Sunday, May 29, 2016

Lightning Safety Lessons

I need to pick on myself today for poor lightning safety practices.  Much like avalanche accidents, human factors often come to play in lightning accidents.

As I was heading out for a quick mountain bike, a cell was popping over the Oquirrhs.  It wasn't much to be concerned with at the time, but I made a mental note to keep an eye on it.  Plus, I needed to be somewhere later and had to get my ride in.

The climb from the valley to the ridge was uneventful, other than running into this not-so-friendly fellow.

I know little about snakes, but I come across one about once a month in the warm season.  Usually they are gopher snakes.  I'm not sure what this one was.  It was fairly non-aggressive and wasn't rattling, but a close look at the tail suggested it may have been a rattlesnake that had lost the rattle.  I watched him slither into the grass and kept my distance.

Getting back to lightning safety, I didn't hear any thunder on the climb, but on the summit, although the main cell was in the distance, it was clear that the anvil had overspread me.

Anvils are capable of producing lightning, so being somewhat removed from the main cell is no guarantee of safety.  As I rode along the trail at elevation, I heard thunder, which was a tell-tale sign that I should have turned around earlier.

I made it home safely and a quick look at showed now cloud-to-ground strikes anywhere near my ride.  However, a post-ride assessment show it would have been best to wait.

Saturday, May 28, 2016

Frustrating Forecasting

Developing thunderstorm over the Oquirrh Mountains yesterday morning
It's been a tough go finding something to blog about in the current pattern.  With weak troughing and instability over the region for many many days, we've had nothing but hit-and-miss showers and thunderstorms.  Such patterns are the ultimate in forecasting frustration for me. There's no magic pill you can take to forecast this stuff.  You can go for modest changes in coverage and frequency (e.g., today probably won't be as active as yesterday in the Salt Lake Valley), but even that's fleeting.  A couple of days of this I can live with, but it's been going on for so long I feel like Bill Murray in Groundhog Day!

It does look like we'll be getting a drying out and a warming up early next week.  Probably by next Wednesday I'll be wishing for a return of the unsettled weather!

Thursday, May 26, 2016

What Is the PDO?

Anyone who follows seasonal predictions, including those critical to Wasatch Weather Weenies like snowfall, is immediately confronted with an acronym stew of climate indices such as ENSO, PNA, AO, NAO, PDO, IPO, QDO, MJO, etc.

This post is concerned with the PDO, or Pacific Decadal Oscillation, because I receive many questions and comments regarding its use for seasonal snowfall outlooks over western North America.  

What is the PDO?

If we skip over the gory statistical details, the PDO is simply the dominant pattern of sea-surface temperature (SST) variability in the North Pacific.  The positive (a.k.a. warm) phase of the PDO features a horseshoe of relatively warm (compared to climatology) SSTs along the west coast of North America and the eastern subtropical North Pacific with relatively cool SSTs over the midlatitude western and central Pacific.  
PDO Positive Phase.  Source: Wikipedia.
During the "cool" or negative phase, the pattern is reversed.


By the mid 1990s, scientists recognized that an abrupt, widespread change in the climate of the North Pacific Basin occurred in the late 1970s.  They were also identifying shifts in ecological indicators, such as production levels of Pacific salmon, that occurred on time scales of about a decade.

Steven Hare, a fisheries scientist at the University of Washington, first used the term Pacific Decadal Oscillation in 1996.  Subsequently, Nate Mantua, an atmospheric scientist at the University of Washington and an avid fisherman, led the seminal paper identifying the main characteristics of the PDO and its relationship to salmon production in 1997.  

Mantua et al. (1997)
Nate's contributions in this area are evidence of the Anthony Doerr quote that "there is a connection between thinking and fishing mostly because you spend a lot of time up to your waist in water without a whole lot to keep your mind busy."  

Driving mechanisms

The PDO was identified statistically and is not a single phenomenon.  Research over the past 25 years shows that the PDO reflects the combined influence of several atmospheric and oceanic processes operating at differing time scales.  One is ENSO, the El Nino/Southern Oscillation, with El Nino and La Nina reflecting the warm and cold phases of ENSO, respectively.  The relationship between the PDO and ENSO is apparent in the illustration above, which in addition to showing the North Pacific SST pattern associated with the PDO positive phase, also shows a tongue of anomalously warm water in the tropical Pacific consistent with El Nino, the warm phase of ENSO.  ENSO contributes to the PDO by influencing the mid-latitude atmospheric circulation over the North Pacific.  Other mechanisms affecting the PDO include interactions between the Aleutian Low and the North Pacific Ocean, a phenomenon known as "reemergence" in which ocean temperature anomalies from the prior cool season persist at depth in the ocean and reemerge the next cool season, and other aspects of ocean dynamics in the north Pacific.  Yeah, there's a lot going on, as illustrated by the "summary" view below.
Source: Newman et al. (2016)
The key point is that the fluctuations in North Pacific SST that we call the PDO are a reflection of a several processes operating in the atmosphere and ocean.  

Implications for climate variability and prediction

The fact that the PDO is a reflection of many processes has a number of implications for climate variability and prediction.  For one, correlation with the PDO does not necessarily imply causality.  For example, a relationship between the PDO and snowfall in a given region could reflect an alternate forcing mechanism, such as ENSO, rather than the PDO.  Assigning causal linkages to the PDO should be done very cautiously.  For two, combining the PDO with other modes of climate variability like ENSO to try and improve predictions for any given season partly represents a form of "double counting" since the two are intrinsically linked.  Whether or not this ultimately degrades the usefulness of seasonal predictions is unclear, but one needs to be cautious.   Like an onion, the more you peel it, the more it stinks.  

For those who are really interested in gory details about the PDO, a review article by Matt Newman and colleagues entitled The Pacific Decadal Oscillation, Revisited, is about to appear in the Journal of Climate.  It's paywalled, but freely available in early release mode to those of you from campus or who have a subscription for American Meteorological Society journals.

Correction: The Pacific Decadal Oscillation, Revisited, is public access, so anyone can have a look.  Thanks to the authors (or their funding agencies!) for making that happen.  

Tuesday, May 24, 2016

The Central Wasatch Need Better Transit and a Better Fee Plan

It's a bluebird powder day a few years in the future and you're heading out for a backcountry tour.  You haven't picked a destination yet, so you bring your Mill Creek Pass in case you tour in Mill Creek, your interagency access pass in case you go to Cardiff Fork, your UDOT Snowpark Pass in case you tour Butler Fork, and your Town of Alta Snowpark in case you decide to up-and-over from Alta to Big Cottonwood.

You pick up your buddies, decide to tour Wills Hill due to the high avalanche hazard, and decide to park at one of the Park-n-Rides at the bottom of Big Cottonwood.  Unfortunately, you got a late start and the lots are full.  You decide your best bet is to drive.

Double unfortunately, it's total gridlock at the bottom of the canyon.  That used to be a thing in Little Cottonwood, but now it's a thing in Big Cottonwood too.

So, you inch up Big Cottonwood, but when you get to the Solitude Lot, not only is it $10 to park (that's not covered by your fee plans either), but the lot is full.  You'd park on the road, but that's impossible.  Cars stretch as far as the eye can see.

All of these fee programs, but none of them have addressed the most critical issue in the canyons: Improving the accessibility, frequency, and reliability of mass transit.

These were my thoughts when I picked up the Salt Lake Tribune this morning and learned that the US Forest Service is considering implementing a fee program in Big and Little Cottonwood Canyon.

To be sure, I'm not opposed to fees.  I buy a National Parks and Interagency Access Pass every year.  For me, the proposed US Forest Service fees in the Cottonwoods would not be an additional financial burden (although I am sensitive to how such a program might reduce recreation access for other groups and individuals).

No, what concerns me is the potential for piecemeal implementation of these and other fees while having little impact on the real challenges facing the central Wasatch.  The US Forest Service desires to improve parking lots, picnic areas, and trails.  While a laudable goal, it is the automobile that is despoiling public recreation in the Wasatch.  It's difficult to imagine that the proposed $6 three-day or $45 annual fee is going to do anything about that, especially since there is no public transit in the Cottonwoods during the hiking season.

What is needed is a real transportation plan, a strategy to fund it, and a unified, non-balkanized fee program to broadly support recreation infrastructure in the central Wasatch.  Yes, I know I live in a dream world, but this is what I want, as opposed to a litany of fee programs that fail to address the 800 pound gorilla in the zoo.  

Monday, May 23, 2016

The Great Melt Is Underway

Anyone who has read the news won't be surprised to learn that it has been an exceptionally hot northern hemisphere cold season (November to April, hereafter just cold season) globally, especially in the Arctic.  Let's have a quick look at the numbers.  Because I'm being lazy, I'm going to mix two global temperature data sets, one produced by the NASA Goddard Institute for Space Studies (NASA-GISS) and the other produced by the National Centers for Environmental Information (NCEI).  Neither of their web sites produced everything I want, but I can get it if I mix and match.

Let's begin with the global temperature anomalies for November to April, which show the past cold season really was quite remarkable, running more than 1ºC (2ºF) above the 20th century average.  The tremendous surge during this period is largely a result of long-term global warming combined with El Nino.

Source: NCEI
The plot below shows the distribution of temperature anomalies for this period (relative now to the 1951–1980 average), illustrating the large positive anomalies in the tropics and most of the northern hemisphere, especially the arctic.  In contrast, the higher latitudes of the southern hemisphere were closer to the 1951-1980 average or in some cases below it.  

Another way to look at this is to average the temperature anomalies around a latitude circle (called a "zonal average) and then plot them from the south to north pole (left to right below).  This shows the near-average temperatures in the high latitudes of the southern hemisphere and the extreme warmth in the high latitudes of the northern hemisphere.

The tendency for the Arctic to warm faster than the global average temperature and exhibit larger positive temperature anomlies is called Arctic amplification.  It is driven by several factors, but feedbacks related to the decline in Arctic sea ice is dominant.

And, speaking of sea ice, the Arctic sea-ice extent is currently running well below prior seasons in the satellite record. Perhaps a record minimum will be reached in September.

Source: NSIDC
Although we may see a temporary decline in global temperature anomalies from their El Nino fueled highs this past cold season, the global warming train has left the station and is accelerating.  The great melt is underway.  

Saturday, May 21, 2016

Overnight Deluge

A slow moving precipitation band brought significant rain to the Wasatch Front late last night and early this morning, especially north of Salt Lake City.  Radar imagery below shows the strong returns over the northern Wasatch and lowlands upstream (northern most red rectangle).

As of 9:30, Snowbasin-Middle Bowl recorded 0.81" of water equivalent since 4 AM.  And yes, some of that precipitation has fallen as snow on the upper mountain.

Ogden airport picked up a half inch, which is a good dousing for the lawns and gardens.

Further south, the central Wasatch (southern rectangle) were late to get in on the action.  Alta-Collins has had only .12" of water equivalent since 3 AM, although temperatures are now down to 30ºF, putting that site above the melting layer for now, and they may get a couple more hours of snow.  A little something for the diehards.

Meanwhile, in the Salt Lake Valley, the U is up to .27", which should be enough to keep my sprinklers off for another week, which is good because I just discovered that I have some work to do to get some of mine working.