Windy Storm on Tap

Batten down the hatches because we have storm that might have everything but the kitchen sink in it for the Wasatch Range.

Right now Thursday looks dry, but the leading edge of the storm looks to move in on Friday with some mountain snow, mainly in the northern Wasatch, but probably tickling the central Wasatch some too.

Then Friday night things really start to get rolling.  The GFS forecast valid 0300 UTC 6 Dec (8 PM MST Friday) call for very strong flow (red ovals) to move over a low-amplitude ridge that is centered west of SoCal.  This leads to the inland penetration of an atmospheric river, as indicated by the filament of high integrated water vapor transport (IVT) that extends from southern Oregon to northern Utah (red arrow).  

This general pattern persists until Sunday morning, although flow, IVT, and precipitation intensity weaken late Saturday (if forecasts hold).  

The Utah Snow Ensemble forecast below focuses on the 24-hour period ending 0000 UTC 7 December (5 PM MST Saturday).  That is probably the wettest part of the the storm.  The ensemble mean for that period is 1.0" at Snowbasin and 1.2" at Alta-Collins (upper right panel).  

The Alta-Collins plumes show a bit of precip on Friday, but things really picking up Friday night.  and persisting until Sunday morning or later in a few members.  

The GEFS ensemble is more bullish on precipitation than the European (ENS).  As I said in the previous post, it's important to be rooting for America and that continues to be the case in this forecast.  

The median water and snow forecast by the ensemble from 5 AM Friday to 5 AM Sunday is 1.5" and 16.2" respectively.  Perhaps a reasonable estimate for snowfall totals during that period is 10-20", although the distribution above skews to higher values so the odds of more is probably greater than the odds of less.  A lot will depend on details that are hard to reliably anticipate this far ahead.

I suspect we will also see wind and rime.  New lifties for riming-prone lifts may have a real initiation Saturday morning.  Good luck. 

I'll see if I have time for a closer look on Friday. 

Limping into December

November is in the books and except for the last day we can be glad it is in the rearview mirror.  The last day did bring a bit of snow to the Salt Lake Valley, resulting in a beautiful start to the morning today. 

Avenues Twin Peaks from University of Utah Campus 1 Dec 2025

That said, it was a bad month for skiing due to warmth and lack of snow.  At the Salt Lake City International Airport, this November was the warmest on record.  

Records in the mountains are spottier.  At Alta, the Average temperature was 37.5°F, which is the 2nd highest on record, but observations there are much spottier and I don't put much faith in that number.  The warmest November on record there (1949) has 9 missing days.  It's safe to say it was warm, but definitive statements are not possible with the historical record at mountain sites due to limited data. 

So we limp into December.  The next storm system comes on Tuesday night.  It's another system dropping in from the northwest with some similarities to Sunday's storm in that it will likely produce snow or a rain/snow mix on the valley floor with accumulations of a trace to 2" in the valley and perhaps a bit more on the benches.  Worth watching forecasts in case this changes.  

For Alta-Collins, there's pretty big spread in the models with some giving less than 2" and the biggest outliers being in the RRFS ensemble where there are two members in the 8-9" range.  

Think 3-6" and hope for more. 

After that, the forecasts range from sad to optimistic.  The Utah Snow Ensemble shows that most members of the European ensemble (ENS, yellow-orange liens below) are calling for a bit more snow later in the week and into the weekend.  The mean of the ENS is perhaps another inch of water and 10" of snow, although there are a few of ENS members going for game-changing amounts in excess of 30".

The US ensemble (GEFS) has more members who are putting out much bigger amounts over a multiday period, yielding a mean snowfall of 40" over the next 10 days.  The difference between most ENS members and most GEFS members is the storm track with the ENS members tending to be a bit stronger on the western ridge, resulting in a drier forecast (although we still get some snow), whereas the GEFS members bring more action into northern Utah.  

Bottom line is that you should be rooting for America. 

All Elevation Snow Possible Sunday

Thanksgiving weekend looks to conclude with a storm that will likely produce some snowflakes at all elevations in northern Utah. It's not a big storm, but being the first that might bring winter driving conditions to some areas so far this season, at the end of Thanksgiving weekend, it's worth monitoring if  you will be traveling.  

The storm will be produced by an upper-level trough and cold front that will drop into Utah on Sunday from the northwest.  Below is the GFS forecast valid 1800 UTC 30 November (11 AM Sunday) showing the trough extending across northern Utah and Nevada.  

Below is the HRRR forecast sounding for the Salt Lake City International Airport valid 1800 UTC 30 November (11 AM Sunday).  It shows saturated conditions down to the valley floor with temperatures just above 0°C.  

