Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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555 FXUS63 KARX 270852 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 352 AM CDT Thu Jun 27 2024 .KEY MESSAGES... - Storm Chances Return Tonight, Lingering Through Friday. A Widespread 0.5" to 1.0" of Rainfall Is Expected. - Slightly Below Normal Temperatures This Weekend. - Subsequent Storm Chances Monday, Lasting Into Tuesday. && .DISCUSSION... Issued at 325 AM CDT Thu Jun 27 2024 Rain & Storm Chances: Initial precipitation chances reach our western peripheral counties in southeast Minnesota and northeast Iowa tonight ahead an upper level trough seen over the northwest CONUS on GOES water vapor imagery early this morning. These initial precipitation chances are expected to remain along our west though as the ridge lingers locally. Eventually, the progressive pattern and veering of the moist low level jet increases precipitation chances through the overnight hours locally. As a result of these passing moisture lobes, have quickened initial onset near 27.21Z only in these western counties. As the synoptic low wobbles and phases east, precipitation and storm potential persists through Friday into early Saturday morning. Rainfall Amounts Through Friday: Higher rainfall amounts overnight are expected to remain along our northwestern periphery aligned with the nose of the heightened low level moisture gradient, northerly lifting low level trough, and associated frontogenetical bands. HREF confidence suggests a mean of 0.25" to 0.5" to a maximum near 1" along our periphery during this time. Through Friday, as a low level trough advects southwest-northeast oriented frontogenesis bands within the heightened low level moisture transport, narrow corridors of ~0.75" mean rainfall amounts spread east through the forecast area. In summary, highest confidence for a widespread 0.5" to 1.0" across the forecast area by Saturday morning. Local Severe Threat: Quite a conditional severe storm threat at the current forecast hour as the main wave passage is expected to remain outside of peak diurnal heating and associated building instability. Therefore, current confidence places heavy rain as the primary hazard. With a quick storm motion, ~30kts, the threat for damaging winds also cannot be ruled out in this scenario. However, quickening of the synoptic pattern would present more of a severe storm threat scenario locally. As a result, the quickest high resolution model solutions show a line of storms building Friday evening and progressing through the forecast area. Given the ongoing precipitation and small storm potential, building sufficient instability remains questionable. Temperatures This Weekend: Slightly below normal temperatures on tap for the week as a cold frontal boundary shifts east across the Upper Mississippi River Valley Saturday morning. An amplified upper level ridge in its wake sustains these slightly below normal temperatures through Sunday. Long term global ensemble confidence suggests temperatures approximately 10 degrees below normal for the weekend. Subsequent Storm Chances Next Week: Long term global ensemble confidence suggests the amplified ridge exiting east into Monday, returning storm activity from west to east Monday into Tuesday. Similar to Friday, separate upper level synoptic troughs are resulting in main impacts remaining to the north and south of the local forecast area. The initial wave is expected to lift north through the Northern PLains through Monday, leaving an increased low level theta e axis draped across the local forecast area. Subsequent perturbations and low level troughs may perpetuate precipitation and storm potential through Tuesday. Spread in individual ensemble (EPS/GEFS) member low locations extends from the Southern Plains into central Saskatchewan and Manitoba. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1037 PM CDT Wed Jun 26 2024 Main taf concerns is development of fog in low lying areas and river valleys overnight. High pressure builds into the region overnight and provides mostly clear skies/light winds overnight. With drier airmass over the area and light north wind aloft near the surface. This will inhibit widespread Mississippi River Valley fog. With confidence low on widespread valley fog development...have continued patchy fog...BCFG...at the LSE taf site. Wind direction switch around to a southerly direction Thursday afternoon...as high pressure moves east of the region. Wind speeds increase to around 10 knots Thursday afternoon/evening. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JAR AVIATION...DTJ