Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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020 FXUS63 KGRB 182338 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 638 PM CDT Tue Jun 18 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Gusty south winds could create large waves and strong currents at Lake Michigan beaches tonight. A Beach Hazard Statement has been issued. - The gusty south winds will also create conditions hazardous to small craft on the lake and bay tonight. - Thunderstorms are likely in central and north-central Wisconsin tonight, with a chance of storms in eastern Wisconsin late tonight. - Periodic chances for storms will continue throughout the week. Some storms may produce strong winds and torrential rainfall. && .DISCUSSION... Issued at 219 PM CDT Tue Jun 18 2024 Short Term...Tonight and Wednesday Main forecast concerns center on timing of convection into the forecast area tonight, risk of severe and potential for heavy rain. The 19Z MSAS surface analysis showed an area of low pressure over southwest MN with a warm front extended northeast/then east across the northern sections of the Great Lakes. A cold front stretched from the low pressure south-southwest through the central Plains. Visible satellite imagery indicated plenty of instability cumulus clouds across the forecast area. Radar mosaic had started to pick up a few showers over western WI. The cold front is forecast to slowly move into western WI by late tonight and be the main focal point for showers and thunderstorms. Despite some weakening of instability through the night, shear is expected to increase into the 35-45 knot range after midnight over northern and central WI. Therefore, some storms may become strong toward central WI later tonight, but severe potential appears minimal due to weaker instability. PW values pushing 2 inches could bring locally heavy rain to central WI with localized 1-2 inch amounts possible. A warm and muggy night can be expected for all with min temperatures to range from the lower to middle 60s north-central WI, to the lower 70s eastern WI (inland from Lake MI). This cold front is expected to sag southeast across northeast WI on Wednesday before grinding to a halt over southern WI late in the afternoon as it begins to encounter the large upper-level high pressure situated over the eastern CONUS. While there will be a good chance of showers and storms (especially over central WI late tonight into early Wednesday morning), model trends are for the precipitation to become more scattered in nature through the day due to the loss of upper support and weakening low-level jet. Behind the cold front, dew points will slowly fall back into the 50s over northern/parts of central WI, so not as humid as the past couple of days. Due to more clouds and continued rain chances, max temperatures will be cooler with readings to range from the lower to middle 70s north-central WI, to the lower 80s eastern WI (slightly cooler near Lake MI). Long Term...Wednesday Night Through Tuesday An unsettled pattern will persist through the extended with several rounds of rain and storms possible through the end of the week. Main concern will be localized flooding due to successive rounds of showers and anomalous moisture. The WPC currently highlights portions of northeast Wisconsin under a marginal/slight risk for receiving excessive rainfall through day five (Sunday). A more robust system will then arrive to start the weekend, bringing another wave of potentially strong storms Saturday into Sunday. Wednesday night through Saturday... Expect a brief dry spell on Thursday as a cold front departs to the southeast, leaving an area of large-scale subsidence and high pressure in its wake. Rain chances will return to the forecast area Thursday afternoon as return flow brings a surge of Gulf moisture up into the western Great Lakes. Active weather will then make a comeback Friday and Saturday as a potent shortwave skims the US/Canada border and spins up a surface low over the Dakotas. Warm air advection precip will likely be ongoing Friday and Saturday as a warm front lifts north before becoming more widespread behind a cold front Saturday afternoon and evening. Some strong storms may be possible Saturday afternoon given favorable placement in the warm sector paired with the return of dewpoints in the mid 70s. As a result, instability upwards of 2,000 J/kg may be enough to sustain stronger storms across portions of central and east-central Wisconsin. Additionally, some synoptic support will be provided by the right rear quad of an upper-level jet generating a convergent zone on the nose of an increasing LLJ (40 to 50 knots). While it is still too early to discern severe weather risk, initial impression is that convective ingredients look favorable for supporting thunderstorm activity Saturday afternoon and evening. Medium-range models should paint a better picture in the next couple of days, so will continue to monitor. Rest of the extended... Scattered showers will be possible across the forecast area through Sunday due to remnant cyclonic flow from the departing system. A pattern change is then expected to start the week as mid-level flow flattens out before a ridging regime settles in across the eastern CONUS. This will bring about a more prolonged period of dry and seasonable weather for much of the Midwest, with temperatures averaging in the low to mid 80s. && .AVIATION...for 00Z TAF Issuance Issued at 636 PM CDT Tue Jun 18 2024 A cold front is forecast to slowly move into western WI later tonight and bring a chance of showers and thunderstorms into central WI. Cigs will lower into the MVFR range once the precipitation reaches the area and it is possible for a brief period of IFR conditions under any storms. LLWS will occur at all the TAF sites ahead of this front tonight. Mainly MVFR conditions persist through Wednesday morning as the cold front crosses the region and becomes stationary over southern WI late in the day. There will still be a chance of showers and thunderstorms with the front in the vicinity, mainly through mid morning and again mid to late afternoon, but the north should begin to dry out in the afternoon. In fact, VFR cigs should return to the RHI/AUW/CWA TAF sites by the afternoon while cigs improve to VFR at GRB/ATW/MTW in the afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement through Wednesday morning for WIZ022-040- 050. && $$ DISCUSSION.....Kallas/Goodin AVIATION.......JLA