Advanced mathematics (chaos theory) proves that, however advanced meteorology becomes, it will never be possible to produce really accurate forecasts, for the UK, for more than about 5 days ahead. The Met Office staff won't commit themselves to anything more than saying that the weather in the North West will 'remain unsettled' around that period:
http://www.metoffice.gov.uk/weather/uk/nw/nw_f orecast_alltext.html
The Weather Channel does attempt to forecast up to 10 days in advance but their forecasts frequently change day by day. For what it's worth, their current forecast for 24 August is warm (21C) but with light rain:
http://uk.weather.com/weather/10day-Crosby-UKX X1230
From Wednesday onwards, you can use one of these links for the most accurate forecasts:
http://www.bbc.co.uk/weather/5day.shtml?id=238 7
http://www.metoffice.gov.uk/weather/uk/nw/live rpool_forecast_weather.html
Chris