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Philadelphia/Mt Holly

Weather Forecast Office

19-20 June 2019 Significant Flash Flood Event in Southeast Pennsylvania and Southern New Jersey

Weather.gov > Philadelphia/Mt Holly > 19-20 June 2019 Significant Flash Flood Event in Southeast Pennsylvania and Southern New Jersey

Overview

Quasi-zonal midlevel flow was in place across the Northeast on 19 June 2019, with weak vorticity maxima progressing through the region.  This midlevel flow was nearly parallel to a surface front stretching west-to-east across the northern Mid-Atlantic, which did not permit much movement of the front.  To the south of the nearly-stationary front, a very moist and unstable environment was present (MLCAPE 1500-2000 J/kg; precipitable water approaching 2 inches).  The presence of a surface front along with weak midlevel perturbations promoted the development of convection several times from afternoon through the overnight hours in portions of the area.  Weak deep-layer shear and very moist low levels resulted in slow-moving storms that generated weak cold pools.  Storms would reinitiate along the outflow boundaries associated with the cold pools, but their weak nature resulted in the training of storms over the same areas multiple times.  Additionally, a deep above-freezing layer of air was present, which allowed for highly efficient precipitation rates with the storms.  This is a setup quite favorable for flash flooding.  During the late afternoon and early evening, storms developed from the north side of Philadelphia eastward to the Fort Dix area, where several reports of 2-4 inches of rain occurred in a 2-hour period, along with reports of road closures from flooding.  Late in the evening into the overnight hours, more storms developed to the south of Philadelphia, spreading very slowly northward.  Numerous instances of flash flooding were reported from the Reading area in Berks County eastward to Gloucester, Camden, and Burlington Counties in southern New Jersey.  The excessive rainfall resulted in the lengthy closure of Interstate 295 in New Jersey in the pre-dawn hours of 20 June, dozens of water rescues throughout the area, the evacuation of several homes along the rapidly rising Rancocas Creek in Burlington County, and inundation of several homes and businesses in the Bellmawr, Barrington, and Brooklawn areas.

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Polarimetric estimated storm total precipitation in southern New Jersey ending 1157 UTC 20 June 2019.

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Polarimetric estimated storm total precipitation in southeast Pennsylvania ending 1157 UTC 20 June 2019.

Meteorological Environment/Setup

Synoptic Overview at 12z 19 June 2019 (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 20 June 2019 (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: 15z surface map Figure 14: 18z surface map Figure 15: 21z surface map
 
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Figure 16: 00z surface map Figure 17: 03z surface map Figure 18: 06z surface map

Observed Soundings
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Figure 19: 12z Upton, NY sounding Figure 20: 12z Sterling, VA sounding Figure 21: 12z Wallops Island, VA sounding
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Figure 22: 00z Upton, NY sounding Figure 23: 00z Sterling, VA sounding Figure 24: 00z Wallops Island, VA sounding
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