West Coast Wind Blog: Strong pressure gradient to Great Basin means…

Strong winds for Southern California… but where, coast or interior?:

by Mike Godsey, mikeATiwindsurf.com

As you follow the Southern California forecasts you probably find yourself looking forward to the words “strong pressure gradient to the Great Basin” Maybe it does not make any sense how a place so far away from the Southern California coast can make for stronger beach winds but you have noticed the relationship between that gradient and strong winds in your kite or sail.

But last Friday you may have been puzzled when my forecast (replete with typos) paired those normally magical words about the Great Basin with a forecast for very weak winds on the entire coast from Pismo to San Diego.

The green circles in the 2nd. image shows that every site on the coast had very weak wind even late Friday afternoon.

But looking at the red diamonds note the very strong  wind in  the  mountains and the desert. How can a strong pressure gradient to the Great Basin low pressure cause winds  in the mid 20’s to low 40’s  inland while the coast only has sub to barely low teen winds?

To  short answer is “isobar distribution”  Let’s explore that topic. This animation shows the western USA and the eastern Pacific. First check our the shape and location of the North Pacific High.

Note that the center of  this wind machine is not the typical oval shape between the west coast and Hawaii. Instead it has been flattened into a sausage shape and much of the high pressure is in Canadian waters far from Southern California.

Now check out the caption in red about isobars. Those white lines in the image are lines of equal pressure. The closer the lines are  together the stronger the pressure gradient and the winds.

Notice the strong NW to NNW winds just off Caand the  the far Northern California coast. Then note that there is only one isobar in the Southern California Bight between Santa Barbara and Southern California. This means that the ocean winds will be very weak along  that stretch of coastline.

The next image is a close up of the Southern California to Great Basin zone.

In this image check out the low pressure in the Great Basin. Notice all the isobars around that low pressure. Especially note how close together the isobars from the low are right over the interior of Southern California.

Also notice how strong the wind flow is in this area all the way to the Great Basin.

Now  imagine that the tight isobars of the North Pacific High you see in the Canadian waters were stacked  in the Southern California bight. With a strong  pressure gradient over the SoCal ocean waters AND a strong  gradient to the Great Basin Southern California would be rocking to crazy strong winds.

 

 

West Coast Wind Blog: Big Eddy and SW flow means…

 

 

Delight for many at sites North of the Bay Bridge but despair to most sites to the south.

by  Mike Godsey, mikeATiwindsurf.com

The banner image above looks all to familiar this year to those who kite or sail the waters of 3rd. Ave. All to often strong NW wind days found unfavorable light W   to WSW  winds inside.

And this was on days when the forecast was for strong NW wind for the entire coast and most of the Bay. So locals on those waters are probably hoping for a transition to a different wind pattern.

We today and especially tomorrow we transition into a different pattern. Sadly it is on that is even worse for the coast and 3rd. Ave.

As you can see in the top image there is a small counter-clockwise spinning eddy west of the Bay Area. I am forecasting this eddy to keep spinning most of the afternoon. When this happens the eddies southerly winds jazz up the SW flow through the gaps in the coast range.

his makes the north tower to Treasure Island to Pt. Isabel winds stronger. But it also pushes W over the coast range near 3rd. and SW flow through the Hwy. 92 gap from Half Moon Bay to near 3rd. Hence the weak winds forecast inside for 3rd. today. It can’t get worse than this for 3rd… yes it can.

Looking at the next image you can see the modeled winds tomorrow morning.

Notice how much larger the eddy becomes. If the models are right we will have southerly eddy winds from past Bodega all the way to Monterey. This means doom and gloom to 3rd. and the coast.

But the huge eddy should favor the north tower to Sherman Island corridor.

So what is with the giant eddy. To answer that we have to look aloft.

The last image is an animation of the winds from the surface to 5000 feet. Notice how the eddy at the surface is augmented by a counter-clockwise spinning low pressure aloft.

Also notice how there are surface pressure gradients towards Chico, Stockton and on to the Great Basin. There is also a strong pressure gradient through Pacheco Pass to San Luis.

More a bit later…

 

West Coast Wind Blog: A day in the life of the North Pacific High and…

What it means for today’s winds in Southern California, San Francisco Bay Area, California coast, Baja and The Gorge

by Mike Godsey, mikeATiwindsurf.com

Today the North Pacific High is the master of the eastern Pacific from The Gorge to Southern California to Baja to Hawaii. All of these venues will have winds today that are mostly the result of the distribution of the North Pacific High’s isobars.

Remeber that the North Pacific High is a dome-shaped mountain of high-pressure air formed as air from the tropical ITCZ (towards the equator) decends over the eastern Pacific. You have all seen the topographic lines that circle around a terrestrial mountain. These lines around land mountains show lines of equal elevation. And you probably know that where the topographic lines are close together the terrain is very steep or even cliff like if the lines are tightly packed.

So think of the isobars you see around the North Pacific High dome of high pressure as being somewhat similar. But instead of showing elevation they are lines of equal pressure. And the closer the lines are to each other the steeper the pressure gradient and the stronger the winds. And due to the rotation of the earth the winds spiral clockwise outward from the center of the North Pacific High. Notice that the isobars are very far apart in the center of the  North Pacific High hence the winds are very weak.

Years ago I used all my scholarship money to buy a tiny sailboat and naively set sail directly from the Golden Gate through the middle of the North Pacific High (NPH? what NPH?) and bobbed around  for a week with diminishing water supplies in a glassy pacific getting more and more frightened until the center of the NPH happened to shift northward.

But back to our topic…

Let’s start with Hawaii. Notice that the North Pacific High’s surface winds are NE to ENE near Hawaii. The winds in this part of the North Pacific High are very reliable and came to be called the trade winds in the days of sailing vessels. The isobars are fairly close together today so the winds in Hawaiian waters should be moderate if there is enough heating to coax the winds to the beaches.

The Gorge is the opposite situation today. The North Pacific High has budded off a lobe of high pressure (see the tiny “H” east of the Gorge) this is an area where the air is descending and compressing making for warm, cloudless conditions. And looking at the isobars spacing what would your forecast be for the Gorge today? Hint… think high pressure to the east and cool dense air towards the coast.

Next look at the northern and central California coast. Note that the North Pacific High’s surface NW winds isobars are very close together hence a strong pressure gradient and strong NW winds (in orange). The trouble with the North Pacific High’s surface NW winds is that they are roughly parallel to the coast. This is fine if you sail right at the coast but if you have a cape or land point up winds (think Pismo) or if you are inside a Bay (think San Francisco) you need another pressure gradient to curve the NW ocean winds into your launch site. (think Central Valley)

oday with the weak northerly winds in the Central Valley (as you see in the animation) the moderate pressure gradient near the Bay Area is towards Morgan Hill and Bakersfield so my bet is that most of the winds will be on the coast and from Treasure Island southward into the Peninsula.

Baja Norte is easy since it usually directly receives the North Pacific High’s winds. However notice how the Catalina Eddy is deflecting the wind heading towards San Carlos. So the winds will be iffy at PSC until later this afternoon. And Baja Sur is usually less reliable since the winds of the NPH are curving away from the coast in this area.

And now for Southern California. Sadly, the California coast takes a dive eastward from Jalama to San Diego making for an open bay or Bight. This means the North Pacific High’s surface NW winds scream through the outer Southern California Bight on their way to San Quintin and San Carlos Baja Norte. Worse the Traverse Range north of Santa Barbara creates a localized low-pressure area as the northerly winds hit it. Together these factors often create the wind killing AM Catalina Eddy you see in the animation. So to get the North Pacific High’s surface NW winds to blast apart the eddy and to curve into the Southern California coast you need a strong pressure gradient to a combo of the inland valleys, Southern California deserts and Great Basin.

So in forecasting, we are looking at the location of the North Pacific High which is often over 1500 miles to the west AND pressure gradients to places hundreds of miles away AND the vagaries of local topogrpahy just a few miles upwind of your launch site.

 

West Coast Wind Blog: Fate of Mid Channel Eddy off Santa Barbara and…

The Isla Vista to Ledbetter to Ventura winds

Rough Draft Part One

You have probably noticed that it is very hard to forecast the winds in the Isla Vista to Ledbetter to Ventura corridor despite the very strong winds that are very close to this area.

This first image shows a common wind pattern. The yellow-green colors show areas of higher pressure. The blue color shows areas of lower pressure. The size of the streaks shows the wind velocity and direction.  Notice the strong NW wind of the North Pacific High to the west. But also notice the moderate winds coming over the mountains due north of Santa Barbara. As this wind climbs up the mountains and then descends towards the coast it compresses and heats.

You can see this by comparing the temperature in the image at Coleta compared to nearby location. Warmer air expands creating lower pressure. This makes some of the NW ocean wind curve in towards Santa Barbara creating the Mid Channel Eddy.  This eddy acts to block the NW ocean winds from curving into the Vista to Ledbetter to Ventural corridor. If the eddy dies midday then solid winds are likely to reach those sites. If the eddy lingers then there are strong winds just offshore but weak winds at the beaches. The key to when the eddy dies is the time the canyon winds descending from the mountains fade. The earlier they fade the greater the likelihood of solid wind.

The next animation shows the modeled winds for today. Can you see why I am forecasting weak winds for the Vista to Ledbetter to Ventura corridor? More later.

West Coast Wind Blog: A forecast decoded: Southern California, S. F. Bay and Southern California.

The Gorge Roars while AM eddies rule in the Bay Area and Southern California.

by Mike Godsey

So on a day like today if we had only ONE wind forecast discussion for the entire west coast it might read like this:

“A large North Pacific High spanning the waters from the west coast to N. of Hawaii brings strong winds near the coast. However as the NPH extends a ridge into the Pacific Northwest and far northern California it’s isobars tighten over the Gorge making for very strong winds. At the same time it’s isobars turn W. to E. over Northern California so northerly wind comes down the Central Valley. The ridge also encourages unfavorable NNW winds in the AM just off the California coast and a low pressure trough over the Central California coast and Southern California Bight. This means weak AM winds and an eddy outside the Golden Gate and in the Southern California bight and even near Pismo Beach. These eddies die midday and the winds in California improve.”

Although this discussion sort of looks like English it, by necessity, uses some meteorology jargon.

Let’s start to decode this discussion using this imagery. First find the Gorge, Bay and Southern California in the image. Now look about 1000 miles to the west where the center of North Pacific High resides today. The NPH is a dome of high pressure created when air from way aloft descends and compresses creating higher pressure. This higher pressure air then spirals outward in a clockwise fashion which you see in the image above. The white lines are isobars and show areas of equal pressure. The closer the lines are to each other the greater the change in pressure. This is known as a pressure gradient. Notice how the isobars are really tight off the California coast and over the Gorge. The direction of the wind is at an angle to the isobars so the shape of the North Pacific High determines the winds direction unless topography steers the wind.

Now notice how the NPH has a bulge over the Pacific Northwest and far Northern California. This is called a surface ridge. In the case of the Gorge the ridge’s isobars run from N. to S. and they are packed close together. However the winds are funneled by the steep topography of the  Gorge so the winds is more W. to E. The narrow walls of the Gorge also accelerate the winds.

Next check out the bend in the ridge’s isobars from the surface ridge over Northern California. Note how they are oriented more W. to E. This means there is an N. to S. pressure gradient. This means northerly winds in the Central Valley.

Then check out the angle of the isobars just offshore of Northern California. Notice they are not parallel to the coast (this would promote NW winds) rather than being at an angle to the coast so the wind is more NNW. This angle to the wind is unfavorable since it makes harder for the ocean wind to curve into the Bay Area and the Southern California beaches.

