Try this url: http://dxinfocentre.com/tropo.html
This guy, William Hepburn, takes all sorts of info into consideration and has a ducting forecast for the world.... including North America. It is usually right on the money for me in Central Kentucky....
How does the weather affect WHAT reception? The radio spectrum is huge and weather affects parts of it quite differently as do seasonal changes and solar activity. Such a vague question opens up a library of answers, a real can of worms, so as always I say ask a specific question for more specific answers.
Already they're way out in left field as you can see, "skip" is in no way related to the "crappy reception" you asked about. Perhaps you should rephrase the question and tell us what you mean by "crappy" to begin with.