898 FXUS63 KGRB 291116 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 616 AM CDT Sat Aug 29 2020 Updated aviation portion for 12Z TAF issuance .SHORT TERM...Today...Tonight...and Sunday Issued at 232 AM CDT Sat Aug 29 2020 High pressure will bring cooler air and dry conditions to the western Great Lakes region this weekend. Today will be breezy behind a departing cold front, with northwest winds gusting to 15 to 25 mph. Highs today are expected to range from the upper 60s across the north, with highs in the middle 70s across east-central and northeast Wisconsin. Winds will die down a bit tonight as the atmosphere decouples and the high moves overhead. This will allow overnight lows to fall into the middle 40s across the north, with lows in the lower 50s across east-central Wisconsin. The high will begin to shift a bit to the east by Sunday afternoon, however surface winds will remain light throughout the day. Despite a similar airmass and boundary layer depth, highs on Sunday will be a few degrees lower than today given less mechanical mixing of the boundary layer given the lighter boundary layer winds, especially across east-central Wisconsin. Highs on Sunday are expected to be in the upper 60s to lower 70s across the region. .LONG TERM...Sunday Night Through Friday Issued at 232 AM CDT Sat Aug 29 2020 Models are in good agreement with the synoptic pattern which will consist of an eastern Pacific upper high that is forecast to move toward the four corners region by late next week, a western Atlantic upper high and a broad shortwave trough that will be located from the northern Rockies to the Great Lakes. Precipitation chances to be tied to the passages of cold fronts or smaller-scale shortwave troughs which may be hard to time. Temperatures should be around normal through Wednesday, then drop below normal late week. As winds turn to the south and the onset of WAA begins, expect to see an increase in clouds Sunday night, especially across central WI. Exactly how fast these clouds arrive will ultimately determine how far temperatures can fall. Look for readings around 50 degrees north, lower to middle 50s south. Models concur in sending a cold front and mid-level shortwave trough into WI on Monday. While models disagree on the extent of instability (NAM has MUCAPES of around 1K J/KG, GFS < 500 J/KG), there will be ample shear (35-45 knots), thus a few stronger storms will be possible. Max temperatures to range from the upper 60s north-central WI, to the middle 70s east-central WI. May need to carry chance pops into Monday evening for east-central WI as the cold front to still be in the vicinity. This front is forecast to slow its eastward progress as it begins to encounter upper ridging over the eastern CONUS and a surface wave develops on the front over the central Plains. Therefore, east-central WI may hang on to more clouds through the night, while northern and central WI become partly cloudy. Min temperatures to range from the middle to upper 40s north-central, middle to upper 50s east- central WI. The cold front eventually stalls from the eastern Great Lakes to the mid-MS Valley on Tuesday with a frontogenetical forced band of precipitation developing north of the stalled boundary. The main question will be exactly where this boundary resides, but east-central WI would figure to be most susceptible to precipitation chances with smaller pops farther to the north and west. More clouds will keep max temperatures in the upper 60s north-central, mainly lower 70s elsewhere. The prevailing northwest flow aloft will send another cold front/ mid-level shortwave trough into the western Great Lakes region Tuesday night and bring an end to the precipitation threat by the late night hours. A weak area of high pressure is forecast to move into the region for Wednesday and bring back a mix of sun and clouds. Max temperatures on Wednesday to be in the lower 70s north-central, middle to upper 70s elsewhere. Models are in much better agreement in sending a fast-moving clipper-type system into the northern sections of the Great Lakes by 12Z Thursday. A cold front will sweep into central WI by daybreak with a trailing mid-level shortwave trough to provide decent Q-G forcing. Bulk of precipitation initially to be from northern WI northward where stronger lift/forcing to exist. This entire system flies across the rest of the forecast area Thursday morning, however models are downplaying precipitation chances mainly due to gulf moisture being cut-off by the prior cold front. The bigger stories could be the gusty northwest winds in the wake of the cold front and strength of the CAA sending 8H temperatures over northern WI to around +6C by 00Z Friday. Max temperatures on Thursday to range from the middle to upper 60s north-central, to the middle 70s east-central WI. High pressure gradually builds into WI Thursday night into Friday with an autumn-like air mass settling over the forecast area. Depending on the trajectory of the wind, cannot rule out lake effect clouds or even a touch of lake effect showers from reaching far northern WI late Thursday night or Friday. Have lowered max temperatures a bit with readings on Friday to range from the lower to middled 60s north-central, upper 60s to around 70 degrees east-central WI. && .AVIATION...for 12Z TAF Issuance Issued at 616 AM CDT Sat Aug 29 2020 MVFR cigs will linger across extreme eastern Wisconsin for the first hour or two of the TAF period, with skies scattering out and VFR conditions expected for the rest of the TAF period as high pressure builds in across the western Great Lakes. Some FEW-SCT fair weather cumulus clouds between 4.5 to 6k ft are expected later this morning and into the afternoon. Northwest winds will increase to 15 to 25 knots today, with gusts near 30 knots possible once the boundary layer mixes later this morning. Winds will then taper off quickly around sunset when the atmosphere decouples and the high moves overhead during the overnight hours. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM.....Kurimski LONG TERM......Kallas AVIATION.......Kurimski