Strange End to 2012

From a weather perspective, 2012 is coming to a strange end.  I did a ski tour in White Pine and in the early afternoon and it was quite nice in the upper elevations.

Upper White Pine Canyon ~1:00 PM

The photo above is taken looking north across Little Cottonwood Canyon.  Note the more solid bank of clouds over the lower canyon on the left.  This brought some snow to the lower canyon.  It wasn't a lot, but it was more than seemed to fall in the upper canyon.

Little Cottonwood Mouth ~2:20 PM

You can see the layer of low-level moisture in the morning sounding from the Salt Lake City airport.  Note how the temperature (red) and dewpoint (green) traces are nearly coincident up to about 700 mb (10,000 ft), which is consistent with a high relative humidity.  The drier air was further aloft.

Source: NCAR/RAL

The bottom line is that there was more moisture to play today in the lower elevations.  

Feeling Chilled?

For the first time since mid November, we are finally into a stretch of days during which the minimum temperatures are a few degrees below their climatological averages.  The past three days we were a few degrees below average for the minimum temperature, and that's the case this morning as well.  

Source: NWS

The last period we had with minimum temperatures so far below average was 10-13 November (top plot).  

In addition, there's quite a bit of low level moisture over northern Utah, and this makes for some spectacular cloud scenes.  Below is a web cam photo taken looking southwest through Provo Canyon from the top of the Arrowhead Chair at Sundance yesterday afternoon.

Source: Sundance, NWS

Utah's Snowpack Doughnut Hole

One of the curiosities of the current snowpack is the local "drought" that exists in the northern Wasatch Mountains near Ben Lomond Peak.

Source: NRCS

Most SNOTEL stations in northern Utah are near average snowpack snow water equivalent (i.e., 80–119% of average), but the greatest clustering of below average sites is on and just to the east of Ben Lomond Peak.  Look at the area just to the north of Ogden in the image above.

Historically, Ben Lomond is one of the snowiest places in Utah.  The snowpack there at 8000 feet usually rivals that near 9,500 feet in the central Wasatch.

A 13 foot snowpack at 8000 feet on Ben
Lomond Peak, 26 April 2005

However, Ben Lomond has a very unique microclimate.  It tends to get pounded in southerly to southwesterly flow, but gets very little snow when the flow is from other directions.  We haven't had many southwesterly flow storms this year with low snow levels.  As a result, the snowpack at Ben Lomond is lagging.  It can, however, catch up really fast.  Check out what happened last year when there was a southwesterly flow storm in late January that put down more than 10 inches of snow water equivalent (see red line below).  That storm was responsible for almost half of the peak snowpack on Ben Lomond last year.

Ben Lomond Snowpack Snow Water Equivalent.  Source: NWS

In many ways, Ben Lomond is an enigma in the Wasatch Mountains.  It has a "feast or famine" snow climate.  Usually there are enough feasts that the snowpack there is impressive, but this year, the pickins have been slim. 

Blessings and Curses of the Low Angle Sun

The sun just above Mt. Baldy shortly after noon today

Typically in Utah, the greatest threats to snow are wind and sun, so there's nothing better than a good early season snowpack combined with a low-angle sun like we have now.  Only on the warmest days can the sun do damage this time of year, so powder frequently lingers for days on most aspects in the backcountry provided it isn't trashed by the wind.  That doesn't happen in March, when the sun is almost always bad for south and west aspects and sometimes can be damaging to all but the steepest, north-facing slopes.

While the low-angle sun is a blessing for backcountry skiing, it is a curse for valley residents.  It doesn't provide enough energy to burn off cold pools (a.k.a., inversions) that form over the Salt Lake Valley and other low-elevation regions of Utah.  This is especially true when there is a fresh snow cover, which reflects a significant fraction of what little sun we get back to space.

We have just exited a fairly stormy pattern, so while there is a touch of smog over the valley, the pollution isn't too bad yet.  

Salt Lake Valley from Alta

That will change in the coming days as we settle into a more stagnant pattern.  There are a couple of weak systems that brush by early next week, but it appears they will stir things up only a little, with Salt Lakers eventually seeing the worst air quality thus far this season as the week progresses.  

