Cooler Temperatures, Rain Bearing Down on Pasadena

On the heels of a warm and sunny stretch, a “massive cool down” will begin around the Southland Thursday, along with rain and mountain snow.

A pair of weather systems are bearing down on the region, with the first expected to arrive Thursday, and wet conditions likely to continue through Saturday.

“Clouds will be on the increase on Thursday and there will be a massive cool down,” according to the National Weather Service. “Rain is likely Thursday night and Friday morning, along with mountain snow and a slight chance of thunderstorms.”

Forecasters said a second, colder system will move in Saturday and continue into the evening, bringing “another chance of showers to the area.”

Thursday’s initial cold front will bring cloud cover to the region and drive down temperatures, with rain developing first along the Central Coast, moving into Los Angeles County by Thursday evening. The rain will taper off later Thursday evening and Friday morning, although some lingering showers are possible Friday afternoon.

Rainfall totals are supposed to be relatively low, with most areas receiving a quarter- to three-quarters of an inch of rain, although the San Gabriel Mountains could get slightly more, forecasters said. There will be a slight chance of thunderstorms developing, possibly resulting in “brief heavy downpours and small hail.” Snow levels will drop to 4,500 to 5,000 feet Thursday evening, with 5 to 10 inches of snow possible at higher elevations, according to the NWS.

The storm will lower temperatures by about 8 to 12 degrees Thursday, and another 5 to 10 degrees on Friday, when temperatures will average about 10 degrees below normal, forecasters said.

Another cold front is expected to arrive by Saturday, bringing another chance of showers and more snow in the mountains. The snow level could drop as low as 3,000 feet, and temperatures will fall a few more degrees, keeping most of the region in the mid to upper 50s.

Forecasters said conditions should begin to rebound on Sunday with clear skies. Warmer weather is expected to return by Monday.

Here’s an up-close look at the National Weather Service forecast:

Today: Partly sunny, with a high near 69. South southeast wind 5 to 10 mph, with gusts as high as 15 mph.

Tonight: A slight chance of showers, then showers and possibly a thunderstorm after 11 pm. Low around 50. South southeast wind around 10 mph, with gusts as high as 15 mph. The chance of precipitation is 80%.

Friday: Showers likely and possibly a thunderstorm. Mostly cloudy, with a high near 59. East southeast wind around 10 mph becoming southwest in the afternoon. Winds could gust as high as 15 mph. The chance of precipitation is 70%.

Friday Night: A 30 percent chance of showers, mainly before 5 am. Mostly cloudy, with a low around 46. South southwest wind 5 to 10 mph.

Saturday: A 40 percent chance of showers, mainly between 11 am and 5 pm. Partly sunny, with a high near 58. North northwest wind 5 to 15 mph becoming west southwest in the morning. Winds could gust as high as 20 mph.

Saturday Night: A 20 percent chance of showers before 11 pm. Partly cloudy, with a low around 41.

Sunday: Sunny, with a high near 61.

Sunday Night: Mostly clear, with a low around 43.

Monday: Sunny, with a high near 68.

Monday Night: Mostly clear, with a low around 45.

Tuesday: Sunny, with a high near 74.

Tuesday Night: Mostly clear, with a low around 47.

Wednesday: Sunny, with a high near 73.