Mike's Weather Blog Archive: July, August 2010

At 7News, we are always looking for innovative ways to do things. In that light, we have recently added a new 9.75 kW solar array to our rooftop right above our news studio.

This new solar array has come on-line and will help to power the 247 Weather Center at 123 Speer Blvd. The system will be connected directly into the Xcel Energy electric grid, so it will mix with the conventional energy produced by the various Xcel generating plants.

We actually have quite a history with solar power. Nearly 6 years ago, 7News teamed up with The National Renewable Energy Lab (NREL), to install a 5 kW solar array on our Doppler Radar - making it the first solar powered radar in the nation.

Our latest project has been in the works for nearly 18 months as we had to go through the various stages of approval, planning, design and construction. The combined systems on our roof and at the radar site will provide the equivalent annual power needs for the lights, cameras, computers, monitors, etc. in the 24/7 Weather Center at 7News. In fact, there is additional capacity so that we actually will put energy back into the grid over the course of an average year.

Our most recent solar project was with Bella Energy, one of the Rocky Mountain region's most established provider of solar power for both commercial and residential customers.

The rebate that was available from Xcel Energy at the time we signed our agreement was $3.50 per watt. This rate has fluctuated from time to time during the past 18 months, but it did help reduce the upfront cost of this system.

At the present commercial electric rates, KMGH will save about $1,500.00 per year with our system. The payback period for our investment will still be about 7 years, but we felt that it was a good project to be involved with as a way to raise awareness for rooftop solar in urban areas.

There is some concern about adding new solar farms to areas such as our San Luis Valley in Colorado. At KMGH-TV, we want to use our new rooftop solar as a means to showcase the vast potential to use roof surfaces throughout metropolitan areas as a great solar power resource.

The energy-climate issues are serious ones as we look to the future. The changes in how we produce and use energy will have great implications to our heirs. Energy, the environment and the economy form a critical triad for the future of our nation.

I hate for America to not be at the energy forefront in the 21st Century. We can lead the world with better and cleaner ways to make power, we have done it before with major endevours. The Transcontinental Railroad in the 1880s, the Manhatten Project, The Interstate Highways, The Space Program, the Computer Revolution.

Instead of bowing down to special interests, we must, for our heirs, do the right things. To paraphrase JFK, "not because they are easy, but because they are hard."

We live in a beautiful part of the country and our Colorado skies offer so many lovely things to enjoy. Here is a little background on the many pretty colors in the sky!

RAINBOWS

The rainbow is a lovely and familiar guest in our skies, especially during the summer months. Rainbows are caused by the light rays from the sun passing through the water droplets of a passing storm. The sun must be at a fairly low angle in the sky, so usually the storm has already passed by to the east and the late day sun shines in from the west. The opposite can happen early in the morning and foretell an approaching storm - but early morning thunderstorms are rare in the Rocky Mountains.

As the light shines through the water droplets, the light is bent or refracted, similar to when light travels through the glass in a prism. The light moves more slowly through the prism or the raindrop and is therefore spread out into the various colors that make up visible light (Red, orange, yellow, green, blue, indigo and violet). The light is refracted once as it enters the drop, then is reflected off the back of the drop and finally refracted again as it exits the drop. Secondary rainbows are often seen and are the result of the light being reflected again off of the inside of the raindrop before it exits. The results of all of this optical bouncing around are the lovely rainbows that we enjoy.

Not all cultures felt the same about the rainbow. In the Book of Genesis ( 9:16 ) the rainbow signified "a covenant between God and every living creature". The ancient Greeks thought that the rainbow was "Iris", the messenger of the gods, who bore news of war and death. Many African and American tribes saw the rainbow as a giant and deadly serpent. The Shoshone people in particular thought the rainbow serpent arched its back against the icy dome of the sky and brought forth the destructive hailstorms that are so common on the high plains. Whew! I think I will just enjoy the beauty of the colors.

