High Impact Weather Overnight

In yesterday's post we discussed the possibility that thunderstorms could affect the Holy War and indeed that happened.  It was fortunate that kickoff happened without a hitch.  Just before kickoff, a moderate precipitation cell passed across Utah Lake and just south of Provo.  It produced one detected lightning strike just west of the southern tip of Utah Lake.  I grabbed a couple of screenshots on my phone while watching the start of the game. 

Source: RadarNow!

Source: lightningmaps.org

Then, in the 4th quarter, another cell moved in and produced a strike about 2.5 miles south of LaVell Edwards Stadium. 

Source: RadarNow!

Source: lightningmaps.org

NCAA policy requires play to be suspended for 30 minutes when lightning is within 8 miles of a stadium.  An already late game became even later.  At least it prolonged the suffering of fans of that school down south. 

Moving on to more serious matters, media reports (e.g., this one from KUTV) suggest that a fire sparked near Bountiful at around 1 AM during a thunderstorm.  The fire spread rapidly, burning 150 acres, destroying at least 3 homes, damaging others, and requiring evacuations along the Bountiful–Centerville east bench.  Despite being called the Gun Range Fire, it sounds like the fire was lightning sparked, although I have not seen official confirmation of this (please post if you have official information). 

Whether human or lightning caused, the situation last night is an example of how fast things can go downhill in the urban-wildland interface.  It was probably minutes from fire spark to dangerous fire spread, requiring evacuations with no warning in the middle of the night.  The thunderstorm last simply provided a lightning strike in the wrong place with little to no precipitation, low humidity, and strong microburst winds, which is a recipe for rapid fire spread.  Indeed, observations from the Bountiful Bench show strong sustained winds likely associated with a microburst or thunderstorm outflow peaking at about 30 mph just after 1 am.  These winds were out of the east, which is favorable for driving a wildland fire sparked above Bountiful or Centerville into the urban interface. 

Source: Mesowest

Fortunately winds died down shortly thereafter, which should allow fire crews to get a handle on things, but not before damage was done.

I can tell you that such a scenario is what concerns me greatly about living near the urban-wildland interface.  What happened last night could easily occur, for example, in the Avenues.  A dry thunderstorm sparks a fire just above 18th Avenue and northerly microburst winds fan the fire directly into the upper Aves.  The fire would threaten homes and residents with little or no warning.  Alternatively, a human caused fire in high winds causes rapid fire spread, as occurred last summer near Ensign Peak.  It's worth a look at Calfire's website that discusses how to prepare for wildfire if you live in such an area. 

Holy War Fireworks?

I had to spend a few hours in Utah County last night.  My skin began to crawl as I passed south across the county line and my stomach churned when I saw the white letter of the school down south on the hill.  There are places where one should not linger, and Utah County is one of them.  It is best to go down there, kick butt, shut people up, and get out, as the Utes will do tonight.

The Holy War kickoff is scheduled for 8:15 PM MDT.  There is a chance of thunderstorms later this afternoon and evening.  These storms are expected to be scattered, so the pre-game festivities, game itself, post-event celebration by Ute fans, and whining by Cougar fans could go off without a hitch.  On the other hand, the potential for a thunderstorm and related impacts is there should they be in the wrong place at the wrong time. 

Chances are you have noticed the increase in humidity since yesterday.  At the Salt Lake City Airport, dewpoints yesterday were in the high 30s in the morning and near or below 30 in the afternoon.  The have, however, climbed overnight and have been hanging in the mid 40s today.  Similarly, at the Provo Airport, they are running in the upper 40s. 

It's not a juicy airmass, but it may be enough for some action to get going this afternoon.  The High Resolution Rapid Refresh (HRRR) forecast model, for example, shows some convective storms firing up in western Utah and moving into the Wasatch Front around 0000-0100 UTC (6-7 PM), with scattered storms for a few hours thereafter. 

The storms are not widespread, but they will be around.  They could kick off some microburst winds and potentially produce a little lightning.  Precipitation will probably be limited.  Hopefully all will go off without incident, but there is a low but non-zero threat of thunderstorm impacts.  Should a thunderstorm approach, don't linger in the open or other lightning exposed areas, even if precipitation is scant.  Stadiums are not safe during thunderstorms.  Heed the advice of stadium officials, even if those officials are from that school down south.

August Running Hot

With four days left in the month (including today), August is running hot at the Salt Lake City International Airport.

