Date: 201906
Local time of day: 1201-1800
Location: AUS.Airport, TX
Flight conditions: VMC
Weather elements / visibility: Rain; Thunderstorm; Turbulence
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C AUS
ATC / advisory: TRACON AUS
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport
Contributing factors: Weather
Primary problem: Weather

Narrative: With one [air carrier] flight going missed and diverting to Gray and several wind shifts and runway changes; we were now on downwind for 35L at Austin. Following another [air carrier] flight; another wind shift occurred and [the airliner] went missed. We then asked for a turn back to the north side of Austin. With the autopilot on and in a left turn; we hit; what at the time we called; severe turbulence. It only lasted about a second. The autopilot and auto throttles kicked off; we lost a few hundred feet and got a bank angle alert. I took control of the aircraft; rolled the wings level and continued heading north. It took a few moments to regain our situational awareness after the jolt we had just experienced. We put the flaps up and got the speed and altitude back under control. All systems and flight controls functioned normally. We [advised ATC] and initially wanted to divert to Gray. We checked with the flight attendants for any injuries and they reported none. After messaging Dispatch; it was decided that the best course of action was to return to ZZZ. I again checked with the flight attendants regarding injuries; still none to report. I made a public address announcement to inform the passengers that we were returning to ZZZ. We made a normal landing and taxi into the gate. At the gate; I again asked the flight attendants if there were any injuries and again; they had none to report. I spoke with Dispatch and [Flight Operations] via phone to fill them in on what happened. I believe it is possible that we encountered a lightning strike and not severe turbulence. I believe that I forgot to tell the flight attendants about [advising ATC] and notifying passengers that emergency safety equipment would be standing by.


Second narrative: As we preflighted the aircraft for AUS; while in ZZZ; we knew there was a small line of weather moving south over AUS. After pushback; the Dispatcher sent a message via ACARS indicating that they were trying to call us on Operations because they wanted to hold us on the ground. That was already our plan and had just contacted Clearance asking about ground stops. Clearance informed us that it would be a 15 minute update. We pushed back as normal; and on time; with the intention to free the gate since the weather appeared to be a non-issue. It was apparent that in less than 20 minutes the weather would all be south of AUS and after a brief hold in the run up pad for [the runway] we would be released to depart. While in the pad; we set brakes and secured both engines. Multiple public address announcements were made by us and the cabin crew. The Captain and I both heavily monitored the weather waiting for it to move south of Austin. As it did; I called Ground and asked for an update. I don't recall exact wording; however; it was basically that multiple aircraft have been released and ground stop was over. They said it's possible enroute delays could occur. We were tankering fuel and had roughly 13;000 pounds.We departed; and stayed low (between 10-12;000 feet). There was an overcast layer of clouds above us with rain. Areas of continuous light and moderate chop for most of the cruise portion. Along the way; we continuously monitored airport weather conditions for AUS. Once we checked on with Austin Approach we heard at least two other aircraft in front of us attempting to land in AUS (landing south). Shortly after; we heard missed approach and break off instructions due to the wind shifting nearly 180 degrees. Now; these other aircraft were discussing vectors to ILS/Visual 35L. We planned the same; but one of the greatest challenges was trying to get a word in with ATC. As the weather moved south of the field we did not want to continue on a long downwind (southbound). It did not look good out the window. We eventually told ATC 'If you're going to vector us around for a while; we want to stay north of the field'. After discussing our options and current weather; the Captain and I decided to follow an [air carrier] flight with vectors to a visual/ILS to Runway 35L. On downwind; at 210 knots (I believe; and Flaps 1) 4;000 feet we experience what I would define severe turbulence and potentially a lightning strike(s). It was violent. The autopilot disconnected; we were in control wheel steering; altitude fluctuated by hundreds of feet as well as airspeed fluctuations. In addition; a moment of high bank angle. The Captain flew the aircraft manually as we turned north and told ATC we needed out of the area immediately. We also determined that we needed to [advise ATC]. We were physically shaken up; unsure of injuries (including ourselves) or damage to the aircraft. Originally; we were going to land immediately; however; the decision to change plans to go to ZZZ became a better option as information about lack of injuries and damage became apparent. We continued to ZZZ; deviated around weather and landed uneventfully. ARFF followed us to [the gate]. Between time of incident and arriving at the gate we made 3 calls to the cabin asking about the condition of the plane and also injuries to anyone. Every time the answer was everyone seems fine and nothing abnormal.


Synopsis: B737 flight crew reported experiencing moderate to severe turbulence and a possible lightning strike during vectors for landing at AUS.