U.S. Energy Statistics

About a month ago, there were a number of reports in the media, including this article in the Guardian, discussing a decline in U.S. CO2 emissions last year to the lowest levels since 1994.  The source of this information was a report by the Business Council for Sustainable Energy (BCSE) and Bloomberg New Energy Finance (BNEF) entitled Sustainable Energy in America 2013 Factbook.

I know nothing about energy or economics, so I can't really comment on the reliability of the report, but for wonks out there who are like me and love to look at graphics and statistics, it's worth a look.  Here are a few that caught my eye.

Source: Sustainable Energy in America 2013 Factbook

I'll blow up Figure 2 from the top as it is most interesting.  

Source: Sustainable Energy in America 2013 Factbook

Those of you out there who are energy and economics wonks, feel free to add your comments and interpretation.

Measuring Snow Is Hard!

All observations are bad, but some are useful

- Paraphrased version of George Box quote

There is a tendency in meteorology to treat observations, especially those that are collected in place by weather stations, as ground truth.  Meteorology is a data starved field, which contributes to the tendency to place great value on any observations, but of course observations are not perfect and one needs to consider the possibility of error.  

There are two major sources of error in meteorological observations.  The first is observational error, which is the difference between what is measured and the true value.  Such errors can by systematic, meaning that they occur regularly, or random, which means they vary from observation to observation. A good example of a systematic error is the tendency for thermometers that are not well ventilated to overheat and record a higher temperature than that in the free air when they are in the sun on days with light winds.  A good example of a random error is that related to round off.  For example, many observations are recorded the nearest whole degree (fahrenheit or celcius) rather than with absolute precision, and this introduces some error to every observation.  

The second is representativeness error, which arises from the observation simply not being representative of the area or location to which it is being applied.  For example, we often use the temperature at the Salt Lake City airport as indicative of the temperature throughout the Salt Lake Metropolitan area.  While easy and convenient, this observation often times departs dramatically from temperatures in other parts the metro area, especially during inversions.   

Yesterday provided a good example of how both observational and representativeness errors can complicate the interpretation of snow observations.  These observations are collected by automated stations similar to the one below, which is our Alta-Atwater site (click to enlarge).  There is an ultrasonic snow depth sensor that measures snow depth from a stick mounted over a white board in the lower left of the photo.  Typically such boards are wiped and repositioned either following storms or at regular intervals of no frequently than every 6 hours.  The white cylinder on the platform is a precip gauge that measures snow-water equivalent.  

Here are automated snow amount, water equivalent, and water content observations from four locations in Little Cottonwood Canyon from midnight to 10 am.  These observations are based on ultrasonic snow depth sensors, which measures snow depth on a white board, and precipitation gauges that measure snow water equivalent.  

Alta-Collins (~9700 ft): 6 inches, .23" SWE, 3.8%
Alta-Atwater (~8800 ft): 8.4 inches, .18" SWE, 2.1%
Alta Guard (~8800 ft): 5.9 inches, .31" SWE, 5.2%
Elberts (~7600 ft): 3.15 inches, .09" SWE, 2.9% 

What is to be believed?  The Alta-Atwater and Alta Guard sites are within a couple hundred yards of each other, yet Alta-Atwater has more snow, less SWE, and lower water content.

There are many factors that contribute to the variability seen above.  One is that there were real variations in snowfall that contribute to some of the differences between the two sites.  Two is that the snow depth and precip measurements are essentially point measurements.  We had very low density snow yesterday and even with a small amount of wind can transport snow.  Thus a single measurement might not be representative of the snowfall in the area around the observing site.  Think about how flow around the platform and other obstacles might affect what is measured by the instruments at the Alta-Atwater site.  The effects are probably not large, but they aren't zero.  

Third, the snow-depth measurements aren't fully consistent.  The snow masurement at Alta-Atwater is based on a difference in measured snowdepth at two times with no wiping of the board during the recording period.  The snow measurement at Alta Guard is based on the addition of two measurements taken before and after a wiping of the board.  Each operating group has different approaches and times that they do this.  

Fourth, most precipitation gauges are prone to undercatch, meaning that flow across the gauge prevents all the snow from falling into it and being recorded.  The winds were not strong yesterday, but the snow density was very low, and low density snow is very prone to undercatch.  Some of the variations in SWE probably reflect variations in undercatch.  For example, we have noticed that our site at Alta-Atwater is very prone to undercatch, probably because it is mounted a few meters above the ground, and this might explain the anomalously low SWE and water content at the site.  

Fifth, low-sensity snow can be a poor reflector of sound, and this can lead to measurement errors by the ultrasonic snow depth sensor. 

I can add a few more, but I think you get the point.  There are lots of potential error sources and this complicated the interpretation of automated snow measurements yesterday.  For this reason, snow geeks typically supplement automated measurements with those taken manually. 

Yup, 250 years after the industrial revolution, and the old fashioned way is still the best way to measure snow.  Of course, manual observations have the disadvantage of not being on demand and all the time.  

Wasatch Winter Magic

This storm simply will not quit over portions of the Wasatch Mountains.  Note on the radar below how orographic (i.e., mountain) precipitation continues to linger over the Wasatch and Oquirrh Mountains.

The snow that is falling is cold smoke and comprised of lots of dendritic aggregates based on snowflake images collected by the University of Utah MultiAngle Snowflake Camera at Alta Ski Area (see Alta's Snowflake Showcase web page).  A sample is below.

Source: http://www.alta.com/pages/snowflakeshowcase.php 

Snow water contents appear to be quite low.   The last 4 inches of snow at Alta-Collins was produced by only .12 inches of water.  That's less than 4% water content!

How Important Is Lake Effect?

Our paper examining the contribution of lake-effect periods to the cool season (16 September to 15 May) precipitation of the Great Salt Lake Basin was published today in the Journal of Applied Meteorology and Climatology.  The study was funded by the National Science Foundation and the paper was lead authored by Kristen Yeager, a former University of Utah graduate student, with contributions from myself and Trevor Alcott.  It can be accessed here, but for most off campus it is paywalled, so I'll hit some of the highlights here.

Let's get right to the point.  How important is lake-effect?  We looked at some 700,000 radar images from the 1998-2009 cool seasons and identified 128 lake-effect periods (LEPs).  We then used a combination of radar and precipitation gauge data to determine how much precipitation (snow-water equivalent) fell during these periods.  The big winners were SNOTEL stations (Snowpack Telemetry stations that report daily precipitation) at Snowbird (SBDU1) in the central Wasatch Mountains and Dry Fork (DRFU1) in the northern Wasatch Mountains, both of which observe an average of about 60 mm (2.4 inches) of snow-water equivalent during lake-effect periods each cool season (left-hand panel below).  If you are wondering why Alta doesn't show up, it is simply because we didn't have access to a complete record of daily precipitation for the study period, so it wasn't considered.

Source: Yeager et al. (2013)

In the lowlands, the Salt Lake City airport (KSLC) observes an average of 16 mm (0.6 inches) of snow-water equivalent during lake-effect periods each cool season.  I suspect that if we had good data, we would find that the greatest lowland precipitation during lake-effect periods is found along the Bountiful bench and east benches of Tooele and Salt Lake County.  Unfortunately, the data at sites in those areas is skewed low because the precipitation gauges are not properly wind shielded and fail to fully catch all the precipitation during snowstorms (this is known as undercatch).  These are the sorts of warts that those of us who work with climate data have to deal with.

At the Salt Lake City Airport and Snowbird this represents 5.8% and 5.1% of the total cool-season precipitation, respectively (right-hand panel above).  Those numbers are not as large as conventional wisdom suggests, but conventional wisdom is wrong.  The lake often contributes to the tail end of a storm and, by association, it is often linked to a greater fraction of the storm total than is merited.

 The aforementioned Dry Fork SNOTEL in the Oquirrh Mountains gets 8.4% of it's cool-season precipitation during lake-effect periods, the most in the Great Salt Lake Basin.   Note that this site gets about the same amount of precipitation during lake-effect periods as Snowbird, so the greater percentage simply reflects that less precipitation is produced during non-lake-effect periods at this site.  The Oquirrhs simply don't see the same diversity of storms as the central Wasatch.