One last variable to note. See the loop in the isobars extending up from Southern California and over the Bay Area and Central California coast? This is a surface low-pressure trough. This will make the AM wind very weak in that area.

The combo of the low-pressure trough and NNW ocean wind tends to cause counter-clockwise spinning eddies to spin just off the Golden Gate and for most of the Southern California Bight.

Today the NPH ridge retreats from over Northern California midday and the low-pressure trough retreats to the Central Valley. If this happens as expected the ocean winds is less NNW and eddies will die. So despite the gloomy start of the wind the winds conditions often improve at select sites.

VLOG: Subtropical Storm Alberto 5/25/18 9:15PM ET Update

By WeatherFlow meteorologist Shea Gibson

Here is my latest comprehensive look at Subtropical Storm Alberto and its future forecast.

Shea Gibson
WeatherFlow Meteorologist/Wind Forecaster
Outreach & New Station Projects
SE Region/East Coast
Twitter: @WeatherFlowCHAS

West Coast Wind Blog: Weak winds turn strong as…

Upper trough departs and upper ridge steers NPH towards California.

by Mike Godsey, mike AT iwindsurf.com

You Sherman Island fans have had good to great WSW winds the last several days. But for rest of the Bay Area and Southern California, the winds have mostly been weak WSW to SW with a nagging marine layer. Meanwhile, our extended forecasts have consistently mentioned building NW ocean winds this coming weekend.

The animation below spans the Pacific from just north of Hawaii to California. Get yourself oriented by finding Southern California and the Bay Area on the right side.

The animation starts showing the surface isobars (lines of equal pressure) and the surface wind for today Thursday, May 24. Notice the sparsity of isobars and winds in the Pacific near California today. This means weak winds along the coast.

 

 

 

 

Now check out how the center of the North Pacific High moves much closer to California Saturday and how the isobars tighten and the NW winds crank on the coast. So far this does not appear to be major NW event since some of the other variables will not be perfect. Still, it will be a welcome change for those who loath SW flow and thrive on NW flow.

Still, the question remains, what caused all this SW flow and deeper marine layer and why do we switch to NW flow on Saturday.

The answers are way aloft in the 500 MB. level (remember that sea level pressure is about 1000 MB). The height of the 500 Mb. fluctuates but averages ≈ 18,000 ft. The winds at this level snake around the globe with northward extending loops of warmer air called upper ridges and the southward extending loops of cooler air called upper troughs. These upper ridges and troughs are critical since they steer and augment the surface lows and highs that make the winds that fill our sails and kites.

Now look at this second animation which shows the winds at ≈ 18,000 ft. AND the surface isobars so we can compare the two.

Notice how that today, Thursday, May 24, there is a strong upper trough just off the west coast. This upper trough is the major factor in our recent wind patterns in the Bay Area and Southern California winds. A summer upper trough near the coast does several things: 1. It allows the marine layer to deepen but the clouds may mix out if they become too deep due to cold air aloft. 2. creates SW flow aloft that sends the marine layer further inland. 3. brings cooler air inland. 4. often encourages a counter-clockwise spinning low-pressure system to develop offshore creating mild SW ocean winds. 5. often it promotes thunderstorm in the Sierra. 6. rarely it can also bring scattered showers near the coast.

Now looking at the same animation for Saturday, May 26 notice how the upper trough is exiting eastward over Nevada while the upper ridge lunges towards the coast. This acts to steer the surface North Pacific High’s surface NW winds closer to the California coast and brings NW winds aloft over California. So, strange as it might seem, the accuracy of my Southern California and Bay Area forecast for this weekend hinges on events almost 3 miles aloft.

West Coast Wind Blog: Upper trough approaches and Sherman roars…

But deep marine layer and SW flow brings weak winds to Southern California and most of the Bay Area!

by  Mike Godsey, mike AT iwindsurf.com

Low 20’s winds have blown a Sherman Island much of May 23, 2018. We have all learned to expect this when the marine layer is deep and far inland. But what is unusual today is that most of the ocean is clear except near Bodega. Meanwhile most of the Bay Area is socked in.

