Google trends v Google keyword tool... i'm confused

I have a site which brings in a good amount of visitors each day and on google trends my keyword reflects this. Now i’m thinking of starting a new site with a new keyword and on the trends tool it shows that i’d get roughly around the same amount of traffic as i am on my current site, awesome yeh? but when i go to the keyword planner tool it only shows a few hundred monthly searches, where as my keyword for my other site shows over 100,000 monthly searches.

This got me thinking about which tool i should be following. My current site shows a good amount of volume on google trends AND on the keyword planner tool, yet the other keyword i tried today for my new site shows similar results on the trend tool but poor on the keyword planner tool.

Any advice?