Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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594 FXUS63 KGRB 260754 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 254 AM CDT Sun May 26 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Rain is expected at times from late this morning through tonight. Non-severe thunderstorms are possible at times this afternoon and tonight. Around an inch of rain is expected across the area, with locally higher amounts up to 2 inches possible. Some minor flooding of streets and small stream is possible. - A few rivers over central and eastern Wisconsin could surpass minor flood stage early this week. - Areas of frost are possible Wednesday night into early Thursday morning across northern Wisconsin. && .DISCUSSION... Issued at 253 AM CDT Sun May 26 2024 Short Term...Today...Tonight...and Monday Mostly cloudy skies and dry conditions were noted across much of the region early this morning, save for some light showers or sprinkles across far north-central Wisconsin associated with some weak low level isentropic lift along a semi-stationary boundary across the north. The main area of precipitation is expected to continue developing across Iowa and track northeast through Wisconsin later this morning and into the afternoon as a negatively tilted mid level trough and attendant shortwave track over Wisconsin. This trough will slowly move away from the region tonight, as the moderate rain continues then slowly ends from west to east later tonight into Monday morning. Some light rain showers could continue through the overnight hours across northeast and east-central Wisconsin as the trough remains close to that area. Instability with the rain showers will be fairly modest, with MUCAPEs of only a few hundred J/kg, but should be sufficient for a few rumbles of thunder at times. Highs today will be a few degrees below normal given the abundant cloud cover and precipitation expected, with highs only in the 60s. The warmest temperatures should be realized before the steady rain begins, with temperatures likely falling during the afternoon as the moderate rain tracks through the area. Lows tonight are expected to range from the upper 40s across the north, to the middle 50s across east- central Wisconsin. Another mid level shortwave will track through the upper Mississippi Valley on Memorial day, which will bring the chance for showers back to the region, especially during the afternoon. MUCAPEs will again build to a few hundred J/kg during the afternoon, which will bring the threat for some thunderstorms to central and east-central Wisconsin. The modest instability should prevent these storms from becoming severe. Highs on Memorial Day should be a bit warmer as there are not expected to be rain showers ongoing for the entire day. Highs are expected to range from the upper 60s across the north, to around 70 across central and east-central Wisconsin. Long Term...Monday Night Through Saturday The passage of two more shortwave troughs will keep the unsettled weather going over northeast WI through Tuesday. By mid-week, the mean flow becomes more amplified with upper troughs on each coast and an upper ridge over the central CONUS. This ridge gets shoved into the Great Lakes by the end of the week as the western trough pushes toward the northern Plains. Some question by late week as to whether this ridge can hold dry conditions intact or have precipitation move into the region. Temperatures look to be below normal through at least Wednesday, then warm to slightly above normal at the end of the week. Monday night through Tuesday... One weak shortwave trough is forecast to swing through the western Great Lakes Monday evening with a second, stronger shortwave trough to follow on Tuesday. No real surface features or jet help, thus precipitation to be dependent on mid-level forcing with each trough. Instability wanes Monday evening and returns in limited fashion Tuesday afternoon. Hardly any shear is advertised by the models, thus any storms would be of the garden variety. Min temperatures Monday night to range from the middle to upper 40s north-central WI, upper 40s to lower 50s elsewhere. Max temperatures Tuesday to be in the lower to middle 60s north- central, middle to upper 60s for the rest of northeast WI. Tuesday night and Wednesday... Any lingering light shower activity will end Tuesday evening as the second shortwave trough departs and high pressure begins to build into the region during the overnight hours. Skies will gradually become mostly clear with a diminishing wind. This would send min temperatures down into the upper 30s to lower 40s north, middle to upper 40s south. The high pressure will be centered over the western Great Lakes on Wednesday, bringing plenty of sunshine and a light north wind to the forecast area. Temperatures to still be a bit below normal with readings in the lower to middle 60s near Lake MI, middle 60s to around 70 degrees inland. Wednesday night and Thursday... Clear skies, light winds and a cool air mass aloft will bring a cool night to the region Wednesday night. Cool enough such that areas of frost cannot be ruled out over northern WI. By Thursday, the high pressure will edge just to our east while the upper ridge pushes toward the western Great Lakes. Anticipate another mostly sunny day on Thursday and as winds veer more to the south- southeast, expect a gradual boost in temperatures. Look for readings in the middle 60s near Lake MI, mainly lower 70s inland. Thursday night and Friday... After a quiet Thursday night, precipitation trends become an issue as the new 00z models are now showing the amplified flow to break down faster than previously advertised. This would allow the western upper trough to move across the central CONUS and could bring a chance of showers to central WI as early as Friday afternoon. A prevailing southerly wind will continue to pull warmer air northward, thus max temperatures Friday to be near 70 degrees lakeside, lower to middle 70s north and middle to upper 70s south. Friday night and Saturday... If the amplified flow breakdown is correct, then rain chances would reach all of northeast WI headed into the weekend as the upper trough moves into the Upper MS Valley. Therefore, will need to carry a chance of showers for both Friday night and Saturday with a slight chance of thunderstorms. More clouds around on Saturday should knock a couple of degrees off of max temperatures with readings still near 70 degrees near Lake MI, but lower to middle 70s inland. && .AVIATION...for 06Z TAF Issuance Issued at 1046 PM CDT Sat May 25 2024 VFR flight conditions will continue through Sunday morning, with mainly mid/high clouds. A few sprinkles are possible in far north central WI early in the TAF period, but will not mention in the TAFs. A low pressure system and associated strong short-wave trough will move into the region on Sunday. Showers will overspread the region from SW to NE in the late morning and early afternoon, and become heavy at times in the afternoon and evening. As the showers increase, flight conditions will drop to MVFR, then IFR/LIFR. Most of the instability is expected to stay south of the forecast area, so will not mention thunderstorms in the TAFs for now. It is possible that a brief period of thunderstorms could impact MTW in the late afternoon/early evening, but will let the next shift assess this for the 12z TAFs. Light S-SE winds will occur tonight into early Sunday, then increase a bit from the SE-E during the day, then NE in the late afternoon and evening. Small pockets of LLWS will be possible in C/EC WI on Sunday. && .HYDROLOGY... Issued at 253 AM CDT Sun May 26 2024 Although heavy rain is not expected from this system, steady light to moderate rain should persist for several hours once the rain begins. There is fairly high confidence in rainfall amounts today and tonight reaching an inch, plus or minus 0.25 inches, as this represents the 50th percentile for all models. The probability of exceeding 2 inches during this event is low but not zero, representing the 90th percentile, and mainly focused across central Wisconsin. Rainfall amounts around an inch would likely have a low impact, while amounts closer to 2 inches would produce street flooding in urban areas and bring small streams to bankfull stage. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski/Kallas AVIATION.......Kieckbusch HYDROLOGY......Kurimski