Tuesday, May 25, 2021

The Great Avenues Foothills Trail Imbroglio

I have lived in Salt Lake City for over 25 years.  During that time, I have been a trail runner, mountain biker, and hiker, although I can no longer do the former.  I recreate in the Avenues foothills probably 3 or 4 days a week, sometimes more.  I've even ski toured in them.  

I'm old enough to remember when the segment of the Bonneville Shoreline Trail from Pipeline Pass to Dry Creek was constructed, as well as the segments from Morris Meadow to City Creek Canyon and from City Creek Canyon to North Salt Lake.  All of these trail additions improved the quality of life and access to outdoor recreation for Salt Lake City area residents.  

So when I saw plans a couple of years ago to expand the foothills trail network, I was excited.  The Bonneville Shoreline Trail was becoming increasingly crowded.  Lots of bikers and hikers.  The plan included hiking only trails, downhill biking trails, hiking and uphill biking trails, and multiuse trails.  It make sense to expand trail opportunities and create a system that segregated users.  

Last year track hoes began to construct the trail system.  By April 23rd of this year, most of the trails in the Morris Meadow and Mountain area were open for use.  Like the Whos in Whoville, hikers and bikers have emerged from the pandemic and flocked to these trails.  I haven't bothered leaving the neighborhood to ride or hike anywhere else as the spring weather has been pleasant and there have been new trails to explore.  

The new "19th Avenue" downhill flow trail in the Avenues foothills

However, on May 12, an article appeared in the Salt Lake Tribune headlined "Are SLC's long-awaited foothill trails falling flat?" that featured numerous complaints about the new trail system.  On Friday, it was announced that city officials had halted trail building until at least October in response to these complaints (see "Work on SLC's foothill trails halted until at least October").  

The city is now collecting input from trail users via an online survey available at https://www.slc.gov/trailsurvey/.  Please take a few minutes to share your opinions and views.

Friday, May 21, 2021

Late May Soaker?

Forecasts for this weekend, especially Saturday night and Sunday, are looking good.  It appears rain is likely, and we've reached the time of year where every storm and every drop should be appreciated.  

Although we may get get some rain today or Saturday in the form of showers and thunderstorms, the best chance for a soaker is Saturday night and Sunday when the upper-level trough that is currently spinning to our west over Nevada finally decides to head across northern Utah.  The GFS forecast valid 1200 UTC (0600 MDT) Sunday shows the trough with widespread precipitation over much of northern Utah.  

The storm will be cold enough for upper-elevation snow.  GFS forecast snowfall for Saturday night and Sunday totals about 10 inches at Alta-Collins.  The downscaled NAEFS has a fairly large range for Alta-Collins, but the mean for the period from 0000 UTC 23 May (1800 MDT Saturday) to 0600 UTC 25 May (0000 MDT Monday) is about 9 inches.  

For the valley, we'll see rain.  Let's hope the storm delivers.  The flowers will appreciate it. 

Thursday, May 20, 2021

Snowbird Closes

Snowbird announced yesterday that last weekend was their last operating weekend of the 2020/21 ski season.  

Such a decision is based on several factors, but we'll focus first here on the state of the snowpack as of today, May 20th.

SNOTEL observations show a dearth of snow across northern Utah (i.e., north of I-70/US-6).  Only USU Doc Daniel (11.5") above Bear Lake, Lakefork Basin (7.9") and Steel Creek Park (8.9") in the Uinta Mountains, and Snowbird (12") report have more than 2" of snowpack water equivalent.  Most of the remaining sites have nothing.  

The duration of snowcover in the spring depends on several factors including the buildup of the snowpack during the cool season, the weather during March through May, and other factors that are difficult quantify at present, such as the amount of dust in the snowpack.  Let's take a look at the first two factors during this season compared to three others: 2014/15 (red line below), 2018/19 (green line), and 2010/11.  

Of the four seasons 2014/15 had the lowest peak snow-water equivalent.  However, a cool, intermittently snowy period in early to mid May extended the snow-cover season to June 1st. 

2010/11 was probably the closest thing you'll see to a dream season.  Massive buildup of the snowpack through April and then slower but continued growth through May.  In fact, peak snowpack (75.1") was reached on May 23rd and then again on May 31 and June 1.  At that point, the pattern shifted and 75" of snow water equivalent melted in just over 5 weeks.  Incredible, but the high angle sun in June is merciless once the storm track has retreated northward.  Snowbird was open through the 4th of July.  

Then there is 2018/19.  The snow accumulation season was generous with a healthy peak snowpack of over 55", but we started to lose snow in mid April, which is a bit early.  Mother Nature, however, shifted gears again in Mid May and brought in colder weather and storms, so that there was a secondary snowpack peak in late May.  As a result, the snow cover season extended to late June.  Snowbird stayed open through the 4th again on upper elevation terrain above this observing site.  

Finally we have this year.  Peak snowpack wasn't very high (it was about 75% of median), but the cooler April meant it was reached in late April at about the time of the median peak.  However, since then the snow loss has been generally steady and consistent, with just one brief cold surge to slow it down.  

Nevertheless, I suspect Snowbird has enough snow to operate if they wanted to.  The decision to close is based on more than just snow, especially this year given all the COVID issues at play.  I thank all the essential employees who helped make recreation possible this past ski season and hope for a more normal season next year.

Correction, I HOPE FOR AN EPIC SNOW AND SKI SEASON NEXT YEAR.   Start burning skis now.

Tuesday, May 18, 2021

Where the Snowpack is Fat

There is a tendency when it comes to SNOTEL observations to focus on the percent of average or median.  That can be useful, but more important for skiing is often the snowpack water equivalent (SWE), as that is what tells you how fat the snowpack is.  

A look at the SWE values for yesterday shows a dismal situation across much of California, Nevada, and Utah, with only a few sites still reporting some snowpack SWE.  

Source: NRCS

If you squint, you can see one of these is Snowbird, which sits at 15.7 inches, about half of the late April peak, 38% of median for the date, and in the bottom 1/5 for the date.  

Source: NRCS

For snow, there are options to our east (Colorado) and north (western Wyoming and Montana), but to the northwest, the snowpack in the Washington Cascades is fat and healthy.  Many sites report SWE in excess of 35 inches.  Here's one for you...Easy Pass at 5270 feet in the North Cascades east of Mount Baker.  Current SWE is 94.2 inches, which incredibly is just a bit above median for the date.  

Source: NRCS

Even Rainy Pass further east and despite the name in the comparatively dry eastern Cascades, sits at a near-median 27.2 inches, plenty of snow for the accessible skiing from the North Cascades Highway.  

Source: NRCS

Similarly, many sites in the southern Washington Cascades sit near median and look to be in good shape.  Paradise Ranger Station on Mt. Rainier has an 84.5" SWE, which is 126% of median (not shown).  

And here's the forecast:

Source: NWS

Should be some good spring skiing up there over the next few weeks.  

Thursday, May 13, 2021

Cloud Generation Downstream of Mountains

When we think about how mountains affect the production of clouds, we often assume that the air rises, cools, and produces clouds on the windward side of a mountain range (i.e., the side facing the flow) and sinks, warms, and dissipates clouds on the leeward side (i.e., the side facing away from the flow.  

Source: Whiteman (2000)

This is often a good assumption at low levels if the flow is moist and sufficiently strong to surmount the mountain range.  However, there are times when cloud generation occurs on the leeward side of mountain range.  

This happened overnight downstream of the Deep Creek, Schell Creek, and Snake Ranges of Nevada.  As shown in the photo below, mid- and high clouds formed or became enhanced downstream (east) of these ranges. 

In this instance, it is likely that the flow at low levels was sinking and warming on the eastern/leeward slopes of these ranges as depicted in the schematic above.  However, at mid and upper levels, it is likely that the air was rising, leading to leeward cloud generation.  

