UPDATE: 8 p.m. Sept 18:
The Haystack Fire was about 5,000 acres on Saturday evening—about twice its size the day before—according to the Jefferson County Sheriff's Office. Pre-evacuation notices remain in place south of Boulder for residents south of the Boulder River and Cattle Drive Lane, west of state Highway 69 and north of, and including, the Boulder Hot Springs, and west of Boulder for "the Depot Hill Road area north of I-15 including the Silver Bell Road area and Boomerang Gulch."
Strong, shifting winds throughout the afternoon at times blew the fire's smoke plume directly over Boulder and, at other times, west of Boulder over Depot Hill. Just after sunset, winds from the west were blowing the smoke to the east of the fire, south of Boulder.
UPDATE: 5 p.m. Sept 18:
A pre-evacuation notice for areas near Boulder threatened by the Haystack Fire has been expanded to cover Depot Hill, immediately west of Boulder.
The Jefferson County Sheriff's Office stated that the area includes "the Depot Hill Road area north of I-15 including the Silver Bell Road area and Boomerang Gulch," in addition to the area south of Boulder already covered under the notice.
High winds feeding the fire initially blew a large plume of smoke northeast of the blaze, obscuring the sky over Boulder and the upper Boulder Valley toward Muskrat Creek, but by 4 p.m., the wind was blowing the plume north, directly across Interstate 15 and over Depot Hill west of Boulder.
Along Patty's Lane, off of Little Boulder Road and in the original pre-evacuation area, Matthew and Colleen Wilson were preparing on Saturday afternoon to evacuate their home if ordered.
"We were ready for it. We knew what we needed to grab," Matthew Wilson, 33, said, as he worked to clear brush and other flammable material from around the house, which he said he and Colleen built about a year ago.
Matthew Wilson said that he wasn't sure where he, Colleen, their 4-year-old son, four dogs, a cat and fish would go if ordered to evacuate, but that he had some places around Boulder in mind.
As they packed a camper trailer hitched to a pickup in front of the house, the plume of smoke loomed overhead, dotted by air tankers circling the sky.
"How do you decide what to bring and what to leave?" Colleen Wilson, 35, said, recalling that she evacuated from the same area as a child in 2000.
She said that her sister and parents live on adjoining properties and were trying to figure out how to evacuate, among other things, as many as eight horses. With the help of friends and neighbors, she said, she believed they had it figured out.
"I like that even though the world's so ugly right now, with something like this, everybody pitches in," she said.
At least three air tankers were flying in loops over Boulder by mid-afternoon, alternating fire-retardant drops on the hillsides immediately south of and along Cattle Drive Lane just outside of Boulder.
In a text message just before 3 p.m., Beaverhead-Deerlodge National Forest Public Affairs Officer Catherine McRae wrote that "resources are staged for fighting fire growth due to these critical fire conditions with gusting winds of 50 mph."
She wrote that a variety of local, state and federal crews and resources, including a variety of aircraft, are working the fire.
"Predicted moisture tonight in the form of snow/rain may greatly alter this fire situation," she wrote.
The National Weather Service predicts a 90% chance of precipitation in Boulder on Sunday.
UPDATE: 1 p.m. Sept 18:
The Haystack Fire has ignited spot fires northeast of Elder Creek, closer to Boulder than this summer's Gatlin Gulch Fire. The Jefferson County Sheriff's Office issued a pre-evacuation notice for residents south of the Boulder River and Cattle Drive Lane, west of state Highway 69 and north of, and including, the Boulder Hot Springs.
Those residents "should be prepared to evacuate soon due to the Haystack Fire. If you feel unsafe, or if you think you will need extra time to leave, you should do so now," the Sheriff's Office said in an announcement posted on Facebook.
Doug Dodge, the county fire warden and disaster and emergency services coordinator, said in a text message around 1:30 p.m. on Saturday that "structure protection is ongoing" at the mouth of the Little Boulder River valley south of the Jefferson County fairground.
Dodge wrote that the potential for a threat to Boulder itself was "unclear," and that private property that could be imminently at risk was covered under the pre-evacuation notice immediately south of town.
"But with fire anything is possible," he wrote, adding that the "timing and necessity for actual evacuation is also quite variable."
For assistance evacuating, Dodge and the Sheriff's Office said, call the American Red Cross at 1 (800) 272-6668.
UPDATE: 12:30 p.m. Sept. 18:
Infrared mapping of the Haystack Fire conducted Friday afternoon showed the fire to be about 2,489 acres at that time—down from Thursday's ground-based estimate of about 2,600 acres.
However, strong winds have caused increased fire activity and sent a large plume of smoke into the sky above Boulder and the upper Boulder Valley on Saturday, casting a haze over the town and darkening the sky.
The night before, on Friday evening, smoke filled the valley floor, clogging the air in and around town and turning the setting sun into a dim, orange dot.
Original story, 4:30 p.m. Sept. 17:
The Haystack Fire southwest of Boulder has grown to an estimated 2,600 acres—an increase of about 900 acres so far this week—and dangerous fire conditions, including strong winds, through Saturday night could cause extreme fire behavior and growth to the northeast and east.
The U.S. Forest Service on Friday issued an area closure spanning from Interstate 15 on the west to Whitetail Road on the east, and from Whitetail Reservoir to the south to the top of Galena Gulch, and including the North Fork Road, to the north.
On Friday morning, Jefferson County alerted residents living from the Boulder River south to the Boulder Hot Springs, and west of state Highway 69, "that extreme winds are forecasted to impact the Haystack Fire today and Saturday."
The message, which was shared online, said that the situation was not an "immediate emergency" but that "residents should be prepared to take safety precautions should the fire impact those receiving this message."
Late Thursday night, the Jefferson County Sheriff's Office announced that Little Boulder Road was closed at West Creek and that the North Fork road from Little Boulder to Galena Gulch was entirely closed. Last week, the Beaverhead-Deerlodge National Forest, in which the fire is burning, closed trail 778, from Eureka Mine to Moose Creek, and Trail 4082, the Haystack Mountain Trail.
The National Weather Service issued a red flag warning, indicating dangerous fire conditions, from 1 p.m. Friday to 9 p.m. Saturday. The agency predicts low humidity and wind gusts of up to 60 mph during that time.
"Saturday will likely be complex and tough days for our men and women on the ground," the forest said in a Facebook post on Thursday night.
The U.S. Forest Service became aware of the fire on July 31, while fighting the Gatlin Gulch Fire that ignited on July 30, and forest officials believe the fires were both ignited by lightning on the same day. The fire smoldered for weeks at around a few acres before intermittently growing throughout late August, experiencing occasional flare-ups but remaining smaller than 500 acres until two weeks ago. By late afternoon Aug. 8, the head of the fire was in the upper reaches of the Buffalo Creek drainage off of the Little Boulder River, according to Shane Martin, the assistant fire management officer for the Butte Ranger District of the Beaverhead-Deerlodge National Forest.
The fire's slow growth early on, officials said, was due to the terrain in the area being mostly rock and large boulders with occasional vegetation, rather than a densely timbered forest where the fire could explode. It is now burning in more fuel-laden terrain.