Updraft: December 7, 2011 Archive

Sunset as early as it gets, but still losing daylight

Posted at 4:10 PM on December 7, 2011 by Craig Edwards
Filed under: Snow cover, Winter 2011-12

The sun is setting low on the southwest horizon these chilly winter afternoons. In the Twin Cities the earliest sunset of 432PM commenced on December 3rd. On the 17th of December you will barely notice the sunset a minute later at 433PM.

Due to the tilt of the earth on its axis and the elliptical trip around the sun, we continue to lose daylight in the morning hours. Sunrise on this date is 737AM in Minneapolis. The latest sunrise will be 751AM beginning December 30th and continuing until January 6th. The shortest daylight occurs on the solstice(1130PM) on December 21st.

Did you also happen to notice the micro-climate in the photo at the base of the evergreen tree? Sunshine captured by the green pine needles reflects back the heat and allows for melting of the snow.

This absorption of heat is evident in the late winter and spring on a larger scale in the Superior National Forest. Sunshine captured by the trees can efficiently warm the lower atmosphere more than the sun's rays reflecting off the snow covered prairie landscape.

Some locations in Minnesota saw the thermometer climb to near 32 degrees this afternoon. I'm thinking part of this nice rise in temperatures is due to the lack of snow cover in western Minnesota as well as in the upstream source region of cold Canadian air.

A colleague with the National Weather Service was in Winnipeg last week and noted the sparse snow cover when flying over the region. At this time of the season a thick snow cover keeps the air mass icy as it travels the mid latitudes. The magnitude of the cold can be modified if moving over bare soil.

A brisk west to northwest wind on Thursday afternoon, particularly in northern Minnesota, will create some numbing wind chill readings. As the winds diminish on Thursday night look for temperatures to drop steadily to below zero in many locations.

Milder temperatures for the season are expected Sunday and Monday.

Precipitation was slowing air and auto travel on the East Coast. Heavy rain today has drenched the landscape from Washington D.C., through Baltimore to New York City.

A snap shot of the radar from late afternoon in theD.C. area.

I am not spying a significant snow in the upper Midwest on the most recent computer models, but that has been known to change. Perhaps Paul will have been luck stirring up some snow when he returns.
CE