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Using XM Weather Wisely

Ironflight

VAF Moderator / Line Boy
Mentor
In the movie ?Kelly?s Heroes?, Oddball (Donald Sutherland) is talking about their specially modified tank, and says something like ?It has four forward gears, and five for reverse?.we like to think that we can get OUT of trouble faster than we got IN to it!? That is a large part of the reason that I like XM Weather in the cockpit!

I have written quite a few times now about trips that I have taken in my RV that would not have been possible - or at least I wouldn?t have been able to complete them ? without having the NEXRAD and other weather data in the cockpit. I know that statements like this can be controversial, and bother some folks, and quite frankly, I understand that, so I think that maybe it is a topic that deserves a little amplification. It would be easy for a low-time weather pilot to consider themselves invincible because they have these tools on board, when in fact, they are simply tools, and not armor plate. I?d like to share some of what I consider to be the limitations of the system, and the ?rules? under which I use them. I am by no means saying that these limitations should or must be followed by anyone else ? they simply work for me with the level of experience and learning that I have. I am actually pretty conservative when it comes to flying safely, and try never to be in a position where I feel uncomfortable or unsure about an outcome in the air. And that is one of the reasons that I find XM weather to be so valuable?it allows me (to quote Oddball) ?to get out of trouble faster than I got into it!?

The best thing that I can say about having XM in the cockpit is that it removes the guesswork involved with flying in weather. Instead of guessing where the storms are, and how intense they might be, you know! And knowledge is power ? power to proceed with caution, or to call it a day. I don?t know how many times in my flying career I have set down because I saw weather ahead and to the sides that I simply didn?t have knowledge of.

The other thing that makes XM so useful ? and the reason the topic is so relevant here ? is that coupled with a fast, long-range airplane such as an RV, large deviations (like the size of a STATE) are reasonable to make if you can get around a known area of weather and continue to your destination. With my old 250 mile, 120 knot Grumman, XM would have been mostly wasted?..

When I fly, I use the concept of the ?Flight Rule? ? pre-made decisions which you make before the flight, on the ground ? to avoid making hurried, bad decisions in the air. They can occasionally be bent with good reason, but as a rule, you follow them or land and re-think. Here are a few ?rules? that work for me personally when using XM weather ? hopefully, with good judgment!

1) If I am IFR and in IMC, I will not fly through anything more than ?yellow? showers, and then only if they are a few pixels wide and there is only one or two pixels of orange or red anywhere nearby. Green is fine.
2) I?ll fly through green or yellow VFR if I can maintain VFR visibility and ceilings ? and you generally can?t do that with yellow returns.
3) The primary purpose of the NEXRAD (for me) is to go around an area of bad weather, and know where the boundaries are. RV?s are fast enough with long enough range to go around weather areas, unless they stretch over several states. I will use XM to penetrate a huge area of weather if the cells are very light (one or two red pixels) and WIDELY scattered ? with clear paths of green only in between, and with good retreats.
4) Large area of southern thundershowers are too tall to climb over in the afternoons, so I will generally duck down underneath areas of showers rather than getting trapped on top in clouds that can go up faster than I can. I use the METAR?s available through XM to assure myself that I have good ceilings along my route ? and ?good? means above the minimum VFR altitudes listed on a Sectional or WAC chart. Those altitudes constitute a ?hard deck?, and I?ll file IFR before violating them unless the visibilities are very, very long. (I have obstacle warnings on my EFIS, but they are only as good as the database?.)
5) I always keep track of my retreat options, and make sure that if I am headed into an area of interesting weather, that I can get through it before it develops into something really ugly, or maintain a clear line of retreat. I never leave myself with no options but to fly through bad weather!
6) I will fly IFR through areas of Precip if there are no storm cells showing and the air temperatures are significantly above freezing.
7) I have little to no experience with XM weather in northern winter weather, and will be very cautious when I try it due to icing concerns. Forecasts of icing scare me much more than forecasts of thundershowers?.I can SEE the showers!
8) I will use the ?animate? function to give me an idea how rapidly the weather returns are growing. Rapid development is a very bad sign, and calls for extreme caution and much conservatism.
9) The cloud images need to be taken with a grain of salt ? or two, or three! They generally don?t show large areas of low morning cloud/fog. METAR?s are much better than the satellite images!
10) I always consider that the most recent update might be the last one I get (if the machine fails, the satellites quit, etc?) and make sure that I have a good plan for staying clear of the weather if this happens.

