"Deformation Zone" Snow Dumped Extra Snow On Narrow Northeast Bands

Radar imagery from Saturday evening showing two
"deformation bands" with heavier snow (in green)
 One extends from coastal Delaware and New Jersey
 into southern New England, while
another longer and more defined one runs from
northeastern Virginia all the way to Maine.

Something weather geeky fascinated me during the snowfall that hit the East Coast yesterday as that southern snowstorm headed north and east and off the New England coast.

The storm had some of the longest and most defined deformation zones of any storm I've seen in awhile.

I know, I  know, I'm already getting you in the geek weeds.

Very often with nor'easters - and this storm was a relatively weak semi-nor'easter - a narrow band of heavy snow sets up and stays nearly stationary to the northwest of the storm.

Under this band, people often get much heavier snowfall than everybody else affected by the storm.  Sometimes there are two or even more narrow bands of heavier zone associated with deformation zones.

Here's why we get deformation zones. To the east of a storm, there's usually basically a conveyer belt of warm, wet air heading north. This warm air finally reaches a warm front associated with the storm. The warm, wet air crosses over the warm front and is forced to rise up and over the cold air to the north of the front.

As this happens, some of the rising air curls west toward the northwest flank of the storm. Other parts of the warm moist air rise and curl to the east. The more rising air you get the more likely you are to get precipitation and the heavier it is likely to be. Also, since the warm air aloft is splitting away, west and east, other air has to replace the warm stuff that split off and away. So even more air has to rise to replace the "missing" air.

So now we have two reasons why the air is rising. Which means it rising most on that narrow band where the warm air is splitting aloft. So you get a lot of precipitation in that narrow band. That's pretty much what happened yesterday.

The storm wasn't all that strong, so snowfall amounts weren't huge. Under one band, six or seven inches of snow fell from south of Albany northeastward into the Massachusetts Berkshires and far southern Vermont. A few miles east and west of this band, snow totals were closer to three inches.

In very strong storms, snowfall in a deformation zone can be really impressive. A deformation zone is a good part of the reason northwestern Vermont and northeastern New York were hammered by two to three feet of snow during the blizzard we had this past March 14.

Almost every nor'easter has a deformation zone, so we'll almost certainly see more of them this winter. The next chance of snow in New England and across Vermont is on Tuesday into Wednesday. Don't know yet if we will be dealing with any deformation zones, though.