The month of October 1999 saw near normal temperatures and below normal rainfall. The continued presence of La Nina (unusually cold sea- surface temperatures in the East Central Equatorial Pacific) was the most significant weather factor during the month. Upper air high pressure was to the west of the region during much of the month. This kept storm features well away from the area, resulting in the very dry conditions.
October 1999 was 3.5 degrees cooler than October 1998, and 7.31 inches drier. Year-to-date rainfall is 2.87 inches less this year than last through October 31st. Rainfall during the past twelve months is 49.86 inches, about 109 percent of normal. The thirty-day outlook for October 1999 had called for above normal temperatures and near normal precipitation. The first week in the month saw temperatures three degrees below normal and no rainfall. A cold front moved into the area on the 3rd. This lowered temperatures through the 7th, when warmer air returned. At upper levels, high pressure was in control. The generalized dry weather, which had been present since early-July, persisted in the region. Significant rainfall occurred in the area on the 8th, though only a trace occurred in Tyler.
The second week in October saw temperatures five degrees warmer than normal and no rainfall. Surface and upper air high pressure remained in control of the area's weather. The two weak cold fronts failed to penetrate the region. The air mass was dry for most of the week, with moisture increasing on the 14th.
The third week in October marked the positioning of upper air high pressure, oriented north/south, over Western North America. The result was a significant change in the area's temperature pattern. Readings were four degrees cooler than normal, and rainfall was about one-fourth normal. Cold fronts passed through on the 17th and 19th, with light overrunning rainfall on the 17th and 19th. Temperatures warmed late in the week before the arrival of another front on the 22nd.
The final ten days of the month saw near normal temperatures and rainfall about 50 percent of normal. A cool and dry air mass was over the region between the 22nd and 27t8th, with moist air returning the 29th. On the 30th, a closed-off low aloft over West Texas combined with another cold front to produce widespread rainfall. In fact, this was the first general and significant rain in the area since July 7th, with amounts averaging between one-half and two inches.
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
October 1999, RECORDS AND SUMMARY: