West Coast Wind Blog: How winds aloft impact the strength of the North Pacific High and California winds April 9.

Upper convergence and divergence the strength of the North Pacific High: 

by Mike Godsey, mikeATiwindsurf.com

ROUGH DRAFT

There is a tendency of many kiters and especially sailors to look at the wind from a 2-dimensional perspective. This means we only care about the direction and strength of the wind. Although kiters are sometimes aware that their kite is feeling winds that they are not feeling at the surface especially in gusty conditions.

Likewise, we are sometimes shocked when our airline flight time is much shorter or longer than the miles alone would predict. And if you live in the mountains you sometimes see evidence in clouds like the lenticular clouds in my banner and the image just above that there are powerful winds aloft even when it is nearly calm at the surface.

In our forecasts, we sometimes mention in passing upper-level winds or upper troughs and ridges but it is hard for us to connect these events to your surface winds in a single paragraph. So let’s take a more detailed geeky look at how those upper-level winds impact the high pressure and low pressures that often deliver our wind.

Simplified Upper-level Convergence and Divergence aloft in a simple 3D image:

First, let’s show  you a very simple 3D graphic of what convergence and divergence look like relative to surface high pressure and low pressure.

At the top of the image we are looking at the winds at about ≈ 18,000 ft. On the left side we are seeing Convergence of those winds. This makes the air more dense in this area so it sinks towards the surface augmenting the surface high pressure (Anticyclone).

On the top right of the image notice how the wind aloft is fanning out creating Divergence aloft. This makes the air less dense creating an area of lower pressure. And this encourages the surface air to flow upward which makes the surface low pressure stronger.

Model output and upper-level Convergence and Divergence in 3D image:

At the bottom of this 3D image for next Tuesday, April 9 and find the North Pacific High with its isobars compacted against the California coast. When the isobars are tightly spaced like this there is a strong pressure gradient on the coast so the NW accelerates. Note that there is also low pressure in the Great Basin and beyond which also contributes a pressure gradient that helps pull the wind down the coast and inland. Clearly, this is a very windy pattern for Northern California and perhaps Southern California. This is the sort of setup we will probably describe in our forecast next Tuesday.

Now let’s look at the back story why the North Pacific High is so strong next Tuesday and the Great Basin has such low pressure. Looking at the top part of the 3D image above notice the upper-level winds at ≈ 18,000 ft. The northward wind pattern is called an upper ridge while the southward pattern is called an upper trough. These are very strong winds that sometimes are over 100 mph.

Notice how these bands of upper-level winds are sort of like a river. In some location the wind band is wide and other locations it is narrow. For this to happen there has to be locations where the winds are converging like a river narrowing and other location where the winds are diverging like a river widening.

Remember that all the colored wind patterns are up at ≈ 18,000 ft. Now find the upper-level ridge and note how the upper winds approaching California are converging above the North Pacific High at the surface.

Now visualize all those rushing air molecules cramming into this zone. This will make the air over this region denser and since it is heavier it will sink in the atmosphere. This creates stronger high pressure along our coast. And as this air sinks it carries some of its motion towards the surface enhancing the North Pacific High’s surface NW winds.

Now check out what is happening over the Great Basin. The upper-level winds in that zone are fanning out or diverging. This means the rushing air molecules are further apart creating lower pressure aloft. And this, in turn, enhances the surface low pressure in the Great Basin.

This lower pressure creates a pressure gradient from the North Pacific High to the Great Basin strengthen the surface NW wind and encouraging it to move inland.

Since these upper ridges and upper troughs normally move from west to east the zones of convergence and divergence will shift eastward and the North Pacific High’s surface NW winds should weaken of following days.

 

 

 

 

 

 

West Coast Wind Blog: 2 North Pacific High’s double-team the California coast!

After long NW wind drought the Northern California coast is poised to rip next week!

by Mike Godsey, mikeATiwindsurf.com

If you kite or sail near the Northern California coast you are aware that our typical NW clearing winds have been sparse this year. First, we had a prolonged Omega Block that kept low pressure just off our coast for over a week. And this week a huge storm system stretching from Cape Mendocino, California to past Alaska has brought only southerly winds to the Bay Area.

All of this action has kept the North Pacific High and its NW wind focused along the Baja coastline. In this first image let’s take a look at the current Pacific scene to see why the wind will be weak today through next Monday.

