By April throughout Cambodia things are starting to heat up with a marked increase in humidity as the monsoon nears. This is still a very good time for touring Cambodia, although an extra bottle of water and a cold towel might be in order for touring the temples at Angkor.
Temperatures are a few degrees higher at this time of year, averaging in the early thirties. The extra degrees and increased humidity can take its toll with busy days clambering over ruins, so bear this in mind.
Rainfall throughout Cambodia is still low at this time of year unless the monsoon rains arrive particularly early, at the end of the month.