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3rd Snowiest December – Dec 2006

December 2006 will go down as the third snowiest December in Denver history with a total of 29.4”!  This ranks behind 1913 with 57.4” which is the most snow ever observed in one month and just behind 1973 with 30.8”.  December of 1982 will now be pushed down to the fourth snowiest December with 27.1”.  Nearly all of the snow came late in the month.  Up to the 19th of December there was only one minor storm for the month and a total of 0.5” observed at DIA.  In the following 10 days nearly two and a half feet of snow fell at the official reporting site with many areas receiving much more snow than that.

Most of the snow came in two storm systems.  The first storm was the strongest with the most intense snowfall rates and highest winds creating blizzard conditions.  This storm dumped 20.7” at DIA and is responsible for nearly 70% of the total monthly accumulation.  This storm ranked 7th all time for largest snow storms in Denver history and is the second largest December snowstorm behind the Blizzard of 1982 when 23.8” fell.

After a short break in the action a quick moving storm system brought some snow showers over Christmas with just minor accumulations.  Not much melting occurred since the first major storm and snow was still blanketing the ground as the second system began entering the state.

It is not unusual to have back to back storms, but is a somewhat unusual to have back to back storms of this magnitude in December and the lack of melting between storms.  As is most often the case for lower elevations along the front range there is a melting period before the next system moves into the area.  In this case conditions were a little different.  The shortest day of the year is December 22nd and the suns angle is at its lowest point.  With the lack of direct sunlight snow becomes more difficult to melt and is partly responsible for the lack of melting between the two storms.  Another reason for melting between storm systems is that when a storm approaches south/southwesterly winds ahead of the system import warmer air form the south as flow around low pressure is counterclockwise.  These south/southwest winds are down slope from the mountains and the air is warmed via compression as the air moves off the mountains adding additional warming to the air and melting of the snow.  This did not happen with the incoming second system as snow on the ground kept a low level inversion present not allowing the warmer air to mix completely to the surface keeping a cool air mass in place over northeastern Colorado.  December is also a month where cold air usually dominates saving the big snow storms for fall and spring when there is a larger clash between warm and cold air masses making the big December snows quite rare.

This second major storm system was touted by local media as, “Round Two”.  In reality this storm was a fraction of the intensity of the first storm and was never positioned in a prime location for back to back top ten storms for northeastern Colorado.  This storm ended up depositing snow amounts about half the total of the previous system in most areas.  Southeastern Colorado and northern New Mexico was favored for “Round Two” and record breaking snowfall amounts fell there.  DIA reported 8.0” with this system which is impressive, but nowhere near top ten status.

With the additional snow for the season DIA has reported 43.6”.  Normal snowfall up to the first of January is 25.6”, as of January 1st, Denver is 18.0” above average to this point and already 70% of the seasonal total of 61.7” which usually ends in May.  At this point it may be safe to say that this snow season will at least be average and more than likely well above average as historically some of the snowiest months are still to come!