The fire crept to within a mile of a mobile home park in the Paradise Ranch area but officials said there was no immediate danger to residents and no evacuations had been ordered.
The blaze has charred at least 27-thousand acres, more than 43 square miles, since it was sparked on Labor Day.
Firefighters have worked to keep the fire from jumping to the east side of Interstate Five, where Paradise Ranch Mobile Home Park residents have watched with fingers crossed.
Thursday morning it looked as though their homes were safe. Officials said the Day Fire was 30 percent contained and all but two lanes of the major freeway were open to traffic.
More favorable firefighting weather was also moving in across the Pacific Northwest, where many of this season's roughly 82,000 wildfires have done their damage.
The National Interagency Fire Center in Boise, Idaho reported Wednesday that 8.6 million acres, or 13,600 square miles, had burned, setting a 45 year record.
But with the cold front moving into the Pacific Northwest set to drop temperatures 20 to 30 degrees across Washington, Oregon, Idaho and Montana by the weekend, the flames of this season may finally start to die down.