574 FXUS63 KGRB 051615 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1015 AM CST Fri Jan 5 2024 New information added to update section .UPDATE... Issued at 1015 AM CST Fri Jan 5 2024 In a weak warm advection pattern, starting to see boundary layer saturation sufficiently deep for freezing drizzle to reach the ground across north-central WI this morning. Have received a few reports over the last hour, and lower visibilities corroborate the reports. RAP forecast soundings show a profile that is intermittently favorable through the afternoon. Have therefore added a chance of freezing drizzle to the forecast across north- central WI for the rest of the day. An SPS has also been issued through the noon hour. Will monitor for deteriorating road conditions. && .KEY MESSAGES... - The weather pattern will be conducive for several wintry systems to impact the region over the next week. - Probabilities for greater than 1 inch of snow have increased to 60-90%, with a 30-60% chance of 2 inches over far northern Wisconsin tonight into Saturday. In general, a 1 to 3 inch snowfall is possible north of a Wausau to Oconto line. - Potential for significant snow on Tue/Wed has decreased. However, the overall weather pattern remains active all of next week, with more chances for snow Thursday and Friday. && .DISCUSSION... Issued at 410 AM CST Fri Jan 5 2024 Short Term...Today...Tonight...and Saturday High pressure will slide off to the east today, allowing a low pressure system across the northern Plains to develop. The high moving off to the east will allow return flow across the area as a negatively tilted mid level shortwave approaches the mid Mississippi Valley region. Moisture will deepen throughout the day; however, snow isn't expected to begin until this afternoon across the far north. Although model soundings indicate some freezing drizzle is possible at the onset, the column moistens rapidly so any period of freezing drizzle would likely be brief and mainly during the daytime hours when impacts would be minimal. Highs today are expected to range from the upper 20s across the north, with lower 30s across central and east-central Wisconsin. Snow should begin in earnest across northern Wisconsin tonight as the aforementioned trough lifts across the western Great Lakes region and the surface low tracks over the upper Mississippi Vally. Snowfall amounts tonight could get to an inch or two, roughly along and north of a line from Wausau to Oconto, with less than an inch or just a dusting south of this area. Lows tonight are expected to only fall into the 20s given the abundant cloud cover across the area. The low itself will slowly make its way over the western Great Lakes region on Saturday as a dry slot lifts into central Wisconsin and the main 500 mb trough pushes east of the area. This will end the heaviest snow across the area Saturday morning with lower amounts than are expected tonight. Additional snowfall amounts Saturday are expected to generally be less than an inch, although amounts could approach an inch close to the Michigan border. Total snowfall amounts are expected to come in at 1 to 3 inches along and north of a line from Wausau to Oconto tonight into Saturday. Highs on Saturday are expected to rise into the 30s. Long Term...Saturday Night Through Thursday An active weather pattern sets up for the long term forecast bringing chances for precip (mainly snow). Upper pattern transitions to a broad upper trough across the western two-thirds of the CONUS early next week, which in turn provides southwest mid and upper level flow into Wisconsin. A progressive stream of shortwaves will bring chances for precip nearly every day or every other day. However, specific details are challenging to pin down because exactly when each shortwave approaches and moves through the GRB forecast area varies from run-to-run and model-to-model. Shortwaves will likely be supported by upper jet energy, surface features, and moisture which will allow for the development of precipitation. Exact amounts will come down to the specifics of all these features. Sunday and Monday...Lingering shortwave every and LFQ of upper will continue to provide some weak lift Saturday night and Sunday, which could keep light snow or flurries around at times. Any additional accumulations on Sat night/Sunday will be a couple of tenths of snow or less. High pressure builds in on Monday, but lingering low level moisture will likely keep skies fairly cloudy. Temperatures Sun/Mon will remain AOA normal, especially lows due to the cloud cover. Tuesday through Friday...The previously mentioned upper pattern makes its transition and begins a series of system through or near the GRB forecast area. A large cyclone tracks from the Southern Plains to the Great Lakes and Northeast Mon-Wed. Trends continue to push this system a little farther east, which puts northeast Wisconsin on the far western fridge. Less confident in getting significant snow out of this system, especially across central and north-central Wisconsin. There is still time for the system to trend back westward. This is followed by a wave coming in from the west which could bring snow Thurs/Fri. Current trends suggest this wave, while of a smaller scale, could bring more snow to central and northeast Wisconsin. But, there are notable differences in output this far out. Stayed with a blended model solution which has chance PoPs in the forecast most days. && .AVIATION...for 12Z TAF Issuance Issued at 514 AM CST Fri Jan 5 2024 Despite models indicating VFR cigs developing, MVFR clouds should hold for much of the period with a strong inversion trapping low level moisture. This should keep cloud bases at MVFR for much of the period as a low pressure system approaches from the west. This system will bring light snow to north-central Wisconsin late this afternoon, then central and east-central Wisconsin later this evening. Although some FZDZ will be possible at the outset, model soundings show the moisture depth increases rapidly with snow the predominant precipitation type. If any FZDZ does form at the outset, it would quickly change over to snow. Ceilings should then drop to IFR across north-central Wisconsin tonight as the snow falls across this region. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE.........MPC DISCUSSION.....Kurimski/KLJ AVIATION.......Kurimski