Herb's Ski Weather Forecast - 2009 Winter Preview
Written by Herb Stevens-The Skiing Weatherman
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10 November 2009
In the past several weeks, we have seen a baseball playoff game in Denver cancelled on a day when the high temperature was 43 degrees below normal, snowfall that caused widespread power outages in Pennsylvania a few days later, and then a rare October NFL snow game in Foxboro, Massachusetts. Were those events the start of an extended and harsh winter? The answer is no, but this winter shows all the signs of being the coldest in the eastern half of the United States since 2002-2003, with the potential to reach the levels of the frigid winter of 1976-1977, a year that was harsh over a good portion of the United States and adjacent Canada.
Let’s start by taking a look at the large scale pieces of the puzzle that are in place as the winter approaches. The global factors include an El Nino, the PDO (Pacific Decadal Oscillation), the current state of the solar cycle, and volcanic activity. Here’s a breakdown of each factor and potential impacts…I must admit that this isn’t exactly light reading, so grab a cup of coffee and get comfortable:
EL NINO:
For nearly the past three years, La Nina conditions have been in place in the Pacific Ocean. La Nina indicates cooler than normal water in the tropical Pacific, while an El Nino is indicative of warmer than normal waters in the same regions of the Pacific Ocean. Starting last spring, the waters close to the equator started to warm, and we have been in a weak El Nino for the past several months. During the past few weeks, a burst of westerly winds from northern Australia along the equator has helped to spread the warm water further east and strengthen the El Nino slightly, and I think that process will continue for a little while longer. I don’t believe that the El Nino will sustain its strength past early winter…it will weaken, in fact…and that is a key component to the construction of the analogs. Why? Well, there have been several years where a weak to moderate El Nino followed several years of La Nina conditions, and they have all produced a cold winter in a good part of the country east of the Rockies. Those analogs include 1976-1977, 2002-2003, 1969-1970, and 1963-1964. The key to the contribution of the El Nino will be how high the deviation from normal reaches in the central Pacific between now and early December…the value is currently around +1.5 and I think that is about as high as it will go. If it does warm a little more, and then starts to weaken as I expect it will, the likelihood of a cold and potentially harsh winter will increase. The weakening of the El Nino by and large is a function of the...
PDO:
The Pacific Decadal Oscillation is a phenomenon of a shift in the water temperatures in the largest body of water on Earth. Every 25 to 30 years, the PDO shifts from the warm mode to the cold mode, or vice versa. From 1978-2007, the PDO was in its warm phase, and given the tremendous amounts of heat that a body of water that large contains, it is not a surprise that the global warming argument gained momentum during that time…it wasn’t CO2 that caused a warming trend, though. The PDO went back to its cool phase in 2007, and it should be just as easy to understand why the planet has cooled the past couple of years. The ocean doesn’t stay warmer or colder than normal all of the time when it is in one phase or the other, and that is another key to this winter’s forecast. While it is currently in the cold phase overall, the warmer waters associated with the El Nino have helped boost the value enough to temporarily produce a slightly warm PDO. Once again, that is a set of circumstances that was also in place in the Fall of 1976, which is why that is the leading analog in my forecast package. When an El Nino is in place against a backdrop of a cool PDO, it has a difficult time attaining and sustaining a high level of strength, due to the preponderance of colder water in the Pacific basin. That is why I expect the El Nino to dissipate fairly rapidly once we get to December, which will set the stage for the cold to dominate. If the El Nino persists deeper into winter, or it doesn’t reach +1.0 before weakening, then the depth and breadth of the winter cold will likely be lessened somewhat. Here’s a look at the past 100 years or so of PDO fluctuations:
VOLCANIC ACTIVITY:
This may not seem like a major player when it comes to a seasonal forecast, but a fairly strong correlation has been discovered between high latitude volcanic eruptions and a blocking pattern that lends itself to colder than normal temperatures in the eastern half of North America. You may recall that Mt. Redoubt in the Aleutian Rage of Alaska erupted late last March, and the blast was strong enough to eject sulfuric aerosols 9 miles into space, which allowed them to reach the stratosphere. Here’s a look at Mt. Redoubt:
An eruption of similar magnitude occurred from the Sarychev volcano on Russia’s eastern coast (north of Japan) in early June, and once again, sulfuric aerosols were propelled into the stratosphere. Here’s a cool shot of Sarychev taken from the International Space Station:
Once they spread out on the winds, the aerosols act as microscopic mirrors, reflecting incoming solar radiation back out to space, producing cooling in the process. The physical reasons for the tendency for a blocking pattern are not fully understood, but the correlation appears to be real. In a blocking pattern, high pressure aloft tends to persist close to Greenland, with an upper level trough upstream over the eastern part of North America. In that position, the trough can spread cold air from central Canada across much of the lower 48, and it can help to generate coastal low pressure areas at the surface, which often produce the lion’s share of snowfall along the eastern seaboard. The aerosols will eventually filter back down to earth, but not before they help contribute to the cold of the upcoming winter.
SOLAR CYCLE:
The solar component of the winter forecast is a bit of an X factor, for the simple reason that the current lack of sunspots is something that hasn’t been seen in 100 years, and it is becoming increasingly similar to the solar state of affairs 200 years ago. In either case, the analog information is more limited than what is available for the past 50-60 years or so. Even though the 11 year solar cycle was close to its minimum level in 1976, we are currently experiencing a low level of sunspots the likes of which have not been seen in at least 100 years, if not 200…there is also a 100 year solar cycle, as you can see on this graphic:
You can see that the last 25 years or so of solar cycles have been quite similar to what lead to the beginning of the Dalton (sunspot) Minimum in about 1790. The Dalton Minimum lasted about 25-30 years, during which time global temperatures were 2-4 degrees Fahrenheit below the long term averages. It is worth noting that during that period, Charles Dickens wrote about numerous ice festivals on the Thames River in London, and the Mississippi River froze over at times…in New Orleans! Now, I am not going to forecast cold of that magnitude for that length of time, but I would be foolish to dismiss the potential impacts of even slightly reduced output from the sun.
