My take on freezing rain - having nearly once crashed as a result of it!
1. It can be forecast - there's a specific set of circumstances where it can occur, under the 'ledge' of warm air under a warm front while flying in the cold sector. This is where you may see it forecast. However, This may not always be the case and it can be present in circumstances where it is very difficult to predict.
2. When you get it, at first it's innocuous but can build up very quickly - very quickly indeed.
3. Use of anti ice/de-ice can make things worse in clear ice. The ice melts off the leading edge, runs back and re-freezes a bit further downstream on the aerofoil section. This is worse than an even layer of ice over the whole aerofoil.
In my case, it wasn't forecast. We were being vectored into an airport in a temperate zone on a winter's day in high pressure system with the gound temperatire only a couple of degrees above freezing. We were level at 3000' above a layer of stratus and had asked for a late descent because air aircraft had engine intake anti-icing, but no airframe anti-icing and we had just completed a long high level transit and knew our airframes would be super cooled. We were told to descend to accommodate traffic going into an adjescant airport so complied. But there was drizzle in the stratus and we started to accumulate ice rapidly. We declared a Pan and aked for a climb out of the straus. This was granted, but now we found we didn't have enough power to climb, so we slowed down and immediately entrered buffet, at a speed some 60% more than the usual buffet onset. Now we were in trouble as we couldn't remain level at full power as the intake de-icing wasn't coping under there conditions.
A mayday was declared and ATC realising we wouln't make our destination offered us vectors to join the ILS at a third airport which we gladly accepted. We flew the ILS at full throttle accepting the increse in speed and made a safe landing, but hardly being able to see forward due to the ice. We were a formation of two and the wingman had only our strobes to formate on. I could see his aircraft and he was covered in a glassy sheet of ice. Luckily, he had a bit of power reserve on me.
The problems didn't end on landing as this third airfield was in another country - one to which we had no clearance to fly. And when I got out of the cockpit, I failed to see the sheet of ice coating the wing and immediately slid off - landing on the ground on my bum looking very undignified. It hurt too!
Subsequent investigation showed the conditions we were in were a very unlucky set of circumstances and had only been encountered rarely. The met office were aware of the danger and had forecast the icing risk as moderate, but not warned of rain ice as it didn't fit the classic pattern. Also, our aircraft was a brand new type and we were still learning about it's performance in icing conditions.
Rain ice - it's very very dangerous.