Big Weather Rolling-in for the Holiday – Up To 8″ of Rain Forecast in the So Cal Region over the week.
Forecasts for the Christmas week storm in Southern California generally project about 4 to 8 inches of rain across coastal and valley areas (including South Pasadena and the Los Angeles basin) over the multi-day event from Tuesday through Saturday. Higher terrain like foothills and mountains could see 8 to 12 inches or more.
Today (Monday, Dec. 22)
Partly to mostly cloudy. Mild temperatures with highs near 68–70°F and lows around 50–55°F. Rain is not expected today, but clouds will increase ahead of the incoming storm system.
Tuesday, Dec. 23
Rain returns Tuesday afternoon and evening. Showers will develop during the afternoon with rain likely increasing late in the day. Rain intensifies Tuesday night, with moderate to heavy rainfall possible.
Wednesday (Dec. 24 — Christmas Eve)
Widespread rain expected, heavy at times. Rainfall rates could be significant, especially late Tuesday night through Wednesday, with totals of 2–3 inches or more possible locally and heavier amounts in foothills and mountains. Flooding concerns are elevated for urban and low-lying areas.
Thursday (Dec. 25 — Christmas Day)
Rain continues on Christmas Day with cloudy skies and periodic showers. Highs are forecast in the low 60s. The storm tapers slowly, but showers are likely to persist through much of the day.
A flood watch will be in effect from Tuesday afternoon through Thursday evening for much of Los Angeles County, including South Pasadena, Pasadena, Altadena & Los Angeles.
This storm pattern is associated with a strong atmospheric river bringing deep Pacific moisture into Southern California, increasing the risk of flooding across the region through mid-week.
Friday (Dec. 26)
Lingering showers and cloud cover with cooler temperatures near the low 60s. Rain chances decrease gradually throughout the day.
Saturday (Dec. 27)
Drier and partly sunny conditions return. Any remaining morning showers taper off, with highs climbing into the mid-60s.
Sunday (Dec. 28)
Mostly sunshine and milder weather, with highs near the upper 60s and low rain chances.
Rainfall and Impacts Summary
Heavy rain is likely between Tuesday and Thursday, with several inches possible across South Pasadena and the Los Angeles Basin. Flooding and urban runoff are primary concerns as ground conditions become saturated. Mud and debris flows remain possible on steeper terrain and recent burn scars. Temperatures remain seasonable, with highs mostly in the 60s and overnight lows in the 40s and 50s.
