Slurry bombers were helping ground crews battle the South Fork Fire in Yosemite National Park/NPS

Humidity has helped slow the spread of the South Fork Fire in Yosemite National Park, though residents of the Wawona community remained under a voluntary evacuation order.

Concerns that the flames might reach Wawona and its historic hotel, as well as the Merced Grove of sequoias, had crews working to put out the forest fire. As of Thursday morning the fire was roughly three-quarters of a mile east of the Swinging Bridge in Wawona.

Fire managers say high humidity levels Wednesday helped keep the fire, which was reported on Sunday, within the western and southern containment lines. The fire continues to slowly spread to the northeast into the Yosemite Wilderness. Air resources were to continue to assist the firefighting effort Thursday as smoke levels allow. Burning operations were possible Thursday to allow for the protection of the Wawona community and the Mariposa Sequoia Grove.

The fire is located in the South Fork drainage of the Merced River, in steep and inaccessible terrain. Crews are hiking in and setting up spike camps in an effort to utilize as much daylight as possible. Pack trains are being considered to support spike crews. The west flank of the fire is approximately 3/4 mile east of the Swinging Bridge in Wawona. The fire continues to pose a threat to Wawona, the Mariposa Grove, US Forest Service lands and a radio and telecommunications site at Wawona point. A combination of air support, direct line construction and use of natural barriers are the current tactics being implemented to meet protection objectives.

Firefighters were working to hold the western and southern flanks of the wildfire, which covered nearly 2,500 acres, while monitoring the northern and eastern edges. "Minimal Impact Suppression Tactics" were being used to manage the area of the fire, using natural barriers such as rocks or streams, trails, and other minimal disturbance methods to contain the fire.

Smoke was expected to be heavy in the fire area and adjacent communities and was likely to be very dense in Wawona in the evenings and mornings. Community members who are sensitive to smoke were advised to consult their physician and may want to remain indoors or leave the area in periods of heavy smoke.

Weather-wise, there was a threat of thunderstorm activity in the fire area as a weak low pressure system remains over the region.