Wasatch Weather Weenies

If you haven't been out in the Avenues foothills lately, do it soon so you can enjoy the new trails that the Salt Lake City Public Lands Division has built and is building while the grass is green, the flowers in bloom, and the mountains white.  Below is a shot  this morning of one of the new flow trails put in above Morris Meadow and 18th avenue. Information on what the are doing is available at  https://www.slc.gov/parks/trails-natural-lands/fts/ , with the latest information on their blog at  https://www.slc.gov/parks/trail-updates-in-slcs-foothills-natural-area/ .  Many trails opened last Friday and. as illustrated by the image below, they include multiuse trails (green; hiking and biking in both directions), hiking only (brown), hiking and uphill biking (orange), and downhill biking (black).   https://www.slc.gov/parks/trail-updates-in-slcs-foothills-natural-area/ The red trails are old trails that are now closed.  I am not sure if that's per...

In all likelihood, yesterday marked the end of the snow accumulation season on upper-elevation northerly aspects in the northern Wasatch Range (we're past snow accumulation season at other elevations and aspects where the snowpack has been melting and running off for some time).   Data from the Snowbird SNOTEL shows (9177 ft) shows that as of midnight last night we were at the highest snowpack water equivalent of the water year (which begins October 1) with 32.7 inches.   Source: NRCS That will almost certainly be the maximum for the year as the forecasts for the next few days suggest an abundance of sunny, warm weather through Saturday.  The snowpack at this location is ripe or near ripe, meaning it's warmed to near 0˚C and additional energy input into it will likely release meltwater.  A weak system on Sunday may bring a few flakes, but not enough to rebound from these losses.   As a friend noted yesterday, this is pretty much right on the date ...

Rain and upper elevation snow are falling across much of northern Utah today as a slow moving front moves across the region.  We desperately need the precipitation and right now it looks like a pretty good soaker.   The latest radar imagery shows pretty solid coverage (given the limitations of the radar due to the region's complex terrain).  This includes strong returns over the central Wasatch.   Surface observations within an hour of 1441 UTC (0841 MDT) show the shallow surface front draped across the central Salt Lake Valley with northwesterly flow at the Salt Lake City airport and in the West Valley region and southerly flow in Draper and Herriman.   Source: MesoWest This leading nose of the front is, however, shallow and the flow became southwesterly in the morning (0600 MDT) sounding at an elevation of only 7000 feet. Source: SPC Thus, most of the precipitation is being generated this morning in the southwesterly flow, which is quite juicy....

The short-lived but frequent post-frontal dust storms we've had over the past several weeks have left their mark on the Wasatch snowpack.   After it snows, the dust is buried, but it doesn't take long for it to emerge as the surface snow melts and the water trickles down through the snowpack, leaving whatever impurities at the surface.  Instead of white snow, it may be "marbled" with areas of tan or brown.  Some people call this "snirt" for part snow part dirt. Due to the uneven distribution of fresh snowfall and melt rates, the emergence of the dust-laden snow varies.  Today, on this southeast aspect, one saw a very heterogeneous (diverse) snow surface with everything fro white to dust-laden brown.   Dust is important for snow hydrology because it affects the amount of solar radiation absorbed by the snow.  Dusty snow is darker and absorbs more sunlight, so there is more energy available for melt.  As a result, a dusty snowpack melts faster ...

Many of the products we provide on weather.utah.edu derive from computer models run by the National Centers for Environmental Prediction, or NCEP for short.  Centers is plural because NCEP actually consists of nine National Weather Service centers that deliver national and global products from weather warnings and forecasts to computer model guidance. We are fortunate in the United States that government weather data from NCEP and other government agencies is for the most part freely available.  This enables groups like mine and others to drive products like those on weather.utah.edu and to develop new forecast techniques.  Many private companies can integrate NCEP model forecasts into their operations, from IBM to Amazon.  This has huge benefits for the nations economy and resilience to weather hazards.  In many other countries, this is not the case as government groups may charge for these products. When I began my education in the late 1980s, there was essent...

 Despite the fact that I've had some decent skiing the past few weeks and conditions on "closing day" at Alta were pretty damn good, the snowpack situation across much of the western United States remains below median at many sites and in many drainage basins.   Source: NRCS The best situation relative to normal is in the Cascades of Washington, the interior northwest, and areas near and east of the Continental Divide.  Southern Oregon, southern Idaho, and much of the southwest is at 75% of median or lower.   Even with the recent snow, Snowbird is 76% of median with 31.8" of snow water equivalent as we approach the climatological maximum of snowpack at the elevation of the SNOTEL site (9177 feet).   Source: NRCS For those of you hoping for a refresh this week, the odds are low.  The best chance will be Thursday when we are tickled by an upper-level trough.  Most of the ensemble members are calling for light accumulations, although there ...

Today was Alta's "closing day", which I put in quotes as they will be open three more bonus days next weekend.   Last year there was no real closing day.  The season simply ended due to COVID.  This year, we were treated with truly spectacular weather and ski conditions for April 18th.   Although the lot was full by 9:15 am, the morning tailgates meant that we had a few runs with few people around. It's always great to have the top of high boy to yourself.   Piste was fantastic.  Off piste varied.  Baldy was open, so we schlepped to the top and enjoyed the views before a run down Main Chute.   Many others were enjoying the hike as well. I don't know if you could have a nicer closing day than today and it was appreciated given the turmoil of the past year.   That being said, I may have a few days left in me this season...

Picking up with the end of the previous post, how do we explain the distribution of snow in the photo below taken on Wednesday, especially in the circled area where there appears to be a decrease in snow with elevation?   Photo: Mike Freeman My best hypothesis is that this is the result of two mechanisms.  The first is the cold outflow that occurred that morning from Parley's Canyon.  The image below illustrates the locally cold nature of this outflow based on station observations from the region at around 1500 UTC (0900 MDT).  The station immediately upstream (along I-80) of the mouth of Parley's Canyon is reporting a temperature of 31˚F, considerably colder than the station south of the mouth of Parley's Canyon where it was 40˚F.  These two stations are nearly at the same elevation.   I suspect the outflow from Parley's was colder than the air south of the Canyon, resulting in locally lower snow levels and colder ground temperatures, enabling ac...

Pretty amazing storm yesterday as the "eastern band" discussed in yesterday's post intensified and delivered heavy snowfall to the central Wasatch Range yesterday morning.  Snowfall rates peaked from 11-12 MDT with several automated observing sites from Little Cottonwood Canyon to Park City Mountain Resort recording more than 4" of snow in that hour.  Alta-Collins ticked off 5.   Radar imagery at just after 11 am showed strong returns over the Cottonwoods and Park City Ridgeline.  Even east of the crest, the reflectivities were quite high.  Because of partial blockage of the outgoing radar energy by the Wasatch Range, there's less energy available to reflect back to the radar, so those are pretty healthy returns for east of the crest.   Consistent with the radar, we saw something that we haven't seen much of this winter: heavy snowfall in Park City and Summit Park.  National Weather Service spotters reported 13" at 6824 feet in Park City thro...

Quite a mess of a storm right now over northern Utah.  I'm not sure where to start, but maybe a look at some of the observations is a good place.  Easterly flow extends from southwest Wyoming to the northern Wasatch Front where strong downslope winds persist from the area around Parleys Canyon northward.  One can also find strong easterlies in local canyons further south, such as Provo Canyon.  In the western Salt Lake Valley and along the US-40 in the Wasatch Back, the flow is northerly.  The former reflects what we sometimes call the "Sandy Eddy", a counterclockwise circulation that often forms over the Salt Lake Valley during downslope windstorms and is centered near Sandy.  Source: MesoWest A look at the flow on Hidden Peak and Mount Baldy in the central Wasatch, however, shows southerly flow.  Indeed, the sounding from the Salt Lake City airport this morning is simply amazing.   Source: SPC The surface flow out at the surface was actuall...

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 t...

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 ...