How long were Madison lakes frozen this year?

Posted on April 21, 2014 by WeatherGuys Editor

Lakes Mendota, Monona and Wingra opened during the second week of April.

Lake Mendota officially froze Dec. 16 and opened April 12, for an ice season  of 117 days, which is 12 days longer than the median duration.

Despite the persistent and sometimes brutal cold we experienced this winter  in southern Wisconsin, the 117-day ice season pales in comparison to the record  for Mendota, set in 1880-81, of 161 days. That’s nearly a month and a half  longer than this year’s ice season.

Lake Monona froze Dec. 10 and opened April 10 for a season of 121 days,  exceeding the median duration by 17 days.

Lake Wingra froze Nov. 27 and opened April 9 for a season of 133 days, also  17 days longer than the median.

Interestingly, the largest lake, Mendota, took only three more days to open  than did the smallest lake, Wingra.

Because there is so much more water in Lake Mendota compared to Lake Wingra,  the big lake froze 19 days later than the small lake. This testifies to the  substantially larger amount of heat energy that must be removed from the larger  Lake Mendota before it can finally freeze.

This energy is deposited in the overlying atmosphere where it can be used to  make the lakeshore temperatures warmer than those at locations far from the  lake. Such heat lost from the lake in late autumn, since it was originally  deposited in the lake by sunlight during summer and fall, represents a delay in  the transfer of energy from the summer-autumn sun to the wintertime air.

Category: Climate, Seasons

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Who controls the tornado sirens?

Posted on April 9, 2014 by WeatherGuys Editor

The sirens around Dane County are not just for warning about tornadoes.

Although tornado warnings are by far the most common cause for the sounding  of the alarm, the sirens are used for other hazards.

For example, they may be sounded for a major chemical release due to some  accident.

The siren system is designed to alert people of health hazards or life-threatening  situations.

In Dane County, the 911 Center is the primary activation point of the county  sirens, with the County Emergency Management office serving as backup.

There are more than 130 sirens distributed throughout the county. Monthly  testing of the sirens occurs at noon on the first Wednesday of the month.

A tornado warning can only be issued by the  National Weather Service, and it is that warning that makes it to the 911  Center.

Local utilities supply the needed electrical power to the sirens, and in the  event of severe weather, a power failure or a lightning strike may shut down the  sirens. So a backup for a weather hazards notification is probably a good  idea.

That can be a NOAA Weather Radio which has National Weather Service  broadcasts of severe weather watches and warnings. Local radio and television  are also good resources.

Smartphone apps are also becoming more popular. The Federal Communications  Commission (FCC), the Federal Emergency Management Agency (FEMA) and wireless  industry carriers have collaborated to produce the Wireless Emergency Alert  system. Through this national emergency alert system emergency managers can send  text-based messages to wireless devices.

Category: Meteorology, Severe Weather, Weather Dangers

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How do potholes form?

Posted on March 17, 2014 by WeatherGuys Editor

Potholes result from a combination of traffic and water.

Roadways are constructed in layers. The top layer is water resistant and curved to drain water off the road and onto the shoulder.

A road surface develops cracks due to the stresses caused by traffic and because of the heating and cooling of the surface. During the day, the sun warms the roadway causing it to expand a small amount, while nighttime cooling causes the road to contract.

Even small cracks in the surface allow water to seep below the surface into the underlying materials. During the cold nights the water freezes and expands.

During a clear sky day, the sun warms the road which melts the underlying ice. The melted water can flow to a different section of the roadway.

When the ice melts, the pavement contracts and leaves gaps in the surface under the pavement, where again water can get in and be trapped.

Stresses on the roadway from traffic can widen existing cracks, allowing more water to seep in and freeze during the night. This freeze-thaw cycle will weaken the surface.

Traffic over the weak spot in the road causes the roadway material to break down, and when that broken-down material is removed by constant traffic, it creates a pothole.

We see many potholes develop in the early spring as that is when we get nighttime temperatures below freezing and daytime temperatures above freezing due to the longer daylight hours.

This temperature cycle results in several freeze-thaw cycles that cause potholes. Early spring can be considered pothole season.

Repairing potholes is a challenge as one has to not only fill the hole but also seal it to keep water from getting into any cracks.

Category: Seasons

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How do I prepare for severe weather?

Posted on March 10, 2014 by WeatherGuys Editor

How do I prepare for severe weather?

Severe weather can happen at any time and anywhere. Your best protection is  to be prepared.

Last week, the National Oceanic and Atmospheric Administration (NOAA) and the  Federal Emergency Management Agency (FEMA) sponsored the National Severe Weather  Preparedness Week. Throughout the week, they organized groups and activities  that highlighted the importance of preparing for severe weather before it  strikes. They pointed out that being prepared for severe weather doesn’t have to  be complicated or expensive. The most important step is to have a plan for what  you and your family will do when severe weather strikes.

An important first step is to know the potential hazards. Weather hazards in  Wisconsin are primarily from tornados, large hail, straight-line winds and  flooding. The summer is when much of this severe weather can occur, though it  can occur at any time.

You should remain alert for potential weather hazards. Get an NOAA weather  radio for weather updates. Also, subscribe to wireless emergency alerts, or  WEAs, that provide free messages to your cell phone that will alert you about  severe weather in your area.

For more information on WEA Alerts, go to ready.gov/warning-systems-signals. These severe weather  alerts provide only basic information; seek additional information. Tune in to  local forecasters on radio or television. Local forecasters are experts on  regional weather and can interpret observations and conditions for you.

Severe weather can strike quickly, so know where to take shelter before  encountering a severe weather event. Learn more at ready.gov/severe-weather.

Category: Severe Weather, Weather Dangers

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How is the wind measured?

Posted on March 5, 2014 by Weather Guys Editor

Wind has both speed and direction. Anemometers measure wind speed and wind vanes measure wind direction.

A typical wind vane has a pointer in front and fins in back. When the wind is blowing, the wind vane points into the wind. For example, in a north wind, the wind vane points northward.

A cup anemometer is a common tool to measure wind speed. The cups catch the wind and produce pressure difference inside and outside the cup. The pressure difference, along with the force of the wind, causes the cups to rotate. Electric switches measure the speed of the rotation, which is proportional to the wind speed.

At wind speeds below about 3 mph, the cup anemometer is prone to error because friction keeps the cups from turning. At wind speeds above 100 mph, cup anemometers often blow away or give unreliable measurements. In freezing rain, the anemometer can literally freeze up and stop turning.

Propellers also can measure wind speed. The propeller blades rotate at a rate proportional to the wind speed.

A windsock often is used at airports. A windsock is a cone-shaped bag with an opening at both ends. When it is limp, winds are light; when it is stretched out, winds are strong. Pilots can quickly determine the wind direction and speed along a runway just by observing the shape and direction of a windsock.

Sonic anemometers use sound waves humans cannot hear to measure wind speed and direction. The instrument determines the wind velocity by measuring the time between when the instrument sends a sonic pulse and when it is received.

Category: Meteorology

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