Mainly Quiet on the Western Front

The current snowdepth at Alta Collins sits at 83" after peaking at 92" on Saturday.

Some people have asked me about the prospects of a Steenburgh Winter this year, that period from when Alta-Collins first reaches 100 inches to February 10th when the mid day sun angle and day length start to really increase and have an increasingly caustic influence on snow, first on south aspects and eventually as we go deeper into spring on all aspects.  Steenburgh winter is the creme-de-la-creme of backcountry ski conditions with a deep snowpack to enable good coverage across a lot of terrain and low-angle sun for powder preservation.

The potential for the start of Steenburgh winter looks quite low for the next ten days.  Ridging is in firm control currently along the Pacific coast this morning.

That ridge meanders a bit, but remains in place really for the next 10 days or so.  About all we can hope for is a trough to slide down its front side and drop into our area.  Unfortunately, such systems are often fairly moisture starved.  Below is an example from the GFS forecast valid 5 PM MST Sunday. 

The Utah snow ensemble thus has just a couple of weak systems coming through such as the one above, with some variations in intensity and timing between the ensemble members.  There's always the hope that one of those systems gives us a decent dump of low-density dendrites, but 75% of the members are producing less than 6" of snow over the next 10 days.  

Thus, I'll call it mainly quiet on the western front, with the hopes that we at least get a little bit of a refresh with the passage of one of these moisture starved systems.  Sometimes a bit of moisture and instability does the job in Little Cottonwood, so maybe we'll get lucky, but the start of Steenburgh winter looks unlikely during this period.  

A Banner Season in Japan

There's so much bad news on the weather front in the US due to the wildfire catastrophe in SoCal, that I thought I would talk about something more uplifting: The remarkable snow season that they are having in Japan.  

I like to say that if Utah has the Greatest Snow on Earth, but Japan has the Greatest Snow Climate on Earth.  Really, there is nothing like Japan's "Gosetsu Chitai" or heavy snow region near the Sea of Japan.  It is the snowiest, densely populated region on Earth with Sapporo the snowiest city in the world with a population of more than 1 million and Sukayu Onsen in the Hakkoda Mountains in northern Honshu the snowiest inhabited place on Earth.  The numbers below are based on 1981-2010 climate normals.

There are three things that make Japan's Gosetsu Chitai so special for snow.  First, it lies downstream of Eurasia, the world's biggest continent, which results in frequent and prolonged cold-air outbreaks over the Sea of Japan during the East Asian Winter Monsoon.  Second, the Sea of Japan is an enormous body of water, 12 times bigger than Lake Superior, the largest of the North American Great Lakes.  The Tsushima Current that flows through the Korea Strait also ensures a steady supply of warm water along the Japanese coast during the winter.  Third, the sea-effect precipitation systems that form over the Sea of Japan (basically the equivalent of lake-effect snow) run into the formidable topography of Honshu and Hokkaido Islands.  

Utahn's are rightfully proud of the snowfall in Little Cottonwood Canyon, but it is worth comparing the numbers from the Town of Alta to Sukayu Onsen.  Not only is the seasonal snowfall more plentiful at Sukayu Onsen, but after a slow start in October and November, it also comes much faster, especially during the peak of the East Asian Winter Monsoon from December to February.  Basically, climatology is a 3-month pig wallow with an average of more than 140" in each of those months, peaking at 180" in January, more than double the Town of Alta.  

This year the snow in has come fast and furious, with skiasia.com reporting remarkable snow depths last month.  Current snow depths in central Honshu include 169 cm/67" at Shirakawa (478 m/1568 ft elevation), 150 cm/59" at Tsunan (452 m/1483 ft), 163 cm/64" at Oisawa (440 m/1444 ft), and 188 cm/74" at Hijiori (330 m/1083 ft).  All of these sites are south of 38.6ºN and at relatively low elevation.

Source: JMA

Given that the Japanese Meteorological Agency (JMA) does not have any high elevation observing sites in central Honshu, I took a look at the snow report for Hakuba Cortina Ski Resort in the northern Hakuba Valley near the Sea of Japan (location on map below).  It is reporting at current snow depth of 340 cm/134 inches.  Event that is probably an observation from below 1400 m/4593 ft as the resort is on the lower slopes of the Hida Mountains.  

Source: Google Maps

A look at the map above for central Honshu illustrates the remarkable transition in snow climate across Japan.  At low elevations near the coast, snow depths are < 35 cm/14".  These areas are actually quite wet during the East Asian Winter Monsoon, but they experience more precipitation in the form of rain.  Going inland and up in elevation and you get into much deeper snowpacks, even at the lower (< 1600 ft) observing sites operated by JMA.  Go across the mountains to the east side of Honshu and there is no snowpack at lower elevations.  

In northern Honshu and southwest Hokkaido, Sukayu Onsen (890 m/2920 ft) is at 380 cm/150", which is down from their peak at over 400 cm.  Kutchan (176 m/577 ft), which is near the base of the Niseko United Resorts, is at 147 cm/58".  

Source: JMA

Media reports suggested that Kutchan was at record snow depths at times in December.  I suspect that's not the case currently, but cannot confirm this.  Regardless, it is an impressive start to the Japanese snow season.  

About Yesterday's Snow Bomb

Impressive snow totals and snowfall rates occurred yesterday in Little Cottonwood Canyon.  The big winner was Alta.  As readers of this blog are well aware, the Alta Ski Patrol maintains a great snow-study plot in the upper elevations of Collins Gulch.  The hourly measurements from this site are a treasure trove to meteorologists like me who are starved for observations from higher-altitude locations.  The "snow interval" data below is collected by an ultrasonic snow-depth sensor that is mounted on a pole above a white snowboard that is wiped every 12-hours.  It recorded 20" of snow over and 11 hour period prior to being wiped just after 1600 MST.  

Really, the 20" mark was attained in only 9 hours, from 0400 to 1300 MST, yielding a mean snowfall rate of more than 2 inches and hour for that period, with a peak snowfall rate of 5 inches from 0600 to 0700 MST.  Due to roundoff of the measurement, there is a little uncertainty in that estimate, but it's safe to say it was snowing very hard at that time.  A bit more snow fell 1300 MST, but its rate of accumulation was roughly balanced by new-snow settlement, so the final tally remained 20 inches.  

Observations from Mt. Baldy show that the first 6 inches fell as the flow switched from WSW to WNW and the temperature dropped about 4F from 0400 to 0600 MST.  That indicates a frontal passage, but even during this period, there wasn't a strongly organized frontal band, although there were scattered showers and clear evidence of orographic modulation of the precipitation, meaning related to flow interaction with the topography.  Radar imagery at 0425 MST (1125 UTC) when snow was picking up at Alta showed strong modulation of radar echoes by the Oquirrhs and the Wasatch with echoes strongest over and/or windward of those features and strong precipitation shadowing in their lees, including over the western Salt Lake Valley.  So, this was very much an orographic storm right from the beginning. 

During the period of heaviest snowfall from 0600 to 0700 MST, the flow on Mt. Baldy was WNW and radar coverage became more extensive.  Still, echoes were strongest over and windward of the Oquirrhs and Wasatch Range, including the northern and central Wasatch and weakest over the western Salt Lae Valley.  

Finally, by 0848 MST (1548 UTC), the influence of the Oquirrhs and central Wasatch remain apparent, but there is also an elongated band of higher reflectivity extending from the Great Salt Lake to the central Wasatch.  

We have done computer model simulations of similar storm periods in the past in which we were unable to reproduce such a precipitation pattern unless we included both the lake and the topography.  Below is an example from one northwesterly flow storm in which we ran with the best representation of the lake and terrain possible (CTL), removed the lake and the topography (FLAT-NL), removed only the topography (FLAT), included the lake and the Wasatch (WAS), included the lake and the downstream terrain but no upstream terrain (DT), and removed the lake (NL).  There's a lot to digest there, but if there's no topography, the event only produces some light downstream snowshowers.  If there is no lake, only light precipitation occurs over the higher terrain including the Oquirrhs and central Wasatch.  However, when you run with them both (CTL), you get a solid storm.  Thus, both lake- and terrain-driven processes contribute. 

Source: Alcott and Steenburgh (2013)

I suspect this may have been the case for this later stage of the storm yesterday, although that's just a hypothesis at this point.  Overall though, I see yesterdays storm as one that was strongly driven by flow interaction with topography, with perhaps some lake influences thrown in later in the event.  

A few more thoughts

Yesterday's storm was impressive for snowfall rate as measured by depth, but less of an outlier from a water-equivalent perspective.  The 20" of snow that fell had a water content around 5%.  During the period when 5" fell, only 0.15" of water equivalent was observed.  That would be around 3% (although that estimate may be a little low due to gauge undercatch of snowfall).  Peak 1-h water equivalent rates were around 0.17".  That's not bad, but it's also not exceptional.  If you are wondering, the highest 1-h water equivalent was 0.17".  That's not bad, but it's also not exceptional.  The record hourly water equivalent snowfall rate at Alta-Collins is 0.54", which occurred from 0300 to 0400 MST 5 Jan 2008 in southwesterly flow accompanying a "warm and juicy" atmospheric river event just ahead of an approaching trough.  

I share these observations to highlight to different ways that one might measure and evaluate extreme snow rates.  One is based on snowfall amount.  The other is based on water equivalent amount.  Yesterday's snowfall extreme occurred due to the high snow-to-liquid ratios (i.e., low water content).  From a water perspective, it all that impressive.  Storms that produce high water equivalent rates are often warmer, with lower snow-to-liquid ratios, yielding lower snowfall amount rates.  For these storms, my eyebrows pick up when we start approaching 0.3" per hour.  

Thus, much depends on the metric that you use, although none of these scientific semantics take away from what I hear was an outstanding day of skiing. 

Yes, 2024 Was Warm

Final numbers will become available in a few days, but it is likely that 2024 will be the warmest year on record globally.  I'm not sure if the difference from 2023 will be statistically significant, but that doesn't really change the story of long-term warming.  

With an average temperature of 57.4F, it was also the warmest year on record in the Salt Lake City area based on observations collected by the National Weather Service, and by a pretty wide margin.

Source: https://xmacis.rcc-acis.org/

If fact, it beat the previous record holder, 2012, by 0.8F.  Given the inevitable grousing about the representativeness of the airport site, I'll also add that this was also the warmest year on record at the Bountiful Bench site, which has continuous records back to 1975.

That site observed an average temperature of 55.0F, topping the previous record holder, 2012, by 0.6F.  

Precipitation for the year at the airport was 14.78" which was just a skiff below normal (15.52").  Snowfall for the year was 26.2" which was about half of average (51.9").  I have not had a chance to carefully break that down to see if that was due to dry cool months or a greater fraction of cool-month precipitation falling as rain, but a quick look at the graphs suggests the latter dominated.  

As an anecdote, we have now made it roughly through my 2024/25 "snow blowing season", that period during which I normally blow out my south-facing driveway after storms since the sun is too low to melt it out in a short period of time.  I haven't run the snow blower once.  It's sitting in the garage collecting dust.  Nothing that has fallen on our driveway or sidewalk has survived for more than a few hours.