Los Angeles, June 6 : Southern California is embracing overcast skies, colder conditions and chances of rain and thunderstorms this week, according to weather forecasts. A low-pressure system is forecast to usher in cooler weather through Wednesday and is likely to linger the rest of the week, resulting in overcast skies and low clouds, Xinhua news agency reported, citing the US National Weather Service (NWS). "Potential for brief heavy downpours and strong wind gusts. Also seeing isolated lightning strikes on periphery of storm that could trigger grass fire activity," NWS Los Angeles tweeted. During the months of May and June, the upper atmosphere tends to be more stagnant, but troughs of low pressure still pass over the region, resulting in the low clouds characteristic of "May gray" or "June gloom", said a report of The Los Angeles Times. The marine layer forms when the layer of air near the ocean's surface is cooler than the air above it, an "inversion" of abruptly warmer air that traps the cooler air and forms clouds. /IANS