Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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235 FXUS63 KARX 240000 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 700 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. && .UPDATE... Issued at 700 PM CDT Sun Jun 23 2024 Continue to monitor incoming guidance concerning the thunderstorm threat for Monday night. Latest RAP/HRRR capping to incoming surface-based instability is really really strong (300-500 J/Kg of CIN) with the elevated mixed layer moving into the region from the southwest. Using 700 mb temperature as a proxy to capping strength, by 00Z Tuesday /7 pm Monday/, the 12C line is well into the area running from KEAU-KDBQ, and only warming into the evening on strong warm air advection from the southwest. The cap weakens to the northeast with the gradient aligning from MSP-EAU-DLL-MSN /I-94/. The latest extended HRRR run from 23.18Z now forecasts speckles of reflectivity over the forecast area later Monday, representative of some mid-level saturation and very limited elevated instability, with the convective system tracking from nrn MN into the UP/nrnWI. This makes sense as it is riding around the capping in place further south, although it may be a bit too far northeast. In any case, should this strong of a cap build in, the chances really increase for a system to track northeast of I-94. && .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 /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 700 PM CDT Sun Jun 23 2024 VFR expected through the period. A thunderstorm complex will likely move through northern MN into nrn WI Monday night. It appears the track probabilities increase northeastward from KLSE. && .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. && $$ UPDATE...Baumgardt DISCUSSION...Ferguson AVIATION...Baumgardt HYDROLOGY...EMS