Slow-Moving Low-Pressure System May Bring Southern California Its Last Decent Rain of the Season

Brian Donegan
Published: May 6,2017
One more decent rain event is ahead for Southern California in the coming days as we near the end of the Golden State's wet season.
A sharp southward dip in the jet stream – or upper-level trough – will engulf the West this weekend and persist into early next week.
(MORE: Atmospheric Clog Will Bring Will Bring Cool Temperatures To The East)

A slow-moving low-pressure system will develop underneath a southward dip in the jet stream.

An area of low pressure will develop underneath that trough and, very slowly, track across southern California Sunday through Tuesday. This will result in continued showers and cloudy conditions along with a slight chance of thunderstorms, possibly containing some small hail at times.
(MORE: 8 Reasons Why Rain Is a Big Deal in Southern California)
Additionally, snow may fall at elevations as low as 6,000 feet, with accumulating snow in portions of the southern Sierra, adjacent foothills and coastal ranges.

Current Conditions and Radar

Forecast Details

Here is a general outlook of what to expect in southern California into next week:

• Sunday: The most widespread shower activity will likely occur on Sunday, and a few thunderstorms are also possible, some of which may contain small hail. Locally gusty winds are also expected. Snow will continue to accumulate for elevations above 6,000 feet.
• Monday through Tuesday: The chance of showers is expected to gradually diminish from north to south early next week. Showers will likely endure longest across interior slopes and the Antelope Valley due to northerly to northeasterly moist flow aloft lingering behind the slowly exiting low-pressure system.

(FORECAST: Los Angeles | San Diego | Bakersfield, California)

Sunday's Forecast

Rainfall amounts are not expected to be overly abundant, but some spots may see more than an inch across much of Southern California through Wednesday.
A few higher-elevation locations – below snow level – could pick up 1 to 2 inches of total rain, particularly in the coastal range east and southeast of San Diego.
Over 6 inches of snow are possible in the highest elevations of the southern Sierra Nevada, with lower amounts closer to snow level around 6,000 feet. Some light snow is possible as low as 4,000 feet in southern California.
(MORE: Crews Begin to Clear Winter's Massive Snowpack in Sierra, Cascades and Rockies)
Snowmelt may cause flooding in the northern Sierras below snow level through the weekend.
Widespread, flooding rain is unexpected, but there could be some minor debris flows where showers and thunderstorms stall.
This rain could be the last soaking of the ground for the next several months as the dry season sets in, so it should be largely beneficial overall.

Rain and Snow Forecast

In addition, wind advisories have been issued into early Sunday for portions Southern California and the Southwest, with wind gusts up to 55 mph possible.
Cooler temperatures will also accompany this slow-moving low-pressure system. High temperatures will be up to 20 degrees below average from southern California into the Southwest into early next week. In downtown Los Angeles, highs will only reach the 60s this weekend, 20 degrees cooler than earlier this week when temperatures climbed into the 80s.

California's Rainy Season Is Ending

While the wettest months in Los Angeles are typically November through April, May still averages 0.26 inches of precipitation in California's largest city.
Through Wednesday, 18.67 inches of precipitation had been measured in downtown Los Angeles since Oct. 1, the official start of the wet season. This is 4.33 inches above average for the date.
For comparison, only 6.83 inches of precipitation was measured in downtown L.A. by that point last year.

During the summer dry season, June, July and August each average less than 0.1 inches of rain in this Southern California city.
Therefore, chances for significant rain will be very low over the next few months. This could very well be the last widespread rainfall for the region until the fall.
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