## Thursday, May 26, 2011

### Fractionally-Cloudy Days

Yesterday we looked at the use of percentages in predicting the weather. Today I'll quickly run over how we can use fractions when talking about weather conditions. We teach both fractions and percentages in our Excel Math curriculum.

Do you like clouds? I like scattered clouds, and partly-cloudy days. Most of the time.

Beautiful New Mexico day with scattered clouds

But not always, especially if we are flying somewhere.

This Greek cloud over Athens made us use airsickness bags ...

CLOUD: a visible aggregate of minute water droplets or ice particles in the atmosphere above the Earth's surface.

There are special weather words associated with cloudy days. Weather forecasters notice how many 8ths of the sky covered with cloud, then use their special terms:
• 0/8ths  – Clear or Sunny
• 1/8th to 2/8ths – Mostly Sunny
• 2/8ths to 3/8ths – Scattered Clouds
• 3/8ths to 5/8ths  – Partly Cloudy
• 6/8ths to 7/8ths – Mostly or Considerable Clouds
• 8/8ths – Cloudy
Some places in the world have dramatic clouds and others do not. I will give you a couple examples so you can see what I mean.

Interesting Swedish clouds

Boring San Diego clouds

San Diego doesn't often get interesting clouds. We are so close to the ocean that we tend to get a marine layer pushed onto us instead.

MARINE PUSH: A replacement of the current air mass with air from off the ocean. Temperatures are much cooler and relative humidities are much higher.

Local residents call this June Gloom. If you come here on vacation to visit the Zoo or Sea World, you are likely (57% of the time) to see grey gloomy days instead of sunshine.

Our sunniest month is actually November. In an average year, San Diego has 68% sunshine, 3055 hours of sun and 146 clear days.

(% Sunshine = percentage of time between sunrise and sunset that sun reaches the earth's surface; Clear Day = when clouds cover less than one-third of the sky on average)

Go here to read about the San Diego Weather Year for yourself.
My favorite partly-cloudy San Diego sky, from the breakfast table at sunrise