Autumn arrived at 10:21 a.m. Thursday. So when will peak fall foliage arrive?
That depends on the weather.
Both the timing and brilliance of leaves' color changes depend on temperature and precipitation, and not just current conditions.
It can be difficult to forecast the peak and intensity of fall foliage, according to Marek D. Rzonca, who operates The Foliage Network, a website that collects reports on autumn color around the country. Much of it depends on larger precipitation trends.
In the Northeast, for example, parts of Massachusetts, New Hampshire and New York are in a drought, as are the Great Smoky Mountain region in the Southeast. That can distress trees and might lead to an early change in leaf color, Rzonca said.
But recent unseasonably warm weather could counteract that effect, Rzonca said.
"As you can see, trying to forecast the foliage season is extremely complicated," Rzonca said in an e-mail. That's why the network's website focuses on real-time information about leaf conditions.
Precipitation has been about normal in Maryland, which provides no hints as to what kind of leaf-peeping season might be ahead. But temperatures have been running almost 6 degrees warmer than normal in September, meaning a cool-down is still needed before leaves begin to change.
Mild fall days and cool — but not freezing — nights make foliage most intense, according to the Foliage Network. Daytime temperatures that are too warm can dull leaves’ color.
Calm winds are also important — they help keep leaves on the trees long enough for us to enjoy them.
So far this season, low levels of color are being reported in northern parts of New England.
Central Maryland has at least two weeks, and likely three weeks, before a significant proportion of leaves change color. In Western Maryland, the changes occur earlier.
In three out of the past five years, Foliage Network spotters haven't reported "moderate" color change in Central Maryland until the middle of October. In both 2013 and 2014, that level of color change occurred by Oct. 9.
Foliage typically reaches peak color in Central Maryland in early November.