Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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086 FXUS63 KARX 071144 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 644 AM CDT Tue May 7 2024 .KEY MESSAGES... - Line of Showers and Thunderstorms Early, Scattered Storms this Afternoon and Evening - Active pattern continues with additional thunderstorms Wednesday evening into Thursday morning. - Cooler Saturday, Potential Shower or Two Friday Night through Saturday && .DISCUSSION... Issued at 244 AM CDT Tue May 7 2024 Today: Line of Showers and Thunderstorms Early, Scattered Storms this Afternoon and Evening Line of showers and thunderstorms are making their way into the area from the west this morning and will continue to shift east through the rest of the morning. Latest RAP analysis suggests up to 700 J/kg of MUCAPE with around 40kts of bulk shear; however model soundings suggest parcels are lifting from around 5kft with nearly uniform winds through the instability - bringing the effective shear down considerably. There`s ample upper-level forcing to support convection through the rest of the overnight/morning hours across the area, but the threat for any severe storms at this time appears low when assessing the radar trends. There remains uncertainty on the chances for thunderstorms later this afternoon across the area as remnant cloud cover could hinder instability. After the line of thunderstorms wraps up by mid- morning, cloud cover will begin to decrease from the SW to NE. While low-level destabilization is less certain, there is good agreement on steepening mid-level lapse rates this afternoon across the area, which will increase fuel for thunderstorms should surface parcels get going. Mean mixed-layer CAPE values for this afternoon are forecast around 1000-1400 J/kg, but the shear decreases as instability increases. CAMs this afternoon show a mixed bag of solutions with some models not resolving any convection and others continue convective rather quickly after the first round exits. So while there`s decent chances (20 to 50%) for afternoon thunderstorms, strong to severe storm chances are rather low with hail being the primary threat. Temps today are highly dependent on exiting cloud cover. Model spread is rather large, with the 25th to 75th percentile temp spread over 10 degrees in spots. NE Iowa is most favored to see clearing skies this afternoon, with temps climbing into the low 70s. SE MN will likely see temps near 70 as well. As for SW into central WI, modeled sky coverage has a larger spread which makes temps less certain. If cloud cover remains throughout the day, could see temps closer to 60; however, if clouds diminish temperatures will climb into the 70s. Wednesday into Thursday: Another Round of Thunderstorms A remnant surface low and longwave trough from the Dakotas dives south Wednesday, bringing upper-level divergence and fgen forcing across the region. While there has been a slight shift to the south from previous runs, an inverted trough and Fgen forcing along 850 to 600mb coupled with a mid-level low shifting over IA and a skinny CAPE profile will bring the potential for more showers and thunderstorms and potentially a localized heavy rain threat. Modeled rainfall amounts among the GEFS/EPS/CMCE rain from near 0 inches of precipitation to as high as 2.50 inches across NE Iowa and SE MN, but as a whole, there`s roughly a 10-20% chance of rainfall exceeding 1 inch across the aforementioned areas Wednesday evening into Thursday morning. This threat will diminish Thursday morning as cooler air moves in behind the exiting trough. Behind the cooler air Thursday, temps will back down a bit to the upper 50s to low 60s. This weekend: Not as Warm, Some Showers Long wave trough drops south from Canada across the Upper Midwest into the weekend bringing temps into the low to mid 60s with scattered showers as the upper level low pivots overhead. The best chances (30 to 40%) for precipitation appear to be on Friday night into Saturday morning at this time with the initial shortwave vort max moving overhead. As broad cyclonic flow remains through Saturday night, expecting additional showers across the area at times - best chances east of the river. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 619 AM CDT Tue May 7 2024 Line of thunderstorms seen moving from south-southwest to northeast early this morning on radar imagery. While precipitation chances are expected to continue into the afternoon, current thunder chances remain primarily along this initial line of storms along and east of the Mississippi River at the 07.12Z TAF issuance. Although, daytime mixing will result in unstable surface air building and scattered thunderstorm chances returning. Areal coverage and confidence remains too low to include for 07.12Z TAF. Confidence in flight restrictions decreases through late morning into the early afternoon as clear skies can be seen on satellite imagery behind the main precipitation shield from south-central to northwest Iowa. Again, scattered CB and restrictions possible. Highest confidence for precipitation chances overnight lingers in central Wisconsin, northeast of both TAF sites (KLSE & KRST). && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JAW AVIATION...JAR