Dry summers delay changes in leaves, but brilliant autumn colors around the corner

Another summer-like fall weekend lies ahead over the next couple of days, offering a great opportunity to view the autumn colors.

This sunny dry weather is expected to continue through next week with the Columbus Day Weekend appearing to provide more unseasonably warm weather for enjoying fall hues.

In the Cascades and Olympic Mountains, the leaves on trees are turning to their vibrant fall colors right now. During the next few weeks, leaves in the lowlands of Western Washington will follow suit.

Cooler weather and clearer skies on tap for Western WA

The change from green leaf colors are driven primarily by the shrinking hours of daylight and the growing length of nights. Depending on the variety of tree, biochemical processes in leaves end the production of green chlorophyll, unmasking two other chemicals within leaves – carotenoids and anthocyanins — revealing their colors.

Higher elevation trees begin this change in leaf colors before lower elevation trees, but only seperated by a matter of days or a few weeks.

Weather conditions play a role in the brilliance of leaf colors with temperature and moisture acting as the primary influences. The amount of moisture in the soil also impacts autumn colors.

Like weather, soil moisture varies from year to year. These two highly variable factors result in autumn season tree colors and timing being alike. A late spring and a dry summer, like the region had this year, can delay the onset of fall colors by a few weeks. A warm, wet spring, a warm summer, and warm sunny fall days with cool nights similar to this year’s weather, can produce the most brilliant fall colors in trees.

With early fall weather remaining relatively warm and dry, the next few weeks will likely be the best time to view fall tree colors along I-90, the Stevens Pass Highway, the North Cascades Highway, as well as the road to Hurricane Ridge in Olympic National Park. Trees in the lowlands should turn colors by mid-October as well while Japanese Maples will reveal brilliant reds before their leaves drop.