Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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201 FXUS63 KARX 230039 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 739 PM CDT Sat Jun 22 2024 .KEY MESSAGES... - One more round of heavy rain is possible this afternoon and evening, with some areas potentially picking up another 2 to 4 inches of rain, with the southern third of the area having the higher relative risk for additional heavy rain. - Severe thunderstorms remain possible, again mainly in the southern third of the CWA. Damaging winds remain the primary threat, but a tornado or two cannot be ruled out. - After a welcome respite from the rain Sunday and Monday, Monday night and Tuesday may feature additional thunderstorms. Monday night has a Slight Risk (level 2 of 5) for severe thunderstorms. && .DISCUSSION... Issued at 120 PM CDT Sat Jun 22 2024 This Afternoon and Evening: Heavy Rain and Flooding, Severe Storm Potential 18z WV satellite shows an upper trough sliding eastward over W MN with an area of thunderstorms ahead of this feature. Multiple weak perturbations are seen in the west-southwesterly flow aloft over the CWA and extending back toward NE. At the surface, quasi-stationary front is draped across IA with this feature extending into NE IA/SW WI. Skies are beginning to modestly clear in NE IA with the exception of a small area of showers along the US 20 corridor just to the south of the CWA. This afternoon, expect yet another round of showers and thunderstorms to develop in the vicinity of the quasi-stationary front as a combination of low level convergence, destabilization due to insolation, and a bit of a cooling aloft ahead of a shortwave occurs. Additionally, a few showers and thunderstorms may develop in the northwestern portions of the CWA as the main upper trough arrives late this afternoon. Once again, the key detail will be where exactly the surface front will be located for our initial shower and thunderstorm development this afternoon. Due to the influence of outflow from our morning storms, only expect the surface front to push as far north as roughly a Charles City IA to Richland Center WI axis. With MLCAPE building to 1500 J/kg along and south of this boundary, 0-6km shear increasing to 35-50 knots as winds aloft increase, and sfc-500m SRH increasing to 50-100 m2/s2, both damaging winds and perhaps a tornado or two would be possible with the thunderstorms. The tornado risk, while present, looks to be brief as upscale growth should occur relatively quickly as the 0-6km bulk shear vectors look to be oriented largely along the the axis of the front. This upscale growth, storm motions out of the west, and PWAT values continuing to run near or above climatological maximums suggest that another round of high rain totals and flooding will be the main risk with the thunderstorms that develop near the surface front in NE IA and SW WI. In summary, this afternoon brings a risk for additional flooding, damaging winds, and perhaps a tornado or two to NE IA and SW WI. Farther to the northwest, scattered showers and thunderstorms may occur. With the risk for additional flooding with this activity being lower due to the progressive movement of the upper trough, have allowed a large portion of the Areal Flood Watch to expire. Monday and Tuesday: Next Round of Thunderstorm Potential Monday into Tuesday, a longwave upper trough looks to advance from the Canadian Prairies to northern Ontario. With high pressure building in the eastern CONUS in the wake of an upper trough, southerly 850mb moist advection looks to resume across the MS Valley. While better shear and support for ascent looks to be located to our north, still plausible severe thunderstorms could occur in our forecast area either Monday night or Tuesday. Indeed, SPC has issued a Slight Risk (level 2 of 5) for the northern third of the area for Monday night. Will need to continue to monitor this period, particularly if the upper trough digs a bit farther south than currently favored. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 730 PM CDT Sat Jun 22 2024 The main area of showers and thunderstorms has pushed off to the southeast, however there is some trailing energy dropping in behind this first wave. Showers and drizzle were noted with this push over more significant cooler air across Minnesota. Not expecting much, but there will be some lingering spotty showers and drizzle this evening with variable VFR/MVFR/IFR ceilings improving to VFR Sunday. Northwest winds continue 5 to 15kts. && .HYDROLOGY... Issued at 124 PM CDT Sat Jun 22 2024 Have cancelled additional parts of the Areal Flood Watch in southeast Minnesota and west-central Wisconsin as the heavy rain threat appears diminished for these areas. However, with additional heavy rainfall possibly bringing another 2 to 4 inches this afternoon across northeast Iowa and southwest Wisconsin, the Areal Flood Watch continues for these areas through this evening. River flooding concerns will last well into next week and multiple rivers could exceed moderate flood stage if the rainfall lines up correctly in their basins. Abundant rainfall fell in the Cedar River basin around Austin, leading to major flooding in this area. This appears likely to cause major flooding downstream at Charles City, with exact crest height dependent on how much additional rainfall falls in the basin this afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...Boyne/Zapotocny HYDROLOGY...Ferguson