Is that photo of circular lightning?

Posted on June 10, 2019 by WeatherGuys Editor

Some see the shape of Wisconsin in this looping lightning bolt that struck near Hager City Wisconsin on May 31. (Credit: Jerry Zimmer)

When we see a flash of lightning, it looks as though it forms all at once.

However, a lightning bolt is actually produced in many steps. The bolt occurs so quickly that it looks like a single brilliant flash, but high-speed photography can reveal several distinct bolts.

Lightning is a huge electrical discharge that results from the rising and sinking air motions that occur in thunderstorms. Lightning can travel from cloud to cloud, within the same cloud, or between the cloud and ground. The lightning in the accompanying photograph appears to be cloud-to-ground lightning.

A typical cloud-to-ground flash begins as negative charges in the cloud that travel toward the ground in a sequence of spurts. These spurts of negative charges are called “leaders.”

Leaders travel a few hundred feet. From the lower end of one leader, another leader forms, and from the lower end of that leader, another. The negative charges hop downward from leader to leader, forming an ionized channel.

Each leader heads in a direction that is independent of the previous ones. Leaders can split, forming tree-like branches resulting in a path that is not a straight line. Most lightning appears jagged because of this, but it also can take a curved path, as in this photograph.

As the negative charges approach the ground, there is an upward stream of positive charges. When the two streams meet, an initial flash occurs in the channel and electricity flows back and forth between the cloud and ground, lighting up the sky.

The ionized channel formed by the leaders is three-dimensional. So, while the bolt in the photograph looks like a 2-D outline of our state, it could be a 3-D spiral that just appears 2-D as we look along its axis. Either way, it is a fantastic and unique photograph.

Category: Meteorology, Phenomena, Severe Weather

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Why was the sky hazy on Thursday and Friday?

Posted on June 3, 2019 by WeatherGuys Editor

Satellite view of wildfire smoke over the Upper Midwest. Via GOES East (GOES-16)

There have been large forest fires in northern Alberta, Canada, and the smoke has drifted over the Midwest, including Wisconsin.

Smoke can cause the sky to appear hazy, even if the smoke is high above the ground. The smoke scatters sunlight to make the sunlight diffuse and grayish. When the smoke is thick, it can cause brilliant red sunsets and sunrises, as it did on Thursday. When light beams interact with particles suspended in air, the light can be scattered or absorbed.

The amount of light that is being scattered is a function of the number of particles and the size of the particle relative to the wavelength of the light falling on the particle. Small particles, like those of which smoke is composed, scatter violet and blue light more effectively than other colors.

So, as the sun sets and its rays pass through the smoke plume, all the blue light is scattered out of the path between the setting sun and your eyes, leaving just the red and orange colors. This results in the sun having a bright red color when it is low on the horizon. Recently, the smoke above us has been thick enough that the red sun disappeared from view before it set below the horizon.

Winds will sometimes transport the smoke down to the ground, resulting in a reduction in the quality of the air we breath. The small particles that make up the smoke can cause respiratory problems, particularly for children, the elderly and people with asthma.

Smoke doesn’t have much of an effect on our temperature or precipitation. However, official weather reports include observations on sky conditions and visibility.

Category: Phenomena, Weather Dangers

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Do cell phones network with weather forecasts?

Posted on May 28, 2019 by WeatherGuys Editor

Use of ultrahigh radio frequencies by 5G wireless carriers could interfere with weather predictions. (Image source: SSEC)

Cell phones do not directly interfere with weather forecasts. However, there is concern with how cell phone signals travel through the atmosphere, particularly the 5G network.

The 5G technology is designed to carry more data and make wireless connections faster.

In March, the Federal Communications Commission began auctioning off ultrahigh radio frequencies for use by 5G wireless carriers.

These frequencies are appealing to telecommunication companies because they need to add capacity in urban areas to keep up with increased demand. But these 5G networks have unintended consequences.

Objections are being raised the National Oceanic and Atmospheric Administration and National Aeronautics and Space Administration and other federal agencies. Use of these frequencies for 5G could interfere with weather predictions.

The airwaves being auctioned are near frequencies used by NOAA satellite instruments to observe water vapor, rain and snow. For example, atmospheric water vapor emits a small amount of energy at these ultrahigh radio frequencies. Weather forecasters measure these signals from satellites and use the observations to understand how weather systems are likely to develop.

If networks transmit frequencies where water vapor emits energy, the satellite measurements will not be able to distinguish between those signals generated by the weather systems and the telecommunication signals. Loss of this weather information will impact the accuracy of weather forecasts.

Dr. Neil Jacobs, the acting NOAA administrator who oversees the National Weather Service, told Congress that loss of these weather data could reduce today’s forecast skill to what it was back in 1980.

This could become a global problem if other countries follow the US in using these frequencies for telecommunication. This fall, the World Radiocommunication Conference meets to set global agreements on use of radio frequencies for 5G.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
Category: Severe Weather, Uncategorized

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What were those flying saucer-shaped clouds?

Posted on May 20, 2019 by WeatherGuys Editor

Thunderstorms rolled through Madison between 8:30 and 9 a.m. Thursday May 16th. Stunning “flying-saucer” clouds accompanied the dark skies of the leading edge of the storm.

These dark, protruding clouds are “shelf clouds.” The clouds look like a shelf and in this case appeared as a stack of shelves. They are one of several distinct visible features of a vigorous thunderstorm complex.

Stunning “shelf clouds” along the northern shore of Madison’s Lake Mendota on May 16.
Credit: Anne Pryor

Air circulates throughout a thunderstorm, some as very turbulent pockets of air. There are also streams of upward and downward moving air. The upward moving air in a thunderstorm is known as the updraft, while downward moving air is called the downdraft.

Air that is cooler than its environment tends to sink as long as it can stay cooler than its surroundings. Sometimes prior to a thunderstorm rain you may feel a blast of cool air. This is the downdraft spreading out as it hits the surface.

The dense, cold air of the downdraft forms the gust front at the surface and flows out ahead of the storm. The gust front can lift the warm, moist air near the ground, forcing it upward to form updrafts in developing thunderstorms.

Clouds are sometimes observed above the gust front. The shelf cloud is one such cloud. It forms as the gust front forces air near the surface to rise.

A shelf cloud looks very ominous but does not produce damaging weather by itself, although it can precede severe weather by a few minutes. This was the situation on Thursday, and the storms produced brief downpours and wind gusts to around 30 mph.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
Category: Meteorology, Phenomena, Uncategorized

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What is the Beaufort scale?

Posted on May 13, 2019 by WeatherGuys Editor

Wave watchers check out the ocean action near Peggy’s Cove, Nova Scotia, during Hurricane Bill in August 2009. Based on observations rather than measurements, the Beaufort scale is a method of estimating wind speed based on the general condition of the surface of a large body of water with respect to wind waves and swell. (Photo credit: Associated Press Archives)

The Beaufort scale is a method of estimating wind speed based on the general condition of the surface of a large body of water with respect to wind waves and swell.

It is based on observation of sea state rather than accurate wind measurements. This scale allows sailors to estimate the wind speed just by observing the state of the sea surface.

The scale has a long history, but was finalized in 1805 by Rear Admiral Sir Francis Beaufort, an Irish hydrographer in the British Royal Navy. It was officially first used during the voyage of Charles Darwin on the HMS Beagle (1832-1835).

The Beaufort scale can also be applied to conditions on land, but it is most often associated with the sea state.

The modern-day Beaufort scale consists of 13 numbers ranging from 0 to 12. A zero value on the Beaufort scale is assigned to calm winds and the water surface is smooth.

A Beaufort force 12 occurs with waves greater in height than 46 feet and the sea is completely white with foam and spray with greatly reduced visibility. Such conditions are associated with wind speeds of greater than 74 mph, which are hurricane-force winds.

The National Weather Service defines sustained wind speeds of 39 to 54 mph as a gale, and forecasters typically issue gale warnings when winds of this strength are forecast. A Beaufort force 6 is a near gale with wind speeds between 25 and 30 mph and includes white foam from breaking waves that begins to be blown in streaks along the wind direction.

A Beaufort force in the range of 6 to 7 is designated as strong winds; 8 to 9 as gale-force winds; and 10 to 11 as storm-force winds.

Category: Meteorology, Severe Weather

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