Ski Weather - November 15, 2009
| 15 November 2009
By this time, hopefully you have had a chance to take a look at my winter preview discussion, one that bodes well for skiers and riders in much of the country. There are a couple of areas of concern, which I will spell out with a regional outlook at the conclusion of this short discussion about the weather leading up to the Thanksgiving holiday. While it will be possible to get some turns in by the end of this month, in general, it looks as though your options will be less than a year ago, both in terms of open resorts and open terrain. Take heart, though, because it looks as though a significant pattern change will take place right around Thanksgiving, and that will help get real winter weather underway in a more consistent fashion.
One of the forecasting tools that I use to help signal a cold outbreak is a dramatic warming trend at the highest levels of the atmosphere. For reasons that aren’t fully understood, when sharp warming takes place in the stratosphere over higher latitudes, it usually foretells a significant shot of cold air into the mid latitudes. Click on this link and take a look at the stratospheric warming that has been taking place over the last several weeks…
You can clearly see that a “stratwarm” episode is underway, and that makes me confident that colder weather will descend into the lower 48 in the not too distant future. Right now, all the cold air is bottled up close to the North Pole, with another chunk circulating around a very strong upper low pressure complex that stretches from eastern Asia across to Alaska. Here’s a map that shows the standard deviations, in terms of temperature, that are expected over Canada for the next ten days or so…
Again, the numbers represent standard deviations, and not pure temperatures, but suffice it to say that the eastern three-quarters of the country are going to be warmer than normal for the near future. Canada is the primary source region for cold air in the U.S., and until it cools down to the north, very little cold air will be available. The question then becomes “what will it take to turn Canada colder?” Well, a sequence of events will have to take place that results in the large upper level trough that is situated over Alaska to build southward into the Gulf of Alaska. In that position, the counter clockwise circulation around the upper low will help build a ridge over western Canada. That would promote a northwesterly flow, which would help to tap into the cold you can see over Alaska and portions of the Yukon…some of the extreme cold over east Asia could also get involved, which would increase the likelihood of a significant cold outbreak in the eastern half of the country in early December, something that looks like a pretty good bet to me right now.
So, for the time being, a strong Pacific jet stream will continue to push stormy weather into the Pacific Northwest, with meaningful snow falling in the mountains every few days until the ridge starts to build during Thanksgiving week. The season has gotten off to a good start in the Pacific Northwest, and as you will find out in my regional breakdowns, I’m not especially bullish on the season in that part of the world. An upper level ridge is in position over much of the rest of the country, and it will be warmer than normal east of the Mississippi Valley right into the week of the 23rd. There will be a couple of nights that are cold enough for snowmaking early this week in the Northeast, but there won’t be any sustained cold air available until the pattern changes. That transition will start to kick in during the week of the 23rd, but right now, it doesn’t look as though it will turn exceptionally cold at that time…normal to slightly below normal by the end of the week, but the air will not be or arctic origin, so it won’t be the cold, dry stuff the mountain crews are looking for right now. Some natural snow is not out of the question in the snow belt areas of the Great Lakes and Northeast over Thanksgiving weekend, but it looks like the cold air necessary for meaningful snowmaking will not be available until the first week in December. Patience will be a virtue the next couple of weeks, as the pattern gradually changes to one that features a western ridge and eastern trough…a set up that will dominate through much of the upcoming winter.
Here’s a region by region breakdown on the new season:
SOUTHWEST (CA south of Tahoe, southern NV, NM, AZ)
This portion of the country has had a couple of so-so years, due to the domination of La Nina conditions in the Pacific. This year, however, a weak to moderate El Nino will be in place, and that means more snow in this part of the country. Why? Well, the abnormal warmth of the water in the central Pacific helps to energize the subtropical branch of the jet stream that flow overhead, and that branch of the jet eventually reaches the southwestern U.S. The added moisture and energy contribute to enhanced storm strength, which translates into more snow and more powder days from the southern Sierra eastward to the Sangre de Cristos and southern Rockies.
NORTHWEST (CA north of Tahoe, OR, WA, BC, AB, MT, WY, ID, ND, SD, CO north of I-70)
An active northern branch of the jet, one of Pacific origin, has gotten the season off to a quick start in the central and northern Rockies, as well as the coastal ranges from Tahoe northward. I wish I could say that the early snow is a sign of things to come, but right now, it looks as though this part of the country and adjacent Canada, will struggle to reach their normal snowfall levels. Analogs and pattern recognition techniques strongly suggest that a higher latitude blocking pattern will be in place much of the upcoming winter, which means that we will tend to see a trough over the eastern half of the country more often than we will see a trough over the West. The Midwest and East will be colder than normal, while above normal temps are a good bet in this large region of the West. While the southern branch of the jet will bring ample snow to the Southwest, the persistence of the ridge further north means a good number of bluebird days, but hardpack will be more common than fresh powder.
MIDWEST
The expectation that an upper level trough will dominate in the eastern half of the country suggests that this region will be embedded in a northwesterly flow much of the time this winter. That should translate to plentiful early season lake effect snow, but it could also lead to some extreme cold during the heart of the season. One of the best analogs for the upcoming winter is 1976-1977…during that season, not only did much of shallow Lake Erie freeze, which isn’t that unusual, but a good portion of deep Lake Ontario also froze…something that is seldom seen. Frozen Great Lakes are much less productive in terms of lake effect snow than Great Lakes with open water, so while I think the snow will fly early and lead to a nice Christmas holiday period, snowfall during the middle and latter stages of the season will be a little harder to come by. Snowmakers will have plenty of cold air…as long as they have water, they will stay busy.
MID ATLANTIC AND SOUTHEAST (south of PA Turnpike)
This part of the country has gotten the short end of the stick on natural snow for several years now, but this year should be different. The southern branch of the jet stream that will deliver bountiful snow to the Southwest will interact with the expected trough over the eastern half of the country on numerous occasions, and when it does, low pressure areas will form over the northern Gulf of Mexico, or the Southeast, and deposit above normal snowfall amounts from the mountains north of Birmingham and Atlanta all the way up to southern Pennsylvania. Temperatures will be below normal for the period from December-February, which will keep the snowmakers very busy, and there is a risk of one or two cold outbreaks that are so intense that they actually discourage some Southerners from hitting the slopes. Overall, this has the potential to be an epic season south of the Mason Dixon line.
NORTHEAST AND EASTERN CANADA
There is a risk that should the cold dig in the way that I think it will during the heart of the season, it could be too much of a good thing. The northwesterly flow could be strong enough to suppress the storm track too far to the south to deliver substantial snowfall to this region. Snowbelt areas of the region will benefit from ample early season snowfall. I do think that there will be normal seasonal snowfall in the Northeast, Ontario, and Quebec, but the snowmakers and groomers will have a major role this season in making this season special. There will be plenty of cold air, and I think it will come early enough to allow for the development of a good product on the hills by the holidays…I just have a feeling that there will be several storms this season that blanket the mid Atlantic but just graze the Northeast. One or two of the mid season cold outbreaks will be extreme enough to limit business to only the heartiest of souls. Overall, though, it looks like a solid season in this region.
Look for my next weather missive during the weekend of the 21st/22nd…sooner if anything changes with respect to the upcoming pattern change.
