Sunday, April 20, 2014

The Deception of City Creek Canyon

City Creek Canyon has to be one of the most remarkably accessible and spectacular canyons in the United States.  It's mouth is just a couple of hundred yards (if that) from downtown Salt Lake City, with the upper basin reaching altitudes of over 9000 feet.  It is also an important source of water for Salt Lake City.

Looking up the canyon from the Avenues foothills this afternoon makes you wonder where all that water comes from.  It was a poor snow season in the lower elevations and, remarkably, there's already very little snow visible in the canyon.

Indeed, the Louis Meadow SNOTEL at 6700 ft in City Creek Canyon bottomed out and went snow free today.  However, City Creek is a very deceptive canyon.  It is very hard to see City Creek's upper basin (purple area below) between Grandview Peak (also pictured above) and Lookout Peak (blocked in the photo above by Black Mountain) from either downtown Salt Lake City or the Avenues foothills (approx location and view of photo indicated by triangle).

If one looks at the Lookout Peak Snotel, just east of City Creek's upper basin at at an elevation of 8200 feet, one finds that the snowpack actually peaked a bit above average and is currently near average for this date.  A hint of this can be seen in the photo where you can just see some of the snow on Grandview.  Altitude makes a big difference this year.

Source: CBRFC
Given the pathetic low-elevation snowpack, the total runoff volume in City Creek will probably be below average this year, but the high elevation snowpack should keep some natural flow going through the spring.

Saturday, April 19, 2014

The Demise of Science Reporting in Utah

Ted Booker of the Watertown Daily Times (NY) attended a talk I gave in
upstate NY on lake effect.  Interactions of this type between scientists and
reporters are becoming less common in Utah (Photo: Ted Booker)
My career has spanned a remarkable transformation in the way that we communicate and receive news.  As an undergraduate, the Internet was still confined to a small cluster of institutions and Universities.  I received my first e-mail address when I started graduate school and it was a big deal at the time (1989) to access the National Center for Atmospheric Research Supercomputer (a Cray Y-MP, about as fast as today's iPad) using the Internet.  Just a few years later, when I completed my Ph.D., we were running forecast models on desktop computers and distributing the output via the Internet.  At the time I remember arguing with colleagues about whether or not anyone would ever make money with the Internet.  I defended my dissertation in February 1995.  Jeff Bezos and Amazon sold their first book online in July 1995.  If only I knew!

Although the Internet has been great, it, along with the proliferation of media via cable and satellite dish, has had some caustic effects on news in general and science reporting in particular, at least at the local level.  When I first arrived at the University of Utah in 1995, I interacted frequently with full-time science reporters.  You can't learn and report about the nuances of climate science in a 5-minute interview, so having a dialog over many interviews, e-mails, phone, etc., allows the reporter to gain a more in depth knowledge of the subject, which leads to better reporting.  Science reporters like Ed Yates of KSL used to sit down with me and ask a lot of questions before even beginning the on camera interview.  There was an effort to both understand the science and it's implications first, and then dig into the subject on camera.  There's only so much you can do in a 60-second TV bit, but I believe this led to better reporting.

In recent years, the science reporter has largely been eliminated by most local stations.  Today, they usually just send a cameraperson who reads a list of questions from the producer, which are provided in advance.  There is no interactivity or probing.  I could just declare that I've discovered a cure for cancer and that would be that.  No followup questions asked.  We can insert that bit after we discuss what is trending on Twitter.

Similarly, print media is now in rapid decline.  Judy Fays of the Salt Lake Tribune covered environmental science extensively and interviewed me regularly for many years in person and by phone.  She worked that beat and knew what questions to ask.  Brian Maffly has done an admiral job trying to fill the void since her departure from the Trib, but he has a broader assignment base.  Further, the Trib just eliminated another 8 newsroom jobs.  One has to wonder if we will soon have nobody in Utah media with at least some focus on science.

On the plus side, the Internet has brought ways for scientists to interact directly with the public, including blogs such as this one.  One can also easily access articles by national or international caliber science reporters via various news feeds or by going directly to outlets like the New York Times and Guardian.  Nevertheless, the decline in science reporting in Utah is a net loss given the opportunities and challenges that can be better seized or addressed with a more informed public.

Friday, April 18, 2014

Recipe for a Warm Night

Last night, temperatures fell little from yesterday afternoon's peak.  At the University of Utah, for example, we peaked at 72ºF yesterday afternoon.  Climatologically, the overnight minimum is roughly 20ºF lower than the afternoon maximum, but last night temperatures remained mild all night, dropping only briefly to a minimum of 61ºF.

Source: MesoWest
The recipe for a warm night is relatively well known.  Rather than clear and calm, you want clouds and wind, and we had them both last night.  But what makes the clouds and winds so effective at keeping temperatures elevated?

