Wasatch Weather Weenies

Yesterday (Tuesday) morning, the Salt Lake City International Airport observing site, which is located at the south boundary of the airport just north of I-80, observed as rogue of a rogue shower as you will ever see.  The storm produced rain at the observing site from about 0725–0755 MDT, generating 0.16" according to the rain gauge.   KSLC Time Series 0725–0755 MDT 6 Oct 2026. Source: NWS. The radar at 1317 UTC (0717 MDT) showed the rogue cell moving over the airport as it intensified.  The cell was perhaps 5 km across and developed pretty much over or just upstream of the southeast corner of the airport.     The weather cam image at the top of this post, taken looking west from the University of Utah, shows just the narrow area of falling precipitation associated with the cell.  What conspired to make such an isolated precipitation shaft is known only to Mother Nature.   Radar-estimated precipitation from the National Severe Storms La...

There are three provocative public lectures coming up this month at the University of Utah.   Two are this week, are hosted by The Wilkes Center for Climate Science and Policy, and will be given by Myles Allen, who is visiting from the University of Oxford.  The first explores the role of climate change in extreme weather events.   The second explores what it would take to stop global warming.   Each of these is being given in the L.S. Skaggs Applies Science Building, which is a new building (and my home) just off of University Street.  I don't think it shows up on Google Maps yet, but it is immediately west (and connected to) the Stewart Building (see  https://map.utah.edu/?buildingnumber=18 ). Do not confuse it with the Skaggs Biology Building which is a bit farther to the east.   The third talk is an evening Frontiers of Science lecture being given by Nobel Laureate Martin Chalfie on October 22.  Parking and RSVP information...

Two very powerful cyclones, one from the tropics and one from the mid to high latitudes, are going to conspire over the next several days to break the jet stream.  The tropical cyclone is Typhoon Choi-Wan, currently southeast of Japan with maximum sustained winds of 110 knots.  Source: Joint Typhoon Warning Center The mid to high latitude cyclone hasn't formed yet, but is expected to develop over the Sea of Okhotsk on Wednesday.  The ECMWF HRES forecast below from Tropical Tidbits is valid 1800 UTC Wed Oct 7 and includes sea level pressure contours (black lines) and 500-mb height (color fill).  The big circle identifies the mid to high latitude system, the little circle Choi-Wan, which at this point is transitioning into an extratropical system, and the black line the upper level ridge downstream of these two systems.   Source: Tropical Tidbits By 1800 UTC Saturday 10 October, those two cyclones have merged into a massive 976 mb low over the Bering Sea....

I never met Alexis Kelner, but I was saddened to see that he passed on September 23rd at the age of 87.   If there was a Mount Rushmore of Wasatch Mountain backcountry skiers, mountaineers, historians, and conservationists, Kelner would surely be on it.  His obituary summarizes many but surely not all of his contributions.   I first encountered his name as one of the authors of the Wasatch Tours series, which was essential reading when I moved to Utah in the 1990s.  By that time, the series, co-authored with another Utah ski legend Dave Hanscom, had expanded to three volumes.  The original, published in 1976, was the first backcountry ski guidebook for the Wasatch.   For the youngsters out there, there were no cell phones or backcountry ski apps.  There was no Utah Avalanche Center (founded in 1980).  Avalanche transceivers were in their infancy and not available for Kelner's early ski touring adventures.  Skis were skinny and...

Updates to weather.utah.edu went in today.  In addition to being on a new server, the site has a new look and feel matching current University of Utah branding and has better fonts, more descriptive alternative text, keyboard navigation, etc.  Bookmarks from the old site have a good chance of working, but if they are broke, you may need to update them.   Much thanks to our partners at the University of Utah Center for High Performance Computing (CHPC) for making this possible.  Thanks as well to data and software providers (NCEP, ECMWF, Penn State, Iowa State, AWS, Unidata), not to mention developers of the many python packages we use, students and other collaborators who have helped with code development, and OpenAI Codex which I've been using for code updates.  It takes a village to build a site like this.   We hope to eventually have a 1-2 month archive available through the "View a Different Run" option at the top for several models.  Rig...

