Blog Break

Taking some down time for a couple of weeks.  See everyone in mid October.  Maybe there will be hope for snow by then.  Until then, begin with a few slow breaths, in through your nose and out through your mouth.  Let your body relax.  Visualize snowy mountains.  Imagine skiing deep powder.  Do this several times a day.  

Avenues 1, Everyone Else 0

Excuse the gloating, but yesterday's thunderstorms favored for once my are with the Avenues, downtown Salt Lake, and the University of Utah coming in with the highest precipitation totals in the Salt Lake Valley. 

Observations for the 24-hour period ending this morning show several sites reporting accumulations of around 0.3 inches.  

Source: MesoWest

Multisensor precipitation estimates of 24-hour accumulated precipitation show a band of precipitation extending from West Valley City across the Salt Lake Valley and into the Avenues Foothills.  This pattern primarily reflects three thunderstorms systems that developed and intensified in the southwesterly flow as they moved across the northern Salt Lake Valley.  The heaviest precipitation was actually in the mountains northeast of Salt Lake City.  

Source: https://mrms.nssl.noaa.gov/qvs/product_viewer/

The first system moved across the northern Salt Lake Valley from about 4:30 to 5:30 PM MDT, interrupting my mountain bike ride through the avenues foothills.  I just barely beat it back to the house.  The second moved across the valley from from about 7:30 to 8:30 PM MDT.  The third developed over downtown Salt Lake City at around 8:50 PM MDT and moved into the Wasatch Range by around 9:15 PM MDT.  As can be seen in the precipitation analysis above, there were a few other cells in other areas that developed and moved northeastward in the southwesterly flow, including one that moved across the Great Salt Lake and affected the Ogden area.  

Thanks Mother Nature.  My plants appreciate it.

UTA Ski Service Cuts

 UTA announced yesterday major cuts to ski bus service for this coming winter.  For the Cottonwoods:

• Route 953 up Little Cottonwood is suspended
• Route 972 up Big Cottonwood cut from 15-minute to 30-minute service
• Route 994 up Little Cottonwood cut from 15-minute to 30-minute service.

A full description of cuts (or what they call "adjustments") is at https://www.rideuta.com/Rider-Info/Ski-Service.  Below is a screenshot from that site, discussing their explanation for these service cuts. 

There are a few other cuts in service on non-ski routes (see https://www.rideuta.com/Rider-Info/Change-Day).  In Salt Lake county, four non-ski routes will see service frequency reductions.  

I hereby declare Joni Mitchell's song Big Yellow Taxi the official song of the Central Wasatch.  "Don't it always seem to go that you don't know what you've got until it's gone."

Bonus Season

Call it Fall if you want to, but what I like to call the "bonus season" is upon us as a ridge in late September and October makes for beautiful weather, cool mornings, and sparkling afternoons.  Add the changing leaves and you have simply spectacular weather for mountain biking, hiking, or any other outdoor pursuits that don't require snow or ice.  

Reds, oranges, and yellows are now dotting the Corner Canyon area and temperatures are near ideal for a steady morning climb.  

It's bittersweet to ride in the Corner Canyon area knowing that expansion of trails in the Avenues foothills remains paused.  Corner Canyon has a great trail network, with a mixture of hiking trails, mixed use trails, and downhill bike flow trails. 

I'm old enough to remember riding there on the old ATV and jeep trails before there was development.  Those trails have now been supplemented with better engineered single track trails, greatly expanding the riding and hiking potential.  I look forward to seeing the trails proposed for the Avenues foothills finished and hope it happens sooner rather than later. 

Storm Peak Lab Field Research Experience

I understand I've missed some exciting weather in northern Utah, but I have been in Steamboat Springs this week teaching an immersive course in mountain field research at Storm Peak Lab with Drs. Gannet Hallar and Sebastian Hoch.  We brought 14 graduate students here thanks to support from the National Science Foundation.  

Hungry students after the long drive to Steamboat

Storm Peak Lab is a mountaintop observing facility that has operated at one location or another near the top of Steamboat Springs Ski Area for more than 40 years.  The current facility was constructed in 1995.  The University of Utah recently took over operations of the lab from the Desert Research Institute.  

