My last discussion was based on the belief that the eastern half of the country was about to enter into a pattern that is much more conducive to colder weather and more snow threats in the coming weeks.  

That pattern is starting to show its' stripes...we just saw a fast moving short wave trough generate 2 to 4 inches of much-appreciated snow in the central Appalachians.  That storm track indicates that the southern branch of the jet stream is getting more active, which is exactly what we need to bring renewed snow threats to the Sierra, the Southwest, as well as much of the East.  We are going to see some snow spread across the Northeast this weekend, and it looks as though there will be additional threats every few days for the next couple of weeks.  Aside from a sharp shot of cold air coming late this weekend, it doesn't look as though we will be at risk for a major arctic outbreak. 

Now, this pattern looks as though it will produce some snow in the central and southern Appalachians, too, and that is something that region has seen precious little of this season.  In the West, the domination by an upper ridge is about to take a break, and that means we will be looking at a renewed snow threat, including over the interior ranges, during the upcoming week.  The upper trough that will dominate in the East and help to cause some stormy weather will provide the Midwest with predominantly northwesterly flow, which infers that normal cold will rule, and there will be light snow periodically as short wave troughs rotate around the larger upper feature.  Basically, the pattern is now much more favorable for new snow coast to coast than it has been much of this season.

Here's the current jet stream set up across the U.S. and Canada...

There is a lot going on here, for sure.  The most prominent feature is the large, cold upper trough centered along the eastern shores of Hudson's Bay.  Underneath that circulation, we see short waves off the New England coast (last night's mid Atlantic snow), as well as a strong short wave moving across New Mexico (this weekend's storm threat).  The large upper low at the tip of the Baja Peninsula isn't going anywhere for now, but it is another indication that the southern branch of the jet is perking up as the La Nina starts to weaken in the Pacific.  The New Mexico short wave will propagate eastward, and it looks as though the orange streak that you see over northern Alberta and Saskatchewan will dive into the short wave and give it a big time kick in the arse over the eastern U.S. Friday night and Saturday.  Low pressure will form at the surface along the mid Atlantic coast, and turn into a very strong system by the time it reaches the Maritimes.  The arctic short wave will spread snow through the Midwest, with the mountains of West Virginia looking like the best bet for significant snow, in excess of 6 inches, with lighter amounts a good bet from the upper Lakes through much of Pennsylvania and New York.  As the storm deepens as it heads for a spot southeast of Cape Cod, we will see the snowfall enhanced from metro New York through most of southern New England.  Right now, it does not look like heavy snow will reach the mountains of New York and northern New England, but there should be enough snow to soften up the surfaces...the mountain crews have done a ton of work making and grooming snow this week, but there is no substitute for several inches of "topdressing" when you are trying to rehabilitate a firm snow surface.  An air mass that will arguably be the coldest of this season will flow into the Northeast in the wake of the weekend low, but with a lack of a strong block over the north Atlantic, we will see that cold shot slide offshore by Tuesday or so.  By midweek, we are likely to see a repeat performance of a southern branch short wave being attacked by energy from the north, resulting in another round of snow from the mid Mississippi Valley eastward through the Lakes and Ohio Valley and on to the mid Atlantic and into the Northeast.   

How about the West?  Well, an upper ridge has called the shots for the past couple of weeks, and that has meant a good deal of sunshine and less snow than skiers and riders would like to see.  As the southern branch has livened up, we have seen several short wave troughs traverse Arizona and New Mexico, so there has been some snow in the southern ranges, and light snow has fallen a couple of times in the past week across much of Colorado.  The ridge has weakened in recent days, which has allowed some moisture and energy to come inland and penetrate into the mountains of Montana and Wyoming.  When a ridge gets "violated" in this manner, meteorologists refer to it as a "dirty" ridge.  A general west to northwest flow will continue from the Pacific Northwest into the central and northern Rockies for the next week or so, which should produce several rounds of light snow...perhaps not enough for an epic powder day, but it should certainly be enough to keep the surface snow soft.  The next round of significant snow across the southern ranges of the West will come early next week, when another short wave of note will move eastward from California toward Texas...that same system will play a role in the snow that I anticipate in the Midwest and East during the midweek period.

