Monday, December 30, 2019

Major Storylines of the 2010s and 2020s

With the 2010s coming to a close, it's time to look back at the last 10 years and highlight some of the major storylines covered by the Wasatch Weather Weenies.  We first started posting in Fall 2010, so the 2010s were our true youth.  Be warned that the 2020s will be our adolescence.

The 2010/11 Ski Season

Let's start on a positive note with the 2010/11 ski season which I suspect we can all agree was the best in the last 10 years in Utah.  The photo below was taken in the Avenues foothills on November 29.

Things just got better from there.  It was full on by mid December as Alta reached a 100" deep snowpack on December 20th.   How's this for coverage in upper White Pine on December 24th.

And Mother Nature just kept bringing the Goldilocks storms all winter long, right up through Memorial Day weekend when we were still skiing powder.

While the powder was gone, Snowbird was for the 4th of July when my son and I were skiing on Mt. Rainier.

One for the ages for sure.  My best estimate as they don't record snowfall after closing was that Alta received 800 inches of snow for the season (see Alta 800!).

Low Snow Years

The 2010/11 season was outstanding, but overall the 2010s also featured poor snow years and in general snowfall was a bit substandard.  Data fro Alta Guard shows that the lowest November-March snowfall occurred in 2014/15 and 2017/18 (sorry about not updating this with last years totals, but you get what you pay for).

As I concluded in a deep dive post examining the spate of poor snow in recent years, sorry kiddies, but your parents had more powder than you (see Your Parents Had More Powder Than You).  As I mentioned in that post, I'm not inclined to blame all that decline on global warming (more on this in a minute), but suspect that slow variations in storm-track are also an important contributor.

Global Warming

Unless you live in a cave or are the President of the United States, you likely recognize that the planet is warming and that this warming is caused primarily by human activity (especially greenhouse gas emissions).

Once fully in the can, the 2010s will be the warmest decade in the instrumented record and there is growing consensus that we are in the warmest period since at least the Holocene about 7,000 years ago and and possibly much farther back than that.

Temperature is important, but as I often say, it water is the agent that delivers weather and climate impacts through sea-level rise, heavy precipitation, drought, etc.  We are now seeing and measuring changes in the cryosphere (e.g., glaciers, ice caps, etc.)  that have long been predicted and that portend a world that could be dramatically different from the one we have built our civilization around.

I could discuss the mass balance of the Greenland and Antarctic Ice Sheets, which are the big concerns for future sea level rise, but I'll instead focus on the European Alps due to my recent time spent in the Department of Atmospheric and Cyrospheric Sciences at the University of Innsbruck.  As discussed in our post The Disappearing Glaciers of the European Alps long-term losses in glacier mass are evident in across the Alps, with total loss of some minor glaciers and extensive retreat of major glaciers like the Hintereisferner in the Ă–tatal Alps of Austria.

Source: Kuhn and Lambrecht (2007)
This is not simply a response to the end of the "Little Ice Age."  Mass loss has accelerated in recent years and, in the case of the Hintereisferner, there has not been a net gain in glacier mass in any year since 1983, and that year was only weakly positive.

Recent studies indicate that if we keep total global warming to 2˚C over pre-industrial levels, the Alps would lose 50% of their remaining glacial ice.  A high emissions scenarios results in a total loss of all glacier ice by the end of the century except in high altitude regions of France and Switzerland.  

Global Warming and Utah

In 2007, I led a team of scientists that prepared a report on climate change for then Governor Jon Huntsman Jr.'s Blue Ribbon Advisory Council on Climate Change (report available here).   In that report, we document changes to the climate of the Earth, western U.S. and Utah and, for the state of Utah, projected that Utah would see fewer frost days, longer growing seasons, and more heatwaves.  We also said that ongoing greenhouse gas emissions would lead to a decline in Utah's snowpack.

Detection of the fingerprints of global warming on Utah climate has been a common theme of this blog.  Often, I emphasize that the ability to detect of climate change trends depends on the variable.  As discussed in Western Snow Trends and Global Warming: Part I, trends in temperature and the fraction of cool-season precipitation falling as snow are the first to exhibit trends large enough to discern from the year-to-year variations.  Trends in peak of April 1st snowpack take longer to emerge, followed last by snowfall.  