One of the more interesting findings we made was that at any given site, about a dozen lake-effect periods produce half of the total lake-effect precipitation during the 12-year study period.  In other words, at a given location, most lake-effect storms are pretty small, but a few big events make-or-break the lake-effect climatology.  Prime examples include the two lake-effect periods during the 2001 Hundred Inch Storm, which produced 107 mm of SWE at Snowbird (more than the annual average).

Finally, we examined the seasonality of lake-effect and found that it features a primary peak in the Fall (October and November), a mid-winter lull, and a secondary peak in the spring (March and April).  For skiing in the Cottonwoods, this seasonality is quite important as it means that the lake effect is concentrated in the fall when it can help build up the snowpack during the early season.  There's not much lake-effect spillover across the Wasatch Crest, so this isn't really much of a help for the Park City resorts.

Source: Yeager et al. (2013)

There is an important caveat to this work, which is that lake-effect periods sometimes feature non-lake-effect precipitation occurring in concert with lake-effect precipitation.  We didn't attempt to account for this, which is an exceptionally difficult task, and it partially explains why sites somewhat removed from the lake observe precipitation during lake-effect periods.

Deja Vu All Over Again (Almost)

The large-scale pattern for the past several days has featured an active polar jet over the north Pacific and an active subtropical jet across the subtropical eastern Pacific, Mexico, and the southern tier of the U.S.  Upper-level troughs have been exiting the polar jet, digging southeastward across the western US, and then merging with the subtropical jet over the southwest US.

On Saturday morning, the upper-level trough that barely missed Utah and wreaked havoc on the PGA tournament in Tucson on Thursday, was over west Texas and was being carried downstream to wreak havoc on the eastern U.S. by the subtropical jet.  The upper-level trough that produced our sublime weekend of powder skiing was over the Pacific Northwest and posed to move into Utah.

This morning, it is nearly deja vu all over again.  The upper-level trough that gave us our weekend powder dug southeastward and merged with the subtropical jet over west Texas.  Another upper-level trough is moving over the Pacific Northwest and is poised to move into Utah.

So, another foot plus dump for the Cottonwoods?  Well, there was a reason why I said nearly deja vu all over again.  Although the pattern is similar, there are some subtle but important differences.  First, the upper-level trough over the Pacific Northwest this morning is not as strong as the one that affected us this weekend.  Second, the pattern upstream is somewhat different this morning (Saturday featured a very strong explosively deepening storm in the western Aleutian Islands that helped further amplify the approaching trough).  Third, the plume of moisture with the upper-level trough over the Pacific Northwest this morning is not quite as juicy as Saturday's Soy Sauce Express.

As a result, the models are calling for snow, but not as much as in the weekend storm.  The latest NAM, for example, is calling for 0.21 inches of snow-water equivalent and 4.5 inches of snow for upper Little Cottonwood.  This is about half of what it was putting out for the weekend storm.

So, a bit of a refill tonight and tomorrow morning, but like a drink in Utah, it will likely be metered a bit more than the weekend storm.  The light powder should be a great frosting for backcountry skiing.

Stormy Adventures and Misadventures

The pre-frontal snow never got going, but Mother Nature finally delivered the goods today with the frontal passage and post-frontal snow.  I had a day of wild adventures and misadventures, all with a strong meteorological influence.

I did about a 5 hour solo ski tour out of Big Cottonwood Canyon and got to watch the front penetrating across the shoulder of Kessler Peak.  All I can say is wow.  The photos below were taken at 9:45, 9:46, and 9:47 am and illustrate the dramatic change that occurred with the cold frontal passage.

Immediately following the frontal passage, there was an extended period with snow pellets or small graupel, which probably reflects the very strong rising motion at the leading edge of the front.  

After a bit of a lull around noon (I could briefly see the sun through the light snow), there was an explosion of dendritic aggregates just after 1 PM, with some very high snowfall rates where I was skiing.  Dendrites are those gorgeous, 6-armed snowflakes, and aggregates mean that they are entangled together.  

