I think you are making the assumption that she is only presenting for
the benefit of people who have a detailed interest in the weather.
99% of the British public couldn't care if it is a plunge, plume,
ridge, trough or anything else.
As long as they know if it is going to be hot or cold.
And blast sounds like something associated with a warhead, so she may
not want to use that terminology, being a woman.