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May 2017 - Report and Summary

The month of May 2017 saw near normal temperatures and slightly above normal precipitation. The thirty-day outlook for May 2017, issued on April 20, called for above normal temperatures and near normal precipitation. The April 30 revision called for below normal temperatures and above normal precipitation. Compared with May 2016, the month was 0.3 deg. Cooler and 2.20 inches wetter. Year-to-date rainfall was 2.70 inches less in 2017 than in 2016.

Following the warmest Winter season on record, Spring 2017 tied with 1902 for the fourth warmest Spring season. The warmest Spring season on record was 2012 with 70.5 F.

The month began cool, with warming on the 2nd and 3rd ahead of a cold front which crossed on the afternoon of the 3rd with two clusters of thunderstorms. These brought hail and strong winds to much of the central and southern portions of the area, with rainfall coverage of about 90 percent and amounts from one-tenth of an inch in the north to up to four inches in the south Toro measured the heaviest with 4.34 inches. Most reports of hail were under 1.0 inch in diameter, though there were reports from southern Smith and western Rusk Counties of hail exceeding 2.0 inches. Wind damage was largely limited to downed trees, which also resulted in power failures in a few locations. There were also a few reports of flash flooding from southern Smith County southward.

Beginning on the 4th, several days of fair weather were in the region. Near to below normal temperatures were present through the 8th, with near to slightly above normal temperatures beginning on the 9th. This pattern is called an "omega block": it means low pressure on both the Atlantic and Pacific Coasts of North America, with high pressure in between. As depicted on charts, the pattern resembles the Greek letter omega thus its name.

This pattern broke down on the 10th as a broad upper air low and cold front crossed on the 11th. There were showers on the 10th with under 25 percent areal coverage, and amounts under one-tenth inch. On the 11th, numerous thunderstorms a few severe crossed the region with the approaching front. Areal coverage neared 100 percent, and amounts were up to nearly three inches. There were three areas of scattered severe weather from Henderson through Van Zandt, Wood and Upshur Counties, from Fannin into Lamar and Red River Counties, and from southern Cherokee into Nacogdoches and Shelby Counties. Heaviest rains were at Karnack 2.85 inches, Van 2.74 inches, and Big Sandy 2.45 inches.

There were five tornadoes: an EF-0 between 3:55 p.m. and 3:57 p.m. south of Edgewood in Van Zandt County, with a discontinuous path length of 2.09 miles and a width of about 50 yards, with two homes damaged by flying debris; an EF-1 tornado west of Gladewater with a path length of 1.52 miles and width of 175 yards between 6:09 p.m. and 6:11 p.m., which snapped numerous trees and with minor damage to one mobile home; an EF-1 tornado with a path length of 2.69 miles and a width of 220 yards near Union Grove between 6:23 p.m. and 6:29 p.m., with tree damage and roof and steeple damage to a Baptist church; an EF-1 with a path of 5.54 miles and a width of 280 yards, between 7:03 p.m. and 7:16 p.m. in southeastern Rusk County, which felled several trees with damage to one home from a falling tree; and an EF-2 tornado, with a path length of 4.64 miles and a width of 800 yards, between 8:33 p.m. and 8:46 p.m., in northeastern Nacogdoches County and southeastern Rusk County, damaging the roofs to several homes and businesses in Garrison, and destroying a chicken coop in Rusk County with all chickens inside killed. There were no personal injuries or fatalities in any of the tornadoes. The fifth storm also felled several trees and utility poles.

Surface and upper air high pressure followed this system, with slightly below normal temperatures, fair skies, and comfortably low humidities through the 14th. High pressure shifted east of the area on the 15th and 16th with temperatures going back above normal, humidities rising, and clouds increasing. This was ahead of another broad area of low pressure which began affecting the region on the 17th.

There were scattered light showers on the 17th some in the morning from the remnant of earlier activity which had formed in West Texas on the afternoon of the 16th, and a few during the afternoon from daytime heating. Amounts were only a few hundredths of an inch, with coverage under 25 percent. Isolated showers occurred on the 18th and 19th, due mainly to daytime heating. Coverage was under 5 percent and amounts were a few hundredths of an inch or less on both days.

The core of the upper air system along with its attendant cold front crossed on the 20th. This brought widespread rain and thunderstorms to the area that morning, with amounts running between one-half inch and three inches. Palestine received the largest amount with 2.90 inches, while Frankston measured 2.27 inches and Arp 2.04 inches. There was no severe weather with the morning thunderstorms. In the late-afternoon of the 20th, a few severe thunderstorms developed along the cold front over the southern counties. Hail in excess of one inch in diameter was reported in Lufkin The cold front went stationary along the Coastal Plain. Moist air overriding the front combined with another disturbance on the morning of the 21st to bring more thunderstorms, with coverage nearing 80 percent and amounts mostly under an inch both increasing from north to south. There were reports of hail up to one inch in diameter from southeastern Smith and southern Rusk Counties. A gauge southwest of Henderson received the heaviest rain from this disturbance with 2.98 inches.

Yet another disturbance crossed on the morning of the 22nd, with coverage nearing 80 percent, and amounts running from about one-tenth of an inch at the few locations in the north which received rain to nearly three inches over the southern counties. Sam Rayburn Reservoir received the highest amount with 3.49 inches, and Broaddus measured 3.33 inches. There was no severe weather with this activity.

Two lines of showers crossed on the 23rd. A morning line crossed from southwest to northeast, with amounts under one-fourth inch and coverage about 40 percent. A second crossed from northwest to southeast during the afternoon, and was associated with a cold front. Coverage approached 90 percent, and amounts ranged from around one-tenth inch over the northern counties to around an inch over the southern counties. Crockett received the heaviest rain with 1.55 inches.

There were no reports of severe weather with the second and stronger line. Temperatures continued running above normal through the 20th, but dropped several degrees below normal behind the cold front of that day, and continued below normal through the morning of the 25th. Upper air high pressure built into the area from the west, raising temperatures above normal through the 27th. On the 28th, a new cold front and the first in a series of upper air disturbances began affecting the area.

There were three lines of showers and thunderstorms on the 28th the first two during the morning hours with rain confined mostly north of IH-20 and with about 60 percent areal coverage. There was no severe weather with these, and rainfall amounts were up to 1.5 inches with amounts and coverage increasing from south to north. Mount Vernon received 1.53 inches for the heaviest rainfall reported. The third line crossed during the afternoon, with a few reports of severe weather southeast of a Gilmer-Terrell line. Coverage was near 80 percent, and both rainfall amounts and occurrences of severe weather increased from northwest to southeast. Crockett received the heaviest amount with 4.11 inches.

Two tornadoes struck on the afternoon of the 28th: an EF-1 tornado had a path of 10.1 miles with a width of 800 yards from 6 miles northeast of Longview to four miles south-southeast of Longview. There were no injuries or fatalities, but numerous trees were uprooted, causing damage to several houses. The tornado was on the ground between 4:53 p.m. and 5:03 p.m. An EF-1 tornado had a path of 4.86 miles and a width of 400 yards from 2 miles west of Easton to 2.8 miles east of Easton in Rusk County. There were no injuries or fatalities, but some homes were damaged from uprooted trees. The tornado was on the ground between 5:07 p.m. and 5:12 p.m.

There were a few light showers on the 29th, 30th, and 31st with under 20 percent areal coverage and amounts mostly under one-tenth inch on each day. Temperatures were near seasonal normals from the 28th through the 31st.

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 2017



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