Then the misadventures began.  I got to the car at 2:30 and enjoyed a snowpacked white knuckle drive down Big Cottonwood.  Upon getting to the bottom of the canyon, I learned that Little Cottonwood was closed until 4:30.  My son was at Snowbird, and I knew the timing of that closure was the kiss-of-death for any hope of him being able to get down the canyon by bus before nightfall.  Thus, I opted to hang around and retrieve him from Snowbird myself.   While killing time, I got this great view of the storm raging above the mouth of the canyon. 

The canyon opened promptly at 4:30, beginning the long escapade up and down the canyon while it was puking snow in the upper canyon.  

White snake going up 

Red snake coming down

Total time from Spruces to my home in the aves, including a 1.5 hour wait at the bottom of the canyon, 4.5 hours.  Blood is thicker than water.

Hope you were able to enjoy it.  Following the passage of the front, snowfall totals at Alta-Collins were 7 inches by 3 PM, 9 inches by 5 pm, and 12 inches by 7 pm.  Finally, a real storm!

Anatomy of Our Approaching Storm

We have a fascinating storm setting up for tomorrow, one that will bring some snow to the mountains and some heartburn to meteorologists.

First, let's talk about the key ingredients.  Over the past few days, moist air, originating over the subtropical Pacific near China has streamed across the North Pacific and is now impinging on the Pacific Northwest.  One of my students dubbed this the "Soy Sauce Express" and it shows up as a filament of high atmospheric water vapor content (a.k.a. precipitable water) in the contours below, which are overlayed on the 1200 UTC (5 AM MST) satellite image from this morning.  

1200 UTC (5 AM MST) 22 Feb 2012 IR satellite imagery and GFS
Precipitable Water Analysis

The water vapor content of this plume is not unusually high, but it will help fuel tomorrow's storm.

Another key ingredient is the low center over the Gulf of Alaska, which has tapped into cold air originating over the high latitudes.  It is the confluence of this cold airmass with the warm, moist air in the Soy Sauce Express that is generating a strong cold frontal passage for us tomorrow.

The wildcard in all of this is the cyclone that was near the western tip of the Aleutian Islands this morning.  This cyclone is forming very rapidly (something meteorologists call explosive deepening, click here for more discussion) and it is going to affect the structure of the jet stream over the North Pacific and the intensity of the duration of the storm here in Utah.

So, here's how things will play out.  The snow showers we've had this morning will taper off today.  Overnight, warm-moist air associated with the Soy Sauce Express will spread into the Northwest and eventually sag southward into Utah.  This will lead to the development of mountain snow late tonight ahead of the approaching cold front.

NAM sea level pressure, surface wind, and 12-h accumulated
precipitation valid 1200 UTC (5 AM MST) 23 Feb 2013.

Things pick up tomorrow morning with the approach and passage of the cold front, which will likely be associated with strong winds and heavy snowfall in both the mountains and valleys.

NAM sea level pressure, surface wind, and 6-h accumulated
precipitation valid 1800 UTC (5 AM MST) 23 Feb 2013.

For the Cottonwoods, this probably means something like 8-14 inches through late tomorrow afternoon.  Storm skiers should be happy.

After that, it's a bit more of a crap shoot given the vagaries of post-frontal snow showers.  Older model runs were calling for a prolonged period of cold, unstable, northwesterly flow, but, due in part to that explosively deepening cyclone, the more recent runs are building the ridge in more rapidly.  As a result, the flow shifts from northwesterly late Saturday afternoon to northerly by Sunday morning.  So, periods of snow are likely in the Cottonwoods Saturday night, but we'll just have to see how productive they are and how long they can last.

How Good Are Snow Forecasts Anyway?

This has been a frustrating winter for me as a forecaster.  We've had some weird storms, and others that just haven't panned out as I thought.  Thus, I thought we would take a look today at how weather forecasts have improved over the past couple of decades and why the Intermountain West continues to be a black hole for weather forecasters.

To do this, we will be examining the accuracy of forecasts produced by the Hydrometeorological Prediction Center (HPC), which provides precipitation forecasts and outlooks for the entire continental United States.

The metric that they use to evaluate the accuracy of their forecasts is known as the equitable threat score.  Without getting into the gory details, the bottom line is the higher the equitable threat score, the more accurate the forecast.

