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/

West Coast Wind Blog: Local low pressure and eddies:

Good eddy, bad eddy.

by Mike Godsey, mike AT iwindsurf.com

There are several scenarios for creating micro to mesoscale eddies. Two of the more common factors is a very localizeed low pressure area and wind shear as wind rounds a point or  cape. Southern California kiters and windsurfers are very familiar with the wind killing Catalina Eddy and the Mid Channel edies off Santa Barbara that deepen the marine layer and often block the inbound WNW to WSW ocean winds. The situation is more complex with the increasingly common Golden Gate Eddy off the Golden Gate. Those plying the waters north of the Bay Bridge love to hear about the Golden Gate Eddy since it usually means solid wind especially at Pt. Isabel and Sherman Island. While those south of the Bay Bridge or on the coast know that and eddy often means W to WSW winds that are weak near shore.

The following imagery shows an eddy with very simple causation. It often occurs in  the morning in the extreme northern end of Baja’s Sea of Cortez near San Felipe.

Notice NNW winds from the North Pacific High streaming down the west side of Baja. Looking closely notice how a bit of that winds turns and is sucke into the eddy in the Sea of Cortez. Likewise wind from the San Diego and Nogales regions are sucked into the the counter-clockwise spinning eddy.

The next image shows the proximal cause of this eddy. In the morning a low pressure area often forms in this region since the Sea of Cortez water is warmer than the surrounding land mass that cools rapidly over night. So wind is sucked towards the pressure gradient and is set aspinning by the coriolis effect. Later in the morning as the land warms rapidly the the low pressure disappears and the eddy fades away.

Waves arriving from Down Under

by Weatherflow, Meteorologist Kerry Challoner Anderson

A cold outbreak for Eastern Australia has not only meant that I am preparing this from under the warmth of some extra blankets but also has brought record wave heights, epic winds for Wind and Kite Surfers here in Brisbane and the potential for great surf later in the week for Californians.

Forecast minimum temperature for Saturday, May 11, 2018

Usually I am forecasting from my home in California but this week I am back in my childhood home in Australia.  Watching the weather patterns here has been a great reminder of how connected we are in this world especially when it comes to winds and waves.

 

This past weekend a series of intense storms have pushed down from Antartica across Tasmania, Southern Australia and New Zealand with very strong winds, severe weather and flooding and sending the mass of cooler air across Eastern Australia.

Campbell Island a remote location south of New Zealand recorded winds in excess of 50 mph and a 78 foot wave.

For Eastern Queensland these storms have meant that the “windy westerlies”, as they are called here, were cranking.   These are cold dry winds that blow from the deserts of Central Australia.  I remember them well from my childhood as we are pretty thin-skinned here and so it meant for a cold day on the playground.  I enjoyed being here for a Westerlies event as they also mean some epic wind conditions wind surfers and kiters at Wellington Point.

Here’s a shout out to our mates down under.  It was great to visit and find out how you use our data and models.

And Californians surfers should benefit from all this energy down under. Waves models show that this energy travels across the Pacific and will arrive in California later in the week.

Cape Verde von Kármán Vortex Streets

By WeatherFlow meteorologist Shea Gibson 5/12/18

One of the great things about the new GOES-16 satellite imagery is the ability to see microscale events in high definition far beyond our coast to the east over the Atlantic ocean.

Check out these ripples called  “von Kármán vortex streets” created from NE flow across the Cape Verde Islands just west of the African Coast. This is caused by the separation of moisture over the mountains of these island as the winds blow across them.

This process is very much like how wind would whip across a powerline and create the vortices on the other side, giving it the ripple-like effect (and that “singing” effect as well).Just as a FYI….another hot-spot for this to occur is Jeju Island off the coast of the Korean peninsula during strong cool Northerly winds across its tall volcano peak.

Just another one of those neat-o things that occurs in the atmosphere that lets us know how the surface and atmosphere can work together to create beautiful patterns. Until next time, take care and keep up with our forecaster blogs at http://blog.weatherflow.com/ – make sure to toggle the varous regions for lots of valuable information from our team!

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

Sources:
https://weather.msfc.nasa.gov/GOES/
GREarth: http://www.grlevelx.com/grearth/
https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_vortex_street

Top