The HRRR keeps surface temps just a smidge above freezing as the front moves through.  If that were to verify, the most likely outcome would be snow for the benches and wet-snow for the lowest elevations near the Great Salt Lake during the passage of the system.  If it were a bit warmer, then perhaps it would be a rain/snow mix at those lowest elevations.

 Below is our HRRR-derived snowfall guidance which suggests 1.6" at the airport, 2.6" at Cottonwood Heights, and 8.4" at Alta-Collins.  This product does not, however, consider on-the-ground melt, which could be an issue on the valley floor and might limit actual accumulations there.  A lot will depend on the snowfall rate during the passage of the system. 

We can also have a look at the 6-member RRFS ensemble.  It appears to be a smidge warmer than the HRRR as most members are producing 0.2" of water or more at the airport, but snowfall is scant with one member getting up to a bit under an inch.    

For Alta-Collins, five of the six members are coming in between about 3.5 and 8", but there is one very optimistic member going for close to 18.  There is always hope. 

So to summarize, a trough and frontal passage will be bringing precipitation to northern Utah on Sunday.  Snow is expected and bench and mountain locations.  At the lowest elevations, temperatures are such that we could see wet snow or a rain/snow mix.  It's worth monitoring the weather and road conditions if you need to travel on Sunday.  

Thanksgiving Weekend Cold Front

There's still not much to get excited about in the forecasts.  The main weather feature of interest over the next several days is a cold front that is currently forecast to be moving through Utah Friday night.  

Below is the GFS forecast valid 0600 UTC 25 November as an example of one model forecast showing some precipitation over northern Utah as the cold air is pushing in.  

Right now, this looks like a "quick hitter" variety of storm.  The GFS is putting out 0.57" of water and 8" of snow for Alta-Collins through 5 AM MST Saturday.  The Utah Snow Ensemble members are less enthusiastic with a median of 0.09" of water and 1" of snow through that same time, although some members are slower with the system and give us some more into Sunday.  Still it's not a lot.  The snowiest member is putting down 20",. but that's not a likely scenario and perhaps we wore out our luck with the U's improbable win over K-State on Saturday.  If we could get a few inches at Mountain Dell, maybe the Nordies would be in luck.  That's possible but not probable.  

Snowmaking conditions will, however, improve.  There will be guns blazing.  

Ghosts of Thanksgiving Past

Thanksgiving weekend 2001.  

We traveled to with the kids to Seattle to enjoy the annual feast with family.  

When we departed, most likely on November 21, there was no skiing.  A look at the Alta-Collins data on MesoWest suggests a 10" natural snow depth.  My recollection was that there was no snow, but perhaps their was a little.  

When we returned, there was skiing.  Plenty of skiing.  

At around 0000 MST 22 November 2001, the start of Thanksgiving Day, it started snowing.  Eventually, 108 inches fell at Alta-Collins, including one hundred inches in one hundred hours.  The press called it the hundred inch storm.  Pretty catchy.  It led to one of the funner papers I've written during my career. 

The hundred inch storm was really produced by two storms or should I say two frontal systems.  Snow at Alta came ahead of each front, with each front, and behind each front, with both post-frontal periods producing incredible lake bands.  

Example radar imagees from the two lake-effect bands that contributed to the Hundred Inch Storm. Source: Steenburgh (2003).

One of my former graduate students, Kristen Yeager, went back several years later and found that the second of the two lake-effect periods was the largest on record from 1998, when KMTX radar archives began, to 2009 when she ended her study.  It produced an unbelievable 3.15 inches of water at the Snowbird SNOTEL.  We really haven't seen anything like it since, so it most likely was the biggest lake-effect storm since 1998 and possibly since the installation of the radar in 1994 (radar data from the first few years of KMTX operations were not archived).  

The snow depth time series from Alta-Collins for the period shows it becan with a scant 10" or snow on the ground (sometimes the calibration of the depth sensor is off so it's possible it was less than this).  The first storm raged through early on the 23rd when the snow depth reached 50".  Then there was a break.  Then the second storm pushed the total depth to 80".  Roughly a 70" increase in four days. 

Source: Mesowest

That number is less than the 100" total because the total snow depth is subject to compaction whereas new snow totals are based on interval samples on a snow board.  

The Salt Lake Tribune ran the photo below of a what appears to be an Alta Ski Patroller getting the goods following the storm.  

Source: Steve Griffin, Salt Lake Tribune

My notes indicate the east bench got 30-33" and the Salt Lake City airport 15".  I do remember having to dig the car out from the airport parking lot when we returned.  

Things can change fast.

A Pretty Splitty Pattern

The mild first-half of November is now in the books.  The Salt Lake City International Airport came in with the warmest on record with an average temperature of 53.0°F.

Source: https://xmacis.rcc-acis.org/

Last night's storm dropped about 4" on Alta Collins.  Not much to get excited about.  I haven't looked carefully, but the big winner appearred to be Ben Lomond Peak which got about 2.3" of water and had a total snow depth of 10" at 5 AM this morning.  

The pattern continues to look splitty for the next few days.  Just an an example, below is the GFS 500-mb height (contours) and wind speed (color fill) forecast valid 2100 UTC 20 Nov (2 PM MST Thursday).  The Pacific Jet is forecast to be well consolidated near 150 W but split upstream of the North American coast into two branches, one moving through western Canada and the other over northern Mexico.  

The various ensemble forecasts either keep us dry or give us some light amounts as systems in the southern branch of the jet brush by.  The Utah Snow Ensemble forecasts for Alta-Collins from last night show a bit with last nights storm through about 25 November, most members give us scant precip. 

A few push the southern track storms far enough north to give us some decent water and snowfall totals, but there are only a few of these.  At least 75% of the members give us less than 10" of snow and less than an inch of water.  

Paraphrasing Thomas Paine, these are the times that try ones soul.  The summer lover and sunshine worshiper will, in this crisis, shrink from the mountain climates; but one that stands by it now, deserves the love and thanks of powder when it returns.  

Overexuberant Starting Dates and Splitting Storms

Delays in starting dates for ski areas are in the news.  Brianhead was scheduled to open on November 7 and has pushed their starting date back to November 21.  Solitude was scheduled to open on on Friday (Nov 14), but has pushed it's starting date back to next Wednesday (see this Trib article).  

In my view, this is much ado about nothing.  November is a fickle month.  Sometimes resorts can open, even as early as late October with natural snow as Brighton did in October 2004.  Sometimes we get a cold spell that enables sufficient snowmaking to get some terrain open with limited natural snow.  And sometimes we get a nothing burger.  We're getting the latter this year.  If you get a warm, dry stretch in February, you get a suntan while doing groomer laps.  When one happens in November, you get a delay to the start of the ski season.  

It is true that temperatures so far this November have been warm, with an an average for November 1-12 of 51.7°F at the Salt Lake City airport.  That is the 2nd warmest on record, but sometimes a ranking hides subtleties.  If we look at records since 1929 when observations were first collected at the airport, there have been 8 other Novembers with average temperatures at or above 50°F.  So, this year is warm, but to some degree it is cooked into the cake of weather variability.  Warm dry stretches in November can happen.  

The plot above also shows a great deal of variability as one might expect for a relatively short 12-day period in the late fall.  The coldest November 1-12 was in 2000 when the mean temperature was 32.6°F.  Holy cold surge Batman!  

The linear trend line is consistent with a warming trend as we might expect.  We will see more warm spells in the future and the resorts will find it more and more difficult to open early season terrain with current snowmaking capabilities. Opening a resort in Utah in early November has always been a crap shoot, but the odds will be decling in the future without advances in snowmaking capabilities.  

Looking to the future, the pattern over the next several days is dominated by splitting storms.  Split is a four letter word around here (yes my math is bad), but the reality is that many of our storms split.  The analysis below shows the average 300-mb (jet-stream level) winds during winter in the Northern Hemisphere.  On average, the Pacific jet is strongest in the western North Pacific.  The western United States is at the end of the Pacific jet in what metorologists call the "jet exit region".  On average, the jet level flow over the western. United States is actually relatively weak and this is consistent with the jet-level flow decelerating and splitting.  This is essentially a consequence of the distribution of continents and oceans in the Northern Hemisphere, the distribution of sea-surface temperatures in the North and Tropical Pacific, and the topography of western North America, among other factors.

So, many of our storms split.  The Wasatch Range gets a lot of snow because northern Utah still manages to get some snow from splitting systems, the split sometimes weakens and storms are able to penetrate directly into Utah, and the topography around here, especially around Little Cottonwood Canyon is just damn good at squeezing every dendrite out of winter storms.  

A textbook case of splitting storms is on tap for the next several days.  The GFS analysis for late yesterday morning [1800 UTC 12 November (11 AM MST Wednesday)] shows a full-latitude trough off the west coast (upper left panel) with and accompanying cyclone centered off the coast of Oregon and California (upper right panel).  

Instead of progressing to Utah, the upper-level trough amplifies through 1200 UTC 14 November (5 AM MST Friday), resulting in split flow with one branch of the jet moving across southwest Canada and the other taking a circuitous route around the upper level trough and into southern California (upper left panel).  As a result, the precipitation system moves into western North America in two pieces, one over central and southern California, the other near the Canadian Border (upper right).  

But the GFS forecast calls for things to get worse, at least temporarily for Utah. By 1200 UTC 15 November (5 AM MST Saturday), the southern storm has continued to dig southward.  SoCal is getting the goods, but we're left high and dry.  

Whether or not all is lost with this storm depends a lot on what it does as it drifts downstream and moves across the interior west.  By 0600 UTC 16 November (11 PM MST Saturday), remnants of the system are moving into Utah.  

Forecasts out to 10 days show a lot of splitting storms.  Our snowfall future depends strongly on the track of these storms and their remnants.  Sometimes we can really get a lot of snow from upper-level patterns that meteorologists from other regions think are fairly innocuous.  However, such details are hard to predict and this is why the Utah Snow Ensemble is a junk show for Alta (and northern Utah locations) with enormous spread in total water equivalent and snowfall over the next 10 days.  And that spread is not because there are one or two extremely high or extremely low outliers.  That's actually a fairly even distribution of members producing a total accumulated snow total through 0000 UTC 23 November between 15 and 50 inches.  

So, a lot of uncertainty, but we might frame that a little differently.  75% of the members produce 1.93" of water and 16" of snow through that time and 50% produce 2.5" of water and 32" of snow, the latter on the cusp of rock-ski skiability (I know some of you go out with less).  

So one way to think about this is there's a 50/50 chance we'll have marginal early season skiing next weekend.  I'll let you decide if you want to be a pessimist or optimist about which side we will land on. 

And if you are wondering, yes, this is one of those blog posts that I start and when I get to the end I realize I bit off far more than I can chew!

Remembering Wendy Wagner

The Department of Atmospheric Sciences and many others at the University of Utah are deeply saddened to learn of the passing of Wendy Wagner after a battle with ovarian cancer. Wendy had a lasting impact on our program and anyone who had the good fortune to know her at the U.

Wendy was a two time Olympian in cross country skiing.  She walked into my office after returning home from the 2006 Olympic Games in Torino, Italy with an intense desire to "get off the hamster wheel" and do something new in mountain meteorology and snow science.  Talk about energy!  During this period, Dave Hanscom who had known Wendy for years through The Utah Nordic Alliance (TUNA) and Utah racing scene, sent me a note saying that she would do great things for our program. 

He was right.

While in our graduate program, Wendy worked with Prof. John Horel to develop techniques to measure snow along cross-country ski racing courses.  She then used a physics-based snowpack model to simulate temperatures along the course.  Work focused on the Whistler Olympic Park in preparation for the Vancouver 2010 Winter Olympics and was ultimately published in the journal Cold Regions Science and Technology.  

Wendy with a skier-transported snow-skin temperature measuring device

During her time at the U, Wendy was an enthusiastic backcountry skiing and mountain biking partner of many, including a cadre of students and faculty in our mountain meteorology group.  The skin track was a common place for us to share thoughts about mountain weather, snow science, and deep powder.  As one of our students wrote shortly after Wendy's passing:

"The first years I was in Utah were such formative elements of my life, and Wendy was part of that... a part of the excitement about what life had to hold intellectually, personally, and, or course, on snow. I recall a tour in those "early days" with you and Wendy, and maybe Tyler, up into Neffs... it set a tone for the years to come."

I recall many great powder days with Wendy and others in the department, but in one of the few photos I have of her there's no powder to be seen.  Instead, Wendy is charging up Deseret Peak to ski wind board in the Twin Couloirs.  In many respects, this captures Wendy's enthusiasm, excitement, and indefatigability perfectly.  Long tour, lousy snow, what are we waiting for?  

Wendy on Deseret Peak

While a graduate student, Wendy also coached the Utah Ski Team and developed a deep understanding of snow science and avalanches.  At that time, if you polled the backcountry community in the Wasatch Range about the best people to ski with, Wendy would have surely been at the top of the list.  She went on to a career at the Chugach Avalanche Center where she eventually became director.  She continued to give back to our program by meeting with our students to talk about her career and profession.  Some additional perspectives on Wendy's life are available from her Salt Lake Tribune obituary and Nordic Insights.  In lieu of flowers, consider donating to the Friends of the Chugach Avalanche Information Center, https://www.cnfaic.org/friends/donate/.

We in the Department of Atmospheric Sciences express our deepest sympathies to Wendy's family and many many friends.  

Thirty Years at the U

This month marks my 30th anniversary as a professor at the University of Utah.  We left Seattle in early November, stopping in Snoqualmie Pass to say goodbye to the maritime climate of the Pacific Northwest and wondering what life would be like in the western interior.  I started work, officially, on November 15, 1995.  What a wonderful ride it has been.  I thought I would share a few career highlights.  