Let's start with the clouds.  It is often said that clouds act like a blanket, but this is a terrible analogy if ever there was one.  A blanket keeps you warm because it prevents the mixing of air near your body with cooler environmental air.  This slows the net loss of heat from your body to the atmosphere. In contrast, clouds contribute to warmer nights by providing an additional source of energy to the Earth's surface—namely infrared (a.k.a., long wave) radiation emitted by the clouds themselves.  Often it is said that clouds "trap", "reradiate", or "reemit" radiation coming from the Earth's surface, but this is also an oversimplification that is somewhat misleading (we will save that discussion for another day).  With this extra source of energy, the Earth's surface cools at a rate slower than it would on a clear night.  All else being equal, low clouds usually result in warmer nights than high clouds because low clouds are usually warmer and thus emit more infrared radiation.

Now on to wind.  On a calm night, there is typically very little turbulence to mix the air near the Earth's surface.  As a result, the cooling is concentrated in a very shallow layer and temperatures fall dramatically.  Sinkholes and basins often observe the lowest overnight minimum temperatures as they become very calm at night.  Wind generates turbulence, however, and instead of forming a shallow layer near the surface with very cold temperatures, you are constantly mixing the air, leading to warmer conditions near the surface.

So, last night with extensive cloud cover and strong winds, we simply didn't see temperatures drop as they do on a clear, calm night.  Thank the radiation from the clouds and the mixing from the wind.

Thursday, April 17, 2014

Altitude and the Timing of Snowmelt

Altitude strongly affects the timing of peak snowpack [snow water equivalent (SWE)] and melt throughout the central Wasatch.  Here's how things are progressing this year.

The lowest SNOTEL station in the Wasatch Mountains is Ben Lomond Trail in the northern Wasatch (6000 ft).  This is a remarkably snowy location for its elevation.  On average, Ben Lomond Trail reaches a peak SWE of almost 20 inches in late March.  This year, however, the peak of about 16 inches occurred in early march, afterwhich the snowpack clung to life until early April when it began to melt rapidly.  More than half of the peak SWE is already gone as of today.

Source: CBRFC
In the central Wasatch Mountains, Parley's summit is the lowest SNOTEL (7500 ft).  Here, the average peak SWE of about 15" occurs somewhere in mid-March to April 1st (more data is needed for a smoother curve!).  This year, Parley's has behaved a bit like a low-elevation station that experiences mid-season thaws.  Note that there was a snowpack peak in mid March, followed by one in early April, both fairly close to the climatological peak.  Since that peak in early April, they've lost nearly half of the snowpack.  

Source: CBRFC
The fact that Ben Lomond Trail, which is 1500 ft lower, has a deeper snowpack than Parley's Summit, illustrates just how wet and snowy the Ogden Valley is.  What a great low-altitude snow climate!

Moving higher we find the Mill-D North SNOTEL in Big Cottonwood Canyon (8960 ft).  Here the climatological snowpack peak of about 24 inches is in early April, and this year was pretty much right on the nubbin for SWE and timing (despite a late start).  We've also seen a small (~15%) loss of snowpack in the past two weeks.  

Source: CBRFC
Similarly, the Brighton (8750 ft) and Thaynes Canyon (9200 ft) SNOTESL have peaked and are on the decline.  Barring a big storm, this is the beginning of the end of the snowpack at this elevation.

Finally, we have Snowbird, the highest SNOTEL in the central Wasatch (9640 ft).  Ah, it's good to be high and on a north facing aspect.  Here, the peak snowpack occurs climatologically in very late April.  This year, we haven't come close to that peak, and we're just starting to get the snowpack ripe enough (i.e., warmed up to the melting point through its entire depth) to start losing snow.

Source: CBRFC
Snowbird may not have peaked yet.  If we can get a late season storm, we might see it go up a bit more.

Wednesday, April 16, 2014

Will Global Temperature Records Fall?

Much has been made of the so-called global warming "pause" or "hiatus", a term that has been used to describe the slowdown in the rate of increase of surface temperatures over the past 10–15 years.  As we have discussed in previous posts (e.g., Global Warming Hasn't Stopped), this period has been marked by continued warming of the ocean, melting of ice, and warming of the land surface, so there is every reason to expect a return to more rapidly rising surface temperatures in the future.

In addition, there is some potential that we will see a new global surface temperature record in 2014 or 2015.  It is looking increasingly likely that El Nino will develop this summer or fall, with some indicators suggesting that it could be a moderate or strong event.  

