C-FNJZ, a CRJ 900 operated by Jazz Aviation LP was conducting flight AC8670 from Vancouver Intl. (CYVR), BC to San Diego Intl. (KSAN), CA. While on top at FL270 Vicinity of PASKE (Porter, CA), the crew encountered clear air turbulence. Airspeed fluctuated +/-30kts but did not over-speed nor did the Auto Pilot kick off. Turbulence and Ignition buttons were on. The turbulence made
reading the instruments on the panel impossible as they were too blurry. The motion was up/down as well as side/side. The seat belt signs were switched on about 2 min prior to the encounter.
Flight crew initiated descent to FL 250 where they had moderate to borderline severe turbulence.
Continuing descent to FL230 flight encountered a severe turbulence event that lasted approximately 5 minutes. Flight climbed to FL250 where the turbulent event ceased. Maintenance is arranging for an inspection.