The mean temperature for the month so far is 80.1˚F, which if it holds, would make this August the 7th warmest on record and warmer than any August prior to 1994. 

Source: NOAA Regional Climate Centers

Last night we got down to 62 and the forecast high for this afternoon is 96, which would make a daily mean of 79˚F.  The subsequent last three days of August have forecast lows and highs of 72/94, 69/95, and 69/96.  These numbers will end up having a fairly small influence on the monthly mean, so 2013's record 82.7˚F is likely safe, but we're still looking at a warm August, even if some recent nights have felt cool.

Meteorological fall starts on Sunday, although it probably won't feel like it. 

To Piste or Off Piste, That Is the Question

An article last week in The Telegraph explored some of the confusion that exists about "itinerary" ski runs in Europe and highlights many of the ambiguities and contrasts that exist concerning controlled vs. non-controlled terrain at ski resorts in Europe.  

Source: https://www.telegraph.co.uk/travel/ski/articles/what-is-an-off-piste-itinerary-ski-run/

Until I saw the article, I'd never heard the term "itinerary" ski run before, which highlights some of the cultural challenges that exist when skiing in a new region where approaches to resort avalanche hazard may vary.  Essentially, itinerary runs are typically ungroomed routes.  For example, freeride-verbier.com states that itinerary ski runs in the Swiss Alps are designated off-piste routes and marked on the ski map, but they are not maintained or controlled (see link).  They are indicated with yellow lines on a piste map.

The culture and approach to avalanche "control" (I put that in highlights because the white beast is never truly controlled) at resorts varies internationally and in some cases within countries.  In the United States extensive extensive efforts are undertaken to reduce avalanche hazard and provide access to avalanche terrain.  This leads to an environment where little thought is given by in bounds skiers concerning avalanche hazard.  Indeed, the avalanche hazard in open in-bounds terrain is quite low, although it isn't zero.  On average, about one avalanche fatality per year occurs in terrain that has been opened by the ski patrol at U.S. ski areas.  

In Europe, the story is different.  Control work focuses on pistes, marked ski runs, and not in the extensive off-piste terrain.  Don't expect a rope line or sign to tell you when you are going into avalanche terrain.  You might find a sign here or there, but you might not.  

Late spring "cream" skiing at Hintertuxer Glacier in Austria.  The markers denote the edge of the piste to the right.  My son is skiing "off piste".  Not pictured are steeper avalanche paths farther up the mountain that could be a concern on higher hazard days, especially closer to the steep rock wall.  Although there were signs at the top of the lift, there are no signs here.  It is essential to recognize that beyond the piste markers, you are entering a higher risk area.

In Austria, some resorts include "routes" on their piste maps, typically with dashed lines.  For example, the "14" ski route at Stubai Glacier is marked with a dashed line and is called a ski route on the map, in contrast to the ski pistes denoted with solid lines.  It is, however, sometimes groomed.  The route itself is intermediate, but traverses avalanche terrain.  

Route 14 at Stubai Glacier

Although control work is done, the hazard along European pistes is reduced but not nonexistent if they are in avalanche terrain.  Below is a slide that hit the piste at Hintertuxer Glacier while it was open for skiing in May.   

If you are skiing in Europe, it is best to assume that off piste is de facto backcountry.  Further, do not assume that skiers and tracks off piste imply "safe" conditions.   In January 2015, an off-piste avalanche in Sölden, Austria took the lives of US Ski Team racers Bryce Astle and Ronnie Berlack.  Off Piste: Tragedy in the Alps is based on their tragedy and worth watching to raise awareness of avalanche safety.  

Off Piste: Tragedy in the Alps from BRASS Foundation on Vimeo.

Not Much Recovery for the Great Salt Lake

Although it was a decent snow year in northern Utah, the reality is that the Great Salt Lake didn't recover much this year.

USGS lake elevation data at Salt Air shows the annual cycle of lake elevation, which tends to be highest in the spring and lowest in the fall.  There was a net decline in lake elevation from 2011 to 2015 and a very modest recovery in 2017.  Currently, we're running a bit less than 1 foot higher than August 2018.

Below are modis images from the NASA Terra satellite from late August 2011 through 2019 (date in the lower left hand corner).  Consistent with the elevation data above, you can see a decline in lake coverage after August 2011 and then the recent spate of relatively low lake coverage years.

