


Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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836 FXUS63 KARX 021824 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 125 PM CDT Wed Jul 2 2025 .KEY MESSAGES... - Low end (20-40%) storm chances through Thu. Where realized, some could be strong. Most location will likely stay dry. - Sultry 4th holiday with heat indices in the mid to upper 90s. Cooler, not as humid by Sunday (highs back into the upper 70s/lower 80s). - Areas of showers/storms continue to look likely for portion of the holiday weekend, but timing shifting back a bit - moreso for Sat/Sat night. Not a rainout weekend but most will see some rain. && .DISCUSSION... Issued at 125 PM CDT Wed Jul 2 2025 > REST OF TODAY-THU: smattering of storm chances. If realized, a few could be strong. An unstable airmass has settled across the region, increasing from day to day as more moist/warmer air pools in from the south. It`s ripe for convection but what remains nebulous is the forcing. MCVs from overnight convection, leftover outflow boundaries, weakly forced fronts could all come into play - but where they move, where they setup is murky. For storms that do fire wind shear is generally meager at best, not providing much support to updrafts and storm organization/sustainability. While there isn`t full agreement on where these micro scale features will lay/move, will trend rain chances where there is more agreement between the CAMS and other short term models - with the understanding that there will be modifications to the forecast based on satellite/observation/radar trends. That said, Thu afternoon is peaking interest with a possible west- east running sfc boundary across the forecast area. Across I-90, south, perhaps north, maybe more of a northwest-southeast running extent - that isn`t clear. But with increasing instability (2500 J/kg of SBCAPE in the RAP/HRRR by late afternoon) in an uncapped environment, even weak forcing could trigger storms. Deep shear around 20 to 30 kts isn`t great, but might provide a modicum of aid to updrafts and limited organization. Some low level jet/moisture transport impingement will aid the lift. Not much of a signal in the CAMS with latest HRRR suggesting a thin line of convection along that front Wed evening - mostly after 00z but across the forecast area. Again, nothing clear cut, but the atmosphere is ready to "go", just needs a spark. Figuring out where those will be, and when, is the challenge. > 4th OF JULY WEEKEND: steamy start, cooler end. Periods of showers/storms (trending for Sat/Sat night) Not a washout for outdoor activities, but will have to dodge some storms here and there. Upper level shortwave ridge axis slips east out of the plains to across the upper mississippi river valley by 00z Sat. Southerly fetch increases, with increasing moisture pouring across the region. PWs push north of 2" in the deterministic GFS/NAM by 12z Sat with warm cloud depths in excess of 4.5 kft at times. NAEFS and EC pw anomalies are +2.5. Rich moisture source, very supportive of heavy rain. Models continue in good agreement with lifting a shortwave trough from the southern Rockies northeast into the ridge Friday night, pushing the ridge east as it spins across northern parts of the region Sat. While the bulk of the upper level forcing would slide north of the local area, an associated sfc cold front would slip west to east across the region - moreso in a northeast to southwest orientation. Speed of the system may not clear the frontal boundary east until Sunday afternoon. - TEMPS: with the influx of more moist air, sfc dewpoints progged to push to/above 70 degrees Friday. With high temps still looking to peak around 90 (or so), resulting heat indices top out in the mid to upper 90s. Not quite heat advisory, but still pretty sweltery. And considering its the 4th holiday with lots and lots of outdoor activities, care will have to be taken to protect yourself-family- friends-pets from the heat. Passage of the cold front will usher in cooler and not quite as muggy air for Sunday. - RAIN CHANCES: ample instability builds across the region ahead of the shortwave/front combo. GFS/NAM a tad enthusiastic with their increase in dewpoints so SBCAPEs likely a bit overdone, but upwards 2500 J/kg reasonable in this regime. Meager capping should be overcome by early/mid afternoon but lacking a discernible forcing mechanism. If general airmass type storms could fire, little if any shear to support updrafts/organization. A more likely scenario for showers/storms will be as the trough/front near from the west, which latest deterministic runs slide in Sat/Sat night. Nearly all the EPS members suggest a bit later for the higher end chances - moving the brunt of the rain chances to Sat afternoon/night. The GEFS suggest perhaps 6 hours earlier. The front doesn`t look strongly frontogenetic, but enough for this kind of airmass to kick of pcpn. Low level jet/moisture transport interactions will also play a role for storm initiation. Upshot to all of that is possible rain impacts to the 4th of July fireworks looking little to none. For the storms that do get going, shear remains meager/weak - not conducive for storm organization, let alone much of a severe threat. A lot can change between now and then, of course, but trends have not favored any kind of organized severe risk locally. Rain chances will linger into Sunday, but if given track/speed of system holds, mostly for southwest-central WI during the morning hours. The rest of Sunday favors dry in the majority of ensemble members. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1225 PM CDT Wed Jul 2 2025 Diurnal cumulus around 5-6kft has developed today, dissipating this evening. Isolated thunderstorms are possible this afternoon and evening, but not overly confident when/where anything will develop given low probabilities (< 30%) and the expected pulse-like nature to them. Probabilities are highest north of I-94, where conditions are most conducive to thunderstorm development. Winds will be from the south to southwest today generally 5-10KT, decreasing to 5KT or less overnight. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Rieck AVIATION...Falkinham