Challenges Forecasting the Snow Level

The snow level is a critical variable for mountain weather forecasting, but it is both difficult to define and predict.  

In fact, there isn't even an agreed upon definition of snow level amongst meteorologists or the public.  One might say it is the level above which precipitation is snow and below which precipitation is rain, but its just not that simple.  Precipitation doesn't just change from snow to rain at a given altitude.  Snow takes time to melt as it falls.  Different types of snow crystals melt faster than others.  Sometimes it is snowing but not accumulating on the ground due to melt.  What do you do when there is a mixture of snow and rain or drizzle?  Where do you put the snow level? 

To begin, perhaps it is easier to begin with a description of the transition zone, the layer in which snow is warming, melting, and turning to rain as it falls.  

The schematic below provides a simple conceptual model of the transition zone.  The freezing level marks the top of the transition zone and is the highest level at which the temperature is 0°C.  Temperatures above this level are below 0°C.  

The transition zone (h/t Ron Stewart)

The freezing level and the snow level are not the same because snow does not melt instantly when it falls below the freezing level.  Instead, it begins a transition as it falls, gradually changing from dry snow to wet snow to slush (part ice part water) and finally rain.  The distance over which this occurs depends on many factors including the profiles of temperature and relative humidity below the freezing level, type and size of the snow crystals, and fall speed of the snow crystals. 

For example, if the relative humidity is low, a given snow crystal can penetrate farther below the freezing level since the crystal will warm more slowly because it is also cooled by sublimation.  A dense graupel particle can generally penetrate farther below the freezing level because they have a high fall speed and take longer to warm and melt fully compared to a small dendrite.  

In addition, because the melting of snow cools the atmosphere to the melting point (0C), there is often an isothermal 0C layer in the transition zone, as depicted above.  This layer can be quite deep, especially if precipitation rates are high.  Because of this effect, the snow level may lower some when the precipitation rate increases and rise some when the precipitation rate decreases. 

In the above schematic, I have denoted the level at which the precipitation is half snow and half slush as the snow level, but that may not conform to what you think is the snow level.  Perhaps it should be lower and at the level where precipitation is all rain or all rain or slush.  Alternatively, perhaps it should be higher and at the level where precipitation is all snow?  

Or, perhaps instead of focusing on the type of precipitation falling, we focus instead on the level at which snow is accumulating on the ground.  That's sometimes called the snow line.  But if we do that, what exactly is the ground?  Grassy surfaces?  Asphalt surfaces?  

There are many ambiguities.

As discussed in Van Cleave et al. 2011, about 15 years ago the National Weather Service Western Region actually established a definition of snow level for their applications:

"The snow level is the elevation above which snow will fall, and below which rain will fall. A mix of rain and snow may be observed at elevations within a few hundred feet of the snow level. Snow will not accumulate on the ground below the snow level and may not even accumulate at elevations above the snow level."

Even that definition is somewhat ambiguous, but they also defined techniques for calculating and forecasting the snow level and identified the wet bulb 0.5°C level as the best proxy for snow level in the western region. That said, there can be variations in precipitation type and accumulations on the ground around this level.  

One situation that can be particularly challenging involves stable layers in which wet-bulb temperatures are very near 0°C through a deep layer.  An example is provided by last night's GFS forecast for 1000 UTC 01 January 2026 (3 AM MST New Year's Day).  At that time, a precipitating cloud layer has spread over northern Utah in southwesterly flow aloft, but stable conditions remain at low levels as the cold air currently in place over the Salt Lake Valley is slow to mix out.  The freezing level in this case is located just above 750 mb, or near about 2500 m MSL (~8200 ft MSL).  Because the atmosphere is saturated at that level, the freezing level in this case also represents the wet-bulb zero level. However, below that level, the layer is very close to 0°C down to almost 800 mb.  This might enable snow to penetrate farther below the freezing level than if temperatures were increasing with decreasing altitude below the freezing level.  

Layers in which temperatures are relatively constant with height are called isothermal, which means having a constant temperature. Having a deep isothermal layer near 0°C is one way for the snow level to penetrate to low elevations.  One needs to keep a close eye on these layers as they can make a big difference for snow level forecasts.    

The Birth of "Snow Augmentation" at Sun Valley

While researching the 1976/77 drought year, I came across the article below in the Salt Lake Tribune describing the benefits of "Snow Augmentation" at Sun Valley (click to enlarge).  

Published in late December 1976 when Utah resorts were not operating due to a lack of snow, it describes initial use of artificial snowmaking at Sun Valley.  Today, Sun Valley probably has one of the best snowmaking systems in the world.  At that time, during the great snow drought of 1976/77, it enabled three runs to be open for the holidays.  As described in the article,

"Ribbons of artificial snow from two to three feet deep have been shot by air compressor-activated snow guns up to two-thirds of the way up the mountain."  

It goes on describe the artificial snow as "cube like crystals" with "a bit more density than nature's snow."  I'm sure that sounds familiar to today's skiers.  The system sounded pretty cutting edge for the time, pulling 1400 gallons a minute and putting down two acre-feet of snow in eight hours.  