I would like to see a run of big snow years not just for my skiing interests, but also to see how much the recovers.  If we had the 1980s precipitation again, would we see the same increase in lake volume (i.e., increase in height and area) as was observed then given our warmer climate and greater thirst for water? 

Notes on comments:

A blog reader wrote me a note earlier this week letting me know that they were unable to post a comment to the blog.  If you are having problems, please send me an e-mail (jim.steenburgh at gmail.com) so I can see how extensive the problem is.  I am hoping it is an isolated case.

For the record, I do not screen comments, other than running the automated blogger spam filter and deleting spam that slips through the net.  I don't think I've ever had to do this before, but I would also delete posts that I consider inappropriate.  I am grateful that comments in the 8 or so years since I've started this blog have been respectful and polite, especially given the decline in civility that has occurred elsewhere in the social media world.

Update on comment issues: Searching through blogger support, I found recommendations that commenters who are having this problem should make sure cookies are not blocked, try clearing their browser's cache and cookies, or if they are running chrome, try it in incognito mode.  Sadly, there is no easy solution but perhaps one of these will work.  

Experimenting with E-Bikes

My ride for the week

The options for commuting to campus continue to grow as the options for electric assist devices such as e-scooters and e-bikes continue to grow. 

For many years, I have biked or bussed to campus.  Our present home in the upper avenues is, however, about a 10 minute walk from a bus stop and it sometimes takes me 25 minutes or so to get to campus, which is longer than I would like. 

If I ride my bike, the short but steep return home isn't something that would bother me for a workout, but isn't what I'm looking for every day after work, especially on hot summer days when I'd like to keep my pasty white skin covered by clothes.    

This summer, my son purchased a refurbished e-bike for commuting to his summer internship.  Now that he's back in school, I borrowed his e-bike to give it a try this week.  It is a class 2 e-bike, which means you can throttle on demand and ride with no pedaling.  You can also use pedal assist.  The motor is in the rear hub and the battery in the down tube.  The bike is fully rigid.  Basically, it is a commuter bike. 

The first thing that I noticed was weight.  You don't get something for nothing, and the electric motor, battery, and my odds and ends for work probably bring the weight to nearly 50 lbs (the GenZe web site reports a bike only weight of 46 lbs).  This is about 20-25 pounds heavier than a typical full suspension mountain bike.  It affects maneuverability and it takes time to get used to when mounting, dismounting, stopping at a light, or just pushing it around when you are leaving the garage, shed, office, or porch.  It also affects stopping distance.  The bike has disk brakes, but they are a poor substitute for what I have on my mountain bike and they are stopping more weight.  I am especially aware of this when I'm descending down from the aves.  I break much of the way down Terrace Hills and keep speeds under 25 mph.  

That being said, the 250 watts of power makes for a very easy commute.  On the flats of 11th avenue, the bike can maintain its governed maximum speed of 20 miles per hour with no pedal assist.  False flats and low-angle climbs are relatively easy climbs.  The bike has 5 different assist levels and I usually just keep it at maximum and pedal gingerly.  I'm interested in leisure on this thing, not a workout.  

On the steeps, pedal assist is required.  The ride up Terrace Hills is pretty steep and the bike nearly comes to a halt on throttle only.  With pedal assist, I can maintain 8-9 miles per hour without a great deal of effort.  Yesterday, when it reached 99˚F at the airport, I rode home at about 5 PM in a pair of pants and long sleeves and just barely broke a sweat when I got to the house.  The electric assist plus my own horsepower probably add up to one Tour de France rider, but the bike ain't a Tour de France bike and rather than revving up the diesel, it's best just to pedal moderately, stay in the saddle, and enjoy the ride.  

The bottom line is that I'm pretty impressed and think this is a good option if you are looking for something easier than a regular bike commute.  For my commute, which is marked by steep downhills and uphills, I might like some suspension, better brakes, and a bit more power although that would add to the cost.  

A Letter to the Future

Iceland's Okjökull glacier once capped the Ok Volcano, but was declared dead in 2014.  This past weekend, a plaque was placed on Ok that included a letter to the future.

Source: Forbes/Boyer/Cymene Howe

Talk about a great way to remind people that indeed we do know what is happening, but we also know what needs to be done.  Really, we have known this for some time, but the "cracks" in the climate system are really starting to open up now and people are seeing it with their own two eyes. 

We could use a few more of these letters.  Here's one for the Wasatch Mountains. 

Whither the 2019 Monsoon?

