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Philadelphia/Mt Holly

Weather Forecast Office

3-4 August 2018 Lehigh Valley and Northern New Jersey Flooding

Weather.gov > Philadelphia/Mt Holly > 3-4 August 2018 Lehigh Valley and Northern New Jersey Flooding

Overview

A surface trough developed in eastern Pennsylvania southwestward through central Virginia on 3 August 2018. In advance of the trough, a long fetch of anomalously moist air was transported northward to the west of a strong ridge of high pressure in the western Atlantic. With the aid of a shortwave trough approaching the region, convection developed near the trough axis during the evening and continued to regenerate on the southwest side as the predecessor storms moved northeastward. As the storms continued to train over Berks County northeastward through the Lehigh Valley into northern New Jersey, a swath of 2-5+ inches of rainfall accumulated in this corridor by daybreak. Several reports of flooding were received, especially from Berks, Lehigh, and Northampton Counties. During the morning, the axis of convection moved northeastward into more urban portions of northern and central New Jersey. Though rainfall amounts were lower in these areas, flash flooding occurred owing to the high rain rates combined with the rapid runoff from increased urbanization.

 Image
Radar Reflectivity Animation for the Event (via GR2Analyst)

Meteorological Environment/Setup

Synoptic Overview at 12z 3 Aug 2018 (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 4 Aug 2018 (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: 18z surface map Figure 14: 21z surface map Figure 15: 00z surface map
 
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Figure 16: 03z surface map Figure 17: 06z surface map Figure 18: 09z surface map

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