The Juneau Empire, Michael Penn, Associated Press
An natural avalanche down Snow Gulch Creek covers Thane Road Thursday, Feb. 2, 2012, in Juneau, Alaska. Juneau police say snow and debris reached the tide line. The road will be cleared when it's safe.

ANCHORAGE, Alaska — Two major highways south of Anchorage were closed for the majority of the day on Thursday as crews removed snow and debris and used military-style cannons to bring down potentially dangerous avalanches.

An avalanche shut down both directions of the Seward Highway about 7 a.m. at its juncture with the Sterling Highway, the Alaska Department of Transportation said. The slide was estimated to be between 3 and 10 feet deep and 100 feet wide, considered a small to medium-sized avalanche.

Seward Highway connects Anchorage to Seward on the Kenai Peninsula. Sterling Highway, which goes to the scenic tourist town of Homer, also closed.

Both were reopened in the afternoon, said Rick Feller, a spokesman for the Alaska Department of Transportation and Public Facilities. Feller said the danger from avalanches in the area was considerable.

Seward Highway cuts through miles of mountains in Chugach State Park and Chugach National Forest.

"If you don't have to travel through the area, don't travel through the area," Feller said.

The National Weather Service said the danger escalated Wednesday with a quick warm-up accompanied by a storm packing snow and hurricane-force winds. Driving conditions along Turnagain Arm south of Anchorage were particularly hazardous, with several school bus routes closed in Girdwood.

The Chugach National Forest Avalanche Information Center said the increased danger was caused by heavy snowfall, rain and strong winds that pounded the region. Avalanche danger in some areas of the backcountry is high, said the center, which advised anyone without expert skills to keep away.

Moderate snowfall and strong ridge top winds were expected to continue Thursday in the Chugach.

Winds, which had abated in the Anchorage municipality, were expected to increase again and reach 80 to 90 mph south of the city.

The warm-up, and the accompanying avalanche danger, came on the heels of weeks of bitter cold during one of the snowiest winters on record for Anchorage. As of Wednesday, snowfall for Anchorage totaled 90.5 inches — well above the season average of 74.5 inches, said Sam Albanese, National Weather Service's warning coordination meteorologist in Anchorage.

The city is coming off the third-coldest January on record, a month where the average temperature was just 2.9 degrees.

On Wednesday, an avalanche off Mount Roberts blocked traffic on Thane Road in Juneau. Police said the road would be cleared when it is safe, the Juneau Empire reported.

Poor weather in the Gulf of Alaska also prevented the ferry Kennicott from making its trip to Yakutat. The delay was expected to last at least 24 hours.