Thunderstorms will bring washout end to week from tomorrow, with more than a month's rainfall possible Worst of conditions on Friday with up to 4in (100mm) of rain forecast over the day in a weather warning Areas hit by storms could receive 1.2in (30mm) of rain in just a couple of hours between 10am and midnight But Met Office expects the second half of August will be 'drier' with 'higher than average' temperatures