Weather Index in Excel

The Task

Create a weather index using spreadsheet software such as Microsoft Excel.
Grab weather data online and use that data to develop a seemingly objective measure of how nice the weather is each day, month, and/or year.

Notes

I personally prefer to use a local installation of Microsoft Excel. Microsoft has a free web-based version at http://office.com/WebAppsThinks. Google also has a free web-based spreadsheet that can be found at https://docs.google.com/.

This may be the first challenge that I have produced, but don't expect it to be simple enough to complete in a couple minutes. Most future challenges will probably be a little less time consuming. I picked this for my first challenge because I had already seen the challenge (Scott Sistek's blog) and have been holding onto my solution for quite some time. You can look for data for your own region, but data for Sea-Tac can be found at the following locations:
http://komonews.s3.amazonaws.com/seatac_daily.txt
http://www.beautifulseattle.com/clisumm.htm
 

Feel Free to Comment

Try to find your own unique approach and share what you are doing in the comments section. These comments can help you and others find new ideas to explore. If you are desperate enough and can't figure out how to accomplish this task, you can always ask. I do not provide storage to those who visit my blog. If you would like to share any files, you are going to have to find your own online storage. At that point, you can provide links with your comments. I would like to point out that macros can create security risks. If possible, save all documents as a standard workbook (not macro-enabled) unless macros are vital to your solution. If you are going to download any solutions, make sure that you are not loading macros by default. If a spreadsheet includes macros, check the code before running them.
 

Follow-up

A follow-up to this exercise has been posted.