Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
229 FXUS63 KMKX 300856 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 356 AM CDT Tue Apr 30 2024 .KEY MESSAGES... - Showers expected this evening into tonight, with some thunder also possible - Additional rounds of showers and storms Wednesday night through Thursday night && .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 356 AM CDT Tue Apr 30 2024 A mix of VFR and MVFR clouds continue mainly north of I-94 early this morning. There should be gradual clearing in the north the remainder of the morning under high pressure. Low pressure will pass by to the north this evening into tonight, with showers likely as this system moves through. A few rumbles of thunder will also be possible, especially in the evening. Ceilings could briefly dip below VFR as the trough swings through tonight, with skies clearing early Wednesday behind the trough. Low level wind shear is expected for a time later this evening into tonight as the the low level jet moves overhead. DDV && .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