Saturday, September 6, 2014

Summer Contrast - Cold Bay and Barrow

In future years when we look back at the meteorological summer of 2014 (June through August), we might conclude from the 850 mb temperature anomaly map that average temperatures were not greatly different from normal in most parts of Alaska (see below).  Mean 850 mb temperatures were slightly below normal over the northern Gulf of Alaska, and the far southwest, southeast, and north of Alaska were somewhat warmer than normal.

However, this conclusion would be incorrect, as in fact surface temperatures were significantly below normal at several interior stations and also at Barrow, while the southwest - and especially Cold Bay - were very warm.

The temperature anomalies at Cold Bay and Barrow are particularly notable - at Cold Bay because of the sheer magnitude of the warmth, and at Barrow because of the change from recent years.  Here are some statistics on the summer temperatures at these two locations:

Cold Bay
  • The June-August mean temperature was 3.8 standard deviations above the 1981-2010 normal (54.1 °F vs 49.8 °F).  An anomaly of this magnitude (either warm or cold) has a return period of about 1700 years if we assume that non-overlapping 3-month seasonal anomalies are independent of each other, the climate is unchanging, and the distribution is Gaussian.
  • The June-August mean daily maximum temperature was 4.5 standard deviations above normal (59.7 °F vs 54.4 °F).
  • Only a single day (August 29) had a mean temperature below normal.
  • 54 of 92 days reached 60 °F, compared to a 1981-2010 normal of 11 such days and a previous record of 24 such days in 1997 (period of record 1950-present).
  • 16 days reached a relatively balmy 65 °F, compared to a normal of 1 such day per summer and a previous record of 10 such days in 1953.  30% of summers fail to reach 65 °F in Cold Bay.
  • 48 days had a low temperature of 50 °F or above, compared to a normal of 10 such days and a previous record (set last year) of 42 such days.

  • Overall it was the coolest summer since 2001 (mean temperature 1.1 SD below the 1981-2010 normal).
  • The average daily high temperature was the lowest since 1983 (1.4 SD below normal).
  • The temperature exceeded 50 °F on only 9 days, the least since 1983.
  • The summer's highest temperature was only 58 °F, which is a tie with 1945 for coldest on record in the Weather Bureau/NWS era (1930-present).
  • The longest period of time at or above freezing was 15 days, the least since 2002.  The chart below shows the annual maximum number of days without dipping below freezing.

The charts below show the time-height cross-sections of temperature (departure from normal) at Cold Bay and Barrow for the summer months.  At both locations it's clear that the temperature anomaly was strongly focused near the surface, i.e. mainly below 2000 feet above sea level.  At Cold Bay the warmth was directly related to the very warm water temperatures in the North Pacific, and at Barrow the anomaly was caused by persistent low-level northerly flow and a cold low-level Arctic air mass.  Higher up in the troposphere the temperatures fluctuated but remained close to normal on average at both locations, as we saw in the 850 mb temperature map.

For the sake of interest I'll throw in the Fairbanks chart, where we see that there was little variation of temperature anomaly with height; cooler than normal temperatures were the rule in June and July, but August was a good deal warmer.

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