Fog in parts of the U.S. from the Midwest to California prevented some flights from taking off at Phoenix Sky Harbor International Airport on Friday morning.

The Federal Aviation Administration issued a ground stop for some flights in Phoenix from 7 to 8:30 a.m. Under a ground stop, planes destined for airports experiencing adverse conditions are not allowed to take off. The ground stop has been lifted and the FAA’s status update website indicated current delays of 15 minutes or less.

As of 8:30 a.m. Friday, the flight-tracking website FlightAware.com was showing 51 delays at Sky Harbor Airport.

Phoenix, Tucson and other parts of Arizona also are experiencing a second day of heavy haze caused by a haboob that blew across New Mexico, carrying thick dust that hung in the air.

This article originally appeared on Arizona Republic: Ground stop in Phoenix delays flights. Here’s what happened