Wasatch Weather Weenies

After major winter storm cycles, especially those that lead to long Interlodge periods in Little Cottonwood Canyon, I get a lot of questions about whether or not snowstorms are getting bigger due to climate change.  Many people assume this is the case, but it turns out to be a difficult question to answer, especially if you are talking about a specific location like Little Cottonwood Canyon.   Let's talk first about what we know.  Globally averaged temperatures have increased about 1˚C and Utah has warmed at almost double that rate.  Recent studies indicate that most if not all of the warming in recent decades is due to human activities, especially greenhouse gas emissions.   Precipitation is a messier variable, however, as it exhibits greater regional variability than temperature.  It is also not sampled as well, with fewer stations and often lower quality measurements.  Finally, there are two questions that one might ask.  First, is th...

Thought that headline might get your attention. Meteorological winter covers December, January, and February and ends this Sunday, the last day of February.  Thus, the last storm of meteorological winter will be this Friday night and Saturday as a broad trough moves through northern Utah from the northwest.  Below is the GFS forecast for 0600 UTC 27 February (11 PM MST Friday) showing northern Utah in the moist, unstable flow.   The time-height section for Salt Lake City shows this is a storm cycle that's a bit less organized and less juicy than last week's.  There's a weak trough passage late Thursday night/early Friday Morning and then another late Friday night/Saturday morning, followed by a moist post-frontal period.   The GFS generates a total of 13.5 inches for Alta between 1 AM MST Friday through 7 PM MST Saturday night, the NAM 7.7 inches.  The SREF mean is around GFS levels, with about 0.75 inches of water and 12 inches of snow. ...

The University of Utah's Annual Giving Day is this Tuesday and Wednesday, February 23-24.  Yes, I know that's two days, but we try to make everything in higher education as complicated as possible.  Technically, the Giving Day is an 1,850 minute fundraising effort, with 1850 being the year of the University's founding.  See, it all makes sense in the end. If you are a fan of this blog, please consider making a donation.  My fellow faculty and I will match the first $3,050 in donations and once we've reached $3,000, Dave and Johanna Whiteman, who started our Mountain Meteorology Fund, will contribute an additional $5,000.   There are two options for donations.  The first is our Mountain Meteorology Fund, which supports interdisciplinary research and education to improve the understanding and prediction of weather and climate processes in complex terrain.  In other words, the things I write regularly about on this blog.  To contribute to the Mo...

It's pretty incredible that with all the snow we received over the past 10 days or so, we are still near or below median at most northern Utah SNOTEL stations.   Source: NRCS I think the only site that is above median in northern Utah is Dry Fork in the Northern Oquirrh Mountains.  The recovery there was pretty incredible, with a net gain of about 5 inches in our most recent storm cycle, enabling it to claw out from near the bottom to 101% of median.   The fattest snowpack in terms of total snow water equivalent is at the Ben Lomond Peak SNOTEL, which now sits at 24.1 inches, which is still only 80% of median.   Source: NRCS The Snowbird SNOTEL is a bit behind in total SWE sitting at 22.4 inches, which at that location is 90% of median.   Source: NRCS So, the skiing has improved immensely, but the snowpack is still below median ! I'm suspect water managers are thankful for the latest storm cycle, but still hoping for more.   Compari...

The snowfall contrast between Little Cottonwood Canyon and Park City Mountain Resort over the past 24 hours is quite dramatic.   In upper Little Cottonwood Canyon, Alta reported 30 inches of snow.  In upper Big Cottonwood Canyon, Brighton reported 22 inches of snow. On the Park City Ridgeline, Park City Mountain Resort reported only 12 inches.   The distance between Alta the top of the Jupiter chairlift at Park City Mountain Resort is less than 5 miles !  That's a huge contrast in snowfall.  How can this happen? One of my late-career dreams is to have the University of Wyoming King Air research aircraft flying through a storm like this one with it's world-class cloud radar.  This instrument takes cat scans in storms.  One thing I would like to have it do is fly directly down the northwesterly flow and examine the storm structure from northwest to southeast.  Here's why. We often generalize the western side of the Wasatch Range as the "wi...

Wow, what a storm cycle.   It continued to snow overnight in Little Cottonwood as well as much of northern Utah.  More on the latter in a minute, but let's first take a look at Alta. The tabular output below includes hourly observations over the 24-hour period ending 0700 MST this morning.  The interval board was wiped after 0700 MST yesterday morning, when there was 15 inches on the board, and after 1600 MST yesterday afternoon, when there was 10 inches on the board.  It now sits at 20 inches.  Thus, the total for the 24-hour period from 0700 yesterday to 0700 today is a remarkable 30 inches.   Looking at the entire storm cycle, total snow depth since 1100 MST 11 February has increased abou 30 inches (ignore the eroneous 136" measurements).  If you add up the interval board measurements at times of peak snow depth, you get a snowfall of 82".   I guess it goes without saying that everything is coming unglued from a snowpack perspect...

Winter took a while to arrive this year in northern Utah, but it is now delivering in spades.   If I'm doing my math right, since 0600 UTC 12 February (2300 MST 11 February) the Alta-Collins interval snow stake has measured 54" of snow through 1400 UTC (0700 MST) this morning.  The Utah Avalanche Center site apparently has had enough this morning as when I went to pull it up, I got the dreaded "Too Many Connections" error. Eventually I got through to find they have hoisted the rare black flag for extreme avalanche danger in the central Wasatch and western Uintas.   Sadly that was the only page I was able to successfully load, so I will need to wait for more details.   The radar image for 1457 UTC (0757 MST) this morning shows the long anticipated unstable northwesterly flow.  I didn't bother doing a loop this morning, but if I did it would show transient snow showers moving from northwest to southeast in the lowlands and more persistent stationary...

