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May 2003 - Report and Summary

The month of May 2003 was slightly warmer and drier than normal. The month began and ended very warm. Air quality deteriorated during the first of the month because of smoke from the Central American fires, and at late-month because of ozone. Strong upper air high pressure dominated the area during the first week or so, and again during the last three days. At mid-month, northwesterly winds aloft allowed disturbances to cross, pulling in cold fronts.

For almost the entire month, there was a layer of very warm air just above the surface. This prevented significant rainfall. For the southeastern half of the region, Spring 2003 will go down in the record books as one of the driest Spring seasons. In Tyler, 7.17 inches of rain fell during March, April, and May. This is 58.1 percent of normal rainfall. Of the Spring total, more than one-third fell during two days in May. Year-to-date rainfall through May 31 was 2.80 inches less in 2003 than in 2002. During the past twelve months, precipitation was 97.3 percent of normal.

May 2003 was 1.2 deg. warmer and 2.22 inches drier than May 2002. The thirty-day outlook for May 2003 had called for near normal temperatures and above normal precipitation.

The week April 27-May 3 warmed significantly. For most of the week, the region was under a Tropical Maritime air mass, with the Sub-Tropical upper air high in place. This caused warm and humid conditions. A cool air mass present early in the week quickly modified with Tropical Maritime air returning on the morning of the 28th. An upper air storm crossed on the early-morning of the 30th, bringing a few showers. Its attendant cold front lowered temperatures only slightly. Another weak cold front reached the IH-30 Corridor on the 2nd. A crossing disturbance on the evening of the 1st brought a few light showers. Another crossing on the night of the 2nd brought light showers to the extreme northeastern counties in Texas. The front retreated northward on the afternoon of the 3rd, with light showers developing over the eastern counties during the late-afternoon.

The week's average temperature was 74.2 deg., which was 4 deg. warmer than normal. Precipitation was 0.13 inch, about 15 percent of normal. The week was 6.9 deg. warmer than the previous week. Compared with the same week in 2002, the week was 2.5 deg. cooler, and 0.25 inch drier.

The week May 4-10 saw temperatures 8 deg. warmer than normal and precipitation about one-tenth of normal For the entire week, a Tropical Maritime air mass was over the region. This brought very warm and humid conditions. The week's only rainfall occurred on the 6th, when a weak cold front approached the area and an upper air disturbance crossed. Upper air high pressure, extending northward from the Gulf of Mexico, largely suppressed any shower development, and kept temperatures quite warm. Windy conditions occurred daily between the 7th and 10th, as air rushed into surface low pressure over the western edge of the Plains. Fires in Central America sent smoke northward. This mixed and caused haze between the 7th and 10th, with the visibility lowest on the 10th--about 4 miles throughout the day. East Texas was on the extreme southern fringe of a week-long severe outbreak over Central North America. On the night of the 6th/7th, a tornado skipped through Wood, Upshur, and Marion Counties. This caused structural damage, and a few minor injuries. Compared with the same week in 2002, the week was 1.2 deg. cooler, and 1.98 inches drier.

The week May 11-17 saw temperatures about 2 deg. warmer than normal, and rainfall about two-thirds normal. The week began and ended with modified Polar Continental air in place. During the middle, Tropical Maritime air was present. The dew point front was active, with disturbances crossing. Thunderstorms developed over West Texas on the afternoons of the 12th, 13th, 14th, 15th, and 16th. These weakened as they reached East Texas during the early morning hours on the first four days, with a shower occurring in Tyler on the morning of the 14th. A line of severe thunderstorms formed just to the west of Tyler on the afternoon of the 16th, and went through that evening.

There were reports of three-fourths inch diameter hail from locations to the south and southwest of the city.

Rain fell in the city on the evening of the 16th with this thunderstorm.

Upper air high pressure was back in place between the 11th and 16th. Smoke from the Central American fires lowered the visibility to 4 miles on the afternoon of the 16th.

The week was 4.3 deg. cooler than the previous week. Compared with the same week in 2002, the week was 4.7 deg. warmer, and 0.44 inch drier.

The week May 18-24 was 1 deg. cooler than normal, and had 20 percent of normal rainfall A weak upper air disturbance crossed on the 20th, bringing the week's only rainfall.

Modified Polar Continental air was over the region early in the week, and following the passage of a cold front on the 20th.

Tropical Maritime air returned on the 24th, with light showers present in the region during the morning.

The week was 1.9 deg. cooler than the previous week.

Compared with the same week in 2002, the week was 3.9 deg. warmer, and 0.25 in. wetter

The week May 25-31 saw temperatures 1 deg. cooler than normal, and rainfall about 250 percent of normal.

A cold front moved slowly through the area between the 25th and 27th. A strong flow of moist air just above the surface interacted with favorable upper air dynamics to bring heavy rains to the northwestern half of the region on the morning of the 25th. Amounts ranged between one and six inches.

Over the southeastern half, amounts were under an inch.

Widespread severe weather occurred the night of the 24th/25th. The surface high pressure ridge, which built in behind the front, held down temperatures through the morning of the 29th. Upper air high pressure built in during the 29th, and caused temperatures to rise to above normal levels for the last three days of the week.

The upper air high caused air quality to deteriorate, with it being unhealthy on the 30th and 31st.

The week's average temperature was 72.9 deg., and rainfall was 2.59 inches. Compared with the previous week, the week was 0.1 deg.warmer.

Compared with the same week in 2002, the week was 3.3 deg. cooler, and 0.31 inch wetter.

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.

May 2003



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