Casey Pozdolski of Los Osos wrote. “I’m mountain biking the Cuesta Grade, and I’m curious what causes the terrible gusts of north wind? The first mornings have been so bad that they can knock you off your bike if you’re not careful! Curious to know if this is a model that will continue? »
I received many other emails commenting on these winds from Santa Lucia (northeast).
As far as the weather is concerned, this year has been the year of the Santa Lucia winds. They were responsible, with a massive high-pressure dome, for the Death Valley-like reading of 122 degrees Fahrenheit at Solvang and 120 degrees at Cal Poly, beating the previous campus heat record of 112 degrees set in September. 1971. San Luis Obispo, Paso Robles and Santa Ynez airports all reported a high of 117 degrees on Sunday, September 6. That day, I turned 60; a day that I will never forget.
So why the stronger than typical Santa Lucia winds this year? For starters, wind speed and direction are two of the most difficult yet critical weather factors to model and understand.
In general, winds develop because of the uneven heating of the Earth’s surface by the sun, which produces pressure differences. Air will flow from areas of high pressure to areas of low pressure. Think of an air leak from a bicycle tire (high pressure) flowing to the atmosphere (low pressure).
In my daily weather forecasts, I often call these pressure differences gradients. The steeper the pressure gradients, the stronger the winds. So it would seem that if you have high pressure in the north and low pressure in the south, then the winds would blow from north to south. However, that is not what is happening. Earth’s eastward rotation on its axis deflects moving air from its original path in the free atmosphere. The free atmosphere is above the frictional influence of the Earth’s surface.
The airflow is deflected to the right of its intended path in the northern hemisphere and to the left in the southern hemisphere.
The apparent force responsible for the rotation of the wind is called the Coriolis effect, named after Gaspard Gustave de Coriolis, a French scientist who worked out his mathematics in 1835.
Think of it this way: even though all areas of the Earth’s surface complete a full rotation every 24 hours, the equator – the thickest part of the Earth – must travel just over 1,037 miles per hour to circumnavigate the globe in one go. daytime.
As we travel north or south of the equator, the relative speed of rotation around the Earth decreases.
At our latitude along the central coast, the speed is 850 mph. In Chicken, Alaska, where I spent time mining gold, it’s about 454 mph, and at the North Pole it’s less than 1 mph.
Last week saw rain, this week it will be dry with cool autumn nights and mild mornings…
As we move into fall, the days get shorter, with less sun and cooler temperatures. On a chronological basis in the fall, a zone of high pressure forms on the surface of the Great Basin – the space between the Sierra Nevada range in the west and the Rocky Mountains in the east – and begins to dominate our coastal climate.
This condition typically produces Santa Lucia (northeast) winds, especially during the night and morning.
These winds flow from land to the Pacific and bring relatively dry air to our shoreline, pushing the marine layer far out to sea, leaving behind sparkling clear visibility along our beaches.
During the fall, coastal temperatures often exceed those in the interior.
Far from the coast, cooler temperatures have already caused some leaves to change color.
Another sure sign of the fall is the increase in the number of people walking around in coats late at night and in the morning.
The other day someone mentioned that it felt more like fall, even though the temps are still in the 70s. He said the air was different, drier and more like what he would experience in the Sierra Mountains than to a summer along the Central Coast, even though the temperatures were about the same.
He is right! The air is drier due to low humidity. As the air mass moves offshore, it descends from the California Coast Mountain Ranges and then heats up due to compressional heating. As a result, the relative humidity decreases. This lower level of humidity makes it dry and cool, more like fall than the heavier air of summer.
High pressure systems over the Great Basin have been persistent and more robust for reasons unknown to me, possibly due to the current La Niña condition which tends to push Jetstream/upper level winds higher north into the Pacific Northwest. Historically, this tends to result in below average rainfall for the central coast.
John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and media relations representative. Email him at email@example.com or follow him on Twitter @PGE_John.