Here are a couple of photos from this morning's flight showing the XM Weather display (and specifically the NEXRAD Radar screen) on N631S' Garmin GPSMap 396. The first image shows us over Delaware Bay east of the Smyrna VOR (ENO) near Dover AFB (KDOV) headed toward the LEEAH intersection.
The next image is a little earlier (note...not yet past ENO) and at a wider scale. I had just accepted a reroute. My clearance would have had me turning left at ENO and going up to Cedar Lake (VCN). The Dover Approach controller said he'd need me to descend from 7,000 feet to 5,000 feet unless I wanted to proceed to LEEAH and thence to Coyle (CYN). A quick glance at the NEXRAD display made this an easy question to answer -- take me to LEEAH!
The ride was smooth and the precipitation was light as I proceeded through the "alley" where the returns were absent then headed up to the Atlantic City (ACY) area through the region of green (= light) echoes.
Having this kind of information on the airplane provides tremendous confidence and terrific decision support. You know what you are getting into. With the caveat that you must understand NEXRAD's limitations, this is a remarkable enhancement to IFR safety.
About the limitations: At the lower left of each screen image is a data label indicating the age of the information (i.e., Wx -00:06 indicates data six minutes old). In addition, the actual returns might be about five minutes old before the NEXRAD system processes them. So I am looking at precipitation areas that may be, in this case, 11 minutes out-of-date. You must avoid putting yourself into any situation where a rapidly moving cell traps you because you cut in too close to its downcourse side.
This is a strategic tool and a weather avoidance tool -- not a tactical tool or a weather penetration tool. (The latter is the onboard weather radar that the Big Iron carries.) But used for what it is, the NEXRAD/XM Weather/Garmin 396 system is incredibly valuable.