Ok, I was wondering why do certain santa ana wind events blow offshore all day, and others only in the morning. On top of that, I was also wondering why the winds blow offshore at my house in Irvine, but onshore at the beach. It was solid offshore at my house, maybe 25-30 mph and really strong onshore at the beach.
My question is, what are the most IDEAL conditions for a santa ana wind event? All the technicalities in pressure gradients are appreciated. I really want to understand what it takes for a wind event to form, instead of depending on a human forecaster, so I can maybe do some of my own foreshadowing of the likelihood.
I know that you need a high pressure over the great basin, but I do not really know much more of what actually goes into an event.Thanks!
Adam Wright – Solspot Forecaster:
Brian, Oh know I see what you are trying to do…just steal my knowledge and go off and start your own forecasting website, leaving me broke, sleeping on the beach, (just easy target for any old dolphin that wants to come along and rough me up)…you are heartless man.
Just kidding, I know there are a lot of people that probably have the same sort of questions…but let’s start with your last one and work forward. I have to warn you…this is a pretty freaking weather nerdy answer. The ideal set up for the Santa Ana (or Santana) winds is three-fold:
1. Having the high-pressure over the great basin and even a little further out…so that the high stretches from the Rockies to about midway between Hawaii and the West Coast. You also want the portion of the high-pressure over land to be fairly zonal…meaning that the southward portion of the high is pretty parallel to a latitude line. It is even better if the high extends that straight line out over the ocean for at least a few miles before it makes any sort of directional change.
2. The second feature that you need to power the Santa Ana winds is a low-pressure holding position around Arizona, or somewhere close to where the Sea of Cortes (Gulf of California) terminates.
3. The final key to make it a truly “ideal” Santa Ana is having the upper atmosphere support what is happening along the surface…so looking at the 500mb and 750mb elevation level is a good idea…if those charts mirror the surface ones, then you get the full force going offshore, not just the surface gradients with the upper level winds working at cross purposes.
You can actually see what I am talking about on this chart (at least at the surface level)…that I pulled from the Santa Ana conditions we had at the beginning of the month.
Notice the dog-leg in the pressure gradient that goes right over Socal…that is actually a really good thing…it doesn’t look like the winds would be blowing offshore…but that hook (dog-leg) is what I look for when I think Santa Ana winds should spin up. No dog-leg and it might be clean in the morning but it won’t be a true Santa Ana.
Now like you mentioned, there are varying degrees of Santa Ana winds…anything from “light offshore” to “batten down the hatches and make sure the cat is tied to something”…oh and there is always the “raging inferno” that the arsonists like to put in that range too.
The speed of the winds is entirely up to the pressure difference between the high-pressure and the interior low-pressure…the bigger the gap (the higher the high and the lower the low) the stronger the wind that blows through that gap. From there it is down to personal preference for “IDEAL” conditions…in my opinion there is such a thing as have winds blowing too offshore…a solid 10-15 knots that stick around all day is what I would be looking for.
The answers to your other questions are basically caused by variations of the “ideal” weather pattern. Most Santa Ana winds are not perfect…they have some of the pattern’s set up…but not all. Which makes the offshore flow a bit more fragile than it would be if everything was lined up (and holding in position).
Generally if we are seeing the offshore winds in the morning but not the afternoon, we don’t have the upper level support…and the offshore winds are set up by weaker high-low pressures, which can get derailed by even subtle changes in the temperature.
So for example…we kick off the day with cold morning conditions and stiff offshore winds…these sort of winds usually blow out any sort of cloud cover so the sun gets a clear shot at the land, heats it up, and causes a thermal low-pressure but in the wrong position…so the offshore winds actually get bent back toward the coast, causing a sea-breeze to try and equalize the shift in land/ocean temps.
Then we get to the most frustrating one of all, where the winds are blowing offshore across the inland areas but the second you get to the coast the winds are onshore and there is chop, fog, and lots of frustration. This is generally a variation of the whole temperature thing…but it also adds in a poorly positioned low-pressure or a funky shaped ridge of high-pressure. So the winds while blowing offshore inland, they help to heat up the land, and along the coast the winds start to shift back to that sea-breeze sort of flow…and the two meet and battle it out right over the surf. If are seeing something like this forming, sticking with spots that have some wind protection, high-cliffs, piers, jetties, or a bunch of kelp, you will have a better chance at getting decent looking waves. Sometimes if you have passes and canyons that can funnel the wind more offshore, if the winds are borderline those areas, mostly in Santa Barbara, Los Angeles and Ventura will hold out longer than the more open beaches in Orange County and San Diego.
Told you it was a totally weather nerd answer.