Wasatch Weather Weenies

The quality of light strongly affects one's confidence as a skier.  On a sunny day, most of the solar energy (about 85% of it when the sun is high in the sky) is direct, meaning that it is traveling along a straight line from the sun to the Earth's surface.  This results in large brightness contrasts between directly illuminated surfaces and those in shadows.  Even subtle textures in the surface of the snow are easily seen.   Descending a groomed run at Ischgl, Austria on a sunny day dominated by "direct" solar energy. All else being equal, it is much easier to ski on such days.  It is easier to see the steepness of the terrain, variations in the snow surface, and subtle changes in the snow conditions.   However, on day with thick overcast, even high overcast, the light can be "flat." Flat light is a colloquialism for situation in which there are no shadows, as was was the case at times at Alta today (Sunday).   Flat light at Alta on Sun...

With yesterday's strong south winds, dust moved into Salt Lake Valley and environs yesterday and lingers this morning with visibility somewhat reduced as one looks to the central Wasatch from the University of Utah. Source: https://home.chpc.utah.edu/~u0790486/wxinfo/cgi-bin/uunet_camera_explorer.cgi Observations from the University of Utah show strong south winds yesterday afternoon and evening with PM2.5 levels increasing after about 1600 MDT from 3 to 8 ug/m3.  After settling some through 0200 MDT, they then climbed again to 13 before settling some this morning.   These numbers are not high and are at good to low-moderate air quality levels, but nevertheless, there's plenty of dust in the air.   Give the overall flow yesterday, the dust in the Salt Lake Valley  was likely from sources to the south and the southwest given the flow direction and not from the exposed Great Salt Lake bed.  The flow direction was such that if there was dust emitted ...

The work week has proven spectacular with mostly sunny skies and mild temperatures.  "Anything season" is here, meaning that you can do pretty much any type of recreation you desire, sometimes on the same day.  The lower-elevation trails have dried out now in many areas and are quite passable for hikers and bikers. Meanwhile, we still have a deep snowpack at upper elevations.   Today's sunrise from the Avenues foothills. We will, however, be transitioning from the dry spring pattern we've experienced the last few days to a pattern that will bring the occasional mild spring storm system to northern Utah.  This transition won't necessarily be abrupt as a couple of weak systems move through Friday and Saturday.  After that, there's a series of troughs that move through.  It's not easy for me to summarize my expectations for the timing and strength of these storms as there's a good deal of variability in the Utah snow ensemble.  Just look at the sprea...

Due to utility work at the University of Utah data center, weather.utah.edu is expected to be down for approximately two days.  Don't shoot the messenger.  In the meantime, enjoy the sunny, warm March weather and stop worrying about the next storm.  The forecasts looked like spaghetti anyway, so who the hell knows what's going to happen.   In the meantime, for your entertainment purposes, there were some beautiful lenticular clouds over the central Wasatch yesterday.   Such clouds are produced by mountain waves, up and down motions produced by the interaction of the atmospheric flow with the topography.  The clouds form where the flow is forced up and dissipate where the flow is forced down.  The layering is produced by vertical variations in relative humidity, which causes saturation in areas of ascent to be reached at different levels of vertical displacement.   Lenticular clouds have been confused with flying saucers.  Let's...

Let's have some fun with a post based on what I'll call "sidewalk science."   The Hall of Fame Baseball catcher Yogi Berra once said "you can observe a lot just by watching."  This applies for sure to both meteorology and snow science. This afternoon, right near my house, I encountered an avalanche in the front yard of a house on 16th Avenue in the upper Avenues. Oh, I didn't actually see the avalanche happen, but I did see the aftermath, which I've summarized in the below.  It contains many of the hallmark characteristics of an avalanche.  The first is the starting zone, which in this case I measured to be 35°.  Most avalanches start on slopes between 30 and 45 degrees, so the slope here was right in that range. There is also the crown or crown line, which is the upper fracture line of the slab that broke away to create the avalanche, as well as the flank or fracture line along the side of the avalanche.  There is one on the other side, although ...

It's sort of weird after a winter with little valley snow to look out the window and see what might be the deepest snowpack of the season in my yard.  Admittedly, "deepest" in the valley this year is a low bar, but it will be good for the gardens eventually.  It was a wonderful storm for skiing too. I can summarize the forecast for the next several days in two words: warming trend. Oh, today will be a cloudy "meh" day and Friday night and Saturday we'll have a trough passage that could bring a bit of snow, but after that a big ridge builds into the west.  Below is the GFS forecast valid 0000 UTC 27 March (6 PM Wednesday) showing the high-amplitude ridge parked just upstream of Utah.   The NWS National Blend of Models maximum temperature forecast for Salt Lake City shows the warming trend nicely after Saturday, with temps climbing through Thursday.   The median maximum temperature forecast for Thursday afternoon is 81°F, which would be the earliest 81 o...

The weather yo-yo of spring continues today and tonight with the approach and passage of a spring cold front.   The 6Z GFS shows the cold front moving across northern Utah tonight at 0600 UTC 18 March (0000 MST Tuesday).  Ahead of the front, today will be mild and windy with the possibility of blowing dust.  The prefrontal environment today looks to be mainly dry, although I wouldn't be surprised to see a spritz or two of valley rain or mountain snow.  Precipitation is not expected for the evening commute.   The front drags through tonight.  Onset time, duration, and accumulations for the valley vary some from model to model.  For brevity, I'll focus here on the 1200 UTC initialized HRRR.  The time-series below is for the Salt Lake City International Airport.  Precipitation onset is just before 11 PM local time, but the turnover to snow doesn't occur until after 2 AM.  I'm not sure if I'd count on that timing given the uncertai...

We really haven't had much of a winter this year in the Salt Lake Valley.  Snow has been scant (only 12.7" through yesterday, the 3rd lowest on record through that date) and temperatures mild (7th warmest mean temperature on record through yesterday).  It's been sunny and mild the past few days, so it definitely feels like spring.  Things will change late tomorrow with the passage of a cold front.  A couple of days ago I was going to call it the Start of Winter for the valley, but the storm is splitting and right now not looking as large as I thought a couple of days ago, although it could still have impacts.  The GFS forecast valid 0000 UTC 14 March (6 PM Thursday) has the front and frontal band moving through northern Utah.   Frontal passage at the airport in the GFS occurs at about 2200 UTC (4 PM Thursday) and the HRRR about 000 UTC (6 PM Thursday) so expect it to get here in the late afternoon to around dinner time.  Pre-frontal conditions wil...

A spectacular early March weekend is now in the books.  For skiers and water managers, March is an important month.  The spigot can stay open, extending the powder season while there is a deep snowpack and delaying the spring runoff (often leading to a more efficient runoff), or we can transition to spring conditions with the snowpack suffering a slow death.   If you are a skier or a water manager, I think you will like the extended forecasts.  For the early part of this week we'll have our share of warmth, sunshine, and spring fever, but the models are calling for a major shift later this week to a more active pattern with a parade of troughs moving across the western United States thereafter.   It's a long-enough range forecast that I don't want to talk about details, so I'll summarize with the Utah Snow Ensemble plume for Alta. It's flatlined for water equivalent and snow until late on the 13th when thigns really start to pick up.  There are so...

After more than a decade of engagement on Twitter/X, I departed from that platform yesterday.   The post prompted people to ask if I was Ok or if I was leaving the U, but I was merely leaving X.  It is a wonderful platform for sharing weather and science information but for some time the meanness and cruelty there have worn on me.  The nonstop bombardment of click bait was affecting my mental health. Enough was enough.  You can find me on Bluesky for now (@professorpowder.bsky.social), although I'm not going to be on it as frequently.   Thank you for keeping this blog a place where science, weather, and snow are discussed respectfully.

Last night's storm period was one that I really enjoyed simply because it shows how remarkably variable snowfall can be in the central Wasatch.  As suggested in the prior post , the low-level ESE flow favored Deer Valley, which received more snow than Alta-Collins.   Deer Valley/Ontario: 1.41"/14+" (snow depth sensor got flaky at 7:35 AM; 14 was the total at that time) Alta-Collins: 1.02"/10" It seems that a lot of data is not flowing into MesoWest from there resorts right now so I couldn't dig much deeper than that, but the Utah Avalanche Center report included storm totals as of 5 am also showing the decrease in snowfall from east to west.  Source: https://utahavalanchecenter.org/ This is not something that is unusual for such a flow pattern or that experienced meteorologists wouldn't anticipate, as illustrated by yesterday's blog post.  However, we don't have a good understanding of the physical processes operating during such storm periods, n...

The model runs are pretty spicy and exciting this morning with a significant storm moving later today.  The latest GFS suggest precipitation beginning in the central Wasatch this afternoon or evening and continuing into Friday.  Let's have a look.   The GFS forecast valid 0600 UTC 6 March (11 PM Wednesday) shows that the early part of the storm is characterized by an deep upper-level trough (upper left panel below) with a lower-tropospheric cyclone (red L in images below) over Nevada.  Associated with this system is an inland penetrating atmospheric river  atmospheric river that approaches northern Utah via the lower Colorado River Basin.  The crest-level 700-mb flow (lower left panel) is southerly or even south-southeasterly in the vicinity of the central Wasatch with 700-mb temperatures near -5°C. Thus, the overnight storm period has all the hallmarks of a warm, high-density storm period.  Through 9 AM tomorrow morning, the GFS generates 0.77" o...

Meteorological winter, which includes December, January, and February, ended yesterday.  In the Salt Lake Valley, it wasn't much of a winter.  The average temperature at the Salt Lake City International Airport was about 36.4°F, making it about the 7th warmest on record*.  The asterisk is because there appear to be two days missing from the records I can access, so those numbers could change slightly.   Snowfall was scant with only 10.4".  A day is missing for the snowfall records too, although I believe the total is probably right (the missing day was likely snow free).  This is the third lowest on record behind 2014/15 (6.0") and 1962/63 (8.8").   Source: https://xmacis.rcc-acis.org/ The SNOTEL data in the central Wasatch has been a bit squirrelly this year, but for end of meteorological winter snowpack, most sites are a bit below average including Snowbird (90%), Brighton (88%), Thaynes (73%), and Parley's Summit (95%).  Mill D N...