Long Duration and Low Impact Storm

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Here’s the forecast that Brad and I came up with earlier today. As I wrote about on Monday this is an odd storm. We have a big ocean low that is getting wrapped up into a large omega block.

The storm will pass well south of the 40N/70W “benchmark” and take an unusual path that involves a stall, probable loop-de-loop and eventual slow meander south and east into the open Atlantic. In addition, a shortwave in the Great Lakes will become entrained in this storm late Thursday and early Friday and may bring a second period of accumulating snow late Thursday night and around daybreak Friday.

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The reason why the precipitation field will be so expansive is that this storm is just a large one from an areal extent. Strong -u wind anomalies will be in place well removed from the storm’s center. Here’s the GEFS mean -u wind anomalies that approach 4 standard deviations over southern New England!

Screen shot 2013-03-05 at 9.58.16 PM

This is what will look like an Atlantic “firehose” with moisture pouring in off the Atlantic. This setup favors areas to our east across the eastern Massachusetts coast but we’ll get in on some of the action – but most of the “good stuff” misses to the east.

In general, with the strongest LLJ staying south and east of the region, the storm center passing so far south of the benchmark, and forecast frontogenesis fields that are spotty at best (i.e. strongest south and east resulting in more meager vertical motion to do the frontogenetical circulation).

More spotty precipitation and snowfall rates less than 1″ per hour will be the main impediments to more significant snow. The arguments of “high sun angle” and “warm temperatures” are not valid. It’s March 5th – not March 20th. If the snow doesn’t stick it’s because we’re getting garbage rates!

With the unusual setup and computer models that have been quite poor and inconsistent forecast confidence is unusually low for 24 hours prior to an event. In any case, the long duration and generally low snowfall rates, should make this a relatively low impact event.

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