AWOS & ASOS - What You Should Know

Knowing the weather conditions at your destination airport is vital, but which system should you use? Learn everything about AWOS and ASOS in this guide.

When you’re planning your next flight, you know what the weather conditions are at your departure airport. Heck, just look outside. Okay, okay, it’s not that easy, but it’s much easier than knowing what the weather conditions are at the airport you’re flying into. To help you fly as safely as possible, systems such as AWOS and ASOS were created. What are they and how do they work?

AWOS and ASOS are weather reporting systems that pilots can use to check the weather conditions at the destination airports they're flying into. Both systems transmit data over the radio every minute to provide real-time information on storms, wind, visibility, temperature, and more.

Aviation weather reporting systems are used to provide information about the current and forecasted weather conditions at an airport. This information is used by pilots to make informed decisions about their flights. There are two main types of aviation weather reporting systems: AWOS and ASOS. In this article, we will discuss what both of them are, how they work, and what they do. We'll also talk about how you can access this information while you're flying. Finally, we will give a comparison of the two systems and decide which one is better!

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‍What do Aviation Weather Reporting Systems Do?

Before we can start talking about the specifics of AWOS and ASOS systems, which we'll define shortly, let's start with the basics and explain what these types of systems are in general. After all, before you started getting into aviation, you probably never heard about these weather reporting stations. I know that I hadn't before I got into this stuff. So what are aviation weather reporting stations?

In short, these types of weather reporting systems help pilots to make decisions about whether or not it is safe to take off and land. They do this by constantly monitoring the local weather conditions and then relaying that information back to a central location where pilots can access it.

There are two main types of aviation weather reporting systems: AWOS and ASOS. Let's start by talking about AWOS.

What is the Automated Weather Observing System (AWOS)?

The Automated Weather Observing System, or AWOS, is a type of weather reporting system that is typically used at smaller airports. It is an automated system, which means that it doesn't require anyone to be manning it in order for it to work. Larger airports that have control towers will often use a manned system known as Automated Terminal Information Service, or ATIS, while the tower is actively manned. But when the airport is not towered (usually overnight at some airports), it will revert back to a system like AWOS.

AWOS systems are operated and maintained by the Federal Aviation Administration, or FAA. With all of the acronyms, it can be a bit confusing since the other weather system we're focusing on in this article is operated by two other agencies with different acronyms, but we'll focus more on that later. Let's dig a little deeper into the AWOS.

How Often Does AWOS Transmit Weather Reports?

The AWOS system is designed to take readings of the local weather conditions every minute and then broadcast that information over a VHF radio frequency that pilots can tune into. The reports will include things like the current temperature, visibility, wind direction and speed, thunderstorm information, dew point, and other important aviation weather factors.

These weather reports are usually about 20 to 30 seconds in length and start every minute at the top of the new minute. So it's almost a constant weather update while you're flying, which is why pilots will often use AWOS as a pseudo-real-time weather update.

What are the Levels of AWOS?

AWOS systems are classified into nine different levels based on the types of sensors that they use to measure the various weather conditions. These levels aren't necessarily dictated by how busy an airport gets or what type of traffic it has, but simply by the sensors installed there and the type of data they can transmit.

The nine AWOS levels and what type of weather information they provide are:

• A:  Altimeter indicator only
• A/V: Altimeter plus visibility
• I:  Altimeter, density altitude. temperature, wind data, and dew point (no visibility)
• II: Everything from AWOS I and also visibility data
• III: Everything from AWOS II and also cloud data
• IIIT: Everything from AWOS III and also thunderstorm and lightning data
• IIIP: Everything from AWOS III and also an indication of the type of precipitation
• IIIP/T: A combination of IIIP & IIIT (AWOS III plus the type of precipitation and thunderstorm & lightning data)
• IV: Everything from AWOS III and also precipitation information, thunderstorm & lightning data, freezing rain, and also the runway condition

As you can see, the levels of AWOS  progress from just an altimeter reading to a fully comprehensive weather station that includes precipitation, thunderstorm, and lightning information. The vast majority of airports will have at least an AWOS II or III, with many having the fully comprehensive AWOS IV.

So that's a quick overview of what the Automated Weather Observing System is and how it works. Now let's move on to the next aviation weather reporting system, which is known as ASOS.

What is the Automated Surface Observing System (ASOS)?

The Automated Surface Observing System, or ASOS, is very similar to AWOS in that it's an automated weather station that broadcasts weather information over a VHF radio frequency. ASOS is also operated by the FAA to an extent, but the two main agencies that run these systems are the National Weather Service (NWS) and the Department of Defense (DOD). See what I mean about all the acronyms?

Since ASOS systems are mostly owned and operated by the NWS, they are not exclusively for aviation use like AWOS systems are. ASOS weather stations are used to provide real-time weather information for a variety of purposes, including aviation, road transportation, shipping, and general weather forecasting. The NWS, DOD, and FAA use a network of more than 900 ASOS stations across the United States to help collect data for their forecast models and to report weather conditions to users all over the country.

So while both AWOS and ASOS are automated weather reporting systems that use VHF radio frequencies to broadcast their data, ASOS is a little bit more versatile in who can use it and why. Unlike AWOS systems, there are no levels to ASOS weather systems, they all report comprehensive data at all times. This includes information such as sky conditions, visibility, precipitation type and intensity, pressure, wind speed and direction, temperature, dew point, and more.

How Often Does ASOS Transmit Weather Reports?

Similar to AWOS, ASOS weather stations transmit their weather data every minute, 24 hours per day according to the National Weather Service. There is some information out there in the aviation world that ASOS systems only report information hourly, but that just isn't the case. This is often cited as one of the main reasons that pilots choose to use AWOS over ASOS, but they both report weather every minute!

How do you Access AWOS and ASOS Weather Information?

Now that you know how weather reporting systems work and what the differences are, let's take a look at how you can actually access this information while you're flying. As a pilot, you have a few different ways that you can get weather data from AWOS and ASOS systems, some of which are much easier to use than others.

The most common way that pilots get AWOS and ASOS weather information is by tuning into the appropriate radio frequency for the station they are trying to reach. Each AWOS and ASOS weather station has its own dedicated VHF radio frequency that it broadcasts its weather reports on.

You can find these frequencies in sectional charts, approach plates, and airport facility directories. Once you tune your radio to the right frequency, you should be able to hear the automated weather report being broadcast.

Some AWOS and ASOS stations also have phone numbers that you can call to get a recorded weather report, but this isn't as common. The same goes for text messaging and emailing weather station operators to get a report, but this is even less common.

Is AWOS or ASOS Better While Flying?

In the end, neither system is better than the other, it just depends on what type of information you need and what is available at your destination airport. If an AWOS system is available and reporting comprehensive data, that's probably your best bet. However, if an ASOS station is the only option or it's reporting more detailed information, go with that instead.