Colder, snowy pattern evolving coast to coast…

As we hit the holiday season, the weather pattern is changing to one that will soon be dominated by colder than normal air.  Cold air has been in relatively short supply for a couple of weeks now, but in the past week, a series of troughs have descended into the West, leading to several sizable snow events that have given the season a badly needed jump-start in the coastal ranges with lighter but helpful snow further inland.  Elsewhere, snowmakers have had to pick their spots for cranking out crystals, and trail counts have been creeping upward in the Midwest, Northeast, and central and southern Appalachians.  What is needed is a jet stream pattern change that taps more cold air from Canada and thankfully, here it comes.

Here’s the current state of the jet stream…

There are several features of note on this map, which is valid on Friday the 17^th.  First, there is the broad ridge over the eastern U.S., with the center of the feature the closed circle that you see north of the Bahamas.  This ridge is a common feature in a La Nina winter…when it is strong, as is the case now, mild air spreads north.  When it is suppressed, cold air penetrates further south from Canada.  There are two troughs over the western half of the country…one over the Dakotas and the other over Baja California.  Both were responsible for snow earlier this week.  The northern feature will help to break down the ridge and produce a light to moderate snowfall over the interior Northeast this weekend.  The last item is the ridge over Greenland and the trough south of it, over the waters of the Atlantic.  This couplet forms a classic “Negative NAO”, or North Atlantic Oscillation.  When the NAO goes negative, it blocks the progression of jet stream features over much of North America.  Typically, a negative NAO leads to a persistent trough over the eastern half of the U.S. and that is where we are headed.

Here is a forecast for the jet stream on Christmas Eve, which I generally agree with…

You can see the negative NAO ridge/trough couplet top right.  The troughs over the east coast AND west coast hold the promise of colder weather and natural snow in both regions.  The ridge over Alaska, with its clockwise circulation, will tap into the very cold air stored over the northwestern part of the continent and send it further south.   As the holiday week progresses, the Yukon connection will bring about a trend toward colder temperatures from the upper Midwest into the East, all the way down into the mountains of North Carolina.  The jet stream setup that you see on this map is just about perfect for benefitting resorts coast to coast…those trail and lift numbers should be on rise from this weekend right through the holiday week.  Here’s a look at snowfall predicted through Christmas Day…              

During the holiday week I expect the snowfall numbers to increase in the East and spread down the Appalachians, in anticipation of the presence of the trough that will enhance snowfall opportunities.

Here are regional highlights…    

Northwest U.S./Western Canada:  Pattern favors a trough offshore for a while…leads to frequent episodes of moderate/heavy snow.          

Sierra:  Quiet weekend but significant snow returns Tuesday-Thursday next week.  Another storm around Christmas Day           

Rockies:  Northern resorts in a good position for snows in the next week…south of I-70 best chance will come late next week 

Midwest:  Upper trough, Clippers, lake effect, and snowmaking keep trail counts growing through the holiday period 

Mid Atlantic/Southeast:   Productive snowmaking next week…natural snow a good bet Christmas Week.        

Northeast/QB:  Moderate snow this weekend north of I-90 in NY/NE.  Snowmaking and natural snow push trail counts up going forward through the holiday 

Pattern coming alive on both coasts…

Thanks to snowmaking and a nice dump of fresh snow last Friday, I kicked off my season with a nice day on the trails of Killington this past Tuesday. The surface midwinter stuff and it was fantastic to be making turns again. The storm late last week helped out across much of the Northeast, but more is needed not only in that region, but across the entire country, as trail counts and opening dates are lagging nationwide this year. Fear not, though…help is on the way!

The current jet stream setup has been in place for a few weeks now, with a western upper ridge coupled with a broad trough over the eastern half of the country, as illustrated by this map, valid the morning of the 3rd….

The ridge (orange) has kept the West high and dry while the trough (blue) further east has supported weak systems that have spun through the Lakes into the Northeast. Each one of those disturbances has delivered a modest shot of colder air, allowing snowmakers from Ontario and Quebec to North Carolina to get the season rolling on a limited basis. The trough will remain in place for the next several days, but by the 6th, changes will get underway. A new trough will dive into the center of the country and deliver a significant shot of cold air…good news in the upper Midwest. To the east, a mild upper ridge will pop up in response, with low pressure taking a track between the two jet stream features, from the mid-Mississippi Valley up through the Great Lakes and on toward Toronto and Montreal. In the East, that track will produce rain and then snow as cold air rushes in on the backside of the storm. Next, a weaker midweek disturbance will bring light to moderate snow from the central Appalachians into New England and eastern Canada.

The biggest pattern change is coming to the West and not a moment too soon with the holidays just a few weeks away. While the initial thrust of cold air will move into the northern Plains, several additional systems will move south from Canada in the coming week, breaking down the ridge in the process. The first will impact the far northern Rockies and southern Canada this weekend, the second will reach the central ranges Monday and Tuesday, and then a late week trough will dive all the way into the Southwest, producing the biggest snowfall of the young season in the southern Sierra and Rockies as it does. Here is a forecast of snowfall through next Friday night…

You can see that significant, beneficial snow can be expected not only in the West, but also in the upper Midwest and the northern regions of New York and New England. Deep cold is still a little tough for the pattern to access, so snowmaking will still be hit and miss in the near term. Longer term, the week of the 13th will bring a western cold trough/eastern mild ridge couplet, with the potential for a nationwide cold and snowy pattern developing the week of the 20th. Here are the regional highlights…

Northwest U.S./Western Canada: Snowy week unfolding…snow levels lower than recent two weeks will help.

Sierra: Dry start, but pattern turns snowy mid to late week onward(north to south)
Rockies: Snowy pattern develops from northern (early week) to central and southern resorts (mid to late week).

Midwest: Favorable storm track and cold period unfolding next 1-2 weeks. Trail counts and bases will grow quickly.

Mid Atlantic/Southeast: Mild weekend/early next week. Colder air supports snowmaking and some snow by midweek.

Northeast/QB: Cold weekend with some light snow. Rain and backside snow early in the week. Light to moderate snowfall midweek.