For planning outdoor events, such as group camping trips, it would be useful to be able to look at a map showing average precipitation across history for a given time of year, week or day. For example, a map showing average rainfall for the second week of March. Does anyone know of such a thing? I'm looking for a generalized tool, but if it helps the specific regions I'm most likely to use this would be northern California.
Climate.org should have what you are looking for. Their website gives downloadable maps for different times of year, and testing lots of different conditions such as rainfall.
For example, we can see from this that the rainfall in March 2016 in Florida was about 1 inch. We can compare this to New York, which had about 3 inches. We can then compare this with other months using the tools on the website.
There are many more options available on the website such as Average Temperatures, Outlooks, Drought Monitors etc
For a more general view, check out these sites;
I have used http://www.weatherbase.com/ in the past Put in a city and get monthly averages highs and lows, rain and snow stats etc. You can also drill down to a particular day but I don’t think it will do it by week.