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Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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290 FXUS63 KGRB 291057 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 557 AM CDT Sat Jun 29 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Scattered thunderstorms are expected this afternoon. An isolated strong storm is possible that could produce gusty winds and small hail. - Conditions hazardous to small craft are possible tonight into early Sunday morning. - Some rivers and streams will remain above bankfull or near minor flood stage into the middle of next week. - The next period to watch for heavy rain and stronger storms will be late Monday through Tuesday. && .DISCUSSION... Issued at 314 AM CDT Sat Jun 29 2024 Short Term...Today...Tonight...and Sunday An area of showers and isolated thunderstorms continues to track through northeast Wisconsin early this morning coincident with a mid level shortwave tracking through the western Great Lakes and some modest MUCAPEs of 200 to 400 J/kg. This activity should move out of the area by sunrise, with mainly quiet conditions expected through the late morning. Another mid level shortwave, shown on water vapor over North Dakota, will track through the northern Great Lakes late this morning and into the afternoon. A secondary cold front will coincide with this secondary shortwave as it tracks through the area. The shortwave is stronger this morning than what was indicated by previous model runs, which will delay the arrival of the secondary cold front as the stronger shortwave will track through a bit later than previously forecast. This will allow highs to be a few degrees higher than the previous forecast, with the biggest difference in temperatures across north-central Wisconsin. The later arrival of the front will mean some SBCAPE will build ahead of the cold front this afternoon across east- central and northeast Wisconsin as instabilities rise to 500 to 1000 J/kg. Effective shear is progged to be around 50 knots; therefore, some strong to near severe storms are possible later this afternoon into the early evening with hail and gusty winds the main threats. CAMs models indicate this activity will be fairly isolated, with a narrow window for any storms to develop, so confidence in these storms having enough time to develop into stronger storms is low. Highs today are expected to range from the middle 70s across the north, to the lower 80s across east- central and northeast Wisconsin. High pressure will build in behind the departing cold front this evening, building across the western Great Lakes on Sunday. This will provide a period of dry weather with cooler temperatures expected across the region. Lows tonight are expected to fall into the lower 40s across the north, with lower 50s across east- central Wisconsin. Highs Sunday are expected to range from around 70 across north-central Wisconsin, to the lower 70s across east- central and northeast Wisconsin. Long Term...Sunday Night Through Friday Focus of this forecast continues to revolve around the thunderstorm and heavy rainfall potential from Monday night through Tuesday night. Monday night through Tuesday night...As a large high pressure system shifts to the eastern Great Lakes on Monday night, return flow will rapidly increase including a 35 to 45 kt low level jet that will lead to surge of elevated moisture into the region from the west. The strong moisture advection and convergence will lead to a large area of rain spreading across the region from west to east. Instability is lacking and less than 100 j/kg, so severe weather is not expected despite decent wind fields. But probabilities indicate 1/2 to 1 inch of rainfall will be possible in some areas. After the first push of precip across the area on late Monday, indications continue to suggest a relative lull in the precip on Tuesday morning. Then precip chances ramp up again late on Tuesday afternoon into Tuesday evening. The GFS has some concerning heavy rainfall parameters including precipitable water values (pwats) approaching their all-time high and relatively slow backward propagating corfidi vectors (12 kts). The ensemble means are more conservative with precipitable water values but still approaching the daily high around 2 inches. Given instability continues to look marginal (600-1000 j/kg) for severe weather, think potential for heavy rainfall has potential for greater impacts, particularly with a moderate rainfall already expected on Monday night. Another round of rain looks possible late in the week. && .AVIATION...for 12Z TAF Issuance Issued at 557 AM CDT Sat Jun 29 2024 IFR/LIFR conditions will prevail this morning ahead of an approaching cold front and attendant shortwave. Some clearing and rising ceilings to VFR is expected mid to late morning. As the cold front moves through the region, some showers and a few thunderstorms will be possible late this morning and into the afternoon. Thunderstorms will be isolated and not high enough coverage to include in any of the TAF sites. Low ceilings will return to north-central and far northeast Wisconsin during the late afternoon and evening hours. Gusty west surface winds will develop in the wake of the cold front passage, especially this afternoon and evening. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski/MPC AVIATION.......Kurimski