As things stand now, it is very clear that warming is happening in Utah, and that we are seeing decreases in frost days, longer growing seasons, and more frequent and intense heat waves.

Large year-to-year variations make snowfall and snowpack trends more difficult to detect and generalize, but the bulk of the evidence indicates that there has been a decrease in the fraction of cool-season precipitation that falls as snow, more frequent mid-season snow-loss events (due to melting or sublimation), and a decrease in the amount of wintertime precipitation retained in the snowpack at the end of the snow accumulation season.  These trends are elevation dependent and largest below 6500 feet and small or non-detectable above 9000 feet.

That's what's been observed to date.  Although we will continue to see large year-to-year variations in cool-season weather over Utah in the coming decades, we will see a shift to warmer winters with commensurate changes in snowpack and snowfall.  For more on what might happen see Western Snow Trends and Global Warming, Part II or the last chapter of my book Secrets of the Greatest Snow on Earth.

The Late October 2019 Cold Wave

While there are many contenders, a strong argument could be made that the late October 2019 cold wave was the most unlikely "black swan" weather event of the last decade.  If you wish to reminisce, see How Hell Freezes Over, Rapid Fire Views on the Octobruary Cold Surge, and Hell Has Frozen Over

Why is it such a black swan?  Well, at least two things happened in Salt Lake that had never happened before in October.  First, upper-air soundings recorded a 700-mb (10,000 ft) temperature of -18.5˚C, more than 3˚C lower than the previous record.  Second, the Salt Lake City airport recorded a minimum temperature of 14˚F on October 30, the lowest recorded in the month of October with records going back to 1874 (if you include observations from downtown Salt Lake City in the late 1800s and early 1900s. 

In fact, it's now late December and we still haven't observed a temperature anywhere near that low so far this winter.  The lowest since October 30 is 20˚F, recorded on several days. 

To set a record like that in a warming climate with a much larger urban area and associated heat island is quite remarkable.  The odds were long, but, as discussed in the posts above, extreme cold in our part of the world requires a series of large-scale circulation changes that allows extreme cold to push into the Intermountain West and Mother Nature can still bring it when the circumstances are right. 

And, to further highlight the regional nature of the cold wave, below are surface temperature anomalies on October 30th relative to the 1979-2000 average.  Globally, we were 0.7˚C above that 1979-2000 average, with the interior western U.S. an extreme cold outlier. 


Air Pollution and Inversions

This has been a frequent topic of our posts but one that I would prefer to forget.  What can I say?  We have met the enemy and it is us.  'Nuff said.

Blown Forecasts

And bad mistakes
I've made a few
I've had my share of sand kicked in my face
But I've come through
- Queen (from We Are the Champions)

I tell people that this is a blog and not a forecast service.  The reason for this is that I often talk more about the forecast process and I don't consider what I do to be a true forecast such as what is issued by the National Weather Service.  

Nevertheless, I do talk about the forecast process, the science behind it, and what I think will happen.  Meteorology is advancing rapidly, but it is still an inexact science, so blown forecasts are inevitable and I've had my share.  

One need only look at the post from a couple of days ago entitled, No Major Storms in Northern Utah for the Rest of the Year... God, what a disaster.  In writing it, my thinking was that there were no major dumps forecast and by major, I meant with a substantial accumulation of snow.  Subsequently, while snowfall has been light in depth and water equivalent, it has been frequent and high impact due in part to the low temperatures and cold road surfaces.  Like a good quarterback forgets bad passes, it is important for a meteorologist to quickly forget (but learn from) such blown forecasts, but the pain of this one will linger for a while, or at least until the next major storm, which looks to be New Years Day (if you still want to buy what I'm selling).   