We are now deep into mid August and thus far the 2019 monsoon has been a bust for precipitation across much of the southwest U.S., including Utah.

Precipitation for the 60-day period ending 18 August is at or below average across much of Arizona, Utah, Nevada, and Southern California.  Much of Texas is similarly below average, with only New Mexico having something close to or above average. 

This past weekend we were in Phoenix helping my daughter move in for her 2nd year at Arizona State.  The high on Friday afternoon when we arrived was 111ºF, followed by 108˚F on her Saturday move-in day.  Brutally hot, with not much in sight but one thin, distant rain shaft on Friday afternoon. 

Although one might hope that in August we'd see a greater likelihood of precipitation compared to July, climate is what you expect and weather is what you get.  The challenge we are currently having in Utah is one in which the mid-latitude westerlies are just far enough south to keep us in a dry airstream, but not far enough south to get us into cooler-than-average air, as illustrated by the GFS 4-day forecast loop below.  The monsoon precipitation (green and blue color fill) remains predominantly east and south of Utah. 

Although I would not rule out the chance of a shower or thunderstorm over the mountains during this period, the coverage and intensity of precipitation is limited.  We just don't have a circulation right now that favors the transport of monsoon moisture into the state.  Hence, dry conditions will predominate through at least the work week. 

How the Alta Snowflake Is Really Created

It may be hard to believe, but not everything you read or see on social media is true.  Often, the fallacy is cleverly hidden because it is distributed by what appears to be a reputable source.  Even experts and professional groups can be fooled or make mistakes.

Several days ago, @ZonePhysics, issued the tweet below showing how a drop of water turns into a snowflake.

How a drop of water turns into a snowflake ..... pic.twitter.com/FVdIa8ROtH

— Physics & Astronomy Zone (@ZonePhysics) August 12, 2019

That certainly looks like a convincing video and a reliable source.   Some people suggested the video showed the creation of the Alta Snowflake depicted on the Alta blue-dot logo below.

Source: alta.com

It's a wonderful story, but unfortunately it's not true.

The video above doesn't show the formation of a snowflake, it shows the melting of a snowflake.  The video is run in reverse, so it appears the water turns into a snowflake.  It's convincing, but misleading and inaccurate.

The Alta Snowflake is a rendition of a snowflake known as a stellar dendrite.  Stellar dendrites have six arms shaped like a tree (dendrite means tree like) and a star-like appearance.  Hence the name.  Ken Libbrect's great guide to snowflakes includes photos of many types of stellar dendrites.    

Source: Snowcrystals.com

Snowflakes of this type do not form from water turning into ice.  When a large water droplet, say a raindrop freezes, you get a ball of ice, often referred to in the United States as sleet.  Sleet is rare in Utah, but a common feature of the so called "transition zone" between rain and snow found in the warm-frontal region of cyclones over the central and eastern United States.

Instead, stellar dendrites form primarily from water vapor condensing directly to ice through a process known as deposition. Liquid water is not involved at all.  It is possible to demonstrate the process in a cold chamber under the right conditions.  Here's an example produced by Ken in his lab.  

Ken has many more videos of snowflake growth available at www.snowcrystals.com/videos/videos.html.  Knock yourself out.  

All of this is not to say that water turning into ice doesn't contribute to the growth of real-world snow. Most snow-producing clouds consist of a mixture of ice particles (including snowflakes) and liquid cloud droplets.  The liquid cloud droplets are colder than 0˚C (32˚F), but have not yet frozen.  Scientists call this supercooled.  Under the right conditions, these droplets collide with and freeze onto snowflakes and other ice crystals through a process known as accretion or riming.  Below are images, reproduced from my book and taken by the Electron and Confocal Microscopy Laboratory of the U. S. Department of Agriculture, of a lightly rimed ice crystal known as a plate (top right), moderately rimed dendrite that has been broken up some (center right), and a heavily rimed ice particle in which the original ice particle or snowflake is indistinguishable (lower right).  The latter is called graupel.  

Source: Secrets of the Greatest Snow on Earth

Stellar dendrites, because of their long branches and arms, typically produce low-density (i.e., dry) snow because of all the gaps and pores within the crystal structure.  Real storms are comprised of many different types of snowflakes and ice particles, but if you want blower pow, stellar dendrites are going to be abundant.  Thus, the Alta marketing people knew what they were doing.  On the other hand, the Alta skiing cognoscenti know that graupel, despite its high density, also produces amazing skiing.  It just wouldn't look that good as the basis for a logo.  

