What you describe is one of the ways FSX handled weather. It's weather was dynamic as well, and the user can set the rate of change.
Here's an example: if you set high humidity, but with no clouds, clouds will form over time. If you set the opposite, the clouds will dissipate. Make the temperature high with no clouds, and thermals will form. Over time, clouds will form on top of these thermals. You can also import real-world conditions into the simulator and have them update every 15 minutes.
However, you cannot do what MadTommy talks about with individual high and low pressure centers, which sounds like it would be very useful.
Just MY to cents.