It’s the time of year when Andy Fles keeps one eye on the thermometer and the other on the rain gauge as he preps 60 acres of Leelanau County vineyards for harvest.

“We’re always nervous at this time of year,” says Fles, the vineyard manager at Shady Lane Cellars winery south of Suttons Bay. “Things can change quick.”

Vintners across the region are hoping for a warm, dry fall stretch to finish off what they say so far has been a solid grape growing season. Degree days, which measure heat levels that determine development of numerous fruits and field crops in northern Michigan, have been near long-term averages for the growing season.

“We’re pretty much on the 25-year average which is good, but things could still go either way,” Fles says. “So far things are looking well. The fruit looks really clean right now.”

Leelanau County’s grape harvest will begin over the next week. It starts with grape varieties used for making sparking wines including Chadonnay, which don’t need as much ripening time. Fles says the bulk of the region’s grape harvest happens in October, and can stretch into early November if the weather cooperates, leaving the fruit to finish as long as possible.

Weather at this time of year is critical to the grape harvest, local agriculture officials say. Nikki Rothwell, coordinator of Michigan State University’s Northwest Michigan Horticultural Research Station in Bingham Township, says warm and dry fall weather helps grapes concentrate their sugars and flavors late in the growing season, while wet falls can over-water plants and dilute sugar levels. Dry autumn air also makes it harder for rots and fungal diseases to set in in at harvest time, and warm conditions also allow for extended hang time for the fruit to finish its ripening.

But much of Leelanau County was doused with more than inch of rainfall early last week. Rothwell said the wet conditions generated some signs of disease at the grape test plots at the Research Station, although she’s not sure how far that’s spread across the county.

“Hopefully the commercial guys are doing better,” Rothwell says. “Those guys want it to get warm and dry.”

The local grape harvest follows what winery operators say has been a solid - but at times challenging - summer.

“I think the summer has been very strong,” says John Heekin, whose family owns three Leelanau wineries including Bel Lago Vinyard, Winery & Cidery near Cedar (pictured above), Dune Bird Winery off M-22 between Leland and Northport and French Valley Vineyard south of Lake Leelanau.

Area wineries – similar to countless seasonal businesses in the region - suffered a downturn in visitors in mid-July during several days of smoke, haze and poor air quality stemming from wildfires in Canada and the U.S.

“There was definitely a week-long stretch where we felt that…it was significant” Heekin says. “But we saw a solid pick-up in August, and September has been very strong.”

Heekin also looks for an upswing in fall visitors, as the fall season is always popular with local and visiting wine tasters that enjoy the seasonal color change. It’s a period when area wineries see some of their busiest weekends of the season. Fall events in the county include two “Toast the Season” weekends coming up Nov. 6-8 and 13-15 sponsored by the Leelanau Peninsula Vintners Association.

Heekin, who grows 65 acres of grapes across four vineyards in Leelanau, says his fruit is “actually a little bit behind normal” in terms of seasonal degree days, but it’s been a good growing season overall.

“We’re very happy with how the year is progressing,” Heekin says. “The fruit looks very good – very clean for this time of year.”

In the coming days, Heekin’s crews will be busy lining his grape vines with netting to protect the fruit from bird and deer damage while the fruit finishes ripening for harvest, which will he hopes continues into early November.

“We tend to let our red grapes hang longer,” Heekin says.

Whether the last month or so of the growing season will help or hinder area grape growers looks like a coin flip. John Boris, a meteorologist with the National Weather Service office in Gaylord, says the long-range temperature and precipitation models generated by the NWS’ Climate Prediction Center project slightly above normal temperatures in October. The Weather Service’s long-range forecast through this week also calls for drier than normal conditions, although October precipitation levels could go either way.

But Boris cautioned that long-range weather forecasting in the fall is tricky.

“October is a very changeable month,” Boris says. A cool air mass settling in over the still relatively warm waters of the Great Lakes can set off days of lake-effect precipitation – similar to lake-effect snows in the winter – that could dampen this year’s harvest.

Fles says vineyard managers can mitigate some of the late-season moisture challenges through maintenance measures that include spraying grapes with food-grade peroxide that kills pathogens on the fruit skin.

“It’s a nice late-season tool to help with moisture management,” Fles says.

Otherwise, Fles says he’s happy with both the quality and quantity of what he describes as a “balanced” grape crop this year.

“We’re really looking at a nice-sized crop,” he says. “We’re not going to have to drop fruit, or be in a place where we don’t have enough.”