November 7, 2012: Winter Storm Watch for the Wasatch Mountains, 3 feet of snow (or more) expected this weekend!

November 7, 2012: Winter Storm Watch for the Wasatch Mountains, 3 feet of snow (or more) expected this weekend!

NAM Forecast Model (2012 07 November 12z run) @ 300mb

Here comes the snow! The National Weather Service (NWS) has issued a Winter Storm Watch for the Wasatch and western Uinta Mountains in northern Utah from Friday, November 9, until Sunday, November 11. The text for this Winter Storm Watch includes, “SNOW ACCUMULATIONS: 1 TO 2 FEET…LOCALLY 3 FEET IN THE WASATCH RANGE.” The NWS Cottonwood Canyons Forecast is on par with these estimations, forecasting 16-30″ of snow between Friday afternoon and Sunday evening with the added note, “GREATER AMOUNTS OF SNOW POSSIBLE IN THE COTTONWOODS IF THE FLOW ALOFT CAN REMAIN NORTHWEST LONGER OVER THE WEEKEND.”

We have been looking at the latest model forecast runs, and, at this point, it looks like frontal passage will occur early Friday morning, bringing about large amounts of heavy snow (starting out around 14% SWE), strong South-Southwest winds (50 knots/~60 mph at 10,000 feet) and much colder temperatures (down to -10° C/14° F at 10,000 feet by Friday night).

NAM Forecast Model (2012 07 November 12z run) @ 300mb
A screenshot from the 07 November 12z run of the NAM Forecast Model at 300mb, illustrating the Wasatch Range’s fortuitous position in the Left-Front Quadrant (LFQ) of the jetstream at midnight Friday evening

After the initial blast of frontal passage plastering the peaks with snow, the strongest part of the storm looks to be passing through the Wasatch Range late Friday night/early Saturday morning, with even colder temperatures, large amounts of available moisture, and enhanced jetstream dynamics (see image at right). Snow densities should get down to our typical 4-6% SWE (blower) at this time. We will have to wait and see if Northwest flow develops and stays in place long enough over the weekend to be a major player. For those who do not know, Northwest flow is highly favorable for the Cottonwood Canyons (particularly Little Cottonwood Canyon), because of their perpendicular orientation to such a flow direction, which brings about enhanced orographic lifting. At this time of year, lake-effect snow is certainly not out of the question, and could be a wonderful addition to this storm, particularly for the Cottonwoods, should Northwest flow develop and remain in place for a prolonged period of time. It is fairly uncertain at this point, but it looks like we may get what we want Saturday night into Sunday, with winds backing off, becoming more Westerly as the bulk of the storm energy moves out of the region. Here’s hoping…

We will continue to monitor this storm as it develops and moves into Utah, and we will most certainly be up in the mountains, sampling its offerings as the snow piles up.

November 8 AM Update: We are already feeling the pre-frontal wind in the Salt Lake Valley, and the forecast is still on track for the most part. Snowfall may begin a bit earlier on Thursday night, as the speed of the incoming cold front appears to have picked up slightly. After the cold front impacts the area, the majority of the storm energy looks to push further south and east, taking most of the jetstream dynamics with it. Hopefully, the Wasatch will still be in a good position for more snowfall under these dynamic upper air conditions. After the cold front pushes through on Friday, unstable air will remain over the area into Sunday, bringing chances for continued snow showers. The odds are looking better, at this point, for lake-effect snow becoming a player for the Cottonwood Canyons on Saturday night and into Sunday evening. There is some slight disagreement in the models on the timing of things in this storm, and there are some major disagreements on what the wind is expected to do over the weekend. If conditions are favorable, and winds shift Northwest, bringing bands of lake-effect moisture into the conditionally unstable post-frontal environment, the Cottonwood Canyons could be looking at steady showers of low-density powder snow over the weekend. Look for zonal flow to return to the area for the first half of next week, followed by another low pressure system moving in for the second half. There should be another strong low pressure trough moving into the mountain states next weekend, and cold temps should remain until ridging and warmer temps return in the following mid-week.

November 8 PM Update: The National Weather Service has upgraded the Winter Storm Watch to a Winter Storm Warning.

