The Next Storm

The parade of warm and windy storms continues this week.  Today and tonight we may see a mountain snowshower at times, but it won't add up to much.  

Tomorrow afternoon is when things begin to get interesting.  The GFS forecast for 0000 UTC 15 March (6 PM MDT Tuesday) shows a Pacific cyclone moving across northern Nevada with the trailing frontal trough extending across northern California and the Bay Area and the accompanying atmospheric river producing moderate vapor transport across southern and central California.  

The lower right-hand panel in the GFS forecast above is an analysis of integrated vapor transport (IVT) magnitude (color fill) and vectors.  Note that the strength of the atmospheric river, as indicated by the magnitude of IVT, declines with inland extent, as is often the case. This occurs due to the loss of water vapor to precipitation.  These losses are especially large over the high Sierra south of Lake Tahoe, which is why there is often minimum downstream of that high barrier over Nevada, as is the case in the GFS forecast above.

During this period, Utah is in strong southerly flow.  This pattern persists through 1200 UTC 15 March (6 AM Wednesday).  The IVT in Utah is generally near or just below low-end atmospheric river magnitude (250 kg/m/s; yellow shading) through this period.  

Thus, we would expect periods of valley rain and mountain snow late tomorrow and tomorrow night.  The models do differ quite a bit on amounts during this period.  For example, from 12 PM MDT Tuesday to 6 AM MDT Wednesday, the 6Z GFS produces 0.41" of water equivalent and 2.9" of of high-density snow for Alta Collins.  In contrast, the 12Z HRRR produces 1.32" of water and 7.9" of high-density snow.  

I suspect the fundamental difference in this case is topography, with the finer-scale HRRR topography yielding more precipitation than the GFS.  That said, we have seen the HRRR overproduce sometimes in situations like this in which the synoptic forcing (e.g., associated with fronts) is weak.  That's not a guarantee, however.  I'm inclined to go with something like 5-10" of high density snow for Tuesday afternoon through 6 AM Wednesday, using the HRRR as near-upper-end guidance.    

But wait, that's not the end of the storm.  During the day on Wednesday, the main upper-level trough and cold front move through.  The GFS currently puts the trough at crest level right over northern Utah at 2100 UTC 15 March (3 PM Wednesday).  The ECMWF HRES has similar timing (not shown).

As things look now, this has the makings of a good day for storm skiing on Wednesday.  The GFS is really cranking out the precipitation during the day on Wednesday.

Overall, this looks to be a higher-density storm.  We might end with some low-density snow on Wednesday if we don't shift to graupel (although I like graupel, so either way its a win).  

Bottom line is that more snow is coming.  Enjoy.  

Gone with the Wind

Given that it is the U's spring break, I was fortunate to be able to get away for a ski tour yesterday.  It was a spectacular day, with fantastic snow and great skiing.  

The Wasatch looked amazing.  The snowpack is deep and the cover extensive.  It's the time of year when the north aspects are beginning to emerge from 24-hour shade and see the sun, making the views even more impressive.  A group of four clearly had a nice run down Stairs Gulch early yesterday.  

I spent most of the day reminiscing about what a great season it has been so far and what a remarkable run of cold snow and cold powder we have had.

As we discussed for several days, the storm track is shifting and we are moving to a warmer and windier pattern.  Indeed, except perhaps in a few highly wind-protected spots, yesterday's powder is now gone with the wind.  Gusts overnight reached over 90 miles per hour at ridge-top locations.  Temperatures have climbed to near freezing at 7500 feet already.  There may still be some good mid-elevation powder on north aspects in a few places, but the damage is being done from the top down and the bottom up.  

On the plus side, there is a storm brewing for today and tonight.  The two key ingredients are strong vapor transport associated with an inland penetrating atmospheric river and a frontal pushing in from the west.  At 0000 UTC 11 March (5 PM MST Friday), the atmospheric river is draped over northern Utah just ahead of the front.  

By 0600 UTC 11 March (11 PM Friday) the front is just south of the Cottonwoods.  

And by tomorrow morning it is through and we are post-frontal, although this is not a situation we would expect the Alta post-frontal magic to kick in as it's simply not unstable enough to generate orographic or lake-effect snow showers tomorrow morning.  

Looking at our GFS and HRRR derived forecasts provides a decent look at the range of possibilities between now and tomorrow morning.  The GFS  cals for mild conditions today and through this evening with Mt. Baldy (11,000 ft) temperatures in the low 20s and the wet-bulb zero level near or just above 8000', which would indicate a snow level near or just above 7000 feet.  Snow-to-liquid ratios are between 5 and 9 during this period, meaning high-density snow at upper elevations with periods of light precipitation.  After this evening, temperatures and the wet-bulb zero drop and snow ratios increase.  For Alta-Collins, the GFS generates 0.89" of water and 7.3" of snow through tomorrow morning.  

The HRRR is warmer and wetter.  It pushes temperatures on Mt. Baldy to 25˚F this afternoon and the wet-bulb zero level to 9000 feet, which would result in a snow level that flirts with the base of Snowbird and Alta.  It is also wetter today and with the frontal passage, generating 1.77 inches of water and 12.3" of snow for Alta-Collins through tomorrow morning.  

My synopsis is that these two model forecasts probably represent a reasonable range for the forecast through tomorrow morning, so my expectation is for 0.8 to 1.8" of water and 7-14" of snow at Alta-Collins by 8 am tomorrow.  Then the storm will be over.  This will be high-density snow and ski quality will probably depend on how much snow comes in the later stages of the cold-frontal passage when snow-to-liquid ratios are higher.  More snow then would at least give a right-side up profile.  

At lower elevations, expect rain today and this evening.  Some snow is possible on the benches or even on the valley floor late in the frontal passage tonight, but it won't add up to much. 

As most of you have probably heard, two skiers were buried in an avalanche yesterday in the Uintas, with one killed.  A preliminary report is available here.  I share my deepest condolences with their friends and family.  

January in March Is Coming to an End

The pattern over the last couple of weeks has been a really great one for late February and early March with lots of cold storms and high-quality snow.  Many mid-elevation areas have a remarkably deep snowpack right now and outstanding ski conditions.  Sure the snowpack is deepest in Little Cottonwood, but I had a meeting in Park City yesterday and was blown away by the amount of snow in town.  I had time for a few laps at Deer Valley and couldn't help but take a photo of the towering snowbank at the top of Sultan.  This is an area that is heavily windloaded, but still, very impressive.  

The view eastward showed a frozen Jordanelle Reservoir and nothing but snow-covered landscape.  Even the south aspects and under-development Mayflower resort have snow.  What a season!

Ski conditions were outstanding with a few inches of cold powder.  It felt like January, but with an epic late season base.  

Change is coming though as we will transition to a warmer pattern later this week.  For tomorrow, however, there is one last cold-powder refresh coming, with a weak trough moving through later today and tonight.  By 1500 UTC (8 AM MST) tomorrow, the 6Z HRRR is putting out about 7" for Alta, just over 5" for Canyons-Daybreak, and about 4" for Deer Valley-Ontario.  

The GFS is also right around 7" for Alta.  I'll call it a 6-12" refresh for Alta and hope we come in on the top of that range.  Additionally, snow-to-liqiud ratios for this one will continue to be higher than average.  

After that dump, change is coming. Temperatures will climb during the day on Thursday.  The next storm, slated for the Friday and Friday night, will be warmer and windier.  There will be snow, and it could ski quite well, but it will be a change from the cold events we've had of late.  Overall, the pattern will remain active, but shifted toward warm and windy events.  Nothing to complain about, but January in March is over after Thursday.   

You Ain' t Seen Nothin' Yet

We begin this Monday
The first day of spring break
With a little from BTO
Because as I look at the forecast
All I can think is
You Ain't Seen Na-Na-Nothin' Yet

The numbers for the past season, each month of the season, the past month, the past week, and even the past two days are astounding.  600+ inches of snow at Alta.  Another 15" last night.  Alta-Colllins snow depth at 7 am: 185 inches!

And our friends upstream in California?  The Central Sierra Snow Lab near Donner Pass reported yesterday that the've had a season total of 562", within a foot of the epic 2016/17 year total, with 2-4 feet in the forecast.  

We have a deep 30.5" (77.5 cm) of new #snow that has fallen over the last 24 hours. Our season total is now 562" (14.29 m) and we're now within one foot of the 2016/2017 winter snowfall total.

We're expecting another 2-4 feet through tomorrow and more this week!#CAwx #CAwater pic.twitter.com/eQE40GPSvS

— UC Berkeley Central Sierra Snow Lab (@UCB_CSSL) March 5, 2023

But as crazy as you think this season has been, it's about to get crazier.

The recent pattern has been dominated by high-amplitude ridging over the north Pacific and a deep trough along the Pacific coast.  This has resulted in a series of cold storms across California, Nevada, Utah, etc.  The GFS analysis for yesterday morning (1200 UTC 5 March) shows this well.

That pattern will bring more snow for both California and Utah this coming work week, but change is coming.  As shown in the GFS forecast, by 1200 UTC 10 March (5 AM MST Friday), the subtropical Pacific Jet will extend across the eastern Pacific and onto the Pacific Coast where it merges with the polar jet dropping down from Alaska.  

This is an important shift in the pattern and the corresponding GFS regional forecast below shows a potent atmospheric river, what we would have once called the Pineapple Express, directed right at California with the parent cyclone making landfall over the Pacific Northwest and trailing cold front across California.  So, after all of this snow, we transition into a windy and warm storm pattern with 700-mb temperatures in the Tahoe area of -1˚C on Friday morning.  Sorry Tahoe, no more blower pow for you!

That system ultimately spreads into Utah giving us wind and warmth Friday night with a big system potentially following.  

