Date: 201208
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: Turbulence; Icing; Thunderstorm
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Anomaly: Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Weather
Primary problem: Weather

Narrative: We were en route on a southerly route for weather. A line of storms was running south to north perpendicular to our route of flight. The line of storms ran almost to Canada to the north and approximately 150 miles to the south. Other aircraft were traversing a break in the weather that was approximately 80 miles wide. The break was closing in; but preceding aircraft were reporting rides as only 'light chop'. We had been cleared to deviate as necessary and proceeded toward the gap in the weather. The closer we got; the quicker the gap seemed to close. We discussed our options; of which our only real option was a 90-100 degree turn to the left for at least 150 miles; possibly over 200 miles. This would have almost certainly put us in a low fuel situation later in the flight. At 50 miles away; the gap had closed to only about 40 miles wide. We asked for a ride report from the preceding aircraft (20 miles ahead on TCAS); and it was reported 'light chop with a little moderate; but closing up fast.' We already had the seatbelt sign ON due to our proximity to the storms; although up to this point our ride had been absolutely smooth. Since it had been smooth; I made a cabin call to the flight attendants to ask them to be seated and buckle up; and then made a PA announcement to the passengers reminding them that the seatbelt sign was on and that we would be passing through a bumpy area around weather in about 5 minutes. As we approached within 10 miles of the gap; ATC asked if we were going to make it through. At this point the gap had all but closed up; however we were close enough that any turn would have put us in areas of heavy radar returns; i.e. we were committed. We could see daylight above and ground below the gap; but the clouds had closed in front of us. As we entered the clouds we immediately encountered moderate chop/turbulence with heavy rain droplets and icing conditions. The anti-ice activated and we observed light rime forming on the windshield wipers. Airspeed seemed to move around +/-10 KTS in the chop; however the airspeed trend vector danced around wildly; sometimes causing the airspeed to flash amber to warn of an impending overspeed. The PLI had appeared and remained on but never changed color from green to amber. We were getting bounced around pretty good; so I reported moderate to extreme chop and asked ATC for a descent. They immediately cleared us down to FL320 (from FL340) and the First Officer initiated a descent. Due to the turbulence the aircraft was slow to respond to autopilot inputs; so I took control of the aircraft and lowered the nose approximately 3-5 degrees using TCS. Before we had reached FL330 we popped out of the clouds into smooth clear air; and I slowly continued the descent to FL320. We had been in the area of turbulence for about 20-30 sec. I then returned control to the First Officer and called the flight attendants to make sure everyone was ok. A Flight Attendant said it was pretty bad but everyone was ok. I reported to ATC that we were fine but that the gap had closed up on us and no one else should try to go through. We continued the flight normally without further event.




Synopsis: ERJ-170 flight crew attempted passage through a narrowing path between thunderstorms; encountered severe turbulence and; with ATC clearance; descended to smooth; clear air.