If you live on the West Coast, you're probably well aware of those stubborn summer clouds known as 'May Gray.' While they might seem annoying, their formation process is fascinating, and they play a crucial role in maintaining the region's unique biome.

'May gray' refers to the persistent gray skies that hover over the southern California coast during the month of May. This phenomenon occurs mostly during the late-spring to early-summer months, typically from the overnight to morning hours. Under the right conditions, overcast skies can extend into the afternoon or even persist for several days.

Cloudy summer mornings are crucial because they significantly impact the climate of Southern California's coastal regions compared to areas just a few dozen miles inland. The cloudy skies trap marine moisture at the surface, fostering a denser and more diverse biome.

'May gray' results from a combination of local climate and geography. On a typical 'May gray' day, a low-pressure system generates steady southeast or northeast winds that carry a dense, moist marine layer, fueled by cold ocean temperatures, to the California coast.

As the marine layer approaches land, it slows and turns east toward the coast. This cool, moist ocean flow leads to the formation of low clouds as temperatures drop in the evening. By early morning, thick clouds have moved several miles inland. If there is enough cooling and upslope lift, light to moderate drizzle may occur. The clouds often remain through the morning and dissipate as temperatures rise in the afternoon.

Occasionally, persistent 'May gray' periods occur when clouds become trapped beneath an inversion layer of warmer air. This inversion acts like a lid, allowing overcast skies to last for days.