Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
097 FXUS63 KMKX 301500 AAA AFDMKX Area Forecast Discussion...UPDATED National Weather Service Milwaukee/Sullivan WI 1000 AM CDT Tue Apr 30 2024 .KEY MESSAGES... - Diminishing line of showers and thunderstorms expected late this evening and overnight. - Additional rounds of showers and storms Wednesday night through Thursday night && .UPDATE... Issued 1000 AM CDT Tue Apr 30 2024 No major changes to forecast expectations this morning. Stratus over east central Wisconsin is gradually diminishing from southwest to northeast. Highs should reach the upper 60s and low 70s for most. As mentioned in the previous discussion, a lake breeze is likely by mid to late afternoon given the good inland heating and light winds, which will knock temperatures down for locations closer to the lake. A broken line of showers and thunderstorms is then expected to approach from the west late this evening into the overnight hours. These should be diminishing fairly rapidly as they push east, with some short term guidance suggesting a good portion of the eastern half of the forecast area may remain dry. Boxell && .SHORT TERM... Issued 356 AM CDT Tue Apr 30 2024 Today through Wednesday: Clouds should gradually decrease across the north today under high pressure. With plenty of sunshine anticipated by afternoon, high temps should reach or approach 70 most places. Winds will likely turn onshore by the lake in the afternoon, bringing some cooler temps to lakeshore areas. A shortwave will swing through the area this evening into tonight, bringing showers and a few thunderstorms to southern Wisconsin. Instability will be decreasing as the area of precip approaches, with models showing a lessening chance for thunder and also decreasing precip amounts. Still, looks like enough forcing and moisture for high precip chances (60-100% most places), so confidence is high in rain this evening/overnight. The higher chances will be in the north closer to the track of the surface low. High pressure will then bring mostly sunny skies and mild temps to the area on Wednesday. Offshore winds should be strong enough through the day to keep the lake breeze away. DDV && .LONG TERM... Issued 356 AM CDT Tue Apr 30 2024 Wednesday night through Monday: Wednesday night marks the approach of our next active weather pattern, with a neutrally tilted trough over the rockies deepening and becoming more negatively tilted and the corresponding ridge axis building over the eastern Great Lakes region, obtaining stronger supergeostrophic flow. The corresponding upper air divergence and lee cyclogenesis develop a deep low pressure in Colorado Wednesday evening, which then elongates meridionally into two separate lows, with the northern low tracking from southeast Nebraska Thursday morning to northern MN / WI by Thursday night. As it travels, it occludes, and a triple- point low develops to its southeast, which may track as close as central-WI Friday night. Showers (and eventually thunderstorms) associated with this event are expected to arrive Wednesday night / Thursday morning, peak in intensity Thursday afternoon / evening, weaken Thursday night, then clear out into Friday. The severe thunderstorm threat for Thursday afternoon and evening is conditionally dependent on the positioning of the warm sector / warm front and wind shear from the jet streak. For example, the ECMWF produces 40 to 55 kts of surface to 500mb bulk shear across the CWA at 1 PM Thursday (sufficient for organized convection and supercells). Then, as the ridge continues to build northward and the jet lifts with it, the shear decreases to 20 to 35 kts at 7 PM (marginally sufficient for organized convection, but supercells much less likely). The GFS exhibits similar behavior, while the NAM allows more consistent favorable shear (jet stays closer to us). Until model guidance converges on a solution, either scenario is in play. For instability, global models have suggested roughly 500 j/kg CAPE (relatively weak) in southern portions of our CWA, with lower values to the north. Depending on the exact track of the system, and how strong the triple point low becomes, CAPE > 1000 j/kg deeper within the warm sector could easily be pulled into our CWA. On the other hand, said triple point low could also strengthen the easterly component of the wind field off of Lake Michigan, advecting cool stable air over portions of the CWA and minimizing the severe threat. Both the warm frontal surge (late Thu morning through Thu afternoon) and the cold front passage (late Thu evening / nighttime) should be capable of triggering ascent, hence our PoPs are 80% and rain is likely in any scenario. Shower and thunderstorm chances continue into Friday behind the cold front, but chances have decreased (25 to 50% PoP in the morning, only 25% in the afternoon) and may continue to trend down. This is due to model guidance converging on a sooner than anticipated passage of the cold front and a dry slot wrapping into the departing low pressure. A shortwave trough approaches Saturday, bringing a small/brief push of moisture and PVA, delivering some rain showers to the area. Our forecast features broad-brushed 30% PoPs due to model guidance disagreeing on the exact arrival time. Dry / quiet weather is the most likely scenario for Sunday, with a high pressure system residing over WI. Sheppard && .AVIATION... Issued 1000 AM CDT Tue Apr 30 2024 A area of MVFR stratus over central Wisconsin should continue to improve to VFR over the next few hours. Otherwise, VFR is likely through the daytime hours today and into this evening. A lake breeze is expected by this afternoon, which will turn winds to an easterly or southeasterly direction as it passes. This is most likely to impact Milwaukee, Sheboygan, and Kenosha, but the boundary may advance far enough west to pass through Waukesha by early evening. A broken line of showers and thunderstorms is then expected to advance eastward into the region late this evening into the overnight hours. Ahead of this activity, expect winds to become gusty from the southwest, with winds turning more westerly behind the showers/storms. MVFR or IFR is likely in and around showers and storms, but VFR should prevail otherwise. Boxell && .MARINE... Issued 356 AM CDT Tue Apr 30 2024 Southerly winds will be generally under 15 knots today, as high pressure slides through the area. Southeast to south winds will increase tonight, as low pressure lifts northeast through northern Wisconsin. Breezy west to southwest winds are expected on Wednesday behind the departing low and as high pressure builds in from the west. Another low will lift through Wisconsin Thursday into Thursday night, bringing breezy east to southwest winds to the lake. Winds will approach Small Craft Advisory levels on Wednesday, especially north of Milwaukee. Onshore winds Thursday may push waves over 4 feet, with advisory conditions possible then as well. DDV && .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