Nationwide Ground Stop Lifted For Alaska Air After "Tech Problem Cropped Up During System Upgrade"

Update (1216ET):

Alaska Air resumed departures around noon after an hour-long ground stop for all departure flights nationwide.

The Wall Street Journal says the ground stop was due to a "technology problem that cropped up during a system upgrade."

Even though the ground stop has been lifted, Alaska Air passengers can expect delays throughout the afternoon.

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Update (1120ET):

Phil LeBeau reports on CNBC television that an earlier malfunction of Alaska Airlines' IT system, which calculates planes' weight and balance, triggered a nationwide ground stop.

For all those pilots out there, weight and balance are critical before running up the pre-flight checklist. 

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Shares of Alaska Airlines are tumbling in New York after the Federal Aviation Administration's Air Traffic Control System Command Center says all of the carrier's mainline and subcarrier flights (excluding SkyWest Airlines) are placed on a "ground stop."

• FAA: ALL ALASKA MAINLINE AND SUBCARRIER FLIGHTS GROUND STOPPED (SKYWEST EXCLUDED)

Here's the advisory from the FAA: 

Alaska Airlines shares tumbled on the news. Still up on the session. 

The FAA did not explain the reasoning behind the ground stop. 

*This is a developing story.