Posts

John Homenuk

PM Zone Update: Multi-day winter weather in New England

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A multi-day (and multi-disturbance) winter weather event will unfold across New England over the next few days, with central and northern parts of New England in line for several inches or more of snowfall. Multiple disturbances in the atmosphere will traverse from the Great Lakes and Ohio Valley into the Northeast, with coastal low pressure systems forming in multiple fashions. The first moves from our southwest on Saturday evening into Sunday morning, and has trend more significantly in terms of wintry precipitation. Much of this can be attributed to the snowpack in place across the interior — keeping low level cold temperatures locked in more effectively.

Warm air both in the mid levels and at the surface will be moving north from the Mid Atlantic states as Sunday morning approaches. But moisture and lift, effective in developing precipitation, will move northward as well, allowing wintry precipitation to break out across the region. Across Northeastern PA, Northern NJ, NYC and LI, precipitation may begin as snow and sleet – remaining a wintry mix for a few hours before a transition to rain occurs. The wintry mix will occur longer across the interior and higher elevations of NJ, SE NY, and CT where low level cold air will remain more stout. Here, freezing rain and sleet are possible for a more prolonged period of time.

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Miguel Pierre

Interior wintry weather expected on Tuesday morning

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Skies will remain mostly cloudy through this afternoon and evening, as a cold front approaches from the northwest. Despite the cloudcover, a deep west-southwest flow will help temperatures will rise into the lower to middle 60s. A cold front will slowly move through the region with some scattered showers late this afternoon and early tonight. Precipitable water values near 1.25 to 1.50″ could support some heavy downpours with these showers.

A much colder airmass will follow behind this front late tonight and tomorrow, as a strong Canadian high pressure starts to build into the Northeast. Temperatures will drop into 30s for most areas by dawn. Cold air will continue to advect into region during the day tomorrow, on light north to northeast winds. Model soundings indicate mixing to 900mb-925mb where temperatures are -6C to -8C. Despite some sunshine, temperatures will slowly rise into the upper 30s to lower 40s for highs tomorrow afternoon. These temperatures are seasonal for this time of year.

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John Homenuk

Rough PM commute likely with snow, sleet expected

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A storm system developing over the Central United States will shift northward today, bringing enhanced lift for precipitation and forcing the development of snow from southwest to northeast throughout the area. As this lift shifts northeastward, snow will become steadier and heavier later this afternoon throughout the area. This snow will be falling as a result of increased lift for precipitation, owing to an increased southerly flow in the mid levels of the atmosphere as a result of warm air advection.

This warm air in the mid levels will continue to shift northeastward from the Mid Atlantic into the Northeast States, shifting precipitation from snow to sleet across much of Northern NJ and NYC by later tonight. In the low levels, however, cold air will remain stout — creating the potential for not only sleet, but ice accretion as well if the depth of the mid level warm layer becomes wide enough to support freezing rain. This will create treacherous conditions on roadways tonight across Northern NJ and the suburbs of NYC in SE NY and Connecticut.

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John Homenuk

Prolonged period of wintry weather to start the week

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A winter storm affecting the Northeast United States will begin as early as Sunday throughout the area, as lift for precipitation develops along a baroclinic zone and thermal gradient near the area. The forecast in terms of precipitation type and amounts, however, is not as cut and dry as it may seem. The thermal gradient both at the surface and aloft will differ in location, creating widespread differences in precipitation type and a very sharp gradient in potential snowfall and winter weather impacts.

In the mid levels, warming will occur between 850-900mb (above our heads, but not very far up in the atmosphere). This warm layer will push northward to a position near New York City on Monday. What this means, is that any snowflake which forms farther up in the atmosphere will fall through a layer of air that is above freezing. Essentially, it will melt. But our problems don’t stop there — the surface layer of the atmosphere (where we are) is very cold. And that means any precipitation which falls as liquid is going to re-freeze on the surface.

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