Epic Upslope

Courtesy: Stowe

I got an email this morning saying:

“I have a condo up north in the mountains and I was very concerned after reading your tweets about up to 2 feet of snow this weekend… you need to be careful about your alarmist tweets”

It turns out that some areas in Vermont will wind up with 3 1/2 feet of snow from an absolutely exception upslope snow event along the spine of the Green Mountains from Killington on north!! Killington has picked up a foot, Stowe and Jay over 30″ as of 7 p.m. Saturday and it’s still dumping.

Snow like this is localized to along the spine of the mountains that run the length of the state. In this case the snow was focused in central and northern Vermont with relatively little in the south.

With westerly and northwesterly wind and plenty of low level moisture the rapid rise in elevation from the Champlain Valley to the Greens forces the air to rise rapidly. The lift  is comparable to a storm that just parks over the same spot and doesn’t move (you can’t move mountains like you can move a storm). Instead of lift being cause by processes in the atmosphere in “upslope” we get lift cause by the wind blowing up over terrain which yields upward vertical motion and if strong enough clouds and precipitation.

Here’s the radar from Burlington that shows the impressive dump of snow that continues in the mountains.

Courtesy: WeatherTap (click on image to animate)

It looks like many areas in central Vermont will see 1-2 feet total from this storm. The mountains in northern Vermont north of I-89 should see around 40″ of powder. Absolutely epic!

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Snow Tonight!

A cold front in eastern New England is producing snow across western New England! Weird, right?

This is what we call an anafront.  These produce precipitation behind the front (as opposed to ahead of it) thanks to strong frontogenesis. In addition there is some mid level “lift” thanks to a series of shortwaves wrapping around the trough to our west.

The radar is impressive and some towns in Connecticut could pick up 1″-2″ of accumulation tonight though most towns will see only a coating. Across Vermont more impressive snow aided by a upslope snow could produce a half foot over the high terrain.

It’s Cold Enough… Where’s the Snow?

Not in Connecticut. And it’s not coming anytime soon. A few days ago Friday and Monday looked good for at least some snow but today it appears that the threat for snow is quite low.

A weak Alberta Clipper is going to go through an atmospheric meat grinder on Friday with little lift and moisture left for snow production. Some flurries or sprinkles are likely but that’s about it.

120 Hour ECMWF 500mb (left) and SLP (right)

 

A storm Sunday into Monday that showed some promise now appears poised to cut into the Great Lakes. A -NAO block is going to shift too far east to keep the storm track suppressed and a strong polar vortex in south central Canada is going to phase with the storm and yank the thing inland. Bottom line is rain. Maybe a lot of rain.

Even northern New England may not be immune from the rain come Sunday. Hopefully this storm will trend a little bit further east to spare the mountains that have done so well from upslope snow this week a monster rainstorm.

Upslope Snow Stays North

It appears that the best upslope snow will stay north of central Vermont as drier air has filtered in to areas south of I-89. Though Stowe and Jay Peak will likely pick up 3″-6″ of snow from this event (and even more by Monday) areas like Okemo and Killington will see little.

Here’s the 12z 4km-WRF run by the National Weather Service in Burlington, VT. This high resolution model helps pinpoint the potential for small-scale snow events like upslope snow or lake effect snow. A model with very high resolution like this one (4km) allows the model to resolve small changes in topography that would be broad brushed in a larger model. You can see 24 hour precipitation totals over 0.5″ across the Chittenden/Lamoille county line along the spine of the Greens (>4000 ft) which indicates significant snowfall. Farther south the precipitation forecast tapers off significantly to the south of Sugarbush as drier air will preclude a more widespread snow event.

This may change a bit on Monday and Tuesday as a second storm rotates in but at this point it looks like northern Vermont will cash in again. Killington and Okemo skiers shouldn’t worry, however, as plenty of cold means plenty of snowmaking and natural snow chances increase quite a bit by late this week!

Snow for the Mountains, Cold Elsewhere

A large low pressure system is part of a major block in the northern Hemisphere that extends from the northeast US through western Europe.  A series of storms will develop around this upper level low but will miss southern New England. Downeast Maine and southern Quebec will be hit with snow over the coming days from these storms and a persistent northwest wind along with waves of moisture and lift will be sufficient for a major upslope snow event in the Green Mountains of Vermont.

Though the bulk of the snow will be across northern Vermont, central and southern areas above 2500 feet will see some flying on and off from Saturday through Tuesday. Generally 2″-4″ is expected for most elevated areas though the higher elevations and areas that tend to get more upslope snow (like Killington) could pick up 4″-8″+ of snow in this long duration event.

For areas not getting snow (like most of southern New England) an unseasonably cold and cloudy airmass will settle in. Periods of flurries are possible but they won’t amount to much. Temperatures will stay in the 30s for many areas though the valley locations and shoreline will be nearly 40. Temperatures will slowly drop through the middle of next week where 30s will be the rule everywhere for daytime highs.

Our next storm threat appears to be in the 12/13-12/14 period as the block relaxes some and the storm track energizes and changes. This could turn into a winter storm for most of us… stay tuned!