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

West Coast Wind Blog: Rio Rips but mild gradients to Sacramento and Redding but…

Strong pressure gradient to the Great Basin!

by Mike Godsey

So we all learned in on-the-beach meteorology 101 that the pressure gradient to Sacramento is critical in Sherman Island winds.

Then in advanced beach lore you may have heard that the gradient towards Redding is also important in setting up the SW flow that Sherman Island thrives on.

And looking at this satellite animation from 9AM this morning, May 3, you can see the fog burying the greater Bay Area and even streaming over Sacramento and turning northward.

Also, notice the fast burnoff that is just starting. We will come back to that.

In the next image of the Bay Area wind map you can see strong winds blowing from Benicia to Sherman Island.

Also, notice the overall SW wind flow inside the Bay despite the weak West ocean wind at the ocean buoys.

Then check out the pressure gradients from SFO airport to Sacramento. It is actually quite modest at 9:30 AM and the pink line that shows the modeled pressure gradient is also mild.

The same is true of the pressure gradients from SFO-Redding and the gradient from the ocean buoy to SFO. So where is all of this wind coming from?

To get the answer check out the very strong pressure gradient from SFO to Winnemucca in the northern Great Basin and the SFO to Reno gradient on the western edge of the Great Basin.

It is those strong pressure gradients that are shooting the streamer of fog across the Central Valley. Meanwhile, the pressure gradient towards Chico and Redding is producing the turn to the west you see in the fog streamer.

The last image comes from the Bodega  Bay 449 Mhz profiler. The blue area you see in the bottom of the image roughly shows the depth of the marine layer.

Notice how it increased overnight. Now notice the lighter color area above the marine layer. This is the inversion layer of warmer air above the marine layer.

In the summer this layer would be much warmer and would try to keep the marine layer clouds intact. Since this is a weak inversion I would expect the clouds to burn back fairly fast today.

That is part of the reason I am forecasting weaker PM winds for Sherman Island and better clearing today at Crissy compared to yesterday. And that means stronger Crissy winds.

 

 

West Coast Wind Blog: First eddy of the year brings…

Southerly winds at the ocean buoys!

by Mike Godsey

Strong NNW winds from the North Pacific High blow just west of our ocean buoys today but with low pressure to over the far North Bay and weak NNW winds aloft it was clear the last few days we were heading in to eddy conditions.

The satellite imagery of the eddy is imperfect today. First find the Golden Gate. Then note the streaming of the clouds from the NNW in the #1 annotation. Then look carefully in the area around #2 and you can just discern the spin of the eddy in the clouds. Much easier to see is the impact of the eddy on the ocean buoy winds and the winds inside the Bay. 

Typically when the North Pacific High is close to the Bay Area we have NW wind at the ocean buoys. So the winds flowing into the Bay towards the  Central Valley have a bias to head towards the sites from Treasure Island southward. But with an eddy in play the bias is more towards sites north of the Bay Bridge.

Most of the time the eddy fades mid day but if lingers it blocks NW wind from reaching the Peninsula and Waddell. Plus it tends to funnel winds towards the north tower to Point Blunt to Pt. Isabel to Sherman Island axis.

The story of how the eddy is created is complex but the following images will give you some  hints of the major players in eddy creating. Note the weak northerly flow aloft in the Bodega  profiler image.

The in the next image note the surface low pressure trough over the far North Bay. With low pressure to our north there is a S. to N. pressure gradient in the Bay Area.

All of this favors eddy formation in the AM. And all of these variables fade in the afternoon. The key to our afternoon winds is how fast or slow these variables  fade which determines the edd resulting eddy fades

 

 

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