Regional Jet 200 ER/LR (CRJ200)
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Workload
Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory
Human Factors; Procedure; Weather
On arrival into the DCA area; we were told to expect the river visual 19. As PM; I loaded the LDA 19 into the FMS as backup to the river visual. We were vectored to final approach and asked if we had the river in sight. While we were VMC; patchy fog was beginning to obscure the surface. ATC asked if we would like the LDA instead. We accepted the approach clearance and began the step downs. Upon crossing the FAF we mistakenly set in MDA instead of the intermediate step down. We descended to MDA with the airport in sight most of the way down. Nearing MDA; and in night VMC with the surface and the airport in sight; ATC issued a low altitude alert and the GPWS alerted us to an obstacle. I had the obstacle in sight and it was below our altitude. However; as the flight conditions were night VMC; I took the controls from the PF and executed the GPWS escape maneuver. I advanced the thrust levers slowly due to not wanting to over speed the engines as the speed controls were MEL'ed under 76-11-1. The stick shaker came on momentarily during the pitch up. When the GPWS no longer indicated the presence of an obstacle; we were still in a position to land the airplane safely so we continued to landing.Factors leading to the missing the intermediate step down was the last minute change in approach as both pilots became task saturated. I should have asked for delay vectors.  Also; the implementation of the planned change to constant descents during non precision approaches would prevent any further events due to missed step down fixes that are not in the FMS data bases on the older airplanes.
CRJ-200 First Officer reported being cleared for the River Visual Runway 19 with the Captain flying. The LDA Z was selected in the FMC for backup then became primary when fog began to obscure the surface. Crossing BESSE; the MDA was set in instead of the step down altitude at WEVPU; resulting in a GPWS obstacle warning and a low altitude alert from the Tower. The First Officer took the controls and began the escape maneuver. When the GPWS went silent; the aircraft was still in position to land and the landing was completed.