On the BBC, all the weather presenters are from the Met Office, so in between reports they're probably looking meteorological maps, forecasts and checking predicted weather patterns using proprietory software.
ITV's forecasts are sponsored both nationally and regionally and many of the ITV regional presenters are either amateur forecasters, naval trained, or ex-Met Office employees.
So between forecasts, the ITV weather reporters normally spend their time looking at the relative dampness of seaweed, checking to see if the cows are lying down, or holding up those toy windmills to see which way the wind's blowing.
They can also be seen checking through the latest River Island catalogue to latest developments in ugly, ugly, ugly, ugly suits.