Monday, November 21, 2022

Historical Context for Warmth, Freeze-Up Delays

Last week's warmth on the North Slope was exceptionally unusual, one of the most extreme temperature anomalies on record for that part of the world in winter.  Amazingly, the Ivotuk CRN (1900' elevation) reported a daily mean temperature of 43°F on Thursday.

To facilitate a consistent historical comparison, I calculated the area-average daily mean temperature for the North Slope climate division using ERA5 reanalysis data back to 1959, and according to this data there's never been a daily mean temperature above freezing for the division as a whole in winter (November through March).  We don't yet have ERA5 data from last week for comparison, but the operational ECMWF model (similar to ERA5) shows a daily mean temperature just below freezing: see the dashed extension to the ERA5 2022 line in the chart below.

The warmest winter day for the North Slope in the 1959-present ERA5 data was January 29, 1963, which had an enormous ridge over western Alaska - only slightly different from last week's anomaly - see below.



While the North Slope extreme has subsided for now, the state as a whole is very much warmer than normal, as evidenced by UAF's statewide temperature index: the chart below shows the last 14 months or so.

The contrast to last year is becoming more significant by the day, as last year the second half of November was very cold indeed.  The brief cold that we saw back at the end of October and the beginning of November this year now looks very mild and fleeting in comparison.

Neither the Tanana at Nenana nor the Yukon at Dawson are properly frozen over yet:

It's a bad situation along the Kuskokwim too, as documented by Bethel Search and Rescue a few days ago in their fifth annual freeze-up survey:

"Summary: For the past several years BSAR has been scheduling our first aerial freeze up survey of the Kuskokwim River on No­vember 18th. Flying the same day each year allows us to look back at previous years for comparison. In 2021, with a record cold November there were well established snow machine trails to nearby villages and even a limited amount of truck traffic on the River by this date. For November 18, 2022 conditions are very different. The lack of cold weather and early snowfall has slowed the freeze up process on the Kuskokwim River and it’s tributaries. THERE IS CURRENTLY TOO MUCH OPEN WATER ON THE KUSKOKWIM RIVER FOR SAFE TRAVEL NO MAIN RIVER TRAVEL RECOMMENDED AT THIS TIME"

Lots of pictures here:

1 comment:

  1. We'll enjoy the relative warmth and lack of snow for Fairbanks while it lasts. Early next year will make up for it as usual. Happy Thanksgiving to all.