The month of May 2009 was slightly cooler and much drier than normal. The cool temperatures were the result of northwest winds aloft down the Plains for much of the month. The dry conditions resulted from dry air in the middle atmosphere which dissipated several lines of thunderstorms trying to move in from the northwest. Compared with May 2008, the month was 1.0 deg. Cooler, and 4.64 inches drier. Year-to-date rainfall through month's end was 6.63 inches less in 2009 than in 2008. The thirty-day outlook had called for above normal temperatures and near normal precipitation. The week April 26-May 2 saw temperatures about 3 degrees above normal, and rainfall about one-half normal. Storm systems crossed on the 28th and 30th. There were torrential rains of up to 6.0 inches along Red River, though rainfall in the immediate Tyler area was around one-half inch.
The week began and ended very warm, with near normal temperatures at mid-week. The week's average temperature was 72.0 deg., which was 2.4 deg. Warmer than the previous week. Rainfall was 0.45 inch. Compared with the same week in 2008, the week was 7.3 deg. Warmer, and 0.35 inch drier.
The week May 3-9 saw temperatures about a degree above normal, and rainfall about 75 percent of normal. A storm system crossed on the 3rd, with a weak feature crossing on the 6th. The first brought most of the week's rain. The system of the 6th brought severe weather to the northern counties, with the squall line dissipating along the IH-20 Corridor as it ran into a layer of warm and dry air in the middle atmosphere. Tropical maritime air was over the region for most of the week. The week's average temperature was 73.0, which was 1.0 deg. Warmer than the previous. Rainfall was 0.77 inch. Compared with the same week in 2008, the week was 2.5 deg. Warmer and 0.25 inch drier.
The week May 10-16 also saw temperatures about a degree above normal, with rainfall about 20 percent of normal. As happened with the squall line of the 6th, thunderstorm lines moving in from the north also weakened significantly on the 11th and 14th because of the same warm air capping layer. Tropical Maritime air under surface and upper air high pressure continued to be present in the region. The week's average temperature was 74.0, and precipitation was 0.20 inch. The week was 7.3 deg. Warmer and 0.95 inch drier than the same week in 2008.
The week May 17-23 saw temperatures about 6 degrees below normal, and rainfall under one-fourth normal. A modified Polar Continental air mass dominated the area's weather through the 21st, holding temperatures well below normal, and keeping conditions dry. A couple of crossing disturbances on the 22nd and 23rd brought scattered showers in the Tropical maritime air mass which returned on the evening of the 21st. The week's average temperature was 67.7 deg., and rainfall was 0.23 inch. This was 6.3 deg. Cooler than the previous week. Compared with the same week in 2008, the week was 11.1 deg. Cooler, and 0.20 inch drier.
The week May 24-30 saw temperatures about 3 degrees below normal, and rainfall about 10 percent of normal. Tropical maritime air brought above normal temperatures early in the week. On the 27th, a cold front introduced Polar Maritime air, which held readings below normal during the latter half. There were showers on the morning of the 24th as a final disturbance crossed from the upper air low of late in the previous week. The cold front of the 27th also brought light showers. The week's average temperature was 72.8 deg., and rainfall was 0.14 inch. This was 5.1 deg. Warmer than the previous week. Compared with 2008, the week was 6.5 deg. Cooler, and 1.13 inches drier.
The month ended seasonably warm and dry under upper air high pressure.
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 2009, RECORDS AND SUMMARY: