Nice Storm Cycle Winding Down

The storm cycle that has blessed us is coming to and end and, when combined with the Thanksgiving weekend storm cycle, leaves us in pretty good snowpack shape for early December.

As of midnight last night, every Wasatch Snotel except for Parish Creek (98%) and Mill D North (94%) was above median snowpack water equivalent for the date.  

Source: NRCS

Those are also the only Snotels in the central and northern Wasatch with less than 5 inches of snowpack water equivalent.  If you are looking for the fattest snowpack, you'll find it in the upper Cottonwoods where Snowbird and Brighton are at 6.6 and 6.5 inches, respectively, and Ben Lomond Peak and Trail, which are at 8.2 and 5.3 inches, respectively.  The 5.3 inches at Ben Lomond Trail represents 241% of median and is especially impressive given that it sits just below 6000 feet. 

Although there may be some lingering snow showers today, the storm cycle is pretty much winding down.  This week represents a break in the action as the next major storm is expected to pass to our south, although it will throw some precipitation our way midweek.  

Most downscaled NAEFS members initialized at 0000 UTC (6 PM MDT) yesterday afternoon are showing less than 6 inches of snow over the next 7 days, and most of that was last night

Thus, this looke like a relatively quiet week.  Hopefully the backcountry snowpack will begin to strengthen and heal.  

Weekend Ski & Snow Update

I got out for my first ski tour of the season yesterday and was pleased to see more snow than we saw probably at any point until late January of last year.  Conditions were good, with the snowpack dictating cautious meadow skipping.

USA bowl was apparently the "it" place for most as it looked nearly as tracked as Solitude did across the street.

The resorts were packed as traffic in the canyon was clogged in the morning and cars were parked up and down the road as far as the eye could see.  Sadly, we enter another season with little progress made to alleviate congestion and no real plan in sight.  

Shifting to more positive news, the snow continues this morning with about 4" of pixie-dust overnight on the Alta-Collins stake through 8 am.  The situation right now is quite interesting as we are basically just to the northeast of an area of strong northwesterly flow where there are a number of small-scale eddies, known as mesovorticies,.  I have identified three of these vorticies in the 1-h RAP forecast below, which is overlaid on the 1500 UTC (8 AM MST) satellite and radar pattern below.  

The circulation associated with the middle mesovortex is clearly evident in the radar image below.  

This is a situation in which the radar isn't really all that useful for inferring what is happening in the central Wasatch.  Note the the lack of echoes, or the existence of only very weak echoes, in the imagery above, especially on the Park City side.  Nevertheless, it is clearly snowing over there.  

There are a number of possible reasons for this.  One is that the storm might be quite shallow, so the radar beam is overshooting shallow snow-producing clouds.  Another is that the water equivalent rates are very low (i.e., the snow is low density) and the ice crystals are relatively small, and thus the snow is producing very little backscattering of energy back to the radar.  

The periods of light snow will continue today and tonight.  I'll be honest.  I'm not sure how much we're going to see.  The flow is weak and shifty and the snow-density is very low (probably 5% or so), so a small amount of water adds up to a lot of snow.  Further, check out the spread in water equivalent for Alta being produced by the models.  Anywhere from 0.1 to 0.9 inches from 2 AM this morning through 5 AM MST tomorrow morning (03/12Z).  

At 5% water content, that's a range of 2 to 18 inches of snow.  Since 2 AM, we've already had 3 inches at Alta Collins.  18 is unlikely, but another 4-8 seems doable, with higher totals if we end up on the high side of these model forecasts.  It should all be cold smoke.  

State of the Snowpack

The last week has been a godsend for Wasatch snow.  Precipitation totals (water equivalent) since Thanksgiving (11/22) are now at about 3.5 inches at Alta Collins and 4.5 inches at Snowbasin Middle Bowl. 

Source: MesoWest

With 8 inches overnight, the total snow-depth sensor at Alta Collins cracked 40 inches, which officially marks the beginning of "early season skiing" based on the Steenburgh snow-depth scale. 

Source: MesoWest

If you are wondering, I consider anything before we get to 40 inches to be "pre season."  Some might grumble about that number being too high, but remember that this blog is about mountain meteorology and snow snobbery.  

Here's something we haven't seen around here in a while, SNOTEL stations with above median snowpack water equivalent.  Paraphrasing Gordon Gecko, "green is good" (blue is even better) and there's quite a bit of it on the map below.  Relative to median, here are a few specific numbers: Snowbird 95%, Brighton 128%, Thaynes Canyon 116%, Mill D North 72%, Ben Lomond Peak 135%, Ben Lomond Trail 191%.  

It's early in the season, so percentages like those can be a bit misleading.  For instance, a station with 2 inches of snowpack water equivalent on the ground and a median of 1 inch is at 200% of median.  Thus, a better metric is the actual water content of the snow on the ground.  If we consider 5 inches to be the start of early season skiing, as a friend mentioned to me the other day, the following sites mentioned above are now above that mark: Snowbird (5.3), Brighton (5.5), Thaynes Canyon (5.1), and Ben Lomond (6.5).  

