Santa Ana Weather...

The extreme wildfire danger that southern California is experiencing right now is caused by a weather pattern that occurs every year in this season, usually a few times each year and lasting a few days each time. The main characteristic is the wind, which gives the weather pattern its name: the Santa Ana winds.

I captured these graphs from my weather station this morning. At top right, you see the raw wind data (gusts and average). The time and date on the graph are GMT, which is currently 7 hours later than local time. Around 9 AM local time yesterday, the winds kicked into high gear – and they've been there ever since, over 24 hours now. My weather station doesn't show the 60 to 70 MPH gusts we've been experiencing, because it can't respond quickly enough to catch these short but very intense gusts. Next down is the “wind run” graph; this shows how far the wind blows each day. You can see that the steady high wind results in a much higher wind run than normal – and this is what makes the winds so dangerous in a fire.

Finally, the bottom graph shows the barometric pressure over the last week – and you can see that for the past 24 hours, the pressure has been rising very rapidly. The center of the high pressure area is to our east, and the Santa Ana winds are caused by the air moving from this high pressure area to the relatively low pressure area off the coast. This is the direct cause of the winds, and this is the pattern that we see a few times each year, this time of year…