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California's Hurricane: The Santa Ana winds
Submitted by Tim Buckley on Thu, 12/01/2011 - 11:19am.
We certainly know about high winds around these parts, but not like this. Imagine a crystal clear sunny day, but the wind around you is whipping over 70 mph - blowing dust and sand (and sometimes snow) everywhere. That's what California is dealing with right now in one of the most impressive "Santa Ana Wind" events in recent memory.
Santa Ana Winds Explained
So what are these guys? Well, it's a phenomenon fairly unique to the west. First, you need an extremely tight pressure pattern. By that I mean you want a huge range in pressure over a small area. The best way to do that is to have a strong high pressure area not far from a strong low pressure area. Differences in pressure are what create winds around the globe each and every day.
Right now, in the west we have both a strong high and a strong low. The low pressure center is right over Phoenix, Arizona. The high pressure center is in Washington State. California is caught in the crossfire by this tight pressure pattern - and there you have you high winds. But that's not the whole story.
You also need high mountains and rough terrain to "funnel" these winds. All the energy from these high winds must pass through tight and narrow mountain passes that we see in the ranges in the west. In California, you have the Sierra Nevada range (near 15,000 ft peaks) near Nevada and also the Sierra Madres (near 6,000 ft) in the Los Angeles area. These, along with any other extreme mountains, work perfectly for funneling the winds.
Category Four Hurricane Gusts?!?
With this particular event, the pressure packing has been so strong, that the wind gusts have been hard to even imagine. In some cases, hurricane force winds up to CATEGORY FOUR strength have been seen. Seriously!
This map shows the Sierra Nevada range Thursday morning, where our models are predicting more gusts over 100 mph. Already, winds had been seen up to 150 mph at Mammoth Mountain - an 11,000 ft peak in the Sierras.
Problems for the L.A. Metro area too
The mega-populated LA Basin gets in on these winds too, especially the suburbs just to the east of the city, often known as the "Inland Empire". While you wont get the extreme winds that you find in the much taller Sierra Nevadas, the Sierra Madre range does a good job funneling in high winds that can get to hurricane strength too.
As of Thursday morning, confirmed winds over 50 mph had been common throughout LA - but our model is indicated gusts over 70 will still be possible throughout the mountains until the end of the day.
It doesn't last forever
Winds will finally start to let up across the area on Friday. Once the low pressure area starts to pick up and move east, the pressure pattern just isn't there anymore to support the crazy high winds seen over the last few days.
Kind of makes you think twice about those "L's and H's" you see on the weather map everyday huh? They actually are the real driving force behind the weather - and this is a great example of why.
Keep on enjoying our quiet, cool weather! We'll warm up at least a little bit once we head into the weekend.
By: Tim Buckley