Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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046 FXUS63 KGRB 201936 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 236 PM CDT Thu Jun 20 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - There is a chance of thunderstorms in central and east-central Wisconsin tonight. Severe storms are unlikely. - Thunderstorms with gusty winds and locally heavy rain are possible Friday and Friday night. The rain could produce small stream and urban flooding. - Strong to severe thunderstorms are possible Saturday with damaging winds the main threat. Heavy rains may cause rivers to rise rapidly. - More showers and thunderstorms are expected Monday night into Tuesday. && .DISCUSSION... Issued at 236 PM CDT Thu Jun 20 2024 Short Term...Tonight and Friday A weak mid level shortwave and upper jet will bring the chance for some showers or thunderstorms across the region tonight; however, most areas should remain dry as the forcing will be fairly weak. Lows tonight will stay fairly close to normal ranging from the lower 50s across the north to around 60 across east-central Wisconsin. A warm front will lift north on Friday over southern Wisconsin. There will be abundant moisture along with a vigorous mid level shortwave tracking through northern Wisconsin along with the right entrance region of an upper level jet. Instability will be fairly modest, with MUCAPEs of 500 to 1000 J/kg, and long skinny CAPE profiles. Given the strong dynamics, moisture, and long skinny CAPE profiles moderate to heavy rain is expected at times on Friday. QPF amounts on Friday should generally be below an inch, as probabilistic forecasts indicate there is only a 20 to 30 percent chance of getting more than in inch mainly across western portions of central and north-central Wisconsin. Therefore, flooding concerns are fairly low through Friday as most area rivers and streams can handle this initial surge of moisture. Highs on Friday should be below NBM values given the abundant cloud cover and precipitation expected. Highs are only expected to get into the middle 60s across the north, with lower 70s across east-central Wisconsin and portions of central Wisconsin. Long Term...Friday Night Through Thursday Models are in good agreement with regards to a persistent upper- level high pressure over the southern CONUS. The main band of westerlies to run across the northern tier of states and bring a series of shortwaves through the Great Lakes. In addition, a wavy frontal boundary to be situated over the Great Lakes to act as a focal point for periods of showers and thunderstorms through Saturday night and again Monday night/Tuesday. Temperatures to be at or above normal for much of next week. Friday night and Saturday... The warm front to stretch across central/east-central WI Friday night. An increasing southwest low-level jet of 35-40 knots will continue to draw gulf moisture into the region with PW values of around 2 inches. This moisture transport, coupled with the passage of a subtle mid-level shortwave and a diffluent flow aloft, will bring the next round of showers and thunderstorms across northeast WI. Exactly where the warm front sets up will determine who gets the heavy rain as convection would tend to train west to east over the same locations. Potential is there for over an inch of rain to fall. Min temperatures to range from the middle to upper 50s north, lower to middle 60s south. This warm front is forecast to remain parked across central/east-central WI through Saturday and continue to be the main focal point for additional showers and thunderstorms. An unknown at this time is whether the remnants of a MCS could be tracking across WI during the morning. If this MCS does develop, a damaging wind event may occur. Otherwise, the air mass south of the warm front will become more unstable in the afternoon as MUCAPES rise to near 2K J/KG over southern WI and with shear of 35-40 knots, will need to watch for stronger storms over central/east-central WI. The main threat though for Saturday will be the potential for more heavy rain with PW values in the 1.5 to 2.25 inch range. If the heavy rains fall over the same area Friday night and Saturday, flooding would become a major concern, along with rapid rises in area rivers. Max temperatures Saturday will be tricky depending on where the warm front resides and any breaks in the rain. For now, have readings in the lower 70s far north to the lower 80s far south. Saturday night and Sunday... The threat for heavy rain will continue into Saturday night as a surface low and cold front move through the region. The heavier precipitation should shift to our south and east later Saturday night once the cold front exits. While too early for specifics, models are indicating the potential for anywhere from 1 to 4 inches of rain with flash flooding and river flooding a concern. Even as we finally say good-bye to the initial system, models indicate a mid-level shortwave trough to dig southeast into the Great Lakes on Sunday. This trough, coupled with cooler air aloft and daytime heating, will bring another chance of showers/slight chance of thunderstorms to northeast WI with northern WI having a higher chance. Max temperatures on Sunday to be in the lower to middle 70s north-central WI, upper 70s to around 80 degrees elsewhere. Sunday night and Monday... The departure of the shortwave trough and loss of daytime heating will end any further precipitation by Sunday evening. An area of high pressure will then move into the region for Sunday night allowing for skies to become mostly clear with a light northwest wind. Will have to watch for fog due to all the rain from the previous few days. As the high pressure slides to our east on Monday, a return flow develops over WI as dew points begin to rise again. Max temperatures Monday to range from the middle to upper 70s near Lake MI, upper 70s to lower 80s inland. Monday night and Tuesday... The next shortwave trough/associated cold front are progged to sweep into the Great Lakes Monday night into at least Tuesday morning. Temperatures on Tuesday will be determined on the timing of this system as models differ a bit. For now, have max temperatures to range from the lower 80s near Lake MI and northern WI, middle to upper 80s south. Tuesday night through Thursday... Toward the middle of next week, models are showing an upper ridge to build across the Rockies into the Plains. This would bring a northwest flow aloft into northeast WI which would then keep temperatures around normal with less humidity and a chance to dry out. && .AVIATION...for 18Z TAF Issuance Issued at 1254 PM CDT Thu Jun 20 2024 MVFR/IFR ceilings are expected roughly south of Highway 29 early this afternoon, with scattered showers diminishing across east- central Wisconsin. VFR conditions are likely this afternoon and evening as slightly drier air arrives thanks to a surface high over Lake Superior. Rain and IFR conditions are likely over most of the region late tonight and Friday as a warm front approaches from the central Plains. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski/Kallas AVIATION.......Kurimski