It seems like the last couple of months have been unseasonably warm, but when we look at the data, it’s not so clear cut. It’s true that in Lafayette we’ve had days with highs of 65 and 70 in late February and early March, but also a lot of low daily temperatures closer to 40. This means that we’ve only had 2 days (March 3 and 27) where the average daily temperature has been above 50.
One way we measure how this year’s weather compares with previous years is by looking at the accumulation of “Growing Degree Days” (GDD). This allows us to see if we’re running ahead or behind previous years at the same date. The rate of tree development, bud burst, flower opening, etc, is closely related to average daily temperature. In general, we expect little development when it’s cooler than 50, so we calculate GDD50 – the growing degree days above 50 degrees F. Growers would like a long cool spring so tree development is delayed. This means that spring frosts cause less damage because the frost hits at a time of lower cold sensitivity. Right now we’re at 4.5 growing degree days – so few that the line hardly shows up on the graph. Also looking at the graph, a couple of things stand out:
- Already we have lower accumulation of GDD than most the last 13 years so crop development is later than it has been in a while
- BUT, every year since I began plotting Lafayette temperatures in 2010 has been earlier than the long term average (heavy green line) – I’m not sure the term “normal” applies anymore!
In southern areas of the state, there was a very early warm up followed by a cooler period. Apples are at half inch green with some cultivars at tight cluster and some with a little pink showing.
We’re keeping our fingers crossed for a few more weeks of cooler weather, but in the final analysis, we’ll take what we get.
