Active Pattern with a Lot of Possibilities

There are a lot of ways to look at the downscaled NAEFS plume for Alta-Collins below. 

One could focus on the upper-end forecasts.  What could be better than 5+ inches of water and 75+ inches of snow?  

Or one could look at the low end forecasts.  Those aren't so bad, but give a pretty different result with less than 20 inches of snow and 1.5 inches of water.  

Or one could see the period beginning on Friday morning (about 12Z 1 Dec) through Monday (about 18Z 4 December) as a stormy period in which there are a wide range of possibilities depending on details that cannot be confidently predicted at this stage.  

Let's take a look at what some of the models are saying. 

The GFS is pretty much right in the mean of the NAEFS forecast and puts out a total of 2.75" of water and 41.8" of snow for Alta-Collins.  A close look at the accumulated precipitation and snowfall traces shows a series of three waves moving through, with precipitation and snowfall waxing and waning with the passage of these systems.  

In addition, one can see that this is a period in which temperatures initially fall through late Friday, but then climb again into Sunday, when the winds also increase.  As a result, snow-to-liquid ratios maximize late on Friday and then decline on Saturday and Sunday.  Thus, should this forecast pan out, we will probably be dealing with upside down snow on Sunday.  

The Euro, on the other hand, is quite a bit drier.  I don't have an equivalent plot for the Euro, but totals for water equivalent in the Alta area are around 1.56".  It's not unusual for the Euro to be drier than the GFS, but there's actually a fairly large difference between the two models in terms of the storm track and strength of embedded features with the GFS favoring a somewhat more southward track with stronger troughs.  

For example, the GFS forecast for 0000 UTC 3 December (5 PM MST Saturday) has a strong, sharp, short-wave trough at upper levels over Idaho.  The 700-mb (crest-level) along the Idaho–Nevada border is 50 knots.  

In contrast, that same trough and flow in the Euro are weaker and precipitation, especially in northern Utah, is also weaker.  

Later in the storm cycle, at 0600 UTC 4 December (11 PM MST Sunday), the GFS brings another strong trough through.

But the Euro has a very different forecast with a trough up in the Pacific Northwest.  

These are very different forecasts and they reflect the challenges of forecasting the evolution of features (e.g., troughs and frontal systems) developing in and emerging from an intense jet over the western and eastern North Pacific and ridge off the coast of California and Baja California.  

I can't pick one of these forecasts over the others.  The troughs above are currently weak features embedded in the Pacific jet.  The models producing different forecasts tell us that their evolution over the next few days is someone chaotic and uncertain.  A stormy period beginning Friday looks likely, but just how big is hard to say and will depend a lot on how things come together over the weekend.  A GFS-like solution might give us a major storm cycle with 30-45" of snow through Monday.  A Euro-like solution is more subdued and perhaps in the 10-20" range.  Stuff at the upper end of the NAEFS is probably unlikely.  

Breath.  Keep expectations low and hopes high. 

A Sea of Stratus

It's pretty rare that stratus clouds, which otherwise are a zero on a meteorological scale of 1 to 10, can make for a great weather day, but they did today.  

Morning dawned in the Salt Lake Valley with dreary, grey overcast in the form of stratus clouds covering the entire sky (the image below taken looking south from the U at 8:12 AM).  However, a look toward the Cottonwoods showed a brighter spot, suggesting that perhaps there was hope for sun at high elevations.  

Source: University of Utah Department of Atmospheric Sciences

Sure enough, the Alta webcam showed clear skies above a Sea of Stratus over the Salt Lake Valley.  

Source: Alta Ski Area

And the morning satellite loop was really quite incredible with snow capped mountains, especially the central Wasatch, Southern Wasatch, and Uinta Mountains, sticking up above the Stratus Sea.  

Source: College of DuPage

And, as we started out ski tour from Alta at 9:52 AM, skies were clear, although stratus clouds hung in the central canyon.  

It's not uncommon for such clouds to work their way up the canyon during the day.  This is a result of thermally forced circulations.  Nocturnal cooling favors down canyon at night and in the early morning, which sometimes keeps the upper and middle canyon cloud free.  Then daytime heating results in up canyon flow with the stratus pushing up the canyon.  Indeed, when we returned to the car at 12:56 PM, shallow but thin clouds had made it to the Albion base area.

The cool thing about this was that there were just enough ice crystals around (some natural, but perhaps some artificial) for a nice atmospheric optics display with a 22 degree halo, sun dogs, and, if you squint, evidence of what is known as a parhelic circle cutting across the sun and through the sun dogs.  

When I lived in Innsbruck, such weather was common.  The meteorologists called the low clouds valley stratus.  Such clouds often filled the deeply incised valleys of the Alps, but spectacular weather prevailed above them at mid and high elevations.  I learned quickly to check the web cams to see if you could get above the clouds.  

That was definitely the case today, and we enjoyed spectacular views from the Supreme Area.  

We need more snow.  Think, pray, whatever. 

Thanksgiving Weekend Crap Shoot

Instead of arguing with your crazy uncle about politics this Thanksgiving, consider arguing about the weather instead.  There's certainly plenty of room for debate and disagreement if you are trying to forecast snowfall in northern Utah.  

The culprit is an upper-level trough that will develop and "dig" (move equatorward) over the Great Basin on Thanksgiving.  at 1200 UTC 23 November (5 AM MST Thanksgiving morning), the trough is forecast to be an open wave with no closed circulation and an axis that extends from Oregon and California. 

However, the trough is also diffluent, with an intense jet on it's upstream side and flow that weakens and fans out on its downstream side.  Such troughs are prone to amplification and digging, and that is exactly what is forecast to happen during the day on Thanksgiving.  By 0000 UTC 22 November (5 PM MST Thanksgiving), the trough has closed off over southern Idaho, and concomitant precipitation is moving into northern Utah.   

This is where things get interesting.  This is not a clean frontal system that just moves through the area with a well defined frontal band.  Instead, the system comes trough as a deep closed low.  At 0600 UTC 22 November (11 PM MST Thanksgiving), the circulation center at 700 mb is forecast by the GFS to be right over Salt Lake City. 

Systems like this tend to have an array of precipitation features that we can't reliably predict the intensity and location of at such lead times.  They also can produce a lot of changes in wind direction, which affects local orographic precipitation enhancement processes.  A look at the time-height section for Salt Lake City shows the arrival of cold, moist air associated with the trough at about 00Z Friday (5 PM MST Thanksgiving) with NW low level flow, then a shift to NE by 12Z Friday (5 AM MST Friday), NNE by 18Z Friday (11 AM MST Friday), NNW 00Z Saturday (5 PM MST Friday), etc.  I think you get the point.  Higher up, there is a progression from southwest to northwest over a two day period, but even that will depend some on the track of the low.  

The net impact of this is a lot of spread in what the models are putting out for snowfall.  For Alta–Collins, the latest GFS is putting out a storm total through about noon Saturday of 0.67" of water and 12" of snow.  Most of this falls from Thanksgiving afternoon through Friday evening. 

The euro only has about 0.38", but you can find heavier amounts elsewhere, such as in the Oquirrh Mountains and Uintas compared to the central Wasatch.  That's unusual, but it reflects the complexity of this system.  Who gets what and when depends a lot of the low-center track and embedded precipitation features.  

The SREF exhibits considerable spread, with a range from about 0.2-1.2" of water and 5–22" of snow.  

As they say in the Hunger Games, may the odds be ever in your favor.  

Looking Backwards, Looking Forwards

Pretty good weekend storm if you happen to be in the hallowed ground that is Little Cottonwood Canyon.  Based on the automated measurements, Alta-Collins got 5 inches of snow on Saturday (with .51" of water), far more than I was expecting (which would have been maybe an inch or two) to get the weekend off right.  Then another 14" with 1.54" of water on Sunday, bringing the storm total to 19".  

Watching the radar yesterday, it was very apparent that the economics of this storm was going to increase the snowfall wealth divide.  Given the northwesterly flow and shallow nature of the storm, echoes tended to be stronger and more persistent over the Salt Lake Valley, lower to middle Big Cottonwood Canyon, and Little Cottonwood Canyon than over the Park City Ridgeline (red line below) or south and east of the Alpine Divide between Little Cottonwood and American Fork Canyon (purple line), as shown in the example below.  

Thus, Alta and Snowbird, which flank Mt. Baldy (indicated on the map above) were often getting the goods.  Solitude and Brighton, despite not being far away, were often on the edge.  Park City and Deer Valley were often skunked.  If the Canyons-Daybreak automated snow depth sensors are accurate, they got 6 to 7 inches, far less than Alta and Snowbird. 

So, we are currently in a situation where high-north terrain, which has not suffered from losses due to solar radiation or rain, is getting there.  Alta-Collins currently has a 32 inch snow depth (this will likely decline some today).  My impression from skiing there on Saturday is that it may have rained at that elevation for a time during the storm last Wednesday Night, but there was no loss of snowpack.  On the other hand, below 9000 feet and even at upper elevations on the south or west side of the compass, there was little natural snow due to the sun and or the rain from that storm.  

More natural snow is needed, but we will be dominated by ridging and a return to mild temperatures until Thursday.  Late Thursday and Thursday night, the models are advertising a digging trough to develop over Utah.  The GFS brings in precipitation over northern Utah by 0000 UTC 24 November (5 PM Thanksgiving).

And then closes off the low over or just east of Utah through Friday.

The Euro advertises something that is generally similar.  The GFS puts out about 0.4" of water and 7" of snow with that system.  Most members of the downscaled NAEFS are in the .25 to 1 inch of water range with some higher outliers.  

So, another storm where it's wise to keep expectations low and hope we come in on the high end.  Don't read into the details at this stage.  

Incoming

Change is coming, albeit a temporary one, in the form of a digging trough that will bring a pretty good round of snow to the Wasatch on Sunday.

Until then, today (Saturday) will be a "meh" day with a few upper elevations now showers in the form of wet snow up high and rain below about 7500 or 8000 feet.  

But Sunday looks better.  The GFS forecast valid 1200 UTC 19 October (5 AM Sunday) shows the trough extending from the Washington coast into western Nevada with precipitation spreading eastward to northern Utah.  

During the day Sunday, we should get an extended period of mountain snowfall with the frontal passage and eventually, as pictured below, the cold northwesterly flow during the afternoon.  

This is not a prolonged storm cycle with multiple waves to really help build snowpack.  Snowfall will begin Sunday morning and probably taper off shortly after 11 PM.  The 6Z GFS is putting out a total (including the dribs and drabs today) of about 1.1" of water and 12.5" of snow for Alta Collins.  The wet-bulb zero level is forecast to be near 7500 feet by 5 AM Sunday so that means snow and not rain for the bases of the Cottonwood Canyon resorts to start, with snow levels dropping to near bench level by Sunday night.  

The HRRR is in pretty good agreement with about 1.2" of water and 15" of snow.  The greater snow totals are due mainly to a bit more at the end of the storm with higher snow-to-liquid ratios.  

Skiing later on Sunday or on Monday looks to be the call.  I'd lean toward the latter unless things come fast and furious on Sunday.  It'll be dust on dirt/crust in the morning and will need some time to stack up.

The NWS is going for 10 to 16" and that seems pretty good for me.  I might go for more if this storm was a bit more unstable and the northwesterly flow more persistent, but right now, that doesn't seem to be the case.  If we had a decent snowpack, this would like like a goldilocks storm with Monday a good day to call in sick.  

After this storm, the models look dry again until perhaps Thursday when another digging trough flirts with us.  Hard to say how that one will work out at this time.  Overall the pattern is one in which we have to live on whatever slips through the net from time to time.  I've yet to see a suggestion of a major storm cycle to really get things rolling.  This year we're just going to limp into the ski season, although the Sunday storm will help.   

Mixed-Bag Storm

Sort of a "mixed-bag" storm last night and this morning with some good and bad news.

The good news is that we got the precipitation that the models were advertising to develop.  The bad news is it was even warmer than advertised a day or two ago, with relatively high snow levels, at least for the overnight and early morning precipitation period. 

Automated observations from Alta-Collins show 0.81" of precipitation, which would be in the upper end of forecasts from a couple of days ago.  The bad news is that temperatures at Alta–Collins during the precipitation period were 34˚F to start and are currently sitting at 32˚F, so this was gloppy, wet snow adding up to only 3 inches.  

It may have even started as mixed rain and snow at that elevation (9662 ft).  Above that elevation, there's probably a pasting of high density snow.  

Below that elevation, it was even warmer at the base of Alta, which as of 7 AM was 35˚F.  As of 7:45 AM, the Mt. Superior Cam looking over the Albion Base area shows just scant snowfall, consistent with it raining to start and then perhaps changing over to snow in the recent past.  

So, a net gain at upper elevations, but no gifts below about 9000 feet.  

Looking at the latest radar, there's another area of precipitation moving eastward across the Salt Lake Valley toward the central Wasatch as I write this.

That and possibly a few more showers later this morning may add a bit more to the totals.  Expect snow levels to be roughly where they are now, near the base of Alta, although they could lower a bit if the precipitation rates really tick up.  

A Tricky One

For the past several days, some of our computer models have been producing a somewhat unusual banded precipitation event for northern Utah on Thursday.  I'm not sure what to make of it, but let's take a look.  

We'll begin with the setup.  Below is the GFS forecast for 1200 UTC 15 November (5 AM MDT Wednesday).   The upper-level flow off the Pacific coast is best described as "split" with a branch of the jet south of a deep low off the coast of California and a second branch over the Pacific Northwest.  The latter has a short-wave trough embedded in it (sashed line).  Over the Pacific Northwest, those two branches come together.  This is referred to as confluence by meteorologists.  

By 0600 UTC 16 November (11 PM MST Wednesday), the upper-level trough in the northern branch of the jet has moved over Idaho and a second trough that is pinwheeling around the low has is over the Sierra Nevada.  The confluent flow has shifted downstream to over northern Utah, Southern Idaho, and Wyoming.  

This looks like a fairly innocuous pattern, and up until this forecast time it is.  However, if you look at the precipitation pattern in the upper-right panel above, you'll see a weak precipitation band extending across Northern Nevada (see red circle).

That band then strengthens and by 1200 UTC 16 November (5 AM Thursday) it extends right across northern Utah (see red circle below) as the upper-level trough that was previously over the Sierra Nevada phases with the upper-level trough in the northern branch of the jet.  This band develops right in the confluent flow region, which is probably not a coincidence.  Such flow patterns, given the right environment, can generate circulation patterns that can lead to banded features of this type.  

The GFS is not overly excited about this storm.  The 6Z run spits out 0.25" of water and 2.2" of snow for Alta-Collins.  Most of the SREF members are in the 3-6 inch range, but about a quarter of the members are a bit more excited and generating 8-10 inches of snow.  

This is a tough forecast.  In the days before numerical weather prediction models, we would probably have no idea that such a band could develop and the forecast would probably be for fair weather.  The models are suggesting, however, that one will develop.  It is, however, fairly narrow, so what happens at a given point, say Alta, is dependent on both band intensity and location.  In the upper-end SREF forecasts, both of those things come together.  In the low end (and if you look carefully there are 3 members that do practically nothing), none of those things come together.  The GFS and SREF resolution is such that they probably overestimate band width.  In reality, things may be even more localized than they suggest.  

Keep expectations low (dust-on crust is most likely) but hopes high (maybe we can get lucky and get several inches).  Note that this will be a warm storm, with snow levels near 8000 feet to start, possibly falling to 7000 feet by late Thursday morning.  

Snow Report and Forecast

Update from Jim @6PM:  Due to an issue on our server, the NAEFS forecast used below is old.  Updated forecasts still show scant precipitation until the 16th.  Let's hope things look better after that.

----

Wait and see is the summary of the forecast today.  

Snow conditions on the "Collins Glacier" improved marginally this past week thanks largely to artificial snow which helped improve the cover a bit, although there are many areas even along the main line where the snowpack remains scant.  The view from Germania Pass pretty much tells the story and shows why Alta is hesitant to open.  There's still a lot of work to do before they have adequate top-to-bottom coverage on even a single run. 

The coverage is probably best in the high collection areas up high (Ballroom, Baldy Shoulder), at least in those areas that are not littered with big rocks, and ironically near the base where they have made a good deal of snow. 

Still, it's low-tide conditions.  I skied cautiously and still tagged a few.  

The NAEFS looks a good deal like it did on Thursday when I last did a post: Flatlined for most of the forecast period.  There are a few excited forecast members out there at the end of the forecast period.  

There's always hope in the extended-range forecasts but there's not point in getting excited until you can see the whites of the storm's eyes.  In this case, less than 20% of the ensemble members are producing ≥ 10" of snow and quite a few others are producing near zilch.  

It's worth keeping in mind that it's early.  We got spoiled the past two seasons with October snow, but some years the start of ski season is a slog.  

Mother Nature Continues to Tease

The start of ski season is always a bit of a crap shoot, even in Little Cottonwood Canyon.  Sometimes we get started in October.  Other times it can be deep into November.  What can be skied varies.

Two of the more memorable starts were in the early 2000s.  In 2001, snow was scant and the resorts were not open on Thanksgiving.  Then Alta got 100 inches in 100 hours during the holiday weekend and it was on.     

In October 2005 2004 (Editor: My bad!), we got pounded and Brighton was open not by Thanksgiving but Halloween.  

This year Mother Nature is electing to tease us with infrequent storms of modest size.  Per the Alta web site, 13.5" on October 11 and 12,  7.5" on October 26, and 11" on November 7.  Storm size and frequency have both been too small to establish a snowpack on sunny aspects, while a very marginal snow depth of 15" lingers at the Alta-Collins observing site.  Snow depth and water equivalent at the Snowbird SNOTEL are similarly a scant 5" and 1.5", respectively.  

The forecast is also a bit of a tease.  The GFS (and ECMWF) has a healthy cold front moving into the Pacific Northwest at 1200 UTC 11 November (0500 MST Saturday).  

That piques the interest, but the front falls apart as it moves inland, providing only some leftovers for the Idaho Panhandle and northwest Montana and just some clouds for northern Utah.  

The NAEFS is pretty much flatlined through November 15.  Then a few members start to tantalize, although there's a lot of spread if one goes beyond that and looks at the varying solutions for what will happen with the trough that is expected to develop near the west coast around that time.  

It is what it is.  Remember, it is early November.  Sometimes it takes time.    

Some Updates on weather.utah.edu

I'd like to share a few updates that we've made to products on weather.utah.edu since last winter. 

The Little Cottonwood forecast guidance derived from the HRRR (https://www.inscc.utah.edu/~steenburgh/ml/hrrrlccforecast.html) and GFS (https://www.inscc.utah.edu/~steenburgh/ml/gfslccforecast.html) has been updated with retrained machine learning algorithms that include last season in the training dataset.  An example from the GFS is below.  

We also added a temperature forecast for the Collins (9662 ft) observing site, which is a bit more representative of mid-mountain conditions than Mt. Baldy, which is still included as it is useful for ridge-top temperatures.

The new snow-to-liquid ratio (SLR) algorithm is based on a technique known as a random forest trained with observations from Alta-Collins.  It is more accurate and should produce a somewhat wider range of SLRs (up to about 25:1 if conditions are right) than the technique we used last year.  We thank Alta Ski Patrol and Alta Ski Area for continuing to provide access to weather observations and snow measurements so that we can produce products like this.  

