If you live in Southern California, you’re familiar with the overcast skies and cool days associated with late spring and early summer. But for those of you unfamiliar with terms like “June gloom”, “May gray”, “no-sky July”, and my personal favorite – “Fogust”- let me welcome you to the least happy time of the year for SoCal natives.
As spring fades into summer, and the once green scenery starts to take on a brownish tint, low-lying stratiform clouds like to make themselves comfortable along the coastal cities here in Southern California. Bringing fog, mist, and sometimes an early morning drizzle, the clouds seem to compliment the drowsiness of those staring vacantly into the thick blankets of cover, hoping for sunshine. These gloomy stratiform clouds are a sign of atmospheric stability and a unique condition common to mediterranean climates.
The gloom is what’s known as marine layer, a sky condition in which a mild temperature inversion (when atmospheric temperature increases with altitude rather than decreases) near the Earth’s surface combines with advection (the horizontal movement of an airmass) to form low lying clouds. When a warm moist air mass moves from west to east across the Pacific Ocean towards the coast, it condenses as it comes into contact with cool oceanic surface temperatures. Currently, sea surface temperatures off the coast are steadily holding around the lower 50’s to lower 60’s (Fahrenheit).
In addition to the relatively frigid sea surface temperatures circulating off the coast, the subsidence of high atmospheric pressure helps create the perfect conditions required for a persistent marine layer. Taking a quick look at the surface analysis chart from June 17, 2019 (below), a large trough or elongated area of low pressure is stretching across all of California and almost extends into Texas!
This thick marine layer lasts the longest and usually occurs during the month of June, but these lingering overcast conditions can also be experienced in the months of May, July, and even into August. However, the clouds commonly start to dissipate in the late afternoon to evening, creating stunning sunsets that pair well with the upper 60 degree temperatures.
So what’s the take-away from all of this? For starters, if you’re planning to visit SoCal to soak up some sunshine and warmth, maybe reconsider before booking the trip during the month of June when the Sun likely is hiding behind the cover of stratiform clouds. On the plus side, the overcast skies and slightly cooler temperatures reduce crowds and make it easier to visit some of the more attractive locations. Next time you’re in the area this time of year and bummed about the lack of sunlight in the Golden State, take a moment to look up and think about all of the conditions needed to make what you are seeing.
National Aeronautics and Space Administration (NASA), 2019, Worldview, https://worldview.earthdata.nasa.gov
National Oceanic and Atmospheric Administration (NOAA), 2019, Sea Surface Temperature Contour Charts, https://www.ospo.noaa.gov/Products/ocean/sst/contour/
National Weather Service (NWS), 2019, Current Surface Maps, https://www.weather.gov/oun/sfcmaps