Climate Watch

By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy, UAF

October is most of the way behind us, and there that has not been much sustained freezing weather yet. Now you might say that’s not too unusual. Which is true. One way that we can track how much overall freezing has occurred is through “freezing degree days.”

This sounds complicated but it’s really quite simple. For each day when the average temperature is below freezing, subtract that temperature from 32°F. So, if the average temperature today were 10°F, subtract that from 32°F, giving 22°F freezing degree days. If we start at the beginning of the autumn and then add each day’s freezing degree day total, we would have a running total for the season. This idea of using the degree day concept is an old one and is widely used in the Lower 48 for estimating energy demand (using 65°F as the base number) and agricultural (different base temperatures for different crops).

Here in Alaska, we’ve found that freezing degree days to be useful as part of the effort to get a handle on the relative safety of early season ice on lower Kuskokwim River, and for gardening efforts across the state.

For instance, the Scenarios Network for Alaska + Arctic Planning (SNAP) at UAF, using the degree day concept, estimates that by the 2050s (that’s only 35 years from now), summers in Nome will be, on average, warm enough to grow broccoli from starts. Can you say “fresh corn of the cobb” from Pilgrim Hot Springs?

Meanwhile, freezing days so far this autumn are running well below normal, and as you can see in the graphic, the early season freezing has declined dramatically over the past 50 years.