Wasatch Weather Weenies

Yesterday's maximum at the Salt Lake City International Airport was 106°F, a record for the day and just a degree short of the all-time high (107°F).  The airport measurement site has been much maligned by some as being "jacked" (i.e., too high) or unrepresentative by some.  This is a subject that we've discussed previously in this blog (see What's Up @ KSLC  and Records Falling ).  What I have noticed in social media is that there is a tendency to assume that the airport site is wrong and the other sites are right.  There is also a tendency to assume that the differences in maximum temperature at the various sites are due to either calibration issues or local siting characteristics.  In reality, there are many many factors that affect maximum (and minimum) temperature readings.   There are tens of thousands of weather sensors in the United States providing data to the internet.  The MesoWest project at the University of Utah (https://mesowes...

I was recently asked about the large difference in snowfall this past season reported by Alta Guard and Alta Ski Area and thought I would take this opportunity to talk about why they might differ and some of the challenges of observing new snow amounts.   The Utah Avalanche Center provides a long record of snowfall at Alta Guard at https://utahavalanchecenter.org/alta-monthly-snowfall.  For this past season (November through April), their spreadsheet reports only 432 inches. In contrast, for the same period, Alta Ski Area reported 606.5" (see  https://www.alta.com/weather ..note that I've subtracted 21.5" that fell in October from their seasonal total through April).  I am often asked how can there be such a large difference since they are "right across the street from each other."  Actually, the observing sites are not right across the street from each other.  The Alta-Guard observing site is located just on the north side of SR-210 just down can...

Those of you keeping score at home know that through last week, the Snowbird SNOTEL had still not eclipsed the peak snowpack water equivalents reached in the 2005 and 2011 water years.   However, things changed over the weekend.   On April 26th, the snowpack water equivalent was 72.3", the highest of this season, but a shade lower than the 75.1" reached on two dates in 2001 and the 74.6" peak in 2005.  However, from April 26th to 30th, the snowpack water equivalent rocketed upwards to 76.2", a new record.   Source: NRCS How did this happen?  Certainly not from snowfall, as the last storm was on April 25th and would have been accounted for by the measurement on the 26th.  The 26th was a spectacular day with great skiing in the wake of that storm and on the 27th the site recorded 72.0", just a shade lower than the 26th.  Then from the 27th to the 28th the measurement jumped to 75.2", despite there being no significant precipitation.  ...

What an incredible night of low-density snow at Alta.  From the 4 PM board wipe yesterday afternoon to 7 AM this morning they've had 10 inches of snow with .31" of water for an average water content of 3.1%.  There is a tendency for precipitation gauges to undercollect snowfall, but still, this is very much cold smoke.  Let's take a look at why the snow is so low density.  Two important clues are in the morning upper-air sounding from the Salt Lake City International Airport.  First, the temperatures between about 750 mb (2500 m/8000 ft) and 650 mb (3500 m/11,500 ft) are between -12 and -18˚C.  This is in the heart of the temperature range for growing dendrites, those six-armed snowflakes that we all love and can create low-density snow.  I've identified this region with the green box.  The second is that the winds in this and the surrounding layers are very light: 15 knots or less.  Thus, Mother Nature isn't bashing these flakes and they are...

Last night delivered in spades with Alta-Collins picking up 17" of snow with 1.04" of water (6% mean water content).  The Utah Avalanche Center reports 14–17" of snow in the upper Cottonwoods, 8-10" of snow on the Park City Ridgeline, and 15" of snow in the Ogden area mountains. Good news for everyone.  Total snow depth at Alta-Collins topped out last night at a remarkable 78 inches.  Periods of low-density snow will continue today and add another 2-4" to the totals at Alta.   Over the past few weeks, members of my research team (Peter Veals, Michael Wasserstein, and Ashley Evans) have been working to install some new toys such as profiling radars and other precipitation measurement systems at Highland High in Sugarhouse and Alta in order to better observed and understand how the Wasatch affect winter storms.  We are especially interested in how storms evolve from the valley to the mountains in northwesterly flow and introducing high-school students to met...

Questions about the representativeness of the KSLC observing site notwithstanding, below are the new records for Salt Lake City based on official records from the National Weather Service.  Figures are from https://xmacis.rcc-acis.org/. 1. Highest average maximum temperature, 94.1˚F.  2. Highest average minimum temperature, 68.8˚F. 3. Highest average temperature, 81.5˚F. 4. Days with a maximum temperature ≥ 100˚F, 27. 5. Days with a minimum temperature ≥ 70˚F, 53. In an earlier post ( A Look at Max Temps @KSLC ) we took a look at temperatures at the observing site compared to site on the Bountiful Bench.  At that site, records go back to 1975 and this summer's mean maximum temperature was the 5th highest (86.5˚F, the record is 87.7˚F in 2007), the mean temperature was the third highest (76.0˚F, the record is 76.4˚F in 2021), and the mean minimum temperature was the second highest (65.5˚F, the record is 65.5˚F in 2021).  Let's also look at the top 5s for each of these...

As of August 23rd, there have been 25 days with a maximum temperature of 100˚F or higher at the Salt Lake City International Airport.  This is a new record for a calendar year, eclipsing the 21 days of 100˚F or higher observed in 1960, 1994, and 2021.   Over the years, I have had many people contact me concerning the veracity or representativeness of observations collected at the airport.  It is something that I have written about previously, including in 2013 (see What's Up @KSLC ).   The reality is non-climatic factors related to instrumentation changes and biases, observing techniques, land-surface change, urbanization, irrigation, and in some instances station moves affect trends and extremes at many observing sites.  Some of these are documented, some not. A good deal of processing is done to identify and adjust for these effects to identify climate trends, a process known as climate data homogenization .   Climate trends are typically d...

