August 2008 Newsletter

The next SKYWARN meeting is 19-Aug @ 7:00 PM, the third Tuesday of the month.

About 19 members attended the 15-Jul meeting. Topics discussed included:

  • The updated City Watch list was passed around for review.
  • There was a demonstration on how City Watch works.
  • New laminated county maps were available. The 11"x17" maps include a summary of spotter information on the reverse side.
  • Parking restrictions at the EOC were covered.
  • There was a walk through of procedures used to activate SKYWARN and the WX Center.
  • Construction is beginning at the Fire Station. Please be extra careful when entering and leaving the area.

Steele County SKYWARN was activated on 11-Jul. About 14 members were out looking at the night sky as storm fronts moved in from the west. Steele COunty was spared, but Steele County SKYWARN was prepared and ready.

EOC Parking
Especially during the day or with an emergency, parking around the Fire Station can be difficult. Parking will be even harder with the construction beginning at the Fire Station, SKYWARN members coming to the Fire Station for an meeting or activation need to be alert to parking restrictions. Be sure to review the parking recommendations.

Seiche Wave From Chicago Tribune
A Seiche wave can be thought of as a mini-tsunami. Over the 04-Jul weekend, a Seiche wave warning occurred on Lake Michigan resulting in beaches closing along the shores. Seiches are produced when fast-moving squall lines push domes of water into the shoreline. Lake levels gyrate rapidly in short periods of time. As they are reflected off the far shore and tugged back to equilibrium by gravity, the water careens back toward the opposite shore.

The National Weather Service's seiche warning was issued after a massive storm front over the lower peninsula of Michigan crossed Lake Michigan in the early afternoon Wednesday and piled the water toward the Michigan shore as it traveled east. The minor seiche flooded St. Joseph Harbor in Michigan as storms pushed the swell east, creeping more than 15 feet across the sand. The swim bans in Chicago were prompted as the wave sloshed back west late in the afternoon. Water levels between Chicago and St. Joseph continued to rise and fall about 2 feet every 20 to 30 minutes until later in the night as if Lake Michigan was a giant bathtub.

Weather Channel Sale From Multiple Sources
NBC Universal, Blackstone Group, and Bain Capital reached a deal to buy The Weather Channel from Landmark Communications for $3.5 billion in cash. NBC was joined in the deal by the private equity firms. The Weather Channel can be seen by 97% of U.S. cable subscribers. The deal also includes several related assets such as weather services for newspapers and radio stations and the widely used website. The Weather Channel was launched in 1982 with about 37 million monthly unique visitors, putting it in the top 15 websites. NBC already operates a digital weather and news service called NBC Weather Plus that was launched in 2004.

Dewpoint and Wind From Minnesota WeatherTalk
The wind directly affects the mixing depth and mixing volume of the atmosphere around us. When the wind is blowing hard, the mixing volume of air is larger, water vapor molecules have ample room, and both relative humidity and dewpoint tend to be lower. When the wind is light or it is calm the atmosphere tends to stratify into layers that don't readily mix, and thus the mixing volume of the air is less. In this condition water vapor molecules are confined in space, and relative humidity and dewpoint tend to be higher. Note that after sunset, the wind usually dies off and dewpoints spike to their highest levels of the day. This is often evident in the summertime when early evening dewpoints can spike in the 70s F, as they have done several times this month.

Flood Terms From USA Today
Fifteen years ago, after the Midwest was swamped with what was pronounced a "100-year" or even a "500-year" flood, some folks figured they would never again see such a disaster in their lifetime. With the region struck by a supposedly once-in-a-lifetime flood for the second time since 1993, some scientists and disaster officials say the use of terms like "100-year flood" should be re-evaluated because they are often misunderstood and can give the public a false sense of security. Many people seem to believe that a 100-year flood should happen once every 100 years, or that a 500-year flood should happen every 500 years. But that's not how it works. A 100-year flood is defined as a flood so big that it has a 1% chance of happening in any given year. A 500-year flood is one with a 0.2% chance of happening in a given year — a 1-in-500 chance. While the rules of probability say that the odds are 50-50 that a coin will come up heads, it is entirely possible to flip a quarter and come up with heads four or five times in a row.

Spotter Reports From NOAA
NOAA has an interesting slide presentation on the quality and errors of spotter reports.

Earth Systems Science Agency From Science Daily
A group of former senior federal officials call for the establishment of an independent Earth Systems Science Agency (ESSA), formed by merging the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS). The groups suggests that federal environmental research, development, and monitoring programs are not presently structured to address such major environmental problems as global climate change, declines in freshwater availability and quality, and loss of biodiversity. The USGS, contributes its geologic, biologic, hydrologic and geospatial expertise to the understanding of natural systems, but also its research capabilities in energy, mineral, water, and biologic resources. Linking the atmospheric and marine programs of NOAA gives the new organization a comprehensive perspective on both environmental and resource systems. The new agency could predict climate change and its impacts, and to help us mitigate and adapt to other changes that have the potential to affect our quality of life and economic well-being.

Rumbling Thunder From USA Today
Sometimes thunder claps, sometimes it rumbles. Claps tend to be 0.2- to 2-second-long cracks that accompany close lightning. Lightning that occurs farther away tends to produce rumbles, rather than claps. This is because higher frequencies tend to be more rapidly absorbed by the surrounding environment, while the lower frequency waves sometimes travel distances of 10 to 15 miles (even 25 miles under the right conditions). These long-distance travelers can come from different parts of the lightning bolt, bounce against terrain and buildings, or be refracted by temperature variations in the atmosphere, resulting in a myriad of sound waves reaching an observer's ears at different times. When this happens from repeated lightning bolts from one storm, and other storms chime in, you can wind up with rumbling, or rolling, thunder. This National Weather Service JetStream webpage has an excellent explanation of rumbling thunder.

Convective Vortices From Univ of Michigan
Most forecasts are based on mathematical models. A new mathematical model indicates that dust devils, water spouts, tornadoes, hurricanes and cyclones are all born of the same mechanism and will intensify as climate change warms the Earth's surface. The new equation more accurately estimates the maximum expected intensity of a spiraling storm based on the depth of the troposphere and the temperature and humidity of the air in the storm's path. Based on Daniel Bernoulli's 18th-century equation that explains how airplane flight is possible, basically saying that as wind speed increases, air pressure decreases.

Bernoulli's equation leaves out variables that were considered difficult to deal with such as friction and energy sources (which, in the case of a whirling storm, is warm air and condensation of water vapor.) Including these additional variables broadens Bernoulli's equation to apply it to more general phenomena such as atmospheric vortices. It suggests that for every 3.6 degrees Fahrenheit that the Earth's surface temperature warms, the intensity of storms could increase by at least a few percent.

Cumulus Cloud Forecasts Science Daily
For three years, a new way to use data collected by NOAA weather satellites has been giving North Alabama short-term warnings of "pop-up" thunderstorms. The UA-Huntsville Satellite Convection AnalySis & Tracking System (SATCASTS) monitors cumulus clouds as they develop, move and grow through time. SATCASTS has been accurate in its storm forecasts between 65 and 75 percent of the time.

Data from the GOES visible and infrared sensors, SATCASTS tracks changes in both cloud temperature (height) and water vapor. This data is updated every 15 minutes. The development team determined that one of the most important factors in predicting thunderstorms is temperature change. If the top of a cloud cools by 4 C (about 7.2 degrees Fahrenheit) or more in 15 minutes, that means the cloud is growing quickly and there is a growing probability of rain beginning within 30 minutes to an hour. A 4 C drop in temperature typically means a cloud top has climbed between 1/4 to 1/3 of a kilometer. This is the first time forecasters anywhere have had a tool to forecast storms that develop locally. This differs from Doppler radar, which only tracks rain after it starts to fall.

While SATCASTS joins a sophisticated and extensive network of weather monitoring systems in the U.S., it is expected to have special value in regions where storm forecasting and monitoring have been limited or non-existent. The system is relatively inexpensive to install and operate, since it uses freely distributed weather data from existing satellite sensors.

Lightning Prediction From Science Daily
Researchers narrowed the search for the source of X-rays emitted by lightning, a feat that could one day help predict where lightning will strike. As far back as 1925, theorists predicted that thunderstorms and lightning might make X-rays. After seeking evidence for decades with little success, researchers in 2001 and 2002 reported solid confirmation that lightning does indeed produce large quantities of X-rays. Scientists have been seeking to understand and explain the phenomenon since then. The researchers used an array of electric field and X-ray detectors at a lightning research facility in North Florida to hunt the source of X-rays emitted by lightning strokes. The researchers trigger lightning using wire-trailing rockets fired into passing storm clouds.

Researchers confirmed that X-rays are produced by the stepped leader in natural lightning. They narrowed the production of X-rays to the beginning of each step of the step leader. As the lightning comes down from the cloud toward the ground in 30- to 160-foot stages known as “steps” in a “step leader” process, the X-rays shoot out just below each step, mere millionths of a second after the step completes.

Telephone Alert From USA Today
Glenpool is a city of about 8,000 people, 14 miles south of Tulsa. The city approved a contract with Media Weather Innovations to alert residents by telephone when a tornado warning is issued specifically for the city. The calls are automatically made as the information is disseminated over the NOAA Weather Wire. Calls are made first to those closest to the storm, and then those directly in the path of the storm. The system won't replace the 10 storm sirens. The cost the new system is about the same as buying a new storm siren.

Word For The Month From Minnesota WeatherTalk
According to the Storm Spotter's Guide, this term is used to describe anything that impedes the ability of a storm spotter in observing the development and onset of a storm. This can be dust, haze, smoke, low clouds, shafts of rain, or fog. Under conditions of extreme gunge, forecasters must rely on satellite imagery and radar, rather than storm spotters.

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Steele County SKYWARN
Owatonna, MN