Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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172 FXUS63 KARX 281143 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 643 AM CDT Fri Jun 28 2024 .KEY MESSAGES... - Periodic showers and thunderstorms will occur through tonight. A severe thunderstorm this afternoon and evening cannot be ruled out, but this appears increasingly doubtful for our forecast area. - A few sprinkles possible Saturday followed by cooler, drier conditions Saturday night into Monday. - More rounds of showers/storms Monday into Tuesday and again next Thursday and Friday. Should details come together, some severe storms could occur Tuesday. && .DISCUSSION... Issued at 425 AM CDT Fri Jun 28 2024 Through Tonight: Periodic Showers and Thunderstorms, Potential Afternoon/Evening Severe 08z WV satellite shows quasi-zonal flow aloft over the upper midwest ahead of an upper low over southern Alberta with multiple perturbations within this flow. An area of showers with sporadic thunder is ongoing from S MN south through IA and a squall line is sweeping east through SD. Today, given increasing 850mb moisture transport as the upper low churns eastward, expect periodic showers and a few thunderstorms as the various shortwave eject downstream. Most favorable times will be this morning as the IA/S MN convection and potential MCV associated with the E SD squall move eastward and again around 4 to 7 PM as a shortwave lifts east northeast out of NE. Primary limiting factor for thunderstorm coverage - and by extension severe thunderstorm potential - looks to be available instability, as insolation looks to be greatly limited by the morning round of activity and mostly cloudy conditions that occur in the wake of this. Time period with a conditional risk for a severe storm looks to be 7 PM to 10 PM in mainly our far west as guidance suggests 750-1000 J/kg of MLCAPE could develop as heights aloft fall ahead of the main upper low. That said, while the mid-levels will cool, am skeptical enough destabilization will occur at the surface. Should sufficient destabilization manage to be realized, with progged sfc-6km bulk shear values of around 40 knots and some turning seen in hodographs, a severe storm could occur. Progged DCAPE does creep toward 1000 J/kg so damaging winds and, given potential for a rotating updraft, hail would be the main concerns. Saturday through Sunday Night: Potential Sprinkles, Cooler Saturday, a few sprinkles could occur in the northeastern half of the CWA as a robust shortwave rotates around the departing upper trough. As a surface high builds over the Dakotas and shift to the Great Lakes, temperatures should drop Saturday and Sunday nights, with values in the lower 40s possible in Taylor County south to the cranberry bogs of Monroe County. Monday through Tuesday: Next Round of Showers, Storms Long range guidance remains in good agreement that the next upper trough will slowly slide eastward over the northern CONUS Monday into Tuesday. PWATs once again approach 2" as Gulf moisture is transported to the region via 850mb moist advection. While the progressive nature of the system should limit flash flooding risk, another few inches of rain could fall over these two days, keeping rivers swollen. LREF joint CAPE/CIN/shear probabilities suggest some chance for severe storms Tuesday, but would need opportune timing of the main upper trough to coincide with peak heating Tuesday afternoon, and this remains uncertain at this time. Next Thursday through Friday: More Rain Chances The upper wave train rolls on Thursday into Friday as guidance is once again in pretty good agreement that the next upper trough will advance eastward sometime during this period. While the pattern in some guidance would suggest less optimal moist fetch will occur compared to our last several waves - i.e. PWATs remain under 1.5" - still a variety of exact solutions, so will need to monitor this period in the coming days. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 639 AM CDT Fri Jun 28 2024 Light rain and stratus will lead to MVFR to IFR conditions at LSE/RST over the next 12-18 hours. Much uncertainty surrounds the potential for thunder, with some ongoing near RST as of issuance time. Have attempted to time out most probable time for thunder at each site and elected to upgrade thunder mentions from VCTS to PROB30 groups. User should however note that sporadic TS could occur at all sites at any time this morning and afternoon and amendments may become necessary. && .HYDROLOGY... Issued at 425 AM CDT Fri Jun 28 2024 With three more periods of precipitation ahead - today into tonight, Monday/Tuesday, and Thursday/Friday - area rivers will remain swollen. Both of those first two rounds in particular show the potential for many areas to pick up around another 1-2". Given this and the large amount of water flowing downstream, the Mississippi River is expected remain in minor to moderate flood through at least the next five days. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...Ferguson HYDROLOGY...Ferguson