I suspect in 1976 there were no Utah ski resorts with snowmaking.  It would be interesting to look into the history of snowmaking investment and expansion at our resorts.  Online articles suggest Deer Valley had a snowmaking system when it opened in 1981.  Prior to the 2002 Olympics, Snowbasin expanded and installed what was probably at the time the state's most expansive and sophisticated snowmaking system.  My recollection is that Alta was not yet making snow when I moved here in 1995, but perhaps my memory is inaccurate.  AI tells a lot of good stories, but they can be authoritative BS so I'm reluctant to use it here.  

That said, as we have learned this season, most contemporary snowmaking systems today are still at the mercy of Mother Nature.   If wet-bulb temperatures are too high, snowmaking efforts are hopeless.  This has been a major issue in Utah so far this season (although guns will be roaring in the during and in the wake of this latest cold surge).  All-weather snowmaking systems are available, but are expensive to buy and operate and not used to cover large areas of terrain.  

Let's hope we see a colder, snowier pattern emerge for 2026.  

Is This The Worst Christmas Skiing Ever in Utah?

I never like to bad mouth Utah skiing but I think it is accurate to say that this is a truly abysmal start to the ski season right up there with many of the worst seasonal starts on record.  

But is it the worst?  

Currently on this Christmas Day there is little to no natural snow at low-to-mid elevations.  For example, the base of Park City is as bad as it gets right now from a natural snow perspective, although there is a white ribbon of death thanks to artificial snowmaking.   

Source: https://www.parkcitymountain.com/the-mountain/mountain-conditions/mountain-cams.aspx. Screenshot from 1:20 PM MST 25 Dec 2025.

Where we have data, there are now several SNOTELs in the Wasatch Range that are at their record low snowpack water equivalent for the date.  These SNOTELs are Ben Lomond Trail, Farmington Lower, Farmington, Hardscrabble, Parley's Summit, and Payson Ranger Station.  At Ben Lomond Peak (records back to the 1978/79 winter), the 4.5" of SWE is just ahead of the record low of 3.7".  At Snowbird (records back to the 1989/90 water year) the 6.0" of SWE is just ahead of the record low of 4.6".

So, at some sites we have the worst natural snowpack during the SNOTEL period of record for Christmas.  Others are close. 

But "during the SNOTEL period of record" is an important caveat.  The oldest SNOTEL stations in the Wasatch Range began operations during the 1978/79 winter.  Others have even shorter records.  They fail to provide a comparison with what is the worst Christmas and ski season start on record:

1976/77

How bad was the start of the 1976/77 ski season?  During November and December of 1976, Alta-Guard observed only 31" of snow and 2.04" of water equivalent precipitation.  How low is that?  Really low.  For comparison, Alta ski area has recorded 44.5" of snow and 6.75" of water so far this November and December (they will get more through this weekend) and the Atwater SNOTEL which is located where those Alta Guard snow and precipitation measurements would have been taken in 1976 has 6.9" of water equivalent in the snowpack.  Thus, precipitation in 1976/77 and far less than we have had this November and December.  

There was also no snowmaking in 1976/77.  Snowmaking has been limited this year due to warmth (more on this below), but it still has saved our bacon and allowed resorts to operate with limited terrain.  In 1976/77 the ski areas didn't have it and weren't even open for skiing during the Christmas Holidays.  Back in 1976 there were these things called "newspapers."  They printed the latest news on paper and were delivered to your door.  It was a predecessor to modern social media.  On December 24, 1976, the Salt Lake Tribune contained an article entitled "Resorts Featuring Snowless Events."  Park City was promoting golf and tennis, gondola rides to view the new Jupiter Bowl Ski Runs, and dryland training classes.  Snowbird had "summer rates," tram rides, and music.  Perhaps it was a predecessor to Octoberfest.

What made 1976 so bad?  The short answer is a big ridge.  Average 500-mb heights for November 1 to December 23, 1976 show a high amplitude ridge along the Pacific coast that acted to reduce storminess, yielding few storms.   Basically, it was a very dry pattern.  

In contrast, the mean pattern for the same period this year is far less amplified and although we are below average for precipitation in November and December, we have had some storms.  

The complicating factor this year, however, has been the warmth.  The high fraction of precipitation falling as rain instead of snow and frequent snow-loss events have prevented the buildup of a low-to-mid elevation snowpack.  

How warm has it been?  To use a scientific term, it has been bat-sh*t-crazy warm.  Below is a time series of mean Nov 1 to Dec 24 temperatures in Salt Lake City since 1875.  Do you see that data point on the far right?  The one that sticks up way above everything else?  That's this year.  

The mean temperature for 1 Nov to 24 Dec at the airport was 47F.  This is 4.1F warmer than the next warmest (42.9F in 1995).  That's like running a 3 minute mile.  Simply unbelievable.  

Unfortunately, we don't have complete records for temperatures at mountain sites.  There's data at Alta back to the 1940s, but there are a lot of missing days.  For what it's worth, the average temperature at Alta for the same November 1 to December 24 period was 35F this year (with complete data coverage).  That's the highest on record, but in other years, there's missing data, so this comparison is limited.  For what it's worth, the average temperature for the same period in 1976, when records were also complete, was 30.1F.

So to summarize, the worst Christmas skiing was in 1976/77.  There was practically no natural snow, even at upper elevations, due to persistent ridging and a lack of storms.  Precipitation was far less than we have seen so far this season and there was no snowmaking infrastructure to save the day.  

But this season is also different animal.  We have seen unusually high temperatures that are really unprecedented and exceptional in the Salt Lake Valley.  More analysis of the mountain observations is needed, but even at upper elevations this appears to have been a remarkably warm period.  This has led to a high fraction of precipitation falling as rain instead of snow at low-to-mid elevations and frequent snow ablation events.  We have even seen a substantial rain event at elevations up to about 9600 feet.  As a result, there's either no or very little snowpack below 8000 feet and a thin snowpack at higher elevations.  Although we now have snowmaking infrastructure, it has frequently sat dormant due to high temperatures.   

Skiing during the 1976/77 holiday period was bad due to a dry snow drought, but it's bad this season due to a dry-warm compound snow drought.  In a dry-warm compound snow drought, warmth exacerbates the impacts of below average precipitation, making a bad situation worse.  I suspect there is no historical analog to the start of this season in northern Utah.  We simply haven't ever seen temperatures in November and December this warm (and this sustained).  A good research question concerns whether or not this reflects an ongoing transition into a future in which dry-warm compound snow droughts become more common, especially during the early season.  This season is not a new normal, but it might reflect a new extreme that became more likely due to warming of the climate system.  

That said, it will be cold this weekend.  You may need to recalibrate.  

Enjoy Your Lump of Coal

Source: Cowboy State Daily

Merry Christmas to all from the Wasatch Weather Weenies.  

Apparently most of you have been naughty not nice because Santa delivered quite the lump of coal for Christmas.  Warmth and high snow levels materialized as anticipated last night.  It was a real soaker even at 9600 feet where Alta-Collins picked up only an inch of snow from 1.01" of water indicating a good deal of rainfall during the period.  

My memory is hazy this morning but I can't recall a mid-winter rain event of that magnitude at that elevation this time of year.  I do recall storms that started with a bit of rain or produced some with mist and rime due to a lack of ice nucleating particles in clouds, but a full inch of water with little snow at 9600 feet in December or January I suspect is pretty unusual.  That said, I'm working off memory here and leave it to you to dig into the data to see what you find.  

Meanwhile, it's 8:00 AM and 55°F at the Salt Lake City International Airport.  Skip the sleigh ride today and take the mountain bike out instead.  

A Rainy Night for Santa

A warm storm is on tap for the Night Before Christmas, one that will not make Santa or his reindeer happy.   

To illustrate this, let's take a look at the forecast from the High Resolution Rapid Refresh (HRRR) for Little Cottonwood Canyon (click to enlarge).  The HRRR calls for periods of precipitation overnight (green box below) adding up to 1.5" of snow water equivalent at Alta-Collins through 7 AM Christmas morning.  

That's the good news.  The bad news is that the overnight period is remarkably warm, with the wet-bulb-zero level, the altitude where the wet-bulb temperature reaches 0ºC and roughly the top of the melting layer, reaching as high as 10,700 feet (the snow line is usually several hundred feet below the wet bulb-zero level).  Our algorithms suggest this period, highlighted with green shading above, may produce rain even at the 9600 foot altitude of Alta-Collins.  

Snow during other periods at Alta-Collins adds up to 8.4" by 7 AM, although we don't account for losses due to rain, so that might be optimistic.  That 8.4" will probably be wet and dense.  Even by 7 am tomorrow, the HRRR has the wet-bulb-zero level at 9300 feet, which suggests that the precipitation will probably be all rain below 8000 feet overnight.  

The HRRR is a relatively wet model.  Others, such as the RRFS ensemble below, are calling for less precipitation.  Through 7 AM tomorrow (14z 25 Feb), the RRFS members produce 0.45 to 1.2" of water.  Some of those members also produce rain to near the Alta-Collins level during the warmest part of the storm.  Snowfall is in the 3-8" range by 7 am, with amounts varying depending on water equivalent, snow level, and snow-to-liquid ratio.  

So, Santa will likely be delivering presents in the rain below 8000 feet.  He might also encounter rain or a rain-snow mix up to 9500 feet or even a bit higher depending on his delivery schedule.  Christmas skiers probably won't find The Greatest Snow on Earth under the tree tomorrow morning, but perhaps 4-8" of wet, dense snow at 9500 feet. Expect a strong gradient in snowfall amount with altitude between about 8500 and 10000 feet and the most snow above 10000 feet.  

This is one forecast that I hope is totally wrong or out to lunch.  There is a wide range of forecast water equivalent being produced by the models, so maybe we can get lucky and we can have the storm come in colder than anticipated and produce a lot of water, with more substantial accumulations over 8000 ft.  It is Christmas after all.  

There will be a cooling trend over the next few days with some snowshowers on the 25th and 26th and a snowstorm Friday night and Saturday.  

Welcome to Mordor

Wind and warmth continue to dominate the weather here in Mordor, with the fires of Mt. Doom casting their glow over the Wasatch this morning.  

The average temperature since November 1 at the Salt Lake City International Airport of 46.3°F is a remarkable 2.4°F higher than any prior November 1 – December 21 period (note: the graph below includes data from the downtown weather bureau office prior to 1928).  

For the first 3 weeks of December (i.e., December 1–21) the mean temperature (43.3°F) is also the highest on record, although the gap to #2 (42.6°F in 1889) is not as large.  

Frodo and Samwise Gamgee continue to their quest to destroy the One Ring and break Sauron's evil grip on the weather of Utah, but remain well short of their goal.  

Hopes for the cover of precipitation increase around 0000 UTC 25 December (5 PM MST Christmas Eve) as southerly flow and an atmospheric river penetrate inland into Utah in advance of the very persistent upper-level trough that has been hanging off the west coast the past few days.  

The 82 members of the Utah Snow Ensemble have various ideas on the timing and intensity of the various bits and pieces of the storm, including the structure of the trough has it moves through Utah, but for the 3-day period from 0000 UTC 25 December to 0000 UTC 28 December (red-box below), 77 of the 82 members are producing 1–2.5" of water equivalent at Alta-Collins and 74 of the 82 members are producing 10–22" of snowfall.  

Most members are also calling for a cooling trend during that 3-day period, although it should be noted that at the start (i.e., 0000 UTC 25 December), median wet-bulb 0.5°C levels, which roughly denote the top of the melting layer, are at 10,000 feet.  This is a storm cycle that is going to start out very warm, perhaps with rain at the base of Park City on the evening of Christmas Eve.  By Christmas morning perhaps snow levels will be down to the base, but that's a touch-and-go forecast right now.  Monitor forecasts for this 3-day period if you are interested in details.  

Whether or not this modest storm cycle will enable Frodo and Samwise to reach Mt. Doom, destroy the ring, and loosen Sauron's grip on Utah weather remains unclear.  

What are the Prospects for a Christmas Miracle?

Based on last night's SNOTEL observations, Snowbird sits at 6" of water (record low for December 20th at that site is 4.4"), Brighton 3.9" (record low 3.2"), Mill D North 3.7" (record low 2.0"), Thaynes Canyon 4.4" (record low 2.9").  

So, technically in the central Wasatch, we're not at record low levels, but we're also not far above those records and remain below a reasonable natural snowpack for proper skiing.

But is there hope of a Christmas Miracle?  

Through Christmas Eve day we'll continue to see warmth and some periods of low-to-mid elevation rain and mid-to-high elevation snow at times.  There's no "big" storm, but perhaps we can get add another 0.75–1.5" of water to the high elevation snowpack in Little Cottonwood from the bits and pieces through 5 PM MST on Christmas Eve.   

But what about the night before Christmas and Christmas?  Is there hope for a Christmas Miracle?

Well the GFS has a menacing trough off the west coast and a boatload of moisture moving into the western US at 2100 UTC 24 Dec (2 PM Christmas Eve).  

It's a slow moving trough, however, and is still off the coast by 1800 UTC 25 Dec (11 AM Christmas Day), so no cold air for Utah.

So, prospects for a white Christmas in the Salt Lake Valleys and other lowland areas of Utah are looking pretty grim.  The Utah Snow Ensemble plume for the Salt Lake City International airport shows some periods of precipitation late Christmas Eve and on Christmas, but the snow plume is flatlined through Christmas.  

Upper elevations may do better.  It's a warm storm, but notice the uptick in both water equivalent and snowfall at Alta-Collins that begins around 0000 Z 25 December (5 PM Christmas Eve).  

For what it's worth, the median 24-h water equivalent and snowfall forecast by the Utah Snow Ensemble for 5 PM Christmas Eve to 5 PM on Christmas at Alta-Collins are 0.87" and 6.9", equating to 12.5% water content Cascade Concrete.  I've spoken to Santa and he tells me that if you are nice and not naughty he will deliver more, possibly in the form of graupel.  If, however, you are naughty, he will bring less and push the snow level 9000 feet.  

Update on weather.utah.edu

I know that weather.utah.edu has been down quite a bit in recent weeks.  The most recent outage last week was a scheduled one as our Center for High Performance Computing takes down our systems for 1-3 days a couple of times a year to do updates and upgrades.  Prior to that, we had a number of unscheduled outages due to excessive loads.  A few changes were recently made that will hopefully help with that, but we will have to see how it goes.  

weather.utah.edu is a labor of love and a way to share our experimental forecast products with the world.  We do the best we can.  Thank you for understanding.  

Save NCAR

I'm currently in Alaska and was planning on ignoring the blog for a few days, but I felt the need to address the news released yesterday that the National Center for Atmospheric Research (NCAR) would be dismantled.   

At this point we know little except that NCAR is under threat based on a social media post by the Office of Management and Budget director Russel Voight stating that the National Science Foundation will be breaking up NCAR, reviewing its activities and "vital activities such as weather research will be moved to another entity or location." 

Subsequently, the National Science Foundation (NSF) announced today the intent to restructure NCAR's activities including "options to transfer stewardship of the NCAR-Wyoming Supercomputer to an appropriate operator; divest of or transfer the two NSF aircraft that NCAR manages and operates; and redefine the scope of modeling and forecasting research and operations to concentrate on needs such as seasonal weather prediction, severe storms, and space weather."

In that announcement, the NSF stated that they remain "committed to providing world-class infrastructure for weather modeling, space weather research and forecasting, and other critical functions."  It's pretty clear that is not the case and that they are embarking on a process that will destroy NCAR.  

Since it's inception in 1960, NCAR has been the undisputed #1 center for atmospheric research in the world.  No other center comes close.  It has built the world's most widely used modeling system, the Weather Research and Forecasting model; operates some of the world's most sophisticated observing systems including the NCAR NCAR Gulfstream GV for high-altitude sampling and C-130; and employs many of the most brilliant scientists in the atmospheric sciences.  It also developed the Community Earth System Model (CESM) and the Model for Prediction Acros Scales (MPAS) model, which is likely to be come the backbone for weather modeling in the National Weather Service (and is currently being used by The Weather Company for their forecasting activities).  

Don't be fooled by suggestions that vital activities will be moved to other entities or locations.  Even if that happens, US capabilities in the atmospheric sciences are going to suffer severely.  NCAR has a critical mass of scientists to tackle some of my fields most challenging problems.  Breaking up NCAR is like breaking up the 1927 Yankees.  You can ship off Lou Gehrig, Babe Ruth, and the rest of Murderers' Row to other teams, but in the end you're left with mediocrity, not greatness.  Thankfully, the 1927 Yankees did not break up and they won the 1928 World Series in four games.  Let's hope that NCAR similarly is kept together. 

Building a Valley Cold Pool the Hard Way

If you want to build a persistent valley cold pool in northern Utah, often referred to colloquially as "an inversion," the best way to do it is to have a strong cold surge followed by the development of an upper-level ridge. The cold surge provides the cold air at low levels while the ridge then increases the temperatures aloft.  During the winter, there's insufficient heating from the sun to warm the cold air at low levels, so one ends up with a persistent valley cold pool that is topped by a stable layer or inversion that prevents the dispersion of air pollution. This process is even more effective if there is snow on the ground.  

The past two weeks, however, provided something a little different.  On December 6 we had an atmospheric river move through the area (indicated by green below...note that the meteograms for temperature and wind do not quite line up vertically).  This was followed by a period with occasional mid and high clouds, somewhat enhanced southerly flow, and rising temperatures.  At the Salt Lake City airport, the afternoon wind often switches to northerly or northwest, but those periods were pretty limited due to the enhanced southerlies.  The southerlies were not strong, but combined with a lack of snow cover and occasional clouds, they allowed us to remain relatively mixed and mild in the valley.  

Source: MesoWest

However, things changed after about December 11.  The flow weakened.  We also saw clearer skies.  The result was the slow development of a valley cold pool with temperatures falling each day.  On the 11th, the maximum temperature at the Salt Lake Airport was 62°F.  Yesterday it was 49°F.  

In contrast, if we look at the temperatures on Hidden Peak at the top of Snowbird (11,000 ft), they show a general warming trend for the period.  

Source: MesoWest

Essentially, we are building a persistent valley cold pool the hard way, without a prior cold-air surge. The ridge is building in, increasing temperatures aloft, but instead of having cold air at low levels to start, we were relatively mild.  Since December 11, however, with the flow weakening and less cloud cover, we are seeing temperatures declining with a valley cold pool slowly strengthening.  Yesterday afternoon we had a bonafide inversion with a surface temperature at the airport of 45°F and a temperature at 7200 feet of 50°F,

Source: SPC

And with the strengthening cold pool and inversion, we are starting to see the buildup of pollution in the valley, as evident from the photo I took yesterday at the top of Mt. Van Cott above the University of Utah campus showing smog in the Salt Lake Valley.

Really we're fortunate not to have had that prior cold surge or snow on the valley floor.  We're also fortunate to have a cold front coming in on Wednesday that will mix out the pollution.  

Note: We are moving into a more active pattern this week, but will be taking a break from blogging for a few days.  Good luck!

A Great Storm in Utah

A Great Storm in Utah is something we are all waiting for but is also an essay that John Muir wrote while visiting the Salt Lake Valley in 1877.  The essay was sent to me by a former student, Matt Jeglum, who knows how much I enjoy this sort of weather and nostalgia, and contained within Muir's book Wilderness Essays.

In the essay, Muir describes a storm on May 19, 1877.  The date is very close to the peak time of year for strong cold fronts in northern Utah and he was impressed.

"Utah has just been blessed with one of the grandest storms I have ever beheld this side of the Sierra.  The mountains are laden with frsh snow; wild streams are swelling and booming adown the cañons, and out in the valley of the Jordan a thousand rain-pools are gleaming in the sun." 

But before describing the storm, he provides some great observations of Utah snow and weather.  First, he suggests a late start to the snow season with snow piling up in the spring.

"In all the upper cañons of the mountains the snow is now from five to ten feet dep or more, and most of it has fallen since March." 

He also describes frequent afternoon thunderstorms, as we often see in the spring:

"Almost every day during the last three weeks small local storms have been falling on the Wahsatch and Oquirrh Mountains, while the Jordan Valley remained dry and sun-filled."

Then there's the storm, which sounds like it packed a wallop.  Read this passage out loud, pausing at each comma, for great effect.

"But on the afternoon of Thursday, the 17th ultimo, wind, rain, and snow filled the whole basin, driving wildly over valley and plain from range to range, bestowing their benefactions in most cordial and harmonious storm measures.  The oldest Saints say they have never witnessed a more violet storm of this kind since the first settlement of Zion, and while the gale from the northwest, with which the storm began, was rocking their adobe walls, uprooting trees and darkening the streets with billows of dust and sand, some of them seemeed inclined to guess that the terrible phenomenon was one of the signs of the times of which their preachers are so constantly reminding them, the beginning of the outpouring of the treasured wrath of the Lord upon the Gentiles for the killing of Joseph Smith."

Muir's essay describes blowing dust and sand (I suspect primarily the former).  In the passage below, I suspect he is describing pre-frontal virga (precipitation evaporating before it reaches the valley floor) and dust in the pre-frontal southerly flow.

"Clouds, with peculiarly restless and self-conscious gestures, were marshaling themselves along themountain-tops and sending out long, overlapping wings across the valley; and even where no cloud was visible, an obscuring film absorbed the sunlight." 

Muir loses me meteorologically for a bit in the passage below, but perhaps he is describing pre-frontal snow falling over the Wasatch and Oquirrhs while the Salt Lake Valley is still dry and perhaps hasn't mixed out yet to produce strong winds on the valley floor. 

"Some of the denser clouds came down, crowning and wreathing the highest peaks and dropping long gray fringes whose smooth linear structure showed that snow was beginning to fall.  Of these partial storms there were soon ten or twelve, arranged in two rows, while the main Jordan Valley between them lay as yet in profound calm." 

But then, the great front arrives, and it arrives at what is typically the optimal time for a strong spring cold-frontal passage with what I suspect is a dark shelf cloud and strong, dust-laden post-frontal winds.

"At 4:30 P.M. a dark brownish cloud appeared close down on the plain towards the lake, extending from the northern extremity of the Oquirrh Range in a northeasterly direction as far as the eye could reach. Its peculiar color and structure excited our attention without enabling us to decide certainly as to its character, but we were not left long in doubt, for in a few minutes it came sweeping over the valley in a wild uproar, a torrent of wind thick with sand and dust, advancing with a most majestic front, rolling and overcombing like a gigantic sea-wave."  

The essay continues to describe important meteorological details.  In particular, the rain followed the dark cloud and dust by an hour.  This indicates that the front preceded the frontal precipitation band and could have been an outflow boundary initiated by precipitaiton-cooled downdrafts beneath the frontal precipitation band.  Today we can see these details in many spring cold fronts thanks to surface weather observing systems and the National Weather Service radar. 

"The gale portion of the storm lasted over an hour, then down came the blessed rain and the snow all through the night and the next day, the snow and rain alternating and blending in the valley."

The description above also suggests that the precipitation persisted through the night.  Most frontal precipitation bands pass over Utah in a few hours, so perhaps there was a contribution from lake effect or orographic precipitation overnight.  The snow and rain alternating suggests the valley floor was probably in or near the melting layer with snow levels dropping during heavy precipitation periods and rising during lighter precipitation periods.  

Muir, however, did not find the snow in the city attractive or share a view that could be used by the Chamber of Commerce to attract tourists:

"It is long since I have seen snow coming into a city.  The crystal flakes falling in the foul streets was a pitiful sight." 

I include below a couple of photos of the essay describing the great storm.  Enjoy the reading. 

All Hail Lindsey Vonn!

Source: AP Photo/Luciano Bisi

It's easy to become cynical about sports these days, but there are some athletes who deliver performances that are truly uplifting and inspiring.  

Lindey Vonn winning the World Cup in St. Moritz on Friday is one of the most remarkable and astonishing performances I can think of in skiing if not all of sports.  

Before Friday, the oldest woman to ever win a World Cup race was Federica Brignone at the age of 34.  Brignone herself is a force of nature and one of my favorite skiers as she sends it with such passion (she is currently recovering from a major knee injury and I am hoping will return for the Olympics).  Vonn is 41. 41!  

Most of you know her story.  She won in every discipline on the world cup and fell just short of what was then Ingemar Stenmark's record of 86 world cup winds with 82 when she retired.  She is unquestionably the greatest speed skier of all time.  

She retired in 2019.  A knee replacement and a hell of a lot of hard work later, she is on top of the world, with Stenmark in her sights again (although she won't catch Mikaela Shiffrin), not to mention a shot at Olympic gold in Cortina.  

