Sunday my daughter and I were flying back to RHV from Willows after a weekend of racing. The enroute forecast reported occasional smoke due to the fires that have been burning around California and Oregon for a couple weeks. I figured the occasional smoke would be either very low to the ground or very high and, either way, being "occasional", not an issue for my flight. My husband was flying another, faster, plane on the same route as well. He took off first, then I did my run up and took off. The sky looked OK from the ground.
On climb out I could see what looked like a wall of smoke, it appeared to start around 3000'. I kept climbing. It looked like I would climb on top of the smoke and be in clear air for the flight. My husband radioed back to say he could still see the ground but there was a lot of smoke. I leveled off at 5500' and it seemed like I was just at the top of the smoke layer. The air in front of me was clear but I could only see the ground looking directly down. The hills to the west were vaguely apparent in the haze and the sun light slanted through the smoke dimly as it set.
Since I couldn't see landmarks ahead of me I practiced my instrument techniques and flew the tracks I programmed into the GPS. The GPS "track" and "desired track" information to guided where I flew. I knew at my altitude I was in no danger of flying into terrain. I was in contact with ATC and under VFR flight following but there were almost no planes flying that night. My husband radioed back to say he was nearing Nut Tree and he couldn't see Mt. Diablo with all of the smoke, or any of the familiar mountain and hill landmarks that we used for flying in the bay area. He was going to stay high until he could see something specific and then descend.
I looked around, the sun was down, the smoke was still thick starting just below my altitude. I couldn't see any landmarks or Mt. Diablo either. I had a decision to make... I could continue the flight VFR (flight visibility met VFR minimums at 5500 feet) and stay high until I could see the mountains and hills. Or I could get a pop up IFR clearance and fly the remainder of the flight IFR. I hadn't flown IFR in that particular plane before, which worried me a bit but I couldn't see the very large landmarks, which worried me even more.
I asked ATC for a pop up clearance to RHV. It was easier than I thought it would be.
Travis Approach, Arrow 55X, with request.
Go head Arrow 55X.
Approach, I need a pop-up IFR clearance to Reid-Hillview.
Arrow 55X, standby.
Arrow 55X, I have your clearance, advise when ready to copy.
I already had "CRAFT" written on my notepad.
Ready to copy, 55X.
Arrow 55X is cleared to the Reid-Hillview Airport via radar vectors, turn 150 and descend to 5000'.
I read that back and with that I was "in the system" with ATC helping keep me from flying into any solid objects in the smoke and night.
I turned to the heading and descended to 5000'. That put me directly into the smoke and true IMC conditions. The good thing was, the air was smooth in the smoke and the winds were consistent so once I dialed in good wind correction angle to stay on the heading I was given I didn't have to adjust it too often. I flew in the smoke for about 15 minutes just taking the headings ATC was giving me and knowing they were flying me east and south. If I had to keep getting vectors they'd probably vector me over the CEDES and then send me in on the approach.
I took my eyes off my scan for a moment every couple minutes and checked outside to see if I could see anything. Eventually the smoke cleared enough after passing the delta that I could see the ground and Mt. Diablo and the hills around the Livermore Valley and Sunol Grade outlined in hazy city lights. That was what I needed to see. I cancelled IFR and turned west towards the Livermore Valley. After crossing the valley I went into the Bay Area proper over the Sunol grade and was cleared to land immediately when I contacted RHV tower.
After landing my husband met me at the plane. He stayed high as planned and was able to see well enough to descend after he passed the delta. In this case both methods (IFR and VFR) worked just fine. It was a good experience for both of us.