Citation Excel (C560XL)
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Human Factors
Departed Runway 1 on NATNL5 SID. Entered clouds at 400 feet. With no visual reference to avoid restricted airspace (the river) the left turn was made as soon as possible as the SID requires. Because our aircraft was light and OAT was low; we turned west to intercept the 328 deg radial prior to getting north of the VOR causing us to go past the 328 deg Radial. The SID should have a defined initial heading to fly to a RNAV fix.
CE560XLS Captain reports deviating west of the of the DCA 328 degree Radial on the NATNL5 departure due to entering IMC and turning to the west prior to the DCA VOR.