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Heavy to Excessive Rainfall in the Central Appalachians; Severe Weather in the Mid-South; Hot Weather in Southern California

Heavy to excessive rainfall may lead to flooding today over southwest Pennsylvania into northern West Virginia, and western Maryland. Severe thunderstorms are possible this afternoon and evening in the Mid-South and across Eastern North Carolina. An extended period of hot weather is forecast for parts of coastal southern California including Los Angeles from today through Thursday. Read More >

Overview

The May 7th severe weather event was, like all sizeable severe weather episodes, the culmination of multiple meteorological factors coming into place at the same time. In the days leading up to the event, rich moisture was brought northward from the Gulf of America, resulting in showers and thunderstorms on both May 5th and May 6th. On May 7th, an upper low moved into the Four Corners, causing a surface area of low pressure to develop across New Mexico. The Panhandles were on the east side of this area of low pressure, setting up winds out of the south and southeast which brought in additional moisture and warmed temperatures through the morning and afternoon hours. This escalation of both temperature and moisture gave the atmosphere increased energy for storms. Furthermore, the approach of the upper low led to an upsurge in wind speeds aloft out of the southwest. The difference between these southwesterly winds aloft and the southeasterly winds at the ground, known as wind shear, escalated through the daytime hours. Finally, a surface front, augmented by cold air rushing out of thunderstorms over Kansas very early Tuesday morning, pushed south into the Panhandles. This front stalled out and retrograded back to the north under the influence of those southeasterly surface winds. This stalled front would provide an additional focus for thunderstorm development.

Strong storms began to fire around noon and quickly became severe, with the first severe thunderstorm warning issued at 12:33pm. The first report of severe weather, quarter size hail 5 miles south of Masterson, came in at 1:12pm. Storms began to increase in number after 1:00pm, becoming numerous after 2:00pm. The largest hail reports of the event were received at 2:02pm, when baseball size hail fell near Lake Meredith and Fritch. With wind shear increasing through the afternoon, a few of the storms became tornadic, with the first tornado touching down 9 miles south-southwest of Spearman at 3:42pm. Six subsequent tornadoes occurred, two associated with a particularly nasty supercell that spawned multiple tornadoes along a line from between Plainview and Hart northeast through Alanreed. The bulk of the storms pushed eastward into Oklahoma after 9:30pm, although a couple additional rounds formed behind them, which had a few cells become severe. The last of the thunderstorms shifted into western Oklahoma after 2:00am.

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