Personal Professional Highlights

A colleague once told me that graduate students can take you to places you can't go by yourself and over the last decade (not to mention my 24-year career at the University of Utah), I've been blessed to work with may talented students who continue to do things that I couldn't do by myself.  They enabled the successful execution of three field programs: the Storm Chasing Utah Style Study (SCHUSS), Outreach and Radar Education in Orography (OREO), and Ontario Winter Lake-effect Systems (OWLeS).
At Pulaski High School with the Center for Severe Weather Research Doppler on Wheels radar
Maybe you caught us during one of our outreach efforts.  Hopefully we inspired a few youngsters to pursue science as a career.  We certainly enjoyed the storm chasing, being in the snow, and the subsequent research.  I thank the National Science Foundation for their support of our efforts, which, now involves significant collaborations with scientists at the Snow and Ice Research Center in Nagaoka, Japan, as it became apparent to us that such a collaboration would accelerate our understanding of how terrain impacts lake- and sea-effect storms. 

An X-band scanning radar at the Nagaoka Snow and Ice Research Center
If you want to learn more about what happens in Japan, see our forthcoming article for the Bulletin of the American Meteorological Society (currently available in unformatted form, but hopefully formally released soon). 

Other highlights include the release of my book Secrets of the Greatest Snow on Earth, serving as a Fulbright Scholar at the University of Innsbruck, and being elected as a Councilor for the American Meteorological Society. 

None of these things were a glint in my eye when the decade started and give me optimism that good things are coming in the 2020s.

The 2020s

So, here are a few predictions for the next decade:

  • While there will still be ups-and-downs in the weather from day-to-day, month-to-month, and year-to-year, there will be no return to the climate of the 20th century.  Baring a major volcanic eruption, nuclear war, or a major reduction in solar output, the 2020s will be as warm or warmer than the 2010s and we will see changes in the cryosphere, oceans and other aspects of the Earth system consistent with that warming.  
  • More energy will come from "clean" energy sources, but these will largely fill the growth in total energy consumption and global carbon emissions will remain steady or decrease little despite some countries and states (e.g., California) shifting dramatically away from fossil fuels and greatly decreasing carbon emissions.  Sorry to be a pessimist, but this is a wicked problem. 
  • Nevertheless, the end of the world does not come.  Skiing continues in the Wasatch, although the caustic influence of global warming becomes more apparent.  
  • Tolls and highway improvements come to the Cottonwoods, but gridlock continues.  
  • The price of a day pass at Deer Valley during the Christmas week increases $209 in 2019 to $509 in 2029.  That sounds crazy, but did you ever imagine a $209 lift ticket?  
  • Advances in computer infrastructure and machine learning, combined with the rise and demands of weather-sensitive (and weather-observing) autonomous vehicles including drones for transportation and commerce, completely revolutionize meteorology.  The market for automated forecast systems grows dramatically and a private company develops the world's best global, regional, and local forecast system, topping even ECMWF.  
Happy New Year and best wishes for the 2020s,


Saturday, December 28, 2019

Major Is Relative

Yesterday I forecast that there would be no "major" storms in northern Utah the rest of the year, but some might be wondering what that means after the mess today in the central Wasatch. 

For that post, I was thinking of major accumulations.  Impacts, however, can be significant even with light snowfall amounts.

For example, snowfall this afternoon apparently made quite a mess in the Cottonwoods, with UDOT hoisting the "Traction Law" flag and the National Weather Service noting that things look "pretty dicey" not only in Little Cottonwood but also Parley's Canyon. 

The snowfall was produced by shallow cumulus clouds that were parked over the mountain ridges much of the day (e.g., see below).  I suspect a little surface heating from the sun, meager as it was, led to upslope flow and cumulus cloud initiation.  The precipitation-generating clouds were so localized and shallow that it was pretty much impossible to differentiate them from ground clutter in the radar imagery during the period. 

Source: NCAR/RAL
I haven't seen any snowfall reports from the lower canyons, but Alta-Collins reported only an inch in the late afternoon, although this is a situation where accumulations may have been greater at lower elevations.   Feel free to share your observations, but for goodness sakes, keep it clean. 

I haven't bothered going up into the Tri-Canyon area since in several days as part of my annual holiday-week exile.  It's not like the skiing elsewhere isn't good. 

With the low angle sun and decent snowpack, much is skiable right now.  Further, the nordic tracks are also skiing well.  We are indeed blessed this holiday season!

Friday, December 27, 2019

No Major Storms in Northern Utah for the Rest of the Year...

Given that it's December 27, I don't think I'm sticking my neck out too far to say that there won't be any major storms in northern Utah until sometime next year. 

The pattern is one of "deja vu all over again."  The loop below begins at 1200 UTC (6 AM MST) 25 December and extends through 0600 UTC 1 January (11 PM MST 31 December).  The pattern is one featuring upper-level troughs digging along the Pacific coast and then moving inland across the southwest. 

Since graphics from the European model are now publicly available, below is the forecast of total accumulated precipitation through 0600 UTC 1 January (11 PM MST 31 December).  Utah is a state divided, with the southeastern half of the state seeing some precipitation, mainly with the trough moving through today and tonight.  Northern Utah is not completely dry, but precipitation is limited and generally near or less than 0.1 inches of water equivalent. 

Source: Pivotal Weather
Thus, nothing major for us, but we shouldn't complain.  While a major refresher is unlikely for the rest of the year, ski conditions are quite good. 

Tuesday, December 24, 2019

Prospects for a White Christmas

Although the Eve of Christmas Eve brought some light rain showers to the Salt Lake Valley, snowfall at Alta yesterday, overnight, and this morning has added up to a surprisingly healthy 9 inches.  If you aren't used to interpreting the "Snow Interval" column below, it's an automated measurement of snow depth on a wooden board that gets wiped from time to time.  You can see below how 2 inches accumulated through 16:00 yesterday afternoon (time increases upward), then the board was wiped, another 4" fell through 4 AM when the board was wiped again, and then another 3 inches fell through 8:00 this morning. 

Source: MesoWest
What will happen tonight as Santa delivers his gifts and tomorrow when Johnny and Jane want to play with their new sleds?  I'm not going to lie to you.  I don't have a good idea and I'm glad I don't have to tell Santa that.  The pattern is messy with a bunch of disorganized areas of precipitation in southwesterly flow initially and a weak front moving through overnight.  There's not much that one can "count on" in a pattern like this, so much is going to depend on luck. 

Downscaled NAM accumulations from 5 PM MST (0000 UTC) this afternoon through 5 PM Christmas Day amount to zilch right on the valley floor, and 4-8 inches in the upper elevations of the central Wasatch. 

A look at the SREF plume for Alta shows this morning's snow, a break today, and then some additional snow tonight and/or tomorrow depending on the member.  Deducting this morning's snow, the average total through 5 PM Christmas Day (26/00Z) is about 6-7 inches.  The range for all but two very excited ensemble members is about 1-9 inches.  

At the Salt Lake City Airport, all but three members generate less than in inch. 

While it won't take a Christmas miracle for there to be an inch or more of new snow on the valley floor by Christmas afternoon, the odds are low.  The east bench odds are a bit better, but still most members are under an inch at the University of Utah.  

However, the forecasts above are based on science and with a little Christmas magic, perhaps the low probability outcomes will verify.  Really, that wouldn't be magic.  Statistics says it could be so.

Monday, December 23, 2019

Relief for Some but Not Others

Strong southerly winds have scoured out the valley cold pools and pollution across much of northern Utah, but not all of it.

The southerlies picked up in earnest on Friday night and Saturday.  At noon on Saturday, peering into the Salt Lake Valley from above White Pine Canyon, one could see significant clearing in portions of the Salt Lake Valley, but thick smog remained over the lowlands further north. 

That portion of the cold pool over the Great Salt Lake and West Desert has been incredibly stingy,  like a bad cold unwilling to go away.  Even by Sunday afternoon, despite a tempest blowing at upper elevations, the cold pool remained.  Check out the observations below from 3 PM MST (2200 UTC) Sunday.  50s across the Salt Lake Valley, but 33˚F on Hat Island, 33˚F along I-80 in the West Desert, and 34˚F in Wendover!

