Whether you’re soaring through the skies for 50 miles or embarking on a longer journey of 500 miles, one thing you surely desire is to know what the weather holds at your intended destination. So when it comes to gathering the weather information upon your arrival, where does it originate from, and just how old is it?
What Enroute Weather Sources Are You Employing?
ADS-B has had a tremendous impact on flying in the recent years. And one of its notable effects is your ability to access weather reports and forecasts directly on your flight displays and tablet while in flight, regardless of how far you are from the airfield.
But there are certain limitations. If you’re seeking the current weather at your destination, ADS-B transmits the most recent METAR from the airport you select.
The problem? METARs are data that are old as soon as they are issued. METARs are generated for airports once every hour, typically between 50 minutes past the hour and the top of the hour.
If the weather undergoes significant changes at an airport, a SPECI, which is a special observation, can be issued. However, the criteria for issuing SPECIs are rather stringent. In simple terms, the weather needs to change substantially for a SPECI to be issued, and weather changes that do not meet the SPECI criteria might still exceed your personal thresholds.
On top of that, there is an issue with the update cycle. ADS-B updates text reports approximately every 5 minutes. So if you rely on your MFD or tablet to obtain the weather through ADS-B, you could be facing a delay of 5 minutes (or even longer) from the time the SPECI or latest METAR was issued (if you use XM weather, the update cycle is similar).
What Will Provide You with the Best View?
Fortunately, there is a much more up-to-date weather source that you can utilize as you approach your destination: ASOS (and AWOS). This is the computerized, repetitive voice that reports the latest weather for an airport.
So just how current is ASOS? It is updated every single minute.
Every 60 seconds, the ASOS station checks its sensors and then encodes the data it collects into a METAR. Subsequently, the computer-generated voice message broadcasts the METAR, along with any remarks, over the radio frequency.
So when you tune in to ASOS, you are receiving the most current weather you can lay your hands on, down to the very minute.
How Far Can You Reach with ASOS?
Typically, you can pick up ASOS within 50 miles of your destination. Since ASOS is transmitted via VHF, it is limited by line of sight, which means that in mountainous terrains, your coverage might be more restricted. However, if you are in an open area, you can sometimes receive it even beyond 50 miles.
Either way, you can typically obtain the weather well in advance of your arrival, giving you a clear picture of what is transpiring at the airport. And it also provides you with time to formulate a good Plan B in case the weather is changing rapidly.
Combine Your Sources for the Optimal Picture
ADS-B has granted us the capability to obtain more weather information in the cockpit than ever before. However, to make the most of it, you need to be aware of its limitations.
When you are en route to your destination, using ADS-B weather is an excellent way to monitor weather trends, but keep in mind that what you are reading is up to an hour old.
As you approach your destination, make sure to listen to ASOS. Combine the up-to-the-minute ASOS with your ADS-B weather en route, and you will have the best possible weather picture from takeoff to landing.
