The convertible is still the car, not a convertible kilt(?!), GP is saying with Scottish as opposed to Californian weather there would be less changing. Say, a single open-top-weather period (two changes) per year. Or none.

(I imagine the Californian poster is changing twice per year too, just using 5-6 ties. With that reading the joke is Hey in Scotland you just keep it closed, never need any more ties.)

California weather vs Scotland weather.

They are opposite, but both are consistent.

In both cases the car's roof position seldom changes.

But, the convertible in California would have a mostly-open roof. Whereas the convertible in Scotland would have a mostly-closed roof.

Gonna go out on a limb here and guess "lousy weather".

Scottish summer - finest day of the year! ;-)

Let me guess, you don't need to look at the weather, you know it is THE day when your inbox is full at 9am of messages from most of your colleagues taking the day off?

There's even a service for it: https://www.taps-aff.co.uk/

Awesome, love the conditions "Decentish" and "Pish"