Source: MesoWest
And I would be remiss if I didn't mention Logan where yesterday's high was 25˚F!  Sadly, the pollution there continues to be awful and is flirting with unhealthy levels. 

Source: DAQ
I thought that might be the worst air quality in the country, but they are currently just behind Seeley Lake, MT, which has PM2.5 concentrations this morning of 63.3 ug/m3 and was as high as 70.8 ug/m3 yesterday.  All of this is a reminder that air pollution is not just an urban problem. 

Saturday, December 21, 2019

Large Gondola in the Cottonwoods?

An article by Brian Maffly in today's Salt Lake Tribune discusses what a large gondola in Little Cottonwood Canyon might look like.   

While in Austia last year, I rode on what I suspect would be a template for such a lift, the Eisgratbahn at Stubai Glacier.  The Eisgratbahn is a tri-cable gondola hauling 48-passenger cars 1200 vertical meters (3.8 km) with a total capacity of about 3000 people per hour.  You can read about it in this BlogTirol article

The Eisgratbahn was built at a cost of 68 million Euro (about 75 million USD), supposedly making it the most expensive ski lift ever built (see this FallLine Skiing article).  For comparison, the Peak-to-Peak gondola at Whistler, discussed in the Salt Lake Tribune, was "only" 51 million Canadian Dollars. 

The Eisgratbahn is largely a people mover.  Most of the Stubai Glacier ski area is at altitudes above the base parking lot, pictured below.  One tends to take the Eisgratbahn up, ski the many lifts on the upper mountain, and then return to the base via the Eisgratbahn.  One can ski to the bottom, but early and late season that's not possible and the routes to the base are often closed or simply not recommended due to avalanche hazard. 

On the other hand, it is a much shorter (3.8 km) lift compared to what would need to be built up Little Cottonwood.  Additionally, there is ample parking at the base. 

The trib article states that the cost of such a gondola up Little Cottonwood Canyon would be north of $300 million dollars. Additionally, parking and transport to the gondola would need to be addressed.  Who knows if any of this will ever happen.  Further, I'm not even sure what to root for.  I sometimes wonder if the best option is to do nothing, as crazy as that sounds. 

Friday, December 20, 2019

Limitations of Purple Air Observations

British statistician George Box once wrote "all models are wrong, some are useful."  When it comes to observations, I like to paraphrase that to "all observations are bad, some are useful."  This statement reflects the fact that all observations contain errors and uncertainty, but they can still be useful.

PurpleAir uses low-cost laser particle counters to estimate PM2.5 concentrations.  The sensors can be purchased and operated by anyone, with data available at  Many groups and individuals have installed PurpleAir sensors across the Salt Lake Valley, northern Utah, and other parts of the nation (and even world).  In the Salt Lake Valley, there is a remarkably high density of stations.  Below is a PurpleAir map of PM2.5 concentrations from 7:09 AM MST this morning.  With such a high density of stations, one can see some of the spatial variability in pollution, including the relatively low values of PM2.5 on the east bench compared to the central and northwest valley.

It should be noted, however, that while useful for examining the spatial patterns of pollution, PurpleAir sensors can have low absolute accuracy.  What this means is that while one can see that the east side has relatively clean air compared to the central and northwest valley in the map above, the actual values for PM2.5 concentrations may be off.  Kelly et al. (2017) examined the performance of PurpleAir sensors compared to research grade instruments and while they found good correlation, they also found that it overestimated particulate matter concentrations during cold air pools.  In other words, during what many Utahns refer to as inversions.  More recently, Tryner et al. (2020) also found PurpleAir sensors overestimated PM2.5  concentrations in the field. 

Data from PurpleAir sensors is now being used on local news broadcasts and by the National Weather Service.  However, the limitations of these observations needs to be recognized.  Last night, the National Weather Service tweeted that air quality was in the red across much of the Wasatch Front, Tooele Valley, and Cache Valley.  In their tweet, they included maps with PurpleAir observations. 

