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April 2001 - Report and Summary

By Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer

The month of April 2001 was warmer and much drier than normal. An upper air high established itself to the south of the region early in the month. This caused a rise in temperatures, and shut down the precipitation of the cool season.

Only twice during the month did significant cooling take place, with a dry air mass late in the month which held temperatures to below normal for a few days. At mid-month, there was also cooling.

April 2001 was 4.5 degrees warmer than April 2000, and 3.62 inches drier. Year-to-date precipitation was 9.42 inches greater in 2001 than in 2000. This reflects the very wet months of January, February, and March.

Precipitation during the twelve months ending 30 April 2001 is 147.3 percent of normal.

The thirty-day outlook for April 2001 had called for above normal temperatures and near normal precipitation.

The week April 1-7 saw temperatures ten degrees warmer than normal, and there was no rainfall. The week was in sharp contrast to the previous week, with temperatures averaging twenty degrees warmer than during that period. An upper air high was over the Gulf of Mexico, accounting for the warmth.

Surface high pressure, which brought brief cooling on the 1st, was over the Southeastern United States with low pressure to the west. This brought humid conditions, resulting in considerable cloudiness during the late nights and mornings. As a result, nighttime low temperatures were high, with three high daily minimum temperature records equalled or broken.

A storm crossing on the 6th/7th, which brought severe weather to the Plains, had little impact on East Texas.

The week April 8-14 saw temperatures eight degrees warmer than normal, and rainfall about one-half normal.

The region continued under a Tropical Maritime air mass throughout the week, with three daily record high minimum temperatures equalled or broken.

A series of upper air disturbances crossed late in the week, bringing the rainfall.

In the counties along Red River, rains were heavy and there were reports of severe weather on the early-morning of the 14th.

Upper air high pressure was shifting slowly eastward from a position over the Gulf of Mexico at the end of the week. It was this feature which contributed to the warmth, and which kept the otherwise active storm pattern over Central North America away from East Texas.

The week April 15-21 saw temperatures near normal and precipitation about one-tenth normal. The week began and ended warm, with a sharp cool snap during the middle.

A storm crossing on the 16th brought light rainfall. It was followed by a modified Polar Continental air mass, which lowered temperatures between the 17th and 19th.

Tropical Maritime air returned the evening of the 19th, warming temperatures ahead of another storm.

Conditions were windy on the 20th and 21st ahead of the new storm.

The week "April 22-28 saw temperatures two degrees cooler than normal, and rainfall about 15 percent of normal. Tropical Maritime air was over the area on the 22nd, with a crossing storm on the 23rd which brought the week's rainfall.

Between the 24th and 28th, a Polar Continental air mass was present, with slow modification because of the high sun angle and upper air high pressure after the 25th.

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 1961-1990.

APRIL 2001



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