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Overview

On the evening of (Sunday) April 12, low pressure was over the central Mississippi Valley. Its associated warm front was over the Deep South while the trailing cold front extended SW into the western Gulf of Mexico. This low pressure system was responsible for strong/violent tornadoes across Mississippi. Locally, temperatures were in the mid-upper 60s with dew points in the low-mid 50s during the late evening hours of 4/12. Some pre-frontal light to moderate rain was over the area, while a strongly forced line of strong-severe thunderstorms extended from southwest Tennessee to Alabama (well ahead of the cold front). Any sort of pre-frontal instability was well to the south/west of the local area. The area of low pressure intensified as it quickly tracked northeast into the southern Great Lakes by early Monday morning. As this happened, the warm front moved northward into our local area as the line of storms from TN to AL tracked  ENE to a position from just west of our CWA (while extending hundreds of miles south to South Carolina/Georgia) by 5-6 AM Monday. The environment at this time was characterized by a strong (60-80 kt) 925 mb jet, temperatures/dew points in the low-mid 60s, and south-southeasterly surface winds. While low-level shear (and resultant storm-relative helicity) values were extremely impressive, no tornadoes were reported as this line crossed the CWA from west to east during the 6-10 AM timeframe (perhaps in part due to the marginal level of instability). However, there were several reports of thunderstorm wind damage over parts of the area from this line.

While the thunderstorms produced some wind damage, the most impressive aspect of this system was the high synoptic/gradient wind gusts observed during the day (mainly from mid morning-early afternoon) after the warm front surged north of the region and winds turned to the south. The aforementioned (60-80 knot-highest near the coast) low level jet remained in place through much of the morning-midday. Frequent gusts of 45-60 mph were observed in many locations during this time, which knocked down several trees and caused numerous power outages (especially on the Lower MD Eastern Shore, Hampton Roads (in SE VA), and NE NC). Between 10 AM and noon, there were a couple of brief periods where gusts of 65-75 mph were observed across Hampton Roads (well after any thunderstorms were ongoing). We are still looking into exactly why this happened, but hypothesize that a series of gravity waves allowed higher winds aloft to briefly mix down to the surface. Lastly, rapid rises in water levels were observed on 4/13 in areas from Edenton to Elizabeth City (adjacent to the northern side of the Albemarle Sound and associated tidal rivers). Elizabeth City saw the worst of the (measured) tidal flooding, where water levels peaked a few tenths of a foot below major flood stage. See the Tidal Flooding/Wind Graphs section for more details on the exact progression of tides at Elizabeth City/Edenton.

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