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The Measurement of Weather
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Hopefully most of you read the columns of Alicia Boor, the ANR agent with the Barton County Extension Office. Last week she discussed the definitions of various types of freezes and what they meant to anyone growing plants in our area. Even with these excellent definitions people still have questions and want to know why the weather reports and statistics they hear don’t match their experience that day. Let’s take a moment to explore why. The major reason involves how the measurements are taken and where.
* Like any measurement overseen scientifically and by the government there are very precise methods to determining official weather records. The precision includes not only the method or instrument used but the location.
* Official temperatures are normally recorded at a standard height of 1.5 meters (five feet) and designed to be protected from the effects of something like sunlight. While five feet from the ground may not sound like much, it can make a significant difference between plants that were or were not exposed to freezing temperatures. Remember under normal conditions air temperature decreases as you move up from the soil surface. Also keep in mind this time of year the ground is a heat source (much warmer than the colder air). While the air at five feet may be below freezing, plants at ground level are receiving heat being lost from ground to the atmosphere and may still be several degrees above freezing. If it stays below freezing long enough that won’t be enough to prevent damage.
* Official weather data is collected from specific, long-term sites, often airports. While the official temperature and rainfall are accurate for that site, a distance of as little of a mile can make a huge difference in something like rainfall and even temperature. An example is the official site for Hutchinson – the airport. It is not unusual for Hutchinson to record the lowest temperature in the state during the winter. The reason? The airport sits in a bowl and when it is cold, since cold air sinks, the cold air pools at the airport. So while the air temperature at the airport may be as an example 26 degrees, just a mile or two away it may be 30 degrees or a little higher.
* Finally, you need to examine your location. Official weather data sites are typically open and away from structures and items like shelterbelts to insure accurate measurements. Often they are above a surface of short grass. Now look at your home or garden. Are there buildings there, especially made of brick, that could radiate heat to the air during the night? Is it sheltered from the wind? Is it a north or south exposure? Is the soil wet or dry? Is the ground covered with vegetation or mulch? Do you live in the middle of Great Bend or in the countryside? All these variables will affect the air temperature and even the amount of effective rainfall. The effect may be positive or negative. Even a difference of several degrees in either direction can make a big difference between a hard frost killing your plants or saving them.
So the next time you hear weather statistics and disagree with them remember why they differ