GPS/XM Weather Question

Jay Honeck wrote:

However, after 30 minutes in the air, she noticed that the METAR data
had not updated. The NEXRAD radar and satellite data were updating
every 6 minutes or so, but the METARs remained the same as when they
initially uploaded.

According to XM the update rate for the Metars is 12 minutes. In my
experience using the system if the airport has an ATIS the weather info
that is displayed will the the ATIS info and not the current conditions.
I'm not sure if that is what you were seeing. This was one of the
shortcomings I found with the system when it first came out. It's good
for monitoring trends in the weather but not actual conditions. To
answer the original question this is why I use it as a strategic tool
and not tactical.

IIRC visible satellite images will show low clouds as very dark... the bright
clouds are higher. Are you sure it showed no cloud-cover?

Both Mary and I looked at the same picture on the Weathermation
computer at Racine's Batten Field, which showed clear skies from
Michigan to Iowa, when, in fact, the entire area was under a relatively
low (2500 - 3000 foot) thin (500 - 1000 foot thick) overcast.

The info on the 496 displayed the same way.

I suppose the low clouds happened to display in the same color as the
ground, but that would seem to be less than helpful.

;-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Jay Honeck" wrote in message
oups.com...
For those of you who have XM weather integrated with your GPS.

Do you use the weather information to paint a big picture of what's going
on
around you. I.E. "If I fly 50 miles thataway, it looks like I'll be able
to
circumvent this line of storms."

The satellite image is an infrared image with all the limitations infrared
has, but it works at night............thus a night image is still available.

METAR is just that. A METAR only gets updated every hour unless there is a
special. Complain to the FAA.

Karl
"Curator" N185KG

which showed clear skies from
Michigan to Iowa, when, in fact, the entire area was under a relatively
low (2500 - 3000 foot) thin (500 - 1000 foot thick) overcast.

Maybe it was thin enough to be transparant when looked at from above,
but not when looked at lengthwise.

Jose
--
The monkey turns the crank and thinks he's making the music.
for Email, make the obvious change in the address.

"Jay Honeck" wrote in message
ps.com...
Strike one for XM. Apparently with a thin-but-solid overcast, the
satellite photo data is worse than useless. In fact, it shows perfectly
clear skies where none exist. (Given the same faulty presentation on
the airport's computer, I'm prepared to accept that this is not a flaw
in XM weather -- but it *is* a flaw, nonetheless.)

I'd say that's a pretty sure indication that the satellite imagery itself
was defective. I don't know what might have caused that, but normally it
should be reliable

Actually, I've noticed this many times in the past. Satellite photos
will show clear skies while we are actually beneath a solid overcast.
I don't know if the operators can selectively set the sensitivity of
the camera to not show thin layers, or what, but this isn't the first
time that satellite imagery of cloud cover has been 100% wrong.

Hi Jay and Mary,

Without appearing to defend the XM Weather technology, here's my put on
what you are seeing based on my experiences in another life working with
some sophisticated and 'spooky' equipment.
Satellite "images" used to construct Wx displays are generally collected
with LWIR [Long Wavelength InfraRed -- 8 to 13 microns] imaging radiometers.
Water vapor [cloud] is generally transparent in the LWIR while percipitation
[rain, snow, etc.] is not. That's why the Wx images displayed can show rain
but not the clouds that drop it. Same with the microwave displays, i.e.
RADAR.
Here's the first hint: you can get the same type of displays on a full
dark night.

What is Atlas' tail number again? I might be coming your way next month.

Regards,

Casey Wilson
Freelance Writer
and Photographer

As much as you fly you (or the little woman) should really think about
finally getting your Instrument Ratings. This way you won't have to
worry about any overcast's and go happily on your way. Just a thought.

As far as METARS go I believe that unless there is a significant change
they only update once an hour. XM doesn't create METAR's they just
display the information.

Sounds a little bit like you were expecting the 496 to be a panacea for
all things weather and it turns out to be just a system of displaying
information you could get from other sources.

Jon Kraus
'79 Mooney 201
4443H @ UMP

Jay Honeck wrote:
For those of you who have XM weather integrated with your GPS.

Do you use the weather information to paint a big picture of what's going on
around you. I.E. "If I fly 50 miles thataway, it looks like I'll be able to
circumvent this line of storms."


Mary and I are very new to XM, but have already used it on several
x-country flights, including one today that highlighted some weaknesses
in the system.

We flew from Racine, WI to Iowa City, IA, about a 1.5 hour flight,
depending on winds. A cold front was approaching from the north, with
a very juicy airmass in place to the south. Flight service indicated
good VFR all the way, leaving Racine around 7 PM. This would put us on
the ground right around sunset, which was our goal.

Using the airport's computer, the satellite pic showed no cloud-cover
over our route of flight at all. This, of course, was contradicted by
our Mark V eyeballs, and METARs that indicated a broken to overcast
layer at around 2800 feet, all the way from the Mississippi east to our
position on the western shore of Lake Michigan. Visibilities ranged
from 7 to 10 miles along the route of flight when we launched.

