Thursday, February 21, 2013

UPDATED Blog : Storm Details...Winter Continues !

  For a third straight weekend a potential major Winter Storm will affect Southern New England. There remains no doubt that a storm will bring wintry precipitation to our area late Saturday through the day on Sunday. Storm details as of now are a bit sketchy though this thing will have plenty of moisture to work with feeding off upper level low energy over the northeastern Great Lakes and moisture sources from the Gulf of Mexico combined with Atlantic moisture being thrown into the primary storm that forms off The Mid-Atlantic late Saturday.
The Players: The piece of energy we are watching now is bringing wild weather to the midsection of the United States today and will move off  to the northeast as an Upper Level Low over the Great lakes. During that process sometime Saturday the energy and lagging moisture from that will form a primary low pressure somewhere between Cape Hatteras North Carolina and Southern New Jersey. THAT placement on where in the end that primary Low pressure forms is extremely important to this forecast. Either way the storm will travel to the NNE, then take a jog east in response to upstream blocking and a negative North Atlantic Oscillation. It will likely slow down a bit on its approach to southern New England and pass near our 40/70 benchmark and then make a pass close or southeast of Nantucket as a 998-990mb low. That is much weaker on a storm than the past 2 so damage hopefully will not be as bad . One thing with this storm as it has rich Gulf of Mexico and especially Atlantic moisture feeding into it, there will be a shot of warm air advection ahead and mixing issues and possibly lots of rain will be present near the coastlines, with potential for snow on front end and back end. That is how it looks just at this point. It is important though to remember as always that slight shifts will and could make a huge difference in both amounts on precipitation and precipitation for any given location geographically throughout Southern New England. Between a spread of operational and ensemble weather models , anywhere from ¾” - 2” of accumulated liquid precipitation can be expected at this time. Along with the precipitation, there will be the potential for a few strong wind gusts especially near the coast of eastern and southeastern areas.The heavy rainfall and especially areas with a deep snowpack still over coastal areas may bring some poor drainage flooding.A minor storm surge is also possible. Wave heights build to 10-20 feet off our coastlines.
How it should play out: Moisture levels in the upper atmosphere start to increase Saturday and especially Saturday afternoon ahead of our pending Winter Storm. We are likely to start to see mixed precipitation break out along the South coast and perhaps a plain rain there Saturday evening. That mix line could make it all the way up to the Mass Pike by late evening. From that point on it will begin to crash back towards the coastlines bringing a flip back to snow for many except extreme southeast Massachusetts and Cape Cod and the Islands.
All the meanwhile a heavy wet pasting snow is likely along and north of The Mass pike into Sunday morning with the heaviest shifting towards the east and northeast areas as low pressure moves off to the east and northeast on our area and a northeast wind will bring some enhancement to eastern , north eastern Mass and into the seacoast of New Hampshire. That area could be the “PivotPoint” zone where the snow hangs on a bit longer with NE fetch and blocking doing it think so to speak.
Winds not a huge problem though sustained winds will increase on the order on 15-20 miles per hour for central and eastern southern New England starting Late Saturday eve and likely sustained to near 25-35mph over Cape Cod and The Islands. Those winds continue right through at least the first half of Sunday before working offshore. Wind gust from late Saturday through Sunday will be on the order of 30-40mph favoring south and east of The Mass Pike and possibly as high as 50mph for Cape Cod and The Islands. While we have seen worse in recent storms it is certainly capable in combination on heavy wet snow expected and even heavy rainfall to saturate the ground/tree structure that some power outages are likely. With all this said, the coast looks to have mixing and or rain issues so accumulations held down low near these areas. Heaviest snowfall at this point is along and especially north of The Mass Pike into southeast New Hampshire where either side of a foot of snow could fall.

This is an initial snow map and further shifts remain possible and even perhaps likely with this storm. Also important to always look at the forecast range amounts .(my motto is low numbers likely-high ,possible). Precipitation ends later on Sunday and winds slacken and we are given a brief break on Monday and much of Tuesday before another potential Winter Storm almost similar to this one. That has potential for stronger winds and also a mix line.
Why all the storms as of late you may ask?. Well, the 500mb pattern has been conducive for development over the past 3 weeks or so and will continue to be right into March and beyond perhaps. Combine that with teleconnections all lined up for potential winter storminess. The AO is providing the occasional cold blasts with the PNA ridging out to the west in a positive phase occasional sending troughs across to the eastern U.S. and most importantly a negative NAO providing a Greenland Block and room for anything that touches the east coast to keep our area on our toes. Beyond mid week next, a cutoff low may form near or off our coast and could deliver multiple surges off moisture off the Atlantic for a couple to perhaps a few days and bring more precipitation and in the form of accumulating snow for many. Stay tuned and thanks for reading   ~Anthony

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