“Atmospheric River” Bears Down on Altadena and Pasadena

A pair of storm systems are expected to dump rain on Southern California beginning Tuesday, again raising fears of possible debris or mud flows in recent burn areas.

The first system is scheduled to arrive sometime Tuesday evening, according to the National Weather Service.

Los Angeles will see rainfall, likely receiving one-quarter to three-quarters of an inch in most areas, but as much as 1.5 inches in “favored hills and mountains, which includes the … Eaton burn scars.”

“This will generally be a beneficial rain for the region,” according to the NWS. “Snow levels will be very high and above any major roads. The risk for burn scar debris flows is very small. Flooding impacts should be minor and confined to localized roads and clogged storm drains. …”

A second storm system is projected to drop more rain from Thursday afternoon into Friday morning.

Although rainfall totals were still being calculated, forecasters estimated that most areas would see a quarter-inch to an inch from that system.

The rain is expected to wind down in the L.A. area by Friday afternoon.

In advance of the rain, the Los Angeles County Department of Public Works was working to clean drainage facilities and debris basins, install additional k-rails near homes and provide sandbags at vulnerable sites.

Daytime temperatures are expected to cool significantly, with highs dropping to the lower to mid-60s on Tuesday and near 60 by Wednesday.

Here is the latest Pasadena area forecast from the NWS, as of 3:25 a.m. Tuesday:

Today: A 30 percent chance of rain after 4 p.m. Mostly sunny, with a high near 63. East southeast wind 5 to 10 mph becoming south in the afternoon. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Rain, mainly after 10 p.m. Low around 51. East southeast wind around 10 mph. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Wednesday: Rain, mainly before 4 p.m. High near 60. South wind around 5 mph. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Wednesday Night: Rain likely, mainly after 10 p.m. Mostly cloudy, with a low around 50. Calm wind becoming southeast around 5 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Thursday: Rain likely, mainly after 4 p.m. Mostly cloudy, with a high near 61. Calm wind becoming south southwest around 5 mph in the morning. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Thursday Night: Rain. Low around 50. Chance of precipitation is 80%.

Friday: Rain, mainly before 4 pm. High near 61. Chance of precipitation is 80%.

Friday Night: A chance of rain before 10 pm. Partly cloudy, with a low around 41.

Saturday: Sunny, with a high near 64.

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

Sunday: Mostly sunny, with a high near 65.

Sunday Night: Partly cloudy, with a low around 42.

Monday: Mostly sunny, with a high near 64.