Date: 201708
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: Windshear
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: First Officer; Pilot Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Rejected Takeoff; Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Contributing factors: Procedure; Weather
Primary problem: Weather

Narrative: Just prior takeoff we received a wind shear alert of 20 knots off the end of the runway. We declined our takeoff clearance; and ran performance weight and balance for wind shear. While waiting for our numbers; another airline departed to the northwest without issue. After reconfiguring for a precautionary takeoff profile with performance weight and balance numbers and briefing the potential for wind shear; we were cleared for takeoff with a 330 heading to avoid the cell off the end of the runway. While taking the runway; Tower issued another 20 knot wind shear alert. Seeing the cell off the end of the runway both visually and on radar; and seeing a clear path to the northwest; we decided to depart with the added margins afforded by the precautionary takeoff profile.At about 90 knots; we received the PWS (Predictive Wind Shear) warning 'wind shear ahead.' I announced; 'Reject; I have the aircraft.' Autobrake Disarm illuminated; and we brought the aircraft to a relatively gentle stop with TRs (Thrust Reversers) and speed brakes. We cleared the runway and briefed the FAs (Flight Attendants) and the Passengers. We ran performance weight and balance Brake Cooling numbers; coordinated with Dispatch; Chief Pilot on Call; Maintenance Control; and determined that after brake cooling; we would be safe to depart with a revised fuel load to reflect the new conditions.In hindsight; we did some things well and others we did not. Having had to reject for PWS Warning; the red flags were certainly there to not takeoff in the first place. But; we were wise to refuse our initial takeoff clearance so that we could acquire wind shear takeoff data from performance weight and balance. The reject decision was assertive and decisive; and transfer of control went well. However; the FO (First Officer) debriefed that it was difficult to hear my reject call over the wind shear warning. Also; he mentioned that he might have inadvertently hit the brakes when I rejected the takeoff; which could explain the autobrake disarm (we did not get the max braking of the RTO (Rejected Takeoff). After turning off; while we did brief the FAs immediately and then the Passengers; we neglected to reference the QRH for the RTO. Additionally; I did not announce to 'Remain seated.' I believe a contributing factor was that the reject was relatively benign due to the RTO autobrake not taking over and being only at 90 knots. It wasn't the 'screeching halt' we've practiced many times. Once off the runway; the FO was quick to suggest releasing the brakes; and we ran the performance weight and balance brake cooling numbers; contacted Dispatch; and conferenced with the Chief Pilot on Call; Maintenance Control to ensure that we did not have to return to the gate; and that we could continue for takeoff after brake cooling with fuel onboard. Maintenance did ask if our performance computer showed a 'high energy' stop. We informed them that we no longer use the performance computer. I tried to look up what the performance weight and balance would say in that case; but was unable to find an example. Also; once we had new numbers for takeoff; we found that there really isn't a procedure for takeoff after an RTO. We ran all checklists from Before Start through Before Takeoff as a precaution (rearming the autobrake; for example). I was happy with how we used CRM throughout the process.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737 flight crew reported a rejected takeoff due to a predictive windshear warning.