The Skiing Weatherman - 2010

[n_alabamaskier]

I guess I will relegate this to the weather thread, although the ski talk thread is described as this:



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2010 Winter Weather Preview

Written by Herb Stevens-The Skiing Weatherman | 01 November 2010





When I put a long range seasonal forecast together, I integrate a wide array of elements from all around (and above) the globe. Some of them are snapshots taken at the time the forecast is developed; others present more of an historical perspective, such as analogs. Once the forecast is finalized, some consideration is given to computer model forecasts, but the truth is that the models do not show much in the way of skill. Now, there are years when the alignment of the forecast elements is very strong, other years when there is a fair degree of disagreement. For the winter of 2010-2011, there are some conflicting signals to deal with, but I am growing in confidence with respect to the forecast that will be presented in this report.



The largest player in the weather through the upcoming winter will be La Nina. After last winter's El Nino (water temperatures above normal in the equatorial Pacific), the profile of those temperatures started to change this past spring, and by mid-summer, the transition to a La Nina (water temperatures below normal in the equatorial Pacific), was proceeding at a very fast clip. In fact, the historical record does not present a year when the transformation happened any faster than it has this year. Here are a couple of graphics to help you understand the phenomenon in terms of rapid change and the areal extent of the new La Nina.









This graph represents the MEI, or Multivariate Enso Index, which is basically a running graph of El Ninos and La Ninas that have occurred since 1950. Basically, any blue spike is a La Nina, and a red spike is an El Nino. Notice that La Ninas were more common and more intense in the 1950-1977 time frame, with El Ninos dominating from 1977-2007 or so. There is a reason for that...during the early period, the PDO, or Pacific Decadal Oscillation, was in its cold phase...the waters of the Pacific were colder than the long-term average more often than not. From the late 70's through 2007, the PDO was in its warm phase, which supported El Ninos over La Ninas by about a 2 to 1 advantage. In 2007, the PDO shifted back to its cold phase, and we are now entering a period of 25 years or so when La Ninas will dominate, and it is pretty obvious that will include the winter of 2010-2011. Notice how deep this La Nina already is! Now, how large an area is covered by the phenomenon? Take a look...







The area of colder than normal water in the Pacific is huge, and the deviation from normal over a large area is greater than 1.5 degrees C, which would categorize this La Nina as "moderate". It won't be long before it reaches "strong" status.



Here is a comparison of the global tendencies when a La Nina or an El Nino are in place...







Now, I know that map is kind of small, but if you look carefully at the left half of the frame, you will see that a La Nina supports, among other things, active tropics in the Atlantic basin. While the U.S. has escaped without a major land falling storm this season, the Atlantic/Caribbean has certainly been busy. We are already up to the "T storm, and I think that there could be another one before the season is done. Some experienced meteorologists for whom I have a great deal of respect theorize that a busy hurricane season leads to a cold start to the winter season in the eastern half of the country. The thinking is that the active and late hurricane season infers lower pressures in the Gulf and Caribbean, with a general rising of the air over that region. Something has to replace that air, and it often turns out to the colder air flowing southward from Canada. Now, in order for November to be cold in the U.S., Canada has to have a good supply or early season chilly air. The current pattern supports the building of very cold air over the high latitudes, as evidenced by the rapid re-freezing of Arctic sea ice that has happened this autumn. That suggests that northern Canada will have plenty of cold air to deliver southward, should the jet stream pattern get set up in a way that facilitates delivery. The La Nina tendency chart also shows a colder and wetter than normal area over western and northwestern North America...that is the part of the continent that is in for the harshest winter but also the best overall snow conditions. Although it is somewhat hard to see, there is an area of the southeastern United States that is shaded "dry and warm" on the same map. Indeed, the southeastern U.S. is going to experience a much more benign winter than a year ago, when heavy and record setting snows fell from the Gulf of Mexico northward to the mid Atlantic region. While the mid Atlantic will receive snow this winter (a little less than normal, I believe), it will be a tame winter in comparison with a year ago...certainly one that will be much more dependent on machine made snow.



One of the conflicting signals for winter '10-'11 has to do with the solar factor. Typically, when solar activity is low, as it most certainly is right now, the atmosphere tends towards persistence...that is, the large-scale troughs and ridges don't change position and/or strength as much as they would if solar activity happened to be elevated. The inferred southeastern warmth will come from an upper level ridge that will start to set up shop after the first of the year over that part of the country, and it will dominate a good portion of the second half of the winter. At the same time, a persistent pattern would suggest that a blocking ridge will be in place over the north Atlantic, which would typically lead to cold weather over the Lakes and Northeast. So, the suggestion to me is that there will be an ongoing battle between cold air to the north that will originate in western and northwestern Canada and the warmth over the southeast that will develop in January. As a result, this winter will be noteworthy because of its high degree of variability. In the heart of the winter, there will be numerous storms that are supported by the thermal contrast across the central and eastern parts of the country, and those same storms will produce a mixed mess of precipitation types over a fairly wide area from the Ohio Valley into the East. The Great Lakes are in for a fairly cold winter, especially the western Lakes, which are closer to the source of the cold air and further away from the warmth of the southeast ridge. Early season lake effect snows should launch the season before too long in the Great Lakes, and some of that action should also develop in upstate New York and northwestern New England.



