2014: A perfect weather year for fall color?

Minnesotans have enjoyed a splendid fall color show this year.

It turns out the weather of 2014 has been ideal for putting on a vibrant, lasting fall color show in Minnesota.

The polar vortex, June monsoon, lack of intense summer heat and a dry temperate fall with lighter than average wind speeds combined to produce excellent, lasting fall color.

Here are some of the ingredients that went into what many Minnesotans describe as the best fall color show in years.

Polar vortex 2014. Cold is generally good for native trees in Minnesota. It kills invasive pests that can weaken trees. Last winter's extreme cold helped cull the emerald ash borer population in Minnesota.

I asked  forestry expert Lee Frelich, director of the University of Minnesota Center for Forest Ecology about how last winter's extreme temperatures may have helped kill ash borer larvae. He wrote:

 Paul:I think the forecast temperatures that we will experience in the next several days will cause a lot of mortality for emerald ash borer in MN. Details below–probably more than you need.

I looked up the most recent research this morning, because I figured I will get a lot of questions about this over the next week.Winter mortality for emerald ash borer is definitely temperature dependent.

The larvae can supercool to a certain point, but they die if they freeze, and there is variability in tolerance among individual insects. A recent study from the Forest Service (Venette and Abrahamson–see attached) in Minnesota showed that 5% of the insects die at 0F, 34% at -10F, 79% at -20F and 98% at -30F.

Wet spring and early summer Abundant rainfall in the early warm season helped trees leaf out vigorously. Rainfall was several inches above average across Minnesota this spring. It flooded our rivers and basements, but the trees loved it.

Lack of intense summer heat The Twin Cities managed to squeak out just two 90 degree days this year. The warmest day was 92 degrees on July 21. The lack of intense summer heat meant less heat stress on trees.

Dry, temperate and less windy fall weather The mild fall weather, lack of driving rain, and relatively tame wind speeds this fall have helped keep the leaves on the trees longer this year than in many past years.

The average wind speed at Minneapolis-St. Paul International Airport has been 9.4 miles per hour so far in October. That compares to a monthly average wind speed of 10.6 mph for October. More importantly, the highest gust observed since Oct. 8 has been just 25 mph at the airport.

It turns out the weather of 2014 has been near perfect for putting on the best fall color show in years.