Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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379 FXUS63 KARX 122329 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 629 PM CDT Wed Jun 12 2024 .KEY MESSAGES... - Shower and storm risk continues through the afternoon, with a secondary round of storms expected to move across the area tonight. Some storms tonight may be severe with the primary threat strong winds and secondary threat hail. - Additional chances for showers and storms spot the forecast tomorrow and then again over the weekend into early next week. - Above normal temperatures for early next week with highs currently forecast into the mid 80s to potentially low 90s. && .MESOSCALE... Issued at 310 PM CDT Wed Jun 12 2024 An MCS took shape across south-central Minnesota around midday and has progressed along the MN/IA border and as of 3pm was located along a line from Fayette to Winona county. Outflow from earlier convection has been undercutting this complex from north to south over the course of the last few hours, limiting the wind threat to the southern apex of the complex along a line from Mitchell to Winneshiek counties. The complex as a whole should weaken as it progresses east of the Mississippi River, but with DCAPE values of 1000-1400 J/kg ahead of the line, cannot rule out wind issues throughout the lifespan of the event as it moves eastward through Grant County. Attention then turns upstream to the cold front that initiates convection over northern and western Minnesota later this afternoon. The CAMSs have failed to adequately handle the strength of the cold pool in our area from the earlier convection both from a temperature and convective morphology standpoint. This does not lend much confidence for how storms will evolve once they reach this modified airmass this evening. Overall, the severe threat with the second line looks to be on par with what is transpiring this afternoon with hail and wind being the main threats. && .DISCUSSION... Issued at 150 PM CDT Wed Jun 12 2024 Thursday and Friday: An upper level shortwave trough is forecast to track north of the area into the Great Lakes area, with an associated 60-90 kt mid- level jet moving eastward across the region. At the surface the cold front will continue to sag down through the area and eventually south of the local area. Hi-res model guidance shows a line of showers and perhaps storms developing and moving down across the forecast area through the day on Thursday. Instability looks to build south of the front locally across our southern counties in the afternoon, but continues to get shunted southward. There still remain some differences in hi-res guidance on the location of storm development with some showing storms on our southern border and others south of our local area. For now, SPC has our southern tier of northeast Iowa and southwest Wisconsin counties in a Marginal Risk (1 out of 5) for severe weather. Otherwise, surface high pressure builds across the region for Friday, with drier conditions and highs forecast in the mid 70s to lower 80s across the area. Weekend & Beyond: Additional Shower and Storm Chances Upper level ridging will continue to build eastward as we head into the weekend. Model guidance shows a couple shortwave troughs lifting northeastward, riding on the backside of the ridge. Moisture will be on the increase with models showing PWATs pushing 1.5+ inches. At the surface a frontal boundary will be lifting up towards the region with an axis of instability (~1000 - 2500+ J/kg) building south of the front. This looks to bring our next chances for showers and storms across the region, with the current forecast increasing chances Saturday afternoon and into Saturday night. There still appear to be some model differences on shower and storm chances Sunday, with some dependency likely on how convection on Saturday plays out. Ensembles suggest quite a bit of instability builds back in Sunday, though current deterministic GFS model forecast soundings do show capping in place for much of the day along with weaker shear values. Overall, will continue to monitor trends in the coming days to determine the severe weather risk. Otherwise, as was previously mentioned moisture conditions suggest that locally heavy rainfall could be a concern for the weekend, especially if storms train over the same areas. Of note, parts of the forecast area are highlighted in the Excessive Rainfall Outlook for this time period. Beyond the weekend, upper level ridging will continue to build across the eastern U.S. resulting in southwesterly flow over the local region. There is still plenty to work out in the details with the potential for various disturbances to move through the flow. The resulting extended forecast keeps broad precipitation chances (~20- 50%) in across the forecast area for the early part of the week. However, with a moist and unstable environment in place across the region, this will be another time to watch for potential strong to severe thunderstorms. Keep up to date as details are refined in the coming days. Early Next Week: Above Normal Temperatures Another point of interest revolves around increased (above normal) high/low temperatures across the region. There are still some differences between the ensemble solutions on just how warm, but current guidance supports temperatures in the mid 80s to potentially lower 90s. As a result, the current forecast would suggest that heat index values could rise into the low 90s for some through the period. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 626 PM CDT Wed Jun 12 2024 Primary aviation concern over the next 24 hours is the likelihood for thunderstorms at LSE/RST this evening. At this time, thunder appears likely at each site, so have continued to keep a few hours of prevailing TS at each site along with associated MVFR ceilings. Following the thunder, some valley fog could affect LSE due to near surface moisture from rainfall and decreasing winds. At this time, low confidence has precluded including any mention in the TAF with this update. && .CLIMATE... Issued at 224 AM CDT Wed Jun 12 2024 A strong upper level ridge will build northward into the region for early next week. Both high and low temperatures will likely climb into the 85th or higher from at least Monday into Tuesday. While high temperatures (mid-80s to around 90) look to be too low for records to be tied or broken, the low temperatures (around 70 to the mid-70s) along and south of Interstate 90 will be warm enough for some potential warm low records to be tied or broken. At this time, the highest chances look be on Tuesday. Looking further out, CPC continues to have a slight (20-40%) risk (20-40%) for excessive heat for areas along and south of Interstate 90 from June 19 through June 25. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ MESOSCALE...Skow DISCUSSION...EMS AVIATION...Ferguson CLIMATE...Boyne