Weather Watch

How winter weather in SLO County plays a role in the worst flu season in years

As we head into the heart of one of the worst flu seasons in years, I have always wondered why it peaks during the winter months in the northern hemisphere. In the tropics, the rate of infection is more constant throughout the year. In the United States, the peak of the flu season usually occurs around February, and perhaps here’s why.

Coughing or sneezing by infected individuals can spread the flu by water droplets, which contain the virus from their throats, mouths and noses that are suspended in the air column (aerosol).

These droplets are tiny and can remain in the air for extended periods if the relative humidity is low enough. Like a rumor, this virus can jump from person to person in an efficient manner. Frightening to think that this bad flu season hits on the 100-year anniversary of the 1918 “Spanish Flu” pandemic, a particularly deadly strain of the virus killed an estimated 675,000 people in the United States — or around the same number killed the Civil War!

There are quite a few hypothesis/theories on why we see a higher rate of infection during winter, and I’m sure they all contribute to the spread of this highly contagious virus.

To start, we all tend to spend more time inside with the windows closed during the winter months to stay warm.

Consequently, we breathe the same air as someone who has the flu. Schools are in session and workers are less likely to take vacation during the winter months, which tends to keep more of us physically closer to each other. When young children, who naturally have a lower level of immunity, go to school and become infected and contaminate their parents, which in turn spreads the virus to their coworkers. The influenza virus left on a doorknob in an office building has the potential to contaminate the entire workforce over the course of the day.

These and many other reasons probably all contribute to the virus’ spread, but the weather may also play a significant part.

You see, the colder air of winter can hold less water vapor. Dryer air allows water droplets that carry the virus to evaporate faster, leaving the germs suspended in the air column where they can circulate unabated. In higher humidity environments, water vapor can condense on the virus, like the silver iodine particles used in cloud seeding, which in turn makes it heavier and more likely fall to the ground.

Unfortunately, a massive ridge of high pressure over California will continue to produce night and morning Santa Lucia (northeasterly) winds. Air from the higher elevations of the Santa Lucia Mountains will flow downward along the mountain slopes toward the Pacific Ocean, pulled by the never-ending force of gravity. As the air mass descends, it warms and becomes bone dry by the time it reaches the valleys below. This condition will produce low relative humidity levels and may lead to a higher number of people infected by the flu.

Here are some tips to avoid the flu from the Centers of Disease Control and Prevention. The single best way to prevent seasonal flu is to get vaccinated each year.

1. Avoid close contact with people who are sick. When you are sick, keep your distance from others to protect them from getting sick, too.

2. If possible, stay home from work, school and errands when you are sick to help prevent spreading your illness to others.

3. Cover your mouth and nose with a tissue when coughing or sneezing.

4. Washing your hands often will help protect you from germs. If soap and water are not available, use an alcohol-based hand rub.

5. Avoid touching your eyes, nose or mouth. Germs are often spread when a person touches something that is contaminated with germs and then touches his or her eyes, nose or mouth.

6. Practice other good health habits. Clean and disinfect frequently touched surfaces at home, work or school, especially when someone is ill. Get plenty of sleep, be physically active, manage your stress, drink plenty of fluids and eat nutritious food.

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at or follow him on Twitter: @PGE_John.

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