However, data from Utah Division of Air Quality sensors, as well as sensors operated by the University of Utah, showed PM2.5 concentrations to be much lower.  At Hawthorne Elementary, hourly PM2.5 concentrations peaked at 37 ug/m3, on the low end of unhealthy for sensitive groups.
Source: DAQ
Elsewhere last night, DAQ sensors in Davis County peaked at 30 ug/m3, Tooele County at 39 ug/m3 (although there was a spike to 54 at 11 AM), and Weber County at 23 ug/m3.  These observations are consistent with air quality in the moderate or unhealthy for sensitive groups depending on location.  In Cache County, PM2.5 concentrations were highest, but still DAQ sensors peaked at 47 ug/m3, still in the unhealthy for sensitive groups category. 
Thus, DAQ sensors did not indicate PM2.5 concentrations were as high as indicated by PurpleAir and the tweet issued by the National Weather Service that air quality was in the red was not consistent with DAQ observations.  

Finally, we could examine observations collected by the University of Utah on Trax Trains and at various sites in the valley.  Below is a map for the period from 6:29-7:29 AM this morning.  Again, values are lower than indicated by the PurpleAir sensors (compare with the first graphic in this post). 

I think that the PurpleAir network is wonderful in the sense that it helps us to identify the spatial patterns of pollution, but it is important that their tendency to overestimate PM2.5 concentrations be recognized by those communicating with the public.

Thursday, December 19, 2019

Pre-Holiday Warmth

After a great run of snowfall, we're in the midst of a break in the action this week.  This has led to the formation of a strong inversion over the Salt Lake Valley.  Yesterday afternoons sounding shows the inversion base at about 850 mb, or about 650 feet above the airport.  Above this level, temperatures increased about 5˚C. 

Source: SPC
Not surprisingly, air quality is deteriorating and is currently in the middle of the "moderate" category. 
Source: Utah DAQ
Above the gunk, wonderful conditions can be found in the mountains.  Yesterday's high at the base of Alta reached 32.5˚F.  Mountain temperatures will climb further today and tomorrow and the inversion will strengthen, or, if you prefer, tighten its noose.  By 5 PM Friday, free-atmosphere temperatures at 700 mb (about 10,000 ft) are expected to reach 0˚C. 

However, with a trough approaching from the west, southwesterly flow is expected to increase Friday night and Saturday.  The NAM forecast for 5 PM Sunday afternoon is calling for 700-mb (10,000 ft) winds of about 50 knots over the Salt Lake Valley. 

Thus, while the inversion will hold through Friday, it will very likely be gone by Sunday afternoon.  Prior to that, on Saturday, it's tough to say.  Right now I'd lean toward a top-down scouring of the cold pool with the benches possibly breaking out for part of the day Saturday, but a shallow cold pool could remain at lower elevations.  Time will tell. 

Where the inversion does mix out, temperatures will be mild for December.  I suspect we could see highs in the 50s at some bench locations Saturday and on the valley floor on Sunday. 

Monday, December 16, 2019

Last Gasp Lake Effect

Lake-effect has brought snow to the western Salt Lake Valley and Tooele Valley and created some traffic mayhem along I-80.  I saw a report earlier this morning of a 2 hour commute from Tooele to Salt Lake.

Radar imagery overnight shows the "pulsing" nature of the lake effect, which occasionally became banded.  There is a brief period of double banding as well.  Although the central Wasatch was outside the main lake-effect area, they got just enough from the edges and orographic snow showers to give Alta Collins 4 inches of what was probably pixie dust. 

Below is a 1400 UTC (7 AM MST) satellite image fro GOES-17.  I've cherry picked this to highlight a time when a clear lake-effect band was apparent.  There is evidence of the cloud band extending well into Utah county at this time. 

Radar imagery at the time shows lake-effect snowshowers extending from the Great Salt Lake and into the Oquirrh Mountains.  A narrow band extends further downstream to Utah Lake.  It's quite remarkable that the radar picks up on that part of the band at all.  Radar overshooting becomes more problematic with distance from the radar, which is on Promontory Point, due to the curvature of the earth, slight angle of the radar to the horizon, and bending of the radar signal by the atmosphere.

