Changing Fast

A change from warmer than normal to colder than normal in interior Alaska at this time of year is always a rather dramatic affair.  This is partly because the climatological rate of change is at its greatest - for example, in Fairbanks the normal temperature drops by over 6°F per week in mid-October - and so it's easy to get a big drop in short order.  And of course it's partly because a good cold spell at this date means freeze-up for the interior, and sometimes quickly.

Fairbanks airport dropped to 14°F this morning, but other nearby locations were colder: +4°F at the Goldstream Creek COOP and +1°F at Eielson.  It was well below zero in favored parts of the eastern interior: -11°F at Chicken and an impressive -17°F at the Robertson River COOP near Tok.

This is not the coldest observed so early at Chicken, even within their relatively short period of record (1997-present).  In 2000 it was -10°F on the 2nd of October, and in 1997 it was -12°F on the 12th, followed by -25°F on the 18th.

Here are a few webcam views to document the state of freeze-up in select locations.

Toolik Lake has frozen over since Tuesday:

Ice is forming in the shallow water of the Koyuk River (always one of the first places to show ice south of the Brooks Range):

A bit of ice is running in the Tanana River at Nenana:

And in the Kuskokwim at McGrath:

No ice on the Kuskokwim River in McGrath yesterday…and ice on the river today! @NWSFairbanks @NWSAPRFC It’s that time of the year again! pic.twitter.com/ioMYhLrbgz

— Bruno (@brunota2003) October 14, 2022

 

And in the Yukon at Dawson (video courtesy of http://dawson.meteomac.com)

Winter's Chill

[Update Sunday 6pm]

Last night was colder, especially in the Fortymile Country, with -35 to -38°F in several locations and a rather remarkable -43°F at Chicken.  Far to the north, satellite estimates suggest it may have been below -45°F in Arctic Village and its environs, but unfortunately the Arctic Village AWOS has not been reporting lately.

[End of Update]

Distinctly chilly conditions have descended upon Fairbanks and indeed most of the eastern interior, with widespread -20s and some -30s Fahrenheit this morning.  Here are some of the coldest spots, with higher-elevation valley sites and the Fortymile Country being well represented:

-38°F  Atigun River HADS site at 2600', near Galbraith Lake (north of Atigun Pass)
-35°F  Chicken co-op site (1800')
-31°F  Fortymile River at the Taylor Highway (HADS site at 2100')
-30°F  Salcha RAWS (900')
-30°F  Wade Creek at the Taylor Highway (HADS site at 1965')
-29°F  Tok 70SE CRN site (2000')

In Fairbanks the international airport reached -23°F, the Goldstream Creek co-op saw -22°F, and Eielson AFB reached -20°F, but North Pole only hit -18°F.  It's quite unusual for the airport to be the coldest spot in the area.  Tonight looks to be colder as the 5-minute observations from Fairbanks airport showed a 10°F temperature drop right after sunset just a short while ago - see below (sunset was at 15:34 AKST today):

This morning's -35°F at Chicken is right on schedule, as the 1997-2016 median date for first -35°F reading is tomorrow, November 19.  In Fairbanks it is "normal" to see the first -20°F or colder on November 17, so again this cold spell is right on time.

Here's the 500mb map (courtesy of Environment Canada) from 3am this morning.  Cold air is being imported from the north in the strong pressure gradient between the Pacific/Bering Sea ridge and the cold low over Canada's Melville Island.  The cold low is really cold - notice the -40s Celsius temperatures around it.  As for the Bering Sea ridge, this has been a persistent feature of the pattern in recent weeks and is a clear expression of a La Niña influence.  I'll have more to say about this in a subsequent post.

Winter Descends

After writing only last week about the lack of a hard freeze in Fairbanks - and indeed the first hard freeze last Wednesday was the latest on record - conditions have suddenly turned more wintry.  The temperature hasn't risen above freezing since Sunday, and there's no immediate prospect of it doing so as the trend remains firmly down for now.

It's possible, though unlikely, that the thermometer will not rise above freezing again in Fairbanks this year.  The last time this happened was in 2008, when the last above-freezing temperature was on October 11; but most years see at least a minor thaw in November or December, and about half of recent years have made it into the 40s in these months.

In keeping with the wintry change, widespread snow showers have brought at least a dusting of snow to much of the interior in the past couple of days.  Yesterday was the long-term median date for establishment of the permanent winter snow cover in Fairbanks, and in view of the chilly forecast it's certainly possible that the snow that's now on the ground could remain until spring.

Here are some webcam views of a hefty snow shower that has passed over UAF's West Ridge in the course of writing this post.

 

Here's the radar image from 6pm, showing the high reflectivities associated with substantial snowfall rates in the localized showers; Fairbanks airport recorded 1/4 mile visibility at 6:04pm.

The snow showers have been forming within an increasingly unstable air mass, as cold air moves in aloft over a relatively warm land surface.  The three charts below show the Fairbanks balloon soundings from 4pm AKDT yesterday (top), 4am this morning (middle), and 4pm today (bottom); note how the temperature (red) curve becomes steeper in the lower levels while the surface temperature remains nearly constant.

As far as freeze-up across the interior is concerned, webcam views suggest there is not a great deal happening yet, but that should change quickly in the next few days.  Temperatures have not risen out of the teens today in the Yukon Flats, so the apparently open Yukon River at Beaver will soon ice up:

To the east, the Yukon is still open at Dawson, and far to the west, the Koyuk River is still open, and there's open water at Selawik.  I'd expect a freeze-up in a matter of a very few days in the latter locations, given the cold air now working its way down across the state.