Complex sentence: Temperatures can be low by Hong Kong standards, varying from around 7 ° C-15 ° C on a colder day, but snow and frost are very unlikely to form (as sub-zero temperatures almost never occur).
Split into simpler sentences: Temperatures can be low by Hong Kong standards, varying from around 7 ° C-15 ° C on a colder day. Snow and frost, however, are very unlikely to form (as sub-zero temperatures almost never occur).