Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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663 FXUS63 KARX 250527 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1227 AM CDT Tue Jun 25 2024 .KEY MESSAGES... - Showers and thunderstorms return to the forecast tonight. While some uncertainty remains, confidence has increased that at least west central Wisconsin will experience severe thunderstorms tonight with primarily a risk for damaging winds. An Enhanced Risk (level 3 of 5) for severe weather is present east of a Oronoco MN to Dickeyville WI axis. Flash flooding may also occur due to high amounts of recent rainfall. - Another brief break for mid-week before additional shower and storm chances return late in the period. Details to be refined in the coming days. && .DISCUSSION... Issued at 145 PM CDT Mon Jun 24 2024 This Afternoon and Tonight: Severe Storms and Flash Flooding 19z WV satellite shows an upper trough over Lake Winnipeg with multiple shortwave in the quasi-zonal flow aloft over ND/SD/MN. A weak area of thunderstorms has been ongoing all day across central and northern MN. At the surface, very rich moisture is advecting northeastward behind a warm front, with dewpoints in the upper 70s common in NW and N central IA with these beginning to be seen in S central MN. This afternoon into tonight, aforementioned rich moisture should continue to advect northeastward, with convection developing in central MN this evening. Progged hodographs are long with plenty of turning in the low levels, so expect initial supercellular development to our northwest late this afternoon. That said, relatively straight hodographs suggest upscale growth could occur quickly with this activity likely an MCS as it approaches our northwestern CWA. While a strong cap should keep thunderstorms from developing in our area ahead of this MCS, low level jet will be on the increase, helping to erode the cap and allowing any ongoing thunderstorms to propagate southeastward this evening. Given the strong EML that was advected eastward today, the probability of moist advection from the 850mb LLJ allowing the cap to be overcome will increase from west to east across the forecast area, thus the relatively higher risk for thunderstorms tonight resides in our east. As for hazards, given the strong instability, robust deep layer shear, and expected upscale growth suggests damaging wind is the primary threat. Additionally, progged PWAT values once again approach 2 inches so expect around 1 to 3 inches of additional rainfall in areas affected by the thunderstorms. Given high antecedent rainfall, This could be enough to see some flash flooding tonight despite expected quick duration of rainfall. Given aforementioned deep shear, cannot rule out a severe hailstone. Finally, with sfc-3km bulk shear vectors of 40 knots but are out of the west- northwest, obliquely along the axis of the MCS, suggesting the QLCS tornado risk is low unless any notable bowing segments developed. Remaining uncertainties surround the strength of the capping inversion. Should this cap be weaker than expected, it is possible a supercell or two could develop in SE MN this afternoon before the main round of convection described above. Should this occur, large hail would be the primary risk with this activity and a tornado could not be ruled out. That said, the chance this potential afternoon round occurs is low (15%). Remainder of Forecast: As expected, blended guidance has trended sharply downward with PoPs for Tuesday with outflow from the overnight MCS likely pushing the front well to our south. After a break from active weather Tuesday through Thursday, next upper trough approaches Thursday night, leading to a chance for showers and thunderstorms Thursday night through Saturday. Operational guidance and ensembles continue to show a variety of timings with this feature. Given this and active weather in the short term, elected to let blended guidance ride for all elements after Tuesday with this update. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1227 AM CDT Tue Jun 25 2024 Main taf concerns is thunder potential at both RST/LSE taf sites early in the taf period. Cold front will track across the area overnight. Latest trends have convection developing and remaining focused over western/northern Wisconsin. This would place and movement of convection to be mainly north of the taf sites. At this time...have removed convection from the RST taf site and have kept a vicinity thunder at LSE for a small chance convection could develop south into southwest Wisconsin. After 08z Tuesday...cold front/convection pushes east of taf sites and VFR conditions are expected to prevail at both RST/LSE taf sites. && .HYDROLOGY... Issued at 610 AM CDT Mon Jun 24 2024 Heavy rainfall over the previous couple of days has resulted in many area rivers and streams running high or in flood stage. Flooding concerns will last well into the week, with the Mississippi River also continuing to rise. Another round of showers and thunderstorms will be possible tonight into Tuesday. Although some details are uncertain at this time, locally heavy rainfall may be possible. With the already saturated soils, will need to monitor for any further potential hydro impacts as any additional heavy rainfall could exacerbate ongoing flooding. Please continue to reference the latest flood statements for additional updates and details. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Flood Watch until 3 AM CDT early this morning for WIZ032>034- 041>043-053. MN...Flood Watch until 3 AM CDT early this morning for MNZ079- 086>088-094>096. IA...None. && $$ DISCUSSION...Ferguson AVIATION...DTJ HYDROLOGY...EMS