It's a sweatshirt tied around your waist kinda day

Over the past weekend, I was discussing weather with friends, and lamented the adoption of Fahrenheit instead of Celsius, and the irrelevance of temperature anyway. We in the bay area are subject to a constantly changing micro-climate, requiring San Franciscans to be prepared with layers at any given time. Recently, I've been a little obsessed with weather reports, as I have access to a current one on my iMac's Dashboard, and have been deciding what to wear that day depending on the weather. I got to thinking, why not just rate the weather in terms of how many layers you will have to wear that day? On a day like today, it will most likely be in the high 80s. Now, this is normally t-shirt and tank top weather. But if you're out in the avenues, or if it's around dusk or later, you'll need to wear a long sleeved shirt or sweatshirt. Too hot for a jacket, but once the wind kicks up, it would be nice to cover your arms as well. A fall day in the low 60s? At least 2 layers and a jacket, or two t-shirts and a hoodie, etc. Anyway, just a thought.