It's a bit early to talk confidently about details, but let's take a look at what the GEFS ensemble is doing.  At the Central Sierra Snow Lab, after the snowfall during the work week, the downscaled NAEFS shows the action picking up around 6Z 10 March (11 PM MST Thursday).  There are, however, a wide range of forecasts.  Some only generate an inch or two of water equivalent (which when added to the precpitation since last night adds up to about 3" of water for the week) but some go off.  The mean for the week is about 7 inches of water and, this will be a warm storm.  Our snow-to-liquid ratio algorithm suggests ratios certainly less than 10:1 and some ensemble members call for rain at this 7000' elevation.  Batten down the hatches!

For Alta-Collins, one can also see significant spread after 6Z 10 March as much depends on the track of the storm and atmospheric river.  Regardless, over the 7-day period (including last night), most of the downscaled ensemble members are producing between 2 and 5 inches with a mean of just over 3. 

The low-end scenario is that the system tracks to the north and we get wind and warmth but not as much snow.  We still get a decent amount of snow.  2" of water equivalent and 20-25" of snow this week (including last night) would be at or just above what we would expect from climatology.  High end scenarios are more than double that.  

So, insanity to continue this week, but expect a change to a warmer pattern later in the week.  You ain't seen nothin' yet.  

Mother Nature Can't Be Stopped!

Do you ever wonder what it would be like if it started snowing and never stopped?

- Steve Casimiro, Editor, Powder Magazine, 1987-1998 

The epic 2022/23 ski season continues. How I have wanted to write a sentence like that since the 2010/11 season!

I wasn't sure what to expect for yesterday, but lo and behold it turned out to be another pretty good day of ski touring. 

I got home and took a quick peek at the 18Z HRRR and it was only putting out about 0.37" of water and 4" of snow at Alta and I though maybe things wouldn't go off for Sunday.  Then at about 3 PM yesterday it started snowing.  Then i picked up to 2-3" per hour snowfall rates.  And by 8 PM there was 10" on the Collins stake.  Then it kept snowing.  They are now up to 21" based on the automated interval observations.

What can I say?  Mother Nature can't be stopped.  She continues to produce.  Total snow depth at Alta is now up to 178".  

Keep skiing. 

Seasonal Stats Update

Winter is over.  I repeat.  Winter is over.

Meteorological winter that is, covering December to February.  I could talk about the snow to come, but the forecast has changed little.  Periods of snow for the forseeable future.  Enjoy.  

So let's look back and look at some stats, starting with the Salt Lake City International airport.  

The average temperature for this winter was 33.0˚F.  That slots in as the 49th warmest out of 149 winters in the period of record.  No biggie in that regard.  

Source: https://xmacis.rcc-acis.org/

I get a lot of gripes about the observations from the airport, but if we look at Bountiful Bench, with complete records back to 1975, it rates as the 20th warmest out of 49 winters.  Still above median.  Basically, the winter hasn't been unusually cold or warm.  It's just a bit above median for temperature.  

How about snow?  For this, I'll look at the period from October 1.  We'll call this the water year through February.  The airport slots in with 56.4".  That's the most snow we have had for the water year to date since the 2013 water year and rates as 24th out of 139 seasons in the period of record.  

Source: https://xmacis.rcc-acis.org/

There is an asterisk though.  Snowfall records are not as complete (hence 139 seasons rather than 149 for temperature) and there are a few seasons that have some missing days, including this one which is missing one day (yesterday...I'm not sure why...and that might add an inch or two).  

In any event, it's been snowy, although a couple of weeks ago the airport numbers were not as impressive for snow as we discussed in a previous post.  The big storm on February 22 helped  push us a bit up the list.  

A lot of people have asked me about the benches.  Again I'll use Bountiful Bench only because it has a complete record back to 1975.  So far the snowfall there is 113", good for 10th out of 49 years.  That's pretty good.  The record for the water year to date at that site is 174.7" in 1993.  

Of course in the mountains the snowpack is fat. Relative to observations from 1991–2020, snowpack water equivalent at basins across Utah ranges from 135% (Upper Bear) to 325% (Lower Virgin) of median.  

Source: NRCS

For watersheds covering northern Utah ski areas, the numbers range from 142% to 165%. For the Jordan, which covers the western portion of the central Wasatch, we are just a shade below the highest since 1990 with an average of 28 inches of snowpack water equivalent at the eight snotel observing sites in the basin.  If you are wondering, the highest is from the 1997 water year (28.4 inches).  

Source: NRCS

By and large, a very very good situation.  If you are looking for a reason for heartburn, here's one.  The Bear River is the biggest tributary of the Great Salt Lake, and the snowpack is not quite as exceptional there (but still well above median).  For instance, below is the situation in the upper Bear.  Average SWE is 17.4 inches, which is pretty good for the year to date, but still only 92% of the median peak [indicated by green X...and higher than the daily median (green line), which smooths out the peak].

Source: NRCS

By and large, the forecast continues to look good for the forseeable future, so we should be adding to these numbers over the next 7 to 10 days.  Enjoy!