Thursday, April 2, 2015

Record Warm Winter Aloft

Now that winter is complete according to my preferred calendar month definition (November-March), here are a few of the many records that were broken in the observations made by the twice-a-day balloon soundings at Fairbanks.

- Highest mean Nov-Mar 1000-500 mb thickness (5233 m vs 5218 m in 1980-1981).  Thickness is an excellent measure of integrated heat content, which means that the lower half of the atmosphere above Fairbanks indisputably saw its warmest winter on record (since 1948).

- Highest mean Nov-Mar temperature at 850 mb, 700 mb, and 500 mb.  At the surface it was the 6th warmest winter on record.

- Highest mean Nov-Mar 500 mb height (pressure aloft).  Last winter (2013-2014) now stands in second place.  Interestingly 2011-2012 saw the lowest mean 500 mb height on record.

It's interesting to note that more than 31% of soundings reported above-freezing temperatures somewhere in the column from November through March.  This is more than twice the 1981-2010 normal of 14.8%, and is very close to the 1980-1981 record.  It's remarkable to consider that above-freezing air can persist in the atmosphere above Fairbanks for almost one-third of the winter.

Here's a time-height cross-section of the lower tropospheric temperature anomalies.


  1. We've had a mild winter in Fairbanks. Is it as simple as having warmth aloft, or as noted, "thickness"? Are clouds a function of warmth aloft? It would seem they also play a role in determining temperatures at the surface. I'm trying to understand the important drivers of temperatures at the surface.


    1. Gary, I'll post some figures on cloud cover tomorrow. I think you'll find the results interesting.

  2. That first graph is remarkable. A statistician would be baffled, I think. As for forcings, according to the good folks at University of Washington, the December, January, and February PDO readings have ALL been the highest ever recorded in 115 years:

    1. Andy, yes indeed - extremely positive PDO, although I've calculated the PDO with different SST data and different climatology, and it makes a difference... this winter may or may not have been a record depending on these choices.

      I'd be curious for more comment on the thickness chart - exactly what is it that you see as statistically unusual? The sudden break of apparent decadal-scale trends in 1976 and 2013-2014?