Saturday, April 22, 2023

Breakup Postponed

Those of us who guessed on the early side for breakup at Nenana are out of luck this year, as the scene is still quite wintry, and fresh cold moved in this morning - with notable wind I might add.  Here's the webcam view at Nenana this morning.

Winds gusted to 35mph in Fairbanks, from a direction just east of due north.  Here are the max gusts since midnight:

So far Fairbanks has seen a grand total of 6 "thaw degree days" this year, which is the accumulation of daily mean temperatures above freezing (e.g. a daily mean temperature of 40°F supplies 8 TDDs).  This amounts to the 8th lowest on record through April 21.

But if we assume the 7-day NWS forecast is correct, then this year will move up to 5th place in the next week.  This all but guarantees a later breakup than normal at Nenana: normal for recent decades is April 30, and the top 35 years for lowest TDDs through April 28 all saw breakup in May (without exception).

Of course the sensitivity of breakup date to temperature increases more and more rapidly as normal temperatures rise, and as the sun gets stronger by the day; so it would take an increasingly unusual level of cold to push the breakup date towards mid-May.  Given the current situation and the latest forecasts, I think it's unlikely to happen before May 7, but May 10 may be near the mark.

The chance of approaching the 1964/2013 record of May 20 is still remote, but just for fun, here's a comparison of this year's temperature trace - including the NWS forecast - with those years.  Even with the fresh cold arriving today, it's unlikely that this month will equal April 2013 for overall cold, and in that year the cold was relentless into May.  As for 1964, April wasn't even in the top 10 for cold, but then the cold was incredibly extreme in May.

1 comment:

  1. Not much for breakup will get serious until we have clear daytime skies and temps that remain above freezing. Some wind helps distribute surface warmth. Any clouds limiting insolation and nightly refreezing can slow the process.

    Ice thickness seems lower than some years I've lived through (

    Follow the river breakup here (