Why this La Niña is wet, not dry

Pineapple3_crop.jpgBlame the "blocking anticyclone." A La Niña condition in the eastern Pacific usually (but not always) means drier than usual conditions for Southern California, and wet times for the Pacific Northwest. But right now, and for more than a week, a persistent region of high pressure in the north Pacific is diverting storms south over us. "There’s a crapshoot or a random component to it, if you like, in the more northern latitudes, that’s adding some extra flavor to what’s going on, I think," says Kevin Trenberth, who heads the Climate Analysis Section at the National Center for Atmospheric Research, on KQED's Climate Watch blog.

The tap could be shut off at any time and Trenberth, for one, still thinks it'll happen. He says this is considered a “strong” La Nina and is still likely to wield influence over the winter as a whole. One clue is ocean temperatures in the central-to-eastern Pacific, which are running 2 degrees C (3.5 F) below normal. "That only occurs—probably less than 10% of the time, so it’s a relatively rare event and certainly stronger than anything we’ve seen in recent years," said Trenberth.

It should clear up here as soon as tomorrow, the National Weather Service said in its 10:30 a.m. discussion of the SoCal storm situation. The offshore low pressure system, still about 2509 miles from LAX, is blowing in towards us and should pass over by tonight. "Today will be stormy with heavy rain showers and thunderstorms. There is a chance of hail as well as strong winds under the thunderstorms. Clouds and showers will decrease this evening. It will be mostly clear and dry through Friday."

More discussion after the jump.

Heaviest rainfall overnight was primarily south of Los Angeles through Orange County and parts east. Other rainfall amounts were in the one to two inch range in Los Angeles County and half to one inch across Ventura County. Santa Barbara County received over two inches in some areas...

Until the upper low center moves by our area and we begin to stabilize and lose any decent dynamics ahead of the low...will need to monitor area for developing thunderstorms and possible associated severe weather...although chances appear less than previously thought. Best threat of severe weather will be with hail as the atmos becomes colder...and some rainfall rates as high as half to isolated one inch per hour within thunderstorms.

Threat of flash flooding still exists with near saturated conditions and the possibility of this intense rainfall. Mainstem rivers appear to be handling the water well with no issues reported. Overall looking at additional rainfall of 1-3 inches through this afternoon across Ventura and Los Angeles counties and lesser amounts north of Point Conception....

Thursday and Friday still on track to be dry with more sunshine outside of some residual low level moisture and some low clouds Thursday morning.


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