Since my last posting, I have only managed a couple of days on snow.  One at Sugarloaf after an 8 inch overnight and then a brisk day at Killington earlier this week on some of that cold, styrofoam that the NBC announcers have been referring to in the Olympic alpine events.  After a superb tuning at the outstanding shop at West Mountain in Glens Falls, New York the day before, that stiff snow at Killington was very playable.

As I look down the road at the evolving weather pattern to close out February and start March, I see a changeable landscape.  After a dominant western ridge/eastern trough couplet from mid-January until just recently, the pattern will be more changeable for the next week to ten days, but signs point to a return to the trough favoring the eastern half of the country early next month.  The changeable nature of things will allow a meaningful snowfall to impact much of the west later this weekend into early next week, as suggested by this jet stream map for President’s Day…

With a ridge poking up into Alaska, very cold air will flow into the western trough and while this doesn’t look like a blockbuster due to the lack of a direct influx of deep Pacific moisture, it should generate moderate to heavy amounts from the Cascades all the way down to the southern Rockies as it slowly pivots southeast and then east Sunday through Wednesday.  With the core of the trough heading down the spine of the central and southern Rockies, the Sierra will pick up light to moderate amounts south to around Tahoe from this system.

In the eastern half of the country, milder air will spread north in advance of the western trough, but not until after a seasonably cold holiday weekend.  By late next week, the trough will start to favor the Midwest and East, a development tipped off by the trend of both the WPO (Western Pacific Oscillation) and EPO (Eastern Pacific Oscillation).  These two indices are based on the relative positions of upper air troughs and ridges over the waters of the north Pacific.  Here is an illustration of a negative WPO…  

The orange indicates an upper air ridge, and the blue areas an upper trough.  The clockwise circulation around the ridge helps to access cold air from the northwestern corner of the continent. It works in tandem with a downstream trough, as suggested by the pale blue over the center of the country.  A negative EPO is similar.  Here is a forecast for the WPO for the next couple of weeks…

The green line is the one to follow and after running in positive territory, which infers a trough over the northern Pacific waters, it switches to negative around the 1^st of March, at which time I think we will see a trough start to strengthen over the eastern half of the country while a ridge returns to the West.  Colder air will populate that trough, and the first part of next month should turn stormy over the Midwest and East.  With the WPO remaining in negative territory well into March, the prospects are solid for late-season snow.  In my next installment, I will explain why March could bring snowy weather to the East AND the West.

Regional details…         

Northwest U.S./Western Canada:  Nice shot of snow late this weekend/early next week.  Next event about a week later.    

Sierra:  Late weekend light to moderate snow…another round next weekend.

Rockies:  Moderate snowfall early next week into midweek.  Next potential snowfall about 5 days later.

Midwest:  Fresh snowfall early next week.  Pattern remains loaded with potential snowfalls for the foreseeable future.    

Mid Atlantic/Southeast:  Mid Atlantic snow on the table for late next week.  Southeast chances enhanced in early March. 

Northeast/QB:  Clipper snow this weekend in the Northeast.  Late next week looks quite promising for more substantial snowfall.  March shaping up nicely. 

I had a couple of days on the snow early this week…a terrific day at Sunday River and a very disappointing day split between Wildcat and Attitash.  You can add me to the list of those taking Vail to task for the manner in which they are operating their eastern resorts and I will leave it at that.  The pattern has not been for the faint of heart of late, as an upper-level trough has been energized by the co-mingling of cold air from the north and milder air to the south.  We saw an east coast blizzard last weekend and an enormous storm this week, one that prompted winter storm warnings from New Mexico to Maine on Wednesday. In my experience, that is something that I have never seen.  While the trough has benefitted resorts in the Midwest and East, the West has been sitting under a dry upper-level ridge much of the New Year and snow has been sparse.  Will that change anytime soon?  Let’s take a look. 

The eastern trough/western ridge couplet will remain in place for a while, and a look ahead to late next week’s jet stream gives me a chance to explain why by illustrating a forecast trick I learned a long time ago.  Here is a look at the jet stream for next Friday…

Clearly, there is a deep trough over the East and a ridge just offshore of the Pac NW.  But I want to focus on the trough east of Hawaii.  When an upper trough is located in that position, or southeast of Hawaii, its’ counterclockwise flow helps to pump warmth into the ridge to its north, which strengthens the ridge.  When the two features get hooked up like that, they tend to remain in place until one or the other weakens or is forced out of the region.  That combo “teleconnects” to an eastern trough, so if you are checking out jet stream features on your favorite weather site, that trough’s position relative to Hawaii can tell you a lot about the near-term weather downstream over the U.S.

So, with that in mind, let’s jump ahead another week, to the start of President’s Day weekend…

It looks like the trough will still be in control from the Plains to the east coast, and the ridge will still be just off the NW coast.  But, the trough east of Hawaii is no longer there.  As a result the ridge is weaker and the northwesterly flow on its’ eastern flank will allow some Pacific moisture to slide down from the northern Cascades to the central and southern Rockies.  That is not a blockbuster storm track, but it will support a break from the recent diet heavy on packed powder and bluebird skies.  There are some early signs of changes in the position of thunderstorms in the southwest Pacific and Indian Ocean by mid-month, and if that comes to pass, we are likely to see a trough…and significant snows…return to the West late in the month.  In the shorter term, though, most of the storm action will remain over the eastern half of the country.

Northwest U.S./Western Canada:  Only the occasional weak disturbance passing through B.C. and Washington will produce snow for the next week or two. 

Sierra:  December’s snow is holding up well, and will have to continue to do so for a while longer.

Rockies:  Only the northernmost and southernmost resorts have a shot at some snow for the foreseeable future…from the two branches of the jet stream working around the pesky offshore ridge.

Midwest:  Every few days, a Clipper system will slide southeastward through the Great Lakes, producing light snow and modest backside lake effect. 

Mid Atlantic/Southeast:   Good temps for snowmaking for the next week or so.  Expect one or two significant snow events this month.

Northeast/QB:  Sizable late week snow gets period off to fine start.  Several shots at fresh snow in the next two weeks thanks to the trough.