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Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
838 FXUS63 KMKX 022035 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 335 PM CDT Tue Jul 2 2024 .KEY MESSAGES... - Showers and thunderstorms are still expected this afternoon & evening. Locally heavy rainfall and flooding are the main concerns in this activity, particularly over the Wisconsin River Valley and southwestern Wisconsin. A Flood Watch is in effect between 3 PM and 1 AM in these locations. - An isolated strong to severe storm can`t be ruled out over far southwestern counties during this afternoon & evening`s storms. - Dangerous swimming conditions continue through this evening at Lake Michigan beaches. - Elevated water levels continue on area rivers and streams through the end of the week. Flood warnings remain in effect in several locations. - Independence Day forecast trends for widespread showers and thunderstorms continue to push later overnight Thursday into Friday. However still will be a 20-40% chance for spotty showers and thunderstorms with lightning through Thursday afternoon/evening. && .SHORT TERM... Issued 331 PM CDT Tue Jul 2 2024 Tonight and Wednesday: Synopsis/Mesoanalysis: Afternoon surface observations depict a cold front extending from the MN Boundary Waters south into the Missouri Valley. Evident in GOES water vapor imagery, an upper shortwave is progressing eastward along the South Dakota-Nebraska border. Both of the aforementioned features are progged to track east toward the region this evening, triggering shower and thunderstorm development in the process. Locally heavy rainfall and flooding are possible in this activity given an unseasonably moist air mass in place across the area, with a Flood Watch in effect across our southwestern counties between 3 PM and 1 AM. Convection will push east of the area during the predawn hours as the aforementioned cold front clears the area from west to east. Post-frontal high pressure will nudge into southern Wisconsin Wednesday afternoon, allowing for decreasing cloud cover and primarily dry conditions. Rest Of This Afternoon & This Evening: Hazardous swimming conditions continue at all Lake Michigan beaches given a combination of high waves and dangerous currents. Already in progress to our west, shower and thunderstorms will continue to fill in as they move toward the area. Storms will be encountering an unseasonably moist air mass characterized by precipitable water values in the 1.75 to 2.25 inch range, which reside anywhere between 1.5 and 2 standard deviations above early July normals. Storms will thus be capable of producing heavy rainfall rates this afternoon/evening, and will pose some potential for flooding. Latest flash flood guidance from the North Central River Forecast Center depicts six hourly values between 1.5 and 2 inches across the region. 6 hour QPF progs from the 12Z HREF, in addition to more recent runs from the HRRR, point toward these thresholds being met in localized pockets across southwestern Wisconsin and the Wisconsin River Valley. Have thus issued a Flood Watch for Sauk, Columbia, Iowa, Dane, Lafayette, and Green Counties between 3 PM and 1 AM. Stay aware for rising water in these locations, and remember to turn around, don`t drown if encountering flooded roadways. While well secondary to the flooding potential, an isolated strong to severe storm can`t be completely ruled out over far southwestern counties (particularly Green, Iowa, and Lafayette Cos) during the 4-8 PM timeframe. This potential will be heavily contingent upon the realization of surface-based instability. Said realization has been hinted in the 12Z HREF, as well as more recent runs of the HRRR and NAM Nest. Damaging winds would be the primary concern in any strong/severe storms, though a brief tornado would be possible in any activity becoming favorably aligned with 40-45 kt, southwesterly shear vectors in the 0-3 km layer. Will continue to monitor trends through the remainder of the afternoon and evening hours. Wednesday: Skies will turn partly cloudy by late morning as the cold front pushes east of the area. Have maintained an entirely dry forecast, but did insert some 10% precip probs over far northern counties, where some mesoscale guidance hints at isolated shower and thundershower development during the afternoon hours. && .LONG TERM... Issued 331 PM CDT Tue Jul 2 2024 Wednesday night through Tuesday: This will be an active period with shortwave troughs arriving within wnwly flow aloft. For Independence Day, a 700 mb shortwave trough will track across nrn IL or far srn WI. Mid level warm, moist advection and PVA along with marginal CAPE will support PoPs of 20-40 percent for the afternoon and evening. The convection may only be elevated and will depend on the amount of clouds and sfc heating. Either way, scattered showers and isold storms are forecast. A larger and slower moving shortwave trough will then approach from the ern Dakotas and MN late Thu nt. A surge of 850-700 mb warm, moist advection and increasing PVA within a PW airmass of 1.4-1.8 inches and marginal CAPE will result in widespread showers and sct storm development. A developing sfc low will move across srn WI during the day on Fri while the upper low moves across central to ne WI. Widespread showers and possibly some heavy rainfall will continue at least in the morning. Some showers may linger into Fri nt, but shortwave ridging and a pleasant day is expected for Sat. A series of shortwave troughs will continue to affect the region from Sun-Tue with chances for showers and storms each day. Temps during the extended will be near normal but below normal on Fri given the widespread clouds and showers. Gehring && .AVIATION... Issued 331 PM CDT Tue Jul 2 2024 A mixture of MVFR and VFR conditions prevail across southern Wisconsin this afternoon as morning rainfall pushes east of the region. Expect that the aforementioned mix of categories will continue through mid-afternoon. Widespread reductions will arrive late this afternoon & evening as an area of -SHRA and embedded -TSRA overspread the area from west to east. Anticipate that IFR-MVFR categories will accompany the precip, with greatest deteriorations occurring within any heavier convection. -SHRA/-TSRA activity will push east over Lake Michigan during the second half of the overnight hours, with dry conditions prevailing through the remainder of the period. Clouds will begin to scatter out behind a departed cold front late tomorrow morning, giving way to VFR conditions. Quigley && .MARINE... Issued 331 PM CDT Tue Jul 2 2024 A broad area of 994 mb low pressure will move from central Canada into the Hudson Bay through Wednesday afternoon, dragging a cold front across Lake Michigan in the process. Showers and thunderstorms are expected this evening along the front, with heavy downpours possible. Severe weather is not expected. Primarily southerly winds will continue through this afternoon prior to the front`s arrival. Gusts will range between 15-25 knots, with the highest readings over the northern two thirds of the lake. Winds will gradually shift out of the west-southwest behind the front on Wednesday, with gusts tapering below 15 knots. Winds will lighten further Wednesday night as 1012 mb high pressure moves in from the Great Plains. Quigley && .MKX WATCHES/WARNINGS/ADVISORIES... WI...Flood Watch...WIZ056-WIZ057-WIZ062-WIZ063-WIZ067-WIZ068 until 1 AM Wednesday. Beach Hazards Statement...WIZ052-WIZ060 until 1 AM Wednesday. Beach Hazards Statement...WIZ066-WIZ071-WIZ072 until 7 PM Tuesday. LM...Small Craft Advisory...LMZ643 until 1 AM Wednesday. Small Craft Advisory...LMZ644-LMZ645-LMZ646 until 7 PM Tuesday. && $$ Visit us at weather.gov/milwaukee Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSMilwaukee www.twitter.com/NWSMilwaukee www.youtube.com/NWSMilwaukee