Accessing Global Variable - DropDown List

I'm trying to pupulate a web page with javascript. I have 2 functions. One that runs on-load so I can populate a dropdown list. The second one to process the selection when the user selects an item from the list. I have a global variable in the top of my javascript that I use in the functions and as long as I set it in it's global scope, everything works fine. But what I really want to do is to pass this into the javascript running on this page via [URL]

I cannot get this to work. First here is what I have that works:
<script type="text/javascript">
weekNumber = "00"
function processSelection(sel) {.....
... [includes references to weekNumber]
.....}

function populateList() {
...
}
window.onload = populateList;
</script>
...
<select name="team" onchange="processSelection(this)">
...

I've got the code to gets the variable passed in properly:
var sGet = document.location.search;
sGet = sGet.substring(1); // Eliminate the leading "?"
var sGetPairs = sGet.split("&") //Get 1st pair
var sGetValue = sGetPairs[0].split("="); //Split it
var weekNumber= sGetValue[1]; //Save it

Where do I put this code so that I can use it to set the global variable "weekNumber"? I've tried putting this code in the populateList function. I've tried referencing it via window.weekNumber and this.weekNumber. I've spent far too many hours trying to understand this without success. Where to put this code so I can set the global variable weekNumber?