Posts

John Homenuk

PM All Zones Update: Interior winter storm Tuesday night

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A low pressure area is expected to shift from the Mississippi Valley into the Eastern Great Lakes on Tuesday, bringing enhanced lift and aiding in the development of precipitation over much of the Ohio Valley and Northeast. Much of this precipitation will be driven by a process known as Warm Air Advection. In other words, warming air surging through multiple levels of the atmosphere will be the impetus for precipitation.

It will also serve to ensure that most areas in the Mid Atlantic and near the coast warm up sufficiently for precipitation to fall as rain. Inland, however, a different story will evolve. Cold air from a high pressure to the northeast will settle near the surface, allowing temperatures to fall into the upper 20’s and lower 30’s. A gradual warmup is expected to occur from southwest to northeast, but not before some light wintry precipitation even in parts of Pennsylvania and Northwest NJ.

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John Homenuk

Snow returns tonight to the interior, higher elevations

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The second snow event in the Interior Northeast in as many days will unfold later this afternoon and evening, likely lingering through Wednesday morning, as a storm system develops into the Ohio Valley and eventually off the Mid Atlantic Coast. The primary surface low will drive northward into the Ohio Valley, helping moisture surge northward into the Northeast United States with a southwesterly flow.

Meanwhile, the secondary surface low will develop off the Mid-Atlantic coast which at least in some small scale will aid in cold air filtration into the system from a cold high pressure to the north. The main process allowing snow to fall in Northeast Pennsylvania, Northwest New Jersey, and Southeast New York, however, will be dynamic cooling, which occurs when precipitation falls heavily enough to cool the air around it.

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John Homenuk

Another interior snow event likely Tuesday evening

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Light snow fell throughout much of the interior on Monday morning, with higher elevations in Northwest New Jersey and Southeast New York reporting nearly 2″ of snow as of 9:00am.While this lighter and weaker disturbance moves away later on Monday, a second and more notable disturbance will be approaching from the southwest. Increasing moisture and lift, as well as warm air advection, will approach the area on Tuesday — allowing most areas near the coast and even in the suburbs to warm up enough to support rain.

But farther inland, in the higher elevations and mountains of Northwest New Jersey and Southeast New York, the atmosphere will remain just cold enough as this moisture and lift approaches. In fact, the dynamics of the storm system itself will help to cool the atmosphere in an aptly-named process called “Dynamic Cooling”. Forecast models are in good agreement that this moisture will overrun cold air — allowing snow to fall later Tuesday afternoon and evening into early Wednesday morning before an eventual changeover to rain.

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