Thousands remain without power in Bonner and Boundary counties following a massive thunderstorm which wreaked havoc Saturday evening

Avista Utilities reported that an estimated 5,887 customers were without power Sunday afternoon while Northern Lights, Inc. officials reported that an estimated 11,600 customers were without power Sunday morning.

While the Bonneville Power Administration system was back up, NLI officials were beginning to assess damage and restore power following the widespread outage.

"Members should again plan for an extended outage," the utility said on its website.

Avista, which reported about 24,000 customers region-wide without power Sunday afternoon, said its crews continue to assess the damage caused by the storm.

"We greatly appreciate our customers' patience through this event," utility officials said in a statement on its website. "Avista crews are working as quickly and safely as possible to restore service."