Winter arrives at 3:38 PM on Tuesday and is beginning with a vengeance across Kern County. Historic rainfall brings much of California into a state of emergency with widespread flooding affecting many this Christmastide.
For the period from Friday through midday on Monday, Bakersfield had accumulated 3.79” of rain. That is 5 times the normal amount for an entire December and represents 58% of a normal year’s rainfall. In fact, for the water year which runs from July 1st through June 30th our total now sits at 5.59” which is a staggering 86% of the average annual rainfall. Normally by this date we would have seen only 24% of the average yearly total.
Truly, this has been one for the record books, a once in a hundred years event. Sunday was the 4th heaviest daily rainfall of all time. Records go back 121 years to 1889. We have witnessed the most rainfall ever to have fallen in the month of December. Flooding has touched many lives in Kern County. While the Meadows Field rainfall numbers are quite impressive, central California from the San Joaquin Valley to the mountains have generally received between 4 and 13 inches of rain. In the mountains up to 9 new feet of snow has fallen. Just as the big valley snow of late January 1999 was in the minds of many years later, this wet storm system will be remembered and told to our grandchildren for decades to come.
But wait a minute- I thought this was going to be a dry year, A “Sandwich Season” due to the strong La Nina. What happened? This goes to highlight the unpredictability of long term forecasts and to another degree all the wild weather that has been seen across the globe this year. From record heat and wildfires in Russia this summer, to LA’s all-time record high of 113 in September, to record rainfall in Pakistan, to early intense snow and cold in November across the west and various storms on the east coast- this extreme wet storm here in California punctuates what has been a violent 2010 weatherwise.
While the eastern Pacific sea surface temperatures are indeed very cool and a strong La Nina episode is in full swing, there are two caveats that came into play at the same time which could only be seen about 10 days before they manifested themselves. First is a large blocking ridge of high pressure at very high latitudes. This phenomenon is not particularly unusual in the winter, but the strength and positioning of it over the Davis Straits of northern Canada is. Together with another weaker blocking ridge over the central Aleutians, the polar jet stream position has been dramatically altered. Normally during a La Nina event, the jet stream is driven far to the north impacting Washington State and British Columbia with heavy rain there. California is left high and dry in this scenario. But with the advent of that blocking ridge, the jet stream was forced farther south. As an example, take a sloping driveway with a garden hose at the top. Water will flow down the driveway directly out of the hose. But if you place a block of wood, say one or two feet across, at the edge of the flow it will redirect the water. Such is the case with the atmosphere when a large high pressure system develops in a place where there is usually a large low pressure system.
The other unusual development has been a flare up of the Madden-Julian Oscillation. This is an incipient atmospheric wave in the western Pacific that has its origin near Indonesia and progresses eastward across the ocean in the sub-tropics. It is a complicated entity that was only recently discovered in 1971. Great tropical convection is generated by this phenomenon as it slowly moves into the central Pacific. What has happened here in the middle of December 2010 is a conjunction of the aforementioned blocking pattern over northern Canada AND the perfect positioning of a Madden-Julian Oscillation event. Thus, copious amounts of sub-tropical moisture have been foisted into an energized jet stream just northwest of Hawaii. The final result has been what we affectionately have come to call “The Pineapple Express”. This garden hose of tropical moisture has drenched California, and Kern County in particular, on this the Winter Solstice. Our storm of historic proportion (in an otherwise dry La Nina year) is the result of a perfectly aligned recipe of unique ingredients: high pressure in Canada (not low pressure) as the catalyst, and a chance encounter with a tropical moisture conveyer belt. Timing is everything!
So, how long will this last? As long as the special circumstances mentioned above persist. That should be for another week. Then what? Well, unless something else unforeseen comes about, La Nina should bring us back into a dry period. Probably more fog than usual for January. But no matter what happens in the next few months, this is almost certainly destined to be a bumper crop water year. As of mid-Monday, only another .90” of rain is required to fall in Bakersfield between now and June 30th to make this an above normal water year. I’m going out on a limb here, but that seems like a slam dunk (emphasis on the word “dunk” after all this rain).