A Break in the Action

The Christmas storm cycle is coming to an end.   The forecasts for the next seven days indicate that split flow will dominate the pattern.  We may see a weak system or two come through, including on Sunday, but precipitation will be light and overall the next seven days will feature below average snowfall.

Accumulated precipitation forecast by the GFS over the
next seven days

We shouldn't complain, the Snowbird and Mill D SNOTELs presently sit at 130% and 112% of average snowpack, respectively.

The Stellar Dendrite et al.

On a short ski tour this morning, I was greeted by an old friend, the stellar dendrite.

Chances are you've seen plenty of these around the past few days.  Stellar dendrites form in a very select temperature range.  Typically something between -12ºC and -18ºC (10ºF and 0ºF).   Perhaps not surprisingly, temperatures at the top of Mount Baldy (11,000 ft) have been in this zone since this latest storm cycle started on Christmas Eve.

If you have a keen eye, you've probably noticed plenty of other ice crystal types.  A wide variety of crystals form in most winter storms, and many of those crystals are beat to hell as they fall to earth.  Sometimes they become rimed, which means that they become indistinguishable as they are coated in tiny cloud droplets.

A wider view of the photo above shows the diversity of ice crystals that were falling this morning (click to enlarge).

There are quite a few stellar dendrites, but also some ice crystals that are very small and not easily classified with the naked eye.  

Watching the flakes was a good way to kill time on the climb, but ultimately, it was all white and skied good.

Nothing Wrong with Leftovers

The Sierra Nevada frequently do some serious damage to landfalling weather systems, leaving on the leftovers for Utah.

That is the case today and tonight as a trough moves through Utah and we see some of the scraps from the storm that impacted the Sierra.

That storm, however, dumped 33" in 24 hours on Homewood, 25" at Kirkwood, and 20" at Squaw Valley, so in this case, there's nothing wrong with leftovers.  In addition, conditions are ideal for producing the cold smoke.  Our algorithms suggest much of the event  will produce snow with a water content of 5% or less.

Enjoy the Christmas that just keeps giving!

Down to the Wire

Our multipart storm has finally arrived, cutting it as close to the wire fore a white Christmas as possible.  The radar image below shows the two main parts of the system that will affect us today.  The first is bringing a "wintery mix" the Salt Lake Valley this morning, while the next part extends across northwest Utah and will move in within a couple of hours.

Source: NCAR/RAL

For the valley, we're going to need that 2nd piece to deliver.  Snow is just starting to stick on the benches, but we're not seeing much in the way of white stuff on the ground on the valley floor.

I-215 just south of Parley's Canyon: Source: UDOT

Source: UDOT

Keep your fingers crossed.

All forecasts point to a spectacular bluebird day on Christmas.  It should be gorgeous for reveling in the valley or heading to the mountains.  Ho Ho Ho.

Spreading the Christmas Cheer

The prospects for a white Christmas for most of the Salt Lake Valley are going to go down to the wire. We had a brief flirtation with dendrites this morning, but alas, it left only a dusting on the grass.

That means we're going to need a Christmas Eve miracle, which is likely to happen.  The models bring a multi-part storm into the state starting tonight and continuing through early morning on Christmas.  The first part of this storm is fairly warm.  At midnight tonight, we are moist southwesterly flow with a 700-mb temperature of almost -6C.  That usually means snow levels will be near bench level.

Snow levels drop, however, overnight and a second colder system moves in during the day on Christmas Eve.

Given the higher snow levels during the first part of the storm, accumulations are likely to be heaviest on the upper-elevation benches, but even the valley floor should should get a coating during the day tomorrow.  Keep your fingers crossed.

With regards to the mountains, this storm is going to spread the Christmas cheer.  Everyone is going to get some snow out of this given the gradual transition from southwesterly to northwesterly flow.  In addition, this is the type of storm that lays down the Greatest Snow on Earth.  It will start out warm, laying down some higher density snow, then transition to cold, so it finishes with some cold smoke.  Our algorithms have it starting out at around 8% water content tonight, decreasing to 4% on Monday morning.  That's ideal snow for deep powder skiing.  Merry Christmas!