The models are advertising a significant pattern change to start October, one that will curl the smiles of snow-safety teams in the Wasatch Range.   Over the past several weeks, the large-scale pattern has been characterized by persistent troughing along the Pacific coast and ridging over the south central United States, as shown by the mean 30-day 500-mb heights for the period from 31 August to September 29.  Source: PSD Maproom This general pattern is consistent with the North American Monsoon, but these two major circulation features were stronger than on average.  In other words, the Pacific trough was deeper and the ridge over the south central United States were stronger than observed.  This "opened the door" for frequent monsoon surges into northern Utah and occasional severe convective storms due to the stronger flow and wind shear between the two circulation features.   The pattern is changing, however, for October.  The ECMWF AIFS analys...

After 16 years, the Wasatch Weather Weenies has a new look and feel as I was getting tired of the increasingly dated look of the old site.  Let me know what you think.  It should also be improved on mobile devices.   The Wasatch Weather Weenies began on October 1, 2010 as an invitation only blog for discussing the weather and climate of the Wasatch Front and Mountains, western United States, and mountainous regions in general.  It started out as invitation only because I didn't want discussions to descend to the levels widely seen in social media.  However, I quickly had so many people asking to read it that I decided to make it publicly viewable and accessible.  Thanks to you, comments have remained mostly substantive and approved for all audiences, and I'm grateful for that.  I'd actually like to see more questions, comments, and suggestions, so feel free to do so liberally.  Total page views for the blog recently eclipsed 10 million, but t...

I spent the weekend in Seattle and got to spy my first fresh snow of the season while hiking south of Snoqualmie Pass on Saturday.  The higher elevations of the Alpine Lakes Wilderness, including Chikamin Peak had a fresh coat of white above 6500 feet.   To the northeast, the Stuart Range was also freshly coated.   Winter is coming....

A monsoon is a seasonal shift in the winds that produce pronounced changes in precipitation.  In North America, the North American Monsoon System is a circulation system characterized by mid-and-upper level high pressure centered over the southwest United States that brings easterly flow across much of northern Mexico and showers and thunderstorms to that region and portions of the southwest United States.   Precipitation associated with the North American Monsoon waxes and wanes.  These variations are called monsoon breaks (little to no precipitation) and monsoon surges (more frequent precipitation).   Precipitation associated with the North American Monsoon is heaviest and most frequent in northwest Mexico and decreases to the west and north.  In northwest Mexico, monsoon precipitation is more frequent and may occur daily except during monsoon breaks.   Source: https://www.climate.gov/news-features/blogs/enso/north-american-monsoon In ...

Friday was a remarkably active thunderstorm day in northern Utah, including a verified tornado in the Wasatch Mountains east of Fruit Heights.   Sadly, a 19 year old man was killed by lightning on the summit of Mt. Timpanogos Friday morning.  Media reports suggest the victim was taking shelter during the storm in the shack on the summit, with authorities called around 6 AM.  Lightningmaps.org provides access to strike data for 24-hour periods.  The map below is for 0600 UTC 18 September to 0600 UTC 19 September (Midnight to Midnight MDT Friday) showing the high density of strikes in the Mt. Timpanogos area and surrounding region.  The prevailing flow was such that the storms on Friday were moving from southwest to northeast and you can see a strong clustering extending from southwest of Utah Lake over Mt. Timpanogos.   Source: https://www.lightningmaps.org/ It's unclear precisely when the lightning strike occurred, but at the time of the rep...

The NWS issued a tornado warning this afternoon for an area including portions of Weber, Davis, and Morgan Counties. Of concern is one of the best developed mesocyclones (a rotating vortex about 10 km across) I've seen in northern Utah.  Radar reflectivity showed a classic "hook echo" associated with the storm as it impinged on the northern Wasatch near Farmington.  NWS Doppler radars measure the radial velocity toward or away from the radar, so mesocyclones produce a very clear signature of rotation with a couplet of inbound (green and blue) and outbound (red) velocities colocated with the hook.  This is indicative of the small scale rotation associated with the storm.  The mesoscale rotation does not necessarily mean that there is a tornado.  About 25% of mesocyclones produce tornadoes, but that's certainly enough to warrant a warning in this case.   Let's hope this was just a well-developed mesocyclone that didn't produce a tornado.  

