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Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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263 FXUS63 KARX 132007 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 307 PM CDT Tue Aug 13 2024 .KEY MESSAGES... - Widespread showers/storms likely from late Wednesday afternoon/evening into Thursday with locally heavy rainfall possible. This looks to be the highest chance for rain over the next week with medium to high (40-80%) chances for at least 1 inch. - Below to near-normal temperatures are expected over the next 10-days and near-normal in the 10 to 14 day period. && .DISCUSSION... Issued at 307 PM CDT Tue Aug 13 2024 Tonight into Wednesday... High pressure will move slowly east of the area. As this occurs, a developing low pressure over the Central and Northern Plains will move slowly east toward the area. 925 and 850 mb moisture transport will gradually increase during the afternoon. This initial moisture transport will result in a gradual decrease in cloud heights. There are still some differences in the CAMs on when showers will move into the area on Wednesday afternoon. The NAM and FV3 has them moving into the area by early afternoon. Meanwhile, the ARW, HRRR, and RAP keep much of the area dry through mid- to late afternoon. Wednesday night through Thursday night... The models are in good agreement that the low pressure system will move slowly east northeast through the area and gradually deepen. Even though it will be deepening, the 0-6 km shear primarily remains at 30 knots or less. There is a small window on Thursday afternoon where the 0-6 km shear does climb up to 40 knots in southwest Wisconsin. However, 0-1 km mixed-layer CAPES at that time ranges from 500 to 1500 J/kg, so the marginal risk from SPC looks good. With precipitable water values of around 1.5 inches and warm cloud depths of 3.5 to 4 km, these showers and storms will be highly efficient rain producers. WPC has the area under marginal to slight risk for excessive rain for this time period and that seems reasonable. Most areas will likely see anywhere from 0.75 to 1.5 inches of rain. The 48-hour HREF QPF has 2 areas where the ensemble probability-matched mean climbs into the 2 to 3 inch range. The first area is in northeast Iowa and there is a secondary area from southwest Minnesota east northeast into the Twin Cities. From Friday into Saturday... The surface low continues to move east northeast into the northern Great Lakes. This will keep scattered showers and maybe a few storms as shortwaves rotate around this low. With limited instability and the best moisture to our east, rainfall totals generally look on the lighter side. 8-14 Day Period (August 21-27)... The ensembles continue to show that an omega ridge will likely remain to our west and northwest from mid to to the latter portions of August. This will favor near- to below-normal temperatures and below-normal precipitation. The highest probabilities for below-normal temperatures will be in the 6 to 10 day period (August 19 to 22). && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1233 PM CDT Tue Aug 13 2024 A scattered to broken deck of cumulus clouds will gradually dissipate with the loss of diurnal heating this evening. On Wednesday morning, mid- and high clouds will gradually increase. Southeast winds will increase to around 10 knots by late morning. There may be even some wind gusts up to 20 knots west of the Mississippi River. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Boyne AVIATION...Boyne