The average May temperature was 76.1 degrees, 0.3 degrees below normal. The average high was 84.9, and the average low was 67.4. Heating degree days 2 and cooling degree days 353. The highest temperature reached 104 on the 31st. This was a new record high for the entire month of May for San Antonio, also a daily record high for May 31st. The lowest was 49 on the 3rd. Highest wind gust was 39 mph from the west, northwest with thunderstorms on the 1st. Rainfall was 1.80 inches, 2.92 inches below normal. Rainfall from January 1st to May 31st, 2004... 13.22 inches or 0.60 inches above normal.

Weather patterns changed some in May 2004, from the wet winter and early Spring of 2004 pattern to a little drier conditions. Stormy periods showed up several times during the month. Storms came May 1st, May 7th and 8th, the week of May 10th to 14th, on May 27th in Val Verde and Kinney Counties, including Del Rio, and on May 31st from near Austin to near New Braunfels. May 2004 showed considerable variability in temperatures for May, beginning much cooler than normal and ended up much warmer than normal.

May 1st of 2004 began with thunderstorms, as a line of thunderstorms moved across the area in the early morning hours. The storms moved east of South Central Texas by the afternoon and evening. A brief spell of quiet weather from May 2nd to 6th, came to an end Friday, May 7th, when thunderstorms returned. Scattered showers and thunderstorms lingered over the area Saturday May 8th. A calm day followed Sunday the 9th. The week of May 10th to May 14th brought another round of showers and thunderstorms to the area. On Thursday morning May 13th, very heavy rains and strong thunderstorms affected the east part of South Central Texas. Calmer weather followed on the weekend of the 15th and 16th.

From Monday, May 17th to Saturday May 22nd, isolated early morning showers came to the east half of South Central Texas with mostly light rain amounts. Afternoons slowly warmed up. This was the week that some locations begin to get close to or reach the 90 Degree Mark. The first 90 degree day at many locations over South Central Texas began with a slow start in 2004. Higher than normal soil moisture associated with winter and early spring rains, more mostly cloudy days than usual, and a few late season strong cold fronts in the Spring, helped to delay the onset of the 1st 90 Degree Day this year. For Del Rio, the latest first 90 Degree Day of record came May 22, 2004. The previous record latest first 90 Degree Day at Del Rio was May 18, 1931, when the high was 90. A few days in March of 2004 saw highs at most locations rise to the 80s, except for Uvalde, where it was 90 on March 7, 2004. Uvalde was the first place in South Central Texas to see a 90 Degree Day in 2004.

Despite the fact that it was slow going to get the first 90 Degree Days this year, the warming trend increased and only accelerated in strength the last 2 days of May 2004. From Monday May 24th to Saturday May 29th, more 90 Degree Days came. On Thursday, May 27th, severe thunderstorms and isolated tornadoes came to Del Rio and parts of Val Verde and Kinney Country in the late afternoon and early evening of May 27th. Just one year earlier Del Rio had 6.53 inches of rain on the 27th, and 7 years earlier on May 27, 1997, the Jarrel Tornado occurred. Thunderstorms entered Val Verde County from the west around 445 pm on May 27th. As the storms moved east and southeast, they gathered considerable strength, becoming severe thunderstorms, with isolated tornadoes. Winds gusted to 73 mph from severe thunderstorms at Del Rio International Airport at 700 pm. Winds at Laughlin AFB gusted to 69 mph at 718 pm. Large hail was reported in Val Verde County, with hail sizes varying from around 1.75 inches to 4.25 inches. Isolated tornadoes were observed over Val Verde County from 7 miles West, Northwest of Del Rio to the Del Rio area and also at Laughlin AFB east of Del Rio after 7 pm, and in Kinney County west, northwest of Brackettville around 730 pm.

On the last 2 days of May the warming trend accelerated markedly. As a powerful storm system moved from the Great Plains to the Mississippi Valley, as subtropical high aloft begin to build over the area, while at the surface much warmer air moved into the area from the west or from West Texas and the Chihuahua Desert Regions of North America to the west. On Sunday May 30th, afternoon highs rose to 106 at Del Rio and Langtry. The high of 106 at Del Rio the 30th tied the record high, previously set in 1979. These were the first 100 degree days for the year, occurring for Del Rio just 8 days after reaching the first 90 Degree Day. At Carrizo Springs the high rose to 102. Isolated showers and thunderstorms in the early morning moved from Llano and Burnet Counties to the Austin Area.

On Memorial Day, May 31st, it was not only hot, it also got stormy from the Austin to New Braunfels. In the late afternoon, with strong heating and very moist air over the eastern half of South Central Texas, widely scattered thunderstorms developed from west of Austin to north and northeast of San Antonio. As these thunderstorms grew in the late afternoon, some of them exploded to become severe thunderstorms from the Austin Area to the New Braunfels Area. Strong winds and large hail was reported. Hail sizes in the Austin Area were reported around 1 inch to 1.75 inches. In the New Braunfels Area 0.75 to 0.88 inch hail was reported. Winds gusted to 42 mph at New Braunfels Municipal Airport at 453 pm and 0.83 inches of rain fell in around 1 hour and 19 minutes. Frequent dangerous lightning accompanied the thunderstorms.

Daytime highs on the 31st set records at several locations. The high of 104 at San Antonio, was a record high for the entire Month of May, and also a daily record high for May 31st. It was also the first 100 degree day in San Antonio, coming only 4 days after the first 90 Degree Day on May 27. The high of 107 at Del Rio was a daily record high for May 31st at Del Rio, and 2 degrees short of the May Monthly High set May 24, 2000. At Austin Mabry the high of 100 was the first 100 Degree Day high for the year, and came only 6 days after the first 90 Degree Day on May 25. The 100 degree high at Austin Mabry was also a record daily high for the Austin City Climate location for May 31st. At Austin Bergstrom the highs was 99, one degree short of the record daily May 31st high of 100 on May 31, 1998. The hot, summer like temperatures, and extreme records on May 31st, came after prolonged periods of cooler than normal weather that affected the area in the early and mid part of May.

May 2004 could be described as a May that brought some extremes from calm weather to stormy weather, and extremes in temperature for May. Even though May 31st was like a hot summer day, Summer will officially begin this year on Sunday, June 20th at 757 PM CDT, and officially ends Wednesday, September 22, 2004 at 1130 AM CDT, when Fall 2004 officially begins.