Tuesday, October 31, 2017

Greetings to a New Snow Year

When it comes to measuring snow and precipitation, Donner Summit offers the gold standard in California. The measuring year begins on October 1 and ends September 30, with statistics going back into the 19th century. Thankfully, someone decided early, that it might be important to keep track!

Located at Donner Pass in the Sierra Nevada, the Central Sierra Snow Laboratory (CSSL) is a research field station of the University of California, Berkeley specializing in snow physics, snow hydrology, meteorology, climatology, and instrument design. Built in 1946 by the (then) U.S. Weather Bureau and Army Corps of Engineers, it is administered by UC Berkeley's California Biodiversity Center.  

CSSL has a close to complete and consistent record of precipitation, snowfall, snow depth, and air temperature for the periods of 1946-1952 and 1957 to the present. The Lab also has long-term data sets on wind speed and direction, solar radiation, snow temperature, relative humidity, and soil moisture. In addition, precipitation and air temperature records from other locations on Donner Summit are available.


Our thanks to staff member Randall Osterhuber, for sending along the updated chart for our readers. It becomes a tradition creating excitement for the new snow, upcoming holidays and another wondrous ski season in the Sierra.


Tuesday, August 22, 2017

Earthquake Swarms and Possible Triggers

If you think the earth is shaking below you — you may be right. In the Lake Tahoe-Truckee region the Sierra Nevada mountain range is moving northwest with the North American Tectonic Plate, about one half-inch per year. This movement is paired with its transform plate boundary: the Pacific Tectonic Plate, moving southeast about 2-3 inches per year. Most of us know that when the plates grind together, the fault lines in certain areas begin to crack and fissure farther. But it does not occur all at once.

A local series of earthquakes caused by the earth’s crust movement is known as an earthquake swarm. Recently, earthquake swarms have become commonplace for the Sierra Nevada. In August 2008, Mogul, a suburb west of Reno, was hit with weeks of small-magnitude quakes, which surrounded a 5.0 temblor and caused around $1,000,000 of damage. In July 2014, a swarm in the northwest region of Nevada, near the Oregon/California border, again lasted weeks with a total of around 800 quakes. The two largest measured 4.7 magnitude. This swarm fortunately occurred in a low population area and didn't cause sizable damage. 
The Truckee area is in a very active fault zone. On June 27 – 29 of this year, Truckee experienced an earthquake swarm which surrounded a 4.0 magnitude quake. Most of these temblors occurred on the intersection of the Polaris Fault and the Dog Valley Fault. (See diagram.) Twenty-eight small quakes were recorded on just June 27, while the largest hit at 2:09 a.m. that day.
































A possible cause of the swarms in our area may be more than just tectonic plates moving. Some researchers believe it may also be due to the epic amount of water added to the ground water table in the Sierra Nevada, after last winter. “Hydrological changes do not need to be sudden or large to change the water pressure in a fault zone. As aquifers are depleted for irrigation, the water table slowly drops, which may also trigger earthquakes. It is thus unsurprising that extreme rainfall events might also encourage earthquakes,” stated Gillian Foulger, Professor of Geophysics, Jon Gluyas, and Miles Wilson, Ph.D. student in the Department of Earth Sciences; all of Durham University in England. In essence, the added ground water works as a lubricant for earth movement. Researchers have also seen increased fault movement with snowmelt in late spring and into summer in countries other than the United States.

A second possibility for earthquake swarms is also related to water. Earthquake trigger studies have been done measuring the depression of soil caused by water content during winter months; called seasonal water loading. In a typical winter, the soil may condense to about one centimeter. The trouble begins when the soil starts to dry out and expand: rebounds that cause stress on the faults leading to upticks in small magnitude earthquakes regionally. "It's not like we're seeing an earthquake season, but the timing of this water unloading is when we're (historically) getting more earthquakes," said Chris Johnson, a graduate student at the Berkeley Seismological Laboratory.

As someone who studies earthquake triggers, Nicholas van der Elst, a research geophysicist for the U.S. Geological Survey in Pasadena summed it up by saying, "We have a pretty good understanding of earthquakes on a basic level and why they happen, however, we don't know things like how quickly stress accumulates and what is the breaking point of a fault.”

It seems we also don’t know how many factors are at play when an earthquake occurs, but the research continues.

Sources:

Monday, May 15, 2017

Amgen Women's Tour De California Stage 1 and 2

What Is The Amgen Tour De California?


Tour De California Is a cycling event for professional riders in the cycling world. Riders are assembled in teams by sponsorship but compete individually through multiple stages across the California landscape. There is a Men’s and Women's competition although the Men didn’t visit Tahoe this year, the Women started with Stage 1 and 2 in the South Lake Tahoe Region. Amgen is the primary sponsor for the race. (They are a medical research company and pharmaceutical producer mostly focusing on treating serious illnesses.)


