Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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566 FXUS63 KARX 231959 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 259 PM CDT Sun Jun 23 2024 .KEY MESSAGES... - Showers and thunderstorms return to the forecast Monday evening into Monday night, with a conditional risk for severe thunderstorms. A Slight Risk (level 2 of 5) for severe weather remains for Monday evening. Should everything come together and severe storms storms develop, significant (75+ mph) wind gusts could occur. - 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 205 PM CDT Sun Jun 23 2024 This Afternoon and Evening: Sprinkles and a Stray Thunderstorm Progged soundings show modest instability this afternoon and evening in the northern portions of the forecast area. While dry air above the top of the mixed layer has inhibited vertical growth thus far in our CWA, plenty of cumulus are seen on visible satellite and, farther northwest, a couple showers and thunderstorms have developed west of Hawyard. Have thus added low end mentions of thunder to the forecast this afternoon and evening. Monday Evening and Night: Conditional Severe Risk After one nice, sedate, temperate day with dewpoints in the lower 60s for Sunday, warm and muggy conditions return by Monday afternoon as southwesterly 850mb moisture advection resumes in earnest. As this occurs, strong EML looks to advection eastward with 700-500mb lapse rates approaching 8-8.5 C/km. Thus, expect CAPE values to increase markedly, with progged MLCAPE exceeding 3000 J/kg in our CWA. Stout capping across the forecast area should keep convection from developing in our area directly but, farther to the northwest, a combination of a slightly weaker EML and cooling aloft ahead of a shortwave may allow convection to develop. Should this occur, progged sfc-6km shear there is around 55 knots, so expect organized convection to develop, with the relatively straight hodographs above 1km suggesting splitting storms and subsequent upscale growth into an MCS would occur. As 850mb moist fetch only ramps up across the CWA in the evening, it is plausible that this MCS would be able to dive southeastward through the forecast area. Given the strong shear and very high instability, this could result in significant (75+ mph) wind gusts were it to occur. All the above said, the strong EML suggests that initiation is not a given and neither is the ability for any MCS to survive the trek southeast. For Tuesday, while blended guidance continues to show the potential for additional convection, am doubtful this occurs as guidance has generally sped up the passage of the front associated with the aforementioned shortwave that may kick off an MCS the previous night. If that MCS does occur, resulting cold pool would likely force the boundary well south of the CWA. In either case, while SPC has a Slight Risk (level 2 of 5) in portions of NE IA and SW WI based on the 00z guidance suite, CSU ML-based outlooks using the 12z suite show a notable trend away from our forecast area in line with a faster progression. Rest of Week: Midweek Break, Another Round Possible Friday/Saturday Surface high pressure in the wake of Monday night/early Tuesday`s front and a reduction in heights aloft should serve to keep things cooler than normal and precipitation free Wednesday and Thursday. Friday and Saturday, next longwave trough looks to advance eastward just to our north. While precipitation is a good bet, guidance shows a variety of timings with this feature, so rain mentions are spread across Thursday night through early Saturday for now. Additionally, severe thunderstorm risk is uncertain as well as it remains unclear just how much instability there will be when best upper forcing arrives. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1248 PM CDT Sun Jun 23 2024 Diurnal cumulus clouds will gradually develop this afternoon and then dissipate with the loss of heating late this afternoon and evening. From late tonight into Monday morning, there will be 4-8K broken deck of clouds moving east through the area. These clouds are associated with a warm front moving through the region. Skies will gradually clear during the mid to late morning Monday. In addition, with diurnal mixing, the south winds will increase into the 10 to 20 knot range and the gusts into the 15 to 25 knot range. && .HYDROLOGY... Issued at 613 AM CDT Sun Jun 23 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. Fortunately, little rainfall is expected into Monday. However, another round of showers and thunderstorms will be possible Monday night into Tuesday. Although some details are uncertain at this time, will need to monitor for any further potential hydro impacts with these storms. Please continue to reference the latest flood statements for additional updates and details. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...Boyne HYDROLOGY...EMS