Saturday, March 12, 2011

Diurnal Ranges and Inversions

Big high pressure, surface and aloft, remains over northern Alaska. Almost every day has brought bright sunshine to Fairbanks-land with no more than some wisps of high clouds, and the temperature of the airmass overall is not changing much. So this is a good set-up to look at the differences in diurnal temperatures between the lowlands and the hills. Plotted on the right are the range between high and low temperatures from the Fairbanks Airport and Keystone Ridge each day so far this month. The airport has consistently had more than twice as big a temperature range, generally around a 40 degrees swing, while Keystone Ridge is averaging about an 18 degree daily change in temperature.

The reason for this is not that the sun is providing more heating on the valley floor that 1000 feet higher. Rather, strong valley based inversion continue to form overnight, but there is now enough local heating from the sun to break that inversion, so some of the the daily temperature range in the valley is simply mixing down the warmer air above.

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