First, notice the isobars around the huge low-pressure #1 that dominates the northern Pacific. Then note #2 how the storm’s southerly winds are hitting the coast from Mendocino to Alaska. Meanwhile, a weak North Pacific High #3 is keeping its surface NW winds focused over Baja waters. Lastly, note the “new” North Pacific High that has formed near Hawaii.

The next image is an animation covering the days from Friday, April 5 to Tuesday, April 9.

Once again notice that there are 2 North Pacific Highs. Keep an eye on both of them as the days progress. Watch how the North Pacific High north of Hawaii merges with the one off Baja and how the combo greatly expands and move towards the California coast. The development is enhanced by convergence aloft by an upper ridge (which is a topic for a future blog)

Looking carefully you can see how the North Pacific High’s isobars tighten along the coast. And, at the same time, surface low pressure develops in the Great Basin and is enhanced by divergence from an upper trough (which is a topic for yet another future blog). This low pressure greatly enhances the strength of the NW ocean winds and encourages their flow deeper into the Bay Area. And all of this also jazzes up the winds just aloft over the Bay Area so expect a strong gust factor.

Remember all of this is a bit speculative. There is a chance that the North Pacific High will move a bit inland north of the Bay Area which would make the ocean winds a less favorable NNW wind direction.

Imagery annotated from windy.com

 

West Coast Wind Blog: Southern California low pressure can bring wind riches or poverty.

by Mike Godsey, mikeATiwindsurf.com, More photos here

Lots of you know about the thermal trough (aka “heat bubble”) that can kill some Southern California sites, especially from Belmont to Seal, when we get a major heat event. But if I am right we will be dealing with another thermal trough tomorrow, Monday, April 1.

This thermal trough starts over Baja and the Sea of Cortez and expands over most of Southern California Monday afternoon. So just as you would expect our normal wind reversal as the Southern California inland valleys heat huge low-pressure balloons over the entire region killing the wind.

You can see this inverted thermal trough in this first image from tomorrow.

Notice the white isobar lines extending up from Baja over Southern California. This is the thermal trough. Then notice all the red and orange colors that represent heat and how they and the isobars extend well into the Southern California Bight. This will probably spoil the pressure gradient from the ocean to the beaches.

This thermal trough is caused by a heat-inducing upper ridge at ≈ 18,000 ft. that will briefly form over Southern California.

What happens next is interesting and exciting for wind. Tuesday the northern part of the thermal trough breaks off and forms a separate low-pressure area over southern Nevada.

At the same time, the isobars of a tiny North Pacific High move towards the coast. So, if I am right, we have a strong pressure gradient from the NPH and the low pressure in Nevada. This should create strong winds for the Southern California coast all the way to Lake Isabella.

You can see all of this happening in this model animation I made from the windy.com website.

 

West Coast Wind Blog: An “Omega Block” is not a watch brand boycott.

by Mike Godsey, Mike AT iwindsurf.com

This symbol, omega, is the last letter of the Greek alphabet and a famous watch brand. But in meteorology, it is the shape of the omega symbol, written in our upper-level winds, that has locked most of the west coast into a weather pattern with little day to day change. Specifically, it has given the Gorge mostly blue skies while depriving the San Francisco Bay Area of NW clearing winds. While Southern California has sometimes benefited from mild NW winds curving into the beaches.

Take a look at the brightest colors in the image below and look for an “omega”  pattern in the winds at ≈ 18,000 ft. When this pattern of upper level ridges and troughs develop it largely blocks the normal movement of weather from West to East.

Let’s take a look at this diagram step by step.

  1. First find Southern California, Bay Area and the Gorge.
  2. Notice the isobar white lines. They represent the surface pressure at different locations.
  3. Now notice the large storm off the west coast. It has been locked near that location for many days and has barely impacted our weather.
  4. Then note how far the North Pacific High is from the Baja and California coast. Not much chance of NW wind on our coast!
  5. The thick red line accentuates the Omega shape of the upper-level winds.
  6. Notice how the upper troughs make up the”arms” of the Omega Block.
  7. And between the 2 upper troughs, there is an upper ridge. Voilà, an Omega Block!

Once this type of block sets up it is slow to change and is keeping the North Pacific High from moving up and towards the west coast. It also makes for boring forecasting since things change little from day to day. Notice how this block does not have a perfect Omega shape and it slowly breaks up the next 4-5 days. As this happens my guesscast is that Southern California will see building NW winds Thursday while the Bay Area has to wait until Sunday or Monday.

West Coast Wind Blog: Unending easterly winds for most of the west coast.

by Mike Godsey, mail: mike AT iwindsurf

Recent days have seen cool powerful easterly winds in the western Gorge, powerful Santa Ana winds for Southern California, nagging wind killing NE winds just aloft over the Bay Area.

And for the great majority of kiters and windsurfers, these easterly winds are useless.

But there is one region that really benefits from this pattern. This animation shows the wind hero for Baja and the wind culprit for the rest of the west coast.

Note how the topography of the Gorge makes the wind pure east. While to backbone of the Baja Peninsula makes the wind there more NNW.

Check out the high pressure and all the winds spiraling out from the High.

All these easterly winds fades the next day or so as the high pressure finally exits eastward.

The wind in all these

 

West Coast Wind Blog: Baja’s East Cape 5 basic wind patterns

by Mike Godsey, Mike AT iwindsurf.com

About 25 years ago, when the first windsurfers “discovered” La Ventana, “Weather Man” Tom and I started studying Baja winds using the daily data collection form you see in this first image.

Since then my main goal was to figure out what caused the La Ventana and Los Barriles, located on Baja’s East Cape, to have the strongest most reliable winter winds in Baja so we could forecast the winds rather than just waiting for wind.

image #1

This first image shows the sort of daily records we kept of variables we tracked to get insight into the wind patterns. One thing that is clear… most of the models do a poor job of forecasting Baja winds. Just check out the notice on the Capt. Kirks web page. A bit exaggerated but it gets the flavor.

Through the years I have concluded that the causes of these highly focused Baja winds are complex. But the short answer is that many places on the Sea of Cortez side of Baja receive the rare very strong El Norte winds.

But most of the time the El Norte winds are relatively weak low to mid-teens range.

So to get winds reliable winds above the low teens you need special topographic features and a combo of winds to augment the El Norte winds to create at least upper-teens wind.

And Los Barriles, and especially La Ventana, have near perfect topography for frequent reliable winds in the mid-teens to mid 20’s range.

Overview of Baja’s East Cape topography:

image #2

Baja is a 760 mile long Peninsula with a mountainous backbone and 1900 miles of coastline.

Baja has a relatively cool Pacific ocean to the west and a much warmer Sea of Cortez to the east.

La Ventana and Los Barriles are located towards the tip of the Peninsula about a 3-hour drive north of the tourist traps of Los Cabos.

Looking at these graphics you can see that both locations have large valleys downwind that impact the local sea breezes and the synoptic scale El Norte wind.

La Ventana’s Los Planes Valley is surrounded by mountains of 3 sides which means that expanding air heated from the sun has nowhere to go but up. And this creates a local low-pressure zone and a strong local pressure gradient from the Sea of Cortez towards the valley.

Unfortunately, the valley downwind from Los Barriles has mountains on only 2 sides and is open to the south. So some of the expanding air “leaks” to the out so this valley produces a weaker local pressure gradient.

This means that Los Barriles has weaker local sea breezes.

However, Los Barriles sticks further out into the Sea of Cortez so it receives stronger El Norte wind and larger swell near the beaches

Five basic wind patterns of La Ventana, El Sargento and Los Barriles

Let’s examine each of these patterns using imagery:

Pattern 1: The strong El Norte (North) wind:

image #3

The strong El Norte has the most powerful winds but it is the least common of the 5 winds patterns and for

last 15 years it has become increasingly rare.

Big El  Norte winds occur after a storm passes over California. Then in the wake of the storm, a large high pressure often settles into the Great Basin.  You can see the start of this process in this animation.  Watch how isobars tighten over the Sea of Cortez as the high pressure moves into the 4 corners.

The perfect location for strong Baja winds is for the high pressure to be centered over the 4 corners area.

With high pressure to the north of the Sea of Cortez and low pressure to the south strong winds rip down the entire Sea of Cortez.

Usually, major El Norte winds arrive in the middle of the night and dawn sees very strong winds just outside and large building surf on the beaches.

El Norte surface winds are often accompanied by strong winds just aloft and as these wind hit the cliffs and points of the rugged Baja coast they become turbulent and transfer a bit of momentum to the surface winds that make the wind in your kite or sail UP AND DOWN and shifty.

image #4

This pattern is easy to forecast since models track such large scale pressure system accurately.

Pattern 2: Mild El Norte (North) wind + local sea breezes pattern:

In this pattern, there are mild El Norte winds in the mid to upper-teens range. By themselves, these winds would mostly stay way outside. But if the skies are blue the inland valleys heat creating a local pressure gradient.

That pressure gradient does 2 things.

1. It causes the El Norte wind to curve in towards the beaches.

2.  it creates a local sea breezes in the low to weak upper-teens range that combines with the El Norte winds. The combo of these winds reaches the upper-teens to low 20’s range.

The key to this pattern is the blue skies or at least patchy clouds inbound towards the inland valleys.

Pattern 3: El Norte winds + weak NW wind from NPH on the Pacific side

This pattern is most common in El Nino years. It happens when high pressure in the Great Basin creates moderate El Norte winds which curve to the beaches due to the local pressure gradient. But as the day progresses the wind winds inside become very gusty or shifty or very weak. This is especially true at La Ventana and especially at El Sargento north of La Ventana. While Los Barriles typically has steadier winds during a strong El Norte.

This animation below shows why this happens. Notice in the left image at 8AM the El Norte winds flow smoothly down the Sea of Cortez. If the North Pacific High and its NW winds are far from Baja this smooth flow continues through the afternoon. So the El Norte winds are steady and close to shore while the big swell is smooth and starts only a few hundred yards from shore.

image #7

However, if the North Pacific High’s NW winds are close to the Pacific side, as in this animation, there is a problem. As the interior of Baja heats up the NPH’s NW winds are sucked through gaps in the mountains of Baja. Looking at the 3PM image you can see this happening. This NW flow from the Pacific tends to push the El Norte winds further from shore.  This NW wind is turbulent so the El Norte winds seem gusty and shifty as the 2 winds interact. This NW flow also causes a small cross chop to develop over the normally big smooth El Norte swell. Even without computer models, you can anticipate this effect.

Pattern 4: Just local sea breezes and NO El Norte.

image #8

image #9

This is the most local pattern and produces the weakest winds except occasional wind drought.  As the inland valleys heat and warm the air a low-pressure zone is created. This air rises and heads seaward for several miles where it cools, descends and is attracted to the low-pressure inland. If you kite far enough out you will run out of wind

The key to this wind is mostly blue skies over the inland valleys. If the weather is fair and cloudless and there is no hint of an El Norte Baja’s East Cape is likely to see these low to weak upper-teen local sea breezes.

However, if there is a storm to the north or if the subtropical jet stream is overhead things get dicey. In this situation, we need a large hole to develop in the inbound clouds from about noon to mid-afternoon that will allow heating inland. And as you can see in these images the cloud pattern can change fast. So if the forecast suggests local sea breezes your best bet is to watch the skies to the east over the valley

If you have binoculars and a good view to the north you will be able to see a dark blue line on the horizon that is the sea breeze

image #10

front moving towards the beach. You can see such a front in image #2 above.

Pattern 5: No El Norte winds but strong NW wind from the North Pacific High + local sea breezes

This is an uncommon pattern and since the NW winds have to travel over relatively warm terrain and take a circuitous pathway across the Peninsula they are usually weak, shifty, up and down with an unfavorable offshore angle.

The next animation shows this pattern in action. First, note that there is NO El Norte wind coming from the Great Basin.

Instead, there is very strong NW wind from the North Pacific High ripping down the Pacific side of Baja.

Since the Sea of Cortez is relatively warm compared to the Pacific there is a slight pressure gradient that curves and sucks some of the NW wind over the Peninsula anywhere where there is a low spot in the mountainous backbone of Baja.

image #11

I have highlighted some of the places where this happen in the animation. Notice how some of this wind comes across the Peninsula and hits the La Ventana and Los Barriles area. You can see how this will be offshore wind.

However, if there is strong heating in the inland valleys near La Ventana this NW wind may curve into N. wind and provide strong wind just outside.

At the beach, the wind will probably be up and down and shifty since some of the NW wind leaks over the mountains just inland.

El Nino & La Nina:

The relative frequency of these 5 wind patterns varies from year to year. And the relative frequency of each pattern seems strongly dependent upon El Nino vs La Nina vs Neutral year. This is because the storm track moves further southward in El Nino years. While the average storm track is more northward in La Nina years.

The more northerly or more southerly route of the average storm track is pivotal in determining the location of the high pressure relative to the Great Basin. And this, in turn, determines the strength of the El Norte wind.

El Nino and La Nina also impact the pathway of the subtropical jetstream and its clouds which in turn influence the local sea breezes.


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West Coast Wind Blog: March 12 brings strong winds to entire west coast!

Strong North Pacific High + low pressure in Great Basin + strong winds aloft = Epic winds!

by Mike Godsey, mike AT iwindsurf.com

Strong wind ruled the west coast on March 12, 2019. Here is a visual summary of the causes and the results:

  1. Note the North Pacific High off the west coast.
  2. Look at how the NPH’s isobars stack up along the west coast creating strong NW wind.
  3. Check out the low-pressure zone in the Great Basin creating a strong pressure gradient.
  4. Note how the NW wind curves inland towards the low pressure in the Basin.
  5. Check out how many of the sensor in the San Francisco Bay Area have winds in the low 20’s to upper 30’s
  6. 3rd. Ave had peak average winds to 37 mph.
  7. And Southern California had sites with winds in the upper-teens to even mid 20’s.
  8. C St. in Ventura had average winds to 26 mph.
  9. A bit factor in the strong surface wind was the strong gusts to 40 mph just aloft over the Bay.
  10. And Southern California had similar winds aloft.
  11. On most days kites way outnumber windsurfers at 3rd. Ave. but not late Tuesday afternoon.
  12. An for a change the Gorge was at the bottom of wind totem pole excepts for Dougs that hit a respectable 29 mph.

West Coast Wind Blog: Eddy & North Pacific High divert wind from Bay Area

Weak winds prevail today as eddy spins.

by Mike Godsey, mike AT iwindsurf.com

There is a robust North Pacific High today stretching from Hawaii to Puget Sound. But it has an extension or ridge that is moving towards the Columbia River Gorge. This means that the North Pacific High’s surface NW winds are more NNE over the ocean rather than the typical NW. This flow direction helps create a large eddy like low pressure off the San Francisco coast. So with no NW wind and low pressure near us the winds will be limp except for some SE winds flowing towards the eddy. You can see all  of  this in this infrared satellite animation I made this morning.

West Coast Wind Blog: Winds just aloft jazz up Baja surface winds.

by Mike Godsey

mike@ikitesurf.com, Photos & Videos

Did you notice how the El Norte this morning forecast upper-teens to low 20’s with periods much stronger especially outside? The baseline for our winds was relatively strong El

Norte winds from the 4 corners with a bit of help from the North Pacific High and our local thermal winds.

However today the models projected much stronger winds just aloft up at the 975mb level which is about 1000 feet aloft.

Since there is topography near that height upwind of us those winds aloft would, in theory, becomes turbulent which would allow some of that stronger energy wind to transfer momentum to the surface winds. Hence the gusts well into the mid to upper 20’s.

ich would allow some of that stronger energy wind to transfer momentum to the surface winds. Hence the gusts well into the mid to upper 20’s.

You can see these winds in this animation. And the two wind graphs show the strong gusts.


West Coast Wind Blog: Clouds weaken local thermal wind

by Mike Godsey, mike@iwindsurf.com

For more photos from Baja and the west coast click this link.

Sometimes I just have to put weasel words in the forecast even when almoat everything looks promising in the early morning. In today’s forecast, Thursday, February 21, 2019, those weasel words were “If heavy clouds to the west do not come over us the local thermal winds reach the mid to mild upper-teens strongest at Rasta and weaker for La Ventana and weaker yet for Los Barriles”

I had to put those weasel words into the forecast since there is a vague cold front sweeping down Baja from a storm system moving in to Southern California and Baja Norte. And at dawn there were hints of some of those cloud not too far away from Baja’s East Cape. And if they arrived early it would kill the wind.

By 9:30AM it was clear to me that some of those clouds were getting too close so I issued this to the forecast: “UPDATE at 9:30 AM. The most recent satellite imagery is showing some heavy convective clouds about 100 miles to the west of La Ventana and their trajectory could bring them over our mountains and perhaps over the Los Planes valley which would really weaken the wind today.”

As you can see in my annotated satellite image for today those weasel words were justified as heavy clouds inland almost totally killed the thermal winds for Los Barriles. While frequent tiny patches of cumulus clouds from the west evaporated over the western Los Planes Valley much of the morning while a swath of heavier clouds closer to La Ventana was the final nail in the coffin for getting winds above the weak low teens.

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