Ringed by mountains and the sea, sunny LA enjoys pleasant weather throughout the year. Temperatures tend to be moderate—seldom exceeding 85 F/29 C or falling below 40 F/4 C—and sunshine reigns most of the year. Even on sweltering summer days, nighttime temperatures can be cooler by 20 F/7 C to 30 F/-1 C. Most rainfall occurs from late October to early April, and morning fog can be dense in winter, especially along the coast. The farther inland you go, the greater the extremes of hot and cold, the more sun and the heavier the rain. The valleys tend to be hotter in the summer and cooler in the winter. Coastal areas can see fog or cloudy weather well into the summer months.
The mountains just inland from the Los Angeles area tend to trap air pollutants, resulting in smog, an unhealthy haze that, at its worst, can give the sky a brownish hue (smog alerts are most frequent during the last half of August and much of September). If the smog level is high, you may have to restrict your outdoor activities. If you have respiratory problems—including common allergies or sinus problems—let your doctor know you'll be in a high-pollution area and ask for advice.
The hot, dry Santa Ana winds (which usually come in fall and winter) blow with less intensity in Los Angeles than elsewhere in Southern California, though dust clouds may occasionally powder some parts of the city (and like the smog, wreak havoc on sinus sufferers). Coastal cities usually don't experience the Santa Anas at all.