A schematic of this process is shown below.  The flow moves over the mountain barrier at low levels, resulting in cloud generation at low levels over the windward slope and dissipation over the leeward slope (this isn't happening in the satellite image above because the low-level airmass is too dry).  At upper levels, however, there is what meteorologists refer to as a vertically propagating gravity wave.  Such waves are sometimes generated by flow over mountains and they lead to an upstream tilt in the wave troughs and crests and rising motion over the lee slopes at mid and upper levels.  

Source: Durran and Klemp 1983/The Comet Program

This can lead to cloud generation downstream of the mountains.  In some situations, such clouds can extend well downstream of the mountain barrier.  

Instead of clear skies, you might get overcast skies.  Meteorologically you might say no biggie.  However, such clouds strongly affect power generation by solar farms and thus are a consideration for power management.  

Tuesday, May 11, 2021

Tahoe Ski and Bike Report

Thanks for letting me disappear for a few days to take a break after the end of the academic year.  It was a long one and I needed to reset my sanity.  

The limited snowfall in the Sierra Nevada this year created an unusual opportunity for early May corn skiing and mountain biking in the Tahoe area.  We took off last week and did a couple of days of mountain biking, a day of Alpine skiing, and a day of ski touring.  

After arriving in Truckee and doing and evening ride on the Donner Crest trail, we skied a day at the famous north Tahoe ski resort that has served as the home or base for many great skiers including Tamara McKinney, Julia Mancuso, Shane McConkey, and Cody Townsend.  Given the limited seasonal snowfall, conditions varied some depending on elevation and aspect...

Sadly, KT-22 was closed, so we kept ourselves occupied with laps involving the One Express and Siberia trails, venturing frequently over to the area around Headwall Express (which was closed although the terrain beneath was open) where we found good corn thanks to the dense and well consolidated Sierra spring snowpack.  

Some route finding was required, but continuous lines could be found and it was entertaining for a couple of hours. 

We then hydrated in the car and shifted over to Alpine Meadows until they closed at 2.  This was my first visit to the resort and it quickly made it on to my "little ski areas that rock" list as we pretty much had the Summit Six chair to ourselves and skied every little line that was still in.

Despite the limited snow, the steeper lines were quite good.  I don't know when it last snowed in the north Tahoe area, but the corn was dense, grippy, and confidence inspiring.  The stuff that spring steeps are made of.  The flatter, lower mountain was an ACL-tear waiting to happen, but thankfully we survived.  

The next day, we rode the northern portion of the Flume trail, which is one of the more famous rides in the Tahoe area.  It's an extremely well constructed trail that contours along about 1000 vertical feet above Lake Tahoe.  The portion we rode as an out-and-back was easy riding.

The attractions are the forest, rocks, and views, which are quintessentially east Tahoe and spectacular.  

I suspect the trail is heavily traveled during the summer.  We saw some people, but not many, making the ride more enjoyable.  

We brought our ski touring gear, but struggled deciding where to go for an accessible option not involving miles of approach or bushwhacking given the meager snowpack.  We had an interest in skiing Lassen Peak, but the 6+ hour round trip from where we were staying wasn't inviting.  We ended up driving down to Carson Pass and eventually touring around the Kirkwood ski area, which was closed.  Since neither of us had ever skied there, it was a pretty good option and it went right from the parking lot.  

After skinning up "The Wall," we traversed on bare ground to near the summit of Thimble Peak.

The skiing from here was mighty fine.  Good corn, with a bit of sun-cupped roughness.  

I suspect a week or two ago would have been best, but it was good enough for a 2nd lap.  Tracks from run one to the left.  

The return enabled us to explore some of the chutes beneath the Thunder Saddle.  Having never skied here, this added a bit of fun adventuring since we hadn't scouted the area and needed to poke around a bit to see if a line went given the meager snowpack.  We fortunately chose wisely, passing on one that we couldn't fully assess from the top and would have cliffed out.  The one below was a better choice and skied well.    

