I've been studying the weather lately and even got myself a copy of "Essentials of Meteorology" which I have been slowly working my way through. I however am getting stuck of something that will seem very basic to others.
To my knowledge high pressure systems are dominated by cooler / colder air which subsides and stops cloud formation, while low pressure if due to surface convergence allowing warmer air to rise and condense into cloud.
I am aware that colder air is denser, therefore exerting more pressure on the surface whilst warmer air is the opposite. I have also been reading on air masses and fronts and I know that a cold front like Perth is about to experience is an advancing cold air mass overtaking warmer air and wedging it aloft.
My question is: In the below thickness / mlsp chart shouldn't the colder air mass (that I've shaded) be a higher pressure compared to it's surroundings? and more confusing for me is why it's actually a low pressure towards to bottom and just ahead of where the front would be is higher pressure, which In my head should be "warmer" and seem's a little back to front
My thinking is that the High at the air mass is only 1008hpa so it's still a little lowish anyway and also the low pressure within the colder air mass may be to do with moisture content which I think I may be over looking.
Is this a case of me over simplifying the "high pressure has colder air while low pressure has warmer air" idea?
Thanks for any help at all and sorry if the question seems a bit convoluted.