XM Weather in the Cockpit? You Cannot Be Sirius!


Aside from Global Positioning Systems, one of the technologies that has had an important positive impact on safer flying is XM Weather in the cockpit. XM Weather, or XMWX, is almost like having The Weather Channel in your panel at all times.  XM weather is provided for a monthly fee from XM/Sirius Satellite Radio, home of Howard Stern. Depending on the data required, the pilot can select from 3 different monthly service plans.

XMWX NEXRAD is a composite reflectivity view of precip, from numerous different radar sites. These images are then uploaded to a constellation of orbiting satellites. Interactive graphical images of thunderstorms and other weather, including satellite imagery, are continuously streamed from those satellites to XM receiver units in our aircraft. These are then displayed on GPS or MFD screens, giving us near-real time images of any precip along our route. Here is a pic of my Avidyne coupled with a HeadsUp weather unit, taken on my way to New Orleans.

Avidyne EX500 showing storm cells near New Orleans, via XM Weather

  

In addition, XMWX transmits text data, such as METARS along your route, winds aloft and visually depicts TFRs.

The mosaic resolution is very good on the higher end display units. Thunderstorms are depicted in crisp, color contours. Light rain is green, moderate is yellow. Red and purple indicate the heaviest areas of precip and possible convective activity, and I avoid them at all costs.

Precip levels depicted on XMWX are logarithmic in nature, however actual rainfall rates are affected by water droplet sizes:

20 dBz (green)
30 dBz (yellow) and 10x heavier than 20dBz
40 dBz (red) is 10x heavier than 30dBz
50 dBz (purple/magenta) is 10x heavier than 40dBz

XMWX is a very cost-effective way to avoid embedded thunderstorms, especially here in the southeast, during the summer months. Small aircraft such as Bonanzas, Cessnas and Pipers, do not have the ability to support a true on-board radar system. A few Bonanza models had an old RCA Weather Scout system with an 8” radar antennae, but these units had very limited usability and had very short range views. XMWX provides the kind of information that allows the airborne pilot to help determine if continued flight is possible, and it has allowed me to complete trips where in the past I may have canceled, landed or turned back.

Another issue with regular weather radar is attenuation. This is where heavy rain nearby literally blocks out distant radar returns. Attenuation can cloak the real heavy weather by displaying only the closest precip, giving the pilot a false sense of security. That is not an issue with XM weather. Here is a photo of onboard radar on the left compared to the same weather using XMWX on the right, courtesy of a member of a user group I follow:

XM Weather allows you to pan or zoom ahead hundreds of miles, and view all the weather along your entire route. The downside of XM is the slight delay in gathering, consolidating and then uploading to the array of satellites the latest weather picture. There can be a 5-8 minute delay from what is happening outside your cockpit to what is displayed on your XM unit. Because building cumulus clouds can develop into a torrential thunderstorm within minutes, you should not rely on XM as your sole source of weather avoidance.

Airborne radar should be used in tactical situations to avoid penetrating the heaviest areas of precipitation within a storm cell, or line of cells. XM NEXRAD composite radar should be considered a strategic tool for avoiding large areas of weather. In my case, I also use a slaved Stormscope WX-1000+ for real-time lightening data to back up what I see out the window and on the MFD. Lightening indicates the most violent part of the thunderstorm cell, and can indicate bad weather before precipitation has even begun.

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One Response to XM Weather in the Cockpit? You Cannot Be Sirius!

  1. Matt T says:

    Well put, “like having the weather channel in your cockpit,” but if you really wanted the weather channel, why not get your cockpit weather from SIRIUS and WSI? WSI is part of The Weather Channel Companies and, btw, also provides the NEXRAD mosaic as part of the FIS-B data stream to ADS-B (service volumes are set-up and running all over the US and AK). Be equipped better and be in-line with the same data the FAA uses for traffic management… I’m in! http://www.wsi.com/products-aviation-commercial-wsi-inflight.htm

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