The snow squalls in New England Saturday night, November 23, formed along the front edge of an air mass arriving from the Northwest territory of Canada.
In Bedford New Hampshire the snow lasted only 15 minutes, but left this parking lot (and all the city streets) coated in snow and ice. Similar to afternoon thunder storms in springtime. These snow shower and squalls formed along an (Arctic) Front due to great instability. Not every weather front is the same. This one was 'special'. Just the right amount of moisture, confluent wind, and steep thermal lapse rates.
Our photographer here in Bedford NH is Weir Lundstedt of Merrimack. He is a meteorologist, Lyndon State College Vermont class of 1986. You may know some other names form that class.. Tony Petrarca in Rhode Island, Russ Murley and Roger Griswold in Maine, Jim Cantore at The Weather Channel in Georgia. I graduated LSC in 1987 and became Weir's roommate in Manchester New Hampshire when he worked at The National Weather Service in Concord New Hampshire and I was at WMUR TV 9.
Weir wrote the seminal paper on how to determine which cold fronts are most likely to cause such snow squalls here in the Northeastern United States. Have you heard the expression Windex? Weir coined the term, standing for 'Wintertime Instability Index' in 1992, long before the weather models were able to forecast such localized special weather events. His paper is here. We have Weir's thought's on winter 2013/2014 below, after a description of the pre Thanksgiving Day storm.
Beyond the local snow squalls, the arctic wind caused more continuous snowfall in up-slope areas of Northern New England. In the case of the squalls, the weather front caused the moist air to rise, cool, and condense into snow flakes. In the mountains, we call it orographic lifting. Wind hits the mountain and rises up with similar result to the weather front. As long as we can maintain a moist flow with steep lapse rates (much colder air in the sky than near the ground) the up-slope snow can continue.
These photos below are from Stowe Mountain Resort in Vermont, where Scott Braaten measured 6"+ snowfall before sunrise Sunday the 24th.
The next image is from the cams on my web site surfskiweather.us
The above was written Sunday, below is from Monday (though maps are from Sunday)
European Model (ECMWF) has been consistent phasing the northern stream (air from North Pole) and with the southern stream (air from east of Hawaii) to the west of New England. Here is ECMWF Sunday Nov 24 run valid Thanksgiving Day. The red ink shows the track of the two lows (North & South) coming together and tracking from Connecticut to Maine. This is a warm solution for New England. We call it an inside runner (west of 'benchmark', 40 degrees north, 70 degrees west), where warm air from the south floods New England. The amount of moisture in the Atmosphere is 3 standard deviations greater than normal for this time of year. That means we get tropical downpours Wednesday. Rainfall may exceed 5 inches in spots. Also the pressure gradient created by the departing 1036 millibar high, and the 'bombing' low pressure deepening rapidly below 990 millibars will generate gale to storm force wind. We may be dealing with widespread power outages for the second time in three days.
The map above is from Sunday. Now that we have access to more weather guidance.. it appears the numbers are low. It could be more like 40-60 mph wind, with many 3"+ rainfall amounts.
West of the storm is where snow falls. The mountains form Pennsylvania to Ontario may measure snowfall in feet.
Needles to say this will create disruptions throughout the northeast.
Our best hope is that we have some drying Wednesday afternoon. But in the time since these maps were created, it appears that is a not the likely outcome.
Thanksgiving Day is little like Sunday, just not quite as cold or windy.
I wanted to highlight Weir's winter outlook.. but the storm takes precedent.
Here's a hint.. "waves of record/near record cold.."
We will get more into the winter outlook as winter gets closer (ha ha).. and we have a few days without an extreme event (if that happens).