Six months have now passed since the dramatic late spring reversal in Fairbanks temperature anomalies, from persistently below-normal to mostly above-normal (see chart below). Since late May, unusual warmth has been quite persistent, with only brief interruptions to the prevailing trend. Remarkably, over 40 percent of the days since May 24 have been at least 1 standard deviation warmer than normal, while only 14 of 185 days have been an equivalent amount below normal. The distribution of anomalies is shown in the second chart below.
The immediate cause of the persistent warmth is the upper-level ridge that has repeatedly redeveloped over southern Alaska and northwestern Canada, as shown below in the six-month mean 500 mb height anomaly.
[Update: per reader Eric's request, below are the corresponding 500 mb height maps for the prior 10 years: 2003 through 2012, in order.]
The June to October time-frame was the warmest 5-month period on record for Fairbanks. It was 54.1 degrees. The second warmest 5-month period was June to October 1923 (53.2 degrees).
ReplyDeleteYes, the warmth was welcome. Tough on trees however via lack of moisture. And the summer's length was compressed.
ReplyDeleteWe lost about 20% of our traditional outdoor summer working and playing season via May's cold WX. Some local large lakes didn't break up until almost the second week of June due to extensive freezing depth and high quality ice.
Gary
Would it be possible to put up the 6 month mean 500 mb charts of the past few years as a comparison?
ReplyDeleteEric,
DeleteNo problem - I added maps for the same period in the past 10 years.
It seems that an intense ridge forms over eastern russia every few years. This time it formed over the Gulf of Alaska.
ReplyDeleteI think it was 2008 when we had the summer of infinite rain. That year there was an intense latitudal trough over Alaska.
Then the summer of 2011 was boring; not hot or cold with rains on the evening and partly cloudy during the day. There was an intense longitunial trough.
But ridges over Alaska are rare.