Tuesday, September 10, 2013

September 1992…Setting the Table

September 1992 brought some of the amazing out-of season-weather ever in Alaska. The Fairbanks area received several snowstorms during the month totaling more than two feet, and amazingly, the snow that started to accumulate on the September 13th remained on the ground until the following April. There was enough snow for people to be skiing on the 15th and I was running dogs with a sled on the autumnal equinox. The snow cover allowed temperatures to remain exceptionally low and produced the longest run of daily temperatures of four or more standard deviations below normal in Fairbanks weather history.

I'll be doing several posts on this historic event, starting with retrospective of September 10, 1992. Here is the mean 500mb pattern and height anomalies. The remarkably deep low north of Barrow was well forecast by the numerical models at the time, though we did not believe it in the days leading up to this event, referring to it jokingly as the "death star". Such a deep low so early in the autumn was beyond reasonableness.

The 850mb temperatures show a deep cold airmass over nearly all of the state. Temperatures in this NCEP/NCAR reanalysis are in degrees Kelvin, so freezing is 273K. The low temperature on the 10th at Fairbanks was 18F, easily a new record low for the date and the first of what would be eight daily record lows set during the month. And there was no snow on the ground yet.

7 comments:

  1. Very interesting. It is impressive that the models did such a good job. I remember the East Coast "Superstorm" of 1993 was excellently forecasted 5 days in advance. Were there ensembles back then? If so, I wonder what the spread looked like.

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    1. There were no operational ensemble forecasts in 1992. As I recall we had the NGM out to 48 hours, the AVN out all the way to 72 hour and then a quasi-manual 3-5 day. Someone please correct if my memory is wrong here.

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  2. We are keeping an eye on this in 2013: http://www.worldagweather.com/arctic/t2m.html

    Gary

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  3. Was this the year the Equinoix marathon was cancelled?
    -Matthew

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    1. Officially, yes. But some folks did run anyway.

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  4. Fascinating, Rick. The month was the most anomalous (3.5 SD below normal) in the historical record after 1964, relative to the 1981-2010 normals. Since 1981, nothing has come close, with only June 2004 and June 2013 being more than 3 SD away from normal.

    Can't help but wonder if there was any contribution from the eruption of Mt Pinatubo about 15 months earlier. We know the global climate cooled slightly in the next year or two, but perhaps there were circulation impacts too.

    Look forward to your future posts on this.

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    1. Pinatubo produced some great sunrise/sets in Fairbanks-land in 1991 (like most of the world), and it's certainly possible that remaining stratospheric dust contributed to such anomalous circulation center. Sounds like a modeling exercise to attempt to tease out the contribution. As I hope to show, the extreme surface temperature anomaly for September 1992 can be tied to the remarkably early establishment of the permanent winter snow cover.

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