Mt. Baker Insanity

Mt. Baker, WA, the recognized king of lift-served snow, is no stranger to huge storms.  This year, they head into the holiday weekend with a 150" base at Heather Meadows, a 179" base at Pan Dome, and 98 inches of snow in the last six days.

All of that sounds great, but nobody has been able to get there due to more than 100 trees falling over the access road.  Today's mountain report tells the tale.

Ah, purgatory for Bellingham-area skiers.  Fortunately, they are hoping to have the road open tomorrow.

A Look at Utah Cold Pools

Warmer air has moved in aloft, but most of the valleys and basins of northern Utah remained mired in cold pools (a.k.a. inversions) that simply will not scour out.  This morning's sounding from the Salt Lake City airport shows a surface temperature of 26ºF (-3ºC), but aloft, temperatures peak at about 37ºF (3ºC) about a kilometer above the valley floor.  Surface winds within the cold pool are light, but there is a 35 knot jet sitting about 1500 feet above the valley floor.

It's colder elsewhere.  Here's some overnight minimum temperatures for you:

Salt Lake City International Airport: 20ºF
Provo Municipal Airport: 12ºF
Vernal: -5ºF (lowest hourly temperature reported, minimum may be lower)
Cedar City: 3ºF (lowest hourly temperature reported, minimum may be lower)
Bryce Canyon: -17ºF (lowest 5-min temperature reported, minimum may be lower)
Peter Sinks: -24ºF (lowest 15-min temperature reported, minimum may be lower)

The evolution of the cold pool at Cedar City is quite interesting.  They observed their coldest temperatures in the early morning hours on Thursday.  This morning was actually quite a bit warmer.  Then, this morning, the cold pool mixed out nearly instantaneously, and the temperature rose from 3.2ºF to 28.4ºF in 40 min.

I think it will be interesting to see what happens today in the Salt Lake Valley.  Perhaps the strong flow aloft will scour out the cold pool from the top down, resulting in warmer temperatures on the benches while the valley floor remains colder.  We often see this in situations like this.  If it's not going to snow, we may as well tap into that warmer (and less polluted) air.

Snowpack Winners and Losers

From a snowpack perspective, there are some winners and losers in the Wasatch thusfar this year.  The snowpack in the Cottonwoods and along the Park City ridge line is pretty healthy (in terms of depth, but not avalanche danger), but in the northern Wasatch it is dismal.

First, let's have a look at two SNOTELs in the Cottonwoods, Snowbird in Little Cottonwood Canyon and Mill-D North in Big Cottonwood Canyon.  Both sit at or above their average snowpack snow water equivalent for the date and well above where we were last year.

In addition, the Thaynes Canyon SNOTEL, which is on the upper mountain at Park City, is just above average snowpack snow water equivalent.

Thus, at upper elevations, the snowpack in the Cottonwoods and along the Park City Ridgeline is fairly healthy.  Unfortunately, there are no low-elevation SNOTELs in the Cottonwoods or near Park City, but I think it is safe to say that the low elevation snowpack is not healthy and running below average.  It's really unfortunate we don't have a low-elevation SNOTEL in the Cottonwoods as such observations will be really helpful for interpreting snowpack changes in our warming climate.

The snowpack in the northern Wasatch, however, is more dismal.  In the mountains near Ogden, much of the snow that fell in that early season storm in late October melted and they have simply missed out on storm after storm.  The Ben Lomond Peak SNOTEL (8000 ft) and the Ben Lomond Trail SNOTEL (6000 ft) are both well below average.

Ben Lomond Trail is even below last year, which is a direct consequence of the warmth of the storms we've had.  They have simply produced rain at that elevation rather than snow.  

So, things are in good shape in and around the Cottonwoods, but the northern Wasatch continues to struggle.  What a difference a short drive can make.

Prospects for a White Christmas

Many of you are wondering if we will have a White Christmas in Salt Lake City.  That's a question that is difficult to answer.

First the easy part.  Warm southwesterly flow will spread over the region for tomorrow and Friday.

With little snow on the ground now, we'll be heading into the weekend snow free.

After that, some models call for a weak system to move late Saturday night and Sunday, but right now valley accumulations appear to be nil to little.

Heading into the holiday, the ECMWF forecast ensemble calls for a trough to move across the western US.

