October 2Ř11 Newsletter

The next SKYWARN meeting is 18-Oct @ 7:00 PM, the third Tuesday of the month.

SKYWARN Breakfast From Mark S
SKYWARN and the Special Deputies are once again teaming up for a fund raising breakfast on Sunday, 11-Dec. The breakfast at the VFW includes french toast, eggs to order, sausage, coffee, milk, juice and all you can eat pancakes. The price of the breakfast "at the door" is $5.00. SKYWARN gets $2.50 for each ticket sold in advance. 400 VFW Breakfast tickets to be sold will be available to the SKYWARN members at the 15-Nov SKYWARN meeting. If you are unable to make the meeting and would like to sell some tickets please contact Chris Gannon at 952-484-1323.

MN Record Wind Speed From Multiple Sources
A thunderstorm passing through northwest MN may have produced a record wind speed. A MNDOT RWIS site located along Highway 11 reported wind gusts at 121 mph around 3:00 AM 0n 01-Sep. The NWS preliminary survey describes the damage and includes some pictures. The old state record of 117 mph was recorded near Alexandria in 1983.

Catastrophic Weather Year From Multiple Sources
The number of Presidential Disater Declarations seems to increase each year. So far in 2011, there have been 77 declarations. The types and distribution of disasters change over time. In the 2000 - 2010 time frame, severe weather accounts for over 70% of the declarations. Going back to the 1965 - 2010 time frame, 37% were for severe storms and 33% for flooding.

The disasters also get more costly. Hurricane Irene was the 10th "billion dollar weather disaster" to hit the USA in 2011. That's the highest number of billion dollar weather disasters to hit the USA since such records were kept starting in 1980.

Click on image to enlarge

Hunter's Moon From Multiple Sources
The full moon closest to the autumnal equinox is refferred to as the Harvest Moon. It is celbrated with the song Shine On Harvest Moon. Hunter's Moon is the full moon after the Harvest Moon. As might be expected, it gets its name from hunters who tracked and killed their prey by autumn moonlight. This year, the Hunter's Moon will appear on 11-Oct. It is also known as Blood Moon or Sanguine Moon.

Doppler Radar From Multiple Sources
Doppler radar uses a well-known effect of light called the Doppler shift. The Doppler effect makes a train whistle sound higher as it approaches a platform and then become lower in pitch as it moves away. Light emitted by a moving object will appear to have a higher frequency moving toward the observer. The result is the object appearing to be more blue. Objects moving away will be shift toward the red end of the spectrum. Doppler radar sends out radio waves that bounce off objects in the air, such as raindrops or snow crystals, and then measures how much the frequency changes in returning radio waves to better determine wind direction and speed.

Measuring Wind Speed From Multiple Sources
Instruments used to measure wind speed are called anemometers. We usually envision anemmeters as the spinning cups. Another type of anemometer is called the Ice Free Wind (IFW) sensor The NWS began deploying the IFW sensor in September 2005. These newer ultrasonic sensors an array of three equally spaced transducers which radiate and receive ultrasonic pulses in a horizontal plane. The triangular design resolves issues due to turbulence. They also minimize maintenance issues because there are not any moving parts.

Fractional Attributable Risk From Multiple Sources
Attributable risk is the difference between two sets of events with a distinct difference. For example, health experts may want to determine the risk of an exposure to something might result in some type of disease. They would make a comparison of the percentage of individuals with a disease that had an exposure to something to others that were not exposed. The attributable risk of the exposure would be based on computing the difference in the individuals in each group that had the disease.

Researchers are looking more and more at how the frequency and magnitude of events are changing due to changes in the overall climate. The forecast models are adjusted based on different levels of climate change. Fractional attributable risk is a method intended to make possible a better characterization of how human activities change the likelihood of specific extreme events occurring. Computer climate models are run with and without human influence values inputted. Scientists can then assess how much of the risk of a past event was attributable to human-caused climate change.

Clouds and Climate Change From Multiple Sources
Cloud formation has a complex role in affecting the Earth’s climate. Clouds absorb only about 3% to 6% of incoming solar energy, while they reflect about 20%. High-altitude clouds reflect little solar radiation. Low-altitude clouds reflect a significant portion of incoming solar radiation. The low-altitude clouds absorb emitted heat from the Earth and reemit this energy back toward the earth. This is why cloudy nights tend to be warmer than clear, calm nights. This NASA fact sheet has a lot of information.

There have been several studies completed looking at the relationship between clouds and climate change. One theory is that global warming will create more clouds that will trap heat. Other theories suggest the additional clouds will act to reflect solar radiation and limit global warming. Researchers have a lot of work to do to develop models on how "cloud feedback" will interact with the other factors relating to global warming.

Roll Clouds
On the subject of clouds, you can view some unusual pictures of roll clouds. Be sure to note the end of the URL for a brief idea of where these pictures were taken.

Term For The Month From Multiple Sources
Station Model
A station model is a symbolic illustration showing the weather occurring at a given reporting station. Elements in the plot show the key weather elements, including temperature, dewpoint, wind, cloud cover, air pressure, pressure tendency, and precipitation. The information is updated every hour. More on the station model and interpreting data presented in this form can be found at the Unisys Weather web site.

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Steele County SKYWARN
Owatonna, MN