December ushers in harsher weather, shorter days Published Dec. 1, 2010 By Jim Robinson Meteorological Technician, 27th Special Operations Support Squadron CANNON AIR FORCE BASE, N.M. -- December generally represents the transition from late autumn into early winter, and features cold air outbreaks of increasing strength on the southern high plains. Both rainfall and snowfall occur at Cannon, sometimes at the same time. A typically late autumnal and early winter pattern of widespread synoptic influence, characterized by approximately five or six strong cold fronts during the month, continues to strengthen. The strong cold fronts often feature temperature drops of 25 to 35 degrees Fahrenheit in a couple hours and wind speeds approaching 60 mph. The highest recorded wind gust in December is slightly more than 77 mph. The amount of potentially available sunlight reaches its annual minimum on Dec. 21 or 22, depending on the year. This date is known as the winter solstice, and is the shortest day (and longest night) of the year for locations north of the earth's equator. The winter solstice marks the beginning of astronomical winter in the northern hemisphere. By way of contrast, the northern hemispheric meteorological winter covers the period from Dec. 1 through Feb. 28; thus meteorological winter begins before astronomical winter and ends before astrological winter as well. In the northern hemisphere, the 2010 winter solstice occurs on Dec. 21, at 4:38 p.m. Mountain Standard Time. The amount of potentially available sunlight reaches its annual minimum around this date. More specifically, at Cannon the amount of potential daylight varies between 9 hours, 51 minutes and 9 hours, 52 minutes, Dec. 15 -27. It is interesting to note that at Clovis the time of latest sunrise is 7 a.m., and occurs daily between Jan. 2 - 12, whereas the time of earliest sunset is 4:42 p.m., and occurs each day between Dec.1 - 8. Thus it can be seen that neither the time of latest sunrise nor the time of earliest sunset actually occurs on the winter solstice. The average December temperature is 39 degrees, ranging from 42 degrees on Dec. 1 to 37 degrees on Dec. 31. The average maximum temperature for the month is 52 degrees, with the average daily maximum temperature dropping from 55 degrees on the first day of the month to 50 degrees by Dec. 31. The average minimum temperature for the month is 26 degrees, with the average daily minimum temperature cooling from 29 degrees on Dec. 1 to 24 degrees on Dec. 31. The highest recorded monthly temperature was 91, on Dec. 25, 1919. The lowest temperature recorded was 9 below zero, on Dec. 25, 1918. Daily record high temperatures are in the 70s for every day except the 25. Daily record low temperatures generally range from the single digits above zero, to the single digits below zero. Cannon averages .6 inch of precipitation during December. This is slightly more than the .5 inch monthly averages of both November and January. Cannon averages three inches of snowfall for the month. The highest recorded monthly snowfall was17.1 inches. December averages two days with measurable (defined as being .1 inch or more) amounts of snowfall. December represents the transition from late autumn into early winter, and frequently features highly changeable weather on a day-to-day basis. The long cooling trend established in late summer and early autumn continues through December, as a manifestation of the low sun angle and relatively low amount of potentially available sunlight.