Why is Your Weather Different Than Mine? 11 Dec 2013

Do you have weather instruments at your house? Are your readings often different than those on the TV weather report or even on a friend’s instruments near you? Why is that?

Instrument Placement is Critical

Weather thermometers should be placed in a location that is shielded from direct sunlight, 4 or 5 feet above the ground, exposed to free air flow, and not too close to objects that absorb or radiate heat. For example, a lot of data that the media use comes from local airports. Their sensors are often mounted on a building surrounded by acres of pavement. Temperature readings in places like that are often higher than you or I may record at home. During the day the airport roads, runways, building roofs, and walls soak up the sun’s warmth, causing the temperature to register too high.

If your home weather station includes a humidity indicator, locate it away from areas that are unusually moist such as flower beds. Electronic humidity gauges are notoriously subject to error and need to be calibrated regularly. Most casual observers don’t have access to calibration equipment, so you may have to settle for something less than perfection.

Wind instruments should be at least 1/3 farther away than the height of the nearest structure, and 15 to 20 feet in the air. Typically, people mount them on a TV mast just over the crest of their roof, a location that gives bad speed and direction readings because wind is forced to swoop over and around the building.

Rain gauges should be mounted 3-4 feet off the ground the same distance from objects that wind direction and speed sensors are located.

Barometers, even though wall-mounted decorative types have words like “stormy, rain, change, fair, dry,” tend to give an unrealistic idea of what to expect from future or even current weather. They do indicate whether atmospheric pressure is falling, stable, or rising, but other factors must be considered as well, including upper level pressure changes, and the passage of cold and warm fronts, or stagnation of a stationary front that may not show up on your barometer.

Incidentally, it is not necessary to mount a barometer outdoors. Because buildings are not air tight, the indoor reading is the same as outside. If that were not the case, as the pressure fell outside, a building’s wall would try to pop out.

Weather Is Not the Same Everywhere

Especially during stormy weather, rain often comes as squalls, showers, heavy downpours, and other variations that occur in very small areas. Even with widespread precipitation, the amount that actually falls can differ widely across a very limited area. You also can’t compare your information with other amateur weather spotters’ data – even those who report to the TV stations each day. There is no way to tell what kind of instruments they are using or exactly where they are placed, and the TV weather people may be using data that is an hour or more old.

Towns and cities also create their own weather. Solar heating of buildings, roads, and parking lots causes rising warm air that can condense into clouds and gives some communities their own private storms.

In a nutshell, if you aren’t getting the same readings as reported by the media, or your friend on the other side of town or even across the back fence, don’t be discouraged. There are many factors at work, all of which interact, and it’s still a lot of fun to keep track of weather information. Weather and climate have major influences on everything on the earth and as you observe, your appreciation of the fields, forests, towns, and cities of East Texas will increase.

If you’d like to visit a great Web site that can help you painlessly learn more about meteorology, try ww2010.atmos.uiuc.edu.

Dr. Risk is a professor emeritus in the College of Forestry and Agriculture at Stephen F. Austin State University in Nacogdoches, Texas. Content © Paul H. Risk, Ph.D. All rights reserved, except where otherwise noted. Click paulrisk2@gmail.com to send questions, comments, or request permission for use.