720 FXUS63 KMKX 130240 AAA AFDMKX Area Forecast Discussion...UPDATED National Weather Service Milwaukee/Sullivan WI 940 PM CDT Sun Sep 12 2021 .UPDATE... (Issued 940 PM CDT Sun Sep 12 2021) Broken band of showers continues to shift east across central portions of the area this evening, with this activity generally extending westward into northwestern Iowa. This is being driven mainly with the 850 mb confluence/weak warm air advection, and some weak 500 mb vorticity maxima shifting through the region. CAMs and synoptic models continue to show scattered showers and perhaps some thunderstorms developing overnight into Monday morning, as the influence of the low level jet nose/flow tries to get into the area from the southwest. Some uncertainty with how much influence this feature will have, as it may focus more to the south. Will continue to bring up PoPs somewhat overnight into Monday morning, as capping to elevated parcels may weaken during this period. Another period for scattered shower/storm activity may occur Monday afternoon into the evening, with the 850 mb boundary influence lingering until the warm front moves back north through the area. Will still need to look out for any sustained elevated convection, if it develops, for large hail potential. Forecast soundings are still showing a good amount of elevated CAPE with fairly strong effective layer shear. This should be limited to a couple of storms and not more widespread, as the modest upward vertical motion will be competing against some capping for elevated parcels. Wood && .SHORT TERM... (Issued 317 PM CDT Sun Sep 12 2021) Tonight through Monday night: A surface cold front slid down through southern WI today and is currently near the WI/IL border. There are a lot of low clouds associated with the low level convergence in the vicinity of the front. Just above the clouds, we have a pretty significant dry layer, and then moisture at and above 8000 ft, in the mid levels. We have a mesovortex feature rolling across central WI this afternoon and there are signs of another one in central to northeast Iowa (RAP 700-400mb differential vorticity advection and satellite/radar trends). There is also some 700mb frontogenesis near the MN/IA border into central WI that is helping to support the ongoing elevated showers and potential isolated thunderstorms. The RAP soundings are suggesting that our cap could break down a little for this evening and allow for about 1000 j/kg of elevated CAPE. With strong shear on the north side of the front and the next mesovortex/subtle shortwave moving into our area this evening, we could see an uptick in thunderstorm activity. Our only isolated severe threat would be hail. Our marginal risk for severe by SPC is still justified. There is really no strong low level jet in our area today, but a westerly component points into southern WI later tonight. There should be another shortwave moving through the WI/IL border area overnight, so this should support more widespread showers and isolated thunderstorms into Monday morning. Again, hail would be our main threat but anything organized could give a damaging wind gust or two. By late Monday morning, we will lose our shortwave energy and better forcing, so showers should diminish. However, a stronger low level jet will start making its way toward south central WI later Monday afternoon into the evening as low pressure develops over southeast MN and tracks into Upper Michigan Monday night. This will give our stalled frontal boundary a push northward Monday night. There is a good chance for storms near the low in central and northern WI Monday night, but southern WI has a chance too due to the warm frontal boundary. Cronce && .LONG TERM... (Issued 317 PM CDT Sun Sep 12 2021) Tuesday through Sunday: A cold front will slowly move across srn WI on Tue while the attendant shortwave trough moves away across the nrn Great Lakes. There a couple weak shortwave troughs that will move into the area from the west however, so will maintain 20-40 PoPs for Tue-Tue nt. High pressure will then move across the region for Wed-Wed eve with pleasant conditions expected. The high will shift ewd for Wed which will begin a prolonged period of sly winds and warm advection into the weekend. This coincides with a developing wswly jet pattern from the Pacific NW toward Hudson Bay. Above normal temps and humidity will prevail during this time with only slight chances of showers and storms for Thu nt-Fri nt. Gehring && .AVIATION... (Issued 940 PM CDT Sun Sep 12 2021) Scattered showers should continue to move east through the area overnight into Monday morning. Some thunderstorms may develop as well during this time, with a few possibly producing hail. Modest northeast to east winds overnight will become east on Monday. May see some light fog develop overnight into early Monday morning as well, especially in areas that receive rainfall. Ceilings should gradually lower below 2000 feet AGL overnight into Monday morning across most area terminals, before rising above 3000 feet AGL by middle afternoon. More scattered shower and some thunderstorm activity may develop again Monday afternoon and early evening, before a warm front moves north through the area. Again, a few storms may produce hail. Winds should shift to the south to southwest and become gusty later Monday evening and overnight. Some low level wind shear conditions may develop Monday night, but will leave out of TAFs for now. Wood && .MARINE... (Issued 317 PM CDT Sun Sep 12 2021) A front continued to slide down Lake Michigan today and it will stall over the far southern part tonight. Expect northeast winds on the north side of this front and southerly winds on the south side. The front will remain over the southern tip of Lake Michigan on Monday and then lift back northward Monday night. Expect gusty southerly winds on Tuesday. Cronce && .BEACHES... (Updated 940 PM CDT Sun Sep 12 2021) Winds and waves have subsided enough to allow for a low swim risk to return to Lake Michigan beaches. && .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