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STRONG TO ISOLATED SEVERE THUNDERSTORMS POSSIBLE LATE SUNDAY

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Synoptic overview:

A complex area of low pressure will move from near Chicago, Illinois to just south of Erie, PA… and continue east-northeastward along or just north of the PA/NY border. This system will arrive later in the day and present a strong to isolated severe weather threat, especially in areas of yellow on the map above. This area is where the strongest mid and upper level forcing and upward vertical motion is expected to occur. Despite the convection arriving later in the evening and mainly after loss of diurnal heating, the threats remain as outlined below.

Timing:

From west to east, the thunderstorm complex is expected to traverse PA and northern New Jersey between 7pm (western areas) and 2am Monday (coastal NJ areas) and timing for this event is 7pm Sunday to 2am Monday.

Impacts in order of significance/likelihood of occurrence:

(1) Damaging wind gusts in excess of 60mph
(2) Moderate lightning, including cloud to ground
(3) Locally heavy rainfall, including flash flooding
(4) Small hail, generally marble sized or less

Line of storms expected later this afternoon and evening will develop near a surface low pressure system in Ohio around 2PM. The organization from these storms will determine the evolution of the storms for later tonight. Right now the thunderstorms roll in late enough allowing a shallow low level inversion to offer some protection to strong wind gusts. Meaning the strong wind gusts will have a tough time getting through an area near the surface where the temperatures rise with height. However, if this line is very well developed or comes in earlier it may overcome this obstacle and produce a much more significant wind threat. Better chance for this will be across Central PA.

There is the opportunity for storms to develop further south based on the track of this intense low pressure, which would keep green areas on guard. If a boundary develops east of the Appalachians this afternoon, a very low chance (less than 20%) of isolated discrete cells can occur anywhere in our coverage area, best chance for that is further south. If discrete cells do form, a large hail and damaging wind threat would present itself earlier, but EPAWA believes this is less than a 1 in 5 chance given current observations as of 8:30am local time on Sunday.

Tornado threat is on the lower end for our coverage area. The main dynamics for thunderstorm development come in before the wind fields become supportive of tornadic thunderstorms. If a boundary is present and backs the low level and surface winds to the south then this will be an issue, but no hint of this until after the best forcing moves out. Please follow the Facebook page for rapid updates and changes as necessary throughout the day.

Forecaster: Martrich/DeFino 27Jul0042z


Current Watches, Warnings and Advisories for Pennsylvania Issued by the National Weather Service

There are no active watches, warnings or advisories
Author: w-nws.webmaster@noaa.gov
Posted: August 1, 2014, 7:44 am

Current Watches, Warnings and Advisories for New Jersey Issued by the National Weather Service

There are no active watches, warnings or advisories
Author: w-nws.webmaster@noaa.gov
Posted: August 1, 2014, 7:44 am

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