Ski Weather - March 6, 2010

Now that meteorological winter has ended (12/1-3/1) and March is underway, the questions on many skiers and rider's minds are "will the cold weather hold, how many more snowstorms can I expect, and when will spring get here"? It's been a good winter in the Northeast, a great winter in the mid Atlantic, pretty good in the upper Midwest, very solid in the Southwest, and spottier in much of the rest of the West, especially the Northwest. Although the pattern across the country will be somewhat chaotic for much of the next week or so, there are strong signs that the pattern will revert to the one that has dominated much of this winter...a western upper level ridge and an eastern upper level trough...for much of the second half of the month. That sort of pattern will remain loaded with potential for producing substantial snowfalls in areas that have enjoyed a snowy season, provided all the pieces come together in the right way.

This winter has been a rough one in a large portion of the country. You want proof? Rapid City, North Dakota experienced its 5th coldest winter on record. Des Moines Iowa set a record for most consecutive days with snow cover. Houston had accumulating snow on two separate occasions, and shivered through its 5th coldest winter. Snow flurries reached as far south as the outskirts of Miami, where the winter of 2009-2010 has been the 2nd coldest ever. Further north, many locations dug their way through their snowiest winter, including Washington, D.C. And last week, snowfall amounts in excess of 4 feet were reported in 4 states in the Northeast in the wake of a monster of a snowstorm. Why did all of this meteorological mayhem take place this winter? Well, a series of global signals conspired to spread arctic air far and wide into the mid latitudes. As was discussed in the winter preview way back in October, a weak to moderate El Nino coupled with a cold PDO (Pacific Decadal Oscillation), a relatively quiet solar component, and a stratosphere loaded with sulfur dioxide ejected by two high latitude volcanoes earlier in 2009 all pointed to a winter when a trough would be persistent in eastern portions of the United States while a ridge parked in the West most of the time. The volcanic SO2, for reasons that are not fully understood, correlates well with a blocking pattern over the North Atlantic ocean, which in turn supports the eastern trough and numerous coastal storms, which is exactly what we have seen. How dominant was the blocking? Well, the negative phase of the AO, or Arctic Oscillation, which is a measure of blocking and also indicative of a spreading out of cold to the mid latitudes, went wild. In fact, this chart shows you that the AO was more deeply negative this meteorological winter than any other winter on record, dating back to 1950.

Notice that the # 3 year was 1968-1969, which is an analog that I have used for much of this winter. Late February of that year also featured a monstrous snow-producing storm in the Northeast, one that resembled last week's event in many ways. The 1969 analog is still a strong one, and it is helping me map out the month of March...I'll get to that shortly.

Those of us here in the U.S. know that much of our country had a deep and persistent snow cover during the heart of this winter. It wasn't just the U.S., though. Take a look at this chart of northern hemispheric snow cover for the 7th week of the year...mid to late February. This year is #1...give a guess what # 2 is...1978...the other analog that I have referred to in my pattern overview discussions through the winter.

1969 wasn't too shabby in terms of snowfall in week 7,either, but that was before the massive storm buried the Northeast in week 8 of that year.

Well, that's enough talk about what HAS happened in the weather. Let's dig into the weather that we can expect in the next few weeks.

The persistent pattern of a western ridge/eastern trough has changed a bit lately, due in large part to the fact that Canada is milder than normal. When the availability of arctic air decreases in the wintertime, as it has at times this winter, the size of upper level troughs tends to shrink, which allows the wavelength between upper level features to shorten. That's what we have right now...a trough over the Northeast, a short wave ridge over the middle of the country, with a trough moving through the Rockies after having being ejected by a larger trough off the West coast. The ridge will send a surface high-pressure center through the Great Lakes and into the East over this weekend and early next week, and that will mean sunshine in abundance, to go along with wonderful snow conditions from Quebec south to North Carolina. In fact, this might be the best weekend of the season in the East, when you combine snow conditions with weather. The Upper Midwest will be mild this weekend, so conditions will be spring-like at most resorts...they have tons of snow, though.

In the West, the trough moving through the region late this week will have deposited a moderate snowfall in Utah, Colorado, and southern Wyoming...a similar storm passed through the southern Rockies earlier in the week, and set those resorts up for some nice sliding. The lower elevations in the Southwest are starting to become quite soft in the afternoon hours, due to the increasing sun angle, but the upper reaches of the resorts still have nice dry surfaces. As for the Northwest, where significant snowfalls have been few and far between this season, there is some good news. It looks as though the trough that has been lurking offshore for much of the winter is going to send a sizable piece or two of energy ashore during the first half of next week (the week of the 8th), so some meaningful fresh snow appears to be on the way to a region that has seen precious little this winter.

