Air carrier captain reported near midair collision at altitude with a weather balloon.

Attributes
ACN	1727852
Time
Date	202002
Local Time Of Day	1201-1800
Place
Locale Reference	ZTL.ARTCC
State Reference	GA
Environment
Light	Daylight
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 459
Events
Anomaly	Conflict NMAC
Miss Distance	Horizontal 0 Vertical 100

Narrative:

In cruise; level at fl 380; we saw a weather balloon about half the size of a 737 with a long cable attached and a large object connected to the end of the cable; too close for evasive action. Object passed approximately 100' to 200' above the cockpit. ATC was quickly advised and other aircraft reported seeing the object. No locator device on an object that large? ATC had no clue it was in their airspace.

Original NASA ASRS Text

Title: Air carrier Captain reported NMAC at altitude with a weather balloon.

Narrative: In cruise; level at FL 380; we saw a weather balloon about half the size of a 737 with a long cable attached and a large object connected to the end of the cable; too close for evasive action. Object passed approximately 100' to 200' above the cockpit. ATC was quickly advised and other aircraft reported seeing the object. No locator device on an object that large? ATC had no clue it was in their airspace.

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.