Snow!

A little something to brighten your day today.  Although there are no freshies in Utah, the Hintereisferner in Austria received a coat of white in the past two days, although it must be thin since the snow did not survive on most of the exposed ground surrounding it. 

Yesterday I had to put a jacket on to descend City Creek Canyon on my early morning ride.  We've had minimums in the 60s five of the last six days.  Day length is decreasing noticeably now. 

It's coming!

The Meteorology of the Salt Lake City Tornado (1999)

Today is the 20th anniversary of the Salt Lake City tornado, which I would rate as the most significant meteorological event to affect my neighborhood (The Avenues) since we moved there in 1996.

A detailed account of the tornado event is described by Dunn and Vasiloff (2001).  The tornado formed just west of downtown Salt Lake City and tracked roughly northeastward through portions of downtown, Memory Grove, and the Avenues.  It produced a path of moderate to considerable damage consistent with a rating of F2 on the old Fujita Scale (since replaced by the Enhanced Fujita Scale).  The damage path looked as if someone had sliced across the area with a surgical knife producing a narrow swath of damage with no damage in the surrounding area.

Source: Dunn and Vasiloff (1999)

The tornado touched down at 1840 UTC (1240 MDT).  I recall that we had gone with a group out to lunch and were returning to the office, commenting about the darkness of the sky and joking as Utah meteorologists do about it potentially being a "severe" day (this isn't tornado alley).  Shortly after returning to the office, someone yelled "tornado to the west", a comment that was initially met with derision, but eventually we all ran outside to watch.  The photo below was taken by our department web cam, looking west from the Browning Building on the University of Utah campus.

Source: University of Utah, Dunn and Vasiloff (1999)

It was the first and thankfully only tornado I've seen personally.  In reality, the smart thing to have done would have been to call my family and the National Weather Service immediately.

The tornado tracked within 2 or 3 blocks of our home.  My parents were in town and as the story goes, my father was eating lunch, looked out the window, and said "holy s---, a tornado."  I do not know if that is true, but it's a good story if it isn't.  He took my year-old son and my mom into the basement where they spent a tense several minutes.  We found some debris on our roof, but that wasn't anything to complain about.

In these pre-twitter days, we had no idea how bad things were until we began looking around the neighborhood that evening.  It was heartbreaking.  The Deseret News published a good review of the event two years ago that is worth a read and included the photo below, which shows the catastrophe suffered by our neighbors.

Source: Gary McKellar, Deseret News

The tornado resulted in one fatality, 80 injuries, and 300 damaged or destroyed buildings, 34 of which were uninhabitable.  Total damage was estimated at $170 million.

Dunn and Vasiloff (2001) show that the tornado formed along a convergence zone that was may have been a lake breeze front.  A strong updraft, associated with convection that formed initially over the Oquirrh Mountains, moved over this boundary and led to tornadogenesis.  The tornado was what is sometimes referred to as a non-descending or nonsupercell tornado.  Such tornadoes are typically short lived and more challenging to forecast, and indeed, the National Weather Service issued no tornado warning.

One reason for the lack of warning is poor observation of the lower atmosphere over the Salt Lake Valley by the National Weather Service Doppler Radar on Promontory Point, KMTX.  That year, however, the FAA installed a Terminal Doppler Weather Radar (TDWR) near Layton.  The TDWR was designed for detecting wind shear and other hazardous weather conditions at the Salt Lake City airport and provides higher resolution and lower altitude surveys over the Salt Lake Valley.  The data it collected was used extensively by Dunn and Vasiloff (2001) to understand the event. 

Integration of the TDWR data into National Weather Service operations, combined with improvements in KMTX scan strategies and algorithms, offer some potential that a warning would be issued for a similar tornado if it occurred today in the Salt Lake City area, although the lead time would likely be short (minutes).  Issuing warnings for this type of tornado is still very difficult and poses many challenges for contemporary forecasters.

One thing I take away from this event is that it could happen again.  Perhaps not in the same way, but the ingredients that came together on August 11, 1999 are not all that uncommon to find.  We often see convection initiating over the Oquirrhs and a convergence zone somewhere over the Salt Lake Valley as the lake-breeze front penetrates southward.  Most of the time, things don't align properly, or the convection isn't strong enough, or the the land-breeze front is sharp enough.  We also see weak tornadoes from time to time in other parts of Utah, something that has become more apparent with the proliferation of smart phones.  We should be cautious about discounting the likelihood of these events and attentive during periods of severe weather.  Know to take action by moving away from windows and exterior walls and into the basement or small interior rooms of your house (e.g., bathroom).  See https://www.ready.gov/tornadoes for more information.

