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.