Similarly, the GFS also brings a trough through and gives us a period of unstable northwesterly flow that would probably bring snow to the valley.

These are still medium range forecasts.  Let's see how things evolve over the next couple of days and hope we see something like the above verify.  Beyond the valley, a forecast like that would be great for Christmas freshies in the Wasatch.

Valley Slight, Cottonwoods Delight

Yesterday and last night were an exercise in futility and frustration for me.  We had a decent idea of what would happen (a frontal precipitation band would form) but we didn't know where.  As things turned out, the frontal precipitation band organized over Salt Lake and Utah Counties and hung out for quite a while, but valley accumulations were limited during the period of heaviest precipitation by the warmth of the storm.  

We got less than an inch at my place in the Avenues.  As one moved southward through Utah County where the frontal band was most intense, accumulations increased.  Here's how things look this morning along US-6 in Spanish Fork.

Fortunately, the Cottonwoods and the Park City area were under the band and got some of the goods. Brighton reported 16 inches overnight, with 8 inches or more reported elsewhere in the central Wasatch.  Alta is up to a 66" base, which is above my magic 60" threshold for good early season conditions.

Setting Up to South

I have a bad feeling about this.  The frontal band has developed, but the heaviest precipitation is to the south of Salt Lake City.

In addition, temperatures remain just warm enough that rain or slushy wet snow is falling on the valley floors.  While that will eventually turn over to snow tonight, this pattern doesn't bode well for accumulations at my place in the Avenues.  GRRR.

A Menacing Frontal Passage

Some nasty looking clouds are accompanying the cold front as it moves across the University of Utah.  Radar shows precip is starting to move into the Salt Lake Valley, but the coverage is far spottier than I would like to see.  Nevertheless, the precip is about to move in and I just heard thunder. Whoot Whoot!

Salt Lake will get some snow out of this eventually, but the GFS has shifted the heaviest accumulations to the south just a bit compared to this morning's run, suggesting the big winners might be to the south.

We'll see how things come together tonight.

A Maalox Moment

Today is the kind of day when a meteorologist could use a bottle of Maalox.  The forecast through tomorrow is very difficult, with divergent views being produced by our two main forecast models: The GFS and the NAM.

To illustrate this, I've put together a paneled chart that shows the guidance being produced by the two models side by side.  The GFS is on the left, the NAM on the right.  The panels are the 6-h accumulated precipitation (snow-water equivalent) ending at the time indicated in the legend at color filled intervals of .01, .05, .10, .25, and .5 inches.  The forecasts start with this afternoon (1800–0000 UTC/1100–1700 MST) and end tomorrow afternoon.  Click to enlarge further.

These panels illustrate a common dilemma facing meteorologists in the Intermountain West.  The GFS (left-hand-side) is a lower resolution model.  It doesn't handle topographic effects very well.  For example, note the lack of structure in the precipitation forecast compared to the NAM on the right.  However, the GFS runs later, sometimes ingests data that the NAM hasn't, and frequently does a better job handling the movement of large scale features like fronts.  For this forecast, that could be very very important.

Notice how the GFS develops an elongated west-east oriented frontal precipitation band that sags very slowly through northern Utah and Nevada.  If such a forecast verifies, there would be major accumulations not just in the mountains, but also the lowlands of Salt Lake and Utah Counties, as well as portions of western Utah and central Nevada.

In contrast, the forecast produced by the NAM is very different.  Beyond the greater detail owing to its higher resolution, the frontal precipitation band is weaker, especially over western Utah and central Nevada, and moves more quickly into southern Utah.  Does one lean toward this given the better handling of topographic effects?

One thing is for sure.  Snow is coming.  Major accumulations are likely in the mountains, but let's hope the GFS verifies so that we get a pasting in the valleys too.

Pretty in Pink

Source: NWS

Pink that is for a winter storm warning.

Source: NWS

Looks like periods of snow through Monday, then the meat of the storm comes in Monday night and Tuesday.  In the Cottonwoods, we are now in the midst of a transition from marginal early season conditions to what will probably be a pretty good upper-elevation snowpack for the holidays.  Conditions outside the Cottonwoods, which have been quite poor, will also be on the upswing.  Whoot whoot!

