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Powerful Pacific Storm to Continue Impacting Northern California; Heavy Snow in the Appalachians and Portions of the Northeast

A strong atmospheric river will continue to impact northern California with heavy rain and life-threatening flooding through Friday. Unsettled weather is expected across much of the Northeast and Great Lakes over the next few days, including the likelihood of heavy snow in the central Appalachians and higher elevations of northeastern Pennsylvania and southern New York. Read More >

Overview

During the morning of April 30, low pressure was strengthening over South Carolina. Meanwhile, a potent, negatively tilted southern stream shortwave trough was lifting northeast over Georgia. Showers and a few thunderstorms were ongoing across the forecast area, with a quasi-stationary frontal boundary positioned from east-central NC to eastern VA. The morning convection was elevated and thus did not pose a severe threat. By early afternoon, another round of convection had overspread eastern VA and NE NC and the surface low deepened to  ~988-990mb as it tracked across east-central NC during the early-mid afternoon. The atmosphere did not have time to recover from the morning storms and there was still not much in the way of  instability across the area. The aforementioned boundary remained in place, and temperatures were stuck in the mid to upper 60s in central/northern/western portions of the Wakefield forecast area. This second round of convection did not produce severe weather. However, the main low pressure system at the surface and aloft was still to our southwest, and there was a zone of mid-level dry air and partly sunny skies immediately behind the convection (which exited SE VA/NE NC by 2-2:30 pm).

With 2 to 3 hours of clearing (and the fact that the low track was just to the northwest of Hampton Roads), the environment changed rapidly between 2 and 5 pm. Deep-layer shear was sufficient for supercells throughout the day. However, instability (especially in the 0-3km layer) increased significantly during the late afternoon before the arrival of the final round of thunderstorms (which were coincident with the upper shortwave itself). In fact, 0-3 km MLCAPE was 150+ J/kg in SE VA by 5 PM. Note that the instability was much less over the eastern shore and cool Atlantic waters, creating a tight CAPE gradient near the coast (in the past, we have seen tornadoes form along instability gradients). Despite the cool water, the dew point at KNTU was 67° at 5 PM. In addition, low-level directional shear increased significantly by that time. In fact, RAP analysis showed close to 150 m2/s2 of 0-1km SRH and 100 m2/s2 0-500m SRH at VA Beach before the storms moved in. Given that the wind at KNTU was from 150° (as per the 2056z/456 PM observation) instead of 170-180° like the RAP analysis showed, the actual 0-1km SRH values were likely even higher. Finally, the low deepened to 985-986mb and was centered over the Peninsula at around 5 PM (see regional surface observations for more details). The final round of convection produced wind gusts in excess of 50 knots as it moved through eastern NC and far SE VA (although most of the severe wind reports were south of our area). The cell that produced the EF-3 tornado in VA Beach turned to the right as it merged with a weaker cell just to its east about 10 minutes before the tornado touched down. The circulation moved over the Lynnhaven River right before the tornado touched down. It was on the ground for 5 minutes, tracking from the eastern branch of the Lynnhaven River to Fort Story before moving over the bay and dissipating. This was the first EF-3 tornado in the AKQ CWA since Tropical Storm Isaias (August 2020), and the first EF-3 in the state of Virginia since April 2019. While over 100 homes were damaged (the worst damage was observed in the Chelsea neighborhood and on Haversham Close) and damage was in the millions of dollars, there was not a single injury or fatality. 

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