The Joy of Solar

I did some work this past week on my chimney, which required me to get up on my roof.  While up there, I was reminded that I have a set of solar panels up there that have been doing the job now for about 2.5 years.

They are pretty stealthy.  Our roof is low pitched, so you can't see them at all from the road or from our yard.  They make no noise.  They produce no emissions.  Yet over the past 2.5 years, they've generated 23.2 megawatt hours of power.  We just pay our $9 grid-tie fee each month to Rocky Mountain Power and call it good. 

We've seen no drop off in production, despite the fact that I've done no maintenance.  July is a good month to gauge production since the weather variability is lowest during that month.  Over the past 3 Julys, we produced 1186, 1163, and 1173 kilowatt-hours of power.  That's pretty damn consistent. 

Whether or not solar makes sense for you depends on many factors.  However, I can give it a big thumbs up for our sun-exposed home. 

Downpours, Debris Flows, and Road Closures, Oh My!

Yesterday evening's storms came through with a vengeance for some areas of northern Utah, generating heavy precipitation and debris flows that forced the closure of SR-210 in Little Cottonwood Canyon, SR-6 in Spanish Fork Canyon, and the Amtrak line through Spanish Fork Canyon, as well as the evacuation of residents near Loafer Canyon.

It was only a couple of weeks ago that the Tour de France was forced to alter stages due to severe thunderstorms and debris flows in the French Alps.  At that time, I wrote that organizers of the Tour of Utah should take the opportunity to learn from that experience since they be dealing with a similar scenario (see Weather Hazards and Bike Racing).  Although I recognized this as a possibility in Utah, I wasn't anticipating that we would see such a severe event this year.  Nevertheless it has happened, and the prologue scheduled for Little Cottonwood Canyon is only three days away (Monday, August 12).  Of course, when it comes to incidents like this, there are more important issues at play than a bike race.  Thankfully, I haven't heard any reports of fatalities or injuries.

Let's take a look at what happened in Little Cottonwood late yesterday.  To begin this discussion, we should first note the conditions leading up to the event.  On August 1st, the Alta Coop Site reported 0.40 inches of precipitation.  On the 3rd, the it reported 2.11 inches of precipitation.  That event produce runoff in the upper canyon, with shallow layers of mud and rocks covering the road in the upper canyon in places (see Saturday's Cottonwoods Deluge).  The next four days leading up to yesterday's event produced 0.01, 024, 0.01, and 0.02 inches of precipitation.  Thus, the water content of soils in the canyon was likely high, limiting their ability to absorb and retain precipitation.

I suspect it rained lightly yesterday morning (although automated gauges at Collins and Alta Base show no measurable precipitation).  As that precipitation band exited, skies cleared and band of precipitation with embedded thunderstorms began to move into northern Utah.  See the tweet below for radar image at 2222 UTC/1622 MDT).  The stage was set for late day thunderstorms.

Time to queue up the Carly Simon. Everyone now. Anticipation... pic.twitter.com/JzaVsI4ajV

— Jim Steenburgh (@ProfessorPowder) August 8, 2019

Indeed, those storms produced, with embedded cells generating locally heavy precipitation.  The radar loop below covers the period from 0102-0220 UTC/1902–2020 MDT with a black line indicating the ridgeline between Little and Big Cottonwood Canyons.  It shows a very intense cell moving across the southern Salt Lake Valley and into the central Wasatch.  Radar reflectivities above 35 dBZ and frequently above 50 dBZ, indicative of heavy precipitation, linger on the ridge for a period of about 40 minutes.

Radar estimates of precipitation have their issues and so one needs to recognize their can be large uncertainties, but the one I have access too pegs the maximum accumulated precipitation for the 1 hour period ending at 0220 UTC/2020 MDT at about 3 inches very near the Little Cottonwood-Big Cottonwood Ridgeline.  That pixel appears to be just north of Lone Peak in the upper Broads Fork/Lake Blanche area.  Although that is north of the divide, there is some uncertainty in the exact location of where precipitation falls out due to transport by the wind and other factors in and below the radar sampling volume.

