# GRANDMA SAYS: It all boils down to science

Last week I was at the fabric store picking up some tartan for my Bay City Rollers outfit (they’re coming to town – a girl has to be prepared) when a lady approached to thank me for writing my book.

The woman holding a bolt of cheery yellow fabric told me she picked up a copy for her grandchildren a few years ago and they still refer to it and continue to enjoy it.  That’s when she asked me if I had a favourite weather saying.  That’s a tough question, but for me, one of Grandma’s gems does rise to the top: the scorched potatoes!

Grandma used to watch over us while mom and dad took care of some barn chores before supper.  Grandma would start the potatoes, then sit with us – or keep the peace between Monique and me.  Every now and again, Grandma would dart from her chair and rush to the stove – it was usually too late.  She would take the lid off the potato pot and proclaim: “Well, I guess there’s rain on the way.”

My sister and I would look at each other with wonderment, but didn’t have a clue what she was talking about.  One day, years later in Mr. Stayner’s physics class at GDHS, it all made sense.

When atmospheric pressure decreases, the boiling point of water becomes lower.  Air pressure drops ahead of a weather system that brings rain or snow.  Low pressure means there is less force pushing liquid particles to stay in a container, so they can leave or transition into the gas phase more easily.

Conversely, as pressure increases, water molecules need additional heat to gain the speed necessary for escape.  This phenomenon is due to the fact the vapour pressure of water is temperature-dependent.  It is raised as temperature increases and is lowered as temperature drops.

So when Grandma put the same number of potatoes in the same old pot and boiled them for the same amount of time, some days the water would be boiled dry.  Those were the days the air pressure was low… ahead of an approaching rain or snow system.

Grandma was right again.  Oh, and yes, we ate those potatoes anyway; nothing went to waste at the farm.  After some chopped onion and garlic, it wasn’t that bad.

Cindy Day is the chief meteorologist for SaltWire Network