The Direct Connection Between Northwest Weather and Los Angeles Santa Ana Winds (and Wildfires)

 It is not an accident that while Los Angeles experiences sustained Santa Ana winds, the Northwest enjoys sunny, dry weather.

As I will show, there is an intimate connection.

Considering the dates on which Burbank Airport (see map) had wind gusts greater than 50 mph and a relative humidity less than 30%, a strong indicator of a strong Santa Ana wind event.

Burbank was surrounded by the fires and is a good location to determine if strong winds getting to near sea level--a hallmark of the recent event.

This wind and humidity criterion found the following dates:

Then I found the the average sea-level pressure distribution on these Santa Ana dates (see below).  

Wow.  A very well-defined (and highly statistically significant) pattern.  Huge/strong high pressure over the Great Basin that extends into the Northwest.  Low pressure over northwest Mexico.     Big pressure change (gradient) over the Sierras.    This pressure pattern is associated with strong easterly flow over southern CA.

But let's not stop there.  Let's also calculate the difference in pressure from normal.  Something called the anomaly of pressure from climatology in the weather biz (see below).  

Double wow.   The biggest pressure anomaly from normal is over Washington State.

So there is an LA/Washington connection!

An interesting question is whether high-pressure periods are increasing over our region...something several of you have asked about.

To check this out, I have plotted the frequency of sea level pressure getting above 1035 hPa (a relatively high pressure) at Seattle-Tacoma Airport from 1948 to now (see below).   

Lots of cases in the 50s, fewer in the 60s and 70s, and higher numbers during the past two decades.   As noted by the thin dotted line, a small upward trend over the entire periods.  But not much trend if one considers the past two decades alone.   

An issue I will be doing more research on.

The latest forecasts suggest major...and I mean major...changes in store for the West Coast for the next two weeks, with substantial rain for southern CA and a potential for some flurries over the western lowlands.

More in a future blog.