Thursday, August 18, 2011

Fire Weather Season About Over

Damp, if not soaking weather persists over most of Alaska, and more than 200 lightning strikes Wednesday not withstanding, the fire season is about over.

According to the Alaska Fire Service, thus far a total of 292,440 acres has burned in Alaska this summer. This number has not changed (or at least been updated by AFS) for more than a week. This is about 27% of the acreage burned last summer. While not the lowest in recent years, it is well below the 20 year median of 681,000 acres.

Like last year, this year was a classic example of how the fire season in Alaska is so completely dependent on warm AND dry weather. Much of Interior Alaska was not especially wet this summer, but after mid-June there was no period of more than a couple days of dry AND warm weather. Here is a plot of the mean July 500 mb height anomalies:

Over land, lower 500mb heights in the summer correspond pretty well with cooler than normal temperatures. This is just what we see over Alaska. A big negative anomaly near the Bering Strait, but with below normal heights extending eastward.

Now here's the same plot for July 2009, which was one of the warmest and driest Julys of record over Interior Alaska, and a big fire year:

A much different picture over Alaska.

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