Event Overview
Violent severe thunderstorms swept through Eastern North Carolina during the afternoon and evening of Sunday July 1, 2012, killing three people, one in a collapsed building, and two due to a falling tree. The deadly thunderstorms were fueled by the extreme heat affecting the Southeast, coupled with unusually high levels of moisture. The extraordinary heat and moisture caused high levels of atmospheric instability rarely seen. The Convective Available Potential Energy (CAPE) in Eastern North Carolina and South Carolina at 2 pm EDT Sunday was 5000 to 6000 J/kg, with a lifted index of -14. The Morehead City NWS office analyzed CAPE levels in excess of 7000 J/kg (Figure 1) in the region, which is a truly rare occurrence.
Figure 1. Convective Available Potential Energy (CAPE) at 3 pm Sunday July 1, 2012
This derecho came on the heels of a stronger derecho event that affecting much of the mid-Atlantic states, and Washington DC in particular, just two days earlier on June 29. A derecho is defined as a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. Although a derecho can produce destruction similar to that of tornadoes, the damage typically is directed in one direction along a relatively straight swath. They often form along the northerly boundary of a hot air mass, right along or just south of the jet stream - where upper level winds zip along at high speeds. The Derecho Composite Parameter (DCP) (Figure 2), developed by the Storm Prediction Center, showed a high likelihood for this type of system to affect eastern North Carolina on July 1. The DCP was developed to identify environments considered favorable for derechos through four primary mechanisms: 1) Cold air aloft, 2) Ability to sustain strong storms along the leading edge of a gust front, 3) Organization potential for any ensuing convection, and 4) Sufficient flow within the ambient environment to favor development along downstream portion of the gust front.
Figure 2. The Derecho Composite Parameter (DCP) for eastern North Carolina at 3 pm Sunday July 1, 2012
There were over 70 reports of severe weather across eastern North Carolina during the afternoon and evening of July 1. A Severe Thunderstorm Watch was issued by the Storm Prediction Center well before the storms reached the region. Numerous Severe Thunderstorms Warnings were issued by the Newport/Morehead City National Weather Service office with an average lead time of around 25 minutes. There was at least one possible gustnado that occurred in Beaufort County. Gustnadoes form due the interaction of the downdraft with the warm unstable air it is moving into. This interaction can lead to brief enhanced low level rotation that can cause considerable damage. Since these gustnadoes form on the gust front of the storm the damage they produce is considered straight line wind damage.
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