Even with these conservative rules, I am finding that my ?dispatch reliability? has grown by leaps and bounds since accepting XM Weather in the cockpit. Understanding its limitations, you can still use it to make the RV a reliable and efficient traveling machine. Oh, and one more thing?..a full-fare airline ticket is generally fully refundable. If you absolutely, positively need to be someplace, buy one?.if the weather is good on the morning of departure, cancel the ticket, and enjoy the flight in your RV! Having a good back-up is the best way to take the pressure off yourself?.

Ten Rules is a good start...but I'm sure that others flying with these tools can add more!

Paul
 
Nice write up Paul, as usual.

I have had XM weather for three years now, and I could not be happier. It is painful to spend $360/year on the subscription (I don't have cloud tops or satellite), but it is a no brainer for me.

Last weekend, I had a short flight (about 120 n.m.) back to my home base in Minneapolis. I looked at the nexrad via home computer before I left, and realized that there was a monster cell pretty much right in the middle of my path, which was a heading of about 120. Based upon the movement of the cell, my plan was to fly straight east, make a right turn and fly straight south to my destination.

So, I fired up, and started to fly east. About 5 minutes after I powered things up, I saw the cell on the screen. It had remained on the track I estimated based upon the image I saw on a home PC about 30 minutes earlier. I continued to fly straight east, staying about 40 miles north of the monster. It was a spectacular sight, since the sun was shining all along the north side of the buildups. Anyway, it was really nice to be able to watch things progress, and to know that I was remaining clear of any sort of convective activity. As I flew along , it was a very good thing to know that even if the monster developed into a line, I would know it before needing to turn around. As I turned south, I lost the sunshine and was flying into an area which was rapidly darkening, as I was to the east of the monster and the sun was setting. The view forward was great, but the relative darkness would likely have caused me to turn around had I not known that there was no precip anywhere on my course.

On another flight recently I was leaving the Boone IA fly-in (later in the afternoon from when most left). There was a small, isolated TS bearing down right on the airport, and I estimated that it would arrive in about 10 minutes (we could hear the rumbling). I knew from the airport weather station that there were a few isolated showers and TS scattered to the north and west of my route, but the cloud bottoms seemed to be at around 7000' or so. I fired up, and headed northeast. Again, a couple minutes after takeoff, I got the updated image in my cockpit. I made a course correction maybe 10 degrees right to stay from what was likely virga (green), and the rest of the ride home was simple.

I really agree with what Paul said about how valuable XM is, being so much more aware of what is ahead, to the sides and behind.

As I've been flying on long cross countries, it is so powerful to be able to start formulating plans b and c well before needing to (possibly) execute them. It is all about being well ahead of the plane.
 
XM convert

Hi Paul, It took only one flight to make me a believer in XM weather. I was flying the Commander from Colorado to Palm Beach, Florida. I had stopped for fuel in Mississippi, and got back underway. When I was handed off to JAX center, they informed me that I probably couldn't get through to my destination, as there was a line of weather from the Gulf coast, across northern Florida, and extending east of Jacksonville.
Also, they were shutting down the arrival routes on both sides of the state of Florida. I had radar and a stormscope, but I took a look at the XM weather and asked if would be okay if I just picked my way through it. ATC said "help yourself"!
Where XM shows that there is weather, then there is weather. If it shows a hole, then there is a hole! I made it through with just a few deviations, had a smooth ride and never even got wet! It's even better and faster now with the new Garmin WAAS updated unit installed. One thing that I'd like to have is tops information. A lot of weather that shows up is below our cruising altitude, and is of no significance. Would be nice to know ahead of time.
 
We used XM WX on Tuesday. We were headed north and turned NW just south of Manhattan, KS, en route to Kearney, NE (EAR). We had just climbed to 6500 to get a comfortable ride on top of a 6000 scattered layer and were ~120NM or 1 hr from EAR. As we got on top, we noticed a HUGE anvil at the 10 position. We had the G396 at about a 50-60 mile range, and there was nothing on it. Zoomed out and there it was - a HUGE cell on the NexRad and visible sat. Folks started to call Center to ask for deviations.

Watching the horizon and the XM, we started to see other cells pop up very quickly. We saw on the XM that there was more activity to our left than right. We got the weather at EAR and decided we wouldn't make it - we needed to get on the ground soon. We diverted 20 right and got to HSI and landed.

So, XM helped us make a decision of which way to go, but reinforced our decision to land. Live to fly another day.
 
Important Limitations!

I forgot one thing that I intended to mention in my original write-up, and that is an important (although somewhat limited in extent) limitation of the NEXRAD coverage - and that is, the coverage! I know it is hard to imagine, but there are parts of this world, even parts of this country, that do not have good weather radar coverage. Wilderness areas in particular - places far away from the major antenna sites.

