“The first day of spring is one thing, and the first spring day is another. The difference between them is sometimes as great as a month.”
Henry van Dyke in Fisherman’s Luck (1899)
What lovely weather we’ve been having! Cool evenings, bright, pleasant days, with a bit of rain now and then. True, it’s not the best for growing – a little warmer and wetter would be a little better – but this year’s cool is far better than last year’s brutal heat wave and drought like conditions. March, the first month of spring, was more than 4°F colder than this past December, the first month of winter. The March 2013 average temperature was 11.3° F colder than last March’s. But why has it been so cool? It has much to do with something called the Arctic Oscillation.
The Arctic Oscillation is a combined measure of barometric pressure and wind current direction and speed that describes the state of atmospheric circulation over the Arctic. A “positive” Arctic Oscillation means the occurrence of lower pressures and swifter wind speeds preventing the seepage of cold air into the south which results in warmer than average weather with less snow for the eastern U.S. (See the orange bars in the graph below.)
The “negative phase” occurs when there is high pressure in the arctic, and the ring of winds circling the pole are weakened allowing the colder arctic air to plunge into the lower latitudes … our latitudes! This means more late spring snow as recently experienced by the Midwest, and cooler, drier conditions for us. But it’s warming up, and the rain is on its way. In fact, the warmth is good news for our tomatoes and eggplants which, as you can see, are nearly bursting from the greenhouse in their eagerness to get their roots into the soil and their leaves into the sun.
Hooray for Spring!