CORONAS

There are lots of Coronas out there... cigars, beer, the hot outer gases of the Sun. The corona that we sometimes see at night involves the moon and a few clouds. When the moon is close to full, ragged clouds drifting in front of it may produce a colorful display. The colors may take on a "Mother of Pearl" appearance that is striking. On occasions when the clouds are fairly uniform, the colors will form a ring around the moon; this ring is called a CORONA.

The corona is caused by the DIFFRACTION of light as it moves around tiny water droplets in the cloud. It is important to note that under certain conditions water can stay in a liquid state at temperatures well below freezing. This type of water is called "supercooled". To explain diffraction, think light as a series of waves on a lake. Imagine some of the waves as they would pass by a pole sticking out of the water. Each side of the pole would create a disturbance as the waves pass by. This disturbance would change the angle of some of the waves and very soon the initial "straight" waves would be crashing into the waves that curled around the pole. In some places the crests of the two different waves would pile up to form a larger wave, in other places a crest and a trough would cancel each other out. In Physics this is known as constructive and destructive interference. The same thing happens as the light waves move around a supercooler water droplet. The constructive interference is seen as a bright light and the destructive interference is a darker light. Because the different wave lengths of light bend around the droplets differently, we see the various colors. The colors will change in a given sequence over and over growing fainter as they extend farther from the source of the light - the moon.

The corona is a beautiful sight, but it also can be somewhat useful. The presence of the supercooled droplets indicates, of course, water in the atmosphere. That water can be associated with an approaching storm system. Our pioneering ancestors used these indicators to help them prepare for a change in the weather. Just as now, the prediction did not always pan out, sometimes the storm would exist somewhere, but just not in that particular area. So "busted" forecasts are certainly nothing new!!

HALOS AND SUNDOGS

The term halo is generic for all rings, arcs and spots produced by the reflection and refraction of light by ice crystals in the atmosphere. There are two major types of ice crystal, the hexagonal (six sided) plate and the hexagonal column - these two types account for almost all observed halos. They can create a variety of shapes - rings, arcs, etc, because the tiny crystals are swirled around in different ways by the motions of the air.

Reflection is a familiar concept to everyone as we see our reflection in a mirror or on the surface of a calm lake. When light hits a flat, smooth surface, it bounces off that surface at the same angle as it approached. Hexagonal plate type ice crystals behave like millions of tiny flat mirrors which reflect the image of the sun or moon. This can create a false sun or moon that can be seen to the side of the actual object. If the ice crystal is shaped into six sided columns instead of flat plates, they reflect the light differently as they tumble through the atmosphere and may create a column of light - we call this a "sun pillar". Sometimes these pillars can be seen in the winter during extremely cold weather as tiny ice crystals float above street lights and create a similar effect.

Refraction is a phenomenon that occurs when light penetrates the surface of a flat water or ice surface and the light rays bend slightly. This is due to the fact that the light travels at a slightly different speed in air compared to liquid water or ice. Because the amount of the bending that occurs depends upon the wavelength of the light (blue is bent more strongly than red light), white light can be separated into its component colors. A prism is a familiar example of this and the hexagonal shape of ice crystals can act as tiny prisms. When light is refracted by ice crystals, the light is bent from its original direction and fans out away from the light source to create an arc of light around the sun or the moon. Depending upon the density, size and the type of ice crystal (plates or columns), the arc may be a complete circle, a partial circle or even two circles, one close to the sun and another farther outside.

Sundogs are created when some of the ice crystals become large enough to line up in the atmosphere so as to refract the light in a less random pattern. Instead the light is refracted to cause a mock sun to the left or right (or both) sides of the sun. These mock suns are called "Sundogs" or more scientifically - "parhelia". Sundogs are not as common as halos, but can be seen a few dozen times a year, especially in the winter months. They can be forecasting tools as the thin clouds of ice crystals are often associated with an approaching storm system.

CREPUSCULAR RAYS

One of the most glorious sights in our skies are the beams of light that stream out from clouds as if they were sent from Heaven. These light rays often take a subtle beautiful golden color in out late afternoon sky as they fan out from between the clouds. The light beams are called "crepuscular rays" and they are yet another optical effect that is very fascinating. The rays are visible because of dust in the air that reflects the light from the sun. The golden color is due to late afternoon or early morning filtering of the incoming sunlight as it travels through more of the atmosphere (due to the low angle of the sun). The more atmosphere the light has to traverse, the more the shorter wavelengths are filtered out by the dust, leaving only the longer yellow, orange and red light. The light rays seem to fan out from a central point, but it is really just an illusion. The light rays are actually parallel! This illusion is due to the fact that the source of the light (the sun) is so far away, that the light essential starts from an infinite point. The best way to think of this is to envision a pair of railroad tracks. If you look way down the tracks into infinity, the tracks seem to converge in the distance. Of course they do not, they remain parallel, but to our eye it would appear that the tracks are fanning out from a point way in the distance. The same illusion is what creates the fanning out of the crepuscular rays. Another phenomena that is seen on rare occasions are "anti-crepuscular rays". These take a little imagination to figure out. If the sun has already set from your vantage point (or has yet to rise), you may see beams of light seeming to come together along the opposite horizon (180 degrees from the sun). This is caused by the sunlight and shadows cast by clouds in front of the sun. At the cloud level (higher in the sky) the sun has already risen about the horizon. The light from the sun shines on to the clouds, casting parallel beams of light and shadow across the sky. In the distance behind you, those beams seem to converge just like the railroad tracks!

The weather will be a little on the muggy side in Colorado over the next few days. In that light, here is a little insight into the ways we measure moisture in the atmosphere.

The moisture that is in our air can be measured in a number of different ways. The dew point is the temperature at which the air becomes saturated with water vapor, in other words - at which dew would form. Once the air is saturated, any additional moisture added to the air will result in clouds, dew, frost or precipitation - depending on the given weather pattern.

The dew point is always less than or equal to the air temperature, it cannot be higher - when the temperature and the dew point are the same, the air is said to be saturated. When the air is saturated, the relative humidity is 100%.

One of the reasons that Colorado is so nice a place to be is because we have a "friendly dew point". Our high elevation and greater distance from the oceans means that our atmosphere is fairly dry and the dew points are often much lower than those of cities farther to the east and south. In the summertime, our dew point is often just in the 40s during a hot summer afternoon. This means that the temperature would have to cool from say the mid 80s - all the way down to the 40s in order for the air to become saturated. In contrast, summertime dew points in St Louis or Dallas might be in the upper 60s. That means the air would only have to cool to the upper 60s for the air to become saturated and dew or clouds to form. This is the reason why we often have little or no morning dew here, especially compared to our muggy neighbors to the east.

Our lower dew points also mean that we have a lot less moisture in the air to help fuel thunderstorms. The storms that develop in Colorado have to "pull" moisture in from a large area in order to blossom into heavy rainmakers. Our storms tend to be small and more widely scattered as there is limited moisture available. In the Midwest, the south and the east, the dew points are higher and there is a great deal more moisture available to feed large squall lines or big clusters of storms.

One of the things that meteorologists watch for is the difference between the temperature and the dew point. If there is a large difference (temperature is much higher than the dew point), then the air is obviously quite dry. If the "dew point spread" is getting larger, the air is getting drier (the relative humidity is getting lower). If the dew point spread is getting smaller, then the air is getting more humid and there could be a chance of fog, clouds or even precipitation.

The dew point is measured by using a combination of a "dry bulb" thermometer (just a regular thermometer) and a "wet bulb" thermometer (a thermometer that has a moistened piece of cloth over the bulb or bottom of the tube). The "wet bulb" thermometer will read lower due to the cooling of evaporation of the moisture on the bulb. The drier the air, the more powerful the cooling will be and the lower the wet bulb will read. If the dry bulb and the wet bulb were the same, the air would have to be saturated (relative humidity = 100%). Under saturated conditions, there is already so much moisture in the air, there can be no more added through evaporation.

In Colorado, most of the time our wet bulb temperatures are much lower than in other, more humid parts of the country. The dry bulb (or regular temperature) may be in the 90s or even low 100s, but it is still much more comfortable than a hot day would be in another part of the nation where the wet bulb temperatures are higher. In those places, weather reporters often speak of the "heat index" - than figure is a combination of the heat and the high humidity that makes it feel even hotter than what the thermometer reads.

In Colorado, we sometimes have a "negative heat index". In other words, the air is so dry, that even with a temperature of 100 degrees, it doesn't feel that hot. This is due to the very effective cooling that our bodies attain through perspiring. Our shirts may stay dry, even on a very hot day, as the sweat quickly evaporates, keeping us cooler. In other parts of the country, working outside on a hot day would leave you drenched in sweat. In Colorado, the same work would leave you not as hot, with a pretty dry shirt. The downside is that we have to watch out for signs of dehydration, as we lose so much water through sweating.

All in all, I will take our "friendly dew point,” it is just one more thing that makes Colorado such a great place to live!

There is a new research project being conducted to help improve the effectiveness of severe thunderstorm, flash flood and tornado warnings. This survey is part of a major study on warning utilization being conducted by students and faculty in the Department of Atmospheric Sciences at the University of North Carolina at Asheville, with the National Weather Service serving as a collaborative partner.

The survey focuses on the extent to which the general public receives and utilizes severe thunderstorm and tornado warnings. As part of an effort to improve our communication of warnings, the study will help us better understand how warnings are received, how the information is interpreted, and how people respond to the warning messages. Participation is free and anonymous and should take fewer than five minutes. Participants must be 18 years of age or older. If you would like to participate, click this link... National Warning Study

Here is a little more information about tornadoes and severe storms...

Most tornadoes in the United States occur in the central plains, with the greatest likelihood of twisters in the southern plains around Kansas, Texas and Oklahoma. Colorado lies of the western fringe of "Tornado Alley", but our state still averages between 40 and 60 tornadoes per year.

The peak season for tornadoes is in the spring and early summer. From March through June, about 70% of all the tornadoes in a year will occur. This is due to the fact that the weather patterns that are needed for tornado development are most common in the spring and early summer.

Most tornadoes form from large rotating thunderstorms called "super cells". These monster storms tend to develop ahead of cold fronts that push southward from Canada across the central U.S. As the fronts sag into the warm and humid air that covers the southern plains, the colder air wedges under the warm air, creating lift. The lifted air rises up to form thunderstorms that can rapidly grow to heights of 40 to 50 thousand feet above the ground.

The storm pushes high into the sky, reaching into the jet stream - the band or river of fast moving air that flows around the world. It is the increase in wind speed with height that causes the thunderstorm to begin a large, slow counterclockwise rotation. This rotating thunderstorm is what is classified as a "Super Cell".

Once the super cell storm develops, the best analogy for thinking about how the tornado forms is to think of a figure skater doing a spin. The skater starts with their arms out, and is rotating rather slowly. As the skater brings their arms in, the rotation begins to speed up. In physics, this is called "the conservation of angular momentum". The rotation gets faster and faster as the size of the rotating column grows narrower. This is a very simplistic description, but eventually this narrow rapidly rotating column of air will drop to the ground as a tornado.

Tornadoes are classified by the wind damage that they cause. The scale was developed by Dr. Ted Fujita from the University of Chicago. Dr. Fujita based his "F scale" on a 0 to 5 basis for tornadoes. The F0 is a weak tornado, while the F5 storms are the most powerful winds ever observed on Earth.

As of 2007 this scale was replaced by the enhanced Fujita (EF) scale. The EF attempts to rate tornadoes more accurately, taking into account that it often requires much lower wind speeds to create F5-like damage. The new EF scale is now the official standard to measure the strength of tornadoes.

EF 0 - 65 to 85 mph

EF 1 - 86 to 110 mph

EF 2 - 111 to 135 mph

EF 3 - 135 to 165 mph

EF 4 - 166 to 200 mph

EF 5 - Over 200 mph