The Big Picture

The Big Picture

Monday
December 30, 2013

Below is a simple visual illustration of the factors at play in the making of this week's potential snow storm.

Here are the key points:

A) Area of low pressure across the Pacific Northwest:
-Will produce a swath of snow across the northern U.S.

B) Area of low pressure over Mexico:
-Will pull moisture up from the Gulf States.

C) High pressure across southeastern Canada:
-Will filter in enough cold air to keep the Northeast below freezing.

The reason that this week's storm looks to be significant is because it is essentially two storms in one. The low pressure across the
Pacific Northwest will trek across the northern U.S. bringing light to moderate snows. At the same time, a low pressure will trek across the
Gulf of Mexico, and up the eastern seaboard.

20131220s_Ngraphic.jpg

The Pacific storm will begin to affect New York early Thursday morning. This system alone would normally be enough to produce respectable amounts of snow across our region. By Thursday evening, however, the Gulf low is expected to pass close enough to the coast to throw moisture (snow) back across the northeast as it intensifies off of the Mid-Atlantic coast. This low will then become the dominant one.

Right now, the main source of uncertainty lies with the Gulf low. The amount that this piece affects us …that is, how far off shore it stays… will ultimately determine our storm totals. Less of a Gulf impact will result in most of our accumulations resulting from the Pacific low. More of a Gulf impact will result in a more equitable contribution… and higher totals.

The Gulf low will also affect how long the storm lasts, since the Pacific low will affect us earlier on Thursday, and the Gulf low will influence overnight snow accumulations into Friday.

Current thinking suggests, the Pacific low will contribute about 3 to 7 inches of snow during the day Thursday. The Gulf low may contribute 3 to 6 inches of snow Thursday night as it strengthens and absorbs the Pacific low.

The third significant factor that will affect our storm totals is the Canadian high pressure. Not only will this keep our temperatures well below freezing for the entire duration of the storm, but it will also result in very fluffy snow (and thus higher than normal totals) as temperatures will be in the teens and 20s.

Friday night, the combination of the strengthening low pressure and the high will produce the coldest temperatures that we have seen this season.
Lows Friday night look to fall to and below zero across the Mid-Hudson Valley, with highs barely getting into the teens. That doesn't even
include the potential windchills!

Long story short: looking at a very favorable set up for at least a moderate snowfall. Best thinking at this time is for a snowfall in the broad 6 to 12 inch range, with that Gulf low ultimately determining whether we fall on the high or low side. The final pinpoint totals will undoubtedly shift around over the next two days.

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