Date: 201205
Local time of day: 0001-0600
Location: LGA.Airport, NY
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Takeoff / Launch
Airspace: Class B LGA
ATC / advisory: Tower LGA
Reporter organization: Air Carrier
Reporter function: First Officer
Human factors: Communication Breakdown; Workload; Situational Awareness; Human-Machine Interface; Distraction; Confusion
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Airspace Structure; Human Factors; Procedure; Weather
Primary problem: Human Factors

Narrative: Prior to our flight; I pulled up our PDC. We were given the La Guardia 4 Departure WHITESTONE CLIMB as our departure clearance. I then called LGA Clearance to verify La Guardia 4 Departure with the WHITESTONE CLIMB along with the current ATIS and transponder code. Prior to pushback; the Captain and I thoroughly briefed the WHITESTONE Departure during the clearance brief. After pushback; we taxied to the runway and were cleared for takeoff. At 400 FT; we began the right turn per the WHITESTONE Departure.At 500 FT; the Tower Controller told us to fly the NTHNS 1 RNAV Departure. I hesitated to answer because I initially didn't understand what the clearance was. He then asked if we could comply. I stated; 'No.' He then gave us a 050 heading and we continued the climb to 5;000 FT. We were then given a 360 heading. We were then told to contact Departure. I told the Controller that if he wanted us to fly the departure; he should have let us known prior to takeoff. I checked in with New York Departure; and we were given immediate vectors around the weather. Once we were clear of the weather; the Controller asked if we had time for a question. I said 'go ahead.' He asked if we were unable to fly the NTHNS 1 Departure. I told him that we could fly the departure if we had been given prior notice. I told him the Tower Controller did not give us any prior notice and therefore we had no time to prepare for the change from the WHITESTONE CLIMB to the NTHNS 1. 500 AGL was not the time to totally change our departure. He said; 'Okay; and said it was not a problem.'I believe the proper measures were in place. The PDC was right. I verified the clearance with Clearance Delivery. The problem is that ATC cannot change the clearance at 500 AGL without any prior notice. I believe this was an ATC error. Someone forgot to amend our departure clearance prior to takeoff.


Second narrative: I actually have no idea exactly what SID the Controller stated. Almost immediately; he asked if we could comply. I told the First Officer to tell him that we were unable. ...the Controller asked us (in so many words) why we were unable to comply with the new SID the Tower wanted us to fly. Due to thunderstorms in the area; the Departure Controller gave us vectors to avoid thunderstorm cells. This event created high stress for the flight crew during a high workload phase of flight topped off with thunderstorms in the vicinity.


Synopsis: Although cleared via PDC to fly the complex LA GUARDIA SID; WHITESTONE CLIMB the flight crew of a B737-700 was asked immediately after takeoff to; instead; fly the NTHNS RNAV SID due to weather. The flight crew responded unable due to workload required and the lack of time to adapt to the change. ATC provided vectors around the weather.