After a dry summer, the weather pattern has changed and fall is here! Temperatures have cooled, leaves are beginning to change color, and we’ve even had some snow on the high peaks surrounding Aspen. Compared to last year, this fall feels much wetter and cooler (though maybe it just feels that way because of how dry the 2025 summer was). Looking at the numbers reveals that we’re about 0.09 inches above normal precipitation for September 1st to date, with a total of 0.94 inches. Last year it rained 1.0 inches in the month of September, which is about 0.75 inches lower than the 25 year average. With such a different weather pattern than last fall, I’ve been wondering what effect the dry 2025 summer and recent rain will have on fall colors.

While weather does play a role in leaf color change, the primary driver of the transition from summer to fall colors is photoperiod, or the amount and intensity of daylight. As the angle of the sun diminishes and days get shorter, leaves slow down photosynthesis. Their sugar production decreases, and eventually, the chloroplasts (the part of the cell responsible for photosynthesis) get broken down and pulled back into the trunk to be recycled. As a result, the leaf’s green pigment (chlorophyll) is also pulled out of the leaf, exposing the yellow and red pigments that we all love to see this time of year.

So what’s the deal with the weather? Temperature, precipitation, and soil moisture can all contribute to when leaves begin to change color and how vibrant their yellows and oranges are. Clear, sunny days (which it seems like we haven’t had many of) and cool nights result in sugars accumulating in leaves, turning them more orange or red. Dry conditions in spring and summer can delay the onset of fall changes and dull leaves. The same can happen if there is excess precipitation in the early fall, allowing leaves to continue photosynthesizing a little longer.

As leaves around Aspen are just beginning to change, it’s hard to forecast this year’s leaf-peeping. Has it been too wet for a vibrant fall? Have nights been just cool enough to get bright oranges? Let us know what you are noticing!