Nagano Olympic Winter Games 1998

In 1998, the Salt Lake Olympic Organizing Committee sent me to the Winter Olympics to learn about weather support for the games.  I spent four days in the Hakuba Valley and Nagano learning about weather impacts on sports and Olympic logistics.  

With Dave Hanscom at the Snow Harp Cross Country Venue

Given that I was there for only four days, I slept little and learned and explored as much as I could. I met with Japanese Meteorological Agency meteorologists at the venues and main operations center (I was provided with a translator).  I learned a great deal about how weather affects ski jumping, cross-country and Alpine skiing, spectator safety, etc.  I even got in a couple of hours of sampling "JaPow" when the Super-G I was supposed to attend was cancelled.  Instead of watching the race, I rented some ski gear and got free refills on the upper lifts of Happo-One ski resort.  There was just me, a couple of security guards (on the lift in front of me in the photo below), and a couple of other people lapping the deep.  

Storm skiing at Happo-One during the 1998 Winter Olympics

When I needed to return the the base, I couldn't figure out how to get down. I ended up skiing pow down the downhill course.  Herman Maier never had turns so good.  

Alpine World Championships 2001

In 2001, the Olympic Committee sent me (along with two other meteorologists) to the Alpine World Championships in St. Anton, Austria.  I actually tried to beg out of the trip because I did not think I would learn much after my trip to Nagano.  They insisted I go.  I decided to look into St. Anton.  I remember going to some web site and reading that it was one of the best expert ski areas in the Alps and had a hedonistic night life.  I said sign me up.

I did do some work on that trip, including a visit to MeteoSuisse, and I did give a talk at the University of Innsbruck which sparked my desire to return to Austria, but what sticks out most in my mind is Daron Rahlves' victory in the Super-G.  

One of the other meteorologists (who shall remain unnamed to protect the innocent) and I opted the morning of the SuperG to ski in Lech rather than go to the race.  Lech though was mired in fog.  Conditions were terrible.  We only took a couple of runs, but on one lift ride, we were joined by an Austrian ski instructor.  He asked us who the big American skier was.  We said "Daron Rahlves."  He responded, "never heard of him."

The skiing was so bad that we returned to St. Anton to watch the race.  Austrian greats Stephan Eberharter and Herman Maier were in first and second place as Rahlves skied down the course.  It was a great run and he crossed the finish line .08 seconds in front.  The crowd went silent while the two of us were screaming "never heard of him." 

Salt Lake City Olympic Winter Games 2002

The experiences above and a whole lot of work over a multi year period led to a successful weather support and forecasting effort for the 2002 Games that involved a partnership between public, private, and academic groups to collect observations, develop forecast systems, and provide weather forecasts.  Although stressful, it was an honor and a privilege to participate and work with so many great people. I'll be retired for 2034, but encourage those following me to get involved if they can.  

Holding an Olympic torch with my daughter Maria before the start of the Games

Department Chair 2005–2011

From 2005–2011 I was chair of the Department, which transitioned from Meteorology to Atmospheric Sciences during my "reign."  I'm grateful to have served in that capacity before the insanity happening to higher ed today.  Being Department Chair is a difficult job as you sit at the pinch point between faculty and administration.  I think it is a job that is much harder today.  

While I was chair, my wife Andrea was diagnosed with breast cancer.  Others on the faculty stepped right up to take workload off of my plate while we were going through the most difficult aspects of the diagnosis and treatment.  Having such great colleagues is something for which I will forever be grateful. Andrea is happy and healthy today.

While Department Chair I was in my late 30s and early 40s and probably at peak fitness.  I did a good deal of ski touring with students.  Sometimes this was by design.  Sometimes we met serendipitously on the skin track.  On one of the more memorable tours during this period, my touring partners and I ran into three Atmos students at the top of the Hogum 200.  We decided to join forces and ultimately did a tour de force that led us to Upper Hogum and eventually Thunder Bowl.   

Hogum Fork

Ultimately they descended Bells Canyon while my old fart friends and I decided to keep skiing and ascended to take another run down the west side of Thunder Mountain and eventually down Coalpit #4.  

Descending Coalpit #4

It ended up being about a 10 hour day and a good example of how graduate students can take you to places you can't go by yourself.

Wasatch Weather Weenies 2010–present 

In late September 2010 I started Wasatch Weather Weenies as an invite-only blog.  Prior to this, I had been sending out occasional e-mails to friends and colleagues about evolving weather and forecast problems.   I found e-mail to be too restrictive and thought a blog format would be better.  Eventually I started getting to many requests for access and I just opened it up to everyone.  

