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December 2000 - Report and Summary

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

The month of December 2000 was colder and wetter than normal. A persistent upper air high pressure, amplified north/south over the Western United States, kept a steady flow of cold air into the region. Three major winter weather events occurred during the month: an ice storm on the 13th, the Great Christmas Ice Storm of 2000 on the 25th-26th, and snow on the 31st.

The storm of the 13th caused major power failures in the Tyler area; that of the 25th-26th brought failures to the extreme northeastern part of the state and extending into Oklahoma and Arkansas, while that of the 31st had little adverse impact--since it was snow.

December 2000 is the fifth coldest December on record. December 1983 is the coldest with an average temperature of 37.9 deg, while December 1963 saw a 38.8 average. December 1909 had an average of 40.2 deg., and December 1905 of 40.5 deg. The previous fifth coldest December was in 1989, when the temperature averaged 41.7 deg. Weather records in Tyler date to 1896.

A procession of upper air storms, interacting with surface disturbances forming in the Western Gulf of Mexico along the remnants of cold fronts, caused frequent occurrences of precipitation. Though December 2000 was a wet month, there are several wetter. December 1960 saw 11.62 inches, while 10.01 inches of precipitation fell in 1987.

December 2000 was 9.5 degrees colder than December 1999, and 3.41 inches wetter. The year 2000 saw a very hot Summer, with record high temperatures for so late in the season and for the month of September. There was also a protracted dry spell, which began in late- June and persisted through mid-October. The Spring and mid-Fall through early-Winter were very wet. Total precipitation was 57.04 inches, compared with 41.70 inches through 1999.

Rainfall for the twelve months ending December 31 was 126.1 percent of normal. The thirty-day outlook had called for above normal temperatures and above normal precipitation for December 2000.

The week November 26-December 2 was one degree cooler than normal, and rainfall was about one-fourth normal. A weak storm crossed on the 29th, bringing light rain to the central counties, none to the north, and amounts of about an inch to the south. A chilly high pressure ridge was over the area early in the week, with cold fronts on the 29th and 1st. The front of the 29th brought only slight cooling, while that of the 1st brought significant cooling. The week December 3-9 saw temperatures six degrees cooler than normal and no rainfall. Upper air high pressure was over the Western United "states throughout the week. This prevented the return of moist air from the Gulf of Mexico, and also kept significant upper air disturbances from crossing. At the same time, it funneled cool air southward behind weak fronts. There were no Arctic air intrusions into the region during the week.

That changed the following week, when Arctic air masses entered the region on the 12th and 16th.

The week December 10-16 saw temperatures eight degrees colder than normal, and precipitation about 225 percent of normal. Most of the precipitation occurred on the morning of the 13th, when a major ice storm struck the region. This caused widespread power outages, which resulted in general school closings. Little ice accumulated on road surfaces, though there was considerable accumulation on vegetation and power lines. Tyler experienced a water emergency, when power to the Golden Road Filtration Plant was down for about 14 hours. Electric customers sustained power outages ranging from a few hours to several days.

On the 16th, winds blew in the strong to high range as the second Arctic air mass of the week plunged into the region. A pressure rise of 6.4 mbs. was noted in three hours during the morning of the 16th just after frontal passage. Three significant upper air storms crossed the region during the week: on the 13th, 14th, and 15th. Each generated precipitation. Amounts were enhanced on the 13th by a surface disturbance in the Western Gulf of Mexico. Arctic air continued in place over the region for all of the week of the 17-23rd except for a few hours on the 20th. As a result, temperatures were eight degrees colder than normal, and rainfall was about five percent of normal.

Two blustery cold fronts crossed the region--on the 18th and 20th. Strong southerly winds preceded each front, and strong northwesterly winds followed them. The only precipitation occurred on the 18th with the first front, though there were trace amounts with the second. Trace amounts also occurred on the 23rd as a warm front moved northward towards the region.

The week December 24-30 brought another disastrous ice storm. The Great Christmas Ice Storm of 2000 brought ice accumulations of more than two inches to the counties along Red River, and from there to the north and east. At one point, 590,000 customers were without electric power in Texas, Oklahoma, and Arkansas. To the south in the Tyler area, the storm brought moderate to heavy rainfall, particularly on the 25th and 26th. Rainfall amounts averaged between three and five inches. The rain fell while a shallow Arctic air mass was in place, continuing the trend of much below normal temperatures. The upper air pattern of amplified high pressure to the west and low pressure to the east, which set up in early-November, continued.

Surprisingly, no daily climate records were set during the week in Tyler. There were both colder and wetter events: 1983 was colder, and 1944 and 1987 wetter. The Christmas Day ice storm was, however, one of the most severe on record. Parts of South Arkansas had been seriously affected by the December 13th storm, as well. Overcast was reported in Tyler between 8 p.m. on the 22nd and 1 a.m. on the 29th--149 consecutive hours.

During the entire week, temperatures held within a range of less than 20 degrees--25 on the 30th to 44 on the 28th. During the storm, the range was within about three degrees in the middle 30s. A strong surface high built in on the 28th as the upper air storm moved off to the east. This permitted clearing, and brought in drier air. Conditions were windy on the 28th and 29th, with wind chill equivalent values during the daylight hours in the teens on the 28th and 20s on the 29th.

Temperatures during the week averaged eleven degrees colder than normal, and precipitation was about 500 percent of normal. With only hours left, the decade 1991-2000 saw its first significant snowfall on the afternoon of the 31st when a fast- moving storm crossed. 1.9 inches of snow was on the ground in Tyler at 6 p.m. Amounts of one to three inches were widespread across East Texas. Visibilities lowered to one-fourth mile or less during the afternoon in snow and freezing fog.

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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