We also updated the SLR algorithm used in our experimental HRRR snowfall products, and example of which is below.  

This also uses a random forest, but trained with data from 12 snow-safety sites in the western continental United States.  We thank everyone staffing those sites for providing data so we can develop products like this.  

I get a lot of requests for "point forecasts" from this product.  I'm trying to move away from autogenerating those.  Instead, you can do it dynamically for any point in the continental US at https://www.inscc.utah.edu/~steenburgh/hrrrqsfts/hrrrqsfts.html. This link is also available if you click on "Point Time Series" under HRRR-Snow (Experimental) in the left hand nav bar on weather.utah.edu.  Below is an example for Paradise Ranger Station on Mt. Rainier.  They will take a minute or two to pull up.  I recommend that you compare the elevation of the HRRR grid point (printed in the second graph) to your site as sometimes there are large differences that can be important for interpretation.  

We are also working on products from the Rapid Refresh Forecast System (RRFS) which the National Weather Service is currently testing and developing to replace the HRRR.  The RRFS is run at comparable grid spacing to the HRRR (3 km) and is currently run as a small ensemble with six members.  

Remember that these are experimental products and not official forecasts.  Feedback appreciated.  

Bike for Sale

If anybody is looking for a cheap bike, I'm selling my 2008 Cannondale Rush 26er for $200.  Full suspension (100 mm travel) carbon fiber frame (medium).  Lefty shock (the one item that has relatively low mileage as it is the 3rd one I had on this bike.  Tubeless.

Teeth on the rear cassette and front chainrings are worn down to nubbins.  

It was once a great bike, but has been lapped by new geometry.  Would work if you are looking for a Lefty shock, commuter bike, or maybe to get your kid into riding at low cost. I've been riding a different bike for a couple of years and need to get this one out of the garage.  

If interested, e-mail me at jim.steenburgh at gmail dot com.  

Collins Glacier Ski Report

I got out for a few turns of the year today on the "Collins Glacier."  Like most glaciers around the world, it's not in good shape right now.  Oddly, the coverage and skiing are probably best on the lower half where humans have decided to help.  

The snow there is firm but generally carveable, at least in the early afternoon when there's been some sun on it.  

The man-made coverage continues to lower Mambo.

There is, however, a gap in coverage just above the angle station that seemed to be growing in size in today's sun.  

It gets grim in places with sun exposure.  

Coverage improves again in Ballroom and environs, although the snow conditions there were challenging, especially for the first turns of the year.  There are also some Great White Sharks looming in places, just waiting to take a bite out of your skis.  

We need snow.  Next shot is on Tuesday, although there's a great deal of spread in how productive that storm might be.  

Some Climate Stats

October is in the bag.  I would describe it as fairly meh with nothing too extreme.  

At the Salt Lake City International Airport the average temperature was 55.9˚F.  This was warm, but not exceptionally so, rating as the 24th warmest October since 1874.  

Source: https://xmacis.rcc-acis.org/

The airport recorded 1.97" of precipitation.  A bit wet, but not exceptionally so, rating as the 36th wettest October since 1874. 

Up at Alta, the cooperative site in town recorded 4.01" of water and 14.9" of snow.  The records for that site are fairly spotty so good long-term comparisons are difficult.  The ski area, which measures higher on the mountain, reported 22", compared to an average since 1980 of 26.6".  

Essentially it was a Goldilocks October weather wise in northern Utah.  

Utah has not had a statewide average annual temperature below the 20th century average since 1993.  Numbers through October are not yet available, but through September, we were just barely above the 20th century mean of 51.0˚F with an average temperature of 51.1˚F.  

I suspect October will push us just a bit higher above the 20th century average.  Whether or not we can have year below average will depend on what happens from here.  Other years since 1993 have been close (2008 and 2011), but have ultimately come in above the 20th century average.