Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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870 FXUS63 KGRB 251145 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 645 AM CDT Wed Sep 25 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Patchy fog may impact the early morning commute today, with areas of fog expected late tonight into early Thursday morning. - Warm temperatures to prevail through the end of the work week, with highs running between 10 to 15 degrees above average. - Slight chance (10-15%) for rain showers Sunday south of highway 10, otherwise the next chance for rain comes Moday afternoon into Tuesday. && .DISCUSSION... Issued at 354 AM CDT Wed Sep 25 2024 Short Term...Today...Tonight...and Thursday Precipitation associated with an upper deformation zone remained well east of the region early this morning. Most locations had clear skies, though low clouds coming off the bay were affecting Door and Kewaunee counties, and some low stratus accompanied fog over north central WI. Mid-level clouds just west of the forecast area were associated with an upper trough axis and the remnants of a weak front. Any lingering fog should mix out by 14z, followed by scattered cumulus development in the late morning and afternoon due to daytime heating and the passage of the previously-mentioned weak front/trough. High temperatures should reach the middle 70s in most places. Clear skies, light winds and a weak surface ridge will lead to fog formation tonight. Conditions should be more favorable than this morning, as boundary layer winds will be around 5 knots regionwide. Areas of fog and patchy dense fog look like a good bet, especially west of the Fox Valley/lakeshore areas. Lows will be in the 40s and lower 50s, except 50s across Door County. After the morning fog mixes out, plenty of sunshine is expected on Thursday. Light south to southwest winds will bring slightly warmer air into the region, leading to high temperatures in the upper 70s and lower 80s. Developing onshore flow near Lake Michigan will keep highs in the lower 70s. Long Term...Thursday Night Through Tuesday Models have been trending toward a drier extended forecast over the past 24-hours. This is thanks in large part to the tropical moisture from what will be the remnants of Hurricane Helene being shunted off to the south by a much drier continental air mass. Precipitation...With a rex block set up across the eastern CONUS to end the week anticipate dry conditions Friday into the start of the weekend across the region. The rex block is expected to starting breaking down this weekend as a ridge moving over the eastern Great Lakes flattens. At the same time the remnants of Helene will be advecting north into the Ohio Valley. As moisture from Helene advects around the norther side of the low Saturday and Sunday there will be a slight chance (10-15%) for a few showers south of highway 10, however, with a dry continental air mass forecast to reside over the wester Great Lakes this weekend the better chances for precipitation will be shunted to the south. Next chance for precipitation is forecast to arrive during the early to middle part of next week as an upper trough and associated cold front move across the region. Forecast soundings don`t show much if any instability during this time which limits any severe weather potential, however, with relatively steep mid-level lapse rates ~ 6.5-7.0C/km there may be a few flashed of lightning and rumbles of thunder. Temperatures... With anomalously warm 850mb temperatures ~ 14-16C more summer like temperatures will persist through this weekend with highs in the middle to upper 70s expected at most locations. Height falls and the passage of a cold front Monday into Tuesday does look to bring seasonal to slightly below normal temperatures back to the region for the middle part of next week. LREF probs show a 40-50% chance for highs in the 50s next Wednesday which, except for a few locations in far northern WI, would be the first day to fail at reaching 60 degrees since May. Wednesday morning lows also look to be chilly with possible widespread frost across much of the Northwoods, and several spots potentially falling below freezing. && .AVIATION...for 12Z TAF Issuance Issued at 640 AM CDT Wed Sep 25 2024 Patchy IFR/LIFR fog should mix out by 14z, followed by SCT cumulus development in the late morning and afternoon. Conditions appear even more favorable for fog tonight, with boundary layer winds around 5 knots and clear skies. Expect fog to be a little more extensive late tonight, with IFR/LIFR vsbys at most TAF sites. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/GK AVIATION.......Kieckbusch