El Nino is characterized by relatively warm sea surface temperatures in the tropical Pacific Ocean which, along with other accompanying changes in atmospheric and oceanic circulations, typically leads to an increase in global temperatures.  Conversely, La Nina is associated with relatively cool sea surface temperatures in the tropical Pacific Ocean and a decrease in global temperatures.  This can be seen in the graphic below, which categorizes years based on El Nino (red), La Nina (blue), or neutral/other conditions (a.k.a., "No Nino").  
Source: NCDC
That categorization doesn't distinguish, however, between weak and strong El Nino events.  1998 was characterized by a very strong El Nino and it remains one of the warmest years on record.  Note what an outlier it was compared to the period in which it is embedded.  There has subsequently been only one El Nino Year (2010) and it was a weak one.  However, the most recent 10-year period is clearly the warmest decade in the instrumented record so it is quite likely that a moderate to strong El Nino will likely yield record global surface temperatures.  

In the above analysis, NCDC classifies a year as El Nino or La Nina based on the first three months of the calendar year.  This reflects that fact that El Nino and La Nina typically reach their peak strength during the Northern Hemisphere winter.  However, this also makes the categorization a bit more difficult since the peak El Nino/La Nina conditions often straddle the start/end of the calendar year.  For example, some classify 2010 as a La Nina year since there was a rapid transition from El Nino to La Nina conditions during the Northern Hemisphere spring and summer.  

On the other hand, there is often a lag of a few months between peak El Nino/La Nina conditions and the accompanying increase/decrease in global temperature anomalies.  This is why we might need to wait for 2015 for a record.  Alternatively, we could bag this calendar year crap and instead look at a 12-month period encompassing the peak El Nino/La Nina period.  Here's what the global temperature trend looks like for July-June average temperatures.

Source: NCDC
In this instance, the hottest year is 2010 (i.e., July 2009-June 2010), which includes the moderate 2009–2010 El Nino, followed by 2007, which was characterized by a transition from weak El Nino to neutral or very weak La Nina conditions, and then 1998, which featured the strongest El Nino on record.

All of this suggests that if we can get a moderate to strong El Nino to develop, we will probably see record setting global temperatures for some 12-month period if not the calendar year.  Perhaps even a weak El Nino will do the job.  We'll have to see how things come together in the coming months and see if there are any surprises, like a huge volcanic eruption to cool things off. 

Tuesday, April 15, 2014

The Central American Cold Surge

We frequently talk about how the tropics and subtropics visit Utah in the form of cool-season atmospheric rivers, but there are situations in which high- or mid-latitude airmasses plunge southward into the tropics.  This is especially common to the east of the Rocky Mountains and Sierra Madre, which frequently act to channel relatively cool airmasses to Central America or, in extreme events, northern South America.

A great example of these Central American Cold Surges is affecting Mexico and Central America today.  Note in the loop below (especially the lower panel), the surge of relatively cool high pressure from the central United States into Central America.   To save bandwidth, I haven't plotted a longer loop to fully show the history of this event, but the airmass currently plunging into Central America originates in northwest Canada.  Brrr...

As these cold surges move southward, they are modified and warmed, but they are still relatively cold when they get to Mexico and Central America.  Check out the stiff north winds observed along the east coast of Mexico this morning.  The 59ºF with a wind of 23 mph at Tampico can't feel too comfortable for sunbathing.

Source: MesoWest
That 59 also represents the lowest temperature observed in Tampico since mid March, which was probably when they had their last major cold surge [note that wind gusts (green dashed lines) are also the strongest since that mid-March event].

Source: MesoWest
The cold surge passed Palenque, MX this morning and is about to reach Guatemala.

Source: MesoWest
Amongst the more remarkable mountain weather phenomenon that are produced by these Central American Cold Surges are strong gap winds that push through Chivella Pass in southern Mexico and extend over the Gulf of Tehuantepec.
Source: The COMET Program
This results in some very unusual phenomena.  First, one often sees a cold front pushing into the tropical eastern Pacific, which can sometimes be accompanied by a narrow rope cloud.

Source: Steenburgh et al. (1998)
Then there are very strong gap outflow winds over the Gulf of Tehuantepec.  These winds are very unusual because along the the center of the outflow jet they are inertially balanced, which causes them to curve rightward (relative to the flow) at a rate precisely predicted by the rotation rate of the Earth.  This is perhaps the cleanest example of atmospheric inertial flow anywhere in the world.   

Source: Steenburgh et al. (1998)
Finally, interactions between the strong winds and the ocean lead to an upwelling of nutrient-rich water to near the surface, which is an important aspect of the marine ecology of the Gulf of Tehuantepec.  

In 1998, I wrote a paper on these gap outflow winds with David Schultz and Brian Colle.  It was an entirely curiosity driven research project for which we had little-to-no financial support.  This paper has become the most popular of my research career, with citations in everything from oceanographic to renewable energy journals.  It is a prime example of why I often tell my students to never let the best laid plans get in the way of good serendipitous research.