Deep Cold

Today's high temperature (so far) of -39°F -38°F at Fairbanks airport is the coldest in 7 years, and it's the coldest February day since 1999.  Since 1930, only two years have seen a daily high temperature this cold in Fairbanks in February: 1947 and 1999.  It also happened in 1910, according to the Ag Farm data.

As for the low temperature, -49°F this morning was also the coldest in Fairbanks since 2017; but there's a chance -50°F could be reached before midnight, with the 5pm temperature already back down to -45°F.  [Update: it was reached]

Unfortunately there's no sounding data to look at the vertical profile of temperature, because the automated balloon launcher is disabled when the temperature reaches -40°.  This is a great pity, in my view, and a loss to science.  If the automated launcher can't operate, then perhaps some hardy soul could be persuaded to launch a balloon manually, as in the old days - like 7 years ago.  Here's the sounding from 3pm on January 18, 2017, the last date Fairbanks saw a high temperature below -40°F (the lowest levels aren't included on the plot, but the data was recorded.)

The 2017 cold snap was much shorter than the current one, but was briefly severe, with more widespread -50s than any day in the current cold spell.  There's a series of posts in the blog archives, e.g.

https://ak-wx.blogspot.com/2017/01/cold-snap.html

Here's a splendid photo published to Twitter today by Cody Moore, showing ice fog filling the valley from a vantage point on UAF's West Ridge:

https://twitter.com/codymoorewx/status/1753549093471998281

Visibility at the airport has been 1/4 - 1/2 mile for most of the day.  Water vapor emissions from the urban environment are to blame for the fog, with a substantial contribution from the power plant plumes; here's another photo, this time from UAF GINA:

https://twitter.com/uafgina/status/1753493360315437259

The FAA webcam on Ester Dome provides another perspective on just how localized the fog is: skies were gloriously clear across most of the interior today.

A simple animation gives a sense of the moisture flowing from the power plants at left towards the Tanana River valley at right.