For many, the weather report is a nightly ritual on the evening news. We take for granted all the elements of a forecast, many of which were unheard of in the early days of meteorology. Here is a guide to those features on the map.
High and low pressure areas. These are the first things to look for on a weather map. Labeled with an “H” or an “L,” high pressure systems mean air pressure is increasing towards the center, while low pressure systems mean air pressure is decreasing towards the center.
Complementing these systems on the map are “isobars,” lines of equal air pressure. Isobars close together indicate strong winds and low pressure systems. Sparsely placed isobars, generally associated with high pressure systems, indicate calm winds.
You can use the pattern of isobars to gauge the direction of the wind in your neighborhood. In the northern hemisphere, winds move in a counterclockwise direction around lows and in a clockwise direction around highs. So if a high pressure system is centered to the north of Duluth, or a low pressure system is centered to the south of Duluth, expect lake winds.
High pressure systems usually mean clear skies and chilly nights during winter, as there are very little, if any, insulating clouds to help trap heat. At any point in the year, high pressure systems can cause stagnant conditions, allowing for rises in air pollution.
Fronts. Fronts mark the boundaries between air masses. Lines with triangles indicate cold fronts and are frequently blue; lines with half-circles indicate warm fronts and are frequently red.
These systems bring changes in the weather. A hot, muggy summer day might suddenly grow cool towards late afternoon into early evening as a cold front arrives, bringing rain and thunderstorms with it.
Radar. Developed during World War II to track aircraft, radar provided the answer to a problem that had been plaguing meteorology—the habit of weather balloons to float beyond range or behind a cloud.
Weather balloons carrying meteorological instruments were utilized in the late nineteenth century (and continue to be used to this day). Sensors attuned to pressure, temperature, and humidity—known as “radiosonde”—were attached to these balloons beginning in the 1930s.
Radiosonde networks expanded over the years, and weather balloons could be tracked from the ground with optical theodolites—instruments that measure angles.
But radar, it turned out, could do more than track aircraft. It could also track precipitation patterns, helping to anticipate the development of fronts, thunderstorms, tornadoes, and hurricanes.
Data from radiosonde and radar allowed for the construction of upper level weather charts. Precipitation scatters radio signals, bouncing some back to the ground-based equipment that initially sends them out. From this, extremely detailed images of weather systems can be created, which is what we see when a meteorologist shows local maps depicting colorful patterns moving across the screen.
Often, the dominant color is green (rain). Heavier rain, associated with thunderstorms, can come up in shades of yellow, orange, and red. This time of year, large swaths of blue are displayed, indicating snow.
Doppler radar utilizes two radar simultaneously to monitor small-scale changes in weather systems by amplifying the perception of changes in signal frequency. This means more accurate identification of severe weather and fewer false alarms.
Satellite. A satellite is any celestial body that orbits another. Our moon, for example, is a satellite.
The concept of man-made satellites was first put forth in 1687 by Sir Isaac Newton. Hundreds of years later, on October 4, 1957, the U.S.S.R. launched Sputnik 1. Today, there are countless satellites in orbit, mostly for scientific research and military reconnaissance.
Radio transmitters send and receive signals to and from the earth. Often a weather map will be covered in white and gray images of clouds as seen from space, and we can watch them move across the screen.
Factor in pressure systems, fronts, and isobars, as well as symbols for rivers, highways and interstates, state and county borders, and you can read the gist of the weather map in your area for yourself.
After the cold spell that descended on the region in the middle of November, I held out hope for a seasonable December. In fact, the middle of the month was looking mild until around the winter solstice on the 21st.
Now expect some chilly temperatures for Christmas, followed by even chillier temperatures as you make your New Year’s resolutions. If you’re not all that into bitterly cold conditions, your best bet for getting outdoors and enjoying the day was probably mid-month.