Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Private
Flight Crew Last 90 Days 30; Flight Crew Total 1576; Flight Crew Type 800
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Regained Aircraft Control
Weather
Descending with vectors from the LARKS8 arrival on an IFR flight plan from ZZZ to APA.  Encountered severe clear air turbulence at approximately 12;500 MSL in the descent over the front range of the Rockies.  Turbulence came on immediately with no prior turbulence. Could not maintain assigned altitude or heading.  I reduced speed to maneuvering speed; deployed the gear and maintained wings level. I reported to Denver Approach that I was below assigned altitude and encountering severe turbulence. I was cleared to a lower altitude and turbulence abated at about 8;500 MSL.  I made a pilot report to Denver approach.  Landing with gusts to 30 kts out of the west was uneventful on runway 28 at APA. This was the worst turbulence I have experience in the Cessna 425 and I have several hundred hours of time in type and have flown the LARKS8 STAR often.
Cessna 425 pilot reported he encountered severe clear air turbulence on descent to APA on the LARKS8 Arrival.