Forecast Tools: Little Cottonwood Model Guidance

Alta and Upper Little Cottonwood Canyon from Mt. Superior
January 27, 2009

If one wishes to access specific forecasts for Little Cottonwood Canyons, you can always turn to the National Weather Service Cottonwood Canyons Forecast or utahskiweather.com.  But what if you want to make your own forecast or look under the hood of the forecast process?  You can always access the model forecasts at sites like weather.utah.edu or Weather Underground's Wundermap.  These sites are great, but if you are like me, you want to also look at numbers.  How much precipitation is the model producing?  What are the snow levels?  Etc.

An option is to turn to our experimental model guidance page for upper Little Cottonwood Canyon.  The data on this site, which was developed by Trevor Alcott when he was a graduate student here at the University of Utah, is based on model soundings obtained directly from the NAM and GFS models (known as "bufr" soundings).   For example, here's the guidance from the NAM model through noon tomorrow based on the Alta bufr sounding.  

Snow level is 500 feet lower than the NAM "wet-bulb zero" level.  Studies have shown that this is usually a good approximation for the snow level.  Snow ratio and water content are based on a non-linear version of the algorithm described by Steenburgh and Alcott (2010) applied to the NAM forecast.  The Mt. Baldy temperature, RH, and wind forecasts involve simple statistical adjustments to the NAM forecast, which does not adequately resolve local topographic effects, to produce a better point-specific forecast.  

The QPF (quantitative precipitation forecast) tells you how much snow-water equivalent the NAM is producing.  Snowfall amounts are based on the QPF forecast combined with our snow ratio algorithm.  

The web site also includes similar guidance from the GFS model, but uses the bufr sounding from the Salt Lake Airport since there is no GFS bufr sounding for Alta.  The GFS bufr data is also available at less frequent time intervals.  

The use of the GFS bufr sounding from Salt Lake City instead of Alta probably doesn't affect results much since the effective horizontal grid spacing of the GFS is only 25-km and the terrain is pretty pathetic.  Thus, there's probably not much difference in the forecast produced by the GFS for Salt Lake and Alta.  

It is important to recognize that this page provides access to forecast guidance and not a forecast.  A meteorologist would take a look at these numbers, as well as those from other models, and combine it with their situational awareness and past experience to produce a forecast.  One of the biggest problems is with the QPF and snowfall amount forecasts, which are frequently (but not always) underdone because neither the NAM nor the GFS adequately resolves the Wasatch Mountains, let alone the fine-scale details of the terrain in and around Little Cottonwood.  Use it with caution for your own forecasting purposes.  

Everyone to Get Some

The next seven days look to be fairly active across the western United States as we should see one of the more progressive patterns thusfar this season.  Like Santa Claus, the GFS gives something to everyone in the west.

Source: NCEP

There's enough variability that I'm reluctant to speculate on specifics, but I'm optimistic that we're going to see some much needed action during this period for the entire Wasatch Range.  Keep your fingers crossed.

A Big Record Will Likely Fall

Source: www.mattbors.com

This has been an exceptional year meteorologically in Utah.  One that lies outside the range of weather that has been recorded previously (since 1895) in the state.

For the year to date (Jan–Nov), our mean statewide temperature is 53.7ºF, the highest in the instrumented record.

Source: NCDC

A close second is 1934 at 53.4ºF (I'm not sure if the difference is statistically significant, but we'll go with 2012 as the leader).  1934 was a real outlier relative to the climate of Utah during the early 20th century.  In fact, despite warmth in recent years, none have exceeded it.  Will we finally top it this year?

Data from NCDC suggests that in December 1934 the statewide average temperature was 1.1ºF above the 1981–2010 statewide average temperature.  I don't have access to statewide statistics for the first 12 days of this December, but we can look at anomalies at specific stations.  At Salt Lake City we ran  7.6ºF above the 1981–2010 average.  At Cedar City we ran 8.0ºF above the 1981–2010 average.  Now that's a fever!

Thus, we head into the last half of December with a very real chance of recording the warmest calendar  year in Utah during the instrumented record.  That sounds impressive, but in the coming decades, this year won't seem all that unusual.