Ski Weather - November 22, 2009
| 22 November 2009
Here it is just a few days before Thanksgiving, and the winter sports season is off to a good start in just one region of the country…the Northwest. The jet stream flow that has been producing plentiful snow in Oregon, Washington, and British Columbia has been dominating throughout the rest of the country, as well, but unfortunately, Pacific air isn’t cold enough to support snow once it gets east of the Rockies at this time of year. Whistler in B.C. has been especially hard hit…they have had about 125 inches in the past week alone, but I hope they don’t have their hearts set on a bountiful snow year. I’ll have more on that shortly, but right now, skiers and riders throughout the Much of the U.S, and Canada are wondering when it will be their turn to feel some cold air and see some flakes floating by. Well, in short…you won’t have to wait long at all.
While a trough of low pressure over the southern end of Alaska has been producing the snow in the Northwest of late, a more benign flow pattern has covered much of the rest of North America. A ridge of high pressure aloft has been parked off the East coast for more than a week, which has helped to produce warmer than normal temperatures east of the Mississippi River. A couple of clear, calm nights have allowed for enough radiational cooling in the mountains of the Northeast for the snowmakers to crank out some “whales” this week…piles of snow that will be spread out later…for now, the mounds do a better job of fighting off the effects of rain and milder temperatures, which will continue to dominate until later this week, when a major pattern change will get underway.
As this week gets started, a low pressure system will be moving up the eastern seaboard, having formed in the western Gulf of Mexico late last week thanks to an enhanced southern branch of the jet. That sequence is worth noting, for a couple of reasons. First, the El Nino enhanced southern branch of the jet will bring above normal snowfall to the southern Rockies and Southwest this season, and that process has already gotten underway. Second, I think we will see numerous storms take shape in the Gulf this winter, and at least a couple of them will turn into major East coast snowstorms…a couple of them could end up bringing heavy snow to the southern Appalachians and mid Atlantic while missing the Northeast, as I explained in my preseason discussion.The low that will move northward early this week will produce nothing but rain from the Carolinas up to New England and Quebec. The storm will help to dent the ridge that is sitting offshore, and that will help pave the way for the next significant assault on the ridge, from a trough approaching from the west later in the week, to basically knock it out of commission. That will pave the way for a trough to set up shop in the East, which will lead to a colder and stormier pattern starting as soon as next weekend.
The latest trough to originate from the waters of the Pacific will move through the northern Rockies early this week, spreading a swath of moderate to heavy snow as it does. With the anticipated pattern change coming up, one that will feature an upper level ridge in the West and a trough in the East, this batch of significant snow could be the last for a while in the West. Typically, El Nino years such as the one that is getting underway are not big snow producers north of Interstate 70/80, in spite of the robust start to this season. There are a number of indicators, such as the injection of sulfuric aerosols into the stratosphere by two volcanoes earlier this year, as well as analog support, for the dominance of a negative NAO (North Atlantic Oscillation) this winter, which strongly suggests an eastern trough/western ridge set-up much of the time. That scenario will make snow harder to come by in the Northwest and northern Rockies.
Okay…back to the shorter range. The western trough will cruise into the middle of the country just in time to disrupt travel for Thanksgiving. There will not be much in the way of cold air associated with this system, but it should be able to manufacture a sufficient supply to set off lake effect snow later this week. The trough will make it into the East late in the week, at which time a coastal storm could form and bring an elevation snowfall to the mountains of the East. The resorts in the East are not going to have much, if any workable snowmaking temps between now and the holiday weekend, but they could get a nice shot in the arm from Mother Nature next weekend. Here’s a map to show you why the air with that system, while generating near normal temperatures, will not be all that cold. It’s a snow cover map of the northern hemisphere.
