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How to Break the Jet Stream

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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 upper level ridge (solid black line) 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....
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Alexis Kelner 1938–2026

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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...
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The Updated weather.utah.edu

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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...
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A Pattern Change to Start October

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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...
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The Updated Wasatch Weather Weenies

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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...
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First Snow of the Season

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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....
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Monsoon Breaks and Monsoon Surges

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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 ...
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