June Recap: Another Wet Month
* Nice Start to Week: Full Forecast *
Although not as extreme as May, June 2009 continued the trend of wetter than average weather in the D.C. area. After almost 6 inches of rain last month, the rain gauge at Reagan National Airport (DCA) has now collected 18.13 inches for the period April 1st through June 30th, almost double the 9.72 inch normal amount-- but still less than the 20.38 inches for the same period last year. As in May, last month's weather was punctuated by several severe thunderstorm episodes resulting in property damage, personal injury, and in some cases, death. Significantly, there were five days during which .50 inches or more of rain fell.
Aside from the heavy rainfall, it was a fairly typical month temperature-wise, with no unusual heat or cold. As heat was building throughout the Plains and the Midwest, a persistent dip in the jet stream kept the Northeast and Mid-Atlantic states relatively cool, except for a few brief periods. As a whole, the month averaged just a little below normal, similar to May in that respect. Nonetheless, we had the fewest number of 90 degree days in 17 years (just 2) and, when combining May (0) and June, the fewest number in 24 years.
Why has it been so wet and relatively cool (for Washington) you ask?
Keep reading for possible explanations for June's weather...
The aforementioned dip in the jet stream is the immediate answer, of course. And why, has the jet stream meandered so far south of its usual Canadian haunts for much of the spring and summer? It's tempting to blame various "teleconnections," or inter-relationships, between large scale atmospheric pressure patterns in different parts of the world. Some of these are the NAO (North Atlantic Oscillation), the PDO (Pacific Decadal Oscillation), and the more well known ENSO (El Niño Southern Oscillation), etc.
Also, it would be easy to blame large-scale volcanic activity, if there were any, or lack of sunspots, which astronomers have reported. (The U.S. had a relatively cool summer after the 1980 Mt. St. Helens eruption and a "spotless" sun has long been associated with the famous, or infamous, "year without a summer" of 1816--see my last post.) But that wouldn't explain the excessive heat that's already occurred in the Midwest. The notorious heat pump known as the Bermuda "high," currently in an anemic state, could also be implicated in our current weather.
But my gut feeling is that currently the weather around these parts is just in a "rut" (meteorological term). Weather patterns are very cyclic in nature and these cycles, once established, tend to last for days, weeks, or even months. And while I'm certainly not predicting a "year without a summer," pleasant Washington summers are not as rare as you might think; at least they weren't a few generations ago. I, for one, would welcome one, even though, for sure, there would be the usual grumblers.
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