Met Office (Scotney Castle Garden)
The key things to look for are:
Wind Speed and gusts... if wind or gusts are more than 10-12mph then it will likely be unpleasant and difficult in a single scull. If you have a double or quad crew organised and your all experienced
and competent then it may be ok. up to 14-15mph... Anything more and it's unlikely you will be going out so call your crew members.
Wind Direction... If Wind from East then Dam Wall may offer some protection. If Wind from West then do not go within 500metres of Dam Wall as wind will blow you onto the concrete Dam.
Air Temperature... if cold wrap up warm
Water Temperature... if low (Nov-April) then never boat alone. If ice on reservoir do not go out.
Also look at forecast at BBC http://www.bbc.co.uk/weather/2645005
If the weather forecast deteriorates then make the appropriate risk assessment... size of boat, competency of crew, water and air temperatures. If in doubt do not go out. If thunderstorms are forecast then again do not go out.