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(Premium) Dynamic cooling may bring snow to some on Saturday

While the calendar has pointed to Spring for several days, the weather pattern has not cooperated. This weekend will be no exception. Forecast models have come into better agreement over the past few days regarding the eventual development of a low pressure system off the Mid Atlantic coast, which will form as a result of a powerful mid level atmospheric disturbance dropping southward from Canada into the Great Lakes and Northeast.

A low pressure system is likely to develop from the Ohio Valley into the Mid Atlantic and off the coast of New Jersey. Precipitation is likely to develop on the northern end of the storm system, as moisture pushes northward from the low pressure area. This will allow for bands of precipitation to develop towards our area, likely falling as rain. The antecedent airmass is quite warm, and likely supports rain over any frozen precipitation, with melting of snowflakes occurring in the lower levels of the atmosphere. However, there is one main caveat in the setup: The potential for intense banding and dynamic cooling, producing heavy snow over some areas.

12z NAM shows moderate-heavy banding over Northern New Jersey, New York City and Long Island tomorrow afternoon. 500mb and 700mb low take track just far enough south to be favorable for heavy banding with inverted surface trough.

12z NAM shows moderate-heavy banding over Northern New Jersey, New York City and Long Island tomorrow afternoon. 500mb and 700mb low take track just far enough south to be favorable for heavy banding with inverted surface trough. These lows cause positive vorticity advection and frontogenesis from over Central New Jersey to Long Island (Image credit: PSU Ewall)

Essentially, this band of heavy precipitation will allow for dynamic cooling to occur, when heavy precipitation cools the thermal column and allows snow to fall. The location, timing and intensity of this band will be of critical importance for the forecast, and will likely determine which areas observe snowfall and which areas observe just rain. Forecast models, not surprisingly, have been wildly inconsistent with the details of this band.

NAM model showing very strong lift in a band of heavy precipitation on Saturday, allowing for dynamic cooling and snow.

NAM model showing very strong lift in a band of heavy precipitation on Saturday, allowing for dynamic cooling and snow.

Over the past day or so, the aforementioned forecast models have trended northward with that band — placing it somewhere in the vicinity of Central and Northern NJ and NYC. This band will elongate from west to east, with the low pressure system passing south and eventually southeast of our area on Saturday. But the fine line between rain and snow will be a nightmare to forecast — and deal with. Once the precipitation rate gets heavy enough, rain will change to snow, and pinning down where that occurs won’t be possible until we are closer to the forecast and short term/mesoscale models become more useful.

The GFS bufkit overview showing strong omega (lift) in snow growth region. This amount of result in more dynamics cooling with higher snowfall rates tomorrow afternoon. Using the the Cobbs13 technique (factors in strong omega) it shows 8.0" of snow accumulation for LaQuardia Airport, NY

The GFS bufkit overview showing strong omega (lift) in snow growth region. This amount of strong lift could result in more dynamic cooling down to surface with higher snowfall rates tomorrow afternoon. Using the the Cobb11 technique (factors in strong omega) it shows 8.0″ of snow accumulation theoretically for LaQuardia Airport, NY.

Some models remain farther south with this band, with an area of heavier snow over Central NJ and rain on the outskirts of the band over NYC and Northern NJ. Both solutions remain on the table. Also with models showing some snow occurring the during the afternoon hours, strong solar radiation at this of year, may keep many roads more wet and limited more snow accumulation to colder surfaces. Especially in more urban areas, such as Manhattan. Over the next 12 hours our forecasters will continue attempting to pin down the bands, timing, and boundary level temperatures in each location.

We anticipate a live blog at some point on Friday Night to discuss the incoming short term weather models, our snowfall forecast, and hazards impact information.

This post was written and edited by John Homenuk and Miguel Pierre.

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