Weather Watch

Wind and ocean current terms can set your head spinning

A Davis Vantage Pro2 weather station on the Lindsey rooftop in Los Osos can measure wind direction and speed
A Davis Vantage Pro2 weather station on the Lindsey rooftop in Los Osos can measure wind direction and speed

A common source of confusion is wind and ocean current direction.

For example, if a wind vane reported northerly winds, does that mean the winds are out of the north or out of the south? Well, from the earliest of times, wind direction has always been reported from which it originates. In other words, a southerly wind comes from the south and blows to the north.

Believe it or not, ocean currents are reported in the opposite direction.

It is uncertain when this convention began, but ancient populations probably associated winds with physical landmarks, such as mountains or oceans. I’m sure, great numbers of folks associated with agriculture noticed the differences in weather due to the direction of the winds.

Winds coming from the ocean were often mild and moist, while winds coming from the mountains could be hot and dry. Perhaps it could be the downwind smell of an approaching fire or possible food. It may be even more basic than the above reasons.

The best way to determine wind direction is by feeling it on your face. Even a slight turn to the left or right causes a change in sensation on your eyes and cheeks. If you ever noticed, cows and other grazing animals will often turn into the wind.

It wasn’t until Aristotle wrote Meteorologica at around 340 BC that Cardinal headings (which include north, south, east and west) were used to describe the wind direction.

Along the Central Coast, the wind direction has a profound effect upon our weather. Santa Lucia or northeasterly winds blow from the Santa Lucia Mountains toward the ocean, and usually produce clear, warm and dry weather.

Northwesterly winds, on the other hand, blow from the Pacific Ocean through our coastal valleys and over our mountains. They often produce coastal low clouds, cooler temperatures and higher humidity levels. Southeasterly winds are sometimes referred to as prefrontal winds and are often a precursor to stormy and wet weather.

The other source of confusion is ocean current direction, especially for landlubbers who don’t often venture out to sea and stumble on the concept of “current direction.” Ocean currents are reported opposite of wind direction.

Since wind vanes and sailing ships have been around for thousands of years, you would think there’d be a clear explanation for why wind and current directions are reported opposite from each other, but I couldn’t find one. I suspect that most of the time ocean currents push ships toward obstacles downstream and “sets” your vessel while docking; more so than the winds.

Anyone who has spent time at sea may have experienced ocean waves that ran into strong ocean currents counter to their direction. When this happens, waves can suddenly increase in height, producing steep forward wave faces and deep troughs. Old salts often refer to these waves as “holes in the sea.”

One convention that is constant in reporting directions of wind and current: The wind and current direction are indicated as “true directions” and not “magnetic directions.” Magnetic declination is the angle between magnetic north and true north. At this time, the magnetic variance along the Central Coast is around 15 degrees.

A weather station that reports and records wind direction and speed is a wonderful way to teach students about the atmosphere. Many accurate and reliable wireless weather stations that report wind and other parameters, such as temperature, humidity and rainfall, along with communications modems for remote viewing and archiving can be purchased for less than $1,000.

If you’re an educator in our public schools, you can apply for a PG&E Bright Ideas Grant. These grants fund innovative classroom projects about energy, conservation, environment, climate and weather. They are designed to inspire the bright ideas of the future and create exciting ways for the next generation to learn and succeed in science, technology, engineering, and mathematics (STEM).

The Bright Ideas Grants program provides $1,000, $2,500, $5,000, and $10,000 grants for K-12 public schools and Community Colleges to develop projects to support solar projects, environmental programs, energy or science-related field trips, green your school projects, or professional development programs.

Applications are due Nov. 1, 2014. For more information and to apply online, click here