The Month of May 1999 saw near normal temperatures and above normal rainfall. It stands in sharp contrast to May 1998, which equalled the record for the warmest May on record and established a record for the driest May. May 1999 was 6.7 degrees cooler, and 6.96 inches wetter.
The May 1999 weather pattern was rather typical for the late Spring, with upper air low pressure over the Western United States for much of the month and disturbances ejecting from that feature and triggering rainfall in the Tropical Maritime air mass, in place over the region for much of the month.
Rainfall through May 31, 1999 was 5.80 inches greater this year than last. Precipitation over the past twelve months is about 126 percent of normal. May 1998 was in the midst of a dry period, which lasted from mid-March through early August. It also marked the beginning of a very hot Summer season.
The thirty-day outlook had called for above normal temperatures and near normal precipitation. The first week in May saw temperatures two degrees below normal and precipitation about 300 percent of normal. A powerful storm system crossed the Southern Plains between the 3rd and 5th. It caused numerous tornadoes, resulting in 47 deaths including one in Titus County.
In Tyler, several severe thunderstorms moved through the area on the afternoon of the 4th, producing mostly heavy rainfall. There were reports of strong winds from the southern part of Smith County about 2 p.m., and from the northern part of the county four hours later. Small hail fell on the 5th briefly as an incipient squall line was over the area.
On the 5th, dust down to about 2,000 feet above ground level mixed with dense fog at early morning and with light rain later in the day.
A strong cold front moved through on the 5th, lowering temperatures through the 7th to below normal levels. The second week in May saw near normal temperatures and near normal rainfall. Tropical Maritime air was over the area between the 8th and 12th, with a weak Polar Maritime air mass replacing it on the 12th.
The week's rain came as a slow-moving migratory storm crossed on the 10th-12th.
Tropical Maritime air returned with the passage of a warm front on the 14th.
Temperatures during the last half of the month were about a degree above normal and rainfall slightly below normal. A slow-moving storm crossed late in the month, bringing rainfall often between the 25th and 31st, though Tropical Maritime air was over the region during that time and for most of the remainder of the month's latter half. At month's end, an upper air high was trying to establish itself over the region.
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
May 1999, RECORDS AND SUMMARY: