Wasatch Weather Weenies

With about 2.5" of water and 23" of snow, the Best Forecast (So Far) This Season, which we discussed on Christmas Eve, is verifying well so far at Alta Collins.  The yellow dots are my best guess of where things stand as of 8 AM/15Z this morning showing us in the upper end of water equivalent and about in the middle of the Utah Snow Ensemble forecasts. For today, the 12Z HRRR is generating 1.25" of water and 10" high-density of snow from 8AM through 11 PM.  This is on top of the couple of inches that it was producing from 5-8 AM earlier this morning, which appears to have verified nicely.  I like another 6-12" of high-density, upside-down snow before this storm winds down this evening. Note that with the KMTX radar out, this is even more of a guess than usual. Did I say high density and upside down?  It's a warm storm though, and getting warmer.  I suspect snow levels this afternoon will be pushing 7500 feet. They may go higher than that this evening if the...

'Twas the night before Christmas when all through the house Meteorologists were stirring, along with the mouse The forecasts were hung by the chimney with care In hope that deep powder, soon would be there Now is not the time to settle your brains for a long winters nap.  The latest forecasts from the Utah Snow Ensemble are the most optimistic I've seen all season for the central Wasatch, although that admittedly is a low bar.  Ignoring the outlier minimum and maximum forecasts, there is a tight clustering of forecasts producing  2.04 to 4.73 inches of water and 25 to 58 inches of snow for Alta-Collins by New Year's Day.   The first storm comes in with Santa's sleigh tonight, but excitement should be tempered with the fact that it's a splitter.  The GFS shows it to be a "full latitude trough" on the west coast this morning with precipitation extending from off the SoCal coast all the way up into British Columbia. But by Christmas morning it's split, al...

A rather unscientific polling of locals on a relatively small number of chairlift rides yesterday suggests that this year is off to a slow start.  Is that really the case? Yes. First we can look at the snowpack water equivalent.  Three of the SNOTEL sites with long-term records in the central Wasatch, Snowbird, Brighton, and Thaynes Canyon sit at their lowest or 2nd lowest water equivalents on record.   Source: NRCS The Snowbird site is near the Gad Restaurant, which is currently under construction.  Site notes indicate that the pillow was moved about a hundred feet on 20 December, and indeed there is a discontinuity in the record around that time with a drop in water equivalent from 4.2", which was near the lowest on record (since 1990), to 3.2 inches, which would be the lowest on record.   How much faith to put into the representativeness of the Snowbird measurements is unclear, but they don't paint a rosy picture.   Brighton is the 2nd low...

By popular demand, we now have a tabular output product from the Utah Snow Ensemble for Alta-Collins available at  https://weather.utah.edu/text/ensgefsdslccforecast.html .  This should provide access to the most recently processed run and provides tables of total water equivalent precipitation, total snowfall, 6-h water equivalent precipitation, 6-h snowfall, snow-to-liquid ratio, and wet-bulb 0.5C height.  Times are local (mountain) time.  Cells are color filled by magnitude.  An example of the first two tables is below. The row labeling for each table goes from the minimum value of the 82 ensemble members to the maximum value.  The P stand for "Percentile" so that P10 means the 10th percentile.  That means that 10% of the ensemble members are below that amount and 90% are above it.   P50 thus is right in the middle, or what statistical types call the median.  50% of the members lie between P25 and P75 (this was corrected from a typo t...

These are desperate times in the natural snow department.  I supposed it could be worse.  Alta has had 105" of snow so far this year and has a base depth of 37", but these are meager numbers for mid December.  Snowpack water equivalent is the best measure of the robustness of the snowpack and we are well below median for that metric at most high-altitude observing sites in the Wasatch including 50% of median at Snowbird, 56% at Brighton, and 43% at Thaynes Canyon.  Somehow, Mill D North sits at 104% of median. Good for them, but that's still only 5.7" of water.   The snowguns continue to blaze, but this is Utah, home of the so-called Greatest Snow on Earth.  Is there hope of a Christmas Miracle? The truth is that the ensembles are not giving us much love. Last night's Utah Snow Ensemble came in with most members under 0.5" of water at Alta-Collins for tomorrow's storm. A look towards Christmas shows that there are some members giving us the goods, but ...

The Alta snowstake cam suggests we're getting more action that may have been advertised by the models with perhaps 6-7 inches on the stake earlier this morning before the ski patrol wipe (kudos to my friends at OpenSnow for producing the Alta Snow Stake time laps so I could grab this image).  And then another inch was added since then (not shown).   The automated sensors are coming in a bit below that with about a 6" increase in the total snow depth and 6" on the interval board (ignore the spurious 34 reading at 08:00).   Those numbers are a bit higher than advertised by the HRRR and GFS over the past few runs.  Below are the forecasts for Alta-Collins going back to 0000 UTC 12 December for snowall amounts through 9 AM this morning.  Only one of the HRRR runs went for 6" and the most recent was only an inch.  The GFS was a bit more optimistic overall, but never got above 4.5 inches.   0Z 12 Dec HRRR: 1.1” 6Z 12 Dec HRRR: 6.0” 12Z 12 Dec ...

The physicist Niels Bohr once said that "prediction is very difficult, especially if it's about the future" and that is very evident when looking at the latest Utah Snow Ensemble (USE) plume for Alta-Collins.  The 82 members of the USE show remarkable spread for total water equivalent and snowfall over the next 10 days ranging from nearly zilch to about 2.5" water/38" of snow.   The period features three storm systems and the 82 members can't seem to show much agreement in the intensity and timing of snowfall associated with each of them.  We'll likely to be in a better place at the end of the 10-day period than we are now (it helps that the bar is set so low), but don't try to pin me down on details such as should I get a parking reservation at Alta for Friday, Saturday, or Sunday.  The first system moves through Thursday night and Friday, and the second Saturday night into Sunday, but I don't have any confidence concerning how much each of them...

During the most recent inversion event, fog developed over the Great Salt Lake, eventually expanding to cover most of the lake and environs.  Below is a series of images from the NASA Terra satellite, which flys over roughly mid morning on December 4th, 6th, and 8th, the latter being yesterday (Sunday).   It was on the 4th that fog first became evident, with a couple of regions of fog extending westward from near Antelope Island over the southern bay of the lake. By the 6th, fog covered most of the lake.   And finally, by yesterday (Sunday, 8 December), the lake was nearly entirely covered and spread into populated areas that included the northern Salt Lake Valley and portions of Davis County.   Given the limited lowland snow cover in this instance, it is likely that the evaporation of water from the lake played an essential role in fog formation in this event, leading to fog development and persistence mainly over and near the lake. I often tell stude...

We are currently mired in the first major inversion and air quality episode of the season, although I don't think it's been as bad as it could have.   First, the valley is mostly snow free.  This likely leads to a bit more energy input into the atmosphere (due to less sunlight being reflected back to space and increased ground heat flux) and perhaps a bit of a decrease in particulate matter generated by photochemical processes (although this is not my area so I'm speculating).   In the case of the former, the soundings released at the Salt Lake International Airport at 0000 UTC each afternoon are too late to capture the structure of the convective boundary layer that develops each afternoon.  The convective boundary layer is the part of the atmosphere in which surface heating by the sun leads to vigorous vertical motions (the updrafts are sometimes called thermals) and mixing.  The depth of the afternoon convective boundary layer varies from meters to...

If you are looking for a good gift idea this holiday season, one that will expand the snow knowledge of your friends and family (or maybe yourself), look no farther than Karl Birkeland's recently published "book" The Starting Zone, available from avalanche.pressbooks.pub  ($49.95). I put book in quotes because The Starting Zone is an e-book available from the Friends of the Colorado Avalanche Information Center.  The Starting Zone is a living document, with tons of figures and videos and more references than you can shake a stick at (these are footnotes, so they don't clutter up the reading).  Everything is hyperlinked, allowing you to watch videos or access supporting materials with the click of the mouse or a tap of the finger (I read it on my tablet).   I am not an avalanche professional or researcher, so my perspective is of a scientist in a complimentary field (meteorology) who has been backcountry skiing for more than 30 years but has little formal avala...

