Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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531 FXUS63 KARX 231814 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 114 PM CDT Thu May 23 2024 .KEY MESSAGES... - Organized showers/storms will spread east late tonight into Friday. Confidence remains on the low side for severe weather, but a few strong to severe storms could not be ruled out late tonight or Friday. - The holiday weekend will start out dry, but the latter half of the weekend may be unsettled at times. && .DISCUSSION... Issued at 310 AM CDT Thu May 23 2024 Today-Friday: Although gradual height rises and mid-level warming will occur today ahead of a shortwave trough across the northern Rockies, there is a weak signal for a few showers/storms to develop towards central WI this afternoon within a diurnal cumulus field. RAP/HRRR soundings become uncapped with cool mid-level temps contributing to modest destabilization. Although lift is nebulous, did add a small (20%) chance for a shower/storm into central WI this afternoon. Small hail could occur with any storms. Otherwise, convection will likely organize to the west this afternoon/evening, approaching the area late tonight. There is some question how intense these storms will be as they approach, given the diurnal minimum in instability, but strong moisture transport/warm advection could help sustain stronger storms, likely elevated, early Friday morning, especially if a more linear organization occurs. The higher chances for severe storms look to hold west of the area tonight, but trends will need to be monitored through the day/evening with lower confidence in convective evolution. The band of showers/storms will move across the area Friday morning, in conjunction with the weakening low-level jet and warm advection. Although the stronger synoptic support will be displaced to the north and west, closer to the trough, some daytime destabilization could occur ahead of the front (30 to 60% for >1000 J/kg SBCAPE across western WI per the HREF) with seasonably strong mid-level wind fields. There is some question on the extent/intensity of re- development as the parent trough lifts into southern Manitoba and the low-level jet/moisture transport weakens through the day ahead of the front. Right now the lower end severe weather risk (level 1 of 5) from SPC seems reasonable for this scenario, primarily across northeast Iowa through central Wisconsin. Any lingering storms should exit central Wisconsin during the evening. The progressive nature of this system should limit rain totals, but localized 1-2" amounts could occur with any more intense storms Saturday-Monday: Weak ridging should provide a dry start to the holiday weekend on Saturday before mid-level troughing in conjunction with a few interacting shortwave troughs develops across the Mid to Upper MS Valley later in the holiday weekend. There is still a fair amount of uncertainty with exactly how the details of this pattern will evolve. Have continued to lean on the blended NBM rain chances, given the degree of spread present with generally 30 to 60% rain chances Sunday/Memorial Day. Overall, instability is forecast to be higher south of the region on Sunday, which would tend to keep the higher chances for severe weather farther south this weekend. Tuesday-Wednesday: Looking ahead towards the middle of next week, a transition to northwest flow aloft is expected with the longwave pattern featuring ridging across the Rockies and high plains and a trough over the Northeast. Broadly speaking, global ensembles broadly support drier conditions through the middle to end of the week as ridging works east, but there is some uncertainty in placement of any shortwaves traversing the periphery of the larger trough earlier in the week within the northwest flow pattern. As a result, at least low end rain chances persist into mid-week. Temps should be fairly seasonable for late May. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1258 PM CDT Thu May 23 2024 VFR expected for most of the TAF period. Increasing upper level cloud cover seen on satellite imagery early this afternoon is mostly associated with widespread storms in the Northern Plains. Other scattered, more local cumulus cloud cover associated with a more moist are mass moving to the northeast into central Wisconsin interacting with a drier air mass. Given the scattered nature, limited impact, and location mostly in central Wisconsin, have not introduced anything at either TAF site (KRST & KLSE). Widespread precipitation and storm chances reach the Upper Mississippi River Valley late tonight from the west, eventually traversing the local Mississippi River waterway into early Friday morning. Have accounted for meager confidence in initial precipitation and associated storm chances with PROB30 (30% probabilities). Lower ceilings eventually move from west to east with these precipitation and storm chances. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JM AVIATION...JAR