By Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer
The month of April 2009 was cooler and slightly wetter than normal. Polar Continental air dominated the region for much of the month. On the 21st, the air mass changed and first Tropical Continental then Tropical Maritime air took over holding through month's end. Compared with the same month in 2008, the month was 2.2 deg. Cooler and 0.31 inch drier. Year-to-date rainfall through month's end was 1.99 inches less in 2009 than in 2008. The thirty-day outlook had called for near normal temperatures and below normal precipitation.
The week March 29-April 4 saw temperatures about 8 degrees below normal, and rainfall about 125 percent of normal. The last freeze of the season in Tyler came on the 29th. Reinforcing cold fronts on the 31st and 2nd kept temperatures low through the week, and brought thunderstorms on both days. The week's average temperature was 56.8 deg., and rainfall was 1.08 inches. This was 1.7 deg. Cooler than the previous week. Compared with the same week in 2008, the week was 8.1 deg. Cooler, and 2.31 inches drier.
The week April 5-11 continued the trend of below normal temperatures, with readings running about 8 degrees lower than normal. Many stations experienced a freeze on the morning of the 7th. The region warmed briefly on the 9th before a storm system and cold front crossed. Severe weather developed northeast of Tyler on the evening of the 9th. The week's average temperature was 57.6 deg., and rainfall was 0.05 inch. This was 0.8 deg. Warmer than the previous week. Compared with the same week in 2008, the week was 10.3 deg. Cooler, and 0.45 inch drier.
The week April 12-18 was cool and wet, with temperatures running about 6 degrees below normal, and rainfall about 300 percent of normal. A storm system crossed on the 12th, bringing widespread rainfall and followed by colder temperatures. Temperatures began to warm on the 16th, ahead of another strong storm system on the 17th and 18th which brought general rains. The week's average temperature was 60.1 deg., which was 2.5 deg. Warmer than the previous week. Rainfall was 2.79 inches. Compared with the same week in 2008, the week was 0.4 deg. Warmer, and 2.49 inches wetter.
The week April 19-25 saw temperatures about 2 degrees above normal, and rainfall about one-third normal. On the 20th, Tropical Maritime air replaced the Polar air which had been over the region for much of the month to date. The result was a sharp warming trend, which kept temperatures above normal for most of the remainder of April. An upper air storm crossed on the 25th, bringing the week's only rainfall. The week's average temperature was 69.6 deg., which was 9.5 deg. Warmer than the previous week. Rainfall was 0.30 inch. A similar sharp warm-up took place during the week in 2008, which was 2.6 deg. Warmer and 0.28 inch wetter than the week in 2009.
Two wet storm systems crossed the region during the final five days of the month. In the immediate Tyler area, rainfall was around one-half inch. Over the extreme northern counties, amounts were between five and seven inches. Temperatures continued above normal.
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
APRIL 2009, RECORDS AND SUMMARY: