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Blog: Ventura fire, Gorge, Bay, SoCal, Baja winds!
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windfind



Joined: 18 Mar 1997
Posts: 1323

PostPosted: Tue Dec 05, 2017 12:50 pm    Post subject: Blog: Ventura fire, Gorge, Bay, SoCal, Baja winds! Reply with quote

Hi Gang,

Kerry, our forecaster who lives near the Ventura fire but is out of the fires path, is carefully watching the local wind scene. Meanwhile I am watching the overall west coast wind situation.

As you can see in the imagery below the huge high pressure in the Great Basin, Columbia Basin and 4 corners is creating strong winds in the Gorge, Baja, Southern California and over the Bay Area.

These winds are extremely impacted by local topography and the depth of the inversion which is why you see in the imagery very weak winds in close proximity to very strong winds.

Right now it does no look like the brunt of the El Norte winds will reach La Ventana. Can you figure out the reason?

Mike



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aeolian



Joined: 31 Aug 2015
Posts: 10

PostPosted: Tue Dec 05, 2017 4:49 pm    Post subject: Reply with quote

What does it take for those beautiful breezes at 1000 ft to descend to the surface? The trees move occasionally in a promising manner, but never steady and strong. I'm looking at diablos and peninsula wind sensors, though the principles ought to apply widely.
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windfind



Joined: 18 Mar 1997
Posts: 1323

PostPosted: Tue Dec 05, 2017 5:39 pm    Post subject: Reply with quote

aeolian wrote:
What does it take for those beautiful breezes at 1000 ft to descend to the surface? The trees move occasionally in a promising manner, but never steady and strong. I'm looking at diablos and peninsula wind sensors, though the principles ought to apply widely.


Hi Aeolian,

In the summer we have dense cool often fog laden air from the pacific coming into the Bay Area. This air slides in below the inversion of warmer air just aloft. So our surface wind is stable and when it hits topography it climbs up the hills and then cascades back to the surface. Sometimes you can actually see this near the Golden Gate.

The air from the huge high pressure you see in red in the animation starts off as chilly air but as it descends over the Sierra and the coast range it undergoes compressional heating. This means this air is about the same temperature and density as the air above and below it.

You can see this in the Bodega profiler data from this morning below.

So when this unstable air hits topography it lifts and does not return to the surface.

This means most of the wind is on the hilltops not at the surface. However if you have canyon that is aligned with the winds direction then the wind will funnel through that canyon and accelerate at the canyons narrowest points. Hence strong wind in some canyons in Southern California and in the Rooster Rock part of the Gorge.

In the Bay Area NE facing canyons are uncommon. However if you head to Ft. Cronkite in Marin in the morning in these winds you may find strong easterly winds since the canyon sometimes is lined up just perfectly.

Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com



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loopless



Joined: 30 Jun 1997
Posts: 347

PostPosted: Tue Dec 05, 2017 6:28 pm    Post subject: Reply with quote

Lake Perris is ripping today. On site reports are 4.2-4.7 and wound up.
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geohaye



Joined: 03 Apr 2000
Posts: 1439

PostPosted: Wed Dec 06, 2017 12:26 pm    Post subject: Reply with quote

Yep- Lake Perris hit some pretty decent numbers the last 2 days.

LAKE PERRIS:
http://wx.iwindsurf.com/spot/171977



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bowtie



Joined: 02 Oct 2007
Posts: 7

PostPosted: Thu Dec 07, 2017 12:00 pm    Post subject: Reply with quote

Regarding the baja winds, the pressure maps show the pressures stacked up tight in the northern baja but the pressures relax considerable in southern baja but still good for 5.0 winds if the clouds clear and hopefully we will have some large swell coming down from northern baja!
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loopless



Joined: 30 Jun 1997
Posts: 347

PostPosted: Thu Dec 07, 2017 7:51 pm    Post subject: Reply with quote

3.7-4.0 in San Diego for a few hours.. that does not happen too often!
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aeolian



Joined: 31 Aug 2015
Posts: 10

PostPosted: Fri Dec 08, 2017 3:39 am    Post subject: Reply with quote

Trying to learn something about weather. Success, though not necessarily the something I was after. Am after - why is the long fetch of the bay (5-20 miles) NE of peninsula bay sites insufficient to allow the NE or N wind to the surface?

Warning, "internet knowledge" follows.

A profiler is not a balloon, it looks like this
https://www.esrl.noaa.gov/psd/data/obs/instruments/WindProfilerDescription.html
915MHz profilers don't read at 100M. This explains the near-surface gap in the profiles. They dont read at 0m either, but maybe these data are filled by a surface anemometer.

Trying to figure out how terrain affects wind speeds. Where the Bodega or Point Mugu profilers are, I haven't found exactly. The former I would guess is on Bodega Head somewhere. The latter maybe on Point Mugu NAS somewhere? Mugu NAS is actually NW of the closest the mountain range. Am guessing both have wind deflected by mountain ranges further upwind. Maybe the Transverse Ranges for Mugu, and North Coast Range for Bodega. 20+ miles or so upwind in both cases. Or does the deflection happen even further upwind at the southern and northern ends of the Sierras?

It's interesting that Mugu has a sharp change in windspeed at ~700m, where Bodega has gradual change all the way up. The Transverse Ranges are significantly taller (5-6000 feet) than most bay area ranges (2-3000 feet). Well, Snow Mountain may be upwind of Bodega and is 7,000. Synoptically, the NE wind crosses the Sierras to reach the bay, where Santa Anas feed from Great Basin (Nevada). Maybe it's simpler and Mugu (Ventura County) had a strong inversion layer, and Bodega did not. Mugu NAS is more or less in a valley where inversions often form. Where to find Pt. Mugu's temperature profile.

I wanted to share what I'd found. I'm happy to hear anything anyone has to add.

Has atmospheric fluid dynamics advanced to where we can understand wind flow across terrain from first principles or is experience with the area a better predictor? Either way, where is a good explanation, preferably with minimal reference to differential equations?
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windfind



Joined: 18 Mar 1997
Posts: 1323

PostPosted: Fri Dec 08, 2017 11:42 am    Post subject: Reply with quote

bowtie wrote:
Regarding the baja winds, the pressure maps show the pressures stacked up tight in the northern baja but the pressures relax considerable in southern baja but still good for 5.0 winds if the clouds clear and hopefully we will have some large swell coming down from northern baja!


Hi Bowtie & Aeolian,

As I guessed La Ventana had a very mild wind day at least according to the sensor which reads 3-4 knots low. You are right about the isobars and the large swell. This is the sort of day where the Sea of Cortez from San Felipe to Loreto blows but the winds weaken to the south. Los Barriles would be a better bet since it is further out in the main wind stream. But you can never completely count La Ventana out since it has a larger dead end valley down wind which can stir up low to mid teen local thermal winds even without any El Norte wind.

Aeolian, responding to your researched points properly would take more time than I have right now as I prepare to leave to Baja. But I will try to get back to you.

Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com
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kevinkan



Joined: 07 Jun 2001
Posts: 1375
Location: San Francisco

PostPosted: Fri Dec 08, 2017 7:56 pm    Post subject: Reply with quote

Lake Mohave was ripping this week. I was there Monday through Wednesday, and my 4.0 was never even a consideration (190lbs). Sailed 3.7 Monday and Wednesday and borrowed my friend's 3.1 on Tuesday. Thursday and Friday were also very windy.

Fantastic week on the lake!

some pics on my instagram:

https://www.instagram.com/sunsetsailboards/

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Kevin Kan
Sunset Sailboards, San Francisco CA
http://www.sunsetsailboards.com
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