Simply incredible.  

Whither the Start of Ski Season

Sigh...what a start to December.

First let's have a look at the northwest storm.  Some bit water totals so far.  For the 3-day period ending at 6 AM PST/1200 UTC today (11 December), more than 10" of liquid precipitation equivalent at many sites in the Washington Cascades including 14.2" at Paradise SNOTEL (agreeing well with the expectations from the previous post) and 18.6" at the Lynn Lake SNOTEL between Paradise and Snoqualmie Pass.

Source: https://www.weather.gov/wrh/hazards

Crystal Mountain is reporting this morning that WA-410 is closed between Enumclaw and Greenwater, essentially cutting them off given that WA-410 is also closed over Cayuse and Chinook Passes to the south.  Most of their web cams are down but sadly, even at 6800' at the top of the Green Valley Express where a cam is working, it looks like a net loss from this storm.

Source: https://www.crystalmountainresort.com/the-mountain/mountain-report-and-webcams/webcams

Could be worse.  Below is the Summit West cam from Snoqualmie Pass.

Source: https://www.summitatsnoqualmie.com/webcams

Meanwhile in northern Utah, December continues to be the new October with yesterday's high of 61 at the Salt Lake city International Airport the average high on October 25.  

I keep thinking how fortunate we are that this low-amplitude ridge developed in a way that we stayed relatively mild at low levels.  If there had been a strong cold pool in place over the valley earlier this week, we would probably be much cooler.  If we can't have snow, then we may has well have a mild conditions in the valley.  We were also fortunate to have that storm last Friday Night and a few days of good snowmaking conditions before the warmth returned.  

A look at the ensembles shows a few members flattening out the ridge just enough to bring some precipitation into northern Utah the middle to end of next week.  An example is the ECMWF HRES. Forecast below for 1800 UTC Thursday 18 December.  

Indeed, for Alta-Collins the Utah Snow Ensemble has a few enthusiastic members, although most of the forecasts are still in the low-end snowfall range and most are warm through the 10-day forecast period.  

Median total water equivalent and snowfall are 0.91" and 8.0" through 5 PM Saturday 20 December, so we will set that as the over/under.  

Now is the time to burn skis.  I'd suggest human sacrifice, but some of you might just take that quip seriously. 

The Northwest Deluge

I've mentioned in prior posts that the storm track will be just to our north over the next several days.  Indeed, the Pacific Northwest is in for a deluge as they are raked by a series of storm systems.  Below is the Utah Snow Ensemble forecast for the 10-day period ending 0000 UTC 18 December.  Ensemble mean (upper right) liquid precipitation equivalents above 9" for most of the Cascades from Mt. Hood to Canada.  

It's worth a look at the plume for Paradise Ranger Station on Mt. Rainier, one of the wetter locations in the Cascades.  The ENS mean is > 20" over the 10 day period with the GEFS mean > 15".  There is tight clustering over the first 5 days of the forecast with most ensemble members between about 12.5 and 17.5".  We see a lot of spread in the ensemble forecasts sometimes, but this is pretty tight clustering for a major events.  

The ensemble grid point for Paradise is at 4942 ft, which is a bit lower than the actual ranger station (~5400 feet), but over the first five days from all of that water most ensemble members are only producing up to 20" of snow.  Rain rather than snow for much of the period.  What a waste of water. 

It's already a sad picture at Crystal Mountain today.

Source: https://www.crystalmountainresort.com/the-mountain/mountain-report-and-webcams/webcams

Worth watching forecasts if you are in the Northwest.  

The Europeans and Americans Simply Cannot Get Along

The overnight Utah Snow Ensemble forecast for Alta-Collins may be the crazies I've ever seen.  Most of the European Ensemble (ENS) members are producing little to no precipitation over the next 10 days including during during the period from 10-11 December (more on those dates in a minute).  The wettest ENS member puts out about 0.8" of water and 11" of snow.  

Some members of the American Ensemble (GEFS) have very different ideas.  There are 31 GEFS members and 10 of them put out more than 1.5" of water just through 00Z 12 December.  Several more put out between 1 and 1.5" of water.  There are some that track with the ENS (hard to see but they are there), but many GEFS members are much wetter.

What gives?

I don't plot or attempt to look at forecast plots like our four panel synoptic diagnostic for all 82 members of the Utah Snow Ensemble.  Nobody has time for that.  So I'm going to start here with the ECMWF HRES forecast that serves as the ENS control and is valid 0000 UTC 11 December.  This forecast captures many of the salient details of the pattern that is going to prevail over western North America the next few days.  A broad, low-amplitude upper-level ridge is centered near the Pcific coast (upper left) with an atmospheric river rolling over this ridge and across the northern US Rockies (lower right).  Heavy orographic precipitation occurs where the atmospheric river crosses major western mountain barriers.

So in the HRES the central Wasatch is just to the south of the action.  There are a few dribs and drabs that make it in, but accumulations are scant.  Most ENS members have a similar forecast.

