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December 2009 - Report and Summary

by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer

The year 2009 began with normal temperatures and below normal rainfall, saw above normal temperatures for the first half of the Summer with continuing dry conditions, and then turned very wet and cool during the final five months of the year.

For the third consecutive year, Tyler measured above normal precipitation following the very dry years of 2005 and 2006.

October 2009 was the second wettest October on record, with 13.69 inches. The highest temperature in 2009 was 101 on July 2 and 16, while the year's lowest reading was 20 on December 5. The temperature exceeded 100 on five days below the normal of eight, and exceeded 90 on 83 days below normal. The accumulation of cooling degree days was 94.7 percent of normal. The 2009 warm season was 148 days, compared with a normal of 146 days. It began May 13, and ended October 8 the first and last occurrences of a 90-degree maximum temperature. The 2008 warm season was 125 days.

The 2009 growing season was near normal length at 248 days, beginning and ending late. The last freeze of the 2008-2009 cool season was on March 30, while the first freeze of the 2009-2010 cool season was on December 3. The 2008 growing season was 235 days. The temperature fell below freezing on 46 days during the 2008-2009 cool season the second consecutive year that these numbers were above normal.

The percentage of normal heating degree-days during the 2008-2009 cool season was 114.0. The temperature extremes in 2008 were 103 and 22. The 2009 average temperature was 65.2 deg., 0.1 deg. Cooler than 2008, and the coolest year since 1993. 2009 was 1.4 deg. Cooler than the yearly normal for the 1971-2000 standard climatic period. December 2009 was much cooler than normal with near normal precipitation. The 43.0 deg. Average temperature was 6.1 deg. Below normal, and the coolest December since 2000 when the average was 40.6 deg. Compared with December 2008, the month was 4.7 deg. Cooler and 3.26 inches wetter. Yearly rainfall was 4.01 inches less in 2009 than in 2008. The thirty-day outlook had called for below normal temperatures and above normal precipitation.

The week November 29-December 5 saw temperatures about 4 degrees below normal, and rainfall about 125 percent of normal. Arctic cold fronts crossed on the 30th, 2nd, and 4th, with rain accompanying the first two. The first freeze in Tyler came on the morning of the 3rd, ending the growing season at 248 days. A hard freeze came on the morning of the 5th, with sub-freezing temperatures for nearly 16 hours and the low of 20 the coldest since February 2007. A trace of snow fell in the city on the afternoon of the 4th. The week's average temperature was 48.0, and precipitation was 1.53 inches. This was 4.9 deg. Colder than the previous week. Compared with the same week in 2008, the week was 3.3 deg. Warmer, and rain did not fall in 2008.

The cool-down continued during the week of the 6th-12th, with temperatures about 9 degrees below normal, and rainfall near of normal. Warmer air overrunning a shallow cold air layer caused rain on the 6th, 8th, and 12th. Another Arctic front arrived on the 9th, with a slow moderation in temperatures ahead of that system. Temperatures began moderating again late in the week. The week's average temperature was 41.4 deg., which was 6.6 deg. Colder than the previous week. Rainfall was 0.99 inch. In 2008, the same week was 4.4 deg. Warmer, and 0.41 inch drier.

The week December 13-19 saw temperatures about 2 degrees below normal, and rainfall about 5 percent of normal. A warming trend began the week, with temperatures falling again after cold fronts on the 16th and 19th. Light showers accompanied the first front. The week's average temperature was 46.7 deg., and rainfall was 0.08 inch. This was 5.3 deg. Warmer than the previous week. Compared with the same week in 2008, the week was 5.7 deg. Cooler, and precipitation was identical in the two years.

The week December 20-26 saw near normal temperatures and precipitation about 200 percent of normal. The near normal average temperature concealed extremes a cold start, a warm mid-week, and a cold end of the week. A powerful storm system crossed on the 23rd, bringing widespread rainfall, with severe weather. Tornadoes caused damage in Longview and Lufkin. A trace of light snow fell on the afternoon of the 24th behind the strong cold front which crossed that morning. The week's average temperature was 46.7 deg., identical with the previous week, and rainfall was 2.39 inches. Compared with the same week in 2008, the week was 1.5 deg. Cooler, and 1.67 inches wetter.

The final five days of the month saw cold temperatures each day, with strong cold fronts on the 27th and 31st. An upper air disturbance crossed on the 29th and 30th, bringing light rain to most of the region.

The reporting period for temperatures and phenomenon on each day is for the twenty-four hours ending at midnight hours GMT--6 p.m. CST and 7 p.m. CDT. The reporting period for precipitation is for the twenty-four hours ending at noon GMT--6 a.m. CST and 7 a.m. CDT. All times are given using the twenty-four hour clock, and are expressed in Greenwich Mean Time.

Observations are from NWS Station 41/9207/4 in Tyler, Texas. The term "normal" refers to averages from the standard climatic period 1971-2000.




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