Ski Weather - January 18, 2010
| 18 January 2010
The jet stream configuration has undergone a major change in the past week…a change from the persistent pattern of eastern upper trough/western ridge that has been in place much of the time since early December. The change will be good news in portions of the western United States, where significant Pacific moisture will come ashore for the first time in a long time.
Heavy snow will fall in the central and southern Sierra as well as the ranges of the Southwest. Lighter snows will fall further north, but even there, surfaces that have become hardpacked and thin in spots will be refreshed. In the Midwest and East, the jet stream shift has allowed a January thaw to get underway, which will transform surfaces that have been packed powder for weeks into something more similar to spring conditions. The Northeast will actually start this period with a snow event…one that looks more like a March storm in that it will be working with limited cold air, but it will be cold enough to spread moderate snow from the Catskills into the mountains of central New England. More snow will fall in portions of the Northeast this week, in spite of the thaw, and longer term there are strong signs that we will see the jet stream pattern revert to western ridge/eastern trough by the end of the month.
This morning’s jet stream map shows the changes that have taken place…
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It’s plain to see that the general flow is west to east, which explains why the persistent cold of the first two weeks of this month has eased off…instead of the arctic region acting as a source for the cold air, mostly Pacific air is moving across the U.S. Now, just because the jet stream flow has lost much of its recent amplitude doesn’t mean that all is quiet…far from it. The short wave trough that you can see close to Nantucket is responsible for the snow and rain that are falling in the Northeast today. The larger scale trough that is just west of California is the first in a series of 5 or 6 such systems that are lined up across the Pacific right now. Those systems will keep pounding away at California and the Southwest during the upcoming week…each one will be enhanced somewhat by an addition of energy and moisture from the El Nino in the central Pacific.
The short waves that come ashore will continue eastward during the week, spreading precip into the middle of the country. At the same time, a small area of high pressure will slide through the Great Lakes into the Northeast, putting in place an area of cold air that will support some light to moderate snow later this week from Interstate 70 northeastward to New England. In fact, due to the passage of an upper level low earlier this week, which you can see on the map over the northern Great Lakes, New York and New England will see a good amount of light snow this week, so surfaces will remain packed powder, albeit a bit moist in the lower elevations.
Next weekend will see a continuation of the stormy weather in the Southwest, as the Pacific “fire hose” jet continues to pound away. As I mentioned earlier, the resorts in the central and northern Rockies will see lighter snows during the upcoming week, but that will help to restore packed powder and to cover up some of the pucker brush that has poked through on the steeper runs. Now, down south it won’t be champagne powder that is falling, due to the tropical origin of much of the jet energy, and some rain will fall in the lower elevations of those resorts that don’t have particularly high bases. The snow will have good moisture content, so it will adhere to the existing base, and hopefully the avalanche danger will be manageable.
The southern branch of the jet will remain active into the week of the 25th, but by that time, a surface storm will move into the Northeast, producing rain and snow, but eventually helping to reestablish a long wave trough east of the Mississippi. At first it will return temperatures to levels just a little colder than normal, especially in the central and southern Appalachians, but by the time we get to early February, some seriously cold air will be moving into the long wave trough, and deviations below normal will start to grow in the Great Lakes, Ohio Valley and East. At the same time, we will see a long wave ridge start to build in the West and that will effectively bring the developing string of storms hitting the west coast to an end. One of the strongest indicators that suggest that we will see a return to a blocking pattern over northeastern Canada and the north Atlantic is a renewal of warming at the stratospheric level over the high latitudes. You may recall that it was a strong episode of “strat warming” in mid November that tipped us off to the developing cold of early December…well, it’s happening again, and that gives me a great deal of confidence that winter will return to the areas east of the Rockies that will experience some level of a January thaw this week. It won’t happen in a short dramatic drop in temperatures, but rather it will be a step-down process that will get underway next weekend and continue during the week of the 25th.
So, a January thaw will impact the Plains, the Lakes, the Southeast and portions of the Northeast this week, while the West will see their fortunes take a turn for the better with persistent and locally heavy snows for the next 7 to 10 days. By early February, we will be back where we have spent much of this winter…a western ride coupled with an eastern trough.
Here are some regional highlights:
PACIFIC NORTHWEST AND NORTHERN ROCKIES
Early in the period, these regions will be closer the core of the jet stream that will be coming ashore along the west coast, so there will be some light to moderate snowfall during the first half of this week. Later in the week, as the jet sags further southward, the snow will become more showery in nature. Surfaces that had become quite firm of late will be softened up by the snows of this week. The potential for snow will continue into the week of the 25th before backing off again as an upper level ridge forms over the West.
SOUTHWEST AND SOUTHERN ROCKIES
These regions will be the focus of most of the heavy snow during the upcoming week. Very heavy snow will fall from the Tahoe region southward through the southern Sierra, as those mountains will be the first to tap into the abundant moisture that is coming ashore. The snow will be measured in feet this week in the mountains of California and northern Arizona. Significant snow will also fall in southern Utah, southern Colorado, and the mountains of New Mexico. Powder hounds finally have something to make noise about.
UPPER MIDWEST AND GREAT LAKES
This week will be a quiet one in the Midwest, with temperatures a little above normal. Because daily norms are just about at their lowest levels, snowmaking will still be possible. The next threat of significant snow will come later in the weekend of the 23rd/24th, when a storm will cut through the eastern Great Lakes…some rain will fall to the east of the track before cold air sweeps in on the backside of the storm.
CENTRAL AND SOUTHERN APPALACHIANS
These regions will have a milder than normal week. However, as a cold front sags southward during the early part of this week, there will be some higher elevation snow showers in West Virginia…rain showers will occur in the lower elevations. A southern stream low will set off rain later this week, with some snow up high across WV. The weekend will start pleasantly before a more significant storm brings rain late in the weekend, with that precip eventually changing to snow region-wide. It will be seasonably cold during the week of the 25th.
NORTHEAST AND EASTERN CANADA
The period will start with a moderate snowfall over interior southern New England, and lighter snow further north. A second upper low will follow through the region Tuesday and Wednesday, which will help to maintain snow showers through the mountains. High pressure will deliver a bubble of cold air midweek that will effectively block the impact of the thaw going on to the southwest and west. A late week storm will pass by to the south, although some snow could reach into Pennsylvania and southern New York as it does. Next weekend looks pleasant, with a storm arriving late in the weekend and early in the week of the 25th. That system will bring a mixed bag of precip types, before cold air sweeps in on the backside of the storm and changes it all to snow before ending. Longer-term prospects for cold and snow as we move into February are very good.
