast Iowa by 12Z. In addition, there is upper level support with the left front exit region of the 90 to 105kt jet nosing into the Plains. With the lowering heights aloft and energy moving through the Plains, a few of the convective allowing models do have a few showers and possibly a storm lifting northeast across parts of the forecast area, however the higher coverage is to the south across parts of Iowa and Illinois. Due to the elevated instability (1000-1500J/kg), cannot rule out thunderstorms, although models have varying degrees of a cap/steepening mid-lapse rates. Thursday afternoon and Thursday night with the approaching lift, convergence increasing along the 850mb front with showers and storms increasing northwest of the forecast area and the surface front tries to push into parts of southeast Minnesota. The main axis of MLCAPE during the afternoon and evening remains to our west, however due to the strengthening deep layer shear of 35 to 50kts, cannot rule out strong to severe storms with a band of northwest to southeast showers and storms that form near the Mississippi River and lift northeast and along the front that organize over Minnesota and shift east overnight. Hail appears to be the primary threat, however the cams are hinting at some bowing structures being possible. In addition, depending on where the warm front is over southeast MN, a tornado cannot be ruled out where the convection is surface based. Later Thursday night, a cluster of storms develops over parts of Iowa. The 16.12Z HREF highlights the potential for damaging winds as the storms move into northeast Iowa late Thursday evening and into the overnight hours as they move into Wisconsin. Rainfall amounts will depend on where the storms occur, however we currently have general .25 to .85" amounts with the higher amounts north of I90. The HREF axis 24hr ensemble max amounts are currently just north of the forecast area. Max amounts locally are 1 to 1.5". The 6-hr flash flood guidance shows we should be able to handle these amounts. There are some low probabilities for 1" per hour rates over Dodge Co in the evening, so will need to monitor for heavy rain rates. Weekend: For Saturday through Monday, a 500mb trough over the Rockies is forecast to lift northeast somewhere over the Mid to Upper Mississippi Valley. The GFS ensemble trends continue to show a more south track since 15.00Z. Meanwhile, the EC ensemble trends have had a more northern track along with the Canadian ensembles. As a result, the GEFS probabilities for .5" or more of precipitation 12Z Sunday through 12Z Monday are 33% at DBQ, but 10% or less at RST/LSE. However, the ENS/GEPS ensembles have a 40 to 80% chance for .5" of rainfall and a 20 to 50% for 1" or more of rainfall. Currently our forecast has pops in more in line with a northern track . && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1050 PM CDT Wed Apr 16 2025 VFR conditions are forecast through the overnight and into the early morning hours. There is a 20-30 percent of thunderstorms in the mid-morning, with the probabilities for storms increasing later in the afternoon. Ceilings and visibilities in these storms could fall to MVFR in the morning, with an increasing risk of IFR conditions with any afternoon and evening storms. Winds remain from the south to southeast through the period, light in the valleys tonight while remaining around 10-15 kts on the ridge tops. Winds increase to 15-20G25-30kts for the daytime. LLWS continues tonight at low-lying locales like LSE. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Zapotocny AVIATION...Skow