After a much colder start to October (first 10 days) than in the past five years, freeze-up is getting under way on area rivers a little early this year. Through October 10, Fairbanks airport has seen 37 freezing degree days, compared to a 1981-2010 median of 9.5 by this date. The total of over 3 times the normal for the date sounds like a significant anomaly, but owing to the typically rapid drop-off in temperatures at this time of year, it is only 4 days ahead of normal.
Here are a few webcam images of freeze-up progress at various locations, starting with today and going back about a week:
Tanana River at Nenana today:
Koyuk River from Koyuk today:
Koyuk River on Thursday Oct 9:
First widespread ice on Teshekpuk Lake, close to the Arctic coast, on Tuesday Oct 7:
Teshekpuk Lake the next day, Wednesday Oct 8:
First ice cover on the lake at Inigok, between Umiat and Tesh Lake, last Saturday Oct 4:
And finally, a grainy shot of Toolik Lake (near the haul road just north of the Brooks Range) freezing over last Friday Oct 3:
Here's a chart showing the lake and air temperatures during the freeze-up of Toolik Lake. I'm not sure of the depth of the temperature sensor in the lake, but it shows nicely how the temperature stabilized at about 2 °C in tandem with the freeze-up. No ice was evident on the lake until this temperature threshold was reached, but since freezing began there has been only a tiny amount of additional cooling. This nicely illustrates the heat exchange processes that are so important in the freezing of fresh water lakes around the world.