969 FXUS63 KMKX 280008 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 708 PM CDT Sat Apr 27 2024 .KEY MESSAGES... - A tornado watch has been issued for Green, Iowa, and Lafayette Counties until midnight tonight. - A severe thunderstorm watch is in effect for most of south- central and southeastern Wisconsin until midnight tonight. - Scattered storms are still expected to develop along a weak cold front late this afternoon and evening. A few of these storms may become severe with large hail and damaging winds, but cannot rule out a tornado or two. - Rounds of showers and storms are expected from this evening through late Sun nt. The flash flood threat will remain low but local urban and small stream flooding is more probable. && .NEW MESOSCALE UPDATE... Issued 655 PM CDT Sat Apr 27 2024 ...SEVERE THUNDERSTORM WATCH 151 IN EFFECT FOR MOST OF SOUTH CENTRAL AND SOUTHEAST WISCONSIN UNTIL MIDNIGHT... In coordination with the Storm Prediction Center, a severe thunderstorm watch has been issued for the majority of south- central and southeastern Wisconsin not included in tornado watch 150 until midnight. The Madison and Milwaukee metro areas are included in this watch. Scattered storms continue to develop this evening as low level lift increases along a southeast- sagging cold front. The lift from said boundary has allowed updrafts to grow and maintain despite dry air in the 700-500 mb layer & subsidence beneath a short wave ridge. Effective bulk shear values ranging between 40-45+ knots along/southeast of the front will support organization in additional convection that develops, with large hail and damaging straight line wind gusts being the main concerns. While not expected to be the primary hazard, an isolated spin-up tornado can't be ruled out either. Have multiple ways to receive warning information this evening, particularly if planning to be outdoors. Be ready to move to shelter if a warning is issued for your area. Quigley && .SHORT TERM... Issued 345 PM CDT Sat Apr 27 2024 Tonight through Monday: A Wind Advisory remains in effect until 4 PM CDT for east central and far ern WI as the LLJ has been slow to exit. A weakening trend in the pressure and wind fields is expected by late this afternoon into the early evening. Cumulus to cumulus congestus are lined up along and east of a weak cold front over ern IA to sw WI and the Madison area. Brief convection has been occurring over ern IA into nw IL early this afternoon. Despite shortwave ridging aloft and weakening pressure and wind fields into this evening, the CAMs and current activity suggest convective initiation will occur along the front from mid to late afternoon and evening. MLCAPE will range from 1500-2000 J/kg with effective shear of 30-40 kts during this time. The 0-3 KM hodographs remain fairly straight for any cells on the front but some 0-1 KM clockwise turning is observed east of the front. Thus a small tornado threat remains with better probs for large hail and strong wind gusts. Since the deep layer shear is parallel to the front, a broken line of storms may seed each other resulting in greater pcpn efficiency and a more solid line of storms. However, at this time the QLCS threat is low as 0-3 km shear is parallel to the front and weakening into the evening. For late evening into the overnight it is possible an area of convection currently moving into srn IA could clip srn WI. There would at least be a small SVR threat with this activity as well. The cold front will stall over far nrn IL on Sunday while low pressure over the central Great Plains tracks to wrn IA. A broad area of 850-700 MB warm, moist advection is expected on Sunday with soundings closer to moist adiabatic and very minor elevated CAPE. Most areas over srn WI will likely see some rainfall. For Sun nt the occluded low will move toward sw MN while its warm front will lift nwd through srn WI. Meanwhile, a shortwave trough rotating around the large upper low will swing newd from the srn Great Plains into the srn Great Lakes. There will be a heavy round of convection with this feature but it may only clip se WI. Overall the heavy rain threat and any flooding will remain localized tnt-Sun nt. The occluded front will then pass Mon AM while the low pressure area tracks from se MN to wrn Lake Superior. Mild temps are still expected with a few lingering showers possible. Another cold front will pass in the afternoon but still just a few showers. Gehring && .LONG TERM... Issued 345 PM CDT Sat Apr 27 2024 Monday night through Saturday: Westerly winds diminish Monday night as low pressure finally departs the region. Winds then shift to become southerly and gusty on Tuesday as a low pressure system develops in Alberta and the northern Plains and progresses southeastward into the Upper Midwest overnight Tuesday into Wednesday. A cold frontal feature will sink through the region on Wednesday, leading to shower and thunderstorm potential and westerly winds. An additional low pressure system may develop in the central Plains and follow along the remaining frontal boundary on Thursday, leading to additional shower and thunderstorm chances. Generally expecting to be within the warm sector, but a change in low pressure intensity is still possible at this time frame and may result in cooler conditions and less thunderstorm chances. Model discrepancy increases going into Saturday, with GFS and Canadian indicating low pressure progressing into Canada Saturday morning, while the Euro keeps the system lingering and stalling over the Great Lakes. MH Gehring && .AVIATION... Issued 345 PM CDT Sat Apr 27 2024 Sct-bkn035-045 cumulus and cumulus congestus this afternoon and evening with scattered to numerous storms developing over srn WI. The passage of a cold front late tonight will then result in a moist enely flow and low stratus development. MVFR Cigs will develop by early morning Sunday then fall below 1 kft for the remainder of the day. Some fog development will also occur during this time. Rounds of showers and storms will also continue on Sunday. Gehring && .MARINE... Issued 345 PM CDT Sat Apr 27 2024 Low pressure around 29.5 inches over Lake Superior will continue to gradually weaken as it moves into Ontario this evening. Gusty south winds are expected across Lake Michigan this afternoon, with a few gusts approaching or reaching gale force, especially in the northeast portion of the lake. Areas of dense fog may redevelop this evening over the northern portion of the lake as the winds become lighter, while dense fog may form over the southern portion of the lake late tonight into Sunday. Winds will then gradually shift from southwest to northerly tonight as a cold front tracks south, but southerly winds will continue over far southern Lake Michigan as the front stalls. Brisk northeast winds will then prevail over central Lake Michigan on Sunday with lighter winds in the north, and variable winds in the south where the stalled front remains. Modest east to southeast winds will then develop over all of the lake Sunday night as the stalled front moves north as a warm front. Brisk east winds, possibly reaching gale force, are expected over the northern tip of the lake late Sunday night into Monday morning. Breezy south winds will develop over the remainder of the lake on Monday. Rounds of showers and thunderstorms are expected tonight into Monday morning. A few of these storms could produce locally gusty winds and hail. Gehring && .MKX WATCHES/WARNINGS/ADVISORIES... WI...None. LM...Small Craft Advisory...LMZ643-LMZ644-LMZ645-LMZ646 until 7 PM Monday. Dense Fog Advisory...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565- LMZ567-LMZ868 until 1 AM Sunday. && $$ 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