Inside and attached to the lab are a bevy of chemical, aerosol, biological, and microphysical instruments to better understand everything from regional air quality and pollution to mountain precipitation processes.  We spent two days at the lab learning about the instruments, planning field activities, and discussing topics such as field-program safety, inclusivity in science, and even how to take effective field notes (this sounds like a yawner but is really important!).  

We also spent time in the field.  Prior to leaving for Steamboat, the students planned a number of field activities to examine mountain weather phenomena.  Then the big monsoon surge forced us to do some pivoting and adapt, which is not unusual in meteorological field work.  We had a couple of sessions using a wind LiDAR, an instrument that can scan like a radar, but uses a laser to detect winds in clear air.   The lidar is pictured below with some of the students and a picturesque rainbow!

Ideally, the lidar is operated when it is dry (the laser does not penetrate well through precipitation and clouds), but we had enough breaks to sample some cool phenomenon, including a cloud waterfall this morning as cooler air penetrated across the ridge pictured behind the students in the photo above.  

Some of the students worked with one of our techs to develop two mobile mesonet facilities, one that attaches to our department truck and another that can be mounted on a vehicle with magnets.  They were able to drive these vehicles from low to mid elevations to sample the thermodynamic (temperature and moisture) structure and dissipation of a fog-filled nocturnal cold pool that developed over the Yampa Valley south of Steamboat on Wednesday morning. 

We've also had students looking at black carbon, which is emitted, for example, by coal fired power plants upstream of Storm Peak Lab, and attending the Yampa Basin Rendezvous, which has also been going on this week and is examining water resiliency in the Yampa Basin.  Finally, there are three students from my class who could not attend as they are participating in another field campaign in the Cape Verde Islands off the coast of Africa.  These students will be examining how the topography of those islands affects cloud and precipitation development.  

The entire week has been a great learning experience for students and instructors.  I hope to be able to incorporate such activities into future classes.  

Downstream Disruptor

Pretty exciting stuff happening right now over the north Pacific and Bering Sea where a powerful cyclone is disrupting the jet-stream level flow with implications for the weather of the western continental United States.  

Understanding the event requires going back in time to 0000 UTC 14 September (6 PM MDT Wednesday 13 December).  At this time, tropical storm Merbok was moving poleward (identified below with an L) and about to interact with a trough in the mid-latitude westerlies (red dashed line).  

These two features got together and decided to "go off."  With an assist from the upper-level trough, Merbok underwent what is known as extratropical transition, evolving from a tropical storm into a extratropical cyclone of the type found in the mid and high latitudes.  It also deepened explosively to remarkably low pressures.  At 0600 UTC 16 Sep (Midnight MDT last night), the cyclone was centered in the western Aleutians (L in the figure below) with a central pressure of 948 mb (average sea level presure is 1013 mb).  Storms like this tend to disrupt the jet-stream level flow by building a downstream ridge that can initiate a process known as downstream development in which downstream features also amplify. Indeed, the cyclone built a strong ridge over the Bering Sea and strengthened the northerly jet downstream over Alaska.  

Subsequently, forecasts indicate that the ridge will broaden and move slowly downstream while the northerly jet "carves out" a deep upper level trough off the coast of California. 

Another perspective is provided by the loop below.

Indeed, the trough developing off the coast of California will be an important weather-maker for the Golden State this weekend and early next week as it "digs" off the west coast and the associated low level frontal system moves slowly onshore.  Below is the GFS forecast for 1500 UTC (0900 MDT) Monday showing frontal precipitation over central and northern California.  

I've been watching this situation closely as my son is backpacking the southern John Muir Trail during this period.  It's hard to say if he might be dealing with significant snow prior to his planned exit on Tuesday.  The frontal precipitation either never makes it to the far southern Sierra or produces only a an inch or two of snow in many ensemble members, but there are a few that produce several inches of snow.  Below is the NAEFS plume for Mammoth Mountain (8885 ft) showing about 1/3 of the members producing 2-6 inches and the other 2/3 2" or less.  He'll be south of Mammoth, so I'm hoping he's dealing with scant snowfall amounts.