A special shoutout to Ben Lomond Trail which at 5972 ft sits at 4.2 inches of water equivalent.  Looks like North Fork Park is now grooming for skinny skiing, although the nordic center is not open yet for rentals.  See http://www.ogdennordic.com/.

Enjoy the early season bounty and keep the snow dances going. 

Remarkable Fog Display

Looking south from the upper Aves at around 7 AM this morning

Yesterday's precipitation fell with little wind, allowing for to develop overnight along the Salt Lake Valley floor.  This has led to a difficult commute in some areas and some spectacular views from bench areas above the fog, such as the upper Avenues pictured above.  I am hoping that the Bay Area feel of the view might be a good omen for the Utes as they prepare to face the Huskies in Santa Clara on Friday for the Pac-12 Championship.

The fog was also evident from the top of the tram at Snowbird. 

Time lapse video from campus, compiled by Brian Blaylock, was really fascinating to watch and illustrates the complexity of local flows and wind shear that exists within the Salt Lake Valley and how rapidly they can change, even in a relative quiescent flow pattern.  Wait for it at 10 seconds.

A Multimodel Perspective on This Week's Mountain Snow

Although it is not unusual for the GFS to be wetter than the NAM, the difference between the two models over the next couple of days is exceptionally large.  For Alta from 5 AM this morning through 11 AM Saturday, the 0600 UTC initialized NAM generates 0.84 inches of water and 12 inches of snow.  In contrast, the 0600 UTC initialized GFS generates 2.84" of water and 39 inches of snow. 

There are several reasons why this is the case, but a major one is the track and characteristics of the storm that will move across the region Thursday night and Friday.  The NAM produces a trough that is displaced further south with precipitation occurring mainly near and south of the Salt Lake-Utah County line.

In contrast, the GFS trough is further north and precipitation occurs all the way up into southern Idaho.  There are also some details about the upper-level trough orientation that are different, but which I won't get into here. 

Although I do not have comparable 4-panels to the one above for the experimental FV3 model, which will eventually replace the current GFS, it too favors the more northern track with precipitation into southern Idaho. 

Another perspective is provided by the SREF plume for Alta.  There are 26 members in this ensemble and 24 of them produce at least 1.5 inches of water and fall in the range between 1.5 and 3.25 inches of water.  However, there are two members that lean toward a NAM-like solution, producing less than an inch of water.  Note how the main difference in these members is what happens after 0000 UTC 30 November, which would be that critical Thursday night and Friday period. 

Finally, the ECMWF model is producing 1.5 inches of water for the period at Alta and has a solution close to the GFS and FV3. 

The tendency in such situation is to toss the outlier solutions and focus on the meat of forecast distribution, which would probably yield a forecast calling for 1.5 to 2.5 inches of water at Alta from now to 11 AM Saturday (01/18Z in the plumes above), which would probably translate to 15 to 30 inches of snow given the anticipated snow-to-liquid ratios.  However, I've always felt that one should be cognizant of the full distribution, so a better interpretation is that 1.5 to 2.5 inches of water and 15 to 30 inches of snow is the most likely outcome, with lower odds that  the trough tracks to the south and we end up drier or that the wetter solutions verify.

My suggestion is that you all do snow dances to ensure that the NAM solution does not verify. 

More on the South Track Storms

The post is a bit redundant with the previous, but it's been so long since I've seen a model forecast like the GFS 10-day loop below that I feel the need to share it.  Check out the action across the southwest. 

The European model is generally similar for the first 6 days or so, but deviates quite a bit on the last few days of the loop.  In addition, the GEFS shows a wide of solutions at 10 days.

Source: Penn State E-Wall

Thus, perhaps the GFS run might overdo the persistence of the southerly storm track, but we can still enjoy seeing it as it sprinkles some variety into our lives.

The downscaled 7-day NAEFS quantitative precipitation (water equivalent) and snowfall probabilities also show nearly the all the mountains of the western U.S. getting some action over the next week. 

For northern Utah, much will depend on how productive the bits and pieces are and how far south the storms track.  For once, we probably need to be hoping the storms shift a bit further north than a bit further south, as was the case last year when the storm track was to our north for much of the winter.  I picked the NAEFS plume for Brighton today for a change of pace.  The most productive period is probably from about 0000 UTC 30 November through 1200 UTC 1 December, which would cover Thursday night through Friday morning.  Mean water (snow) totals for the entire 7 day period produced by the GEFS is about 1.75 inches (25 inches), with the Canadian as usual being more optimistic. 

Probably the best chance for snow will be Thursday night through Saturday morning.  Note that the large spread in these solutions, and the different accumulation rates that one can infer from individual plumes indicates some uncertainty and the intensity and timing of periods of snow during the period.  Nevertheless, things look good that we'll continue to build the snowpack at modest rates.