Weather Watch

‘Red sky at night’ has meteorological might

Before the latest computer models or satellite images were available, sailors depended upon observations of the ocean and the sky to forecast weather.

I can only imagine what it was like to be in the middle of the vast Pacific Ocean on a vessel without the use of modern weather forecasting tools and instrumentation. The threat of large waves or strong winds would be a constant concern.

Out of necessity, sailors came up with sayings or proverbs such as, “distant shores loom up nearer before rain because of thinning of the air,” and if the air is humid, “rain is most frequent at the turn of the tide.”

Many of these sayings have been proved mostly untrue over the years, but some may have scientific merit. One well-known proverb seems to hold some water: “Red sky at night, sailor’s delight. Red sky in the morning, sailor’s warning.”

Not to be outdone by the Discovery Channel’s “Mythbusters,” a few meteorologists for years have studied this proverb at our latitude along the Central Coast and have concluded this saying is more often true than not.

Here is why: At our latitude, the jet stream often steers areas of high and low pressure from the west toward the east. High pressure usually produces clear weather as the air sinks toward the surface, while low pressure often produces unsettled or stormy weather.

When an area of high pressure is to our west, red sunsets are often produced because of air contaminants such as dust, aerosols, salts and smoke near the Earth’s surface. The sun’s light shines through these particulates, which scatter and greatly diminish the shorter wavelengths that reflect the blues in the visible light spectrum. This leaves behind the longer wavelengths, such as the red hues seen by our eyes.

If a sailor sees a red sunset at sea, it most likely means that the area of high pressure is to the west and moving eastward toward them, indicating clear and dry weather on the way.

On the other hand, if a sailor sees a red sunrise, this could mean an area of high pressure is to the east, with an area of low pressure following close behind. Stormy weather will likely be on the way.

Most readers would agree that today’s forecasters, including myself, are sometimes wrong despite the use of modern weather forecasting tools. With that in mind, even old weather sayings may have far more value than meets the eye.

This week’s forecast

Partly to mostly cloudy weather with high temperatures only reaching into the mid-50s will continue through this afternoon.

An omega-shaped jet stream will allow a cold air mass from Canada to push a low pressure system over our area tonight.

This system will pick up some Pacific moisture and will swing rain and low snow levels over the Central Coast late tonight into Monday afternoon.

Limited moisture will be associated with this system, and rain totals will be about a quarter to half an inch across most areas. Gale- force northwesterly winds will develop late Monday afternoon through Monday night.

The snow level is expected to drop to 2,500 feet or lower on Monday.

The heaviest snow will be across the Sierra south of Lake Tahoe, where about a half an inch of liquid water will translate to about a foot of snow above 2,000 feet.

Tuesday will be partly cloudy and dry as the northeasterly (offshore) winds develop. Temperatures will dip down into the 20s across the interior and 30s elsewhere by early Tuesday morning.

Sunny skies and cool temperatures in the 40s and low 50s are expected Tuesday afternoon, then another cool night will occur Tuesday night.

A wet weather pattern will develop next week as the mid-latitude westerly winds increase and the eastern Pacific high shifts southward.

Skies will turn cloudy on Wednesday when a much warmer weather system crosses our area Wednesday night into Thursday, with periods of heavy rain and gusty southeasterly winds. Rainfall totals with the system should range between 2 to 3 inches.

Unsettled weather will continue through the remainder of the week. Another potentially wet weather system could hit our area next weekend.

Surf and sea report

Today’s 3- to 5-foot northwesterly (300-degree deep-water) swell (with an 11- to 18-second period) will continue at this height but with a shorter period through Monday morning.

Gale-force northwesterly winds will generate a 6- to 8-foot northwesterly (300-degree deep-water) sea/swell (with a 5- to 15-second period) on Monday afternoon through Monday night.

A 948-millibar storm about 3,000 miles west of California will produce a long-period swell. This long-period, west-northwesterly (285-degree deep-water) swell will arrive along our coastline on Tuesday at 5 to 7 feet (with a 20- to 22-second period), building to 10 to 12 feet (with an 18- to 20-second period) on Wednesday.

This swell is forecast to peak on Thursday at 11 to 13 feet (with a 16- to 18-second period).

Combined with the west-northwesterly swell will be increasing southerly seas. Fairly rough ocean conditions are expected to continue along our coastline through late next week as a series of storms moves across the northern Pacific.

John Lindsey is a media relations representative for Pacific Gas and Electric Company. He is also a local weather expert and has lived along the Central Coast for more than 22 years.