 So far so good.  The Utah Avalanche Center reports that yesterday's storm produced 13" of snow and 1.36" of water in upper Little Cottonwood Canyon.  Storm #2 of the cycle moved in late last night and with warm advection occurring in advance of the upper-level trough, the radar coverage is currently as widespread as it can get.  The only areas without returns are areas with terrain blockage that the radar can't see.   In the central Wasatch, I expect continuous snowfall this morning.  The trough at crest level is forecast to pass in the early afternoon and should be accompanied by a shift in crest-level winds from southwesterly to northwesterly.  Snowfall will be heavy at times and looks to continue through evening.  The Utah Avalanche Center anticipates 8-14" through early evening, and that's aligned with my thinking.  The radar and model forecasts all point to a significant event.   If you are looking for something to give y...

It took me a while to dig out from the latest problems with the National Weather Service server from which we obtain most of our model data.  So it wasn't until this afternoon that I took a look at the model guidance. Wow. I hesitate to throw gas on the inferno of hype currently burning through social media, but on paper, things are looking good. I like large-scale patterns in which the flow is progressive with "open wave" troughs, and this is what we have coming.  This means the waves are lower amplitude.  Think of them as ripples in the flow rather than North Shore monsters.  They move quickly, but come in succession, and give us moist flow with a strong component across the Wasatch Range.  Ideal for orographic snowfall generation. This is what we have coming over the next six days [defined here as 0000 UTC 12 February (5 PM MST Thursday) through 0000 UTC 18 February (5 PM MST Wednesday)]. Just look at the GFS 5-day time-height below.  Lots of low level m...

Questions about possible linkages to climate change are bound to arise whenever something unusual or exceptional happens, and this year's weak snowpack and high number of avalanche fatalities is no exception.   Let's start with what we know and what we can say with some confidence.  We are in a period of climate warming, driven by human activity, and this is changing the snow climates of the western United States.  Weather and climate variability give us ups-and-downs even in a changing climate, but we are seeing a shift to warmer mean temperatures, more winter warm spells, and fewer winter cold spells.   Trends in snowfall and snowpack measures vary, however, depending on the measure, regional climate, and elevation.  In northern Utah, at elevations below about 6500 feet, we are seeing declines in the fraction of wintertime precipitation that falls as snow, more frequent mid-season snow-loss events, and a decrease in the amount of wintertime precipita...

This is my first post since Saturday's tragic avalanche in Wilson Glade.  My heart goes out to the victims and their friends and family.  Let me also express my gratitude to all of the first responders, rescue and recovery personnel, and Utah Avalanche Center staff for all of their efforts.   I've decided to focus on temperature for this post rather than snow.  Often temperature is an "easier" forecast variable than precipitation or snowfall, but that's not the case for this weekend.   A look at the GFS forecast for 1800 UTC (1100 MST) Saturday shows northern Utah in an arctic airmass that has surged across the Continental divided, dropping 700-mb temperatures in the Salt Lake Valley and Wasatch Mountains to -20˚C or colder.   In fact, the GFS forecast 700-mb temperature for the Salt Lake City International Airport is -21.4˚C at that time.   Readers of this blog know that I get excited about 700-mb temperatures above 20˚C or below -...

Yesterday's storm delivered with Alta, Snowbird, and Brighton all apparently colluding to report 15 inches this morning.  Poor Solitude reported only 10 inches.   It's a wonder anyone could measure anything yesterday given the wind.  I was out during the relatively peaceful mid-morning hours and caught some beaten up snowflakes on my ski pants.  Look closely and you can find a few pristine ones, but otherwise it was mostly fragments.   Later in the day, as Gordon Lightfoot once wrote about the storm that wrecked the Edmund Fitzgerald, "the wind in the wires made a tattletale song" as a few gusts of over 100 mph were recorded at one mountain top observing site.  Snowfall rates also increased, maximizing in the late afternoon, resulting in the temporary closure of Little Cottonwood Canyon.   The storm persisted, however, for a few hours longer thanks to the so-called "Alta Cloud." If you ever wondered what the Alta Cloud looks like, below ...

This morning dawned as expected with grey skies and a bit of light snowfall over the Wasatch Range, providing an illustration of the orographic processes that will play a major role in the storm for today and tonight.   Orographic means related to mountains.  Meteorologists use words like orography, orographic, orographics pretty regularly in places like Utah because the mountains have such a dramatic influence on our weather.   Orographic precipitation is precipitation that is generated or enhanced by the interaction of moist flow with orography.  If one looks at the 24-hour GFS accumulated precipitation forecast for northern Utah through 1200 UTC (0500 MST) tomorrow, one can see to some degree the influence of the mountains with precipitation greatest along a north-south corridor that is roughly aligned along the Wasatch, with the precipitation maximum in the central Cottonwoods.   The corridor of precipitation is, however, much wider than th...

There are some recurrent things that happen during storms over northern Utah that I don't understand.  Here's one of them. Early this morning in the pre-frontal southwesterly flow, precipitation developed downstream of Mount Timpanogos and the surrounding Wasatch Range in the area circled in red below.   The precipitation pattern was somewhat disorganized, but exhibited some banded structures at times.  Echoes clearly were forming near and downstream of the Wasatch Crest and extended well downstream into the western Uinta Mountains.   I have seen a few examples of leeward precipitation over the years, all typically associated with strong cross-barrier flow.  I have some hypotheses for how this happens, but have never been able to explore them.  In this case, I think it is especially interesting that the echoes appear downstream of the range, suggesting that this is not a case of precipitation forming on the windward side and being carried into th...