August 1974

Here's a quick follow-up on the question I posed a few days ago: has anywhere in Alaska ever previously observed a temperature rebound to high summer warmth/heat after a really severe early autumn freeze (e.g. less than 20°F)?  This recently happened at Chicken: they dropped to 14°F on August 30, but rebounded to 80°F only 5 days later.

I sent the question over to former blog contributors Rick Thoman and Brian Brettschneider, both of whom have encyclopedic knowledge of Alaska's climate history.  Among the various candidate events they proposed, here's one that looks legitimate and was even more extreme than the recent Chicken temperature swing: in August 1974, the Mile 41 Steese co-op site reported a low of 16°F on the 22nd, followed by a high of 85°F on the 30th.  That's a rebound of 69°F, exceeding the recent 66°F change in Chicken.

Here's a chart of the data, courtesy of xmACIS2:

There's no doubt the freeze was severe in parts of the interior; the 17°F in Allakaket was the earliest date on record for a low below 20°F (data from 1908 through 1982).  At Bettles the 22°F still stands as the earliest below 25°F, and in the Fairbanks area there was a 22°F at North Pole (only 1°F shy of the record minimum for August).  Here are maps of low temperatures reported on the 22nd and 23rd (click to enlarge; the Mile 41 Steese site is in the middle of the maps, just to the north of Fairbanks):

The heat wave less than 10 days later was the real deal too; Fairbanks airport reached 83°F, and the university farm reached 84°F; both stand as the second latest on record for such warmth (after early September 1957).  Here are the regional maxima on August 30 and 31:

The sequence of mid-atmosphere circulation anomalies is quite interesting: a cold upper-level low dropped into eastern Alaska from northwestern Canada, but as it swung back into Canada, a strong ridge developed in its place.

The recent event at Chicken was different: the severe freeze was more localized, being a "Chicken special" in terms of how extremely cold it was in the valley.  The cold air mass wasn't all that extreme for the time of year (see my post here).  Here's the map sequence: