Here is an analysis of a near mid air between a Discus 2A "WX" and a Cessna 421 over mountains 
north of Santa Barbara last September 20, 2015. Included is the FAA ARTCC radar video and ATC voice
audio of this encounter at 10,000 msl zero vertical and around 0.21NM NM.

https://dl.dropbox.com/s/k8ph9wogyifvjsf/NearMidAir_SBA19NNE_20150920_RadarVideo_N53LK_N821TT.wmv?dl=0

A near mid air statement was filed with the FAA in order to test: 1) Was my new Mode S transponder
working 2) Did the FAA use the glider target to call traffic. The answers was a resounding ...YES! In fact traffic was called to the C421 at 8nm out! Here's my statement:

https://dl.dropbox.com/s/e6gvhn6dybxg6n3/NearMidAir_SBA19NNE_20150920_StatementToFAA.pdf?dl=0

Please note, that I originally identified the twin as a King Air passing by at around 500 ft horizontal. The radar track showed around 1200ft.

The ARTCC controller called first at 8nm out... then again at around 5nm (2:37 from tangent point) with the C421 pilot saying "...still searching [FOR TRAFFIC]".

Only at around 1.5nm and :33 seconds from tangent point when Conflict Alert "CA" went off did the controller point out the traffic again (C421 moving at 160kts). The only confirmation from the pilot of visually seeing the glider was when he said "...might have to maneuver to avoid them..." that phrase ending at 25secs from the encounter. After looking at the radar track, any deviation was practically undetectable.

There was no serious concern expressed from the controllers (Did you notice shift change? - see time line below). It would have been great if he'd noticed that the glider was probably circling and climbing through his altitude directly at twelve o'clock.
Perhaps this can be used as a training aid for controllers on the typical behavior of gliders and using that to communicate traffic to conflicting powered aircraft.

FOR MY RECORDS C421 N821TT _________________________________________________________________________

SECS FROM NEAR MISS    COMMENT

3:17            ATC called traffic to C421 TT 8nm out
2:37            C421 TT "...still searching"
1:50            Shift Change at Sector "Couple of gliders
                here 82-92 he's still looking for them"
 :33            "CA" goes off; ATC called C421 traffic 2nm.
 :25            C421 TT "Might have to maneuver to avoid them"
 :15            Glider N53LK Walt Rogers visually sees C421
 :12            PowerFlarm PCAS goes off
 :00            C421 Passes by 100msl same as glider. 0.21NM horizontal.       

Glider was climbing at 500fpm directly on flight path   

Walt Rogers "WX"