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Scattered Severe Storms to Continue Over the Central and Southern Plains this Weekend; Snow in the Sierra Nevada

Scattered strong to severe thunderstorms will persist over the central to southern High Plains this weekend with a severe weather and flash flooding threat. A late season storm will bring low elevation rain and high elevation snow to portions of California, Nevada and Oregon through the weekend. Winter Weather Advisories are in place for the Sierra for snow totals of 3-6", locally higher. Read More >

Philadelphia/Mt Holly

Weather Forecast Office

April 21 Scattered Severe Thunderstorms with Wind and Hail

Weather.gov > Philadelphia/Mt Holly > April 21 Scattered Severe Thunderstorms with Wind and Hail

Overview

A strong cold front moved through the eastern mid-Atlantic during the early to mid afternoon hours on April 21. Showers and thunderstorms developed ahead of the front. Some storms became severe, with sporadic reports of storm damage from southern New England southward through much of the coastal mid-Atlantic. The front moved through a couple hours before peak heating, which combined with an air mass that was not overly warm to begin with limited instability. However, steep mid-level lapse rates helped to compensate for this and allowed up to around 1000J/kg of surface based CAPE to develop. Strong frontal forcing and strong shear (deep layer shear of 50 to 60 kt) combined with the sufficient instability to allow convection to develop and intensify. Mainly linear storm modes with some discrete elements were observed. The strongest storms produced hail up to quarter size, aided by cool air aloft thanks to the lapse rates, and scattered instances of downed trees and power lines due to damaging winds. Convection moved offshore by late afternoon, and a much cooler and drier air mass overspread the region.

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KDIX radar loop of the April 21, 2021 severe weather at half hour increments from 1530 UTC to 1930 UTC. Note the rapid development between 1530 and 1600 UTC (11:30 AM - 12:00 PM EDT) and how convection consisted of a mix of discrete and linear elements, as opposed to a solid squall line such as on March 28, 2021.

Meteorological Environment/Setup

Synoptic Overview at 12z 21 April 2021 (courtesy of SPC)

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Figure 1: 250-mb analysis Figure 2: 300-mb analysis Figure 3: 500-mb analysis
 
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Figure 4: 700-mb analysis Figure 5: 850-mb analysis Figure 6: 925-mb analysis

Synoptic Overview at 00z 22 April 2021 (courtesy of SPC)

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Figure 7: 250-mb analysis Figure 8: 300-mb analysis Figure 9: 500-mb analysis
 
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Figure 10: 700-mb analysis Figure 11: 850-mb analysis Figure 12: 925-mb analysis
 

Surface Maps (courtesy of WPC)

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Figure 13: 06z surface map Figure 14: 09z surface map Figure 15: 12z surface map
 
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Figure 16: 15z surface map Figure 17: 18z surface map Figure 18: 21z surface map

Observed Soundings
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Figure 19: 12z Sterling, VA sounding Figure 20: 12z Wallops Island, VA sounding Figure 21: 12z Long Island, NY sounding
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Figure 22: 0z Sterling, VA sounding Figure 23: 0z Wallops Island, VA sounding Figure 24: 0z Long Island, NY sounding
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