It's the zone between the two air masses that are expected to dominate that will provide the greatest forecasting challenges...I can see the stripe between I-70 and I-80 being a real pain. North of I-80, snowfall amounts will be above average. With cold air slipping across the northern states, we are likely to see a good number of instances when "warm advection" snow piles up in the interior Northeast. That phenomenon occurs when warm air streams in aloft above a cold air mass at the surface. It very often precedes a storm that is tracking through the eastern Great Lakes, which often results in a change to rain, at least briefly, before the precip ends, but not before a sizable snowfall has occurred. New Jersey, Pennsylvania, and westward through Ohio are a good bet to experience a number of storms with snow, sleet, freezing rain, and rain within a 24 hour period. Now, when the cold air mass lying in wait is deep, and high pressure over eastern Canada is stalled in a position where it can feed low level air into the path of a storm, the setup will be favorable for an ice storm, and I think we will see several of those from the eastern Ohio Valley to the Atlantic seaboard. With a variety of precipitation types on tap for this winter, portions of the East will be dealing with numerous challenges for the groomers, as surface conditions will be changing quite often.



As the heart of the winter progresses in late January and February, the southeast ridge will flex its muscles, resulting in a milder than normal spell, overall, that will reach northward into the mid Atlantic region. Now, before you grow concerned that a milder February will extend into March and bring about a premature end to the winter sports season, here's a look at March temperatures in the analog years that I have identified...1950, 1955, 1965, 1971, 1973, and 1996.







So, although the middle of the winter will be rather benign in parts of the East, and a little warmer than normal, as well, by no means will that spell the end of winter, as a comeback of cold and potential late season snow is supported by the analogs once we get to March.



Working backwards, compare that with the temperature anomalies from December through February for those same winters...







This isn't a perfect fit for what I think will happen...I think it will be a little colder than normal north of a line from Chicago to Portland, Maine, and the core of the warmth in the South will be located a little further to the east, but this is a fairly good match with my ideas.



Here's a plot of the precipitation anomalies from the same composite of winters...







Notice the enhancement through the Ohio Valley into the Northeast, where the battle royale between air masses was (and will be once again) fought out. New York State to central and northern New England also received normal to slightly above normal amounts of precip in the analog years, and I feel as though that scenario is a good bet for the upcoming winter.



Lastly, here is a plot of the November temps that led to these winters...







It represents pretty much what I expect this month, although I think the cold will extend westward to the northern Plains more than is depicted here. The first real shot in a change to a colder regime is going to take place late in the first week of November, and even though it will turn milder in the second week, it bears repeating that the contrast between last November and this November will be a rather stark one in the East.



Around the rest of the country, La Nina will also dominate through the upcoming season. As I mentioned, the Southeast will be in for a rather dull and mild spell of weather during the middle and latter stages of the season, while the upper Midwest is looking good early. As we get to the heart of the season, the Great Lakes will be recipients of persistent cold air through much of the season, and Alberta Clippers will deliver the cold air, along with light to moderate snowfalls. All in all, I love the prospects for the upcoming season in the Midwest.



I also love the way the pattern is going to develop for the Pacific Northwest and northern Rockies, and that certainly includes the resorts in southwest Canada. After a bit of a slow start...while there will be a trough in the East for much of November and December, some ridging will be present a good deal of the time in the West at the same time. Occasional troughs will penetrate the ridge for some early season snow, but it will take a little while for the season to gain traction north of I-80 and west of the spine of the Rockies. Once it does, though, the snow should be spectacular for several months. Now, further south, along the I-70 corridor through Colorado and into Utah and westward to Tahoe, the season is a bit of a toss-up, to be honest. I think that snowfall will be normal, but there will be a few periods when natural snow takes a bit of a sabbatical, as storms pass by to the north. The Southwest typically has a lean year in terms of snowfall when La Nina is in place, and this winter will not be an exception. I am afraid that resorts from southern Colorado westward to southern California will experience below normal snowfall amounts this season. Why? Because the northern stream of the jet stream will dominate in the western United States, while the southern stream, absent the energy provided by the warm waters of an El Nino, will underperform by comparison.



So, in summary, the winter will be a struggle at times in the Southwest and in the Southeast (after a solid start). The northern Rockies and Pacific Northwest will fight upper ridging early in the season, but soon thereafter, the snow will fly often through the remainder of the season...one that will be outstanding in those regions. The upper Midwest is also in for a terrific season, by the looks, with plenty of natural snow and the temperatures to sustain and maintain deep bases and soft surfaces. The mid Atlantic will start on time, and the holidays look good from there in to the Northeast, but after the first of the year, a shift in the pattern to one dominated by "kitchen sink" storms with a variety of precip types will make conditions more variable. Northern New York and northern New England should see above normal snowfall, but messy storms that result from a storm track from the Ohio Valley to Quebec will deliver other precip forms to the northern mountains from time to time, as well. Quebec province will stay north of those storm tracks and that should produce a fine season in eastern Canada. Eventually, the cool air from the La Nina will overwhelm the pattern, which should result in a cooler than normal March and April, which bodes well for a long season. That's the way it looks now, and I am looking forward to keeping you apprised of the weather for skiing and riding around North America through the season. I will start a weekly discussion in about ten days or so, and ramp up to twice a week around December 1st.

[carvebeast]

that was a fun read for a non weather expert like myself, thanks! it sounds like, from what i've read here, that you are predicting the southwest to mimic (in its cycle, obviously not in actually snowfall totals) the southeast as a result of la nina? fast start, a lack of snowfall in the primetime months, then a late surge of snowfall before spring? i have a late january/early february utah trip booked, let's hope that's not the case! they are definitely already seeing the "fast start" out there...