How the weather affects fall colors

September 14, 2017 0 Comments

Fall color is starting to pop around North Central Wisconsin and has really picked up in the last two weeks. In fact, our weather conditions have been great for developing vibrant fall colors. There are three factors that determine fall colors: leaf pigments, the length of the night, and the weather. The amount and intensity of colors that develop are related to the weather conditions before and during the time chlorophyll in the leaves begins to dwindle, with temperatures and soil moisture the main influences.

Chlorophyll is one of three pigments in leaves, and is what gives them their green color. It’s production starts to slow down and stop as our nights become longer, which is common in September as we are losing about 3 minutes of daylight per day. Once no more chlorophyll is being produced, the other two remaining pigments are no longer covered up, exposing their colors.

As I mentioned before, our weather through the summer and into these first couple weeks of fall have been pretty ideal for the development of vibrant fall colors. First, you need a strong summer growing season with ample soil moisture. We had more than enough rain this summer (13.53″), especially in the first half of summer. So much so that the soil is still rather moist despite August being cooler and drier than normal. Had we had a late spring or summer drought, the onset of these fall colors would have been delayed by a few weeks and would not be as intense.

Once you move into fall, you want a succession of warm, sunny days and cool, crisp nights in order to maximize the fall color. We had a couple of cool nights in the low 40s in Wausau and even 30s in the Northwoods towards the end of August and through the first two weeks of September, which made the leaves start turning a bit earlier than normal. This is evident by the fall color map, which shows a handful of counties in our area with over 25% color. However, we were somewhat stuck in a cool and wet pattern during this time period. Since the pattern flipped, we have been in a stretch of glorious sunny and warm weather with highs in the mid 70s to low 80s. There were a couple of nights where locations in the Northwoods were in the mid 30s or close to the freezing mark, which actually hurts fall foliage as the cold air causes the leaf stems to become brittle and kills the remaining leaf pigments responsible for the bright colors.

The great news is the warm weather will continue into the end of next week. The Climate Prediction Center has a 70-80% chance of temperatures being above our normal high of 70 degrees through next weekend. However, there will be some chances of cloud cover and rain at times this weekend through next week, so we may not see too many cool and crisp nights during this stretch, but there is still a good chance of sunshine during the daylight hours. If you want to keep up on the fall foliage across the state over the next few weeks just click here.

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