3.6 inches of rain puts downtown L.A. below Palm Springs' annual average of 4.98."
The combination of persistent high pressure and unfavorable oceanic temperature patterns combined to make 2013 the driest year on record for Los Angeles.
Since records began here in 1877, every calendar year has yielded more rainfall in Los Angeles than the period from Jan 1 through Dec. 31, 2013.
Scientists can't attribute this condition to any single factor such as global warming; to the contrary this is the result of multiple, complex and interrelated elements, both short and long term.
But the primary and most outstanding mechanism would be a persistent pattern of blocking high atmospheric pressure which prevailed through much of last winter, and is so far re-occurring this winter also.
Moderate high pressure exists over the eastern Pacific most of the year, this “Pacific high” in tandem with the cool offshore California current is what gives southern California its mild year – long climate.
Normally, 14.93 inches of rainfall occurs annually in Los Angeles, mostly from winter storms passing to the north. Over the past 100 years, fluctuations have brought winter storms directly into southern California at somewhat regular intervals, averaging about once every 3 to 5 years. This is presumed to be associated with the El Nino phenomenon, the abnormal warming of low latitude sea surface temperatures affecting jet stream winds across the eastern Pacific.
Statistically, Los Angeles should have experienced a wetter than average winter within the past two years.
Moisture bearing storms from the Pacific continue to be blocked far to the north, up and over prevailing west coast high pressure only to drop what moisture they do retain elsewhere. Palm Springs, normally receiving moisture from summer storms, has a higher annual average than downtown L.A. received in 2013; that being 4.98 inches compared to downtown L.A.'s recorded total of 3.60 inches.
Even during drier than normal years, Los Angeles still receives winter rainfall from minor, temporary variances in blocking high pressure patterns, this has not been the case in the past 18 months. In late December, 2013, long range models had hinted at one such variance developing this first week in 2014; so far, this has failed to materialize.
Things don't appear promising. Long range outlooks continue to project more of the same; a continuation of well -- entrenched west coast surface and upper level ridging, with storms riding up, over and inland leaving Los Angeles high and dry, with periods of gusty offshore Santa Ana winds and unseasonably mild temperatures.