If you are wondering, I've now down 3,830 posts and the blog has had 6.7 million page views.  That number is inflated by spambots and the like, but still it's much more popular than I could have ever dreamed, especially since I sometimes write some techy posts. 

OWLeS 2013-14

Circa 2010 a group of colleagues from other Universities contacted me about the proposed Ontario Winter Lake-effect Systems (OWLeS) field campaign.  They were wondering if I might want to look into the processes that cause intense snowfall on the Tug Hill Plateau.  Of course my answer was YES!

The field campaign took place in December 2013 and December 2014.  We operated profiling radars at four locations on and west of the plateau, launched weather balloons, etc.  We had great support from the local community and even were able to rent a house with a heated garage from which we could do balloon launches.  This was a huge coup as it gets really cold in upstate NY.  Additionally the family groomed 5K of cross country trails, so we essentially had our own ski resort! I got to reconnect with my love of cross-country skiing, which I did a lot as a kid (including in this area of Upstate NY) but had abandoned during my early adulthood.  

During OWLeS We got over 100" of lake-effect snow in December and collected incredible data that led to many publications that I think transformed our understanding of snowfall processes over the Tug and downstream of bodies of water in general.

Secrets of the Greatest Snow on Earth 2014

In Fall 2014 the first edition of Secrets of the Greatest Snow on Earth.  It was a labor of love that was an outgrowth of my experience writing for this blog.  

Japan 2017

After OWLeS I got really interested in what happens in Japan.  Tug Hill is a remarkable place for snow, but it rises only 500 m above lake level.  Western Japan has big topography downstream of the Sea of Japan, which is 12 times bigger than Lake Superior, the largest Great Lake.  Not surprisingly nearly all of the work done on sea effect in Japan was done by Japanese scientists.  I began to read the publications that were in english and stare at the graphics in those that were in Japanese (online translators were still non-existent at that time).  

It struck me as I did this that Japanese and American scientists had been working on similar problems but with little collaboration.  I thought we could do better.  One of my students received a fellowship to work at the University of Hokkaido for a few months and then I decided to write a proposal to the National Science Foundation to forge stronger collaborations.  It was funded and in 2017 one of my graduate students and I went to Japan to visit the Nagaoka Snow and Ice Center.  As I am wont to do, we skied for a few days in the Hakuba Valley before the meeting, including a couple of days of bluebird ski touring.  I started calling him the luckiest graduate student on the face of the Earth. 

Me on the right with the "luckiest graduate student on the face of the Earth" 

The collaboration with the Nagaoka Snow and Ice Center proved to be quite fruitful, leading to a number of papers exploring the mechanisms affecting the inland penetration and orographic enhancement of sea-effect snowfall.  Sento Nakai and I also penned an article for the Bulletin of the American Meteorological Society to better introduce North American scientists to the climate of Japan's Gosetsu Chitai (heavy snow region).

University of Innsbruck 2019

In 2019 I served as a Fulbright Scholar at the University of Innsbruck.  What a dream that was being able to teach and research in a beautiful place with great mountain culture.  I skied a lot of bad or tracked out snow even when touring, but didn't care.

Atmos 1000: Secrets of the Greatest Snow on Earth 2021-present

During the pandemic, I was looking for something to do and came up with the totally insane idea to develop a completely asynchronous online class about snow, weather, and climate change for skiers.  I worked on it for several months and eventually offered it in Spring 2021.  It proved to be very popular and I ended up updating my book with expanded material to make it a better "textbook" for the class.  In spring 2025 enrollment was more than 500 students, but would have been higher with more TA support. 

An unfortunate aspect of the online format is I rarely meet the students who are taking the class.  It's always great when someone on campus or in town comes up to me and says the took it.  It's even better if they say they enjoyed it!

Special Thanks

Looking back, it is the many undergraduate and graduate students that I have had the privilege to work with who have made this job so much fun.  I avoided naming names in the post above simply because I don't want to single anyone out.  I just want all of my former students to know how much I have appreciated having them as students and in many cases friends.  I also thank all of the faculty and staff I have worked with at the U and other institutions, especially those in the Department of Atmospheric Sciences.  

And thanks to you for reading this blog.  It has been inspirational to write and in many cases has led to new ideas for research or teaching.  

See you on the lift or skin track.

Dust on Dirt

A few days ago we discussed how the GFS was an outlier of the many forecasts for the storm that will come through northern Utah tonight (see Some Thoughts on Using Long-Range Forecasts).  Specifically, it was producing a good deal more precipitation than most members of the Utah Snow Ensemble, which is derived from the US Global Ensemble Forecast System (GEFS) and ECMWF Ensemble (ENS).  