CPC released their latest seasonal outlooks yesterday.  These are based on overlapping 3-month periods.  For November to January and December to February, all or nearly all of Utah is in "equal chances" for precipitation, which means there is no significant shift in the odds for below normal, near normal, or above normal compared to climatology.   Source: https://www.cpc.ncep.noaa.gov/products/predictions/90day/ In other words, that period could go any way.  There's no useful skill.   Later in the winter, during January to March and February to April, most of Utah is in the first level of "above normal" or, in the case of southern Utah, especially later in the winter, in the second level.  For southern Utah, this means there is an increase in the odds of above normal precipitation to 40-50%.  For northern Utah, that shift is much smaller and perhaps to around 35% or so for the Wasatch Range.   Source: https://www.cpc.ncep.noaa....

Some of you have asked about the status of weather.utah.edu as it has been down for off campus access now for at least 24 hours.   I was told that "the campus default deny seems to be blocking weather.utah.edu from outside of campus."  I really have no idea what this means other than you can't get to it from off campus.  The people that help me with the web site told me they have contacted the powers that be, but it remains down.   Those of you who are affiliated with the University of Utah, including my students, can access weather.utah.edu if you fire up the campus VPN from an off campus location.  That's the best I can do for now other than hoping we'll be back in business soon.  I'll just say that the struggle at the U is real.  

Yesterday's high of 93°F at the Salt Lake International Airport was a record for the day but not really all that exceptional when you consider that the record high on the previous day (September 11) is 99°F and a couple days later (September 15) is 97°F.  Somehow September 13 has never gone out-on-the-limb for maximum temperature compared to the surrounding days.  Such are the realities of climate statistics.  That said, yesterday's maximum temperature was out-on-the-limb in terms of what was forecast.  Several days ago, we posted that the forecast for tomorrow (Sunday) was uncertain.  Some models, like the GFS, were bringing in a cold front on Saturday , resulting in much cooler weather for Sunday.  Others, like the ECMWF AIFS brought the front in during the day on Sunday.  I'm not sure if any called for the cold front to come in Sunday evening.     These days one can process the forecast from well over 100 ensemble forecasts to produce...

This is not a comprehensive sample, but it appears that all of the persistent snow patches that linger deep into summer and fall that I can typically spy from the top of Snowbird are gone.   I hiked up the bird this morning and it was about as clear as it gets when I arrived on the summit.  I couldn't spy a single patch of snow below the American Fork Twins (this has been the case for at least a couple of weeks) or in upper Hogum Fork where snow tends to linger.   Thus it appears that this summer we have had a full and complete reset of the central Wasatch snowpack, although perhaps one of you out there can tell us that there is a patch lingering somewhere.  Central Wasatch does not include Mt. Timpanogos where it is more likely that something remains around the Timpanogos Snowfield and rock glacier.   Snowbird though is preparing to do something about this as I noticed they are beginning to deploy their snowguns.   Meanwhile, Ski Utah i...

Yesterday I submitted a final report for the last grant I received from the National Oceanic and Atmospheric Administration (NOAA), which ended on July 31.  This brings to an end 28 years of continuous funding from that agency, so I'd like to give a big thank you to NOAA, the NOAA/National Weather Service, and NOAA Oceanic and Atmospheric Research for supporting the work of my graduate students and collaborators at the University of Utah and beyond.   If my math is right, I've served as principal investigator (PI or lead scientist) or co-principal investigator (coPI or someone with shared leadership responsibilities) on 15 NOAA grants from 1998–2026.  In 1998, we began to receive annual grants from NOAA for weather support for the 2002 Olympic Winter Games, including the installation of weather stations at Olympic Venues and around the Great Salt Lake, the creation of what became MesoWest (led by John Horel), the development of numerical and statistical forecasting ...