CFI RPTED SEVERE TURB IN THE VICINITY OF ROA; CAUSING A BROKEN WINDOW DURING A TRAINING FLT.

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CHKED WX (METARS AND TAF) ON INTERNET PRIOR TO TRAINING FLT INVOLVING XCOUNTRY FLT TO KLYH AND RETURN. WIND AT TKOF WAS 280 DEGS AT 12 KTS. TKOF AND DEP CLB WERE NORMAL WITH LIGHT TO MODERATE TURB. LEVELED FOR CRUISE AND CLRED ON COURSE. A LEAR JET ON APCH TO ROA RPTED SEVERE TO EXTREME TURB. I DON'T KNOW THE LEAR'S POS RELATIVE TO ROA; BUT SUSPECT WAS N OVER MOUNTAINOUS TERRAIN. ABOUT 30 SECONDS LATER; WE ENCOUNTERED A BRIEF POCKET OF MODERATE TO SEVERE TURB OVER A RIDGE LINE. ATC ASKED US ABOUT OUR 'RIDE;' AND I RPTED 'GENERALLY LIGHT TO MODERATE TURB WITH A BRIEF ENCOUNTER OF SEVERE;' AND RPTED THE LOCATION OF SEVERE. DURING THE ENCOUNTER; I HAD HEARD A METALLIC SOUND FROM THE REAR OF THE ACFT. WHILE SUBSEQUENTLY (ABOUT 1 MIN) SCANNING TO MY R FOR TFC I CAUGHT SIGHT OF MOVEMENT IN MY PERIPHERAL VISION AND OBSERVED THAT THE R REAR WINDOW IN THE BAGGAGE AREA WAS BROKEN. THE DAMAGE TO THIS APPARENT NON-STRUCTURAL WINDOW WAS CAUSING NO ADVERSE HANDLING OR AERODYNAMIC RESULT. I ADVISED ATC THAT I WISHED TO RETURN TO KROA AND LAND. I WAS CLRED TO DO SO AND LANDED WITHOUT INCIDENT. THAT EVENING I CONTACTED 'WX BRIEF;' AND ASKED IF ANY AIRMET OR SIGMET HAD BEEN ISSUED FOR THE TIME OF MY FLT AND WAS ADVISED THAT THEY DID NOT RETAIN EARLIER AIRMETS; ETC. I CALLED THE NATIONAL WX SVC ALSO; AND WAS TOLD THAT THEY DID NOT KNOW EITHER. I SHOULD HAVE; BUT DID NOT CHK THIS BEFORE THE FLT. ALSO; I DO NOT KNOW IF THE DAMAGE MIGHT HAVE BEEN CAUSED BY THE TOW BAR IN THE BAGGAGE COMPARTMENT AND/OR A QUART OF OIL ALSO STOWED THERE; OR WHETHER FUSELAGE TWISTING CAUSED THE WINDOW TO BREAK.