Without question, the authority on eclipse weather is Jay Anderson. Read his expert analysis here.
Web sites with up to date weather data.
- NOAA climatic search tool for past weather statistics
- Satellite page: RAP Real-Time Weather
- Weather Central
- Weather Underground - also includes excellent historical weather tool
- EOSDIS Worldview - full globe view of clouds
Time specific data is best. Generalizations of the day can be misleading. Most of the central part of the USA will experience totality around local noon when the Sun is highest in the sky. This is often a time when weather data is recorded. It helps if you can figure out when the data was recorded to know just how close to eclipse time it might actually be.
When studying weather maps the key is to remember that you want to forecast where the clouds are going to avoid them. The further out into the future you forecast, the less accurate you are going to be in this task. Computer models that look at such things have been developed and one of the best for astronomers is a tool known as the Clear Sky Clock. This is a cool tech tool and may require a bit of time to figure out how to use it best. Our local astronomical society uses the Clear Sky Clock and it has been fairly reliable at predicting clear holes for observing sessions. The idea would be to find observatories and astronomy clubs along the line of totality who have Clear Sky Clock links. From them you could learn about possible observing sites.
Or you can go with plan B...
|Plan B: Consult a fortune teller|