Low Temp Gauge??

Hello, I have a 2009 Ford Focus SE. I recently noticed the temperature gauge drops while at idle and rises to normal after driving for a while. The temperature outside is average -15c. My heat seems to work ok.

Does anyone have an idea as to what the issue is?

With a thermostats, I would suspect the heat would drop while driving and not at idle. Doesn't make sense to me.

Thanks

Jon