I've noticed that the policy on the BBC is for male weather presenters to wear suits when they present the national forecast, but to dress casually for regional broadcasts. God knows what they'd wear if we got down to the level of truly localised bulletins.
Women presenters usually opt for maternity wear. Mrs W has observed the propensity of weathergirls to get themselves in the family way, but hasn't been able to explain the phenomenon to me.
Yes, I do understand how it happens. It's the why that I'm less sure about.