The Apogee Algorithm

Many fell walkers will be aware of Naismith's Rule for calculating how long a route should take.
Many bar room philosophers will be aware of Murphy's Law.
Anyone watching Brexit would do well to remember Acton's dictum.

But today I give you my own Apogee Algorithm. Used for calculating when the heavens will open if the forecast is indeterminate but threatening.
Calculate the point at which you will be furthest from shelter. This may not be the furthest point of your walk from your destination, it may be fairly early in your day but in exposed country. It may be just after you've ascended something that can't be descended when it rains.
Consider all these variables - then factor in your decision to only wear a lightweight mid-layer because "it'll hold off for a while".
Multiply the likelihood of a soaking by increasing factors the further North you live in the UK (* if you happen to be in the Lake District double the likelihood of any final result - there's a reason for all those lakes...)

Today a gentle wander with Missy after a couple of hours in the gym became a sodden trudge with little warning. I had plenty of time to consider my choices.

Fortunately (see extras) Missy is an expert in finding the joy in absolutely everything!