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Multi-hazard system will affect the area midweek

A large and intense low pressure system will form over the Mississippi River Valley and move northward toward the Ohio Valley and Southeast Canada this week, as a result of an impressive phase in the mid and upper levels of the atmosphere. In our area, two distinct areas of low pressure will actually impact our weather; the first from Tuesday into Tuesday Night, and the second from Wednesday into Thursday. Both will feature wildly differing weather conditions, with snow possible across the interior on Tuesday and then heavy rain, warm temperatures, and thunder on Wednesday Night from the second storm system.

The initial storm system will form as a result of a weak disturbance in the mid levels of the atmosphere. On a height gradient shifting northeast, the storm will remain quite progressive. However, precipitation will form on the leading edge of warm air advection in the mid and low levels, while cold air hangs on just a bit with high pressure shifting northeast away from the area. The result will be the potential for a brief period of snow before a changeoever to rain, with snow hanging on for a longer period of time throughout the interior/higher elevations of Northwest NJ, Southeast NY and Connecticut.

To the northwest of a “coastal front” which forms as warm air pushes in from the coast and cool air remains entrenched inland, a few inches of snow will be possible. This is most likely, as mentioned above, in the higher elevations and interior. Nearer to the coast, Tuesday’s event is more than likely to be a brief period of snow, followed by a cold rain which will end later in the evening.

NAM model showing a period of snow in the interior on Tuesday.

NAM model showing a period of snow in the interior on Tuesday.

A much larger storm system approaches on Wednesday, as it strengthens in the Mississippi River Valley (producing severe weather in the Southeast States) and then moves northward toward the Ohio Valley. A deep southerly flow will advect warm, moist air into the region, allowing temperatures to warm and atmospheric moisture content to dramatically increase. Periods of heavy rain are likely on Wednesday as the storm system moves toward our latitude.

On Wednesday evening into early Thursday morning, a period of heavy rain is likely. A cold front approaching the region will force heavy precipitation, while atmospheric dynamics will bring the potential for thunder and gusty winds. Accordingly, the potential will exist for localized flooding, as well as coastal flooding with southeasterly winds and a low pressure to our west.

NAM model showing thunderstorms approaching our area late Wednesday Night in association with a cold front.

NAM model showing thunderstorms approaching our area late Wednesday Night in association with a cold front.

While the wind potential will be somewhat limited by a low level inversion, the heavy rain is currently modeled to be quite impressive. Especially directly near the cold front, forecast model show a narrow band of instability which could support very heavy downpours in thunderstorms. The storm system will shift northward, with the cold front crossing the region early on Thursday.

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