Blue skies provide sharp backdrop for airplane contrails, and they can be predicted

Since the outbreak of the COVID-19 pandemic, I do not think I have ever seen our skies so blue.

However, on Thursday afternoon and evening on May 7, I received numerous emails asking about mesmerizing white, thin clouds that were plainly visible in the skies over the Central Coast.

These clouds called condensation trails or contrails were from planes traveling up and down the West Coast on their way to and from Los Angeles, San Francisco, Seattle and overseas along with Navy F/A-18 Super Hornets from Lemoore Naval Air Station.

If your curious about contrails, here is a method to predict them.

First, you need to find and identify the aircraft that create them. To do this, there is a fascinating website called FlightAware.

This program allows you to track the real-time flight status of private and commercial flights worldwide. Click on an aircraft icon over the Central Coast and the program will tell you the aircraft type, registration, airline name, speed, and, most importantly, for its potential to produce contrails in its altitude, and here is why.

Most commercial jet airliners fly at an altitude between 28,000 and 35,000 feet — about six miles up in the sky — where temperatures are frigid.

Contrails typically form when the air temperature is at or below minus-40 degrees Fahrenheit or Celsius, and relative humidity is elevated.

At these temperatures and humidity levels, small clouds form when moisture condenses and instantly freezes around the tiny particulates found in jet airliners’ exhaust. These clouds are ice crystals and look like wispy strands of cirrus clouds.

They can evaporate swiftly if the relative humidity of the surrounding air is low and the upper-level winds are gusty. Conversely, if the relative humidity is high and the winds calm, contrails can last for many hours.

On May 7, at 30,000 feet, the air temperatures were cold, the dew point temperature — the temperature at which air can no longer hold all its water vapor — was unseasonably high. Consequently, relative humidity levels were elevated. Overall, the perfect conditions for the formation of contrails.

This leads to the question; how do we find air temperature and relative humidity so far up in the sky?

Every morning, the 30th Weather Squadron from Vandenberg Air Force Base launches weather balloons with a tiny transmitter called a radiosonde attached.

As the weather balloon climbs through the atmosphere, its transmitter broadcasts back to the receiving station readings on temperature, dew point temperature, pressure and GPS coordinates for the winds.

This data can be seen as a Skew T chart at http://weather.rap.ucar.edu/upper/vbg.gif.

The red line to the right on the chart is the air temperature in degrees Celsius, the green line to the left is dew point temperature also in degrees Celsius. On the x-axis of the chart is altitude expressed in millibars.

The air (red) and dew point temperature (green) lines start at the earth’s surface 1,000 millibars (near sea level) and climb to 100 millibars or over 50,000 feet of altitude.

Commercial aircraft usually fly around 300 millibars or 30,000 feet.

If the green line and red line are close to each other near this altitude, the air is near saturation, and the air temperature is around minus-40 degrees, contrails will inevitably form and, depending upon the upper-level winds or wind shear, can last for hours.

By the way, rockets launched from Vandenberg Air Force Base near or after sunset can produce remarkable displays of contrails and pressure waves of ice crystals.

On Nov. 7, 2015, an unarmed Trident II ICBM was launched unannounced right after sunset from the USS Kentucky, an Ohio-class ballistic missile submarine, off the Southern California coast and gave a dramatic display seen as far away as Arizona, Nevada, and even Utah.

I was in the front yard of our house in Los Osos when my daughter, Chloe, said, “Look at that!”

As we looked to the south, a broad V-shaped bluish trail of light rushed westward across the sky. Mistakenly, I thought it was a meteor. It caused quite a stir throughout Southern and Central California with its haunting display across the sky.

PG&E safety tip

As warm weather speeds snowmelt and increases river flows, the public is advised to use caution around waterways. Although California’s snowfall is below normal, runoff is expected to continue into early summer.

“Public safety is our highest priority. We encourage everyone recreating in or near water to plan at all times how they can quickly and safely escape in case of changing water flows and cold temperatures,” said PG&E’s Jan Nimick, vice president of Power Generation.

Most California rivers are fed by snowmelt, making them cold even in summer.

Simple actions such as recognizing if the water is too cold or swift, knowing your limits, wearing a life jacket and simply not entering the water when conditions are deemed unsafe can save a life. For more information, please visit www.pgecurrents.com.