Flight out towards Prudhoe Bay, sample plume on the way out. Spiral up at farthest point out to 24 kft, then descend back to low levels, try to locate the warm front off the coast. No clear indications from sat images or in-situ cloud obs, but frontal passage visible in Deadhorse METAR data. Pollution embedded in mid-latitude air behind the front. "Parking garage" moved north according to front by 2 deg, going back and forth in the front. Parking garage back down again behind the Brooks range to get as low as possible.