Area Forecast Discussion
Issued by NWS Green Bay, WI

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000 FXUS63 KGRB 062328 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 528 PM CST Sat Mar 6 2021 Updated aviation portion for 00Z TAF issuance .SYNOPSIS... Issued at 220 PM CST Sat Mar 6 2021 Warm for the start of the upcoming work week (at least away from Lake Michigan). Some rain mid-week, then temperatures returning closer to seasonal normals by next weekend. The period begins with quite amplified upper flow across North America. Deep troughs were off the West Coast and over eastern Canada, bracketing a sharp ridge from the western High Plains to western Hudson Bay. Energy ejecting out of the western trough will flatten the mid-continent ridge early in the week, with a subsequent piece of energy generating a cyclone on a cold front crossing the area mid-week. The main energy from the western trough will temporarily separate off into the Desert Southwest before ejecting toward the area next weekend. But it is unlikely to reach the forecast area until after the end of the forecast period. The initial shortwave ejecting out of the western trough will flatten the upper flow to a more zonal nature, allowing a stronger push of modified Pacific air to reach the area for the early to middle part of the work week. That will result in well above normal temperatures for the first half of the work week. Readings will settle back closer to normal after that. The main precipitation event will be associated with the frontal system and cyclone crossing the region mid-week, and should result in AOA normal amounts for the period. && .SHORT TERM...Tonight and Sunday Issued at 220 PM CST Sat Mar 6 2021 Tranquil conditions to prevail through the end of the weekend with temperatures holding above normal. The only difference on Sunday will be more wind. The 19Z MSAS surface analysis showed a ridge of high pressure that extended from central Ontario south through central WI, then southwest into the southern Plains. After some early morning fog far north, current visible satellite imagery indicated nary a cloud to be found over WI. Temperatures ranged from the lower 30s to middle 40s. The surface ridge axis will slowly edge eastward tonight and extend from eastern Ontario south-southwest through Lake MI to northeast TX. Mainly clear skies and light winds will lead to another cold night across northern WI where a deeper snowpack still exists. Based on how far down temperatures reached this morning, anticipate readings to be fairly similar and again drop into the zero to 5 above range near the MI border, while only falling to around 20 degrees over east-central WI. As the surface ridge heads toward the eastern Great Lakes on Sunday, the pressure gradient over WI will tighten between the high pressure and an area of low pressure near Lake Winnipeg. The resulting gusty southerly wind will also begin to tap warmer air to our west with the help of a modest upper-level ridge. 8H temperatures climb to around +4C and even with some increase in clouds in the afternoon due to a shortwave trough moving into western WI, look for max temperatures to range from the lower 40s near Lake MI, to near 50 degrees west of the Fox Valley. .LONG TERM...Sunday Night Through Saturday Issued at 220 PM CST Sat Mar 6 2021 The main long-term forecast issues were attempting to hone-in on temperatures early in the week, and precipitation chances mid- week. The NBM has recently been too cool with temperatures-- both highs and lows. So, edged readings up Monday through Wednesday, though increasing south winds may keep readings close to the lake quite chilly. Stayed close to NBM values after that. The details of the precipitation that will accompany the front/cyclone through the region mid-week remain murky. It would be surprising if it doesn`t rain at some point. But given the uncertainty in timing, likely PoPs seemed sufficient for now. Given the steepening mid-level lapse rates, introduced a mention of thunder on Wednesday into Wednesday evening--mainly across central and east-central Wisconsin. && .AVIATION...for 00Z TAF Issuance Issued at 528 PM CST Sat Mar 6 2021 Ridge of high pressure to remain the dominant weather feature over the Great Lakes through Sunday. VFR conditions will prevail, although some fog development is possible across northern WI where a decent snowpack still resides. As the ridge slides to the east on Sunday, winds will veer to the south-southeast and increase as the pressure gradient tightens over WI. Winds could gust over 20 knots by Sunday afternoon. The approach of a mid- level shortwave trough late on Sunday is expected to bring an increase in clouds to central WI. Cigs will remain VFR until Sunday evening when MVFR cigs are forecast to overspread the area. && .GRB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS.......Skowronski SHORT TERM.....Kallas LONG TERM......Skowronski AVIATION.......Kurimski

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