Tuesday, April 13, 2021

Dirty Harry Forecast

Yes, I know the wind is blowing, but my time this week is limited and I'm more interested in whether or not I can have another powder day this season.  

The forecasts through 1200 UTC (6 AM MDT) Thursday vary tremendously depending on what model you look at.  Some promise dust on crust for Thursday, others a deep-powder day.  

Below is the 1200 UTC initialized GFS total accumulated precipitation over the 48-hour ending at that time.  For the mountains of northern Utah, this is a wet forecast with over an inch of water equivalent for the Alta area.  

Source: Tropical Tidbits

The 0600 UTC GFS was even wetter.  Below is the meteogram for Alta from that run showing heavy precipitation starting tomorrow and continuing tomorrow night, with over 2" of water and 25 inches of snow by Thursday afternoon.  Whoot whoot!


On the other hand, the 1200 UTC HRRR is much drier.  Our area appears to be in a dry slot with the heaviest precipitation to the north.  Water totals at Alta through 1200 UTC (6 AM MDT) Thursday are less than a half inch.  Dust on crust.  


The majority of downscaled SREF members lean towards the HRRR-like solution and produce about 0.5" or less of precipitation, although there are 3 that go for bigger amounts of an inch or greater.  


On the other hand, most of the NAEFS members are wetter like the GFS and suggestive of deep powder.  


With model guidance like this, you must ask yourself one question...





Sunday, April 11, 2021

Spring Ahead

Forecasts for the coming week look to be spring like, but are uncertain in terms of precipitation details.  The GFS forecast valid 0000 UTC 15 April (6 PM MDT Wednesday) shows a cold, closed low parked right over northern Utah.  


That would favor colder, unsettled weather, but other models have different ideas concerning the position of the low and associated precipitation features.  

Let's start with the easy stuff.  Tomorrow (Monday) will be dry and cool.  After that, the possibility for showers increases on Tuesday as the low digs southward into the Intermountain West. Wednesday may be unsettled, with the possibility of lingering showers on Thursday.  

It's difficult, however, to pinpoint details.  The 0900 UTC initialized Short Range Ensemble Forecast System forecast through 0000 UTC 15 April (6 PM MDT Wednesday) shows enormous spread with a several members producing little or no precipitation at the Salt Lake City Airport, but some others producing more than 0.4 inches.  

An additional complication for Wednesday (and Thursday) is that snow levels could be down to the benches and potentially the valley floor.  It's too soon to say if things will come together for bench accumulations.  Much is going to depend on the track of the low and the associated precipitation features.  

The bottom line is this is a spring-like pattern with the potential for precipitation.  Best to keep an eye on forecasts over the next few days as forecasts are likely to evolve.  

Wednesday, April 7, 2021

April Powder Brings June Flowers

It's impossible to know when we will have the season's last powder day, but if today was it, that's OK.  

With perhaps 15-20 cm of new snow, Room of Doom in upper Mineral Fork was ours this morning.  One could feel the stout melt-freeze crust at times, but the skiing was still fun.  

Given our fair snowpack conditions, this storm was desperately needed.  We need more, but every little bit helps.  Some of the moisture from this most recent snow will evaporate into the atmosphere.  Some of it will be used by plants.  Some of it will recharge our soils, which are remarkably dry.  And some of it will enter Big Cottonwood Creek and provide the water we all need for taking showers, flushing toilets, and watering gardens.  Thus, it is not a stretch to say that April powder brings June flowers, at least in this part of Utah.  

The view below from the top of our climb shows the upper reaches of the vast Mill-B South drainage, also known as Lake Blanche Fork.  What you see in white is our summer water supply and one of Salt Lake City's most important water towers.  

Let's give thanks for the snow we have and hope that next season is better.  



Monday, April 5, 2021

Winter Returns (Sort of)

Yesterday we tied a record for April 4 with a maximum temperature of 79˚F at the Salt Lake City International Airport.  Impacts on snow aside, the weather was about as delightful as it could be in early April.  It's a bit of a shame we can't bottle up a day like that and open it up in mid July.  

It was very warm in the mountains as well with Alta setting a new maximum temperature record of 58˚F.  

The heat has done its damage as several SNOTEL sites have seen declines in snowpack snow water equivalent, despite their relatively protected locations, indicating that the snowpack has ripened and begun to decline to melt.  Parley's Summit SNOTEL, which is on a north aspect, dropped from 15 inches on April 1st to 12.2 inches last night.  

Source: NRCS

Even upper-elevation Brighton saw a decrease in snow water equivalent.  This site is a bit sunnier than most SNOTELs, but this is a substantial drop for early April.  

That all ends after today, at least temporarily.  A strong cold front will pass through northern Utah later today.  The latest HRRR forecast has the cold front arriving in the Salt Lake valley around 0000 UTC (6 PM MDT) this afternoon.  Expect a breezy afternoon ahead of the front as well.  


I suspect it will be an exciting period with and following frontal passage due to the strong winds and the instability that accompanies and trails the front, which could lead to some thunderstorms.  

Overall, the system is one that has an upper-level low that is tightly wound and moisture is limited primarily to northern Utah.  Precipitation will likely be greatest in the northern Wasatch.  Our downscaled GFS snowfall product shows absolutely nothing south of the Provo-area mountains, 4-8 inches in Cottonwoods, and the heaviest snowfall in the northern Wasatch and Bear-River Ranges. 

Most members of the downscaled SREF for Alta lie between 4 and 12 inches. The large range partially reflects sensitivity to the track and structure of the close low.  A few have a skunking, but there are a couple that go for bigger amounts.  


I think the most likely amounts are 4-8" for Alta-Collins, but it could be less or more depending on the gory details.  Truth be told, these are the situations where I just plan on waking up in the morning and seeing what happened. 

After this storm, it will likely be dry with a return of spring through next weekend.  There are a couple of brush-by systems that maybe could bring a few showers, but that's about it.  

Saturday, April 3, 2021

Alta and Snowbird Skiers Need to Up Their Game

 In recent years, a wiggle (or snake) has appeared at Alta or Snowbird.  

Some get excited about these slope enhancements, but not me.  

During my sabbatical in Innsbruck, I encountered figl skiing, or figln (see Tirolean Figln).  Figln becomes a thing in April at Nordkette ski resort above Innsbruck in April and involves the use of short skis to go downhill, using the tails to control speed.  As I understand it, the history of figln derives from mountaineering as the light, short skis could be used to quickly descend remarkably steep slopes back in the day.  The Nordkette has ideal conditions for Figln as it is steep (especially off the upper Hafelekar Tram) and south facing.  

Here's a video demo.  Start at about 1:12 for the Hafelekar footage and slot-canyon experience at about 2:10.  

Bottom line: Alta and Snowbird skiers need to up their game. 

Thursday, April 1, 2021

April Fools Snowpack Update

April 1st is near the time of peak snowpack for many Utah SNOTEL stations.  On average, lower elevations peak earlier than this, whereas upper elevations peak later, but April 1 is traditionally a good date for getting an idea of how fat the snowpack is for the spring runoff.

This year's April 1 snowpack is no joke, with the vast majority of stations below median (note the plots below are technically through March 31).

To show this, below is a plot of the percentile snow water equivalent.  This percentile represents that percentage of previous seasons in the period of record with a lower snowpack snow water equivalent (SWE) than current.  A value of 25 means that 25% of the seasons have less (SWE), whereas 75% have more.  The higher the percentile, fatter the snowpack compared to past seasons. 

Many Utah SNOTEL stations are at or below 37.5, some well below.  A handful are near or above 50.  This includes sites in the northeast Uintas, and scattered about in central and northern Utah.  

NRCS

For sites in the central Wasatch, Mill D North is at 44, Snowbird 32, Brighton 18, and Thaynes Canyon on the Park City side, 13.  This hasn't been a great snow season, but it has been especially bad on the Park City side of the central Wasatch, which is a bit of a double whammy since that area climatologically gets less snow in the first place.  

A look at the seasonal snowpack trace shows there is currently 16.3 inches of water equivalent at Thaynes Canyon (elevation 9247 feet).  Only 12% (4) of the 33 seasons in the period of record were worse than this on this date.  Median for 31 March is 21.5 inches, so we sit about 25% lower in SWE compared to a winter in the middle of the distribution.  

NRCS

The natural advantages of Little Cottonwood become apparent when you look at Snowbird (9177 feet), which is at a comparable elevation, but the SWE is nearly double that at Thanes Canyon (29.7 inches).  However, by Little Cottonwood Standards, this is still only good for the 32nd percentile.  Basically, 2/3 of the seasons had a fatter snowpack then we have presently.  

NRCS

What can I say.  It hasn't been a great snow season.  Maybe next season will be better.  There's always hope for the future.