LOS ANGELES, July 1 (Xinhua)-- The National Weather Service (NWS) issued a heat-wave warning for Southern California on Sunday, signifying high wildfire danger as the region heads into its first heat wave of the summer.

    Temperatures in some mountain areas will reach some 100 degrees Fahrenheit (about 37.7 degrees Centigrade), while the relative humidity will dip to about 10 percent at times, according to the NWS.

    High pressure building over the region is expected to drive temperatures to near record levels by the Fourth of July. That means valley and inland temperatures in excess of 100 degrees Fahrenheit.

    The heat wave is arriving as the region ends its driest year on record. Since July 1, 2006, only 2.31 inches of rain has fallen at the downtown-area, making it the driest winter since record keeping started in the late 1870s. The norm is about 15 inches per year.

    According to a county fire department study, the moisture level in the chaparral covering the hillsides is at its lowest level in 26 years, making it ripe for explosive fire growth.

    Humidities will be lowest in the high country, generally above 4,000 feet, where there will be the potential for strong winds. Potentially damaging gusts could hit 50 mph, making driving dicey for tractor-trailers and other high-profile vehicles along the Interstate 5 corridor.

    Because of the extended hot spell and the coming holiday typically celebrated with pyrotechnics, the NWS may well extend the "Red Flag Warning" beyond tonight and through the mid-week Independence Day holiday.

    Last year, a record-breaking heat wave hit the region, causing the deaths of about 150 people.