June 2Ř11 Newsletter

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

SKYWARN was briefly activated on Saturday 21-May. A cell with tops climbing in excess of 40,000 feet passed through the northwest corner of Steele County.

Tornado History
New Scientist posted an interactive graphic showing historical data for tornado related deaths and intensities since 1950.

Southern Tornado Outbreak
Tornadoes have certainly filled the news over the past several weeks. We have been fortunate locally (so far) to have been spared from these deadly outbreaks. The year is not over and Minnesota topped the list in 2010 for the number of tornadoes.

NOAA has a comprehensive report out about the historic and tragic tornado outbreak of April 25-26. Preliminary estimates suggest 305 tornadoes, and the National Weather Service issued warnings on over 90 percent of them with an average lead time of 24 minutes. NOAA has a discussion with 2011 tornado information, that includes statistics and additional stories.

At the May SKYWARN meeting, Dave KCŘUVY reviewed some of the video and radar images from the Tuscalosa event. Below are links to some of the material:

One ham in Alabama recorded the net communications and is making them available on USTREAM. Click on the Audio Only for 04/27/11. It is over an hour long, but is interesting to losten to if you have the time. Some of the things you will hear:

  • Discuss about using generators or batteries.
  • One of the mobile operators reported he thought he was having a heart attack.
  • The Public Service group lost their commuications and was going to use one of the amateur repeaters to continue communications.
  • Being sure there are liasons between different groups.

Weather Brains From AR Newline
Weather Brains is a weekly audio show delivered by the Internet. The show is produced each Monday and generally runs 60 to 80 minutes. The show is usually available Tuesday morning. The group has produced over 200 shows, never missing a week in the past 5 years.

No Such Thing As A Tornado? From Multiple Sources
Those that have ever seen the old television comedy Get Smart may remember Max's line "Would you believe....". Well, would you believe that the term "tornado" was banned from weather forecasts? When the US Weather Bureau started back in the late 1800s, the possibility of tornadoes was not allowed becasue of the potential for panic. The idea of forcasting tornadoes in the 1940s was stopped for similar reasons. Severe weather conditions were observed and reported, but not forecasted. In the late 1940s, conditions were identified in the Southern Plains that were favorable for tornado formation. The ban on the word "tornado" in weather forecastswas lifted in the 1950s.

Clear Skies From USA Today
Clear skies after a thunderstorm can partly be explained by the particulates that get washed out of the air due to the rainfall. When these tiny particles are abundant, they act as condensation nuclei (that is, water vapor molecules condense on them) and as they grow, they scatter sunlight. This is why it can look hazy on a hot, humid day. Raindrops can scrub these haze particles out of the sky as they fall to earth. As for the cooling during a thunderstorm, a summer thunderstorm can produce some nice cooling due to its outflow. These are the winds that can precede the storm itself. Typically they result as dry mid-level air is drawn into the rain shaft of the storm. The downward momentum of the rain can drive this air downward and evaporational cooling of the raindrops in the dry air (a process that takes energy) can make the air even cooler and denser. This cool, dense air hits the ground and spreads out in all directions and can produce a sudden drop in temperature. This cool air can act like a mini cold front (sometimes referred to as a gust front), lifting other warm moist air and triggering additional thunderstorms. This is why forecasters keep an eye on “outflow boundaries” from thunderstorms that have fallen apart as possible locations for additional thunderstorms to initiate.

Tornadoes and EMR From New Scientist
We all know that tornadoes form out of supercells. German researchers have been able to pick up low-frequency electromagnetic waves. Using a simple receiver and arook mounted antenna, they believe the frequency of the signal should even be able to tell them the ferocity of the storm. The dust particles inside the swirling action of the supercell generates the electromagnetic radiation. If successful, the process could provide local information and help spotters gauge developing storms when they cannot get a clear picture of the area of rotation.

Dams Could Alter Local Weather From Multiple Sources
Dams continue to be compared for the benefits they may produce against the possible ecological effects. Research suggests that large reservoirs may be partially responsible for the intensity of extreme rainstorms in their immediate vicinities. The water that evaporates eventually condenses and falls as precipitation. Since dams were generally designed for the climate conditions before they were built, the designs may not appropriate for the new local conditions. Over time, the silt build-up in the reservoirs will reduce the available capacity in the reservoirs and might cause the reservoir to overflow.

Radiosondes From Multiple Sources
A radiosonde is an instrument used with weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. Radiosondes can rise at a nearly constant rate of 300 meters/minute. They are designed to reach an elevation of approximately 19 miles, which is nearly 99 percent of the Earth's atmospheric mass. The 19 mile elevation includes NOAA launches weather balloons at 12-hour intervals to measure temperature, pressure, humidity and wind. Data is summarized at specific atmospheric pressure levels to use as part of forecast models. The data from radiosondes is available from UNISYS.

Term For The Month From Multiple Sources
Pitchforks and Hammer Handles
This would have been used in the past to describe a storm so bad that you shouldn't go outside. You wouldn't want to go be in the middle of a hard rain if it really was raining pitchforks and hammer handles. ice in a lifetime.

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Steele County SKYWARN
Owatonna, MN