Where is the pattern headed longer term?  Well, based on the MJO, or Madden Julian Oscillation, it looks as though we will see a trough of varying strengths dominate in the Midwest and East for the next couple of weeks, with a modestly moist northwesterly flow in the central and northern Rockies in place much of the time.  Lastly, the southern branch should continue to send short waves from California eastward, and this "split flow" is really going to be quite productive in terms of new snow from coast to coast...I am pretty sure that is the first time I have been able to say that all season!  Here's is a look at a forecast for a week from now that I generally agree with...

This is an ensemble forecast, which means it is the combination of 20 or so individual forecasts.  When you see a feature as distinct as the trough over the middle of the country or the short wave trough approaching the B.C./Washington coast, then you can infer that there is a lot of agreement among the members of the ensemble.  Notice also the strong looking lobe of the trough over the Southwest...that suggests that the split flow will continue for a while, and that means widespread snow threats.  If we look 11 or so days down the road, we see more of the same...

Southwestern trough, eastern trough, two distinct branches of jet energy.  I would expect that that general configuration to continue to dominate through the end of the month.  While we are not at risk for a major arctic outbreak, we have seen, and will continue to see, air masses that are cold enough to support predominantly snow, including in the Southeast, where the high base elevations should help to turn southern branch energy and moisture in to some late season snow...better late than never!                             

NORTHERN ROCKIES AND NORTHWEST

The ridge has been sullied by Pacific moisture, which is great news.  While the snow coming in the next week or so will not be monumental in depth, it should be enough to restore a predominantly soft surface after a spell of carving snow across these regions.  Bluebird skies have been common of late...they will be less common in the next couple of weeks.  

CENTRAL ROCKIES  

The northern branch systems will deliver some snow to this region, but it looks as though the general track of southern stream systems will be a little too suppressed to the south to deliver the goods to any great extent.  There is a risk that a stripe that runs northwest-southeast will be in no-man's land for the next week or more...that is, they will receive snow from neither branch of the jet.  If such a zone does develop, it should be quite narrow, but it could impact a cluster of resorts such as those in the Wasatch around Salt Lake City.  

SOUTHERN ROCKIES, SOUTHERN SIERRA    

The enhancement of the southern branch of the jet stream will bring some much needed snow to the southern Sierra in the next week, although it doesn't look like the amounts will be anything outrageous.  It will help though.  The southern Rockies will definitely benefit from the southern storm track, and there will be fresh snow every 3-5 days as short wave trough start to roll across the Southwest, on their way to causing trouble further east. 

UPPER MIDWEST  

With the axis of an upper trough either overhead or located a couple of hundred miles to the east, this region will be entrenched in a seasonably cold air mass, with the occasional shot of arctic air chilling things down and setting off some lake effect snow in the process...the first such intrusion will take place this weekend.  Check out the lack of ice in the Great Lakes...

There's a lot of open water, and if a sufficiently cold air mass passes over that water, we could see a somewhat unusual late season lake effect episode of some magnitude.   Even if the lakes don't "go off", short wave energy rotating around the upper low will deliver episodes of light snow every few days, which will maintain nice packed powder at most resorts.  

SOUTHEAST   

The Rodney Dangerfield of winter sports regions has not gotten any respect from Mother Nature all season long, with most cold shots remaining off to the north, with upper level ridging poking its' way into the region from the south from time to time, keeping temps above normal most of the time.  Snowfall has been scarce, but the re-energized southern branch of the jet stream will bring some natural snow to the region over the next couple of weeks.  It won't be especially cold, but the high base elevations should be enough to ensure that we are talking about crystals and not raindrops.  

NORTHEAST AND QUEBEC

This has the makings of a busy period in terms of snowfall.  The first system will develop this weekend, but the heaviest snowfall will occur over southeastern New England, although the mountains of this region should get a nice shot of light snow as arctic air presses into the region.  It will be quite cold across the north on Sunday and Monday, and that will seem like a slap in the face after so much mild air thus far this season.  The next snow threat will come in the middle of next week, and although temperatures will have modified from the start of the week, it will be cold enough for snow north of I-80 with the next system.  Late next week, a low pressure area will try and move up west of the Appalachians, but a secondary low should take shape along the coast and then head northeast.  Depending on how fast the secondary takes shape, we could see a mix of precip types as far north as I-90 before colder air returns to turn the precip to snow.  That one is a long ways off, but right now, it looks as though the President's Day period could get off to a sloppy start in parts of the East. Overall, though, we are entering a spell of weather that skiers and riders in this region should be generally happy with.