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April 2017 - Report and Summary

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

The thirty-day outlook, issued on March 16, had called for above normal temperatures and above normal precipitation. It was not changed with the March 31 revision. Compared with April 2016, the month was 0.5 deg. Warmer and 4.72 inches drier. Year-to-date rainfall was 4.90 inches less in 2017 than through April's end in 2016.

Weak storm systems crossed on the 2nd and 5th, with showers and thunderstorms both days. Otherwise, a weak cold front went stationary near the area with the first system, retreating northward on the 3rd. The front had little effect on temperatures. Another, and stronger, front crossed on the 5th, lowering temperatures on the 6th and 7th. Warm air returned on the morning of the 8th ahead of the next storm system.

That system crossed on the 10th and 11th with an attendant cold front. Thunderstorms developed on the afternoon of the 10th with two severe clusters: one moving from Hopkins County northeastward into Bowie County, and a second from eastern Smith County northeastward into Harrison and Panola Counties. Though rainfall amounts were generally between one-half inch and two inches, Cumby measured 8.64 inches, Sulphur Springs 6.23 inches, and Longview 4.21 inches. An EF-1 tornado uprooted several trees in eastern Smith county, touching down twice between 7:10 and 7:35 p.m. once northwest of Arp and a second time in Overton. There were no injuries or significant property damage. Tyler clocked a peak wind gust of 54 mph at 1:06 a.m. on the 11th at Pounds Field.

The cold front lowered temperatures slightly on the 11th and 12th, with readings warming again under weak upper air high pressure on the 13th. This ridge persisted through the 16th, though a weak disturbance on the latter date permitted some afternoon showers to form south of a Rusk-San Augustine line. This was the season's first sea-breeze front.

A quasi-stationary front combined with weak upper air low pressure to bring showers and thunderstorms to the region on the 17th and 18th. Amounts on the 17th ranged up to nearly two inches, while amounts on the 18th were mostly under one-fourth inch. Coverage on the 17th was near 90 percent, with about 25 percent areal coverage on the 18th. Continued upper air weakness combined with very moist air on the 19th to generate afternoon showers with about 50 percent areal coverage. Amounts were mostly under one-half inch. There were isolated showers on the afternoon of the 20th due to the sea-breeze, with coverage under 10 percent.

Upper air high pressure built back over the area between the 19th and 21st with continuing above normal temperatures. Another upper air storm crossed on the 22nd with an attendant cold front. These brought showers and thunderstorms to the region, with a few severe on the evening of the 21st and afternoon of the 22nd. Coverage of rainfall was about 75 percent, with amounts ranging from one-fourth inch to one inch. Temperatures were below normal from the 22nd through the morning of the 24th, with above normal temperatures returning on the 25th.

A cold front and upper air low crossed on the afternoon of the 26th with widespread thunderstorms. Rainfall coverage was near 100 percent, and amounts were up to three-fourths of an inch. Severe weather was reported from parts of Navarro through Henderson, Wood, Gregg, and Marion Counties, and a second cluster of severe thunderstorms affected parts of Cherokee and Angelina Counties. Warm temperatures returned on the 28th and 29th with the warm season commencing on the 28th with the first 90-degree temperature. This was ten days ahead of the median date.

A significant severe weather event affected the western counties on the evening of the 29th. At least nine tornadoes touched down in a 55-mile strip from Henderson through Van Zandt into Rains, Smith, Wood, and Hopkins Counties. Four persons were killed and 56 injured in Canton, where there was extensive property damage from three of these storms one of which was an EF-4 tornado and another an EF-3. Several fixed homes and numerous manufactured homes and automobiles were destroyed, along with a significant power failure.

What first appeared to be a single tornado but was actually two, had a path of 55 miles in length from northern Henderson County through east Canton and Fruitvale, and across Rains into southern Hopkins County north of Yantis. They existed for about an hour and 50 minutes (from about 5:40 p.m. through about 7:30 p.m., and may have been a mile wide. The first was an EF-4 storm, and the second an EF-3. Another EF-3 had a 22-mile path from near Eustace to west of Canton also up to a mile in width, and was active for about 40 minutes between about 5:30 p.m. and 6:10 p.m.

Earlier an EF-0 tornado formed over east Canton about 5:10 p.m., resulting in damage to some trees and barns, but resulting in no injuries. Two EF-1 tornadoes occurred in Smith and Wood Counties one about 4 miles northwest of Lindale and another about 3 miles east of Mineola. There was little property damage with the former, and one damaged home with the latter. There were neither injuries nor fatalities with either- both of which occurred about 7:45 p.m.

An EF-0 tornado formed near Cumby in Hopkins County about 6:30 p.m., with no injuries but with one home burned when a power line fell on the structure from a falling tree. Another EF-0 tornado formed in southwestern Van Zandt County about 7:15 p.m. near Mabank again with no injuries and little damage. Earlier in the afternoon, an EF-0 tornado formed near Grand Saline about 4:15 p.m., with neither injuries nor significant damage.

(EF refers to the Enhanced Fujita scale. The categories are as follows: EF0...Weak......65 TO 85 mph
EF1...Weak......86 TO 110 mph
EF2...Strong....111 TO 135 mph
EF3...Strong....136 TO165 mph
EF4...Violent...166 TO 200mph

Rainfall coverage neared 100 percent, with amounts running from around one-tenth of an inch in the south to more than an inch at some locations in the western and central counties. Canton received the heaviest rainfall with 4.73 inches. The attendant cold front lowered temperatures on the 30th.

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.

APRIL 2017



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