Saturday, September 13, 2014

Upper Air This Summer: Part I - Temperatures

Summer 2014 will long be remembered in the Interior for the amount of rain that fell. Most stations around Fairbanks had their wettest summer on record. Bettles had their second wettest summer and their greatest number of days with measurable precipitation. In addition to the moisture, the temperatures were generally a degree or two below normal. Those are all surface based statistics. How did the upper levels look?

Figure 1 provides a point-specific summary of conditions for the Fairbanks upper level balloon soundings. For all categories, the 2014 temperatures were slightly below the normal value. Somewhat surprisingly, the precipitable water (PW) value was also slightly below normal. This phenomenon was discussed earlier in the summer. A summary can be found here.

Figure 1. Upper level summary at Fairbanks during June-August time period.

If we move beyond Fairbanks, a more complete picture of upper level conditions can be assessed. In regards to temperature, the upper levels were slightly below the 1981-2010 normals. Figures 2 and 3 show the normal 850 mb temperatures and the 2014 850 mb temperatures and Figure 4 shows the 2014 value as compared to normal (units are Celsius). Only Nome, Annette Island and St. Paul had appreciable warmer than normal 850 mb temperatures in 2014. As Figure 5 indicates, with the exception of Cold Bay, the 850 mb temperature anomalies mirrored the surface anomalies. Surprisingly, Cold Bay had near normal 850 mb temperatures even though they experienced their warmest summer on record. Kotzebue's surface departures were also somewhat disconnected from their 850 mb temperatures. In the case of Cold Bay the significantly warmer than normal sea surface temperatures kept temperatures in the lowest levels significantly above normal.

Figure 2. Normal (1981-2010) 850 mb temperature for the June-August time period.

 Figure 3. 850 mb temperature in 2014 for the June-August time period.

Figure 4. 850 mb temperature difference from 1981-2010 normal for the June-August time period.

Figure 5. Surface temperature departure from normal for the June-August time period.

At the 500 mb level, we see a similar pattern; i.e., most of Alaska was cooler at 500 mb except for Nome, Annette Island and St. Paul (see Figures 6 and 7). Again, Cold Bay and Kotzebue were extremely warm this summer but at 500 mb they were below normal. This would seem to indicate that their atmosphere was more unstable (steeper lapse rates) but both stations were below normal for the summer.

Figure 6. Normal (1981-2010) 500 mb temperature for the June-August time period.

Figure 7. 500 mb temperature in 2014 for the June-August time period.

Part II of this post will look at the precipitable water values statewide and how well it correlated to observed precipitation.

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