B737 flight crew reported unexpected turbulence and windshear causing a 3;000 feet altitude loss.

Attributes
ACN	1742905
Time
Date	202005
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Captain Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Instrument Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Speed All Types Inflight Event / Encounter Weather / Turbulence

Narrative:

As we were deviating right to avoid a magenta area associated with a minor buildup we encountered an area of choppy air the quickly turned to turbulence. Airspeed was fluctuating but then continued to decrease. Corrective action was taken that led to a 3;000 foot loss. Center was advised and gave instructions to climb to 38;000 feet. Before the event I noticed the winds aloft to be a left quartering head wind; and after the event it was a left quartering tailwind. It's highly suspect that a high altitude windshear was the cause.

Original NASA ASRS Text

Title: B737 flight crew reported unexpected turbulence and windshear causing a 3;000 feet altitude loss.

Narrative: As we were deviating right to avoid a magenta area associated with a minor buildup we encountered an area of choppy air the quickly turned to turbulence. Airspeed was fluctuating but then continued to decrease. Corrective action was taken that led to a 3;000 foot loss. Center was advised and gave instructions to climb to 38;000 feet. Before the event I noticed the winds aloft to be a left quartering head wind; and after the event it was a left quartering tailwind. It's highly suspect that a high altitude windshear was the cause.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.