Those of us who are really into the weather, it’s not enough to say it’s warm outside or it rained yesterday. We want to know how warm it was or how much rain fell. Besides satisfying our meteorological curiosity, measuring the weather puts us more in touch with it. And by closely observing the current weather, we can even make forecasts about our future weather, and in the process, become experienced weather watchers.
Weather Instruments 101
A variety of weather instruments are available to everyone. For all of the “standard instruments,” many of which were developed centuries ago, there are electronic counterparts. You may give up some accuracy, but you gain continuous readings that can be monitored remotely.
Measuring the amount of rainfall isn’t just for weather enthusiasts — it’s critical for gardeners too. Rain gauges come in a variety of sizes and prices, and are sold in many stores. Cheap, plastic gauges cost only a few dollars, but they’re not always accurate. A popular and accurate standard is the classic 4-inch gauge (the measurement refers to the diameter of the tube), which is made of durable plastic. The surface area of the top funnel is 10 times the area of the measuring tube that sits inside the larger overflow tube, which magnifies the actual amount of rain and makes it easier to get an accurate measurement. If you receive more than 1 inch of rain, the overflow will be caught by the outer tube. The electronic version of a rain gauge is called a “tipping bucket.” An electrical signal is generated every time 0.01 inch of rain is collected, and this is sent to a display and/or recorder that tracks how much rain has been collected.
In winter, you can remove the funnel cone from the top of the 4-inch gauge and use it to measure snowfall. Bring your gauge indoors and allow the snow within to melt. This will give you a rainwater equivalent for your records. You can also go around with a ruler and measure snow on the ground, taking several readings and averaging them. Be sure to avoid snow drifts or bare spots.
Outdoor thermometers will show you the current temperature. If you want to keep track of the high and low temperatures for the day, you can get a maximum/minimum thermometer, which uses indicators that become fixed at the warmest and coldest points after measuring the temperature over a period of time. After you record your readings, just reset them. There are electronic temperature sensors that are actually very accurate, and again provide the convenience of remote readings and constant monitoring.
Hygrometers typically give you the relative humidity reading: how saturated the air is in terms of a percentage. Again, you can either use a mechanical or electronic sensor. The humidity reading will vary greatly between outdoors and indoors.
Barometers measure atmospheric pressure — simply put, the weight of the air above you. Atmospheric pressure is another measurable element that can tell you a lot about current, and even future, weather conditions. More air means higher pressure, and less air means lower pressure. Higher pressure typically means better weather, while lower pressure means worse.
One problem with measuring atmospheric pressure is that higher elevations have lower air pressure, but this fall in pressure has nothing to do with weather systems. To compensate, we use standard sea level pressure (see “Gritty’s Tips”) as a base value. We then put in a correction factor for the elevation effect. However, you don’t have to do the math yourself; home barometers have an adjusting screw, and electronic ones have a digital adjustment. Simply get the corrected sea level pressure for your location — your local National Weather Service Forecast Office will have this — and adjust your barometer accordingly.
The wind has two measurable components: direction and speed. WEATHER vanes show the direction of the wind. Whether the design is simple or highly decorative, the basic principle is the same: you have a smaller front piece and a larger “tail” that points the vane into the wind. You can even make a simple weather vane yourself.
Anemometers have three or four small cups extended from a hub that spin with the wind to measure wind speed. Although you can tell wind direction by simply looking at a weather vane, an anemometer must be connected to a device to tell the wind speed. The rate at which the cups are spinning, along with the diameter of the apparatus, will be converted to a speed in miles per hour (mph).
If you want to go full-bore into weather observing, you can buy a complete electronic weather station. The actual cost will depend on how much instrumentation you want and the degree of accuracy you require. Once set up, the sensors will take the readings for you. All the information can be shown on a display inside, or you can connect it to your computer and have access to your home weather wherever you go. You can even connect your station with the networks of other weather observers.
Locating Your Instruments
Siting your instruments in the correct location is essential for getting accurate readings.
You should place your rain gauge in a location that’s as open as possible — away from any trees and other vegetation, or structures that could block precipitation from entering the gauge (a horizontal distance of four times the height of the nearest obstruction is recommended). And make sure it’s level.
An outdoor thermometer should be sited in the open, about 5 feet high, and in the shade. Heat from the sun will artificially raise the thermometer’s readings, giving you a false air temperature.
Officially, wind measurements are taken about 30 feet above the ground and away from any obstructions (10 times the height of the obstruction). Not possible? Do the best you can to get the instruments up in the air and away from obstructions.
Fortunately, air pressure is the same outdoors and indoors, so barometers can be located conveniently inside your home.
All good weather junkies write everything down. Many people do this their entire lives and have decades of records. You can even buy specific “weather notebooks” designed for this purpose. Of course, along with the instrument records, you should also include your own personal observations. What were the general sky conditions — clear, partly cloudy, or cloudy? If you had precipitation, when did it occur? Were there any other special weather occurrences?
You can keep these detailed records for your own fulfillment, or you can share them with others. One group of weather observers, the Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), report their 24-hour precipitation totals on their site each morning. There are thousands of observers throughout the United States, as well as Puerto Rico, the U.S. Virgin Islands, Canada, and the Bahamas. If you want to join these volunteers, visit the CoCoRaHS website. You’ll need to buy an official 4-inch rain gauge; a recommended supplier is listed on the website.
Feeling even more inspired? The federal government has several volunteer weather observing programs, including the Citizen Weather Observer Program and the Cooperative Observer Program. Interested in reporting severe weather? You can join the National Weather Service’s SKYWARN® Storm Spotter Program.
Forecasting the Weather and Using Your Observations
Widely distributed public forecasts have only been around for about a hundred years. Before that, people had to make their own forecasts using whatever instruments they had available. You can do the same — but no cheating by looking online!
A basic tenet of weather forecasting is, “Will tomorrow be the same as or different from today?” In terms of the weather elements you’re measuring, are they changing or static? The tendency is more important than the actual reading.
Take atmospheric pressure, for example. To forecast future weather, the change in pressure is often the most important factor. Rising pressure typically means improving weather conditions, but often lower temperatures. Falling pressure indicates an approaching low pressure area or weather front; clouds and precipitation are often on the way.
Wind direction is another factor that can be used to forecast the weather. Depending on where you live, especially in terms of geographic and topographic features, different wind directions mean different types of weather. On the East Coast, an easterly wind arrives off the Atlantic and brings moderate temperatures and often clouds and precipitation. On the West Coast, an east wind blowing off the land is very dry and especially hot in the summer. For most locations, north winds bring in cooler air, while south winds bring warmth.
A rapid change in wind direction often indicates a passing weather front. If the wind direction changes from a southerly component to the west or north, this indicates a cold frontal passage. Expect improving weather, but conditions will be cooler and windy for a while. Showers may develop ahead of an approaching cold front. If the wind direction changes from easterly to southerly or southwesterly, this indicates a warm frontal passage. Expect warmer temperatures with an end to any continuous precipitation.
Changes in relative humidity (RH) are fairly straightforward. A decrease in RH means drier air and improving weather. If the RH is increasing, look for more clouds and increasing chances of precipitation. If clouds start moving in, that means the RH aloft is increasing.
Now put all these elements together. If you can utilize this information, while expanding your experience and knowledge of your typical climate, you can become a good weather forecaster. Joining the worldwide community of weather enthusiasts is an accessible process, and you may find that it quickly becomes a lifelong passion.
Humidity varies greatly from outdoor conditions to indoors, where living areas often are heated or air-conditioned.
Low temperatures usually occur around sunrise, and high temperatures in the afternoon — but a strong frontal passage (particularly in winter) will affect these times.
Standard atmospheric pressure at sea level is 29.92 inches.
Wind direction is always given as the direction the wind is blowing from. Therefore, an east wind blows from east to west.
Bio: Ed Brotak taught thousands of college students about the weather for 30-plus years, and helped many pursue careers in meteorology. He lives in Asheville, North Carolina, with his wife and his two daughters. He still goes outside when he hears thunder.