Ineresting Reading - Or - How I Mis-spent My Vacation

[BeauV]

There is a weather pattern off of Santa Cruz, CA that drives race officers nuts. The "normal" west winds will turn around and blow from the east, about 75% of the time it seems, wrecking havoc with the racing. It turns out the weather guys have studied it.

The plot's not gripping, but it's a pretty good read.

http://journals.ametsoc.org/doi/full/10.1175/MWR2885.1
http://journals.ametsoc.org/doi/abs/10.1175/MWR2979.1

[SloopJonB]

Is that like the Santa Ana winds in L.A.? So hot & miserable that it "Has wives looking at their husbands backs and fingering the edge of their knives" (as Raymond Chandler put it).

Edit: just read those reports - very different from the S.A. winds - cooling instead of heating.

[BeauV]

I LOVE Raymond Chandler's writing!! Great stuff. But.... Nope, these winds aren't like a Santa Ana wind. We do get a Santa Ana wind syle breeze from the North, but it usually only arrives in November. To give a little background on the situation, so that folks understand a bit better, I've made up an "annotated" chart.



Basically, the third dimension (altitude) has the following characteristics. The Marine Layer is quite cool and lives beneath a warm layer creating an Inversion Layer effect. The mountains are warmer and warmer the farther up you go - the opposite of most mountain ranges - because they get a lot of sun while the ocean and coast are covered in fog and remain cool. Thus, there is a general pull of cool air up towards the mountains by the rising of the hot air at high altitudes. Keep this Inversion Layer in mind, as it serves as a "lid" on the cool Marine Layer air, because the cold heavy air won't rise up through the hot light air even if it's bumping into mountains as it goes along. As a result, almost all of the wind effects in the area happen is a rather two dimensional way.

For example, when the prevailing NW winds bump into the mountains that are North and West of Santa Cruz, they don't go over the mountains, they turn and run down the shore and then bend around the point into Santa Cruz. This turning of the winds causes what I've labeled a Compression Zone. In the area from the shore to about two miles out there are substantially stronger winds as the cold marine north west wind gets turned down the coast and compressed with the rest of the north west wind that is arriving. Winds 5 miles off shore will typically be 20-25 knots, winds in the Compression Zone will be 30-35 knots. This is why the races down the coast are such fun and why everyone tries to get as close to shore as possible from Pidgeon Pt. and Año Nuevo onward as they race down the coast.

The second thing that's going on is that the center of Monterey Bay is a lot colder than the warm land of Santa Cruz and the mountains behind it, so there is a pressure to move air from the center of the bay in a northward direction towards the rapidly rising air over Santa Cruz. This combines with a the Prevailing Wind's desire to release the compression and fan out into Monterey Bay to provide some impetus to turn the breeze from NW to SW as it goes around Pt. Santa Cruz.

Eventually, the wind speed through the compression zone gets great enough that we start to get a vortex forming in the lee of Pt. Santa Cruz (Where the Flashing 5sec 60ft light is on the chart) and the wind completely dies on the shore of Santa Cruz. The heat inshore continues to pull on the marine air and the prevailing winds bang into the mountains to the east of Monterey Bay and over 70% of the time in the summer we get a full cyclonic rotation with the wind on the beach in Santa Cruz shifting to the East at about 10 knots, while three miles offshore the breeze is howling from the NW at 25-30 knots.

This is all probably more than you ever wanted to know.

BV

[SloopJonB]

Weather behaviour on the coast can be very strange. Right near me there are three very localized oddities. I live at the mouth of Howe Sound a 30 mile long, very deep, steep sided fjord. There is what appears to be a very open and exposed bay two blocks away that faces directly up Georgia Strait into the prevailing northwesterlies but the weather never goes in it - always across the mouth of it. Bad weather southeasterlies do the same, as do the winter "Squamish" winds that blow down the sound.

Around the corner of Point Atkinson there is a very small, narrow cove we call Tiddlycove. It looks like a perfect hurricane hole, faces across the harbour to land on the other side - max 3 or so mile fetch, high sided etc. In fact it is a total catch basin - full of drift logs, fairly large wave action etc. Three moored boats sank at their moorings in it last winter.

Lastly, there is a phenomenon that occurs across the mouth of Howe Sound - this mouth is 3 to 5 miles across - pretty open. Under certain conditions the wind will blow strongly across the mouth in an extremely sharply defined way - withing 150 yards you will go from near calm to 20+ knots. We call it "The Wall". It's like God blowing across the top of a bottle.