I was trying to get Ghost running on my local Windows box and everything was going great until I got the following error:

ERROR: Unsupported version of Node
Ghost supports LTS Node versions: ^4.2.0 || ^6.9.0
You are currently using version: 7.7.2
This check can be overridden, see http://support.ghost.org/supported-node-versions/ for more info

So, basically, I'm running a version of Node greater than what Ghost supports. If you read their docs, you can override this by setting GHOSTNODEVERSION_CHECK to false. But how to do that in PowerShell? Here's how:

$env:GHOST_NODE_VERSION_CHECK = "false"
npm install --production

Boom! Good to go running Ghost locally!