Wasatch Weather Weenies

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 ...

Forecast uncertainty doesn't always grow continuously with forecast lead time.  Sometimes there is an issue with the intensity and timing of a weather system that can cause uncertainty to increase temporarily and then decrease at longer lead times. A good example is the forecast for northern Utah this weekend.   The models all bring in a strong cold front, but there are variations in the timing and intensity. The GFS forecast valid 1200 UTC 13 September (0600 MDT Sunday) shows one scenario with the cold front through northern Utah, a deep trough at 500 mb centered over the central Idaho Mountains, and cold post-frontal flow over northern Utah.  700-mb temperatures in far northwest Utah are below -2°C.   The ECMWF AIFS has different ideas.  The front is much slower and for the same time valid above (0600 MDT Sunday), the front is just getting to Salt Lake City and the upper-level trough is centered over northeast Oregon.  The 700-mb temperatures in...

Weather for the start of the Labor Day weekend today (Friday) looks pretty good.  The large-scale pattern hasn't really changed dramatically for some time.  There's a trough centered over the Pacific Northwest coast and a ridge over the central US.  These features have been around for some time, shifting in strength and position.  Right now, the southwesterly to southerly flow between these features is relatively dry, so shower and thunderstorm activity is suppressed or limited.  Today should be quite nice across most of Utah other than some gusty winds, as indicated by the ECMWF HRES forecast for 0000 UTC 5 September (1800 MDT Friday).   However, lurking in that forecast is Hurricane Marie off the coast of Baja (Hurricane Karina is also visible in the plot farther to the west).  Marie is expected to move northwestward over the next few days, and therein likes the forecast problem.  Although Marie will weaken, her moisture is going to move in...

Meteorological summer (June, July, and August) is now in the books and as usual it is great to have it in the rear view mirror.   Summer was a scorcher by long-term standards at the Salt Lake City International Airport.  The average temperature was 80.2°F, the 7th highest all time (the record is 81.4°F set in 2022).  A look the long term trends in summer temperatures shows we are no-longer operating in the climate that prevailed during the 20th century.  The 10 hottest summers on record were all in the 21st century when the trend is clearly upward.   Mean Average Temperature June-August at the Salt Lake City International Airport.  Source: https://xmacis.rcc-acis.org/. We also set an all time maximum temperature record of 109°F on July 12th, tied the all time high minimum temperature record of 82°F on July 27 (set previously in 2021 and 2023), and saw 20 days with a maximum temperature of 100°F or higher (the record for summer is 27 in 2022 a...