Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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634 FXUS63 KARX 261941 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 241 PM CDT Sun May 26 2024 .KEY MESSAGES... - Monday morning and afternoon will likely bring a round of showers and a few thunderstorms. While a severe thunderstorm cannot be completely ruled out in northeastern Iowa, the chance for a severe thunderstorm is very low (5%). - Additional shower and storm chances again Tuesday before drier conditions return for mid-week. && .DISCUSSION... Issued at 228 PM CDT Sun May 26 2024 Immediate term rain: 19z WV satellite shows an upper trough shifting eastward over the MS River with a broad area of moist fetch east of this feature wrapping over N WI. Radar returns show associated precip shield shifting eastward accordingly. After a small pocket of enhanced rain rates affected the greater La Crosse area around noon, latest dual pol rain rates have returned to being under a half inch per hour. Aside from a few reports of urban ponding and a couple rivers reaching action stage in NE IA, flooding impacts have been minimal. Given that the best forcing is departing to the east, do not think impacts will become greater than those already seen. Monday storms: Monday, potent shortwave, currently located over MT, looks to eject southeastward to N IL, passing over the forecast area in the process. With modest wrap-around 850mb moist advection continuing to occur as the surface low becomes centered over MI, this should likely (60%) set the stage for showers and a few thunderstorms, particularly in NE IA, where cooling ahead of the shortwave looks to be maximized. In any case, HREF probability of at least 500 J/kg of CAPE is around 50 percent, so have included mentions of thunder in the forecast. As for severe thunderstorms, these appear doubtful as, in addition to questionable instability, the probability of appreciable (30+ kts) sfc-6km bulk shear remains generally 20 percent or less, with this confined to NE IA. In any case, shallow surface mixed layer and cold temperatures aloft suggest severe hail rather than wind would be the favored hazard. Monday night through the week: Another shortwave trough is expected to dive down across the region, keeping shower and storm chances in the forecast for Tuesday. A few models are hinting towards some showers pushing in a bit earlier in the day, though there still remain some differences on timing and extent of these showers. Have some lower chances in for early Tuesday for now with chances increasing into the afternoon, highest east of the Mississippi River (40-60%). Showers and storms will be on the decrease into the late evening/overnight as the shortwave exits and surface high pressure starts to build into the region behind it. By early mid-week model guidance continues to highlight upper level troughs over the Pacific Northwest and Great Lakes with an upper level ridge building into the central U.S. Overall, this looks to bring a short break in rain and storm chances across the local area. However, the upper level ridge will continue to get pushed eastward as the upper level trough moves into the region over the weekend, bringing back shower and storm chances to the forecast. There remain some uncertainties in timing of this precip, with noted differences in details such as the strength of the trough among ensemble solutions. The latest blended model guidance seems to have trended a bit slower in bringing in precip chances Thursday night/Friday. Still some time to monitor trends and make refinements as we move closer in time. Both the GEFS and ECMWF ens show some general increasing trend in temperatures into the end of the week, with highs currently forecast to rise into the 70s for most to end the week. However, will note that temperature spread among ensemble solutions does begin to increase further into the period with the aforementioned differences. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1239 PM CDT Sun May 26 2024 Light rain and associated ceilings and visibility reductions remain the primary concern for aviation interests this afternoon and evening. While some guidance continues to suggest IFR ceilings are favored this afternoon, it has generally been too pessimistic all morning. Have therefore elected to keep conditions MVFR with this update. In any case, flight rule restrictions should end by 01z at RST and 07z at LSE. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson/EMS AVIATION...Ferguson