Narrative:

Cruising on autopilot (ap) at 9;000 direct ZZZ1 about 30 nm southwest of the VOR; I asked ATC for a deviation to the right to avoid an area of heavier precipitation; which they called out to me and I could see on my [GPS weather display]. Once clear of that heaviest area; I turned back north direct ZZZ1; and from ZZZ1 turned direct ZZZ2. I had been in and out of the bottom of the ceiling at 9;000 MSL; no ice and mostly smooth. Near ZZZ1 I started to encounter a lot more turbulence and entered solid IMC; in snow and clouds but still no icing. I was keeping an eye outside to watch in case I needed to ask for lower if evidence of icing began. ATC called and asked me to maintain 9;000 and repeated the altimeter setting; and I scanned and saw that I was descending through 8;600 MSL; and that the ap had turned off; probably due to the turbulence. It does have an alarm when this happens but I did not hear it. At that point I raised the nose to climb back to 9;000; but when I looked over at the airspeed indicator (asi); it was dropping rapidly below 80 knots. Not wanting to stall in IMC; I lowered the nose substantially. At this point my scan was uneven and not making sense. I have read a lot of accounts of pilots who are rapidly overcome in situations like this. At that point I decided that the safest course of action would be to continue to descend rapidly to what I knew was warm VMC below me. I lowered my landing gear; started a rapid descent to around 4;000 MSL; where I broke out of the snow and clouds and could reorient myself. ATC advised me of closest local airports and asked about assistance; I asked them to stand by. Once I was back in control and everything was looking normal; I flew on for a while; and continued on to my destination at 7;000 MSL; which from that point would keep me in VMC. ATC asked me about the nature of the problem and I told them that I lost my ap in IMC and had loss of control.it is clear in hindsight that the reason I was seeing the drop in the asi was that the pitot was being plugged with ice or snow or water. I should have had the pitot heat on but did not. The rest of the instruments could have shown me that; if my scan had been good; but I was only intermittently scanning while the ap was flying in cruise. While my reaction was certainly a way to stay safe; it may have been an overreaction. However; I was tired after a long day and knew I was not at my best; and I wanted to get somewhere safe quickly. I was far from any busy airspace; and [advising ATC] and descending did not cause a scramble to move other aircraft; as far as I know.

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Original NASA ASRS Text

Title: A BE36 pilot reports encountering snow and turbulence at 9;000 feet causing an autopilot disconnect that is not noticed. ATC does notice and a climb back to 9;000 is initiated before very low airspeed is detected. A rapid descent to 4;000 feet is initiated and ATC is advised. Lack of pitot heat was the likely cause of the low airspeed indication and the flight is able to continue to destination.

Narrative: Cruising on Autopilot (AP) at 9;000 direct ZZZ1 about 30 nm southwest of the VOR; I asked ATC for a deviation to the right to avoid an area of heavier precipitation; which they called out to me and I could see on my [GPS weather display]. Once clear of that heaviest area; I turned back north direct ZZZ1; and from ZZZ1 turned direct ZZZ2. I had been in and out of the bottom of the ceiling at 9;000 MSL; no ice and mostly smooth. Near ZZZ1 I started to encounter a lot more turbulence and entered solid IMC; in snow and clouds but still no icing. I was keeping an eye outside to watch in case I needed to ask for lower if evidence of icing began. ATC called and asked me to maintain 9;000 and repeated the altimeter setting; and I scanned and saw that I was descending through 8;600 MSL; and that the AP had turned off; probably due to the turbulence. It does have an alarm when this happens but I did not hear it. At that point I raised the nose to climb back to 9;000; but when I looked over at the Airspeed Indicator (ASI); it was dropping rapidly below 80 knots. Not wanting to stall in IMC; I lowered the nose substantially. At this point my scan was uneven and not making sense. I have read a lot of accounts of pilots who are rapidly overcome in situations like this. At that point I decided that the safest course of action would be to continue to descend rapidly to what I knew was warm VMC below me. I lowered my landing gear; started a rapid descent to around 4;000 MSL; where I broke out of the snow and clouds and could reorient myself. ATC advised me of closest local airports and asked about assistance; I asked them to stand by. Once I was back in control and everything was looking normal; I flew on for a while; and continued on to my destination at 7;000 MSL; which from that point would keep me in VMC. ATC asked me about the nature of the problem and I told them that I lost my AP in IMC and had loss of control.It is clear in hindsight that the reason I was seeing the drop in the ASI was that the pitot was being plugged with ice or snow or water. I should have had the pitot heat on but did not. The rest of the instruments could have shown me that; if my scan had been good; but I was only intermittently scanning while the AP was flying in cruise. While my reaction was certainly a way to stay safe; it may have been an overreaction. However; I was tired after a long day and knew I was not at my best; and I wanted to get somewhere safe quickly. I was far from any busy airspace; and [advising ATC] and descending did not cause a scramble to move other aircraft; as far as I know.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.