Why is there a heat wave in March? The science behind high pressure
By CBS Bay Area
This week, the Western US is facing an atypical March heat wave, bringing near-record high temperatures across many locations.
San Jose, Livermore, Napa, Concord, and many other inland areas will be within reach of the 90° mark, which would either tie or break all-time record warm temperatures for the month of March. The reason? A strong area of high pressure is building overhead.
In general, high pressure brings dry and warm weather. But why? Today, we are zooming in on the science behind high-pressure and heat domes.
High pressure in the upper levels of the atmosphere creates sinking air, think of a ceiling fan blowing air towards the ground. Sinking air dries out as it moves towards the ground. It also gets compressed, which squeezes the air and puts even more pressure on it, which heats it up.
To recap, high pressure creates sinking air, and sinking air gets drier and warmer as it moves towards the ground.
High pressure also spins clockwise, deflecting moisture and storms off to the north and keeping dry air underneath it. Sometimes, this storm track can become stuck and trap the area of high pressure in the same place for extended periods of time.
When the ground is hot and dry for a prolonged span, it dries out the soil and plants which makes it feel even hotter. The ground is now releasing heat, which rises into the atmosphere, only to be stopped by the sinking air from high pressure. This traps both the warm, sinking air and warm, rising air underneath the area of high pressure in a sort of bubble — This is known as a heat dome. And it is exactly what’s happening this upcoming week across California, the Desert Southwest, and of course the Bay Area.
In fact, this type of weather pattern is becoming more and more common in the spring. San Francisco sees an additional 20 days of above average temperatures each spring compared to the 1970s, Sacramento is 14 days and San Jose seven.
Prepare for the heat this week, and be prepared for more and more hot spring days as the years go on.
