By Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer
The month of April 2002 was warmer and drier than normal.
An upper air high pressure ridge, building northward from the Gulf of Mexico, established itself early during the first week of the month. Except for a few minor interruptions by weak fronts which managed to make it this far south, the ridge persisted.
April 2002 was 1.1 deg. warmer than April 2001, and 1.73 inches wetter. Rainfall through April 30, 2002 was 12.07 inches less than that through the same time in 2001. Twelve-month rainfall through April 30, 2002 was 46.83 inches, which is 103.4 percent of normal. The thirty-day outlook for April 2002 had called for near normal temperatures and above normal precipitation.
The week March 31-April 6 saw temperatures about three degrees cooler than normal, and precipitation about 125 percent of normal. Two Polar Continental air masses were over the area during the week. The first exited on the 1st, and the second entered on the evening of the 2nd, persisting through the 5th.
Tropical Maritime air was over the area briefly on the 2nd before the arrival of the front of that day. Rain, which fell on the 30th, were counted in the week's total.
Light rain fell on the 6th. The week's average temperature was 61.0 deg., which was 0.8 deg. warmer than the previous week.
The week April 7-13 was one degree warmer than normal, and precipitation was 225 percent of normal. Heavy rain fell in the area on the 7th with the crossing of an upper air storm. A Polar Maritime air mass, which built into the area on the afternoon of the 8th, cooled temperatures until Tropical Maritime air returned on the 10th.
This raised temperatures to above normal levels through the end of the week. The week's average temperature was 66.8 deg., which was 5.8 deg. warmer than the previous week.
The week April 14-20 saw temperatures nine degrees warmer than normal, and rainfall about 10 percent of normal. Surface and upper atmospheric high pressure controlled the area's weather. Record high minimum temperatures were tied or broken on two days during the week. Tropical Maritime air was over the region during the entire week. The week's only rainfall fell on the afternoon of the 16th from a crossing upper air disturbance. The week's average temperature was 76.0 deg., which was 9.2 deg. warmer than the previous week.
The week April 21-27 saw temperatures three degrees warmer than normal, and precipitation about one-fifth normal. Two weak cold fronts passed through the region--one on the 21st and the second on the 24th. The air mass behind the first front was Polar Maritime, and that behind the second was modified Polar Continental. The upper air high pressure ridge over the Gulf of Mexico, which took control of the area's weather early in the month, shifted slightly southward. This permitted the fronts to reach East Texas. Both of the occurrences of rain were warm advection rain, occurring as the fronts retreated northward as warm fronts on the 23rd and 26th. Since there was no upper air support with the return of either front, amounts were light. The weak's average temperature was 71.6 deg., which was 4.4 deg. cooler than the previous week.
The last three days of the month were also quite warm and dry under continuing 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
APRIL 2002, RECORDS AND SUMMARY: