Saturday, November 27, 2021

Haves and Have Nots

The gap between the snowpack haves and have nots in the Wasatch Range right now is staggering.  There's essentially little to no snow below 7500 feet and on south aspects.  On the other hand, there is a very stout 30+ inches on north aspects at and above 9500 feet in upper Little Cottonwood Canyon.  

Collins Gulch is the one percenter of the Wasatch by snow depth.  Alta-Collins has 31" on the snow stake.  On the other hand, look across the canyon and there's little to no snow left on the south facing slopes.  


Today Alta had Collins, Sugarloaf, Sunnyside, and Supreme spinning.  Cover on the main runs is pretty good.  Off piste coverage is pretty good in some areas too (although not so good in others).  Contrast this with other Utah ski resorts that are either closed or spinning a couple of short lifts.  

I see this season as a harbinger of things to come, with the gap between the snow haves and have nots growing during the 21st century as the climate continues to warm.  If you think the upper elevations of Little Cottonwood are hallowed ground now, wait until 2050 or 2070.

Friday, November 26, 2021

Will It Ever Snow Again?

No.  Last night's 0600 UTC GFS below.  Nothing.  Granted its one model and only for 7 days into the future, but if you extrapolate this out it won't ever snow again.  

Did I mention it's also warm?  

Wednesday, November 24, 2021

Taking Requests

 

If all goes well, I will be working this spring on a new edition of my book Secrets of the Greatest Snow on Earth.  Thus, I'm taking requests.  Let me know of any topics you'd like to see covered better or in greater depth.  

Tuesday, November 23, 2021

The Cross-Valley Contrast in Air Quality

Yesterday morning we discussed how a meteorological inversion had developed, but that the air quality was still good to moderate.  There just wasn't time yet for emissions to accumulate within the valley cold pool.

However, by late afternoon, it was clear that the air quality was declining, with smog evident over the Salt Lake Valley as the sun set over the Oquirrhs.  


This morning, one can still see a veil of smog over the valley.  It seems to be particularly bad over the western valley.  


The way that sunlight is scattered by pollution is such that one needs to be cautious assuming that what looks more polluted is more polluted, but that's not the case this morning.  Purple air observations confirm what one infers from the photo above with a clear increase in PM2.5 concentrations across the Salt Lake Valley.  On the east bench, PM2.5 concentrations are at good to moderate levels, whereas in the West Valley, they are higher and in some cases in the unhealthy for sensitive groups category.  


The purple air sensors sometimes read high that appears to be the case today. However, if we look at observations from PM2.5 sensors operated by the Department of Atmospheric Sciences on TRAX trains we still see the increase in PM2.5 concentrations across the valley.  Values are not as high as suggested by PurpleAir, but still max out very near the threshold for unhealthy for sensitive groups.  

Source: https://utahaq.chpc.utah.edu/. 

The situation above is not uncommon.  The reality is that the air quality in the West Valley is often worse than on the east bench.  This is a consequence of several factors including spatial patterns of emissions, elevation, and circulations such as cleaner canyon outflow jets in the morning on the east side.  

The good news is that we have a front coming in tonight, so this episode should be short lived.  The bad news is that ridging will predominate through at least the middle of next week.  Lack of valley snow cover will help, but expect to see declining air quality after Thanksgiving.  

Monday, November 22, 2021

Inversion Season Is Here

Don't be fooled by the lack of snow and sunny skies.  Inversion season is here and this morning a fairly strong one exists over the Salt Lake Valley.

The term inversion has different meanings for meteorologists and the public.  Meteorologists consider an inversion to be a situation in which instead of temperature decreasing with height, it increases.  We have such an inversion in place this morning.  As shown in the sounding below, the temperature at the surface this morning at the Salt Lake City airport was -0.30˚C, but as you went up, it climbed to 4.2˚C at 767 mb (about 8000 feet).  That is a meteorological inversion.  

Source: NOAA/NWS/SPC

To the public, an inversion is a situation with poor air quality, typically occurring the winter.  These events often feature high PM2.5 concentrations and in some cases fog.  

However, meteorological inversions and what the public calls an inversion are equivalent.  It is possible to have a meteorological inversion, but good air quality, and it is possible to have a poor air pollution episode without a meteorological inversion.  

For example, the meteorological inversion present this morning formed late yesterday and last night as high pressure built over the area and temperatures aloft increased.  As a result, there hasn't been sufficient time to build up high PM2.5 concentrations and cause an air quality event with PM2.5 levels at unhealthy for sensitive groups.  Although a meteorological inversion is present, the air quality is good to moderate.  A look at purple air data shows PM2.5 concentrations generally less than 5 at many east bench locations and 12-20, with a few outliers, along the valley floor.  


On the other hand, some poor air quality events are not bonafide meteorological inversions.  During winter, the air in the Salt Lake Valley can become highly stagnated even if a true meteorological inversion is not present.  This is because the stability of the air depends not only on temperature, but also pressure.  Situations in which the temperature does not increase with height, but instead decreases very slowly with height, are still very stable, and prone to poor air quality.

Remember that the air quality isn't bad because of the "inversion."  The inversion is a naturally occurring phenomenon.  The air quality is bad because of emissions related to fossil fuel combustion and other activities occurring in the Salt Lake Valley (click here for more information). 

Sunday, November 21, 2021

Closing Day

 Closing day of touring season at Alta was a beautiful one with a low-angle sun lighting the scene.


Conditions offered up a mixture of cream on crud, gunpowder, and groomers as the resort prepares to open for lift-served skiing on Wednesday.  Natural cover in upper Collins Gulch is quite good for mid-to-late November.  


It was a pretty interesting day meteorologically if you're into the snow energy balance.  Check out the observations from the top of Mt. Baldy.  Temperatures climbed during the day, reaching almost 31˚F by 2 PM, but dewpoints were quite low.  


As a result, the area in the shade of Mt. Baldy was a pretty good icebox.  With clear skies and very very low humidities, conditions were ideal for radiative cooling due to the lack of incoming short-wave and long-wave radiation, as well as sublimational cooling.  

Alta should have good lift-served conditions for opening day on Wednesday.  If you are hoping to see more natural snow, however, pickings look slim for the next week.  Give thanks for upper-elevation north-facing terrain and hope that Mother Nature changes the pattern soon.