


Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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657 FXUS63 KARX 181640 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1140 AM CDT Sat Oct 18 2025 .KEY MESSAGES... - A fairly active pattern with systems moving through every couple of days into mid-week. Rain chances have been increased tonight (~60-70%), with a dry Sunday expected. Rain chances again Monday into Tuesday, mainly in WI (20-50%). - Weather systems will bring windy periods with Sunday and Tuesday afternoons gusts of 30-35 mph looking probable (60-80% chances). - Forecast remains consistent of a moderate chance (50%) of a widespread frost across the area Wednesday morning. High temperatures are in the seasonal/normal 60s for highs with colder days Sunday and Tuesday/Wednesday (50s). && .DISCUSSION... Issued at 237 AM CDT Sat Oct 18 2025 Rain Looking Likely Tonight For Most GOES Water Vapor is looking quite fall-ish this morning with an impressive large scale trough digging southeast through MT with a band of showers on the MT/SD border westward to the Continental Divide. This matches well to a QVector convergence signal in the 300-500mb layer per RAP analysis. Good agreement exists on the phasing of this wave with the s/sw U.S. wave energy, causing rapid cyclogenesis over the Great Lakes. By Sunday morning, model consensus places a surface low around 990 mb over northern MI. As these waves phase, the excellent lift suggested by the QVector convergence moves over the area tonight bringing rain chances. Much of the QVector convergence signal in the lowest levels is centered across eastern IA and southern WI...suggesting that area should have the highest rain chances. Teaming up with the Qvector convergence is a moderate intensity mid-level frontogenesis band consistent across CAMS and deterministic solutions that drags across the area tonight. Many 18.00Z CAMS suggest a narrow rain band with this feature being the key forcing mechanism. Have increased the rain chances to ~60% along a N-S band shifting east across the area: early evening MN/IA -> late evening+ WI, drying Sunday. Most rain amounts will be around 0.10 to 0.20 inches with the progressive nature to this system. Most of the action (rain) is to the east of the area in the Great Lakes. Winds Ramp Up on Sunday As the surface low deepens over Michigan Sunday and low-level lapse rates steepen locally, wind gusts will kick in late morning. 17.12Z ECMWF ensemble suggesting much of the area has a 60-80% chance of wind gusts over 35 mph Sunday afternoon, however this family is on the higher end of the solutions. 18.00Z HREF guidance shows 90%+ chances for 30+ mph gusts, but probabilities rapidly drop to 30-50% for 35+ mph. Have increased the forecast wind gusts above the NBM guidance on Sunday afternoon into the lower 30s mph. Rain Chances Monday-Tuesday, Windy Tuesday Afternoon After ridge building on a cooler, breezy Sunday, another strong system moves in for early in the week from the west in the continued progressive pattern. This system again has moderate amplitude, a nice warm/cold advection signal in the low levels and moderate-strong QVector convergence aloft. These low/high level forcings are about 12 hours out of phase, but the cold frontal forcing is in concert with the QVector forcing aloft by late Monday. Drier air in the wake of tonights wave causes some of the lift to work to saturate. Model QPF from the forcing signals in the 18.00Z deterministic models arent consistent with the forcing, sans the 18.00Z ECMWF which is more in line with the 17.12Z LREF guidance suggesting a very light rain period Monday. LREF guidance has a 60-70% of 0.01" but only 10-20% for over 0.10" Monday afternoon. However, there is still uncertainty about this wave and the surface cyclone intensity and placement. It appears the main impact will be wind gusts in the 30-40mph range, with the 17.12Z ECMWF ens suggesting a 30-40% for 40 mph gusts in southeast MN and northeast IA. The 18.01Z NBM suggests a less than 10% chance of 40+ mph gusts. The forecast will remain with the NBM guidance of 30-35 mph gusts and rain chances of 30-50%. However, it is very possible these rain chances will increase based on the signals in the forcing. Frost or Freeze Possible By Mid-week Some of the seasons coldest air will settle in for Wednesday morning. It appears skies could be clear southwest of I-94, but winds may still be around 10 mph. This would limit frost production, but temperatures will probably be in the lower 30s in many locations outside the Miss river valley. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1140 AM CDT Sat Oct 18 2025 CIGS: increasing mid level deck tonight, associated with a cold front and upper level shortwave. Should stay VFR. Cigs don`t hang around long and expect mostly SKC conditions Sunday. WX/vsby: Thin band of showers will work in from the west this evening. Won`t stick around for long (a few hours at best) with minimal vsby restriction and QPF (under 1/10"). WINDS: Tightening pressure gradient moving in Sunday will promote northwest gust into the mid 20 kts. A couple more rounds of windier conditions looking likely on Mon/Tue. Some 35+ kt gusts currently possible Tue. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Baumgardt AVIATION.....Rieck