Bike for Sale

If anybody is looking for a cheap bike, I'm selling my 2008 Cannondale Rush 26er for $200.  Full suspension (100 mm travel) carbon fiber frame (medium).  Lefty shock (the one item that has relatively low mileage as it is the 3rd one I had on this bike.  Tubeless.

Teeth on the rear cassette and front chainrings are worn down to nubbins.  

It was once a great bike, but has been lapped by new geometry.  Would work if you are looking for a Lefty shock, commuter bike, or maybe to get your kid into riding at low cost. I've been riding a different bike for a couple of years and need to get this one out of the garage.  

If interested, e-mail me at jim.steenburgh at gmail dot com.  

Collins Glacier Ski Report

I got out for a few turns of the year today on the "Collins Glacier."  Like most glaciers around the world, it's not in good shape right now.  Oddly, the coverage and skiing are probably best on the lower half where humans have decided to help.  

The snow there is firm but generally carveable, at least in the early afternoon when there's been some sun on it.  

The man-made coverage continues to lower Mambo.

There is, however, a gap in coverage just above the angle station that seemed to be growing in size in today's sun.  

It gets grim in places with sun exposure.  

Coverage improves again in Ballroom and environs, although the snow conditions there were challenging, especially for the first turns of the year.  There are also some Great White Sharks looming in places, just waiting to take a bite out of your skis.  

We need snow.  Next shot is on Tuesday, although there's a great deal of spread in how productive that storm might be.  

Some Climate Stats

October is in the bag.  I would describe it as fairly meh with nothing too extreme.  

At the Salt Lake City International Airport the average temperature was 55.9˚F.  This was warm, but not exceptionally so, rating as the 24th warmest October since 1874.  

Source: https://xmacis.rcc-acis.org/

The airport recorded 1.97" of precipitation.  A bit wet, but not exceptionally so, rating as the 36th wettest October since 1874. 

Up at Alta, the cooperative site in town recorded 4.01" of water and 14.9" of snow.  The records for that site are fairly spotty so good long-term comparisons are difficult.  The ski area, which measures higher on the mountain, reported 22", compared to an average since 1980 of 26.6".  

Essentially it was a Goldilocks October weather wise in northern Utah.  

Utah has not had a statewide average annual temperature below the 20th century average since 1993.  Numbers through October are not yet available, but through September, we were just barely above the 20th century mean of 51.0˚F with an average temperature of 51.1˚F.  

I suspect October will push us just a bit higher above the 20th century average.  Whether or not we can have year below average will depend on what happens from here.  Other years since 1993 have been close (2008 and 2011), but have ultimately come in above the 20th century average.  

A Healthy Front

I like the looks of the storm on tap for late tonight and tomorrow.  It's a pretty good front that is going to usher in the coldest air of the season so far for northern Utah.  

We'll start with a look at the GFS forecast valid 0900 UTC 26 October (3 AM MDT Wednesday) when a compact upper-level trough is centered over southeast Oregon and the preceeding cold front is draped across northern Utah.  At 700 mb, roughly 10,000 feet or crest hight of the Wasatch Range, there is about a 12˚C (22˚F) temperature contrast across this front, so it's a whopper. 

By 1500 UTC (0900 MDT), the trough is over southwest Idaho and the front is draped over Salt Lake City.  We will be post-frontal by this time with steady rain on the valley floor and snow intensifying in the mountains.  Woo hoo!

By 2100 UTC (3 PM MDT), the cold air is into northern Utah in earnest with 700-mb temperatures over the Salt Lake Valley below -6˚C.  This will mean some flakes down to bench levels.  

The phasing of the frontal band with the coldest air is such that accumulations below 6000 feet will probably be limited, but I'd keep an eye on forecasts as such details are hard to anticipate with precision.  

For Alta, most of the models are producing forecasts clustering around about 0.7 to 1.2" of water and 8-16 inches of snow.  The latest HRRR generates a quick hitting frontal passage with precipitation beginning just before 3 AM tonight and ending by about 10 or 11 AM tomorrow, resulting in just over 8 inches of snow from about 1" of water.  

The GFS, has somewhat different ideas on timing, with precip starting after midnight and continuing until the late afternoon.  This solution would be more favorable for some flakes on the benches since the precip keeps going until the arrival of the coldest air.  That said, the GFS produces a bit less precipitation with just over 8" of snow and about 0.7" of water.  

The downscaled SREF is coming in with 0.5 to 1.5" of water with a mean just under 1".  The snowfall range is around 7 to 17".  There are a couple of members going for a bit more with a second trough friday night and Saturday, but right now I'm not expecting that to do very much. 

Bottom line is this looks like an 6-12" storm for Alta.  We may do a bit better if the front moves through slowly.  

A look at the High Rustler cam this morning shows this will fall on dirt and grass on the lower mountain and on old snow from prior storms on shadier aspects (other aspects have melted out even at upper elevations).  

Anyone skiing is going to experience the lowest of low tide conditions with plenty of buried and unburied hazards.  I haven't been up to poke around the snowpack where it exists, but early snow often becomes weak snow, so be careful out there.  

About Cody Townsend's Sierra Rotor

I'm a big fan of Cody Townsend's The Fifty, which documents his efforts to ski all the lines in the book Fifty Classic Ski Descents of North America.   I've skied a few of these lines and dreamed of skiing a few others.  Some are beyond either my physical or technical abilities, or the suffering to powder ratio is too high to interest me.  Cody and cinematographer Bjarne Salén do a remarkable job capturing footage of their adventures and bringing me along for the tour.  I keep thinking about all of the parameters they are dealing with including the snowpack, weather, route finding, climbing hazards, and ski challenges, and yet they are also shooting some great footage (and carrying all that gear).  It's an impressive accomplishment.  

The latest episode, Tragedy and Triumph in the Split Couloir, documents their attempts to ski the extremely challenging (and often snow starved) Split Couloir on the 14,058 foot Split Mountain in California's Eastern Sierra.  In one attempt, they are blown off the mountain by strong winds.  In a recent Instagram Post, Cody attributed these winds to "the Sierra Rotor", an "extreme terrain-induced downslope wind."   

View this post on Instagram

A post shared by Cody Townsend (@codytownsend)

I'm not sure what day they were on the mountain, but watching the episode a couple of weeks ago, I immediately thought that they were in a downslope windstorm.  Let's take a look at what may have happened and why the term "Sierra Rotor" is perhaps not best used for what they experienced.

Severe downslope windstorms occur on the lee-side of mountain ranges around the world.  They have many regional names including the Foehn (northern Alps), Bora (Croatia), and Chinook (Rockies).  In Utah they are sometimes referred to as "Canyon Winds." They are produced by what meteorologists call "high-amplitude mountain waves."  These are the atmospheric equivalent of a hydraulic in a river in which the flow accelerates downstream of a rock or rocks and then decelerates in a turbulent hydraulic jump.  

Source: Wikimedia Commons, Author: aokomoriuta

This also happens in some situations during flow across mountain ranges as shown in the schematic below. In some cases a rotor can form downstream of the hydraulic jump.

Source: Whiteman 2000

The rotor is a component of the downslope windstorm system.  In a well developed rotor, there is flow reversal at the surface.  Incredibly, you can go from severe downslope winds in one direction to relatively light flow from another direction over a short distance.  

The eastern Sierra and especially the Owens Valley are well known for severe downslope windstorms and rotors.  Some of the seminal research on severe downslope windstorms was conducted in this area during the Sierra Wave Project in the 1950s (see Sierra Wave Project Revisited by Vanda Grubišić and John M. Lewis) and the Terrain-induced Rotors Experiment (T-REX) in 2006.  

Below is a classic photo of a Sierra downslope windstorm taken by Robert Symons.  The view is toward the south with the eastern Sierra on the right.  The flow is from right to left.  Strong downslope winds extend from the Sierra across the Owens valley where they pick up dust.  This dust is then elevated in the rotor circulation.  The ascent is deep enough that clouds form near the top of the rotor. 

One of my favorite papers on rotors (and subrotors, which are embedded in rotors) is Doyle and Durran (2007).  In it, they present the average cross-mountain wind speed (top panel color fill with reds away and blues toward the mountain) and vectors (bottom panel).  Note that in this figure the mountain is on the left. One can see the intense flow descending the mountain, with the speed maximizing just before the rotor.  The strong winds then elevate in the hydrolic jump and follow an arc over the rotor.  Near the base of the rotor (i.e. at the ground), the flow is actually reversed and is moving toward the mountain. The transition from strong downslope flow to light reversed flow occurs over a distance of less than 2 kilometers.  

Source: Doyle and Durran (2007)

The rotor is not the cause of the downslope windstorm, it is a component of it.  Not all downslope windstorms produce rotors and in some the rotor circulation may wax and wane.  The rotor circulation is sensitive to the of the characteristics of the atmospheric flow impinging on the mountain range (i.e., wind and stability) and affected by the presence of downstream ranges like the Inyo Range in the case of the Owens Valley.  

So, Cody Townsend did not experience the rotor while on Split Mountain.  He experienced the downslope wind.  The rotor, if it existed, would have been over the Owens Valley.  It's probably best not to call this phenomenon the Sierra Rotor since the rotor is a component of the downslope wind system and isn't always present.  That said, it would be appropriate to refer to the circulation beneath the hydraulic jump and Owens Valley as the Sierra Rotor.  

Congrats to Cody for eventually skiing the Split Couloir. 

A Cold October Trough

The last week of October is going to be an interesting one for mountains of the western United States.  I've been watching forecasts for a cold trough to drop into the Pacific Northwest for about a week now.  It's going to bring significant October snows to portions of the western United States.  

It's worth a look at the origins and forecast evolution of this trough.  It all began with the formation of a midlatitude cyclone off the coast of Asia late last week and over the weekend.  This cyclone built a ridge that was over the Behring sea at 1800 UTC 22 October 2023 (1200 MDT Sunday, orange line).  Just east of this ridge was a weak trough and jet streak that I've circled in red. These represent the incipient cold trough.  

Both the ridge and the incipient cold trough are forecast to amplify through 0000 UTC 24 October (1800 MDT Monday) with the trough digging southward over the Gulf of Alaska. 

By 0000 UCT 25 October (1800 MDT Tuesday), the now well developed high-amplitude ridge is parked over the Gulf of Alaska with the cold trough over Vancouver Island.  This is a dream mid-winter pattern for Northwest Skiers and potentially a horror show for lowland snow in the Puget Sound area, although in October, the latter won't happen.  Still, it is a recipe for the first big snow of the year in the Cascade Mountain Passes.  

Finally, that trough swings eastward across the interior Pacific Northwest.  By 1800 UTC 26 October (1200 MDT Thursday), the trough axis is moving over Utah and a second trough is dropping into the Pacific Northwest.

  

Let's start with a look at what this will do in the Cascades through 0600 UTC 25 October (Late Tuesday Night).  Our HRRR derived snowfall product shows 24-h accumulations in some mountain areas of over 16 inches. Although the snow starts a bit before this accumulation period, this is the bulk of the snowfall through that time.

Below is a time series from a HRRR grid point very near Stevens Pass Ski Area.  The HRRR is going for 1.25 inches of water and about 13 inches of snow, with more to come from the second trough after the end of the HRRR forecast period.   

Here in Utah, the forecast is trickier as much will depend on the track and structure of the trough and the models have been all over the place on those two storm characteristics.  Over the weekend, I saw a GFS run that was putting out about 18" for Alta with the trough passage, now it's down to about 9". 

Let's have a look at the latest GFS-derived forecast guidance for Little Cottonwood. In this forecast, the bottom drops out with a frontal passage around noon on Thursday.  Temperatures at Alta-Collins and Mt. Baldy drop, the wet-bulb zero crashes from 9000 ft to 6000 feet (and then lower Thursday night), and there is a pulse of snow adding up to about 3 inches.  This is followed by a second round on Friday that brings the storm total to an inch of water and about 9 inches of snow.  

The latest Euro too is right around an inch of water.  

The normally jacked downscaled NAEFS is a bit more optimistic with a mean of about 1.3" of water equivalent with the frontal passage and then a few members that are excited about the second trough pushing storm totals over 2 inches of water and nearly 30 inches of snow.  

These are fairly extended forecasts covering a period of 72 to about 144 hours out, so uncertainties are to be expected.  Note that the NWS is also advertising a range of outcomes depending on storm characteristics.  

Bottom line.  Keep an eye on the forecasts.