Temperatures might be running in the 80s and 90s, but in some ways autumn is already here.

Yellowed leaves have been lining Twin Cities streets, birds are on the move south and the sun is setting an hour and 15 minutes earlier than it did back in June. And although Labor Day hasn't come around yet, Saturday is the first day of "meteorological" fall, under a scheme the weather record-keepers use because it works more cleanly than equinoxes and solstices.

No matter when it starts, though, autumn has become perhaps Minnesota's longest season, said University of Minnesota Extension climatologist Mark Seeley.

"I think it's universally recognized that in our lifetimes the falls are getting longer," Seeley said.

At a recent contractors' conference, Seeley said, house painters noted that their work season now extends well past what used to be the customary end in early October. "They paint until Mother Nature tells them to stop," he said. "Some years, that's late November."

The national Climate Prediction Center's outlook for Minnesota shows a good likelihood of warmer-than-normal conditions for September through November, most strongly in the latter part of that period. For precipitation, the outlook is noncommittal. A developing El Niño underlies both outlooks.

A warm fall would be in keeping with recent history. Since 2000, the Twin Cities has experienced three Septembers that rank among the 12 warmest; three Octobers in the top 15, and three Novembers in the top 10, including the two mildest. The lists go back to 1871. Two recent Octobers -- in 2002 and 2009 -- are among the coolest seven.

Warm, but calm, summer

The Twin Cities also has had its third-warmest meteorological summer, behind 1988 and 1933. July was the second-hottest on record, but August cooled off considerably, finishing less than a degree above normal.

Despite the heat, the season was arguably benign. There were spotty drought conditions, but the entire state saw only nine small tornadoes over the three months, including a waterspout on Lake Superior. Also, the Twin Cities experienced an estimated 177 hours with dew points of 70 or greater -- about normal but well below the 347 last year and the 256 in 2010. That made the heat more tolerable and was one reason Xcel Energy experienced only minor power failures.

"It's been an excellent summer," said Robin Lepowsky, sales manager at Bob and Judy's Farm Market in Big Lake. "Heat's been the biggest problem for us. Then in early spring we had 10 days of rain. That made it tough getting the crop in. But once we did, everything went well. Compared to last year, the tomato crop is excellent."

On schedule

Naturalists note that even though the warm season got off to an early start -- ice melted off many lakes sooner than ever, and plant and animal routines kicked in two to three weeks ahead of schedule -- fall appears to be starting pretty much on schedule. That means male hummingbirds are just beginning to head south and leaf color is still far from the peeping stage, even in northern Minnesota.

"Everything after that early spring fell back toward normal," said Grand Rapids phenologist John Latimer. "I'm still seeing monarchs [butterflies]. I don't think we're looking at an early fall."

Some fall-blooming wildflowers were a little early this year, but lake temperatures are still summer-like, noted Jim Gilbert, a veteran nature observer in Waconia. The 30 species of migrating birds he watches are all moving on their normal schedules, he said.

Val Cunningham, a St. Paul bird surveyor and columnist for the Star Tribune, said that in any case, birds are programmed to respond more to changes in day length and food sources than temperature. She recently got a report of nighthawks migrating south in great numbers from Duluth, in sync with a late-August peak.

Bill McAuliffe • 612-673-7646