SPOKANE, Wash. — Fall is upon us, and there are already a few signs of color around Spokane and Coeur d’Alene. Don’t expect an early turn for the autumn leaves though while our current weather pattern continues.
Shorter days as summer turns to fall are the first trigger for trees to start preparing for winter. Cool fall nights then come in to signal the trees to shut down nutrient transport between the leaves and the tree itself. Once the leaves stop producing food for the tree, yellows and oranges are revealed. Sunny days will create reds as sugar is produced in the dying leaf.
coldhot leaves 2024-09-19 164448.png
The key however, are cooler nights. That hasn’t happened so far in September. Through the first 18 days of the month, 2024 has the warmest September nights on record (1881-present). That’s a recipe for waiting for fall, despite some severe drought in the Spokane area. Severe drought can cause leaves to drop early, but moisture’s impact on leaf timing is less well understood than how temperatures influence them.