So, there are some of the large-scale players in this winter’s forecast. They are significant and they all point, to one degree or another, toward a colder than normal winter from the Rockies eastward. Here’s how I think it will play out…
SUMMARY:
The month of November will not be as cold as October was nationwide…typically, Novembers that precede cold winters are mixed in terms of the weather that they produce. October rainfall is a much better indicator of winter cold, and much of the eastern half of the country was wetter than normal last month. October of 1976 was a wet month, and a cold one. Temperatures will be on a bit of a roller coaster this month, as systems continue to move across the country at a rapid clip just as they have for the past several weeks. The blocking pattern that was in place much of October, which accounted for the chill that most of us felt, has broken down temporarily, but I expect the blocking to return by late November, which will help produce a slow but steady trend toward colder than normal weather that starts in the Midwest around the 15th or so, and develops in the East a couple of days later. That outbreak will be the best snowmaking opportunity prior to Thanksgiving, and it appears as though the pattern will become more conducive to natural snow in the Great Lakes and east by Thanksgiving week or so. Meanwhile, the West will be sitting under a ridge of high pressure during the latter stages of this month, which will likely slow down the start of the season somewhat in that region.
This summary is just a start of my thoughts on the upcoming winter. I will break down the entire season region by region in the next couple of weeks, but suffice it to say that there will be plenty of snow and cold to go around this winter from coast to coast. If you are looking for the one area that is likely to see the most snow with respect to normal, it looks to me to be the central and southern Appalachians, where natural snow has been rather scarce for several years…it won’t be this season. As for the prospects for the Olympic Winter Games in British Columbia? Well, I hope that the snowmaking system is well tuned. Again, I will have much more in the next couple of weeks, but hopefully this will serve as an appetizer.
As we move into December, I will be watching the status of the El Nino like a hawk. As I mentioned, I expect it to start to weaken, which will only firm up my belief that my analog years are the right ones. Right now, I think that the first half of the month will be back and forth with respect to temperature, with a couple of good sized storms along the way. Those storms will produce some base building snow that will supplement the snowmaking effort. By the time Christmas rolls around, I believe that the pattern will be locking in for an extended run of colder than normal weather from the western Great Lakes to the east coast, including the Southeast. Obviously, the timing on the onset of the cold will be critical with respect to the holiday period, and I will be fine tuning that timing in the coming week. January looks very cold to me for much of the time, and I would have to say that the prospects for any sort of an extended January thaw are rather limited this winter. One potential problem is the cold itself…January will likely bring some days that are cold enough to be detrimental to skier visits. The cold will dominate into February, but then relent somewhat. Overall, I would expect the second month of 2010 to still be colder than normal in most locations, but it will not be as severe as what could develop in January. Right now, I am still tangling with forecast for the month of March. Some of the analogs suggest a flip to warmer than normal weather, while others are more consistent with a weakening El Nino, where the transition into spring is a bit of a knife fight. The disposition of the El Nino in early December will go a long way toward sorting out the forecast.
As far as snowfall is concerned, here again, the El Nino will play a prominent role. The warmth of the Pacific waters associated with the El Nino helps to energize the southern branch of the jet stream that passes overhead. Even if the El Nino dies a swift death early in the winter, the enhancement of the southern stream tends to have a bit of a hangover effect for a couple of months. A busy southern stream means an active storm track out of the south and up the east coast. Assuming that there will be blocking much of the winter, the question then becomes whether or not the storms can turn the corner and bring snow all the way up the eastern seaboard. In 1976-77, the heart of the winter was dominated by a cold northwesterly flow, one that suppressed the storm track to the south, with the mid Atlantic and Southeast becoming the winners in terms of snowfall. I can see that happening this year, too. I think Philadelphia, Baltimore, and D.C. will see above normal snowfall, with a couple of blockbuster storms thrown in for good measure. The Northeast will see above normal snow right along the coast, but the further inland one goes, the more likely it is that snowfall amounts will taper off toward normal levels. The Midwest will see slightly below normal snowfall, although there will be a busy lake effect season, especially in December as the cold air deepens. Eventually, the shallow waters of Lake Erie will freeze, shutting off the lake effect in the process. In 1976-1977, the eastern end of deeper Lake Ontario froze…a very unusual occurrence…but one that might be repeated at some point this winter. In places like Chicago and Madison, it will be colder than normal, and there will be at least average amounts of snowfall, but the excessive snowfall of the past two years does not appear to be in the cards. Now, even though a given location may not receive above normal snow this winter, the abundance of cold air will ensure that any snow that does fall stays around for a good long while.
Not everyone will be cold and snowy this winter. The Pacific Northwest and British Columbia will start out stormy and cold, but it will be milder than normal during the heart of winter…not the best news for the Winter Olympics in February. The enhanced southern branch means above normal rainfall for California and Texas, as well as a fair amount of inclement weather for those who are escaping to Florida. I will update the winter outlook in about a month, when I will hopefully be able to supplement the discussion with additional graphics to illustrate analogs. In the meantime, I will be monitoring the El Nino and focusing on the lack of sunspots…these two components could conspire to produce a memorable winter.