Forecasts produced by computer models (i.e., the NAM and GFS) and by the HPC forecasters show considerable progress going back to the beginning of this record in 1993 (and certainly much progress before that).  For example, for storms producing an inch of precipitation (snow-water equivalent) in 24 hours, the NAM and GFS equatable threat scores have climbed from about .15 in 1993 to about .25 in 2006, with some evidence of a plateau thereafter.

Source: NOAA/NWS/NCEP/HPC

The forecasts produced by the HPC forecasters also improve over time from about 0.22 in 1993 to about .32 from 2008–2012.  Note that the gap between the model and human forecasts hasn't closed much, which suggests that when given better model forecasts, human forecasters continue to find ways to exploit and improve those forecasts.

So, forecasts are better today than they were 10 or 20 years ago, and there have been some major forecast victories (e.g., Hurricane Sandy) that could not have been achieved with the tools and models of 20 years ago.

However, those statistics are for the entire United States.  While it is likely that forecasts have improved everywhere since the early 1990s, they haven't improved uniformly.  If we look at the equitable threat scores for precipitation forecasts from 16 April 2011–15 April 2012 by region, we find they are highest along the U.S. west coast and in the northeastern U.S., and lowest in the western U.S. interior and southeast U.S.  This holds for both modest (a threshold of 0.5") through large (2.0") 24-hour accumulation thresholds, although there is more scatter in the highest bin due to the small number of events.

Equitable threat scores for HPC and calibrated ensemble modeling system
forecasts from 16 April 2011–15 April 2012 by region.  Courtesy
Keith Brill, HPC 

These variations partially reflect differences in the climatology of precipitation systems in these regions.  For example, over the western U.S., precipitation systems tend to be big and broad over the Pacific Coast, but splintered and broken up over the interior, and this is one factor that makes forecasting very difficult.  Over the southeast, difficult to pinpoint thunderstorms contributes to lower accuracy.

Based on these statistics, the most reliable snow forecasts are likely to be for the Cascades and Sierra, followed by the Northeast, and then the interior (e.g., Utah, Wyoming, Montana, Colorado).  Wasatch powderhounds who feel battered and bruised by forecasts have every right to complain to their brethren to the west.  However, while we don't know precisely when or where a storm will produce, we don't have to worry as much about snow quality.  

Of course, there are some caveats to this analysis.  It would be good to examine statistics strictly for winter.  Snow forecasts in the Sierra and Cascades also depend on the snow level forecast, and this can be a challenge in some storms.  Finally, there is the issue of converting from snow-water equivalent to snowfall amount, which contributes to errors in the forecast of snow amount. Nevertheless, if these factors are considered, I think we will find that the interior west remains the most difficult ski region in which to forecast snow.

The Digging Trough

It's always disappointing when a storm decides to wreak havoc on a golf tournament in southern Arizona (i.e., the Accenture World Golf Championship near Tucson) rather than giving us deep powder, but that is the case today.

The culprit is what meteorologists call a digging trough, which is a trough that is amplifying and "digging" southward rather than progressing from west to east.  The loop for the last two days shows this rather well.  Note how the upper-level (500-mb) trough (indicated by the black contours) and the surface trough and cyclone move from the northern Gulf of Alaska into the Southwest U.S.

This type of storm evolution is not uncommon over the western U.S. [for you techies, there is considerable discussion of this in a recent paper by U atmospheric scientists Lareau and Horel (2012)].  Troughs that tend to do this are typically diffluent, meaning that the flow spreads out on their downstream (eastern) side.  As is the case above, there is typically strong northwesterly flow on the back (western) side of the upper-level trough, which decelerates and spreads out on the downstream (eastern) side.

The Wasatch Mountains will see some snow showers today and tonight, but it looks like a dust-on-crust event with perhaps 2-4 inches.  Areas of southern and central Arizona will get more precipitation (in terms of snow-water equivalent).   For more on the weather near Tucson, see Bob Maddox's MadWeather blog.

The weekend storm continues to look good.  Keep your fingers crossed.

Addendum @ 9:55 AM

It's not too often that you see a winter storm warming for the Tucson area and a blizzard warning for areas as far south as the Mexican border, but that is the case today.

