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August 1999 - Report and Summary

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

The month of August 1999 was much warmer and much drier than normal. In fact, it is the second driest August in National Weather Service records. The record for a dry August is 1913, when 0.10 inch of rain fell.

August 1999 replaces August 1910 as the second driest August. In August 1910, 0.20 inch of rain fell.

For most of the month, a stubborn upper air high pressure ridge held in place over the Southern United States. This typical summertime feature was responsible for the high temperatures and lack of rainfall. Indeed, rain fell on only one day during the month.

August 1999 was 0.2 deg. warmer than August 1998, and 4.56 inches drier. August 1998 marked the end of the rainfall deficit of the Spring through mid-Summer 1998. Rainfall through August 31 is 7.37 inches greater this year than last. Rainfall over the past twelve months is 126 percent of normal. The thirty-day outlook had called for near normal temperatures and near normal precipitation.

The first week in August saw near normal temperatures and rainfall about one-fourth normal. Upper air and surface high pressure controlled the region's weather for most of the week. A weak cold front moved through the area on the 3rd, causing the week's only rainfall and lowering humidities for a couple of days. Excessive ozone accumulations were observed late in the week, with the air quality unhealthy on the 5th and 6th.

The second week in August saw temperatures about four degrees above normal and no rainfall. Upper air high pressure oscillated in an east-west direction between the Mississippi River Valley to the Southern Rockies. This feature dominated the region's weather, and caused high daytime temperatures. The humid air held nighttime temperatures up. The combination of heat and humidity required heat advisories for the area for many days during the week. In addition, the stable air mass and ample sunlight continued the poor air quality, and ozone advisories were displayed as well. High temperatures were aided by the drying of vegetation and topsoils, caused the the lack of significant rainfall since late-July.

The third week in August saw temperatures four degrees above normal, and there was no rainfall. High pressure aloft was the dominant weather feature. This was responsible for the high temperatures and lack of rain. Stagnant air caused the issuance of ozone advisories by the Texas Natural Resource Conservation Commission for most of the week. Air quality was moderate to unhealthy for most of the week, as well.

The final ten days in August saw temperatures four degrees above normal, and no rainfall. Upper air high pressure continued in control of the region's weather. This suppressed precipitation, and held up temperatures. Ozone advisories continued through the period.

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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