The bottom line is that heavy precipitation fell in a short period of time in an area where soils were already somewhat compromised by prior precipitation.

Given that the storm came in at dusk, UDOT is just starting to send out videos of the damage.  Here's one from their Public Information Officer John Gleason.

UDOT crews making progress clearing debris in Little Cottonwood Canyon. Some of our folks that have worked in the canyon for 30 years say they have never seen anything like this. pic.twitter.com/c90ShC3Xz1

— John Gleason (@johnegleason) August 9, 2019

Inevitably, I expect that we're going to hear that this was a "one in whatever year" event.  Based on the NOAA Precipitation Frequency Data Server, a three inch accumulation in 60 min has an average recurrance interval at 10,500 ft in the central Wasatch of about 500 years.  Or, better put, the odds of such an accumulation happening at any point in that area in any given year is about 500 to 1.

However, some caution is needed here.  First, I'm not sure how confident to be in the radar precipitation estimates.  That is going to require some digging.  Sadly, I don't think there is a precipitation gauge very near the area of maximum precipitation.  Alta-Collins, Alta-Base, and the Snowbird SNOTEL reported .45", .59", .7", respectively, in the 1-hour period ending at 0200 UTC/2000 MDT, but they were outside the core of heaviest precipitation.

Second, as you can infer from the 1-hour accumulation image above, thunderstorm accumulations can be very localized.  Remember that 500 to 1 is a point probability, not an area probability.  The odds of such an accumulation happening somewhere in the Wasatch Range would be greater.

Nevertheless, this was certainly an exceptional event with remarkable impacts.  It serves as a reminder of the vulnerability of mountain communities and highways, especially SR-210, to severe and hazardous weather.

Blogger's Note: The recurrence interval figure has been updated from the original post to include the legend. 

"Perfect" Weather

If you've lived in Utah long enough, you know that a "perfect" weather day in July or August isn't sunny, but instead cloudy with rain or at least rain showers.  Today nails it as far as I'm concerned.

As of 2:30 PM MDT, we've had predominantly cloudy skies all day with some showers and some drippy rain at times.  Temperatures overnight were warm and the overnight minimum was only 69ºF, but after a warm start to the morning with temperatures in the mid 70s, rain moved in and dropped the temperatures to as low as the mid 60s at about 1 PM.  At 2:20 it was 71ºF with a dewpoint of 62ºF.  PERFECT

Source: MesoWest

Really, on the regional scale, the airmass we're presently in isn't all that cool.  Move south and you'll find an 88ºF in Milford or north for an 82˚F in Dubois.  Thank the well timed showers for the natural air conditioning today.  

And, as I like to say, things are going to get interesting later today.  The band of showers that came this morning and early afternoon is exiting to the north and a nice clear slot is opening up over northwest Utah.  Further upstream and just beginning to move across the boarder are some stronger storms. 

Lightningmaps.org shows that the stronger cells are producing lightning.  

So, speaking like a meteorologist, if we're lucky, we'll get some action later this afternoon and this evening as the sun juices things up.  Keep your fingers crossed.

Secrets about Syllabi

OK, this isn't really about secrets about syllabi, but that's a catchy headline and since the Salt Lake Tribune decided to make the addition of safety information in syllabi at the University of Utah a major story (click here), I thought we could talk about it a bit today.

The University of Utah and other institutions of higher learning in the United States are facing many challenges related to campus safety and student mental health.  In the case of campus safety, I think it is safe to say that gun violence is an omnipresent concern, but there are other concerns including rape, sexual assault, harassment, etc.  In the case of student mental health, an increasing number of students at U.S. institutions of higher education, including the University of Utah, are seeking mental health services (see Under Pressure: The Growing Demand for Student Mental Health Services).

As a faculty member and a parent with two kids in college, one at the University of Utah, these issues concern me greatly.  In addition, spending time teaching at the University of Innsbruck earlier this year was a real eye opener.  First, gun violence is much less common in Austria and I can't recall ever having to do active shooter training as I have done both voluntarily and as mandated here at the University of Utah.  Second, stress amongst students is noticeably lower.  I didn't think once about adding statements about campus safety or counseling services to my syllabi there.

