Tuesday, January 6, 2015

Warmth Aloft Persists

Valley locations in the Fairbanks area continue to see cold and stagnant conditions under high pressure, but temperatures aloft are much warmer, resulting in a strong inversion.  Yesterday evening saw a temperature of -31 °F at Goldstream Creek and +9 °F on Keystone Ridge, a difference of 40 °F in a short distance.  Farther aloft, the temperature measured by balloon sounding yesterday afternoon was as high as +18 °F at 869 mb or 3766 feet above ground level; and other soundings have been even warmer in recent days.

The persistent absence of cold conditions aloft has been a very prominent feature of the winter in Fairbanks so far, and in fact it's record-breaking by quite a large margin.  The chart below shows the lowest observed value of the column maximum temperature in the early winter, i.e. prior to the turn of the year, for each year since 1948.  Remarkably, this winter's balloon soundings from Fairbanks have not yet observed a column colder than -11.1 °C (+12 °F) throughout the troposphere; there has always been air at least this warm at some level.  The previous record in this respect was -18.5 °C (-1 °F) in 1953.  The chart shows an interesting pattern of rising minima in recent decades, indicating that this year's outcome is a continuation of a long-term trend.

Another way of expressing the extreme persistence of warmth this winter is that only two soundings so far have observed a column colder than -10 °C throughout (back in November).  The next closest winter in this regard is 2000-2001, with 13 soundings colder than -10 °C by the turn of the year, and even the exceptionally warm early winter of 2002 had 22 soundings meeting this threshold of cold.  


  1. One thing that you have done before is take the difference between the surface and the maximum temp in the column. I think that this would be interesting as compared to other years - especially years with a strong positive PDO.

    Which brings me to the question: is the warmth aloft a characteristic of strong positive PDO? And is the warmth just around the 800 level or does it extend up to the tropopause?

    1. Eric, the inversion strength has been only modestly higher than average - i.e. warmer aloft relative to the surface. The November-December average inversion strength was barely within the top tercile. In other words it's been warm at the surface too.

      Good question regarding elevation dependence of warmth in positive PDO. I'll take a look.

    2. Thanks Richard.

      So it's been warm on both the surface and aloft. And these "normal" temperatures we've been having are not atmosphere deep but simply cold air that managed to slip underneath the warm air. Which then makes me think: how persistent is this warm air over all of Alaska? Does Chicken, Bettles, and Barrow have relatively warm 800 levels despite the cold snap? You could go down a rabbit hole on this if not careful.

    3. Eric, here is what I came up with for upper air temps for all of 2014 and how they stand up all time:

      Highest surface temperature at RAOB sites (2nd: 1978)
      Highest 1000 mb temperature (2nd: 2002)
      Highest 850 mb temperature (2nd: 1957)
      Highest 700 mb temperature (2nd: 1957)
      Second highest 500 mb temperature (1st: 2013)
      Fourth highest 300 mb temperature (1st: 1989)
      Greatest 850-500 mb thickness (2nd: 1957)
      Fourth greatest 1000-500 mb thickness (1st: 1957)
      Sixth greatest 1000-850 mb thickness (1st: 1968)
      Eighteenth greatest PW (1971-2014) (1st: 1991)
      Seventeenth greatest 850 mb height (1st: 1989)
      Sixth greatest 700 mb height (1st: 1989)
      Fourth greatest 500 mb height (1st: 2013)
      Fourth greatest 300 mb height (1st: 2013)

    4. Brian, so if I'm reading those stats right, 2014 has been the warmest in the first few thousand feet but then taper off quickly to high but not record breaking. And for pressure, the values have been somewhat mediocre at the surface but become relatively high at altitude. Wouldn't this imply that while warmer than normal, the upper levels have not warmed as much as the surface? Just guessing here.

    5. Eric, 2014 was the warmest year during the weather balloon era at all levels below about 10,000'. Given that the 500 mb temp was the 2nd greatest and the 300 mb temp was the 4th greatest, I would not characterize it as tapering off quickly. I'll have to check the tropopause levels but it could be related to stratospheric cooling. Counter intuitively, surface warming promotes stratospheric cooling.

  2. Warmer air aloft and thin clouds is what I recall from flying during the regime change in the mid '70's to later '90's.