Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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892 FXUS63 KARX 030617 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 117 AM CDT Mon Jun 3 2024 .KEY MESSAGES... - Another rounds of showers, a few storms overnight through Mon morning (60-90% chances). - Additional showers and storms (70-90% chance) will push through the region Tuesday bringing additional rainfall amounts around 0.5-1" with locally higher amounts. Isolated severe storms will be possible, mainly earlier in the evening. - Below normal temperatures are expected for the second half of the week with occasional shower chances into the weekend. && .DISCUSSION... Issued at 235 PM CDT Sun Jun 2 2024 * SHOWERS, A FEW STORMS TONIGHT - severe storms not expected First for this afternoon and early evening, a broken band of north- south running convection continues to press east from western MN, along a weak ripple in the upper level flow. CAMS models shift that band into eastern portions of the Gopher state by late afternoon, but it becomes more broken and more favored in the north, following the more dominate upper level feature. It is also pushing out of the ridge of higher instability while running into a drier near sfc layer. May have a smattering of mid level showers make it into southeast MN, but coverage it expected to be spotty at best, favored by a bulk of the CAMS. Will hold low end (20%) chances for the afternoon/early evening west of the Mississippi River. Moving back to tonight, more bits of upper level energy progged to shift east out of the northern plains while a mostly MCV derived feature from convection over the central plains lifts northeast overnight. The instability axis will also ease a bit east, but not by much according to the RAP (holds the main pool centered over western/central MN). Some elevated instability around 500 J/kg could spark a few storms, mostly west of the Mississippi river. Meanwhile the low level jet/moisture transport push northward across the local forecast area overnight/Mon morning, with PWs of 1.5+" and warm cloud depths flirting with 3500 m helping to fuel pcpn chances. Some disjointness between the various short term guidance in how the two perturbation come together (if at all) and the resulting spread of showers/storms. The mixed bag keeps forecast confidence low with how the radar reflectivity will look as the pcpn moves in overnight, but high that most of the local will get wet. Will follow the blend for chances, leaning into the CAMS for some details in timing. Expect some refinement to these chances as we move into tonight. Current trends shift the pcpn east/southeast by 17-18z and generally dry after that. There have been hints that a linger west-east sfc boundary could layup over northern IA, working on the instability pool with some help from the low level jet to trigger a thin line of convection for the afternoon. Not a lot of support at this time, but worth monitoring. * TUESDAY/TUESDAY NIGHT: Warmer with Showers and Storms, Isolated Severe Potential with Locally Heavier Rainfall As we head into Tuesday, a deepening 500mb trough will eject from the Rockies into the Northern Plains with a developing surface cold front situated along the exit region of the aforementioned trough. Ahead of this trough, fairly robust southerly surface flow will allow for some moisture advection into our region with precipitable waters in the 02.12z NAM/GFS reaching to around 1.75", well above the 90th percentile for KDVN sounding climo. Consequently, with this warm and moisture rich airmass being pushed into our region, expecting temperatures to warm well into the 80s with corresponding dewpoints into the middle and upper 60s. Exactly how warm we get will largely depend on a weak warm front noted with some subtle theta-e advection shown in the 02.12z NAM during the late morning and into the afternoon in addition to how any cumulus deck and diurnal mixing plays out as well. There is some potential this weak boundary could initiate shower activity along it during the late morning and into the afternoon, however guidance is a bit spotty in how this resolves. As a result, kept with lower precipitation chances for now during this period. Eventually, the cold front approaches the region and convection will spread into the local area from west to east during the evening hours. Instability profiles shown during this period generally begin to wane through the evening, however will have a reasonable amount to work with initially as the 02.12 NAM/GFS show values of MLCAPE approaching 1500-2000 J/kg by 7pm before diminishing rapidly as convection pushes eastward towards midnight. Additionally, shear profiles still appear fairly lackluster for any organized severe threat with much of the more favorable bulk shear maintaining behind the boundary. As a result, could end up having evening convection manifesting as pulse thunderstorms that may produce some large hail (up to quarter sized) earlier in the evening, before quickly turning more into non-severe linear convection. Additionally, not overly impressed with the low and mid-level wind profiles, reaching only to around 25-40 kts, suggesting maybe you squeak out a couple 40-50 mph gusts. Consequently, the SPC has a marginal risk (Threat level 1 of 5) for the western two-thirds of the local area for Tuesday. Regardless of severe threat, there will likely be some healthy rainfall totals with this system as well albeit expecting a fairly progressive motion with these storms. Currently, ensemble guidance in the 02.12z GEFS/EC ensemble, favors respectable probabilities (40- 70% chance) for over 0.5" of precipitation with the Tuesday round of storms with localized amounts of up to an inch not completely out of the question (10-30% chance) when considering the aforementioned higher precipitable waters and deeper warm cloud depths (around 3.5km). When combined with the prior precipitation, this could certainly result in widespread around 1" totals with locally higher amounts from now through Tuesday night which could create some river rises in areas that are already susceptible. * WEDNESDAY INTO NEXT WEEKEND: Relatively Cooler Pattern The second half of this week will feature a broad synoptic trough that will entrench itself over the eastern half of the CONUS subjecting our region to a general north/northwesterly upper-level flow pattern. Consequently, expecting temperatures to trend below normal into the weekend with the 02.00z grand ensemble (GEFS/EC ens/Canadian ens) keeping median high temperatures in the lower to middle 70s at La Crosse beginning Thursday. Keeping with lower end precipitation chances into the weekend in accordance with the NBM to account for the shower potential consistent with this type of synoptic pattern. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1232 AM CDT Mon Jun 3 2024 VFR will continue over the next couple of hours. Incoming precipitation and storms seen to the northwest through central Minnesota moving northeast, grazing the northwest periphery of southeast Minnesota counties of Dodge and Wabasha counties. The southeastern periphery of this area of storms continues a farther extent locally, further impacting aforementioned counties into west-central and central Wisconsin. A subsequent area of precipitation extends through central Iowa with a similar northeast movement. Primary impacts within these areas of storms will be lightning and increased winds, especially within the scattered strong to severe storms. Timing places these storms reaching the aforementioned areas over the next few hours, before subsequent TAF issuance at 03.12Z. Therefore, amendments may be needed based on upstream reflectivity observations. Flight restrictions expected to abate until later in the morning hours after next planned issuance at 03.12Z. Increased clarity for impacts expected at this subsequent TAF issuance. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor/Rieck AVIATION...JAR