Creating Massive Grid With Loop Without Freezing?

I have been struggling with a loop of mine. The loop should create a grid, of 204,000 squares(div's). And the total would create a grid field of 340 pixels by 600 pixels. All div's are sized 1 pixel.The idea is to create a grid, that shows temperature data in a gradient style, like a weather heat map. The data is collected from temperature sensors which are connected to a database.The only problem is that because it's such a massive amount of calculations to be calculated by javaScript, the whole thing freezes. Here is a sample of my code:

Code:

function makeGrid()
{
for (var i = 0; i < 8160; i++)
{

[code]....

Another problem is, the grid should be reloaded every 5 seconds or less.Because that's the interval used by the temp sensors, and for the usage that's planned for the project, its really important that the data is constantly up to date. using another web based language are welcome, as long as they are combinable with PHP or AJAX. Or maybe there is a ready to use library that I dont know of. Couldn't find anything for jQuery.