Sadly, the latest forecasts continue to produce light precipitation and just a frosting of snow for Alta-Collins.  As an example, the six members of the Rapid Refresh Forecast System (RRFS) ensemble produce 0.25" of water equivalent or less and 3" of snow or less for Alta-Collins.  

The latest HRRR and GFS are also below those thresholds.  The 0600 UTC GFS is down to 0.08" of water and about an inch of snow.  Dust on dirt if it verifies, although the snow might be somewhat wet and not cold smoke.  

Sometimes an outlier forecast like the one from the GFS verifies.  Low probability doesn't mean no probability.  It can be helpful to recognize there is the possibility of something happening and many of the products we have on weather.utah.edu are designed to illustrate the potential of outlier events such as high precipitation intensity periods.  But knowing the odds puts that potential into context.  

One question I was asked about that post about using long-range forecasts is shouldn't we weight the ensemble members?  For example, lean toward the ENS control and the ENS ensemble over the GEFS since the ECMWF model is "better." Being an academic, whenever I'm asked a question, I think of the goblin Griphook in Harry Potter and the Deathly Hallows: Part 2.  

The skill of any forecast model decreases with increasing lead time (model skill might increase in the first few hours of a model forecast due to spin up, but we'll ignore that here).  Eventually, even the best model in the world has no skill relative to climatology, meaning you're just as good forecasting with the long-term mean or probabilities as using the forecast model.  

As a result, the performance of a better modeling system over another modeling system is maximized at shorter lead times and decreases with time.  I have illustrated this conceptually below.  

How quickly model system skill degrades is dependent on the variable being forecast.  One can skillfully predict temperature or geopotential height farther into the future than precipitation.  In addition, forecast skill in northern Utah is lower than in many other regions of the US, so the rate of decline in forecast skill is higher here. 

The last comparison of GFS and ECMWF model forecasts for precipitation at mountain sites in the western United States that I am aware was done by my group (see Caron and Steenburgh 2020).  For the modeling systems available at that time, the 12-36 hour precipitation forecast produced for SNOTEL sites by the ECMWF was clearly superior to the GFS.  However, by 60-84 hour lead time, the gap was much smaller and not statistically significant (based on a 95% confidence interval).  So for the GFS and ECMWF available at that time, at about day 3, the overall skill of their precipitation forecasts at mountain sites in the western US became somewhat similar.  

So, how much you should weight one modeling system over another when looking at an ensemble likely decreases with time.  It might make sense to weight the ENS over the GEFS at short ranges, but it's unclear is such weighting makes sense at longer time ranges, at least for precipitation in the mountains of the western US.  Rather than basing the Utah Snow Ensemble entirely on the ENS, we included the GEFS because studies have show that doing so results in better probabilities.

The discussion above is informed by experience, but ultimately the only way to know is to do the math.  Once again, I leave this for you to do.    

Not So Bad for No Skiing

After July, November is probably my least favorite months due to its "tweener" status between seasons.  However, if we can't have snow, the start to this November is a pretty good one with spectacular fall weather.  One of the nice things about northern Utah is that you can find fall colors somewhere from late September to early November.  The mountain aspens may now be leaf free, but the valley and foothills still have some great color.  

The bucks have also returned to lower elevations.  I had a brief conversation with this trophy on Sunday.  I gave him a wide berth.  

Some Thoughts on Using Long-Range Forecasts

Snow is currently short of scant in the Wasatch with 6" being reported by the Collins automated sensor and spotty coverage on high-north aspects.

Alta Ski Area cam image from 8:40 AM MDT 31 Oct 2025. Source: Alta Ski Area.

While there's no skiing, it does look like a splendid Halloween and weekend for late fall, so enjoy.  

Given that we are playing the waiting game for snow, I thought I would share a few thoughts on using long-range forecast guidance.  

The National Weather Service Global Forecast System (GFS) produces forecasts at ~13 km grid spacing out to 16 days.  The European Center for Medium Range Weather Forecasting similarly produces a "control" forecast at ~9 km grid spacing out to 15 days with their Integrated Forecast System.  For simplicity I will call this the ECMWF control, although you may know it as the Euro, EC, ECMWF, or HRES.  Plots from these modeling systems are readily available on weather.utah.edu and other sites.  However, when you are looking many days out, there is little point in relying on forecasts from the GFS or ECMWF "control" when a large ensemble is available.  Here's why.