November 9 AM Update: Precipitation began at about 1 am last night in Little Cottonwood Canyon with a hail/graupel mix. Frontal passage actually occurred a few hours later, at 6 am, with intense graupel fall and high winds (80 mph gusts at ridgetop). The first few inches of snow are starting to pile up at Alta and Snowbird, and we are looking at PI rates of 1″/hr into the evening. Look for PI rates to dissipate slightly as the winds die down in the late evening. Things are looking pretty promising for lake-effect snow developing Saturday night and lasting most of the day Sunday. Low-density snowfall should begin tonight and last through the weekend, as temperatures drop and winds calm, particularly if Northwest flow develops and remains in place for an extended period of time. Translation: Deep blankets of blower pow Sunday morning.

November 9 PM Update: Things are unfolding beautifully, in terms of snowfall, for the Wasatch Range at the moment. The Collins plot at Alta is currently registering 14″ of new snow/1.64″ of water in the past 17 hours (11-12% Average SWE). Look for precipitation totals to continue rising with lower-density snow (4-5% SWE) as temps drop overnight and winds veer to the Northwest, bringing bands of lake-effect snow into the Wasatch Range. The best chance for lake-effect snow in the Cottonwood Canyons looks to be Saturday night/Sunday morning, just as we called it in our original post on Wednesday. It feels good for that early prediction to now be backed up by the good people at the University of Utah Atmospheric Sciences Department.

 

 

 

 

 

 

Lake-Effect Guidance 11.10.12 PM snippet
A snippet of the University of Utah Department of Atmospheric Sciences’ Lake-Effect Guidance, showing >99% chance for lake-effect snow in the Cottonwood Canyons from 12 AM Saturday night to 6 AM Sunday morning

 

 

 

 

 

 

November 10 AM Update: It dumped all night, bringing the storm total to 23″ and counting at the Collins plot. The Snowbird SnowCam is showing over 16″ (I think we’re seeing some settlement in the layer of snow that came in during frontal passage). Look for ideal lake-effect snow conditions to begin this afternoon, covering most Salt Lake Valley neighborhoods, and dropping blower snow in the Cottonwood Canyons.

November 10 PM Update: Lake-effect snow was in full effect today, followed by a short-lived break in the valley that led to a period of greenhousing. Watch this beautiful lake-effect animation from the University of Utah’s Mountain Meteorology Group. Things were just fine up in the mountains, however, as the snow has continued piling up throughout the day. Lake-effect snow started up again around 8:30 pm, turning the fire hose back towards the Cottonwood Canyons. Expect this snow to continue and intensify during the late night and early morning hours. Considering 30″ have already fallen and another 10″ is certainly possible overnight and into tomorrow morning, this storm is looking to be a 40-incher by Sunday night. The storm is expected to lift Sunday afternoon/evening, as a short-wave ridge builds in.

 

 

 

 

 

University of Utah Weather Time Height 11.10.2012
Here is a snippet of the latest Time Height from the University of Utah’s Atmospheric Sciences department, estimating the storm’s exit in the evening hours tomorrow.

 

 

 

 

 

 

There has already been some avalanche activity in the Alta/Brighton periphery at the heads of Big and Little Cottonwood Canyons. If there is enough snow to ski or snowboard, there is enough to avalanche. 30-40″ of new snow falling at the precipitation rates we have seen during this storm is certainly a reason for caution. KNOW BEFORE YOU GO! Visit the Utah Avalanche Center website and read the current avalanche advisory. Check out the Newest Avalanche Content (formerly known as Current Observations) for great local info on conditions and avalanche reports. Have fun, and stay safe out there!

November 11 AM Update: Lake-effect snow continues dumping low-density (blower) snow in the Wasatch Range! 12″ at Alta overnight! That brings our storm total to 42″ thus far. Watch for lake-effect snow to continue into the afternoon hours and begin tapering off in the evening. Accumulation totals today shouldn’t be anything enormous, like we have seen in this storm previously, but the Cottonwood Canyons will likely pick up another 4-6″ by the time the storm moves out of the region this evening. A short-wave ridge will be building in overnight, and tomorrow should be a beautiful bluebird powder morning. Be wary of widespread avalanching with daytime heating tomorrow!

November 11 PM Update (final): Winter Storm Brutus made its departure from the Wasatch Range late this afternoon, leaving 52 inches of immaculate powder snow in its wake. What a wonderful storm! The skiing has been absolutely incredible everywhere, from the Cottonwood Canyons to the foothills below. Winter has arrived! Let us not forget to use caution when venturing into the mountains in search of the great white wave. Read our 2012-2013 Ski Season PSA on Snow & Avalanche Safety, and be safe out there!

 

 

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Justin
Professional Outdoor Guide, specializing in backcountry skiing, heliskiing Stomping grounds: Wasatch Range, Andes Mountains

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