What the Numbers on Your Home Weather Station Mean

So, you already made the leap and joined the home weather station bandwagon by installing one in your home. Now, the question is: do you even know how to read the information that it’s feeding you?

Deciphering the numbers that come from your home weather station is not rocket science. However, it does take some understanding about the concepts at play in order to interpret what your device saying.

Here is a rundown of the measurements you can  expect to see on your weather station.

(NOTE: If you don’t already own a home weather station, you may find our recommendations helpful.)

Temperature

Temperature is the most basic measurement of weather. It influences almost every aspect of the weather and is a key variable that many other measurements depend on. Temperature can be measured in different ways, most commonly in Fahrenheit or Celsius. Whereas people in the United States are familiar with Fahrenheit, most of the world actually uses Celsius. If you’re curious about how Celsius feels, you can set your weather station to Celsius or simply take a look at the following classifications (3):

  • Freezing: < 0 degrees Celsius
  • Very Cold: 0 ~ 5.9 degrees Celsius
  • Cold: 6 ~ 9.9 degrees Celsius
  • Cool: 10 ~ 13.9 degrees Celsius
  • Mild: 14 ~ 17.9 degrees Celsius
  • Moderate: 18 ~ 22.9 degrees Celsius
  • Warm: 23 ~ 26.9 degrees Celsius
  • Very Warm: 27 ~ 29.9 degrees Celsius
  • Hot: 30 degrees Celsius or greater

Atmospheric Pressure

According to the National Geographic, atmospheric pressure is the phenomenon which explains the pressure that air exerts on anything it touches as gravity pulls it towards the Earth (7). In other words, air has weight and we can feel it. In places of high altitude, for example, atmospheric pressure is typically lower since oxygen is lower. Less oxygen, in turn, mean less weight. Normal pressure, on the other hand, is an indication that plenty of oxygen is present. Your home weather station uses a barometer to measure atmospheric pressure.

We often use atmospheric measure to predict upcoming weather events. If your weather station is reporting a drop in pressure, you can be sure that a change is about to occur. Low pressure systems attract air from high pressure systems, which is what causes the weather to change. It could be something subtle, like a temperature drop or a nice breeze. If the pressure reading is very low, however, a storm is probably headed your way. 

Here are some useful guidelines for interpreting barometric readings (8):

If your weather station reads above 30.20 inHg:

  • Rising or steady pressure means continued fair weather.
  • Slowly falling pressure means fair weather.
  • Rapidly falling pressure means cloudy and warmer conditions are coming.

If your weather station reads between 29.80 and 30.20 inHg:

  • Rising or steady pressure means present conditions will continue.
  • Slowly falling pressure means little change in the weather.
  • Rapidly falling pressure means that rain is likely, or snow if it is cold enough.

If your weather station reads below 29.80 inHg:

  • Rising or steady pressure indicates clearing and cooler weather ahead.
  • Slowly falling pressure indicates rain
  • Rapidly falling pressure indicates a storm is coming.

If you’d like to know more about how high and low pressure systems work, check out this YouTube video: High and Low Pressure Systems.

Humidity

The National Geographic describes humidity simply as the “amount of water vapor in the air (1).” The question is how do we measure the water vapor? Without quantifying it, we can only gauge humidity by the way it feels to us, which can be misleading since temperature, sunlight and wind chill can greatly influence the way we experience humidity. Thus, science provides us with 2 ways of measuring it: absolute humidity and relative humidity.

Absolute Humidity

Considered the “most accurate (2)” measure of humidity, absolute humidity is the total mass of water vapor per a given volume of air. Subsequently, absolute humidity is expressed in “grams of moisture per cubic meter of air (2).” For predicting the weather, however, absolute humidity does not give us a complete picture. Other conditions, such as atmospheric pressure and temperature, need to be factored in because they affect the way moisture behaves. This brings us to the topic of Relative Humidity.

Relative Humidity

This is the measurement that your home weather station uses. Unlike absolute humidity, relative humidity is not a measure of how much water vapor is in the air. Instead, it is a measure of the percentage of water vapor present in the air before the water starts to condensate, which begins at a relative humidity of 100%. For example, if the relative humidity is at 30%, it means that the air can hold 70% more water before it starts to condensate.

Aside from the concentration of moisture, there are 2 other factors that influence condensation: temperature, atmospheric pressure.  For atmospheric pressure, the heavier the air is, the easier it will be for water to condensate, resulting in higher relative humidity. The easiest way to understand this is that the heaviness of the air will push the moisture out of it, causing condensation. As for temperature, the hotter it is, the harder it will be for water to condensate, resulting in lower relative humidity. This is because hotter temperatures tend to make water evaporate, which is the opposite of condensate. As the temperature drops, however, water condensation may occur in the form of dew. As a side note, “dew point” is the temperature at which condensation begins. We often see dew form at night time when the temperature drops after a hot day. 

Wind Speed

Wind speed is another important aspect of the environment, which can be used as a signal for upcoming weather events. Air will naturally move away from higher pressure areas and towards lower pressure ones. If there are extremes in pressure between 2 areas, you can be certain that there will also be fast winds as the pressure system works to balance itself out. Your weather station measures wind speed with an anemometer.

While wind speed can vary dramatically, it is often classified according to its magnitude (5):

  • Light and variable: < 7 kts (8 mph)
  • Breeze: 13 ~ 22 kts (15-25 mph)
  • Gust: 10+ kts (12+ mph), then decrease by 10+ kts (12+ mph)
  • Gale: 34 ~ 47 kts (39-54 mph)
  • Squall: 16+ kts (18+ mph) and maintains an overall speed of 22+ kts (25+ mph) for at least 1 minute

For a wind speed to become dangerous, it must reach a speed of at least 39 mph (6). This is the level at which branches can be torn from trees and cars can be pushed off the road.

Wind Direction

Since wind is a vector, it must not only have speed, but also direction, which is best described as the wind’s intended destination coming from its point of origin. As mentioned above, atmospheric pressure will determine which direction the wind will blow. Wind will always move towards an area of low pressure. With it, the wind will transfer moisture (or lack thereof) and temperature. 

Rainfall

Rainfall is yet another important aspect in the assessment of weather conditions. By using a rain gauge, which comes with many weather stations, rainfall can be measured. These measurements are useful when comparing historical data to identify regional patterns. They can also be used to anticipate a floods, keeping you out of harm’s way. 

Conclusion

Predicting the weather has always come with its fair share of challenges. There are countless variables that influence the forces of nature that we still have yet to quantify, which is what makes meteorology so interesting. Home weather stations give us the ability best predict what weather conditions may be coming our way, but we first must understand the concepts of behind these amazing devices before we can use them to our benefit.

References

  1. “Humidity,” National Geographic. Retrieved from https://www.nationalgeographic.org/encyclopedia/humidity/
  2. “What is Humidity and Why Does It Matter?” Go Blue Ox. Retrieved from https://www.goblueox.com/blog/what-is-humidity-and-why-does-it-matter/
  3. “What do you consider dry, moderate and humid? (temperatures, humidity, dew point),” City-Data. Message posted to http://www.city-data.com/forum/weather/2123073-what-do-you-consider-dry-moderate.html
  4. “Your Personal Temperature Colors and Descriptors (climate, snow, hot, warm),” City-Data. Message posted to http://www.city-data.com/forum/weather/1620160-your-personal-temperature-colors-descriptors.html
  5. Tiffany, M. (2019) “Understanding Winds,” Thought Co., Retrieved from https://www.thoughtco.com/understanding-winds-3444496
  6. Sigafoos, S. (2018). “Severe Weather 101: Wind gusts and the damage they can cause,” The Morning Call. Retrieved from https://www.mcall.com/news/weather/mc-nws-severe-weather-101-wind-gusts-20180302-story.html
  7. “Atmospheric pressure”. National Geographic, Retrieved from https://www.nationalgeographic.org/encyclopedia/atmospheric-pressure/
  8. “How to Read a Barometer,” ThoughtCo. Retrieved from https://www.thoughtco.com/how-to-read-a-barometer-3444043

 

 

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