Source: NWS

Here's the winter storm warning for the Tucson metro area, which includes 3-7 inches forecast for 3000-5000 feet, 7-14 inches for 5000-7000 ft, and 14-19 inches above 7000 feet.  Forget about golf.  Mt. Lemmon freshies anyone?

Source: NWS

Flirting with 50!

We are awfully close to the coveted 50ºF mark this afternoon at the University of Utah campus.  If we get there, it would be the highest temperature observed thus far this calendar year on campus (eclipsing 49ºF on February 8).  Further, it's is a coveted mark for both old school (US units) and new school (metric) types since 50ºF=10ºC.

Enjoy it now.  Change is a comin'.

Mountains and Lake-Effect Snow

Did you ever wonder what all the mountains around the Great Salt Lake do to lake effect?  Trevor Alcott and I have a paper on this subject that was accepted and was released today in early online format by the American Meteorological Society journal Monthly Weather Review.  You can find a summary of the article on the University of Utah web site or, for those of you on campus or with a  subscription to the American Meteorological Society journals, the full article at http://dx.doi.org/10.1175/MWR-D-12-00328.1.   The National Science Foundation and National Oceanic and Atmospheric Administration sponsored the research.

A key finding for skiers is that we need to mow down the mountains northwest of the Great Salt Lake.  Drying and warming of northwesterly flow in the lee of those mountains makes for weaker lake-effect storms.  We'd be much better off if cold air over the Snake River Plain could penetrate directly into the Great Salt Lake Basin.  On the other hand, the funneling of flow into the Salt Lake Valley can strengthen some lake-effect storms, not only over the mountains but also over the southern Great Salt Lake and Salt Lake valley.  This topographic effect doesn't always play a role, but it can have a strong influence on some events.

An Encouraging but Uncertain Forecast

This is probably a poorly kept secret for those of you who are constantly on the lookout for snow in the forecast, but there is going to be a major pattern shift this week that could give us one of the more active patterns of the winter.  First lets talk about what is encouraging about the forecast.  The Climate Prediction Center 6–10 day outlook has my favorite combination of colors.  Blue for below average temperatures and green for above average precipitation.

Source: NOAA/CPC

In addition, the GFS has three major systems coming through over the next ten days.  The first is a mid week storm, the bulk of which moves through southern Utah, but the latest computer models suggest it will give some of the goods to the north too.  

This is followed by two direct hits for the weekend and early next week.  Looking at the four-panel forecasts from the GFS, you can barely tell these two storms apart.  Both feature troughs in large-scale northwesterly flow.

That's a very encouraging forecast, but I must bring up the uncertainty.  One way to evaluate uncertainty is to compare forecasts from different models and ensemble forecast systems, which produce a suite of forecasts.  For next weekend, all of the members of this morning's GFS ensemble seem quite similar to the run above and produce a direct-hit trough.  

Source: Penn State E-wall

I like that forecast, but the ECMWF (European Center for Medium-range Weather Forecasting) forecast ensemble has somewhat different solution.  It has the storm track further to the south and the trough going through the Southwest.  We'd probably get some snow, but not necessarily a lot.

Source: ECMWF

So, we can be reasonably confident that we will be seeing a pattern change and that we have a fairly cold period ahead (after tomorrow) relative to climatological averages.  For snow it appears we will see something, but how much of a pounding remains in the ether.  Keep you fingers crossed. 

A Question for You

There are many things I love about ski touring.  Yeah, there's the powder and the endless possibilities for adventuring, but then there are all the weird things you see because of the viscoelastic properties of snow.  It helps stimulate the synapses.  On today's tour, we noticed that the snow was much deeper on the south side of these aspens than on the north side.  The slope wasn't very steep, perhaps 10 degrees.  So, my question for you snow types out there is how does this happen.  Is the tree preventing settlement on the uphill side?  Was there wind transport during the storm with snow collecting on the south side?  Inquiring minds want to know.

Perfect Weather for Skiing

Presidents weekend will begin with a 10+ day tomorrow in the mountains as a high amplitude ridge builds over northern Utah.  By tomorrow afternoon, 700-mb temperatures (near crest level) are up near -2ºC.

