October 2008 Newsletter

The next SKYWARN meeting is 21-Oct @ 7:00 PM, the third Tuesday of the month.

The 16-Sep meeting was a very short meeting (or at least a limited agenda). Topics discussed included:

  • Sweet Spots - We would like to identify and review possible locations during the off season and redo the maps for spring with a published set of locations. If anyone has suggestions, please forward them to me. We are looking for locations with good visibility (horizon not obscured by trees), room to pull out of traffic lanes, and multiple exit routes. Prefer paved roads though that is not absolutely required. A nearby shelter location makes it even "sweeter".
  • A request for GRLevel3 training this winter.

Steele County SKYWARN did not activate during September.

September Perseids From Space Weather
The September Perseids (not to be confused with the more famous August Perseids) are normally dim and few. The shower produces only 3 to 6 meteors per hour at maximum around Sept. 9th of every year. But on Sept. 9, 2008, the sky lit up with fireballs. The SENTINAL all-sky camera at the Marshall Space Flight Center picked up 25 bright meteors in a shower that began at 0620 UT and lasted approximately 4 hours. Browse the gallery for images of the surprising outburst.

Lunar Perseids From NASA
There's more than one way to watch a meteor shower. the old-fashioned way is to find a dark place with starry skies and count the meteors streaking overhead. The new way: Find a dark place with starry skies and then completely ignore the meteors and watch the Moon, where the explosions are. A pair of amateur astronomers fixed their cameras on the Moon and watched meteoroids slam into the lunar surface. Silent explosions equivalent to ~100 lbs of TNT produced flashes of light visible a quarter of a million miles away on Earth.

MN Tornado Summary From Minnesota WeatherTalk
Todd Krause of the National Weather Service Office in Chanhassen was kind enough to provide a preliminary look at tornado reports in Minnesota for 2008. The earliest date was May 25th, when 5 tornadoes were reported, including the EF-3 storm that hit Hugo, MN. July 24th was the last report of a tornado, and that was in Mahnomen County. In all there were 43 tornadoes in Minnesota this year. There were 3 reports of EF-3 storms (136-165 mph winds). These occurred at Hugo, another between Dorset and Park Rapids, and one near Kandiyohi. There were 2 reports of EF-2 tornadoes (111-135 mph), 15 reports of EF-1 storms (86-110 mph), and 23 reports of EF-0 twisters (65-85 mph winds). In all these 43 tornadoes resulted in 1 death and 24 injuries.

Hurricanes, Typhoons and Cyclones (Oh My!) From USA Today
There are three different names for the same type of storm, collectively known as “tropical cyclones.” A “cyclone” is also a generic meteorological term for any spinning area of low pressure, which includes both extra-tropical and tropical cyclones. It's also a term that at one time described tornadoes in the Midwest. What they’re called depends on where they form. Hurricanes form in the Atlantic Ocean (which includes the Caribbean and Gulf of Mexico) and the eastern Pacific Ocean; typhoons form in the western Pacific Ocean, and cyclones in the Indian Ocean.

August and September have been a busy period for hurricanes. It may not be a surprise that Florida leads the nation in hurricane landfalls, with a total of 114 strikes since records began in 1851. That represents about 40 percent of the 286 hurricanes that have hit the USA. Texas is second with 62 landfalls and Louisiana third with 52. Every state along the Gulf and East Coasts has been struck by at least one hurricane since 1851. Additionally, 83 percent of all Category 4 or 5 hurricanes have hit either Florida or Texas. Category 4 hurricanes have wind speeds of greater than 130 mph. This National Climatic Data Center map shows the location of all U.S. hurricane strikes since 1950.

Sunset From Multiple Sources
Sunset occurs when the upper edge of the Sun -- called the upper limb -- sinks just under the horizon. The actual sunset can happen earlier or later than expected. The atmosphere bends the light rays near the horizon making the Sun appear to be above the horizon when it is already beneath it. Twilight is the period after the top of the sun's disk crosses the horizon and the center of the sun is 6 degrees below the horizon. The amount of time between sunset and complete darkness will vary depending on latitude and season.

Hail, Sleet, Graupel From USA Today
Hail tends to be associated with warm-season (spring, summer, even fall) thunderstorms. The more vigorous updrafts associated with warm-season storms helps to keep a hailstone in the cloud longer, allowing it to grow to a larger size (technically, hail is considered to be a dense ice pellet at least 5 millimeters in diameter). A hailstone can have concentric layers (like when you slice an onion down the middle) of hard and soft ice, depending on the temperature of the hailstone at the time the layer formed.

While sleet is also ice, it forms in an entirely different way than either hail or graupel. Sleet typically starts out as a snowflake as it leaves the base of a cloud. It then encounters a layer of above-freezing air that partially melts the falling snowflake. The partially-melted flake then refreezes as it falls through a layer of sub-freezing air and eventually hits the ground as an ice pellet.

Graupel is also known as “soft hail.” The formation of graupel is very similar to that of hail. Both hailstones and graupel grow in size through a process called riming – supercooled water droplets and ice crystals freeze or stick to the initial hailstone as it rises and falls within a cloud. Graupel tends to be typically less than 5 millimeters and is usually produced in cold-season storms. Less vigorous updrafts limit the size to which the ice can grow and the cold temperatures within the cloud result in ice and water droplets freezing directly to the embryo graupel – rather than melting and refreezing as ice. This direct-freezing process traps air and makes the graupel opaque and less dense than a hailstone would be, thus the moniker “soft hail.” On occasion, graupel can grow in thunderstorms and wind up as large as hailstones.

Check out this interactive graphic that describes the differences between snow, sleet and freezing rain.

From WeatherBill
Ever thought about betting on the weather? WeatherBill is doing exactly that by offering "financial instruments" to help protect business and events that could be affected by weather. WeatherBill sifts through historical weather data to calculate the odds it might rain or snow on any day or week. Available tools include graphical data identifying up-to-the-minute extreme weather events throughout the United States and estimating the probability of a weather event happening in a specific location. WeatherBill sifts through historical weather data to calculate the odds it might rain or snow on any day or week

Temperature Readings From USA Today
Many National Weather Service observation stations use aspirated shields to shade temperature sensors. Older stations may use a Cotton Region Shelter, also known as a "Stevenson screen" or "Stevenson box." Certainly, a temperature sensor exposed to direct sunlight will result in erroneous readings. Likewise, it can feel a lot hotter when the human body is exposed to direct sunlight versus relaxing in the shade.

Cumulus Clouds From USA Today
Ever wonder why cumulus clouds appear fluffy on top but flat on the bottom? Cumulus clouds have flat bases and fluffy tops because they grow vertically. As warm air rises, it cools and eventually water vapor in the air condenses. The level at which this starts to happen is called the “lifting condensation level” (LCL) and is typically where you will see cumulus clouds begin to form. However, updrafts of warm air don’t just stop there. They continue to rise, with water vapor within the air continuing to condense, resulting in the fluffy, puffy, “cotton ball” nature of cumulus clouds. The higher cumulus clouds go, the more likely weather will turn bad. Strong winds upward can stretch them into cumulonimbus clouds, which produce heavy rain and thunderstorms.

Fog Fence From Minnesota WeatherTalk
Capturing the water out of fog has been attempted for centuries. Since the 1980s a number of fog fences have been constructed throughout the world to capture and store the fresh water from fog. They are usually located in arid or semi-arid coastal regions that have a significant frequency of fog, particularly along upland areas. The fog fences are constructed out of mesh with a significant vertical extent positioned at right angles to the prevailing wind. Wind driven fog passing through the fence where the micro-scale droplets are captured on the mesh and coalesce into larger droplets that fall into PVC pipe at the bottom of the nets then flow to a storage container. Successful fog fences have been deployed in countries like Chile, Yemen, Guatemala, Haiti, Nepal, Ethiopia, and Oman. Depending on the density and persistence of fog in the local environment, fog fences have been known to yield from 1 to 10 gallons of fresh water per day from one square meter of fence.

Listening to Lightning From USA Today
Lightning emits a wide range of radio frequencies, but is mainly concentrated in the very low frequencies, ranging from a few hundred hertz to 10 kHz. Lightning can produce radio waves farther up the spectrum, which is why it can sometimes interfere with AM radio (535 kHz – 1700 kHz) reception, but is never a problem with FM radio reception. You can listen to lightning live on NASA’s online VLF online receiver. You can also build your own lightning radio detector that is tuned to 300 kHz, as it is a fairly uncluttered frequency that will pretty much only yield lightning static.

Autumn Equinox From NASA
The April Newsletter had a brief discussion on the difference between the Equinox and Equilux. September brings us the autumn equinox, when day and night are equal. A solstice occurs when the days and nights are the least equal. This picture is a composite of hourly images taken of the Sun above Turkey on solstices and an equinox:

  • The bottom Sun band is the 2007 winter solstice in December.
  • The middle band is the 2008 Vernal Equinox in March.
  • The top band is the June, 2008 summer solstice.

Ball Lightning From USA Today
Ball lightning is a short-lived floating sphere of energy that forms in the aftermath of a lightning strike. While human observation of the phenomenon is relatively rare, an estimated 5% of the world's population has witnessed ball lightning. Typically the size of a grapefruit, ball lightning can range from pea-size to the size of a beach ball. As for duration, ball lightning can last as short as a few seconds to as long as several minutes, with the average occurrence around 25 seconds. An explanation of ball lighning can be viewed at USA TODAY WonderQuest.

Word For The Month From Minnesota WeatherTalk
Toggy Tool
Bill Togstad recently retired from the National Weather Service Office in Chanhassen, MN and studied severe weather for many years. He developed a numerical algorithm to evaluate the risk of EF-2 (winds of 111 mph or greater) or greater tornadoes. This tool, called the Toggy Tool is still used by the National Weather Service, and especially the NOAA Storm Prediction Center in Oklahoma.

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All Rights Reserved
Steele County SKYWARN
Owatonna, MN