Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
694 FXUS63 KMKX 220036 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 736 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - Showers and thunderstorms are likely through the overnight. - Most of southern WI will see some beneficial rainfall from the cold front passage with amounts generally ranging from 0.1-0.7 inches with locally higher amounts with any stronger thunderstorms. - Cooler/near normal temps are expected behind the cold front Sunday through the start of the week with daily highs in the upper 60s and lower 70s. && .UPDATE... Issued 736 PM CDT Sat Sep 21 2024 Scattered showers and thunderstorms continue across the region this evening. Any meaningful severe weather threat has likely ended. Occasional showers and thunderstorms will persist overnight and into tomorrow morning, as a broad area of warm/moist advection remains in place ahead of a slow moving cold front. Tough to say just how widespread coverage will be, and it may ebb and flow a bit as various weak shortwaves ripple through the area. More organized shortwave energy will lift across northern Illinois and extreme southeastern Wisconsin tomorrow morning, so suspect will see some uptick in coverage over the eastern third to half of the area early to mid morning. The front will finally clear the area tomorrow afternoon, though clearing will lag by several hours. Boxell && .SHORT TERM... Issued 336 PM CDT Sat Sep 21 2024 This Afternoon: Showers and thunderstorms are developing in a north-south oriented line that is right along the 1000 j/kg CAPE gradient, within an area of steady 925-850mb warm air advection. There was an outflow boundary that developed from the morning convection over the Twin Cities that is tracking straight down the instability gradient, and this feature is causing the intersecting storms to be stronger as the boundary propagates south-southeast. The area of stronger storms is currently over Dane County and is producing marginally severe hail and wind. The next feature of interest is the surface warm front which is moving into the Mississippi River Valley. There are showers and a few thunderstorms along this front. The two areas of warm air advection will slowly track across southern WI through the evening and therefore, the chance of storms will persist all evening. Severe storms are not expected, but if there are any areas of extra forcing such as an outflow boundary of surface convergence with a lake breeze, then isolated severe is possible. We will have up to 1500 j/kg of elevated CAPE and around 30 kt of bulk shear to support a few stronger storms. Tonight through Sunday night: The cold front is also going to move through in a couple waves overnight. There is a surface wind shift to the northwest that is already in southeast MN and north central IA. This surface warm front may be enough to kick off a few thunderstorms as it gets into western WI late this afternoon, but it is also possible that our environment could be worked over by previous storms and not amount to much. There is a secondary cold front back in central MN which has more upper level support with the mid level vorticity advection. Since the upper wave will be weakening, its movement toward southern WI will slow down overnight into Sunday. This means our chance for showers and storms ahead of an along this secondary cold front will persist all the way into Sunday afternoon, especially over southeast WI. Cronce && .LONG TERM... Issued 336 PM CDT Sat Sep 21 2024 Monday through Saturday: One more mid level shortwave will track along the WI/IL border on Monday. This will keep clouds over southern WI. Then an upper low should develop and stall over the Upper Midwest Tuesday. This will keep us cloudy and keep our temps down in the 70s. Lots of uncertainty with how that low will move later in the week, with a trend away from southern WI and retrograding toward the south central U.S.. Cronce && .AVIATION... Issued 736 PM CDT Sat Sep 21 2024 Rather complex aviation forecast on hand for the next 24 hours, with occasional showers and thunderstorms into the daytime hours on Sunday, ahead of a cold front. Have utilized PROB30 groups to indicate the more favored windows for thunderstorms, but overall forecast confidence is low. Lower ceilings and visibilities are expected as well, especially early Sunday as the front starts to move through the region. Winds this evening and tonight will be south to southeast, though will be variable in and around thunderstorms. Look for a turn to westerly and then northwesterly winds as the front moves through on Sunday. Boxell && .MARINE... Issued 336 PM CDT Sat Sep 21 2024 Expect southerly winds increase through the evening as low pressure lifts from MN to Ontario, which will in turn drag a cold front across WI and Lake Michigan overnight through Sunday. Showers and thunderstorms will develop ahead of and along the cold front. Southwesterly winds will become northerly behind this front Sunday night into Monday. Given the strong cold air moving over the warmer lake waters, expecting to see gusty northerly winds during this timeframe. Gusts up to 30 knots and a few gale force gusts cannot be ruled out, especially for the southern portions of Lake Michigan. Will see winds weaken a bit for Monday as high pressure builds in across the Great Lakes region, but the northerly component will persist through the start of the week. Cronce && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...None. && $$ 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