Further East, the trough that comes out of the Rockies late this weekend will eventually form a storm in the South later in the week, and with an upper level trough taking shape...again...over the East, it looks like there will be a significant precipitation event along the length of the Appalachians late in the week and over the weekend of the 13th/14th. There isn't a lot of cold air around, so there is a risk of a heavy rain event in the southern Appalachians and mid Atlantic...the highest elevation resorts could have their height bail them out with this one. In the Northeast, it looks like another elevation storm...some of the lower elevation areas could take a pretty good hit from cold rain, it appears, but even in those areas, I would expect some snow accumulation as colder air moves in on the back end of the storm.

Beyond that event, it looks to me as though the trough associated with the coastal storm will dig in and gradually turn colder, while at the same time another ridge builds in the West. This setup will dominate by the week of the 15th, which will turn it colder than normal in the East, with a rather benign pattern persisting in the central and northern Rockies. The southern branch of the jet, as it has much of this season, will remain quote active. That enhances the prospects for additional snowfall in the southern Rockies and southern Sierra. As the southern branch sends impulses across the southern Plains and into the Gulf region, there will still be a shot that phasing with the eastern trough will take place and produce a late season snowstorm in the East. Once the trough gets set up again, the Lakes and Ohio Valley will be dominated by a northwesterly flow...again, that doesn't necessarily mean cold, due to the relatively mild air covering much of Canada, and if wavelengths shorten (as explained above) a ridge could press into the western Lakes and turn things mild for a few days later in the month.

Now, here's what it will take to turn it milder for real. The eastern trough will deliver a cold air mass late in the month as high pressure at the surface presses southeastward from Canada...it may be relatively mild for Canadians, but if the air gets delivered here fast enough, it is colder than normal in the U.S. As the surface high moves offshore, it turns milder on the backside. The wavelengths at the jet stream level shorten enough to allow the blocking ridge over Canada to hook up with the western U.S. ridge...that feature then migrates eastward and as it does, it turns to spring in a hurry. I tend to think that scenario will unfold in early April, which could bring a rapid end to the season in areas that currently have a deep supply of snow. Moral of the story? Use it while we have it...

REGIONAL SUMMARIES:
NORTHERN ROCKIES/NORTHERN COASTAL RANGES/WESTERN CANADA
After a rather quiet weekend, things look like they will pick up in this region early in the week of the 8th, as a significant piece of an offshore trough comes eastbound into the mountains. The pattern will revert to an upper level ridge in about a week or so.

SOUTHERN COASTAL RANGES/SOUTHWEST
These areas will continue to be favored in terms of new snow as we move through March, thanks to the southern branch of the jet. Even though the El Nino is weakening, it still has enough energy to fire up the atmosphere downstream. Sun angles are rising; so dry snow will be confined primarily to the higher lifts, due to the absence of an injection of arctic air from the north.

CENTRAL ROCKIES
Like the northern Rockies, early in the week of the 8th looks promising. Several moderate snowfalls in the past couple of weeks have improved conditions in Colorado, in particular, and many resorts will have their best snow of this season by the middle of the week of the 8th. Beyond that, the pattern will switch back to western ridge/eastern trough, which will tend to quiet down the storm track again.

UPPER MIDWEST
After a mild weekend courtesy of a short wave upper level ridge, this region will be rather quiet during the week of the 8th. Surfaces will be more spring like, but the development of new upper level trough over the eastern half of the country will deliver colder air later in the week, which will help to preserve base snow. The northwesterly flow that will develop will be a dry one, however, and for the next couple of weeks, the prospects for significant snow will be limited to the passage of Alberta Clippers, provided that the system has sufficient moisture.

MID ATLANTIC/SOUTHERN APPALACHIANS
After a remarkable season of deep and consistent snowfall, this region enters the stretch run of the season in fantastic shape. Late in the week of the 8th, a coastal system will bring rain to the lower elevation resorts, which will certainly test the bases, and snowfall will be limited to the highest base elevation resorts. Beyond the weekend of the 13th/14th, a northwesterly flow will dominate, which will serve to preserve the base snow and perhaps deliver enough cold air to allow additional snow to fall from a southern storm track that will remain active.

NORTHEAST/EASTERN CANADA
A great stretch of weather for enjoying the recent snowfall will be in place through the 11th or so. The weekend of the 13th/14th will bring a coastal storm to the waters off New England, with rain a good bet in the lower elevation resorts of the Northeast, but heavy wet snow will fall above 1,000-1,500 feet away from the ocean. An upper level trough will dominate the second half of the month, which will serve to preserve snow and deliver additional snow threats. Overall, the prospects are very good for skiing and riding in this region during the Easter holiday.