Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
Issued by NWS Milwaukee/Sullivan, WI
991 FXUS63 KMKX 210912 AFDMKX Area Forecast Discussion National Weather Service Milwaukee/Sullivan WI 412 AM CDT Sat Sep 21 2024 .KEY MESSAGES... - Another day with above normal/summer-like temps in the mid to upper 80s today. However 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. - Increasing shower and thunderstorm chances (50-80%) return this evening through Sunday. Cannot rule out a stronger thunderstorm or two capable of producing gusty winds this evening east of I-39 corridor, but confidence remains on the lower end. - 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 closer to the WI/IL border or with any stronger thunderstorms. && .SHORT TERM... Issued 409 AM CDT Sat Sep 21 2024 Today through Sunday night: As the surface high pressure gradually slides east through the morning, expect the dry airmass in place continue to limit fog development through daybreak. Also seeing some scattered light reflectivities pop up with the low-level WAA upstream along the Mississippi River Valley early this morning. However, that dry air will limit any of this activity from precip as it pushes eastward across the CWA through the morning. Expect southerly flow to pick up through the day ahead of the incoming cold front. Will once again see summer-like temps in the mid to upper 80s this afternoon and given yesterday`s trend, would not be surprised to see a few locations creep toward 90F. Accompanying the warmer temps will be gradually increasing precip chances. While the 00z CAMs, such as the HRRR suggest we could see showers and storms develop as early as later this afternoon, the model trend favors the drier air to win out and limit the earlier development, especially as the forcing lingers further west at this time as the 06z runs suggests. While the 06z HRRR still seems to bullish developing a line of showers between 00-06z that is able to tap into the instability with mean MUCAPE values around 1000 J/kg from the afternoon, still seeing disagreement between the the models with timing and forcing. I think the biggest hurdle for this early evening thunderstorm activity is the timing of upper-level dynamics just being offset from the surface forcing. Nevertheless, if the mid- level shortwave trough ejecting out ahead of the main mid- level trough out across the Plains matches up with the timing of the surface front better, then we could see a few stronger thunderstorms develop this evening. If this ends up materializing, given the model forecast sounding, could see a few storms capable of producing gusty/downburst type winds given the the dry air aloft paired with the elevated instability. Otherwise, the better upper-level forcing (right entrance region of the upper-level, 500mb dCVA, 700mb frontogenesis) tends to align better overnight after 09z through Sunday morning. The overnight timing of this forcing would limit the stronger thunderstorm potential (diminishing instability and deep-layer shear <35 kt), but would favor more widespread shower activity through Sunday morning as the front pushes east. Models prog the cold front to clear the CWA from west to east through Sunday afternoon with drier conditions establishing themselves by the evening. Overall, pinpoint exact rainfall amounts remains a challenge given the aforementioned issues of timing and alignment of the forcing. nevertheless, there will be the potential for most of the area to see some much needed rainfall. Areas generally north of the US-18/I- 94 favor the lower amounts ranging from few hundredths to around a quarter of inch. Meanwhile areas along and south of US-18/I-94 have a 50-70% chance of seeing up to around a half an inch or more, while the higher potential to see an inch or more remains south of the Cheddar Curtain in IL. However, if any stronger thunderstorms materialize and/or rainfall trains over the same area then we could see some localized higher rainfall amounts nearing the one inch mark. Wagner && .LONG TERM... Issued 409 AM CDT Sat Sep 21 2024 Monday through Friday: While Monday looks to start of dry with building surface high pressure and post cold front conditions, there are hints of the mid- level trough working its way through the area. This mid- level disturbance paired with some lingering moisture may spur some scattered shower activity on the backside of departing surface trough and northside of another incoming surface low into Tuesday. Thus low-end shower chances (<40%) linger Monday and Tuesday. Behind the weekend cold front expect a cooler, Canadian airmass to settle across the region for the start of week. Building high pressure Monday will bring temps more in line with normal for this time of year with daily highs in the the upper 60s to lower 70s and nightly lows in 40s-50s. Otherwise midweek onward, the pattern becomes a bit more uncertain given the long range model difference and variability. However, the general pattern as suggested by the WPC Cluster Analysis does favor upper-level ridge building over the Upper Midwest through the later half of the week, which would bring a return of above normal temps. There are hints from the 00z deterministic models where an undercutting mid-level trough sets up somewhere south of our neck of the woods. So will monitor trends to see how the pattern shapes up in the coming days. Wagner && .AVIATION... Issued 409 AM CDT Sat Sep 21 2024 VFR conditions will prevail through the morning as high pressure skirts southeast of the area. Will see southerly winds pick up through the afternoon ahead of an incoming cold front. Expect to see increased shower and thunderstorm activity ahead of the cold front this evening into Sunday morning. The better thunderstorm potential remains this evening for areas west of I-39 corridor and cannot rule out a stronger storm or two this evening with localized gusty winds, but may carry east a bit with the shower activity through Sunday morning. With any shower and thunderstorm activity will likely see lower flight conditions either in the form of lower ceilings and/or visibility accompany it. The cold front will push east across southern through much of the day Sunday and southerly winds are expected to turn more north-northwesterly behind it. Wagner && .MARINE... Issued 409 AM CDT Sat Sep 21 2024 Weak high pressure is skirting east across southern Lake Michigan early this morning. This has brought light winds and patchy fog for the north and east side of the Lake this morning. As the high pressure pushes further east, expect more southerly winds increase through the afternoon as low pressure lifts northeastward up through MN into Ontario, which will in turn drag a cold front across WI and Lake Michigan overnight tonight into Sunday. Expecting to see showers and thunderstorms to develop along the cold front and track across the Lake through Sunday. Will then see southwesterly winds turn northerly behind this front overnight Sunday into Monday. Given the strong cold air moving over the warmer lake waters, expecting to see gusty northerly winds during this timeframe with gust 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. Wagner && .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