Friday, February 9, 2024

Follow-up on Cold

A couple of quick items of follow-up regarding the recent cold snap.  First, here's a look at temperatures in the hills above Fairbanks, using data from several of the SNOTEL sites (not all of them have been reporting data lately).  The two distinct waves of cold are evident - the first culminating in the January 27 cold, and the second reaching its nadir 6 days later, on February 2.

The second cold wave was colder at valley level, with Fairbanks seeing its first daily-mean temperatures below -40° since 2017.  But some of the SNOTEL sites were no colder in the second round, and so the temperature inversion was stronger.  The climatological average inversion at this time of year is about 10-11°F between Fairbanks and most of these sites, although Little Chena Ridge runs a few degrees warmer (as in this event).  So the inversion was roughly normal in the second cold wave, but was certainly weaker than normal on January 27.

We can't confirm the temperature profile for February 2, because the NWS balloon sounding auto-launchers are automatically disabled below -40°, but the 3pm January 27 Fairbanks sounding confirms a total lack of inversion in the lowest 1500 feet or so.

Rick Thoman comments and explains on his blog:

Rick also comments that late January may have been the coldest in the hills since February 1999, based on data from Keystone Ridge and the Fairbanks soundings.  Certainly the -40° on Keystone Ridge on January 27 was the lowest minimum temperature since February 5, 1999, but it's worth mentioning also late January 2012, which saw a high temperature below -30°F on Keystone Ridge (not seen in the recent event).

Looking at the SNOTEL historical data, we get the following comparison for coldest daily mean temperature (°F) in the two years (2024 vs 2012):

Eagle Summit: -30.0 (2024) vs -38.5 (2012)

Munson Ridge  -35.5 vs -33.5

Mt Ryan  -31.5 vs -33.5

Upper Nome Creek  -39.5 vs -39.0

Little Chena Ridge  -32.0 vs -32.0

With the exception of Eagle Summit (which was much colder in 2012 and also colder in other recent years), I'd say it's a toss-up: the recent cold was comparable to 2012 at elevation.

Rick's copious notes from January 2012 (the coldest month statewide since pre-1925) are worth perusing:

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