FXUS63 KARX 191853 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 153 PM CDT Fri Apr 19 2024 .KEY MESSAGES... - Chilly start to the weekend with temps near/below freezing expected for many locations tonight and Saturday night. - More seasonable by Sunday into next week with the next more widespread rain chances (60-80%) late Monday into Tuesday. && .DISCUSSION... Issued at 153 PM CDT Fri Apr 19 2024 Tonight-Sunday: Chilly start to the weekend A cumulus field has thickened this afternoon beneath cooler mid- level air on the southern flank of an upper level trough across Ontario, especially north of I-90. The combination of steep low- level lapse rates and a few embedded shortwave perturbations dropping southeast late today into the evening around the parent trough could yield a few snow or rain showers (10-30%), with the higher chances heading northward. With deep mixing, occasional wind gusts have reached 40-45 mph in open areas. Winds will subside gradually this evening. A seasonably chilly airmass will remain in place into the start of the weekend with low-level cold advection persisting and northwest flow aloft. Temps should begin to moderate by Sunday with plenty of sunshine and warming 925 mb temps. Elevated fire weather conditions are possible on Sunday with RH potentially falling to 20-25% and deep mixing above 850 mb. Boundary layer flow does not look overly strong, but some gustiness is possible with diurnal mixing. With the cooler airmass, frost/freeze will be a concern through Sunday night, with tonight/Saturday nights the coldest. High probabilities (>90%) exist across most areas tonight for freezing temps with the higher chances (50-90%) for temps below 28F centered west of the Mississippi River, on ridgetops, and areas north and east of I-94. With some mixing/wind overnight, conditions may not be ideal for true frost development, but it will be chilly regardless. Given the temperatures, we issued a Freeze Warning for our counties we have activated for frost/freeze headlines so far this spring, based upon vegetation susceptibility. Monday-Tuesday: Shower chances A healthy Pacific shortwave trough remains on track to impact the region later Monday through Tuesday. Some showers will be possible by Monday in association with mid-level warm advection leading the parent wave, with additional chances into Tuesday or even Tuesday night as the associated front/trough slides through, dependent on the timing of the trough. Overall, moisture transport/instability look modest, likely limiting thunder chances (20%) and higher rain amounts. As it stands now, global ensembles (EPS/GEFS/CMC) show around 40-60% chances for 1/4" of rain near and north of I-90 with lower (20-30%) chances for at least 1/2" of rain in this area. Very few members show 1" amounts. Fairly seasonable temps are expected ahead of the system. Wednesday-Friday: Seasonable, rain chances late week In the wake of the early week trough, broad, progressive mid to upper level ridging will spread east across the Upper Midwest for mid to late week. Overall, the airmass looks seasonable for late April (50s and 60s), with some modest warming through late week. There is a signal for increasing shower/storm potential towards the end of the work week as the ridge axis passes east and deeper moisture lifts back north across the Upper Mississippi Valley. Predictability of shortwave passages within the southwest flow pattern remains lower, but NBM precipitation chances are medium (40- 70%) by Friday. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1150 AM CDT Fri Apr 19 2024 A VFR stratocumulus field will impact KLSE/KRST through early evening before scattering with some additional VFR cumulus development by Saturday morning. Small (10-20%) chances for a shower as far south as I-90 will continue through this afternoon, although the higher rain/snow shower chances will be farther north across WI/MN. Gusty west/northwest winds will gradually weaken early this evening, but some gustiness could persist at times. Winds will become a bit more northwesterly on Saturday, but speeds will be lower compared with this afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Freeze Warning from midnight tonight to 8 AM CDT Saturday for WIZ032-033-041-053>055-061. MN...Freeze Warning from midnight tonight to 8 AM CDT Saturday for MNZ079-086>088-094>096. IA...Freeze Warning from midnight tonight to 8 AM CDT Saturday for IAZ008>011-018-019-029-030. && $$ DISCUSSION...JM AVIATION...JM