Two stages in The Tahoe Area. (below are the stage maps).


Standings after Stage 1 and Stage 2 


(screen shots taken from www.amgentourofcalifornia.com/competition/2017-women-standings)


Below are Pictures of the riders descending Kingsbury Grade in the last leg of Stage 2.

Sneezing at Pine Pollen

           Pine Pollen is a topic of allergy conversation every spring. Pine Pollen is coarse yellow powder, which is scientifically the male microgametophytes (the sexual phase in the life cycle of plants). The powder is windblown from male cones (the small orange granular kind) and then floats into a receptive female cone (the large, hard, drop-to-the-ground kind) and fertilizes the egg located in the center of the female cone. This process grows pine nuts that either are eaten by wildlife, harvested for cooking, or left alone to grow into new pine trees.
There are many different types of pine trees in our area, which provide a long period of pollen shedding. Ponderosa Pines generally flower between April and May but pollen has been collected as early as April 15, and on average May 11, on the west slope of the Sierra Nevada Range. Jeffery Pines typically flower between June and July.
Lodgepole Pines vary by temperature and elevation, but as studied by the U.S. Forest Service, lodgepoles at 6,000 feet elevation in the Sierra have a peak pollen shedding period around June 22. Keeping all this in mind, remember that the rate at which cones develop in the spring is primarily determined by temperature—the warmer the temperature the more rapid the development. Pollen release is also dependent on dry granular pollen cones. In wet weather, pollen release may be delayed for several days and in dry weather, it is hastened.
As seasonal allergies become full blown, most people want to blame yellow pine pollen they see floating in a wind gust, or on the surface of Lake Tahoe, for their misery. The pine trees may not be to blame! Pine pollen is heavy and waxy and drops quickly to the ground. Because it drops so quickly, it usually isn’t a cause of allergies. Those who may be allergic to pine pollen aren’t normally allergic to anything else…just pine pollen.
The main cause of most sniffling, sneezing and congestion around Tahoe in spring may be allergies to many of the other indigenous trees and plants that are producing pollen concurrently with the pines.

So…go hug a pine tree this month, and steer clear of the huckleberry oak, the willows and the quaking aspens instead.

Thursday, January 19, 2017

Temperature Inversion



What is Temperature Inversion?

Basic Scientific Fact: cold air is denser than warm air and in a normal weather pattern this helps circulate air and dilute pollutants. Air normally gets cooler the higher in altitude it goes—to be more specific—3.5º cooler every 1,000 feet in altitude. A temperature inversion is exactly what it sounds like, the cold and warm air switch position. In our area, there are 3 possibilities for the cause of an inversion layer:

1. A low-pressure system, warmer air, is pushed down towards the earth’s surface, while a high-pressure system, cooler air, moves over and traps the warmer air; this is most common after a storm.

2. The air near the ground rapidly loses its heat on a clear night. In this situation, the ground becomes cooled quickly while the air above it retains the heat the ground was holding during the day.

3. Topography can also play a role in creating a temperature inversion. Cold air can flow from mountain peaks down into valleys. This cold air then pushes under the warmer air rising from the valley, creating the inversion. Inversions can also form in areas with significant snow cover because the snow at ground level is cold and its white color reflects almost all heat coming in. This means the air above the snow is often warmer because it holds the reflected energy. 

In and around the Tahoe Basin, this can happen usually after storms and is evident in local valleys on a small and large scale. You can see examples of this when you drive on Highway 267 from Truckee to Northstar in the early morning. There is usually fog low to the ground in the surrounding Martis Valley. On a larger scale, Reno, Nevada in the Truckee Meadows is constantly experiencing inversion layers over the city. This occurs in the weeks after a winter storm or when cold air from the Sierra crest settles in and pushes the warm air up, causing the inversion. This can mean clouds and no direct sunlight from days to weeks!

How Does it Affect Us?

Directly: the buildup of moisture due to the inversion layer can cause early morning fog on your way to work or that pesky frost you must scrape off your windshield of the car before even beginning your commute.

Indirectly: An atmospheric stabilization can lead to a concentrate of pollutants like car exhaust and wood fireplace smoke. Long periods of an inversion layer can cause thick smog to form in the Lake Tahoe Basin and Truckee Meadows. Trapped smog can cause winter allergies and make existing asthma symptoms worse. Studies have shown that increases in particle pollution in the air, like those from fossil fuels, lead to more hospitalizations for children who have asthma.

What’s a Kid (AdultsToo…) To Do?


Go skiing, sledding, hiking, snowshoeing or any other outdoor activity at higher elevations. Get above the clouds to breath in the fresh air. Your lungs will love you for it.

Saturday, December 10, 2016

Bears: Not Hibernators

Bears: Not Hibernators

Torpor versus Hibernation
What if I told you that you have been lied to for years? Well its true. Bears aren't hibernators they enter torpor instead. Torpor is the short-term reduction of body temperature (for bears, up to 100 days). Torpor is controlled by ambient temperature and food availability or, in a bear's case, energy stores.  Torpor allows a bear to regain consciousness in a matter of seconds and be ready for action (running, attacking, eating, etc).  For animals in hibernation, on the other hand, it may take hours to days, to gain back the energy they had before they began their long sleep.

How do Bears Survive During Torpor?
Bears prepare their dens well before they need them and rarely use the same den two years in a row. Once they settle down for the cold months, their bodily functions change greatly. The flow of blood becomes concentrated to the heart, lungs and brain.  The bear is then further protected from the cold by their fur and up to four-inches of fat under the skin. The digestive system shuts down while asleep as no water or food is entering and waste is not exiting. The bear still needs sustenance every day consisting of water, protein and 4,000 calories. The animal’s energy stores provide this through its own metabolic system. Fat is broken down into calories and water, and muscle is broken down into protein and Nitrogen Urea. Nitrogen Urea is normally highly toxic in an animal’s system but a bear’s metabolic system recycles this through the liver and kidneys to produce amino acids. Those attach themselves to muscle tissue and are broken down into protein yet again.

What can Wake a Bear from Torpor?
A bear’s torpor is a lethargic state in which it can awaken from in just seconds. Loud noises such as trees falling, avalanche blasting caps or even a garbage truck can wake a bear from torpor. Here in Tahoe and Truckee we have bears that do not to enter torpor at all and roam our neighborhoods looking for food all winter long.  Our civilization in their habitat has changed the way they expect food and thus changed their torpor and breeding patterns. 

Warnings and Precautions
I have recently seen a few bears in a couple of neighborhoods in South Lake Tahoe and Stateline. At this time of year, they are desperately looking for a den and food. Remember to always put your trash in a secure location: bear box, your garage, or indoors. Remember also to double check that you have secured your doors and windows. As for wilderness areas, just be cautious. For those of you who go out and cut your own Christmas tree with a permit, be loud and aware in your surroundings to avoid surprising a bear. If you see a bear in a populated area this season don’t approach it; it is probably hungry and defensive. You can always call #911 in an emergency or the Tahoe Bear League 24/7, at (530) 525-7297. Also, visit their website to learn more about their amazing organization, http://www.savebears.org/.


Resources:
https://www.youtube.com/watch?v=buQaIannwz0

https://www.youtube.com/watch?v=5wC0iuJCrYg

Tuesday, November 22, 2016

La Niña: What it Means for the Sierra Nevada Snowfall

La Niña: What it Means for the Sierra Nevada Snowfall
La Niña is a cold event. Historically speaking, it’s brought massive amounts of snow to our area with cooler than normal temperatures keeping the snow pack around. (That might be good or bad depending on your feelings about cold wet weather.) It has also brought disappointment in the past as a weak La Niña system (2011-2012) initiated the first year of the record breaking California drought. NOAA forecasters have determined this upcoming season to be a strong La Niña year. 

What is La Niña?
La Niña is identified by cooler than normal water in the east-central Equatorial area of the Pacific Ocean. This is caused by stronger than normal Trade Winds pushing warm water westerly towards Australia and Indonesia creating a void, which is filled with cold water along the east-central Equatorial Pacific. For a visual explanation visit oceanservice.noaa.gov/facts/ninonina.html.

What Does La Niña Cause?
This cooler water in the east-central Equatorial Pacific pushes the Pacific Jet Stream and Polar Jet Stream farther north creating dry and warm conditions in the southern United States, while the Pacific Northwest is cool and wet. Below you can see a generic model of a normal La Niña weather pattern. We have already seen this pattern in affect with snow in the Rocky Mountains and in the Great Plains area. Snow in our area will greatly depend on variability in the Polar Jet Stream to drop lower and bring wet weather with it.




A Look Back at La Niña Past
Looking at the past La Niña years and what they did for the Sierra Nevada meant finding which years were moderate or strong; a weak La Niña system yielded little for our slopes. Below is a table of snow base totals by month from December to March of La Niña years from 1973 to 2011 of the Tahoe area on average.



Data from wunderground.com


What's Next?

For now, we are just going to have to wait for Mother Nature to do what she does best. Accuracy in future casting isn't a sure thing and as we can see from the La Niña snow depth table, each year was radically different from the other making it hard to predict anything. We are a hopeful bunch and we believe we will see a benefit to our ecologic and economic systems in the Sierra Nevada this winter.