Weather Up There: Because of Southern California’s...

Weather Up There: Because of Southern California’s wide variety of landforms, weather patterns can differ dramatically over just a few miles. That’s why the foothills surrounding the San Fernando Valley are routinely much wetter than the Valley floor. Topographic differences also explain why the Valley is warmer than much of the rest of the L.A. Basin. Valley Briefing: B2

Weekend Ride: About 750 riders on Saturday took advantage of the first day of weekend MetroLink service between the Santa Clarita Valley and Los Angeles. MetroLink officials said they were pleased with the turnout and hope it will grow in coming months. Until now, MetroLink has operated commuter trains only Monday through Friday along the 38-mile route. Weekday MetroLink service attracts 3,000 riders daily.

Marathon Tuneup: Two thousand runners stepped to the starting line Saturday at Pacoima’s Hansen Dam Recreation Center for an 18-mile warmup to the Los Angeles Marathon. The first finishers crossed the line about two hours after the 8 a.m. start, but hundreds of others trickled in past noon. Those finishing the course are considered to be ready for the more demanding marathon, the 12th running of which is scheduled March 2.

Sour Notes: Protesters fighting to save radio station KSCA’s alternative adult rock format plan to take their campaign to the station’s Burbank offices today. Station supporters are being encouraged to gather in the parking lot at 2 p.m. to sign petitions and hold a candlelight vigil. The station is scheduled to switch to Spanish-language programming.