In some respects, the lack of snow was a bit of a bummer, but the skiing was good and the mixture of riding and skiing was just what the doctor ordered.  

Now to get those grades in...

Wednesday, May 5, 2021

Abnormal Climate Normals

I've never been a fan of the phrase "climate normals" to describe averages of past climate.  It perpetuates the myth that climate is stationary and it suggests that an average is normal when weather normally fluctuates in a range.  I grimace whenever I hear someone say "normally the high today is 64˚F."  

I always wondered who started using this phrase and why.  I don't know the answer to that question, but according to the National Centers for Environmental Information (NCEI), about 100 years ago the World Meteorological Organization (WMO) instructed member nations to calculate climate normals using 30 year periods, beginning with 1901-1930.  

So, near as I can tell, we call them climate normals and we average over a 30-year period because we've always done it that way.  That's simply not a good reason, especially now that we are living in a period of accelerating climate change and we know that for some regions, a 30-year average is likely insufficient for some variables like precipitation, which exhibit slowly evolving decadal or multidecadal variations.  

This issue has come to the forefront this week because NCEI issued the new 1991-2020 climate normals.  Below is a series of maps produced by Jared Rennie of the North Carolina Institute for Climate Studies showing how the 30-year temperature normals have evolved compared to the 20th century average.  The warming trend is apparent.   

Source: https://www.noaa.gov/news/new-us-climate-normals-are-here-what-do-they-tell-us-about-climate-change

Precipitation is more complicated, however, as there's more regional variability and variations that occur over decades.  For example, 1941-1970 was relatively dry over the southwest, 1971-2000 relatively wet, and 1991-2020 relatively dry again.  

Source: https://www.noaa.gov/news/new-us-climate-normals-are-here-what-do-they-tell-us-about-climate-change

For the southwest United States, annually averaged temperatures have increased at a rate of approximately 0.7˚F per decade since 1975.  Thus, the 1990-2010 temperature normals are probably already about 1˚F lower than they should be.  They reflect the past climate average, not the current climate average.  

Source: NCEI

For precipitation, the situation is more complicated.  Instead of there being a clear long-term trend, precipitation in the southwest has exhibited wet and dry periods, with the latter predominating in the past 20-25 years.  

Although there is strong evidence that drought will become more frequent, prolonged, and severe over the southwest US during the 21st century, it is less clear what long-term trends in annual precipitation will be (drought is affected not only by precipitation amount over long periods of time, but also temperature, precipitation type, precipitation intensity and other factors).  Thus, we should be cautious interpreting the recent spate of low precipitation years as a long term trend.  

The climate system is changing and while knowledge of the past is helpful, it is increasingly important that those of us in Utah recognize that these climate models are averages of the past climate and that the future will be hotter and drier, even if the average annual precipitation doesn't change that much.  

Monday, May 3, 2021

Over the Snowpack Crest

We suggested a few days ago that the end of the snow accumulation season was nigh.  Observations from the Snowbird SNOTEL show that peak snowpack water equivalent was reached on April 28 (32.7") and that we dropped below 30" yesterday.  

Source: NRCS

The Alta-Collins snow depth fluctuated around 100 inches for the better part of a month, but is now in decline, having dropped to around 90 inches this morning.  

Source: MesoWest

Forecasts through the end of the work week keep us generally dry.  We're likely over the crest now even on high north facing terrain.  

We got out for some "snirty dancing" on Saturday.  At the start of our tour, it was 47˚F at 7 am.  Disgusting.  Nevertheless, there was a shallow freeze and turns were good on southern aspects where the most recent storm snow had melted out.  Look close and you can see the snirt – dirty snow where dust from storms over the past few weeks has emerged onto the snow surface.  

North aspects were already soft by about 10 am and still had some of that storm snow remaining, which was sticky and grippy.  I suspect this snow will be melted off soon if it hasn't already, leaving snirt on all aspects.