Warmth in the East, Snow in the West Is Bad News for Leaf Peepers

Linda Lam
Published: October 4, 2017

Recent weather conditions have left many asking what happened to fall and to the colorful foliage that typically marks the season.

(MAPS: Current Fall Foliage)

The weather pattern changed in mid-September and brought record warmth to parts of the Midwest and Northeast and early-season snow to portions of the West. These weather changes have impacted fall foliage across much of the U.S.

Trees in the Northeast and Midwest behind schedule with leaf color changes. In the West, the pretty fall colors have been replaced by a blanket of snow, especially in the Rocky Mountains of Montana, Wyoming and Colorado.

Typical timing of peak fall colors.

It is important to note that weather conditions are among one of many factors that influence the vibrancy of leaf color. The shorter amount of daylight is the primary trigger for the color of the leaves to begin to change. As the night's become longer and colder, chlorophyll production slows and eventually stops. Without chlorophyll, the yellow and orange pigments of the leaves become dominant, resulting in the many beautiful colors of fall.

Below is a closer look at what the recent and persistent warmth in the eastern U.S. and the cold, snowy pattern mean for fall foliage.

(MORE: Big Weather Changes You Can Expect in October)

Extended Warmth in Midwest, East

Since mid-September, both high and low temperatures have been well-above average in the Midwest and Northeast, thanks to a northward surge of the jet stream.

Temperatures soared into the 80s and 90s for several days across the Midwest and East. In fact, the heat wave in late September was historically late in several areas, including Chicago and Burlington, Vermont.

Temperatures did cool down to start October, but yet another round of above-average temperatures returned early this week and will continue into early next week.

(MORE: Indian Summer Engulfs the Northeast)

This latest spell of warmth is not as hot as the record-breaking heat in late September. Highs will typically be in the 70s and 80s and lows will also be 10 to 20 degrees warmer-than-average, with temperatures only dipping into the 50s and 60s for most areas east of the Mississippi River. 

It is this lack of cool temperatures overnight that has influenced the color of the leaves changing. 

According to the Southeast Regional Climate Center, the three-week period ending Oct. 1 had the warmest low temperatures on record for numerous cities including Boston; Concord, New Hampshire; Burlington, Vermont; Hartford, Connecticut; and Binghamton, New York. In addition, this period has been a top 10 warmest on record for overnight lows for most cities from Minneapolis to the Northeast Coast.

The absence of chilly conditions has resulted in a delay in the leaves changing. In addition, the lack of cool temperatures may impact the brilliance of the color of the leaves.

Temperatures did cool down with lows in the 30s and 40s in portions of the Great Lakes into northern New England at the end of September into the beginning of October, helped in prompting the leaves to change color. 

However, as you can see in the image below, there is not much fall color yet in the Northeast. Much of the interior Northeast usually sees peak leaf color by mid-October, but this will likely be delayed this year.

High-resolution satellite images from Oct. 3 across the Northeast, with little fall color visible.
(NASA)

This overall trend of above-average temperatures will likely last in the East and Midwest into mid-October and possibly into the second half of the month as well. 

(MORE: October 2017 Temperature Outlook)

Areas that experience strong winds and heavy rain can cause leaves to fall off the trees, which may be a concern later in the month, possibly shortening the time that fall color is apparent.

Winter-like Conditions in the West

Parts of the West have been experiencing conditions more common in late autumn or winter. In mid-September, the jet stream dipped southward over the region and this setup has generally continued into October.

In Havre, Montana, the first blizzard of the season resulted in widespread power outages early this week and broke a record for two-day snowfall in October with more than a foot of snow accumulating. This early-season snowstorm also brought up to 18 inches in Steamboat Springs, Colorado and up to 30 inches in Rocky Boy, Montana.

The heavy, wet snow downed trees and weighed down branches, impacting the leaves on those trees as well, bringing a rapid end to any colorful displays.

Portions of the northern Rockies and Sierra Nevada mountains already had snow on the ground before this latest snowstorm, as several disturbances have brought accumulating snow to the higher elevations.

(MORE: Snow Is Already on the Ground For the First Day of Fall)

Early on Wednesday morning, 5.3 percent of the contiguous U.S. was covered in snow, with the greatest snow depths in Montana and Wyoming.

Snow depth early on Oct. 4, 2017.
(NOAA)

This pattern has also resulted in cold temperatures. Havre saw temperatures plummet to 8 degrees Wednesday morning.

Freezing temperatures can quickly put an end to the colorful foliage as they destroy the ability of leaves to manufacture the red and purple pigments. These pigments are created by sugars that are trapped inside the leaves and are important in the production of the vibrant leaf colors.

Therefore, when there is an early frost this reduces the length of time of the colorful foliage, as the leaf typically falls from the tree sooner.

(MAPS: 10-Day Forecast)

In addition, strong and gusty winds that have accompanied these recent low-pressure systems moving through the West, which can cause the leaves to fall before their color is fully developed. 

There are areas in the West, however, that have not seen freezing temperatures or snow and are enjoying beautiful fall scenes.

These colorful displays will continue to spread as October progresses.


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