A good example was a flight that Louise and I made a few weeks back from El Paso to Carlsbad, right across the Guadalupes. There were scattered thundershowers about, and one was just slightly to the left of our course. We could see the rain, and even a few strokes of lightning - but nothing at all was showing in that location on the XM receiver! All around the area, we were seeing other storms, but that particular location over the ground was "blind" to NEXRAD sites, and therefore, if we weren't looking out the window we wouldn't have know it was there. This problem is not extensive, but it is something to consider. It's always good to look at a display and ask yourself "is there some way that I am being fooled?"

Inconsistencies between what your eyes see and the XM shows should be a red flag to be on alert for other differences. And, as with all tool limitations, once you understand it, the effects on your operation can be minimized...

Paul
 
Paul, excellent point. Somewhere I saw a map showing exactly where there was and wasn't nexrad coverage. I try to dig it up and post it or its location.
 
AlexPeterson said:
Paul, excellent point. Somewhere I saw a map showing exactly where there was and wasn't nexrad coverage. I try to dig it up and post it or its location.
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The map shows coverage in the area of non-coverage that Paul was talking about. I have observed exactly the same thing though. In some areas of the Guadalupes there can be a significant thunderstorm that doesn't show at all on the XM weather. I find that I do tend to show lightning in those areas though, which is a good reason to have the lightning service.

It is interesting that if I go to my local weather service page to look at nexrad radar it will not show thunderstorms in that same area, although it shows that area, however if I pick long range images it does show the echoes in that area. There is a bunch of stuff going on that I don't understand.
 
Paul - For what it's worth, your 396 knows where all the antennas are located, and it will show you areas where it knows there's no radar coverage due to there not being an antenna nearby... you can see these areas shaded in purple in the Weather tab in the main menu. It even knows when a radar site goes offline, which you can occasionally see as a change in the shape of the purple "no-coverage" area. However, the 396 does not know about other things that can interfere with radar signal propagation, such as ground clutter, terrain near the antenna site, or local atmospheric conditions.

fly safe,
mcb
 
NexRad

Another thing to remember is that the signal from the satellite can be blocked by a CB with heavy rainfall, similar to Dish and Direct TV signals. This happened to a friend picking his way between cells when he lost all XM signal.

Took a while to figure out what happened but finally realized there was a heavy cell close by that was directly between him and the satellite which completely shadowed the signal from his reciever. At least that's his story and he's sticking to it!
 
mburch said:
Paul - For what it's worth, your 396 knows where all the antennas are located, and it will show you areas where it knows there's no radar coverage due to there not being an antenna nearby... you can see these areas shaded in purple in the Weather tab in the main menu....
Matt, how do you do this? I had never heard of it or seen it so I went out and turned my 496 on. I wanted to compare it to the graphic I pointed to above.

I assume you mean to go the the radar section of the weather tab. I did that and let it download the current info, but I can't see the purple areas. I tried a lot of different zoom levels. Also can't find anything in the manual about it.
 
n5lp said:
I assume you mean to go the the radar section of the weather tab. I did that and let it download the current info, but I can't see the purple areas. I tried a lot of different zoom levels.
Go to the main menu, scroll down to Weather, and select NEXRAD Radar. The purple areas are locations known to be without radar coverage. If you activate the map cursor and pan over to one, it will say "No Radar Coverage". You should certainly see areas like this in places outside the US or southern Canada.

However, come to think of it, I'm not sure at the moment if the radar coverage data product is included in all the different subscription packages. You can tell if you're getting radar coverage data by going to the main menu, scrolling down to XM, scrolling over to the Info tab, and looking in the weather products list for Radar Coverage.

mcb
 
mburch said:
Go to the main menu, scroll down to Weather, and select NEXRAD Radar. The purple areas are locations known to be without radar coverage. If you activate the map cursor and pan over to one, it will say "No Radar Coverage". You should certainly see areas like this in places outside the US or southern Canada....
Thank you Matt, I got it working this time. It appears that the radar coverage data is on a different download schedule than the NEXRAD radar schedule. This time I got the coverage information even before the radar data. I must not have waited long enough for the data to download before. The broadcast rates table in the XM Smart Antenna Manual does not list this item.

Oh, and the area where Paul and I have noticed no coverage in real life is an area that it shows radar coverage on the radar coverage data of XM Weather so I guess where the Garmin shows no coverage there is really going to be no coverage.

It's good to know about this capability that does seem to be a bit skimpily documented.
 
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