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November 1999 - Report and Summary

The month of November 1999 was warmer and much drier than normal. It was, however, far from the warmest November on record for the Tyler station. That distinction goes to November 1902 when the temperature averaged 64.9 deg., with 1913 in second place with an average of 63.8 deg. Nor was it anywhere close to the driest November on record. That honor belongs to November 1912 when but 0.07 inch was measured, with 1955 receiving 0.25 inch. The main culprit in the warm and dry weather was an upper air high pressure ridge, which re-established itself over Western North America about the 3rd, and persisted for nearly three weeks. That phenomenon was, in turn, the result of "La Nina"- -cool sea-surface temperatures in the East Central Equatorial Pacific Ocean. Dry weather has persisted in East Texas since early- Summer. Between July 3 and November 30, Tyler received 4.97 inches of rainfall. This is 31.8 percent of normal for that period.

November 1999 was 2.4 deg. warmer and 6.15 inches drier than November 1998. Year-to-date precipitation through November 30 was 10.03 inch less in 1999 than in 1998. Precipitation over the past twelve months has been 43.70 inches. This is about 97 percent of normal. The thirty-day outlook had called for near normal temperatures and near normal precipitation.

The first week in the month saw near normal temperatures and no precipitation. The first freeze of the season occurred on the 3rd-- about twelve days early. A modified Polar Continental air mass was over the region between the 1st and 3rd, which held readings well below normal. Readings rose to well above normal on the 4th, when return flow around the west side of the surface high pressure and an upper air ridge sent the thermometer up. The upper air ridge also kept storm features away, resulting in the dry conditions.

The second week of November brought temperatures eight degrees above normal, and no rainfall. Upper air high pressure persisted over Central North America. This steered storm features away from the region. The air mass was quite dry through the week. Low humidities combined with subsiding air beneath the upper air ridge to send daytime temperatures to around 80 just about every afternoon during the week. There were weak cold fronts, but they had little effect on temperatures.

The third week in November saw temperatures seven degrees above normal and no rainfall. Upper atmospheric high pressure was over Central North America. This continued to keep storm features and significant cool air masses away from the area. With a dry air mass in place, there was a large range between nighttime low and daytime high readings. The final nine days of the month saw temperatures lower somewhat, and the month's only rainfall. Temperatures were about two degrees above normal, and rainfall was about 80 percent of normal. The upper air flow pattern became more progressive, as upper atmospheric high pressure over the Western United States was replaced for much of the week by upper air low pressure over Western and Central North America. Disturbances rotating about the base of this low pulled cold fronts through, which brought two rain events and outbreaks of cooler air.

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.

November 1999



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