I use a combination of:
www.wunderground.com
www.weather.com
www.accuweather.com
www.wunderground.com is my favorite.
Weather Crystal Ball
"I recently discovered the National Weather Service's site. I haven't used it much yet, but it's the official site. It also provides a long-range forecast going out several months saying whether precipitation and temperatures are expected to be above/below/at normal. (For July, August, & September, both are supposed to be normal for the upper east coast.)
Link to National Weather Service"
I think long-term weather forecasting, ie more than a month ahead, falls into the same category of informative bollocks as astrology.
All of the long-term weather forecasts in the last couple of months of last year failed to predict the cold winter the US Midwest and Northeast endured, so I wouldn't rely too much on any predictions for July, August and September.
Wettest June on record and the month isn't even over yet.
The weather gods must be seriously pissed - time for a bike sacrifice to appease them, maybe?