Large Transport
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Flight Instructor; Flight Crew Multiengine
Flight Crew Last 90 Days 250; Flight Crew Total 32000; Flight Crew Type 12000
Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Human Factors; Weather
We were cruising at approximately FL300. We encountered a line of thunderstorms that extended far north and to the south with few gaps. There was a gap about 30 miles wide at about 11 o'clock and what appeared to be the south end of the line at about 2 o'clock beyond which appeared to be clear of thunderstorms. We asked ATC about going around the south end of the line and he said he would arrange for it.As we were deciding the best course of action; we saw some of the gaps in the line continue to close. We decided to go around the south end of the line which appeared to be clear of thunderstorms and advised ATC. Some period of time passed and suddenly what had appeared clear at the south end of the line of weather now showed more thunderstorms continuing much farther to the south; continuing off the edge of the radar scope. At that point we decided the best course would be to turn back to the north to fly though the only gap that looked reasonably good before we decided to try to go around the south end of the line.ATC said that appeared to be the best route and all previous aircraft had reported nothing worse than light turbulence through there. I had previously contacted our cabin crew to advise them that I was putting moderate turbulence procedures into effect. I checked with them again to make sure that all of their service items had been stowed and everyone was seated.First Officer (FO) was the flying pilot and he steered us toward the remaining gap in the line of weather. We were flying at .76 mach. Just as we approached the entrance to the gap; the Doppler showed some pink just off the nose from 12 - 2 o'clock. FO began to steer left around the Doppler return. The cells to the left and right were rapidly closing in on us. It was night time and up until this point we were in VMC and had been able to see the outline of the cloud tops ahead. Suddenly; we became IMC and began to encounter continuous moderate to severe turbulence with major wind shear. According to the radar; we were not in the cells and had at least 10 miles clearance on each side.There was not enough room to turn around at this point. The autopilot disengaged itself. FO hand flew the aircraft as we tried several times to re-engage the autopilot to no avail. The weather caused substantial pitch; roll; airspeed and altitude variations with the altitude varying by up to 500 feet and airspeed by up to about +/- 30 knots. Several times the wind shear caused the airspeed to shoot up into Vmo. I estimate the maximum exceedance was about 5 knots. It was difficult to read the instruments at times. We never encountered any hail.I estimate that the encounter with the moderate to severe turbulence lasted about five minutes. Once we cleared the weather; I advised ATC of the specifics of our encounter and recommended that they advise other aircraft behind us not to take that route; at least not at our altitude. I called the cabin crew to make sure everyone was OK and they said that they were. We sent an ACARS message to dispatch/maintenance to advise them of the severe turbulence and airspeed exceedance and entered it into the logbook. The remainder of the flight was uneventful as we continued to our destination.Had we known what the experience of flying through that gap in that line of weather would be like; we would not have flown through that area. We likely would have contacted dispatch to get their take on this. My belief is; though; that based on what we could see and what ATC told us; the best course of action would have been to turn around and either divert to another airport or return to the departure point until the weather cleared or better route could be planned.
Air carrier flight crew experienced moderate to severe turbulence while deviating around and through weather.