Some of the GEFS members, however, shift the storm track far enough south to get us in on the action.

Diagnosing the why this occurs in this case is beyond my abilities.  I'll just say that I lean heavily toward the view that the central Wasatch may see some dribs and drabs over the next week but it's unlikely we'll see the game changing major accumulations that we need. 

Mother Nature Delivers the Concrete

Twenty-four hour totals at the Alta-Collins automated observing site added up to 1.79" of water and 15" of snow, yielding a mean water content of 12%.  Snowbasin-Boardwalk came in with 1.26"/8"/16%.  As evidence of the wet, windy, and rimey nature of the storm, I couldn't verify our 70 mph forecast for Mt. Baldy because the sensor rimed and is no longer spinning.  The Utah Avalanche Center report this morning says that "at 11,000 feet the wind is absolutely ripping, with sustained speeds at 50–60 mph with gusts pushing into the upper 70s."  That's good enough for me.  

The Alta-Collins snowstake photo this morning is one of the most comical I've ever seen.  Dense snow apparently carved by wind?  Perhaps with the flow wrapping around the Alta sign?  Who knows.  Come up with your own explanation.  

Snowfall at lower elevations is certainly lower and probably a soggy mess between 6000 and 7000 feet (or higher), but that's just a guess.  

The Cottonwoods might get a bit before things taper down later this morning.  The extended forecast shows that you should continue to root for America.  The European Ensemble (ENS) is giving Alta practically nothing after today.  The American (GEFS) is more generous around the middle of the work week.   

USA. USA. USA.

Friday Morning Update

In the previous post (Windy Storm on Tap) we discussed an approaching storm system that would come in today (Friday), but really pick up Friday night as strong flow and an inland penetrating atmospheric river move into northern Utah. 

That forecast is still on track.  Overnight last night and today we are seeing the dribs and drabs at the leading edge of the storm system, as expected.  Overnight through 8 AM this morning Alta-Collins picked up about .16" of water and 2" of snow and Snowbasin-Boardwalk came in with 0.24" of water and 3" of snow.  

But the big story is not today but tonight when the precipitation efficiency looks to increase as an upper-level trough moves through and high integrated vapor transport (IVT) noses into northern Utah.  The GFS forecast valid 0600 UTC 6 Dec (11 PM MDT Friday) shows heavy precipitation over the mountains of northern Utah (or better put what the GFS thinks is the mountains of northern Utah) as the trough (dashed line below) as the trough moves through.  

Our HRRR-derived forecast for upper Little Cottonwood (click to enlarge) shows relatively light periods of precipitation through 5 PM today (top left), afterwhich hourly liquid-precipitation equivalent rates really pick up as the upper-level trough approaches.  Precipitation rates maximize at around 1 AM Saturday with periods of precipitation continuing through 7 AM tomorrow (Saturday) after which precipitation becomes widely scattered.  

This is a warm and windy storm.  Our forecast winds for Mt. Baldy peak at around 700 70 mph [Apologies for the typo! - Jim] at 4 AM Saturday.  Temperatures overnight are forecast to be around 27 F at Collins and 30 F at the base.  As a result, snow-to-liquid ratios are low and generally less than 10 for the period.  This keeps the HRRR-derived snowfall relatively low and around 13" including the dribs and drabs today.  That said, at this point with the need for base, Cascade Concrete is better than Cold Smoke. 

The overnight six-member RRFS ensemble shows a range of liquid precipitation equivalent of between about 1.1 and 2.3" and snowfall between about 13" and 26".  Thus, the HRRR is on the low end of the RRFS.  

My take is that 1.2-2.2" of water and 12-22" of snow from 7 AM this morning through 7 AM Saturday represent the most likely range of outcomes for Alta-Collins, with much of that coming this evening and tonight.  The water amounts are most important right now to build base.  Let's hope we can eclipse 2".

Looking to the north, the story at Snowbasin is much the same with the overnight period being the wettest and then things settling down towards morning.  Snow-to-liquid ratios are quite low at Boardwalk, which is lower than Alta-Collins and thus warmer in this storm.  I'm expecting this to be a very wet snow event up there.  

The HRRR Skew-T for Ogden shows a freezing level near 775 mb or about 7000 ft.  Conditions are saturated, so that also represents the wet-bulb zero level.  

If we zoom into the plot of wet-bulb zero height with time we see that it just about reaches the altitude of boardwal (~8000 ft) and after midnight the base is below that level.  This raises the possibility of a bit of rain or mixed rain and snow at the base depending on how things shake out.  

The extended forecast after this storm is not great for us, but maybe we can get something.  The GFS, for example, has a monster atmospheric river roaring across the northwest next week.  Batten down the hatches for the Cascades, and mountains of the Idaho Panhandle, Montana, and northwest Wyoming.  Goodness gracious that is a tempest of a forecast for them.  

We're to the south of most of the action.  Best case scenario is we get some storms to dip into our area and get some modest accumulations.  Worst case is we don't get much at all.  Odds favor below average precipitation next week, but if the storm track can dip a bit further south than currently forecast, we could get something.

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.