Here, however, I've voluntarily included a statement on counseling services in my syllabi for several semesters.  I decided to do this after visiting Penn State where, while discussing the difficulties contemporary students are having managing stress and other challenges, I learned they were requiring such a statement.  I read over their statement, decided it was a good idea, and adopted it to suit my needs.  It's not much, but at least I can mention it to students and let them know that I'm thinking of them and provide them options for professional support. 

I will add the campus safety statement, although I do have some concerns.  As noted in the Tribune article, there are some professors that are concerned that there are simply too many things being added to the syllabus.  Indeed, each semester, I consult the University of Utah Center for Teaching and Learning Excellence Syllabus Checklist, which includes a list of essential and strongly suggested content for syllabi.  It is now seven pages long.  Amongst the essential and strongly suggested content are statements or recommendations to include statements on sexual misconduct, campus safety, the academic code of conduct, student names and personal pronouns, diversity/inclusivity, undocumented student support, faculty and student responsibilities, content accommodations, syllabus changes, plagiarism software policies, official drop/withdraw date, attendance/tardy policy, wellness statement, the veterans center, learners of English as a second language, plus some additional statements concerning online and hybrid courses.

I don't wish to argue that any of these are unimportant, and I recognize that it is my option to include some of these in my syllabus, but the University needs to think much more carefully about how to prioritize this information and select what is most effectively provided via a syllabus versus other means of dissemination.  As the proverb goes, "the road to hell is paved with good intentions."  There are certainly good intentions behind these efforts, but with prioritization and pruning, we have a better chance of ensuring that our desires lead to effective outcomes.  Just because the syllabus is a convenient place to add statements, doesn't mean that it will be an effective place to provide information.  Let's make it easier for students to sip from the fountain of knowledge rather than being soaked by a firehose.

Saturday's Cottonwoods Deluge

In late July, the last two mountain stages of the Tour de France were shortened due to hail and mudslides associated with severe convective storms of the western Alps.  As we discussed in a blog post following stage 19 (see Weather Hazards and Bike Racing), there is a very real possibility that the Tour of Utah could be affected by a similar storm.

Indeed, it is a good thing that the Tour of Utah wasn't being held in the Cottonwoods yesterday afternoon when severe thunderstorms dumped their goods in the central Wasatch, producing what the National Weather Service reported as two-inch per hour precipitation rates.  

Hail was also observed and covered the highways in both canyons per the National Weather Service.

Hail is covering the roads in the upper reaches of both Big and Little Cottonwood canyons!!! (Image courtesy of the Utah Dept. of transportation) #utwx pic.twitter.com/uS6FqsFJbA

— NWS Salt Lake City (@NWSSaltLakeCity) August 3, 2019

Alta today showed plenty of evidence of heavy rainfall and associated runoff with a shallow layer of mud and rocks covering the highways and parking lots in places.  It must have been a scary experience for anyone caught out hiking, climbing, or biking during this storm. 

Let us hope we don't have a repeat for the Tour of Utah.  

July Was Hot, but Thankfully Is in the Rearview Mirror

Yesterday was a wonderful last day of July.  Temperatures at the Salt Lake City International Airport topped out at 92˚F, but with rain moving it, it was drippy and 69˚F by 6 PM.  It was wonderful to feel the cool air and let my skin soak up the moisture.

It was my impression that July wasn't horrible.  This might reflect the fact that I lived through the European June heat wave or that we did have the occasional cool day to break up the July low-variability monotony.  However, a look at the numbers shows that the average temperature at the Salt Lake City Airport this July was still remarkably warm compared to the past.  It rates as the 9th warmest since 1874.  And, just to illustrate that you aren't living in your grandparents climate, there wasn't a single July as warm as this one until 2003.  In other words, this July was hotter than any July on record in the late 19th and 20th centuries.

Source: NOAA Regional Climate Centers

Further, the 12 warmest Julys have all occurred in the 21st century.  Brutal.

Elsewhere in July, probably the two biggest stories globally have been the extreme warmth observed in late July in Europe, during which all-time high temperatures were recorded in Belgium, Germany, Luxembourg, the Netherlands, and the United Kingdom, as well as significant melting events on the Greenland Ice Sheet.  The World Meteorological Organization (WMO) provides a summary here.  June 2019 rated as the warmest on record, and I suspect July will rate amongst the warmest if not the warmest.

Thus, it's good to have July in the rearview mirror.

Addendum:

Posting time series from Heber City and Tooele for comparison and to illustrate that similar trends are seen elsewhere and in less urbanized areas, although the urbanization may exacerbate things in Salt Lake.