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.
Your graph there also correlates very well with solar cycle activity. I wonder if that could be a thing?
ReplyDeleteIt appears there is also a rough correlation with global mean temperature, which fell between 1945 and 1975, and which then began to rise again after 1975.
DeleteI am not enjoying this dry spell, bring us some precipitation!
ReplyDeleteIt will be a 20 day dry spell when all is said and done and even after the ridge breaks down, it doesn't look like there's going to be very much precipitation. It's most disappointing. Let's hope La Nina works her magic in February and in March. Every now and then we get a winter like this.Where it's dominated by high pressure. Like in Jan/Feb 1993, 2001, and 2003, 2009 and 2015.
DeleteIt seems like every few years, the jet stream just becomes a wobbly mess in January and February.
ReplyDeleteCan you explain why the air quality has been unhealthy in parts of Washington (and northwest US) today? Thanks.
ReplyDeleteWe are in an inversion. That causes the air near the ground to stagnate if winds are light as often happens in an inversion. Though I noticed that the air was very clear over the weekend. There has been some light wind in most of Western WA, which I guess has been enough to flush out the pollution at least in the north central Sound where I live.
DeleteCould you explain why PV=nRT would not cause pressure to increase with global warming?
ReplyDeletethat is easy. The pressure at the surface depends on the mass of the atmosphere above you, not your local surface temperature. The total mass of the atmosphere is not changing with warming. By the way, did you now that CO2 increases causes COOLING in the lower stratosphere?
DeleteYes, please tell us when we are going to get substantial rain. What happened to La Nina? It looks like they are already starting to waffle on Friday and Saturday's promise of rain...
ReplyDelete