In the case of models run by the ECMWF, the ECMWF control is simply the so-called "unperturbed control member" of their 51 member ECMWF medium-range Ensemble Prediction System or ENS.  This means that the initial conditions for the ECMWF control represent the "best guess" as to what the atmosphere looks like when the model run is started.  The other 50 members are run with the exact same model, but with perturbed initial conditions.  Differences in the forecasts arise from these slightly different initial conditions, as well as the perturbations that are added to the model physics to account for uncertainties in how we simulate physical processes such the generation of clouds and precipitation.  The latter is referred to as "stochastic" (or random) physics.  We don't know for example exactly what the characteristics of cloud droplets are in a cloud, so we use stochastic physics to try and account for the range of possibilities.  Together, the differing initial conditions and stochastic physics lead to differing forecasts, with the spread growing with time.  

It turns out that the ECMWF control slightly outperforms the other members of the ENS at short lead times.  However, at longer lead times, the advantage becomes small and in a statistical sense it has very little advantage over the other ensemble members.  So, when you are looking 5+ days into the future, there's little point in relying on the ECMWF control.  Each member of the ENS is equally likely, just as when you roll a die, any of the six faces is equally likely to end up on top.  The ENS die just has a lot more faces.  

The National Weather Service Global Ensemble Modeling System or GEFS has 31 members.  The GFS is NOT a GEFS member.  The GFS and GEFS use the same modeling system, but the GFS is run at higher resolution (~13 km) than the GEFS members (~25 km), including the GEFS control run. Despite this resolution advantage, the gap between the GFS and the individual GEFS members closes with lead time. 

The Utah Snow Ensemble attempts to squeeze as much as we can from the 51 ENS members and 31 GEFS members through the use of downscaling and other techniques.  We are trying to take advantage of all of those runs to provide information as to the likelihood of precipitation and snowfall amounts at high resolution.  Rather than relying on the GFS or ECMWF control, I think of all members of the ensemble as equally likely.  Additionally, over many events, the GEFS or ENS mean is going to outperform the individual forecasts from the GFS or ECMWF control.  There's strength in numbers.  

Let's use last night's forecast as an example.  The GFS is bringing in a pretty healthy system for next Thursday.  Below is the forecast valid 1500 UTC (0800 MDT) Thursday 6 November.  

If we pull out the forecast for Alta-Collins, the GFS puts out about 1.3" of water through 1200 UTC (0500 MDT) Friday 7 November.  Bank on it?  
  

Well if we look at the Utah Snow Ensemble, a different picture emerges.  The GFS is actually an outlier compared to all of the forecasts produced by the GEFS and ENS (note that the Utah Snow Ensemble goes to 10 days instead of 7 like the GFS forecast above).  Through 1200 UTC 7 November, only 4 out of 31 GEFS forecasts produce > 1" of water equivalent.  The wettest ENS member is around 0.6".  

The GFS could verify, but it's a lower probability outcome than inferred from the full GEFS and ENS ensembles.  

We provide tables for Alta-Collins precipitation and snowfall at https://weather.utah.edu/text/ensgefsdslccforecast.html.  It takes a bit of time to get used to these, but I'll focus solely on the total water equivalent precipitation table below (right click and open in another window to enlarge).  I've highlighted in red the total accumulated precipitation through 6 AM MDT Friday 7 November (we have a bug for dealing with daylight time so that's going to be 5 AM local time).  The rows include the minimum from the ensemble on the top and maximum on the bottom.  P10 indicates the so called tenth percentile.  10% of the forecasts are at or below this value.  P50 is the fiftieth percentile or median.  Half of the forecasts are below this value and half are above.  In this case P50 is 0.17", so half the ensemble members are at or below 0.17".  Much lower than the GFS.

The GFS's 1.3" sits somewhere between the P75 value and the P90 value.  Those are the seventyfifth and ninetieth percentiles.  Let's guesstimate it to be at about P85, which means 85% of the ensemble members are below the GFS amount and 15% are above.  

So, the GFS could verify, but a look at all of the forecasts suggests that's a lower probability outcome.  The full Utah Ensemble suggests the "over under" through Friday morning is not the GFS's 1.3" but more like 0.16" (the P50 value).

The discussion above assumes the Utah Snow Ensemble is unbiased.   In other words, on average, it produces about the same amount of precipitation at Colins as is observed and that it's probabilities, evaluated over many events, reflect real world probabilities (i.e, when the Utah Snow Ensemble says there's a 10% chance of 1" or more of precipitation it actually happens 10% of the time).  I don't actually know if this is the case.  The GEFS and ENS underpredict precipitation at most mountain sites.  Our downscaling helps with this, but undoubtably biases remain, vary by site, and in some cases could be high rather than low biases.  I haven't had time to look into this, so I'm going to leave this for your, the student, to investigate.