by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer
The month of December 2002 saw near normal temperatures and above normal precipitation. For most of the month, the southern branch of the jet stream was active. This is typical in El Nino years. Frequent storms crossed in this upper air flow, bringing rain. The northern branch of the jet for most of the month was displaced to the north over Southern Canada. this kept Arctic air from reaching the region. The month was 1.9 deg. cooler than December 2001, and 0.57 inch wetter. Year-to-date rainfall through December 31 was 12.07 inch less in 2002 than in 2001. The year-s lowest temperature was 17 on the morning of January 3, while the highest temperature was 99 on July 24. 2002 was the second year running without the mercury reaching 100 in Tyler. The thirty-day outlook for December 2002 had called for near normal temperatures and above normal precipitation.
The week December 1-7 was seven degrees cooler than normal, and rainfall was about 150 percent of normal. An upper air low pressure feature crossed on the 3rd. This occurred at the same time as a cold air mass moved into the area. The result was cold temperatures and general rains on the 3rd of between one and four inches. Temperatures continued running well below normal after the 3rd, as a Polar Continental air mass settled over the region. The week's average temperature was 44.5 deg., and rainfall totalled 1.58 inches. This was 2.9 deg. cooler than the previous week. Compared with the same week in 2001, the week was 18.9 deg. cooler, and 0.63 inch wetter.
The week December 8-14 was four degrees cooler than normal, and rainfall was about 200 percent of normal. Winds aloft for most of the week were southwesterly as the southern branch of the jet stream again became active. This caused two storm features to cross the region--both of which caused general rains. The first was on the 8th/9th, and the second was on the 12th. Rains with the first storm averaged about an inch, with like amounts with the second storm. That one caused rains of as much as two inches below a Lufkin-Shreveport line, and only a few hundredths of an inch above a Corsicana-Greenville line.
A Polar Maritime air mass moved into the region on the night of the 12th, which brought the week's only sunny day on the 14th.The week's average temperature was 46.2 deg., and rainfall totaled 1.65 inches. This was 1.7 deg. warmer than the previous week. Compared with the same week in 2001, the week was 1.0 deg. cooler and 0.38 inch drier.
The week December 15-21 saw temperatures nine degrees warmer than normal, and rainfall about five percent of normal. A sharp warming trend began on the 15th and continued through the 18th. Record warm temperatures were observed on the 18th. This was caused by upper air high pressure, and a Tropical Maritime air mass moving into the area ahead of a cold front and storm system on the 19th. The southern branch of the jet stream remained active. The storm which crossed the night of the 18th-19th caused severe weather in the counties to the south and east of Tyler, and rains of from two to four inches there. From Tyler to the north and west, amounts were only a few hundredths of an inch.
The week was also windy, with fresh to strong south winds blowing on the 17th and 18th, and again on the 21st ahead of yet another storm. The week's average temperature was 58.0 deg., and rainfall totalled 0.05 inch in Tyler. This was 11.8 deg. warmer than the previous week. Compared with the same week in 2001, the week was 7.0 deg. warmer, and 3.10 inches drier.
The week December 22-28 was six degrees cooler than normal, and rainfall was about 150 percent of normal. A strong upper air storm crossed on the 23rd. It brought general rain, and severe weather. This storm also produced a broad band of heavy snow from the mountains of Arizona northeastward into New England. Rainfall amounts in East Texas ranged from half an inch over the northwestern counties to as much as five inches over the southeastern. Some flooding occurred in the southeast. There were numerous reports of severe weather on the afternoon and night of the 23rd from Lufkin northeastward into Louisiana. The departing storm was followed by a Polar Maritime air mass.
Temperatures were lowered further by a northwest wind which blew on the 24th and 25th. This air came off the snowpack, which was over Northwest Texas and Oklahoma. by late-week, winds became westerly to southwesterly, and upper air high pressure was present. This allowed for warmer daytime temperatures, though nighttime lows remained cold because of good conditions for radiational cooling. The week's average temperature was 42.4 deg., which was 15.6 deg. cooler than the previous week. Rainfall totaled 1.69 inches. Compared with the same week in 2001, the week was 1.1 deg. cooler, and 1.51 in. wetter.
Another strong storm crossed during the final three days of the month, bringing widespread heavy rains and severe weather on the afternoon and evening of the 30th.
On the 31st, strong high pressure built into the area, lowering temperatures and resulting in fresh to strong northwesterly winds. Small hail fell in Tyler on the late-afternoon of the 30th.
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.
MX MN OBS PCPN REMARKS
DECEMBER 2002, RECORDS AND SUMMARY: