As much as I brag about XM weather and the revolutionary way in which it enhances cross-country safety, I like to remind myself (and everyone else), that like any tool, it has it's quirks and limitations. I've written before about seeing a full-grown thunderstorm over the Guadalupe Mountains that showed nary a breath of green on the XM return because there are no radar sites there. Well I just came back from a flight with the opposite extreme - false echoes.
We're sitting here in Houston waiting for T.S. Eduard, currently a couple hundred miles to the east southeast. Since it is bright (hot) and sunny out, I decided a short local flight was in order. much to my surprise, as I fired up the 396 and XM weather, it was showing widespread patches of green precip all around me. This picture certainly didn't agree with the merciless sun beating through the canopy as i climbed out for some acro. Certainly there were some afternoon buildups, but as I cleared the Class B I climbed and determined that these scattered Cu's were only going up to about 10,000', and most of the area was clear! Hmmmm....what gives with XM?
I zoomed out to get the big picture, and realized that all of the false echoes were along the coast from the mouth of the Brazos up towards Louisiana, and nothing was showing inland from Houston. Way out to sea to the east, you could see the outer fringes of the tropical Storm. This is what tipped me off - the local radar antenna was being depressed as low as it would go to pick up the outer edges of the storm, and this was in turn creating returns from the local terrain - ground clutter! The green was land within 50 miles or so of the antenna.
Now none of this is to brand XM as "unreliable" - it is still a remarkable tool! But like any tool, it has it's limitations, and once you know how to use it in concert with your other tools (in this case, Mark I eyeballs), you can accomplish the ultimate goal - understanding the weather picture in it's big and true form. Never fail to ask yourself "does this make sense?" when looking at data. I'm glad I saw this little anomaly today - it's one more lesson to store away for the future when using just one of my many tools.
Paul
We're sitting here in Houston waiting for T.S. Eduard, currently a couple hundred miles to the east southeast. Since it is bright (hot) and sunny out, I decided a short local flight was in order. much to my surprise, as I fired up the 396 and XM weather, it was showing widespread patches of green precip all around me. This picture certainly didn't agree with the merciless sun beating through the canopy as i climbed out for some acro. Certainly there were some afternoon buildups, but as I cleared the Class B I climbed and determined that these scattered Cu's were only going up to about 10,000', and most of the area was clear! Hmmmm....what gives with XM?
I zoomed out to get the big picture, and realized that all of the false echoes were along the coast from the mouth of the Brazos up towards Louisiana, and nothing was showing inland from Houston. Way out to sea to the east, you could see the outer fringes of the tropical Storm. This is what tipped me off - the local radar antenna was being depressed as low as it would go to pick up the outer edges of the storm, and this was in turn creating returns from the local terrain - ground clutter! The green was land within 50 miles or so of the antenna.
Now none of this is to brand XM as "unreliable" - it is still a remarkable tool! But like any tool, it has it's limitations, and once you know how to use it in concert with your other tools (in this case, Mark I eyeballs), you can accomplish the ultimate goal - understanding the weather picture in it's big and true form. Never fail to ask yourself "does this make sense?" when looking at data. I'm glad I saw this little anomaly today - it's one more lesson to store away for the future when using just one of my many tools.
Paul
