I would also think you are talking in C as only us stubborn Americans think regularly in F
Yes I am talking °C.
I think I would like to avoid areas prone to 30 degree changes.
You don't get any warning or indications that you are about fly into such areas. They are localised and transient events. With experience you start to get a feel where there is an increased risk of it occuring, but that's about it.
My experience, and it seems it is the same as some of the other posters on this thread, is that the common conditions in which large OAT rises have been seen are:
- tropics
- over water
- nearby or recent convective activity
- flying in stratform cloud (appears as widespread speckled green wx radar returns)
The last time I experienced a large OAT rise was over the Pacific Ocean at about 20°N. We were in widespread upper level Nimbostratus cloud. There were no active cells in the nearby region and we assessed the cloud to be from decayed CBs. The radar return was speckled green. Over the space of about a minute (~10nm) the OAT(SAT) went from about -55°C to about -25°C. Fortunately our aircraft had enough excess thrust available to be able to cope with such conditions and we were able to maintain speed and Flight Level.