I'm calling this a last gasp as it brings an end to this storm cycle and otherwise things look dry through Wednesday.  There is a splitting storm moving through the region Wednesday night, but right now it doesn't look like much from a mountain snow perspective.

Sunday, December 15, 2019

Bus and Ski Report

Skiing conditions are excellent in the Wasatch right now, especially for mid December.  I've probably said that a few times in the past week or two, but one shouldn't take these things for granted.

Today we elected to take the bus.  Kudos to everyone packed liked sardines for an hours drive up the canyon.  It's great that UTA increased service this year, but we need even more during peak periods.  Further, trips like this are a reminder why more people don't voluntarily opt for the bus.  Sadly, real solutions, if they exist, are still years or decades away. 

Thankfully, ski conditions were excellent.  No photos from our descents, so the skin track is the best I can do. 

Source: Erik Steenburgh
I got a pit in my stomach around 1:30 PM or so when we noticed a heli hanging over the Park City ridgeline.  Sadly, a skier was killed in an avalanche in Dutch Draw.   I thank the patrollers and responders for their efforts.  With persistent deep instability, this is a season that will demand patience.  Remember that sidecountry and slackcountry are still backcountry.  We have a long season ahead and the skiing is really outstanding right now even on low-angle terrain. 

Friday, December 13, 2019

Let's Do It Again!

It's a solid start to the ski season in the Wasatch Range.  The Snowbird SNOTEL is at 11.8 inches of water equivalent, above the 10 inch threshold for the start of what I'll call solidly good early season conditions.  That's also 146% of median and 131% of average.  Ski touring conditions today were quite good for mid December, although avy conditions kept us confined to lower angle slopes.

The forecast for tonight and tomorrow suggests we have another major storm coming in.  The  SHREF forecast below shows a mean of nearly an inch of water and 15 inches of snow through 0000 UTC 15 December (5 PM Saturday). 

That's the good news.  The bad news is this looks like a setup for messy travel up the canyons.  Hopefully people have upgraded their tires, UTA has better trained their drivers, and desires for carpooling are higher. 

Stay safe and enjoy.  I'll be working to make up for my ski time today.

Wednesday, December 11, 2019

Decent Dumpage Coming

An active weather period is coming over the next few days as several systems rumble through and eventually tap into moisture from a landfalling atmospheric river.

The NAM time-height section shows copious low-level moisture from later today all the way through the end of the forecast period at 0000 UTC Sunday (5 PM MST Saturday).  During the period, several deeper systems rumble through, some associated with mid-level or surface fronts and associated troughs.  Timing these systems is difficult and so it's best to say that we're going to be seeing periods of mountain snow that will add up to a considerable total by the end of the NAM forecast period on Saturday afternoon. 

The GFS integrated water vapor transport forecast for 1800 UTC (11 am) Thursday shows a broad atmospheric river making landfall along the Pacific coast and penetrating inland across the northern Great Basin.  We never get into full-blown atmospheric river conditions, but this is still a nice corridor of moisture transport into the region. 

The image below shows our downscaled snowfall estimates from the NAM for the period.  For the upper elevations of the Wasatch, amounts exceed 24 inches, with the northern Wasatch, which does well in patterns like this, over 36 inches.  The NAM downscaled snowfall for Alta is 31 inches.

The SREF ensembles show precipitation beginning in earnest at Alta late tomorrow.  Most members through 0000 UTC 15 Dec (5 PM Saturday) produce 1.2-2.2 inches of water and 18-34 inches of snow.  There is one member that is much lower and two that go for more. 

Numbers for the period are fairly similar at Snowbasin, but I suspect they will do better tomorrow (Thursday) and tomorrow evening when the pattern should favor environs to the north. 

The bottom line is that a decent dumpage is coming.  When each "wave" will come through is difficult to say, but totals should be significant through Saturday.  I haven't bothered looking beyond that.  A bird in hand is worth two in the bush. 

Saturday, December 7, 2019

A Partial Cold Pool Mix Out

Air quality has improved over the Salt Lake Valley the past two days, but is still in the moderate category in some areas.