Source: http://weather.utah.edu

With the sun higher in the sky, it's going to feel quite warm, but the snow should hold up well at upper-elevations on the north side of the compass.  For those of you looking for a bluebird resort day, you really can't do much better, and you should take full advantage as the weather will be changing on Sunday.

I conclude today with a big congratulations to Ted Ligety who won his 3rd gold in the 2013 Alpine World Championship today.  It's the first time an individual has won 3 golds at an Alpine World Championship since Jean Claude Killy won 4 in the 1968 Olympics (which at the time also served as the world championship).

Source: US Ski Team

I attended the 2001 Alpine World Championships in St. Anton.  I recall riding a chairlift with an Austrian ski instructor on the morning of the super-G and he asked us who the big American was.  We said "Daron Rahlves," to which he responded, "never heard of him."  A couple hours later we stood in the finish line area and watched Daron win the gold.  What an experience.

Baby Graupel

The area around campus was littered this morning with small, spongy, ball-shaped snow pellets that fell over night.  They are indeed fully recyclable.

Most clouds are comprised of a mixture of ice crystals and supercooled cloud droplets.  Supercooled means that the droplets are below freezing, but remain in the liquid phase.  Graupel is a type of snow pellet that forms as an ice crystal falls and collects these supercooled cloud droplets, which freeze on contact.  This leads to the formation of a ball or lump shaped snow pellet.

Source: Parkerjh, Wikipedia Commons

The snow pellets that fell last night were, however, quite small.  I don't know if there is a minimum size requirement for graupel, so I'll call them "baby graupel."  The formation mechanism was probably similar to that of graupel.  Small ice crystals collected supercooled cloud droplets as they fell.  They just didn't grow to a large size. 

Goldilocks Snow

Big storms are overrated.  We did a dawn patrol this morning and found that the new snow wasn't too shallow and wasn't too deep, but was just right.  My partner commented that the snow was so sublime that it was almost as much fun trail breaking up as going down.  Get out and enjoy!

Northeast Snow Totals

This is old news, but I thought I'd share the snowfall total map from last weekend's Northeast snowstorm, which was produced by Brandon Vincent at the Raleigh North Carolina National Weather Service Office.

Source: http://cimmse.wordpress.com

Central Connecticut is now ahead of Alta for February snowfall!  Fortunately we still have them beat in total snow depth.

Another Year without a Winter

I know what your thinking.  We've had a hell of a winter down here in the Salt Lake Valley.  It was more than 10ºF below average at the Salt Lake International Airport last month, we've had a deep snowpack on the ground since Christmas, and there's been that nasty inversion.  So what do I mean when I say this is a year without a winter?

There are many ways to define winter.  There's astronomical winter, which runs from the winter solstice (about 21 December) to the spring equinox (about 20 March).  There's meteorological winter, which includes the months of December, January, and February.  Finally, there's Steenburgh winter.

Steenburgh winter is that period during which we have the crème de la crème of backcountry powder skiing with both a deep snowpack and a low-angle sun.  It starts when we hit 100 inches at the Alta-Collins snow-depth sensor.  Anything less is still early season conditions.  I've been amazed at what people have been skiing this year, but there are still plenty of unburied rocks, brush, and pucker trees out there.

Steenburgh winter ends on February 10th, which seems to be the day that the sun begins to have an increasingly caustic effect on the snow.  South aspects don't survive more than a day or so after a storm, the cone of shadow on clear days becomes increasingly confined to northerly aspects, and the sun becomes increasingly important to consider in your backcountry travel plans.  Note that concern about warming on south facing slopes got a mention in today's avalanche report, which we can expect to see more of in the coming weeks.

Excerpt from the Utah Avalanche Center advisory for February 11, 2013

This is the second consecutive year that we reached February 10th before reaching 100 inches at Alta-Collins.  Thus, this is another year without a Steenburgh winter.

Many have accused me of being a powder snob, and Steenburgh winter is all about such snobbery.  It concentrates on that period when powder can linger for long stretches in the backcountry without much solar molestation.  Of course many powder days come after the end of Steenburgh winter.  In 2010/11 we were getting freshies on Memorial Day.

However, as we move farther away from Steenburgh winter, the sun will tighten the noose on backcountry powder following storms and it will be imperative to plan and adjust for its caustic effects.