Storm Peak Lab is a permanent mountain-top research facility located at 3220 m (10,564 ft) near the summit of Steamboat Springs ski area.  The lab has been in existence for more than 40 years, with equipment initially operated from a small trailer and now as a permanent facility.   Storm Peak Lab This summer, ownership and operation of the lab transition from the Desert Research Institute to the University of Utah under the direction of Dr. Gannet Hallar, with significant support for the lab coming from the National Science Foundation and other agencies.  Earlier this week, I made my first visit to the lab with a group of undergraduates who are participating in our Research Experience in ALpine Meteorology program (REALM). REALM students and other visiting scientists and students at Storm Peak Lab There are remarkably few mountain-top or high-altitude scientific laboratories in the world that collect a comprehensive suite of meteorological, cloud, trace gas, and othe...

Yesterday's high at the Salt Lake City International Airport of 107˚F set a record for the calendar day and tied the the all-time high temperature reached previously on 26 July 1960, 13 July 2002, and 15 June 2021. Nearly all stations reporting to MesoWest at elevations below 5000 feet elevation in the Salt Lake Valley were at or above 100˚F.  Record highs for the calendar day were also set at the City Creek water plant (98˚F), BYU (104˚F), and Tooele (105˚F).   I fielded a number of question yesterday about why the airport is so warm and whether or not the instrument is properly calibrated.  We have dealt with such questions many times since I started this blog over 10 years ago (for example, see What's Up @KSLC ).  Only the National Weather Service can comment on the current calibration of the KSLC instrument.  I'll address here the representativeness (or lack thereof) of the airport observing location.   Urban and near-urban areas exhibit large...

Data assimilation is the process of determining the best initial estimate of the state of the atmosphere, ocean, and land using prior forecasts and observations.  It is an absolutely essential first step in numerical weather prediction since weather forecasting is what scientists would call an initial value problem. The best data assimilation system in the world is the European Center for Medium Range Weather Forecasting (ECMWF) 4DVAR system.  4DVAR stands for four-dimensional variational assimilation. 4DVAR at ECMWF is an incredible marvel.  According to their web site, ECMWF processes and uses 40 million weather observations daily, most from satellites.  Incredibly, they have a web site where you can actually see the observations going into each forecast cycle.  The slides below summarize everything that went into the 0600 UTC 3 April initialized ECMWF forecast cycle.  You can click to enlarge, although for the purposes of this discussion, the detail...

I've been in Austria for almost a month and thanks to a little help from my friends, especially Lukas Lehner here at the University of Innsbruck, I'm finally beginning to get a handle where to find weather, snow, and avalanche information.  I'm interested in a lot more than the avalanche report, but also mountain snow and weather observations, and there are multiple sources for those.  In part, the complexity of finding all this information reflects the jurisdiction of European countries and Austrian States.  I will focus today on western Austria, which includes the Tirol and Voralberg.  Source: WIkipedia Tirol is the German spelling and I will use that here.  Curiously, the Tirol is divided into two pieces, despite it being one state.  As I understand it, this is an artifact of the World War I armistice, which ceded the Südtirol (South Tirol) immediately south of the Alpine divide to Italy.  Multilingual avalanche forecasts and information f...

The Bonneville Salt Flats, a remarkable geological wonder, in July 2008 The Bonneville Salt Flats are a remarkable geological wonder and well worth a visit and a hike of a nearby mountain.  Most people drive through them at a high rate of speed trying to get to Nevada or California as quickly as possible, but even a quick stop reveals a world completely different than any other you have experienced. The Bonneville Salt Flats are perhaps best known for land-speed events that take place on the hard salt crust to the northeast of Wendover.  In recent years, however, that salt crust has thinned and degraded, forcing cancellations or restrictions in speed events and sparking controversy concerning management of the salt flats . Brenda Bowen, a professor of Geology and Geophysics and director of the Global Change and Sustainability Center at the University of Utah, is leading a 3-year study to improve understanding of the Salt Flats and their recent change (see this Scienti...

Some of you have commented about the large difference between the DAQ sampler at Hawthorne and the observations collected along the Trax line as well as at Neil Armstrong Academy and the University of Utah. For the most part, these sensors have generated pretty similar results for the first few days of the inversion.  PM2.5 at Hawthorne has risen fairly steadily during the period (with some ups and downs) with a range from midnight on the 9th to midnight on the 10th between about 38 and 54 ug/m3.  PM2.5 at Neil Armstrong Academy (sorry for change of scale) was generally close to Hawthorne through midnight on the 10th, with the range from midnight on the 9th to midnight on the 10th of about 39 to 65 ug/m3. Source: MesoWest Source: MesoWest The divergence begins shortly after midnight on the 10th (last night), with NAA going to much higher values.  Similar, other samplers operated by the University of Utah at the University of Utah and along Trax are also repor...

This snowfall measurement brought to you by The Home Depot In a season in which we are seeing seeing remarkable snowfalls in the east (a lot of snow) and in the west (not enough), I've been dealing with a number of questions concerning long-term snowfall trends and records.  Answering these questions is sometimes complicated by the warty nature of our long-term climate records.  We have a saying in meteorology that all observations are bad, but some are useful, and this is especially true for snowfall observations, which are probably the worst of the lot. Here are just a few things that affect snowfall observations: On what surface was the snow depth measured? How frequently were observations taken? Was the measurement taken right after the storm or a couple hours later? Was the measurement taken right after the precipitation changed to sleet/freezing rain/rain or a couple of hours later? How hard was the wind blowing? Was the measurement location sheltered or ...