Friday, December 27, 2013

Importance of Snow Cover and Daytime Temperatures

Winter daytime temperatures and snow cover in the  middle latitudes.

Snow cover during the Winter has a dramatic impact on observed daytime temperatures. Although the intensity of solar radiation on sunny winter days is much smaller than during the Summer, it can still warm the surface of the earth during the day.  

The following satellite image shows a swath of snow cover extending from south central Kansas up to northeast Kansas, the far southeast corner of Nebraska and on into central Iowa.

The reflection of sunlight from a surface is termed the "albedo".
File:Albedo-e hg.svg
Notice from the above diagram that from 40-85% of the incoming solar radiation is reflected away from a snow covered surface and is unavailable for surface heating.  In contrast only 25 to 35% of the solar radiation is reflected back to space from the bare soil.

December 26, 2013 was basically cloud free across the Plains from Nebraska to Oklahoma allowing solar energy to strike the earth's surface throughout the day.  The following maps show the highest temperatures observed during the day.  It is very evident that the high temperatures were suppressed in the snow covered region extending from Kansas up into Iowa.

Notice (on the Weather Channel map of December 26, 2013 high temperatures) the blue color corresponding to the snow covered area in Kansas showing suppressed daytime highs. Temperatures were warmer to the west and the east of this snow covered region in Kansas.

The second map is a close up view of the observed NWS high temperatures for December 26, 2013.  Notice the highs in the 50's to the west and east of the snow covered area.  Snow covered Salina, KS, (KSLN) had a high temperature of only 40F and snow covered Manhattan, KS (KMHK) only had a high temperature of 44F.

The presence of a snow cover appears to have kept the daytime high temperatures from 10 to 15 degrees F cooler than the non snow covered area to the west and east of this location.

December 26, 2013 finds Lincoln, NE and Omaha, NE snow free

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