Eclipse 500
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 110.6; Flight Crew Total 3324; Flight Crew Type 180.7
Human-Machine Interface; Training / Qualification
Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Aircraft; Weather; Human Factors
Initially I was at FL340 enroute to GCK.  I was deviating to the NE (just W of DDC) for weather near GCK.  There was a line of thunderstorms running from west to east that was just south of GCK.  On the XM radar depiction; there appeared to be an opening to get north of that weather and allow me to approach the airfield from the north; clear of the thunderstorms.  I requested to stay higher until I got through that weather.  As I got into the small opening; the XM radar depiction updated and indicated that some weather had moved into that opening and it was not as clear as I believed it would be.  Since I had requested to stay high; I was going to be a potential conflict with some other lower traffic if I were to try to descend into GCK.  Therefore; as I was approaching that opening; ATC asked me to descend to FL310; which I did.  As I approached FL310; I hit some severe turbulence which was enough to disconnect the autopilot.  I immediately dropped about 600-700 FT.  I began a climb back to FL310.  As I approached FL310; I hit another pocket of severe turbulence; this time gaining approximately 800 FT; putting me in conflict with traffic at FL320 that ATC had originally descended me to avoid.  ATC asked why I was climbing again; to which I replied that I had hit some severe turbulence and was descending back to FL310.  One of the lessons re-learned is that there is a lag in the NEXRAD data provided by XM.  Having used it in conjunction with the onboard weather radar in the past; it has proven very effective in picking through weather and precipitation.  This most likely led to some complacency on my part that the hole I was seeing in the weather depiction would be enough for me to get through.  However; the hole closed about the same time that I flew through it; causing severe turbulence and large altitude deviations.  A better alternative would have been to turn around and divert to an alternate south of the thunderstorms or attempt to go around them to the west.
EA-500 pilot reports encountering severe turbulence at FL310 while attempting to avoid thunderstorms using XM Radar and altitude deviations occur. The next XM update showed the gap chosen as closing up.