Likewise in Southern California, the winds will be weak today with clouds lingering over the land while the coast is clearer.

So what is behind this Bay and Southern California wind pattern. And how did Mark know to forecast these winds over a day in advance?

In this first image first, find Southern California and the Bay Area. Then note the southward extending loop of upper-level wind at 500mb at ≈ 18,000 ft. This loop of wind is known as an upper trough. The air within the loop is relatively cool and the pressure is relatively low.

As this upper trough moves eastward it is bringing cooler air to the west coast and the lower pressure is allowing the marine layer clouds to deepen. Meanwhile, the SW flow you see in the animation extends close to the surface blowing the marine layer clouds far into the Bay Area. The same process is happening in Southern California.

Now check out this satellite animation of marine layer clouds from dawn to mid day May 23.

First, find the Golden Gate. Notice that the deeper marine layer and SW flow from the upper trough sent a broad streamer of marine layer clouds over the Bay Area, across the Central Valley and even over the foothills of the Sierra.

Also, notice how this streamer evaporates as the morning progresses. As the land heats up it makes the fogs water droplets turn into invisible water vapor. Since Sherman Island is the only sea-level pathway for these SW winds it, and to a lesser extent Benicia, are the focus of the strongest winds.  Meanwhile, in Southern California, there are similar gaps in the mountains but these gaps are landlocked so only a street kiter could use that strong wind.

Next notice how the marine layer clouds over the ocean become increasingly patchy as the day progresses. This process happens when the air aloft from the marine layer is so deep and the upper trough is so cold that it breaks up the inversion. So paradoxically an upper trough can both deepen the marine layer and also cause it to break up.

Lastly, notice how the ocean winds north to the Bay Area are a bit NNW. This is stirring up some eddies that will keep the North Coast winds weak.

Kite Surfer Rescue

by Weatherflow Meteorologist, Kerry Challoner Anderson

Last night I was out walking near sunset, checking out the marine layer development north of Santa Cruz, California when I noticed a Kite Surfer struggling to make it back to shore.

The winds were quickly fading as the temperature over the land cooled off.  High pressure over the Pacific had strengthen and moved closer to shore which turned the winds along the California shoreline more northerly.  Consequently the coastal winds were well offshore at Santa Cruz.

Wind speed and direction for the Northern California coast on May 17, 2018

It was interesting to take a look at the observations at this time and see how quickly the wind dropped as the temperature dropped, which showed that the coastal winds were not in play and the only fuel for the Bay winds were sea breezes.  Once the temperature cooled over the land the convection cell vanished and the winds died.

Fortunately rescue crews  arrived just before the light faded to provide assistance back to shore.

Severe weather in the Northeast

Thunderstorm season in the Northeast US is off to an eye opening start after yesterday’s severe weather outbreak. A strong squall or line of thunderstorms passed through MA down to NJ in the late afternoon and evening bringing damaging winds and localized hail. 

 

 

In the radar image below, note the gust front ahead of the thunderstorms and the high dBZ signatures (in purple) over CT as thunderstorms barrel through. Dime to golf ball sized hail was reported in parts of NY and CT.

WeatherFlow stations recorded several gusts around NY and CT exceeding 60 miles per hour!

Honorable Mention: WeatherFlow station, Eaton’s Neck Lighthouse measured a 50 knot gust (~57.5 mph).

Let’s remind ourselves to stay safe when severe weather approaches and heed the watches and warnings issued by your local NWS offices.

This image was taken in Milford, Ma before thunderstorms passed through. These are mammatus clouds, formed by cold dense air sinking downward into warmer air causing groupings of ominous lobes. These types of clouds are often seen out ahead of thunderstorm clouds and are therefore harbingers of imminent severe weather. Source: WF Forecaster Tim Nicholas.

Sources:
Wind data courtesy of WeatherFlow
http://www.spc.noaa.gov
http://www2.mmm.ucar.edu
College of DuPage: http://weather.cod.edu/

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