Northern Utah Mesocyclone

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.  

Latest CPC Seasonal Outlooks

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.gov/products/predictions/90day/

In other words, something like a 36% chance of above normal, 33% of normal, and 31% of below normal.  

The long and short of this is that the far southwest has the highest likelihoods of above normal.  These odds decline and northern Utah is pretty much in a spot where there is not a lot of weighting of the dice.  The outlook this year largely reflects historical influences of El Nino and strong El Ninos, although predictions by climate forecast systems (numerical models that forecast several months in advance), and other tools. 

So, whether we see an above average snow season in the Wasatch this winter is still pretty much up in the air.  My advice is to just ignore all these predictions for the Wasatch and spend that time getting into shape and enjoying the outdoors.  

Status of weather.utah.edu

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.  

An Out-on-the-Limb Maximum Temperature

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 a range of possible forecast outcomes.  This is what the National Weather Service does for their National Blend of Models (NBM) forecast.  On Tuesday we posted about the enormous spread for the maximum temperature forecast for yesterday (see An Uncertain Sunday) with the middle 50% of high temperature forecasts lying between 68° and 84°F (see the tallest red box in the left-hand graphic below).  

That middle 50% is sometimes referred to as the interquartile range.  However, half the forecasts lie outside of that box.  The whiskers surrounding the box extend through the middle 80% of forecasts (or from what is called the 10th to 90th percentile).  In this case, the top whisker extended to 92°F.  That means that 90% of the forecasts called for a maximum temperature at or below 92°F.  

I went back to that NBM forecast distribution and it turns out it ended at 92°F.  In other words, not a single forecast member called for a maximum at or above 93°F.  The observed maximum temperature on Sunday was outside of the entire predicted ensemble range.  

Ideally that would not happen except in the most exceptional circumstances, but our ensembles are not perfect.  Forecasts do sometimes verify outside of the ensemble range and that's a sign that we still have work to do.  

Part of what made the forecast for Sunday challenging was the occurrence of something called anticyclonic wave breaking (AWB).  If you have been to the beach, you have experienced wave breaking.  As water waves approach the shore, they decelerate and steepen.  Eventually the waves steepen to a point where they overturn and break down into turbulence, or what scientists call wave breaking.

Breaking wave. Source: NOAA.

The waves you experience at the beach are gravity waves that occur at the interface between the high-density water and the lower-density atmosphere.  Gravity waves also occur in the atmosphere where gravity wave breaking is one important cause of aircraft turbulence. 

In AWB the waves that are breaking are not gravity waves but very large-scale atmospheric waves known as Rossby waves.  Rossby waves are named after Carl-Gustaf Rossby, who did pioneering work on the jet stream and the dynamics of upper-level waves in the middle 20th century.  He was even featured on the cover of Time Magazine in December 1956.

Source: https://content.time.com/time/covers/0,16641,19561217,00.html 

Rossby waves are the large-scale upper-level troughs and ridges that we observe at upper-levels (i.e., jet-stream level) in the atmosphere.  These waves are so big (1000 km or more across) that the rotation of the Earth strongly affects their behavior.  

Like waves at the beach, Rossby waves can also "steepen."  In contrast to water waves that steepen in the vertical, Rossby waves "steepen" in the north-south direction, which is what happened last week over the north Pacific. At 1200 UTC 10 September, there was a ridge over western Alaska and a trough over the northeast Pacific.  This ridge-trough system amplified over the next 24 hours, with the 500-mb height contours "steepening" and turning clockwise (anticyclonically) on the downstream side of the ridge.  Eventually, the 500-mb height contour "broke" in the sense that higher 500-mb heights were north of lower 500-mb heights.  This is consistent with the red contour crossing the purple meridian three times at the end of the plot sequence below.  Think of the ridge pushing over that meridian as an overturning wave with the surfer in the the tube or trough at lower elevations.  

AWB is associated with the amplification of a strong upper-level ridge, which is often related to the release of heat by condensation in precipitation systems just upstream of the ridge.  Although AWB events are often predicted reasonably well in terms of their occurrence, the details (i.e., the "turbulence") can be hard to get right.  Sunday was a hard forecast because the strength and position of the trough and cold front was challenging to anticipate.  The 93°F we hit on Sunday reflects the fact that the AWB produced a stronger trough than anticipated, delaying its progression across the Pacific Northwest.  

Surfers can be surprised by breaking wave behavior.  So can meteorologists.  

Reset of the Central Wasatch Snowpack

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 is pinning all of their hopes on the Super El Niño.  One of my students gave me the sticker below from yesterday's Utah Avalanche Center Backcountry Benefit.

It remains hard to say if a vote for Super El Niño will yield change we can believe in.  I suspect a continuation of the incredibly poor status quo from last winter is unlikely, but whether a change in the majority climate party turns inflation (i.e., rising temperatures) around and results in improved job (i.e., powder) prospects for Wasatch citizens remains uncertain.  

Thank You NOAA

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 systems for northern Utah, and a major field campaign to understand winter storms in the Wasatch Range known as IPEX.  Impacts of this work for regional and Olympic forecasting were described in a series of articles in the February 2002 Bulletin of the American Meteorological Society, coinciding with the 2002 Olympics.  

After the Olympics, we received a series of grants over the next 15 years or so from the National Weather Service Collaborative Science Technology and Applied Research (CSTAR) program, which was designed to transfer basic and applied research into operations through collaborative research between academic groups and National Weather Service Forecasters.  This work enabled continued expansion of MesoWest (led by John Horel) but also efforts to advance understanding of the meteorology of the western United States including the Great Salt Lake effect and atmospheric rivers.  

One key advancement during this period was improved understanding of the inland penetration of atmospheric rivers over the western United States.  This work was led by one of my graduate students, Jon Rutz, who also served as an intern at the National Weather Service while in graduate school.  His paper, Climatological Characteristics of Atmospheric Rivers and Their Inland Penetration over the western United States, published in 2014, has been cited more than 700 times and amongst other things illustrated key pathways for atmospheric river penetration into the western US interior.  It also illustrated the more "fickle" relationship between atmospheric rivers and precipitation over the interior compared to the coastal ranges, Cascade Mountains, and Sierra Nevada upstream.  This work is important not only for weather prediction, but also for understanding and projecting future changes in climate and snow hydrology over western mountain ranges.  

About ten years ago, as the CSTAR program was reaching an end, Justin Minder at SUNY Albany contacted me about a new opportunity at NOAA for winter weather funding.  This led to three more grants, the most recent ending on July 31, exploring ways to improve snowfall prediction not only over the western US, but across the continental United States.  This was a dream project for me.  Our most recent publication based on this work explores the use of machine learning to improve snow-to-liquid ratio prediction.

Readers of this blog have benefited from this work as many of the forecast techniques we've developed have been tested and evaluated on https://weather.utah.edu/.  The Utah Snow Ensemble, for example, could not have been developed without the capabilities developed with this NOAA funding.  We are working on upgrades to weather.utah.edu that will more prominently feature the many snow guidance products that we've developed over the years.  Below is a preview of what the new site will look like.

Our most recent proposal to NOAA to continue our work was recommended for funding but was ultimately unfunded due to cuts during the DOGE operations.  While disappointing, I've had an unusually productive run of NOAA funding and am grateful for 28 years of solid support.  I am also grateful for talented students and collaborators who have worked with us on these projects and made the journey fun and exciting.  All of my graduate students have benefited from NOAA funding and are now contributing to the success and growth of the weather enterprise.  Thanks again NOAA.