 | There are two things worth noting on this map. First, the abundance of snow cover over Asia, where it is well ahead of schedule. That snow cover will help promote the formation of a vast supply of very cold air over the coming weeks, and I believe that the pattern over the pole will allow for a connection to that supply sometime in January, when the United States will experience some very cold weather. For now, though, we’re just trying how to hook up with the Arctic. I think that will happen by early December, but notice the absence of snow cover over the southern third of Canada. Until that land gets tuck into a blanket of white, which will be accomplished to some extent this week, any air mass that arrives from the north will be modified. That said, I believe that the development of a western ridge/eastern trough set up by early next month will tap into enough cold air to promote some round the clock snowmaking from the Great Lakes to all of the East, including the southern Appalachians, as well as meaningful lake effect episodes. The southern branch will continue to fire away, and base depths will continue to grow in the Southwest. When the southern branch interacts with cold air diving out of Canada, we will see storms form that will crank out some early season natural snow in the East. I will go so far as to say that by December 15th, the amount of open terrain from the upper Midwest to the southern Appalachians and north to Quebec will be quite impressive, accomplished by either snowmaking or natural snow. |
So, don’t despair, even though Thanksgiving weekend skiing and riding will be quite limited this year. The pattern is about to change in a steady fashion over a two week period, and by the time we reach the end of the first week of December, there will be no doubt as to what season it is. Here’s a region-by region breakdown of what to expect over the next week or two.
SOUTHWEST AND SOUTHERN ROCKIES...Much of the upcoming week will be quiet…dry and mild by day, but it will turn sufficiently cold during the overnight hours to allow the mountain crews to establish base depths on the main feeder trails on the lower portions of the mountains. This is especially important in the lower latitude resorts where spring sun is especially efficient at eating away at the lower runs. Next opportunity for meaningful snow will come along around the 1st of the month, when a southern branch trough will move through the region. Prospects for meaningful snow in this region during the next 2-3 weeks are excellent.
NORTHWEST AND NORTHERN ROCKIES…The persistent Alaskan trough will be moving slowly southward in the near term, which will help to pump the upper ridge over the western part of the continent. That will effectively shut off the hose of Pacific moisture that has led to a fast start to the season in these regions. One last short wave trough will move through the northern Rockies early this week, producing a moderate to heavy snowfall as it does. So much snow has fallen in the mountains of B.C. of late that avalanches are a major threat. A couple of weeks from now, when cold air will overwhelm much of the lower 48, some natural snow will again be a threat in the northern Rockies, but overall, the pattern is headed toward a quiet stretch for these areas.
UPPER MIDWEST…The incoming trough will bring rain and then some snow to the resorts in the northern Great Lakes later this week. As mentioned above, the new air mass will be only seasonably cold, which will limit the contrast with the water temps of the lakes. That contrast is what drives lake effect snow, so I don’t see a major episode coming up, but it should snow enough to whiten the landscape in the U.P. of Michigan by next weekend, when some limited snowmaking will be possible, as well. The following week, when increasingly colder air arrives from the north, both snowmaking and lake effect snow will be reach a new level and the season will gain a good deal of momentum at that time.
SOUTHERN APPALACHIANS AND MID ATLANTIC... The storm currently moving out of the Gulf will generate plain rain, as the air mass won’t cool enough to support snow. Snow showers will reach well down the Appalachian chain next weekend, but here again, it looks like a teaser and not the real deal. By sometime in the week of the 30th, the snow guns will be firing in earnest, and I expect natural snow to fly by the end of the first ten days of next month. This region will have multiple storm threats during the first half of December. It doesn’t look to wintry now, but that is about to change pretty quickly.
NORTHEAST AND EASTERN CANADA… While the storm moving up the coast will produce nothing but rain early this week, there is the potential for a meaningful snowfall across the interior next weekend. An upper trough will be in place over the region by that time, and I wouldn’t be surprised to see a coastal system form, act upon marginally cold air, and lay down some thick base building snow from the Poconos northeastward to the mountains of eastern New York and New England next weekend. Beyond that, it will turn a little milder for a couple of days before another trough takes temperatures down another step toward what will turn out to be a significantly colder than normal December. The ground is brown, green, and soft right now, but that is about to change…unfortunately, the change will not come in time to allow for more than very limited skiing and riding over the Thanksgiving weekend. Shortly thereafter, the season will really kick into gear.
