The October 13th Pacific storm that hammered California is awash in superlatives. Records fell by the wayside in most areas north and south of Kern County for a storm so early in the rainy season. But the strength of this powerful former super typhoon was precisely the reason many parts of Kern County received next to nothing. Indeed the rule of thumb is “The stronger the storm, the LESS rain we get in Bakersfield”.

It will be studied as a text book example of orographic influences on weather, namely how the mountains all around us shape and focus storms such as this. An unusually strong jet stream for mid-October transported the system across the Pacific. Winds in the high atmosphere around 30,000 feet were blowing at almost 200 MPH. This river of wind took aim on the central Sierra Nevada mountain range and coastal mountains, which are both oriented north to south. Moisture laden air came rushing toward the ranges at an angle perpendicular to the mountains. And thus an upsloping rain machine switched on. Extremely heavy rain was squeezed out of the air by wind being forced up a mountain wall. Mining Ridge (in Monterey County) along the Big Sur received over 20 inches of rain. Three Peaks, just down the road, picked up 16 inches. Keep in mind that Bakersfield typically gets only 6 ½ inches of rain over an entire year. In the Sierra more than a foot of rain fell in the Kings River basin with up to 5 feet of snow above 10,000 feet. Major cities from San Francisco to Sacramento to Fresno, and south to San Luis Obispo, Santa Barbara and Los Angeles all got tremendous rainfall- breaking many records. The 2009-10 water year is certainly well underway. The Bay area is currently over 400% of normal rainfall.

But across the mountains it was just the opposite. While rain piles up on windward sides of a mountain range, downsloping occurs on the leeward side. This happened in Kern County. Mid level winds were southerly to southwesterly running 60-80 MPH. This dynamic continued throughout the event leading to gusty dry winds that kicked up significant blowing dust in the south valley which resulted in a multi-vehicle crash on I-5 with several fatalities. No rain occurred in Bakersfield at all, until early the next morning. Downslope winds are forced down the back side of a mountain range. Air molecules being pushed to lower elevations warm up while being compressed. They also dry out dramatically.

This classic storm was very rare, being compared only with the “Big Blow” Columbus Day storm of 1962 and another deadly storm that hit our region in 1899. It must be noted that computer models were exceptionally good on this one, forecasting with uncommon clarity highly anomalous rain and wind values for more than a week ahead of time. But it goes to show how important specific strong wind direction can be during a storm in an area surrounded by mountains. While the south valley was virtually the only place that didn’t benefit directly from autumn rains, this will be the first of many other storms that hit the Golden State between now and April. So bring on El Nino. A wet year awaits.