December arrives with the dreaded "Rex Block" firmly in charge over the western United States.  A Rex Block is a large scale pattern characterized by high pressure "over" low pressure as is evident in the GFS forecast valid for 0000 UTC 3 December (5 PM MST Wednesday) with an upper-level ridge centered over Oregon and a weak trough off the coast of Baja California.   Rex blocks are named for meteorologist Daniel Rex who published an early article on blocking in 1950.  Given the stability of this pattern, all members of the Utah Snow Ensemble are snow free at Alta-Collins through 0600 UTC 6 December.  After that, you can find a few members that try to bring a storm or two to Alta, but most keep us dry.    It's easier to forecast the onset of a block than its demise, so perhaps the odds will ever be in our favor as we approach 10 December, but for now anticipate dry conditions, valley inversions, and faceting snow on shady aspects.  

What will certainly be the last storm of November and possibly the last storm for some time is now in the books.   As a recap, I thought we would do a comparison of the total storm depth change at Deer Valley Ontario (9100 feet) and Alta-Collins (9662 feet) as they illustrate two different pathways for increasing the total snow depth about 15 inches.  I've take the liberty of stretching the Alta-Collins plot from MesoWest so that the y-axis scale increments are comparable in scale to those at Deer Valley Ontario. Most of the snow at Deer Valley Ontario fell from about 0000–1400 MST Thursday (red shading).  This was during the pre-frontal storm stage discussed in the prior post (see Can You Help Explain the Overnight Snows ).   The Deer Valley Ski Patrol was caught mocking the Alta Ski Patrol on their snow-stake web cam. Of course, Alta is Mother Nature's favorite son, and with and following the passage of the front late yesterday afternoon and last night (b...

Sometimes those with investment portfolios and trophy homes get the last laugh and that was the case last night with Deer Valley the big winner in the central Wasatch.  Below is a look at the Ontario Snow Stake Web Cam at 8:05 AM showing a solid 8". Source: https://www.deervalley.com/explore-the-mountain/webcams Meanwhile, on the other side of the Wasatch, at a ski area also frequented by people with investment portfolios and trophy homes but better known for deep powder, pickings were much slimmer.   Source: alta.com This is a pattern that does sometimes bless the Deer Valley side, although I confess I don't exactly know why, in part because of poor radar coverage, poor radar estimates, and limited observational data.   The issues with radar coverage are apparent in the plot below, which shows the accumulated precipitation estimated from the National Weather Service Radar (KMTX) for the 6-hour period ending at 1400 UTC (7 AM MST).  The radar thinks th...

Introductory meteorology textbooks depict a world of cold front, warm fronts, and occluded fronts. The cold front separates two airmasses, one the colder "polar" airmass, the other the warmer "tropical airmass."  The cold front is a long-lived feature in that intrudes into the warmer airmass, lifting it and producing a band of heavy precipitation.  Chance are you have seen conceptual models of this type. If only the world were so simple. The reality is that the atmosphere is a dynamic, complicated place in which troughs, fronts, and other atmospheric features are constantly evolving.  You can't put a line on a map in one area and expect it to move continuously, without evolution into another.  The developing storm for tonight and tomorrow is a prime example. There are a lot of moving parts, to take this discussion for what it's worth: A summary of a complicated atmosphere. The GFS forecast valid at 1200 UTC 26 November (0500 MST Tuesday) is below.  I've ...

Looking for powder?  Head east to the Catskills and the Poconos.  Some decent 24-hour totals out there, including 16.5" near Delhi.  It's a bit of a strange pattern, resulting from the downstream development that we've talked about in prior posts and which also led to the bomb cyclone in the eastern Pacific.  In the northeast, that eventually led to a deep closed low over the mid Alantic states.  Even Cleveland got in on the action for a bit.  Meanwhile, looking to our west, the upper elevation site (7617 ft) at the Mount Shasta Ski Park had a pretty good run the past couple of days for snowfall, but appears to be either in or just below the melting layer now.  Observations from that site show total snow depth increasing from 15 to 63 inches in about 24 hours,but temperatures also steadily increasing through the period.  Currently it is 35F, so I suspect they are seeing either rain, slush, or wet snow.  Quite a recipe for a deep, upside down ...