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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Does the jet stream have something to do with our winter?

Posted on March 3, 2014 by Weather Guys Editor

Our exceptionally cold winter has been the subject of this column a couple of times in the past few months. Some readers have asked how the jet stream might be related to cold air outbreaks.

As we have mentioned before, the jet stream is a ribbon of strong west-to-east winds located approximately 6 miles above the ground. The jet exists as a result of a pole-to-equator temperature difference throughout the entire depth of the lowest 6 or so miles of the atmosphere.

Naturally, when the polar regions get colder in winter, this temperature difference increases and the jet stream intensifies. A strong, mostly west-east oriented jet can act like a dam to the southward progress of cold air produced in the polar regions.

However, the Northern Hemisphere winter jet is usually quite wavy, and this waviness allows excursions of warm air poleward or cold air equatorward. This winter, the waviness has led to repeated equatorward excursions of polar air over North America.

A recent study, co-authored by one of our colleagues at UW-Madison, has suggested that reductions in Arctic sea ice, which have made the Arctic warmer, have effectively reduced the pole-to-equator temperature difference. The suggestion is that this has weakened the wintertime jet and increased the likelihood that it will be wavier than normal. Such increased waviness, coupled with a related tendency for the waves to move more slowly, might underlie an increased frequency of such cold winters.

This theory – though plausible — has not gained wide acceptance and is being challenged from a number of different perspectives. But that is the nature of science. Ideas are constantly compared with each other, and skepticism prevails among colleagues as to what is the best answer. Only the most comprehensive explanations of nature emerge from this relentless and intense intellectual competition.

Category: Meteorology

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Is this an unusual winter?

Posted on February 18, 2014 by Weather Guys Editor

There is no doubt that this winter’s prolonged and sometimes desperate cold has been unusual.

Interestingly, for all the talk of the “polar vortex” and our unusually prolonged cold in central North America, it has been a remarkably “warm” winter when considered from the hemispheric perspective. Unusually warm weather in the West has offset the frigid winter across the East and much of the Midwest.

But closer to home, scientists at the National Weather Service Forecast Office in Milwaukee just reported that this year’s start to winter (defined as the period from Dec. 1 to Feb. 11) is the 10th-coldest of all time and the coldest in 35 years. To this point in the winter, our average daily temperature has been just 13 degrees Fahrenheit.

Four times each day we calculate the areal extent of air colder than minus 5 degrees Celsius ( 23 degrees Fahrenheit) at 1 mile above the surface using weather data analyses (not forecasts) supplied by the National Center for Environmental Prediction. Averaging the four measurements per day together creates a daily value of the areal extent of this cold pool.

In the accompanying chart, this daily value is plotted (thick line) against the 64-year average (dashed line) for each calendar day from Dec. 1 to Feb. 11. Thus far, this season is one of the most below-average years in the 64-year record.

Some have suggested that this winter’s cold proves that global warming is a hoax. Conversely, it has provided clear evidence that regional weather drives local cold snaps while climate lurks in the background — testifying even in the face of our cold that the hemisphere is unusually warm.

Category: Meteorology, Seasons

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