Posts

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

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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John Homenuk

Monday’s snow threat trends north, still a concern

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The winter weather potential for late this weekend into early next week has been well advertised. A low pressure system is forecast to develop from the Ohio Valley into the Northeast states late this weekend, along a thermal gradient otherwise known as a baroclinic zone, and force the development of precipitation in the Northeast States. Forecast models, however, had been displaying tremendous uncertainty with the positioning of that thermal gradient — uncertainties which were well documented. The past 48 hours have seen forecast models trend farther north with the thermal gradient, changing the complexion of the storm threat completely.

What this means for our area, is that precipitation type and amounts become less certain. The thermal gradient, essentially, is a boundary where there is a large temperature gradient over a short distance. Along and just north of this zone, enhanced lift for precipitation can occur as the development of a low pressure system is promoted near or just south of it. With this gradient trending north, forecast models have introduced warmer temperatures in the mid levels, and have shifted precipitation northward into New England.

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John Homenuk

Freezing rain, warmup prelude polar air intrusion

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As crazy as it may currently sound, temperatures in the 40’s and 50’s are not far away. The teens and 20’s which settled into the area behind the significant snowstorm on Friday have essentially dominated the weekend, but an increasingly strong southerly flow will eventually push out the cold air in favor of warmer air surging northward. The cold air will be slow to scour out at the surface, however, which could create the potential for freezing rain across the interior.  Below, a forecast sounding from Northeast NJ shows the very cold air trapped at the surface — but warm air aloft. This kills the development of snowflakes, so precipitation falls as rain, but the rain can refreeze at the surface once it falls as temperatures remain a few degrees below the freezing mark of 32 F. By later Sunday into Sunday night, forecast models are in good agreement that precipitation will have changed to all rain across the forecast area.

The warmup will come to a crescendo on Monday morning and early afternoon, just ahead of an approaching cold front. A large and powerful system forming over the Central United States (more on that below) will drive extremely cold air into the Central and Eastern United states by Tuesday. But along and ahead of the front, increasing low level moisture and rising temperatures will be the cause for showers and temperatures into the 40’s to near 50 early on Monday. Behind the front, the coldest air in recent memory will begin surging into the area.

A forecast sounding from the NAM model in Northeast NJ on Sunday. Notice the cold air (below freezing) trapped near the surface while warm air dominates aloft.

A forecast sounding from the NAM model in Northeast NJ on Sunday. Notice the cold air (below freezing) trapped near the surface while warm air dominates aloft.

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