Weather Blog: Why are airports used for official readings?
I am often asked why we use the airport for our temperature reports when no one lives at the airport? I bet you have wondered the same thing. There is actually a very good reason.
If you think about it, your personal observations might answer the question. Temperature readings vary greatly depending on topography, sensor location and actual conditions outside. People that ride motorcycles have observed that when they ride bikes at night, temperatures are much cooler when they go down into the low spots. This is due to cold air being heavier and draining to the lower spots after dark. On a sunny day, you may notice it feels warmer as you walk up toward your home or a building as heat bounces off the structure. You can walk across a lot and notice heat builds up in areas with little air flow. Walk near a patio or driveway and you will feel heat coming from that. The above scenarios are just a few of the possibilities that will alter temperatures by several degrees over a small area of just a few feet.
In you car, it will often register a few degrees hotter due to the heat off the highway and even your engine. Readings on the bank thermometers and other businesses may also get heat from roadways, driveways, buildings, etc.
To forecast the weather, we need to first have a good understanding of our current conditions. If temperatures on a single property can vary by more than 10 degrees, imagine the uncertainty of using such reports over a larger area, state, region, etc. Given that surroundings vary greatly it is impossible to have a fair comparison in most environments.
The standards for an accurate temperature measurement are pretty straight-forward.
- Sensor must be 5 feet above the ground (+/- 1 foot).
- Must be over a level terrain with an open area clearing so the thermometers are freely ventilated by air flow.
- Sensor should be no closer than 4 times the height of any obstruction (tree, fence, building, etc.).
- Sensor should be at least 100 feet from any paved or concrete surface.
There is one place that we do usually see the conditions above met. The airport. If everyone uses the same equipment over a similar surrounding, we get good comparisons. I have always viewed it as comparing apples to apples. Home reports are more often comparing apples to oranges. Still, I have maintained a home weather station since I was a kid and enjoy monitoring the weather from my home. But, I realize I have limitations with my readings.