Weather Watch

Exploring the meaning of an Indian summer

The weather of San Luis Obispo County can be difficult to forecast and can change drastically from one day to the next, or from one part of the county to another.

After the rain and cool weather during the last week of October, the first few days of November saw abnormally warm temperatures, with highs reaching into the high 80s and even low 90s, breaking records throughout our region.

Many local folks referred to this as our “Indian summer,” which from a meteorological standpoint refers to a period of above-normal temperatures, after a spell of cool weather during autumn.

As so often occurs during this season, an area of high pressure will build at the surface over the Great Basin and will produce northeasterly (offshore) winds, especially during the night and morning hours.

These winds often bring relatively dry and warmer air to the county. Last week’s ridge of high pressure was referred to as a “dirty” ridge because it wasn’t quite strong enough to scour out all the upper-level clouds and haze along the beaches.

There has been a lot of research on where the term “Indian summer” originated.

While no one knows for sure, it may have been first recorded in the late 1700s by a New England farmer named J. H. St. John de Crèvecoeur, who wrote in a letter, “Then a severe frost succeeds which prepares it to receive the voluminous coat of snow which is soon to follow; though it is often preceded by a short interval of smoke and mildness, called the Indian Summer.”

The phrase may have come from the fact that many American Indian tribes deliberately set fires to promote a diversity of habitats.

While fire is often viewed as destructive, the truth is that it is a necessary part of nature.

Along the Central Coast, Bishop pine groves thrive on periodic burns as they need heat in order for the pine cone seeds to germinate.

The burning was useful to divert deer and other big game into small, unburned areas for easier hunting.

As the days became shorter during the fall, the Indians discovered that deer, especially bucks, were preoccupied with the rut and less cautious than usual.

The early European settlers in the country, witnessing the smoke and hazy conditions along with the greater amount of hunting activity by the tribes during autumn, probably associated this weather phenomenon with the Indians.

The common reference to the term “Indian summer” over the years has increased. This could very well be associated with a warming climate, which is a sad irony.

This week’s forecast

A weak 1,015-millibar surface low pressure system produced scattered sprinkles throughout San Luis Obispo County and light rain south of Cuesta Grade in many areas Saturday afternoon.

Areas of ground fog will burn off quickly this morning, leaving behind partly cloudy weather.

An energetic cold front will cross California from northwest to southeast through the day and will pass the Central Coast between 2 and 8 p.m. with rain and moderate to fresh (13 and 24 mph) southerly winds.

Rain will turn to showers north to south by tonight, ending by Monday morning.

Rainfall totals with this fast-moving weather system will range between a tenth to a half of an inch.

Higher precipitation totals are expected across the coastal mountains. Snow is forecast above 5,000 feet north to 6,500 feet south by tonight.

The main effect of this weather system will be a steep pressure gradient developing along our coastline. This gradient will produce strong to gale force (25 to 38 mph) northwesterly winds, cooler temperatures and partly cloudy weather Monday and Tuesday.

A slight chance for rain is forecast Tuesday night. However, most of the settled weather should remain north of our area.

Skies will clear by Wednesday morning as high pressure builds over the Great Basin. This condition will produce gusty night and morning northeasterly (offshore) winds and generally clear, dry and warmer weather through the remainder of the week into next weekend. In other words, another round of “Indian summer” conditions.

Surf and sea report

This morning’s 5- to 7-foot northwesterly (300-degree deep-water) swell (with an 11- to 13-second period) will decrease to 4 to 5 feet by this afternoon.

Combined with the northwesterly swell will be 2- to 4-foot southerly (195-degree shallow-water) seas today.

Strong to gale force (25 and 38 mph) northwesterly winds will produce a 7- to 9-foot northwesterly (310-degree deep-water) sea and swell (with a 5- to 12-second period) Monday through Tuesday, decreasing to 6 to 8 feet by Wednesday.

A 6- to 8-foot northwesterly (290-degree deep-water) swell (with an 8- to 12-second period) is forecast along our coastline Thursday and will remain at this height and period through Saturday.

A long-period westerly swell could arrive along our coastline Nov. 17.

Seawater temperatures will range from 56 to 58 degrees through Monday morning, decreasing to 53 to 55 degrees Monday afternoon through Wednesday.

Conservation tip

Follow these tips to save on energy costs:

Caulk windows, doors and anywhere air leaks in or out. Do not caulk around water heater and furnace exhaust pipes. For more energy-saving tips, visit www.pge.com.

John Lindsey is a media relations representative for Pacific Gas and Electric. He is also a local weather expert and has lived along the Central Coast for more than 23 years. To subscribe to his daily weather forecast or ask him a question, e-mail pgeweather@pge.com.

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