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Localized severe thunderstorm event possible Sunday

A complex weather system will shift toward the area from late Saturday into Sunday, with tropical moisture surging northward as it moves into parts of the Northeast United States. The main surface low pressure area will track into Southeast Canada, while a secondary low pressure area will dip southward into New York State and New England. This will help draw in more southerly winds with moist, unstable air making its way toward the area as Sunday goes on.

At the surface, a warm front will move northward from the Mid Atlantic states towards Central New Jersey by Sunday afternoon. As it does so initially, showers with embedded thunder will likely shift northeastward through the area. Occasionally torrential downpours are anticipated as it does so. The main story, however, will come during the afternoon as the warm front sets up shop near Central New Jersey on a west to east axis.

NAM model showing supercell parameters over New Jersey and Eastern PA on Sunday afternoon. Note the sharp cutoff near the warm front.

NAM model showing supercell parameters over New Jersey and Eastern PA on Sunday afternoon. Note the sharp cutoff near the warm front.

As this occurs, near and to the south of the warm front, further atmospheric destabilization is anticipated. Forecast models indicate the presence of 1000-1500 joules of surface based CAPE, occasionally more than that, within this “warm sector” (i.e south of the warm front, but ahead of the cold front). Meanwhile, favorable wind fields and shear for the organization of thunderstorms will be approaching that same area.

The juxtaposition of instability, and very favorable shear for storm organization, as well as an approaching front and associated lifting, will be the focal point for the development of strong to severe thunderstorms on Sunday afternoon. Of additional concern is the presence of the aforementioned warm front, which may enhance southeasterly winds in the low levels, causing additional rotation within thunderstorms. In these areas, a few tornadoes are possible as the severe thunderstorms move through.

NAM model forecast sounding for Western NJ, showing the potential for tornadoes in severe thunderstorms.

NAM model forecast sounding for Western NJ, showing the potential for tornadoes in severe thunderstorms.

Strong winds and isolated hail will also be threats with these strong to severe thunderstorms. The main question, at this point, is exactly where the warm front sets up. To the northeast of the warm front will be stable, marine air with northeast winds (near the NYC Metro, and Long Island). To the south of the warm front, as discussed earlier, will be a moist, unstable south/southwesterly flow. Pinning down exactly where this front sets up will be critical to the forecast.

The Storm Prediction Center has issued an “Enhanced Risk” of severe thunderstorms for much of Southwestern New Jersey and the Mid Atlantic States, with a “Slight Risk” farther north into New Jersey and towards New York City. The higher chances for more organized severe weather, currently, are to the southwest of the city and away from the coast. Here, several strong to severe thunderstorms with the potential for impactful weather hazards (strong winds, hail, a few tornadoes) appear likely on Sunday afternoon.

Stay tuned for updates over the next 24 hours as the forecast comes into better focus. And, as always, follow our social media accounts for up to the minute information. Finally, if you’re looking for a more detailed and technical forecast, make sure to register for our Premium Membership.

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