Yesterday and overnight, the valley cold pool mixed out from the top down and from south to north.  This left a shallow lens of cold air over the northern Salt Lake Valley that was filled with fog and low clouds this morning.  A look at the photo below, taken looking south from the upper Aves just before sunrise, shows fog or valley stratus over the central Salt Lake Valley, but clear skies near and over the east bench around the University of Utah. 

Observations at 7 AM show relatively mild air in the upper avenues (39˚F) and at the University of Utah (35˚F) compared to sites along I-15 from the I-215 junciont northward where temperatures were 28–30˚F.  Thus, the fog evident above was coincident with a shallow cold pool over the lower portion of the northern Salt Lake Valley.  Clear air near the University of Utah was also favored by downslope northeast flow. 

Source: MesoWest
By around 2 PM, the fog dissipated, but the cold pool remained, along with a thin lens of pollution.  Note that this pollution spread eastward into areas that were clearer this morning. 

Observations within the hour ending at 2:38 PM showed a remarkable contrast in temperatures in the Salt Lake Valley.  To the south, near Bluffdale and Draper, it was in the 50s.  In the northwest Salt Lake Valley and Downtown, it was in the low-to-mid 30s.  Near the University of Utah, it was 49˚F, but the low level flow was westerly, so pollution was moving in. 

Source: MesoWest
The Trax-mounted PM2.5 sensors from the University of Utah show very nicely the pollution associated with the shallow lens of cold air over the northern Salt Lake Valley.  PM2.5 concentrations are < 2 ug/m3 near Herriman, but increase northward, reaching into the mid 20s near downtown Salt Lake City, solidly in the moderate category. 

So, the good news is that the air quality is much better, especially in the southern Salt Lake Valley and along some bench areas.  The bad news is that there is still a shallow lens of cold air and pollution floating around with elevated PM2.5 levels.  Forecasts suggest that we'll probably mix out the rest of the cold pool tonight or tomorrow as temperatures cool aloft.

Thursday, December 5, 2019

Poor Forecasts, Wintery Mix, Ongoing Misery

There's a lot to talk about this morning, so I'll go into rapid fire mode.

1. Poor Forecasts

The new GFS model really handled last night's and today's event quite poorly. The 72 hour forecast valid at 1200 UTC (0500 MST) this morning called for precipitation to be confined to southern Utah, reaching no farther north than Provo. 

Instead, the 1201 UTC radar imagery shows precipitation all the way into southern Idaho. 

Although we can't share the Euro forecasts here, they definitely did better on location. 

On the plus side, Alta-Collins has picked up 4 inches of snow, so maybe we shouldn't complain.

2. Wintery Mix

Freezing rain doesn't happen a lot around here, but there was a period of it last night at the airport where light to moderate freezing rain was reported from 10:04 PM to 12:25 AM when the precipitation changed to rain.  Freezing rain is rain that freezes upon contact with the ground or solid objects.  It can occur when the airmass aloft is above 0˚C, which results in the melting of precipitation falling form aloft, but there is a shallow layer near the ground below 0˚C or the ground is frozen. 

This morning's sounding shows a deep layer from the surface to 780 mb (7000 ft) in which temperatures are at or just above freezing.  Snow falling from aloft in such a layer will begin to melt, transitioning to wet snow, slush, or rain.  Given that temperatures in the layer are barely above freezing, there can be a lot of variability spatially or with time in the precipitation type at the surface depending on the precipitation intensity and the size and type of snowflakes falling from aloft. 

Overnight at the airport, precipitation fell as rain, but ground temperatures were apparently low enough for that precipitation to freeze on contact.

3. Ongoing Misery

Although we've had some rain and the strength of the inversion has weakened some, PM2.5 levels remain in the "unhealthy for sensitive groups" category.  The DAQ sensor at Hawthorne Elementary peaked yesterday at 64 ug/m3.  At 7 AM this morning we've dropped to 41, which is still high.   

Source: DAQ
Fog and low clouds are now blanketing much of the Salt Lake Valley.  Yeah, it's depressing.  Sadly, we're probably stuck with this through at least tomorrow, then we'll see what the new storm system does over the weekend.