Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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761 FXUS63 KARX 011738 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1238 PM CDT Wed May 1 2024 .KEY MESSAGES... - Periodic showers and scattered storms from tonight into Thursday night. Rain amounts and severe weather chances have decreased some. - Decreased or removed the rain chances for Friday for much of the forecast area. - Scattered showers from Friday night into Saturday evening. 60 to 80% of the grand ensemble have rain totals less than a tenth of an inch. && .DISCUSSION... Issued at 208 AM CDT Wed May 1 2024 Wednesday Night through Thursday Morning - Another round of showers and scattered storms A 500 mb shortwave will eject out of the Central Plains tonight and then move northeast through the area on Thursday morning. As this occurs, the 850 mb moisture transport will increase on the nose of a 45-knot jet which will be moving northeast through the area. While this enhances the 0-3 km shear into the 30 to 40 knot range, the 0-4 km most unstable CAPES remain less than 250 J/kg. The highest values are south of Interstate 90. The 30.12z LREF 10th-90th percentiles for precipitable water increases on Thursday morning from 1 inch to 1.4 inches. With less instability, rainfall amounts have come down some in the 01.00z HREF. Through Thursday morning, the HREF 10th to 90th percentiles ranges from less than a tenth of an inch to three- quarters of an inch north of Interstate 90 and from a tenth to 1-inch across the remainder of the area. Thursday Afternoon through Thursday Night - Another round of showers and scattered storms On Thursday afternoon, negatively-tilted shortwave trough will eject out of the Central Plains and then move northeast through the region on Thursday night. The CAMs are in general agreement that another round of showers and storms will move northeast through the area on Thursday afternoon and night. The 01.00z HREF 10th to 90th percentiles range for Thursday afternoon ranges from 0 to 410 J/kg. The greatest instability will be located southeast of an Oelwein, IA to Black River Falls, WI line. This is also the area where the 0-3 km shear is the weakest (20 to 30 knots), so severe weather chances have decreased. For this period, additional rainfall amounts range from a 0.25 to 0.50 inch west of the Mississippi River and 0.50 to 0.75 inches for the remainder of the area. Friday - Looking Dry In the wake of the front, subsidence quickly build across the area. The NBM continues to hold onto a 20 to 25% chance of rain for the entire area. Meanwhile, less than 10% of the GEFS, Canadian, and ECMWF ECE have any precipitation at all. Since this trend has been showing up the past several days, it was agreed to remove these small rain chances for much of the forecast area. Friday Night through Saturday Evening - Scattered showers - Rain amounts look light A broad longwave trough will move east through the area. Our area is on the southern extent of this trough, so the forcing is rather weak. This results in the 60 to 80% 01.01z NBM grand ensemble having less than a tenth of an inch of rain. For Early Next Week - Uncertainty on rain chances The models are in general agreement that a closed 500 mb low will eject out of the southwest US into either the Northern Plains or the Upper Mississippi River Valley. Due to uncertainty on how this pattern will evolve stayed close to the NBM. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1238 PM CDT Wed May 1 2024 Besides some MVFR ceilings to the north, that are becoming more cellular, VFR conditions prevail with a fairly brisk west to northwest low level flow. The winds will diminish quickly going into the evening as we are start to feel impacts from approaching trough that promises to bring abundant convection back to the area starting late tonight. As ceilings gradually lower overnight, expect VFR conditions to last for a bulk of the time but as lift and moisture advection continues, we will see gradual drop to MVFR to IFR ceilings, especially as bulk of convection impacts area early Thursday. Details on the impacts from thunderstorms will have to be resolved in near-time. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Boyne AVIATION...Shea