Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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925 FXUS63 KGRB 022353 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 653 PM CDT Tue Jul 2 2024 Updated aviation portion for 00Z TAF issuance .KEY MESSAGES... - Another round of showers and embedded storms will push across mainly central and eastern WI late this afternoon and evening. Highest rain totals are expected across east-central WI, where some locations could see over an inch. The rain could lead to minor river and stream flooding, along with urban flooding and ponding on roads. - Conditions will be hazardous to mariners and beachgoers on the bay and Lake Michigan through early Wednesday due to gusty winds and high waves. - There is a 50-percent chance to get measurable rain in central Wisconsin sometimes Thursday afternoon and evening, with around a 25-percent chance in far northeast WI during the same time. The better chance for rain and a few thunderstorms arrives Friday. && .DISCUSSION... Issued at 345 PM CDT Tue Jul 2 2024 Short Term...Tonight and Wednesday This Afternoon into Tonight: The lull in the heavier/widespread shower activity will continue early this afternoon, but come to a quick end as another large area of showers and embedded storms will push northeast across mainly central and eastern WI. The showers/storms will be associated with a shortwave trough swinging across the western Great Lakes, along with an approaching weak front, weak LLJ and the RRQ of an upper jet. PWATs around 2" will favor some heavier rain through the evening, with the heaviest swath of rain expected to be across east-central WI, where some totals could top one inch. Overall flood threat looks low as the rivers have had a chance to come down and this area of rain will be moving through pretty quickly, but some minor low-land flooding and ponding on roads will be possible where the heaviest rain falls/training storms occur. The activity will end overnight with clouds slowly towards/after sunrise on Wednesday. The gusty south winds will slowly weaken through the late afternoon and evening hours. It will be a relatively warm and humid night, with lows mainly in the 60s expected. Wednesday: Dry conditions are expected for most of the day. However, some of the latest CAMs (especially the HRRR) are showing some showers developing in the heat of the day as a weak boundary drops across the area. If we can get some showers to pop, could be enough instability (up to 1000 J/kg) to get a rumble of thunder as well. Have added some low chance PoPs to account for this chance. West winds look to gust to 25-35 mph. Highs will be in the 80s for most spots, with humidity levels remaining high across central and east-central WI as dewpoints remain in the 60s. Long Term...Wednesday Night Through Tuesday Focus is on the July 4th forecast and the potential for any rain and thunderstorms, along with temperatures. Wednesday night through Thursday night...Upper level pattern shows broad troughing across the Northern Plains and into the western Great Lakes, with multiple embedded shortwaves rotating into Wisconsin which will lead to opportunities for precipitation. The best chance will be Friday when the associated surface low also moves through Wisconsin. Good consensus that conditions will be dry Wednesday night through Thursday morning, but there is more variable when the first wave will impact central and northwest Wisconsin later Thursday, which impacts when any rain would begin. Some models show scattered rain activity as early as 11AM/Thurs, while other hold off until after midnight. NBM probability of precipitation greater than 0.01 inches before 1AM/Fri is right around 50-percent across all of central Wisconsin, and gradually decreases towards the east, with the Fox Valley anywhere from 25 to 45 percent, and less than 25-percent in far northeast WI and along Lake Michigan. Increasing precipitation to 0.10 inches the percentages decrease significantly, with around a 25-percent chance of getting this much rain by 1AM/Fri in central WI. All this to say, there could be some rain Thursday afternoon and evening, especially in central WI, but amounts will be rather light and scattered, with more widespread rain chances holding off until Friday associated with the low. Thunderstorms are also possible, but with instability in the 300 to 600 J/kg range and lapse rates around 5.5 C/km do not currently expect severe thunderstorms. High temps on Thursday will be AOA normal from the upper 70s to low 80s. Friday...Rain becomes more widespread. Again, some thunderstorms are possible within the rain, but rain will be the main focus. The rain and clouds will lead to a cooler day, with highs in the mid 60s to low 70s. Saturday through early next week...Surface low moves east leading to mainly dry conditions and temps rebounding into the mid to upper 70s on Saturday. With some lingering moisture and small bits of mid-level energy would not be surprised to see a few brief showers. The overall upper troughing pattern continues into early next week with shortwaves and fronts bringing on and off chances for showers and thunderstorms. && .AVIATION...for 00Z TAF Issuance Issued at 642 PM CDT Tue Jul 2 2024 A large swath of moderate to heavy rain showers and a few embedded storms will impact the forecast area this evening, then pull out of eastern WI overnight. The best chance of storms should occur at the eastern TAF sites this evening, as a low- level jet strengthens there this evening. Widespread MVFR/IFR conditions will deteriorate to IFR/LIFR later this evening and overnight. Increasing west winds should cause ceilings to rise slightly late tonight, followed by a clearing trend early Wednesday morning. Gusty west winds will occur during the day on Wednesday, and scattered cumulus clouds are expected to develop. There is a small chance of afternoon showers, but confidence is not high enough to acknowledge these in the TAFs at this time. LLWS will impact the eastern TAF sites (GRB/ATW/MTW) this evening and into the early overnight period, then weaken late tonight. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement through Wednesday morning for WIZ022-040- 050. && $$ DISCUSSION.....Bersch/KLJ AVIATION.......Kieckbusch