West Coast Wind Blog: Dec. 5, 2017. Huge high pressure creates powerful easterly winds

Ventura fire, Gorge, Bay, SoCal, Baja winds!

by Mike Godsey

Today we are seeing unusually strong late easterly winds over much of the west coast from the Gorge to the Sea of Cortez. These winds are stirring unusual late season fires in Southern California.

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.

In the first set of images you can see the strong winds that are whipping the Ventura fire. Also notice the Strong western Gorge winds.

Notice how localized the winds are in the canyons and ridges.

Likewise in the Bay Area notice how the winds are strong on the East Bay ridges but weak at the surface inside the Bay.

Kerry notes that the Pt. Mugu 449 Mz. profiler show a similar pattern is Southern California with very strong Santa Ana winds aloft.

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.

Looking at the animation below you can see the huge high pressure zone that extends from west of the Pacific Northwest into the Columbia Basin, Great Basin and 4 corners. Anos note the low pressures west of Northern California, Southern California and south of Baja. Check out the isobars and you can see see the areas which have the strongest winds.

Can you figure out why Rooster Rock in the Gorge has such strong winds despite the isobars being relatively far apart?

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

Posted in Cape Cod, Columbia River Gorge, Los Angeles, San Diego, San Francisco

West Coast Wind Blog: “I don’t sail at Viento so why should I care about the new Viento sensor…”

Because Planning, Swell Size,

Fades, Directions…

by Mike Godsey, mike@iwindsurf.com

How to use the Viento sensor:

1. Most days the winds build at Viento before reaching the Hatch, Swell, Event Site launch sites. So the Viento sensor gives you an early hint for planning your day.

2. Likewise a mid day fade at Viento often gives a hint of an upcoming fade at the Hatch and Swell.

3. Often on light wind 4.7 – 5.2 days there is not much swell and people do not make the drive to Hatch and Swell. On these small swell days the wind is concentrated just in the Hatch and Swell zone.

But other times on light wind days there is great swell at Hatch and Swell IF Viento is also blowing. Even mild wind can make good swell if the entire corridor is blowing making for a long fetch.

4. And for those who are here only for a short time… they can now catch the early morning winds at Viento before the Hatch and Swell zone becomes reliable.

 

5. And of course for the increasing numbers of kiters and SUP folk who are doing downwinders this sensor is great.

 

Updated Nov. 1,2017:

There appears to be another use for the new Viento sensor. At the Hatch and Swell there are many days when the winds goes from a very favorable WSW to a less favorable W or to even an unfavorable WNW which leaves the WA. side of the river in a wind shadow.

Looking at the first image below you can see that the overall wind pattern from Rooster Rock to The Dalles is W to WNW. Notice how the Swell sensor is showing very weak wind since it is partially in a wind shadow in this wind direction.

But the Viento sensor is more open to W to WNW winds. This can give you a heads up before you make the drive to Hatch and Swell.

If you are seeing WSW winds a Viento then it is fairly safe to make the Hatch and Swell drive. But if the winds at Viento are turning more NW then you may find squirrelly wind at Hatch and Swell.

At present you can access the Viento sensor at the classic IW or at:

http://wx.iwindsurf.com/map#45.695,-121.623,13,1

 

 

Posted in Cape Cod

West Coast Wind Blog: The science and the beauty…

From a scientific perspective the shorter days of fall and the decreasing angle of the sun bring weakening pressure gradients while the North Pacific High moves further from the San Francisco Bay Area coast. This all means weaker winds. This week saw all of that plus an  upper ridge of high pressure at ≈ 18,000 ft. moved over the west coast. Upper high pressures create strong downward motion of the air as depicted in the top image. In the second image you can see the winds and distribution of this upper high pressure over the pacific near the Bay Area. In the 3rd. from the Bodega 449 MHz profiler you can see how the high pressure aloft has crushed the marine layer into the sliver of its summer time plumpness.

All this captures the thinning of the marine layer with scientific precision. However the cam images below are better for capturing the beauty.

 

 

 

Posted in San Francisco

West Coast Wind Blog: Satellite imagery of smoke hundreds of miles into the Pacific from North Bay fires.

This satellite imager from dawn to dusk Oct. 12 gives you a feeling for the scale of the tragic North Bay fire.

Mike Godsey

MikeATiwindsurf.com

Posted in San Francisco

West Coast Wind Blog: Unusual Oct. NW winds raging at the ocean buoys but…


 

2 factors make it unlikely much of that wind
will reach into the San Francisco Bay Area.

by Mike Godsey, mike AT iwindsurf.com

Take a look at the powerful NW winds in the mid 20’s to low 30’s at the ocean buoys predawn today when I was doing your forecast. Then look at the model output for 6AM. Both see really promising for a wicked strong NW winds for the coast and NW favored sites within the Bay. At a glance this looks like the sort of day that Marin windsurfers would think about heading to the waves at Tubamancha as seen in my banner above.

But my 7:30 AM forecast is for mostly weak or unreliable winds:

7:30 AM: A beefy summer type 1500 mile wide North Pacific High pushes an extension or ridge into Northern California and all the way to North Dakota. This causes its isobars to stack up over California from the Oregon border to near the Bay Area. So North wind is blowing the Central Valley and just aloft over the Bay while our ocean winds are NNW in the mid to upper 20’s just offshore. Meanwhile i can see the reflection of the Golden Gate towers in the mill pond like bay waters. So what are the odds of getting that powerful ocean wind to the coast and Bay? We have 2 unfavorable factors: 1. The N to NNE winds aloft continue all day and will fight against the NW wind trying to curve into the Bay. 2. Relatively air from the Central Valley will encourage a bulge in the valley low pressure to stay over much of the Bay Area so we have a weak pressure gradient. So the only weak winds at most Bay sites. Waddell and Coyote have the most promise.

So, why the pessimism?

This animation shows the strong NW winds as modeled by a medium res. model. Note at 6AM the strong NW winds are almost at the Golden Gate. But then mid morning strong N to NNE winds roar in from the Central Valley. This is due to a ridge from the North Pacific High that moves in over Northern California from near the Oregon border to near Sacramento.

While this imagery shows the surface N-NNE winds there is similar wind just aloft. Note how the NW ocean wind becomes weaker and more patchy as the day progresses. This happens as the 2 winds battle just offshore. At the same time the northerly flow encourages the Central Valley thermal low to bulge over the Bay Area keeping the pressure gradient weak.

But also notice how the N-NNE wind weakens some around 2-4 PM. And how the NW ocean wind builds and moves closer the coast.

This makes for very tricky forecasting since if the N-NNE winds were to fade early Waddell and Coyote and 3rd. Ave. could see strong winds.

But my reasoning is that this late in the year the pressure gradient will not have time to build to make this happen. Anyone want to take bets?

 

Posted in San Francisco

West Coast Wind Blog: Strong NW to NNW Fall winds but….

Central Valley thermal low over Bay so glassy AM and weak PM winds.

by Mike Godsey, mike ATiwindsurf.com

Check out the reflections at Pt. Diablo in my banner above and the reflection of the south tower of the Golden Gate this morning. It is rare to see such calm conditions even in fall.

It is even weirder since there are very strong NNW to NW ocean winds just west of the ocean buoys today. But only a hint of those winds will curve into the Bay this afternoon. So let’s take a look at the story behind these reflections.

 

In the first animation follow the time from 4AM to 5PM. Note how the North Pacific High’s wind are NNW in the AM. Winds from this direction have a much harder time curving into the Bay since they are parallel to the coast.

Notice in the PM that the ocean winds turn a bit more NW and actually become WNW over the Peninsula. These wind direction hit the coast at an angle and readily move into the Bay if there is a pressure gradient.

But also notice the AM wind coming from the Central Valley is N to NE to NNE. This wind direction tends to push the ocean wind away from shore and makes the PM winds later and weaker.

Equally important is that when we have NE flow the low pressure in the Central Valley often bulges out over the coast.

You can see this in the next animation.

Watch the time in the upper left and note the location of the isobars of the Central Valley thermal low.

The lowest pressure is in the Central Valley but from 2AM to mid day you can see that the isobars show a lobe of low pressure that extends over the coast almost to the Farallon Islands.

This means very weak AM wind since there is no pressure gradient over the Bay Area at the surface.

The image at the bottom of this page shows the overall pressure situation in the AM.

The weak NE flow aloft over  is due to a pressure gradient from a high pressure in the N. Great Basin. And with low pressure just west of the Bay Area in the AM we will have weak NE winds.

However since this is relatively warm air when it hits the coast range north of Sherman Island it tends to rise and most of the wind goes over the Bay Area. This NE flow helps to keep the low pressure over the ocean and also blocks the NW ocean wind.

In the PM the NE wind typically fades and as this happens the isobars of the Central Valley thermal low pull back to about mid bay. And this allows mild ocean wind to curve into sites like Waddell, Crissy, Coyote & 3rd that are on or near the coast.

 

 

 

Posted in San Francisco

West Coast Wind Blog: WNW winds and NE winds fight near Pismo making for…

Up and down winds at Pismo while locations nearby rip!

By Mike Godsey

Don’t you hate it when the wind forecast is full of wishy washy “ifs” and “maybes”! Today forecast was a classic weasel word forecast:

“Now at 11:30 AM Southern California looks on track as does San Diego. The Pismo forecast hinges on the NE winds just aloft and at the surface. Lopez and Nipomo Dunes are seeing weak unfavorable N to NNE winds while Branch Mountain just to the west is seeing NE winds averaging 19 knots. All of this will make it hard for the ocean winds to curve into the Pismo beach reliably. So…. I am sticking to the current forecast for UP AND DOWN low to possibly weak mid teens BUT if you see the sensors just inland staying NE all bets are off.”

So what does all that jargon mean? First look at the wind graph inset into the graphic above. Notice that from 1 PM to about 2:30PM the winds at the Pismo sensor (green circle) did reach the forecast values and were pretty up and down as forecast. But why did they fade so fast by 3PM and why up and down? And why were the WNW winds so powerful at the nearby Red Diamonds?

The local cause is the weak NE winds you see in the purple circle in the top imagery.

But the large scale answer starts far away from Pismo. Today there is high pressure in the Great Basin. That is creating NE weak offshore winds for much of California today. Those winds were funneled over the coast range and reached very close to Pismo. You can see this is the animation above. Look from the upper right corner to Pismo and you can see the NE wind flow at 2PM. Meanwhile as the pressure gradient to towards Cuyama Valley & Los Olives picked up in the afternoon the North Pacific High’s surface NW winds started curving in towards Pismo which you can see in the right side of the animation.

Now look that the area where the text says “Wind battle zone” In this area the WNW ocean winds and the NE winds from the interior collided. This NE flow tends to delay the arrival of the ocean wind and when there is a NE gust the winds ocean winds are blown away from shore so you experience a lull. But when there is a lull in the NE winds the WNW ocean winds slam back to shore and you experience a strong period.

Trying to put all this into a forecast is impossible hence all the weasel words in my brief forecast this morning.

Banner photo by S. Anderson

 

 

 

Posted in Los Angeles, San Diego

West Coast Wind Blog: The North Pacific High pushes a ridge into the Basins so…

Powerful easterly winds rip Rooster Rock.

by Mike Godsey, Mike AT windsurf.com

We have already seen one strong east wind event this fall and that event had devastating consequences for the Eagle Creek fire causing it to sweep from Eagle Creek to almost the outskirts of Corbett.

As you can see in Ben’s forecast for today we are in for big east winds again today. And as Ben says we can only hope this event does not stir up the fire.

So where do these east winds come from and why are they so tightly focused from Home Valley to Rooster Rock while rest of the Gorge barely has any wind?

First we have to look at the big picture. The first animation shows the west coast and much of the eastern Pacific.

Find the center of the North Pacific High WSW of the San Francisco Bay Area. The North Pacific High is further south than it was in the summer since it  has begun its annual migration to its winter time home closer to the equator.

Typically in the summer the North Pacific High is more oval shaped but sometimes when a low pressure system passes to the north the NPH extends a ridge towards the Pacific Northwest.

In the summer this usually means stronger west wind since we have high pressure just to our west.

But in this animation you can see that the North Pacific High has a narrow extension or ridge that extends into eastern Oregon and Washington. And you can see  the winds in the Gorge are EASTERLY. Also note the low pressure trough along the west coast. So we now have a E. to W. pressure gradient.

This happens as fall progresses since low pressure systems take a more southerly trajectory and the ridge from the North Pacific High moves way inland and sometimes high pressure ends up in the Columbia River Basin out past the Tri Cities and even into the Great Basin.

Hence we  have high pressure EAST of the Gorge rather than to our west as we see in the summer.

Now let’s zoom in and look at the isobars of the region.

Picture the North Pacific High as a dome or mountain of high pressure air. You are probably familiar with topographic maps land where lines of equal elevation show you where the terrain is flat or steeper.

So think of isobars as lines showing you areas of equal pressure. Where the isobars are packed closely together there is a abrupt change in the barometric pressure. And this means there is  a stronger pressure gradient and hence stronger wind.

The next image shows the isobars line of the North Pacific High’s surface ridge and those of the low pressure thermal trough along the coast.

The orange area and the isobars around it show the high pressure from the North Pacific High’s ridge.

The yellow area shows the low pressure thermal trough and its isobars.

Notice how the isobars are packed most densely right around the crest of the Cascades. This is where the pressure gradient will be strongest as well as the east winds.

In the last animation you can see the isobars from the high pressure to the east and the low pressure trough along the coast are packed tight near the crest of the Cascades in the Rooster Rock to Home Valley region. While the corridor from Viento to out East has very few isobars.

This happens because the crest of the Cascades acts as a barrier for the two pressure zones so the isobars stack up here.

Also note how the isobars are only tight in morning then become further apart in the PM. This means the strongest winds are typically in the morning and early afternoon.

The next question is why the winds are strongest in the morning. But that will have to wait. I am heading out now for some of that east wind.

Posted in Columbia River Gorge

West Coast Wind Blog: Slight shift in ocean winds from WNW-NW to NW-NNW…

Makes Piedras Blancas sensor read low while accelerating the Arroyo Laguna winds

by Mike Godsey, mike AT iwindsurf.com

Mike
As you work to understand the central coast winds, I thought You might be able to explain the winds the last couple of days at Arroyo Laguna. If you look at the 11am to 3pm time period on Wednesday and Thursday for Arroyo Laguna, you see wind speeds on the 15-20mph range and a fairly normal direction. However the reality was that we were sailing 5.2-4.2 and max powered on Wednesday and 3.8-4.7 max powered on Thursday. The winds were also a bit more side-off than usual with the strongest wind inside blowing the tops off the surf.
Was the true wind direction different than normal and Piedras Blancas was not picking up on the strong winds at Arroyo? There was definitely a disconnect between the two as Piedras Blancas normally would be a bit windier than the reality of Arroyo. Let us know what you think. Thx Hitech.

 

Hi hitech,

I am not remotely, yet, an expert on the Central California coast winds especially since you can count the times I have sailed Arroyo on one finger.

But in this case I can make a fairly useful analysis. Many sites along the coast such as Waddell, Piedras, Cabrillo. Leo etc have their winds slightly accelerated from a one sided venturi effect. This happens when the ocean winds compresses against the coastal hills or bluff and locally speeds up.

In your case the venturi is most commonly focused near Piedras when the ocean wind is more WNW-NW which, as you can see in our archive data, image #1 is the most common Sept. winds at our Piedres sensor.

But on Thursday image #2 from our Piedras sensor and the San Martin buoy #3 and had winds more NW-NNW. (this occurs when the NPH extends a ridge into the Pacific Northwest.)

When this wind shift occurs the max venturi will move further south which probably caused the acceleration you noticed at Arroyo. And with the venturi weaker at Piedras the sensor would read low compared to the wind at Arroyo. If you look carefully at the time slot the previous evening (red diamond) you can see when this wind shift occurred.

The last two images also show this effect. Looking carefully at #4 you can see how the NW wind would focus a venturi at Piedras while more NNW winds #5 would focus it more to the south.

There are hundreds of such effects we have to learn before we can do really useful forecasts for a region. After 20+ years I am still learning lots of new things about such effects in the Bay Area.

It is not so much that I am a slow learner but rather that our wind pattens are changing from year to year compared to the norm 20-30 years ago.

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

 

 

Posted in Los Angeles, San Diego, San Francisco

West Coast Wind Blog: 2017 Gorge daily fire expansion map.

 

“Smoke on the water” is a phrase that normally brings excitement to Gorge sailors & kiters… but not this time!

by Mike Godsey, mike AT iwindsurf.com

Below is a map I prepared using our weatherflow.com sensor data and a fire map from the Incident Management Team 2. Note that the most catastrophic fire expansion happened on Sept 5. when the fire swept over 11 miles of the Gorge in 12 hours driven by winds over 30 knots between Stevenson and Rooster Rock. Click on the map for a larger version. Click on the map for a larger version.

Posted in Columbia River Gorge, Los Angeles, San Diego, San Francisco
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