The XM weather on the 496 takes around ten minutes to upload, which
meant that we were already airborne by the time we were getting useful
weather. Although this is something we will learn to work around, I
find this time lag to be a bother. (I know, much wants more!) We're
going to have to get in the habit of turning on the 496 before engine
start, to allow time for downloading.

We were soon buzzing along under the overcast in smooth air but really
crappy visibility (especially when the sun would occasionally break
through and hit that moist, tropical air), and we were really glad when
the METARs finally downloaded into the Garmin.

We've mounted the 496 on the co-pilot's yoke, so Mary was working the
GPS for the first time, but had only minimal difficulties navigating
Garmin's excellent menus. She laughed when she was able to look at the
"live" satellite photo, which (like the one in the airport) showed
nothing but clear, blue skies ahead, while we were obviously under a
pretty thick overcast.

Strike one for XM. Apparently with a thin-but-solid overcast, the
satellite photo data is worse than useless. In fact, it shows perfectly
clear skies where none exist. (Given the same faulty presentation on
the airport's computer, I'm prepared to accept that this is not a flaw
in XM weather -- but it *is* a flaw, nonetheless.)

She then started checking METAR data ahead, to make sure that things
weren't falling apart along our route of flight. Having this data on
board is priceless, IMHO, and it showed that conditions were stable
until the Mississippi, and then improved dramatically to the west.
Obtaining this data is as easy as running your cursor over a little
triangle next to each reporting station, and having it in the plane was
a major reason for purchasing the 496.

However, after 30 minutes in the air, she noticed that the METAR data
had not updated. The NEXRAD radar and satellite data were updating
every 6 minutes or so, but the METARs remained the same as when they
initially uploaded.

Obviously, in changing flight conditions this slow rate of change is
simply unacceptable, and we quickly reverted to listening to AWOS's
ahead on the radio.

Strike two for XM.

By the time we hit the Big Muddy, we were able to climb on top of the
layer, which rapidly diminished to a thick haze layer. The rest of the
flight was uneventful, and we didn't refer to the 496 again.

IMHO, the jury is still out on the unit. It's wonderful for
watching/avoiding precipitation and storms, to be sure, but it
certainly proved to be less than useful on this flight. And I can
assure you that we fly in these kinds of fuzzy VFR conditions FAR more
often than we do when thunderstorms are threatening.

I'm going to contact Garmin about the update rate on METARs, and hope
there's some setting or software update I can install to improve the
rate of change. If it can't be improved, the unit will end up being far
less useful than expected.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

"Jon Kraus" wrote:

As much as you fly you (or the little woman) should really think about
finally getting your Instrument Ratings. This way you won't have to worry
about any overcast's and go happily on your way. Just a thought.

Indeed. I've got the satellite image feature turned off because I don't need
it; the clouds just get in the way of other stuff on the screen.

--
Dan
C-172RG at BFM

"Peter Duniho" wrote in message ...

:
: As I already said, all that XM does for you is show you the data in a
: friendlier way, and avoid the radio call to the FSS. Expecting more from
: them is unreasonable and will guarantee disappointment on your part.
:
: Pete
:
:

All said and done, I still consider the monthly ~$30 charge to be a user fee of sorts. You can call FSS on the radio or
pay the fee and receive the same info. More convenient to use the GPS? Maybe for some...

..Blueskies. wrote:
"Peter Duniho" wrote in message ...

:
: As I already said, all that XM does for you is show you the data in a
: friendlier way, and avoid the radio call to the FSS. Expecting more from
: them is unreasonable and will guarantee disappointment on your part.
:
: Pete
:
:

All said and done, I still consider the monthly ~$30 charge to be a user fee of sorts. You can call FSS on the radio or
pay the fee and receive the same info. More convenient to use the GPS? Maybe for some...



I dunno, I have much better luck loading weather on the MX20 than
I have communicating with Flight Watch/FSS over the radio. And
the graphical presentation is much easier.

"Ron Natalie" wrote in message m...
: .Blueskies. wrote:
: "Peter Duniho" wrote in message ...
:
: :
: : As I already said, all that XM does for you is show you the data in a
: : friendlier way, and avoid the radio call to the FSS. Expecting more from
: : them is unreasonable and will guarantee disappointment on your part.
: :
: : Pete
: :
: :
:
: All said and done, I still consider the monthly ~$30 charge to be a user fee of sorts. You can call FSS on the radio
or
: pay the fee and receive the same info. More convenient to use the GPS? Maybe for some...
:
:
:
: I dunno, I have much better luck loading weather on the MX20 than
: I have communicating with Flight Watch/FSS over the radio. And
: the graphical presentation is much easier.

I agree about the graphical representation... picture says a thousand words...