Mine drops a lot when I am very warm and peaks when I am chilled.
The mechanism is easy:
When you are hot, your body tries to cool and the millions of arterioles in the skin open wide to allow hot blood to reach the surface to lose heat, It's akin to opening all the fire hydrants in the city at one time...and down goes the BP.
The converse happens when cold: aerterioles slam shut and prevent much blood flow to the skin and up does the BP.
I think it's part of the reason for my White Coat symndorme...all my docotr's offices arre always FREEXING, Summer and Winter.
Once I showed consistenly low BP readings with no meds in a hospital...like 105/65. The place was heated liike it was owned by Beelzebub Medical!
I lay in a puddle of sweat the whole time.
In fact thinking back a LONG time, my first BP crisis was in mid December...lots of booze, frigid weather, and an icy apartment. My BP's are always nice in Summer.