West Coast Wind Blog: We can forecast the eddies arrival and departure pretty good…

But often fail at the exact focus of it’s winds.

by Mike Godsey, MikeAT iwindsurf.com

Years ago when I first began forecasting when the models could barely resolve the entire Bay Area I and the NWS were oblivious of eddies off the Golden Gate. Sure ocean fishing party boats knew that sometime there were mysterious SW winds near the coast while northerly wind blew out at the ocean buoys. But know one was looking at how these eddies impacted Bay Area winds.

So these days we are pretty good at forecasting when an eddy is likely to spring up and produce SW winds inside the Bay. But we are still pretty poor at forecasting the exact sites  where the southerly wind will focus other than saying the wind focus will be mostly N. of the Bay Bridge. Why is that so hard? Well…..

First let’s look at the big picture. Way out in the pacific is the center of the North Pacific High and the winds spiraling clockwise from the high pressure.

But today, in response to upper level winds, the NPH has a extension or ridge leaning into the Pacific Northwest.

Why should bay kiters and windsurfer care about events off the Pacific Northwest? Because when the North Pacific High forms a ridge it’s NW coastal winds turn more NNW. Which means:

  1. Given the angle of the California coast it becomes harder for the ocean wind to curve into the Bay Area.
  2. And if conditions are right (or wrong if you sail the coast or most of the Peninsula) this NNW wind helps a counter-clockwise spinning eddy form west of the Bay Area like you see in this second animation.

In this second animation the wind focus looks easy to forecast. The SW flow should be strongest at Pt. Isabel, Berkeley and Sherman Island with weaker winds at Larkspur and Brickyards/Peacock Gap.

The problem is that this animation is just what one model suggests about the eddies location and shape. We typically look at about 5 models each day to get a rough handle on what the wind is likely to do that day. But when it comes to eddies the models can differ wildly.

This last animation show how today’s eddy (August 16, 2017) is modeled by the NAM3, ECMWF and GFS models. Notice that all 3 models depict an eddy off the Bay Area. But notice how differently they are in the shape and location of the eddy and the focus of the SW wind.

So how do we make a forecast from this mess? We look at the empirical data like the satellite imagery and the reports from all the ocean buoys and coastal sensors and see which model most closely reflects the reality.

From there we look at the focus of the pressure gradients to different parts of the Central Valley versus all the gaps in the coast range to see how the wind is likely to be funneled towards different sites.

So far so good! But the eddy often changes location and shape during the day. Which means blown forecasts.

Now you take a try at it. Here is the satellite imagery from about 8AM this morning. See the eddy just west of Pt. Reyes? Now which model from the animation above would you start your forecast from?

Posted in San Francisco

West Coast Wind Blog: Rex Block brings…

Endless heat and brown skies to the Gorge… comes to an end tomorrow!

by Mike Godsey, mike AT iwindsurf.com

My banner above shows the almost daily view of the Hatchery from my house the last 2 weeks. The smoke is mostly from fires in Canada but its unusual persistence and the unending heat wave is the product of a meteorological phenomenon known as a Rex Block. This type of weather block was discovered by Dr. Daniel F. Rex in the 1950’s and for whom it was named.

You may have seen mention of this phenomenon in the media in recent days along with a stylized diagram like the one on the right.

Let’s do a more detailed analysis of the Rex Block that has been impacting the Pacific Northwest.

The next animation shows the Rex Block on a day last week where it looks like a text book Rex Block. In reality the shape of the Rex block varies a lot and sometimes is disappears for a day or two.

First find the Gorge in the middle right of the image.

Then notice the cool upper trough at ≈ 18,000 ft. on the left edge of the image far out in the pacific. In normal conditions upper troughs like this move to the west coast in a day or two and bring a deeper marine layer, cool clear air and strong westerly winds the Gorge. But in this case the upper trough has been blocked for almost 2 weeks. You will really feel the impact of this upper trough tomorrow Friday Aug. 11!

But back to the Rex Block! Next notice the upper ridge at ≈ 18,000 ft. feet. Upper ridges like this used to develop a couple of times per summer over the North Pacific High and Canada but as you have noticed more frequent heat waves in the Gorge and a thinner marine layer have become the new norm. But that is a different story.

Going back to the upper ridge… The air within this northward looping flow of air is warm and descending, compressing and heating. So it flattens the marine layer clouds from the coast to the western Gorge and traps smoke and pollutants near the surface and the expanding heat destroys the pressure gradient across the Gorge so normally we  have a few days of weak winds followed by a blast as the upper ridge departs.

But in the present Rex Block there is a upper high pressure within the ridge and aligned to the south is a counter-clockwise spinning upper Cut-Off Low over California. This alignment of an upper high pressure and a upper Cut-Off Low is called a Rex Block and acts to blocks the eastward moment of weather systems like the wind creating upper trough you noticed before on the left margin of the image.

This Rex Block also means that weak pressure gradients, smoky conditions and heat have also been locked over the Gorge due to the Rex Block.

In the next image you can see how the upper ridge with the Rex Block dances around but mostly keeps a heat producing upper
ridge over the Pacific Northwest. Especially watch the very last frame of the animation for tomorrow Friday Aug. 11 for therein lies salvation for the wind hungry.

In a normal heat waves forecasting is very easy in the Gorge. No wind, glassy conditions for a few days. Then the forecasters see the upper ridge beginning to depart and the upper trough moving towards the Pacific Northwest so they forecast winds for Jones Beach as the marine layer moves inland with strong gusty winds for the corridor the next day.

But our Gorge forecasters have rarely seen a Rex Block and this has made forecasting very tricky. The upper teens to low 20’s wind of recent days is caused by very local difference in heating from Portland to the corridor that develop abruptly and unpredictably. But the last week has been a learning experience and we will do better for the next Rex Block. And this is important since extreme upper ridges with nagging heat waves and winters like the past one where lingering upper trough brings prolonged bad weather will become more common in the future.

Added Aug. 11, 2017: It is nice where a prediction made in a blog comes true. Today, Aug. 11, 2017, the smoke is thinning and the wind is definitely back.

 

 

 

Posted in Columbia River Gorge

The 2017 Cape Verde Season Begins

By WeatherFlow meteorologist Shea Gibson

8/3/17 Tropics Update:

The Cape Verde season is getting underway…with the NHC 8AM update giving a strong tropical wave coming off of Africa (#Invest99L) a 30% chance next 48hrs for development….and a 60% chance next 5 days.

A break in the Saharan Air Layer (mid level desert dust) and a few pockets of relaxed upper shear may be just what it needs to become a tropical cyclone.

The purples represent lower shear environments, and the warmer colors represent higher upper shear zones. The lower shear environments favor tropical development.


Sea Surface Temps are plenty warm ahead
 at 28°C (82.4°F)…and increasing w/ time –> distance over higher TCHP (tropical cyclone heat potential derived from warmth/fueling of pelagic/epipelagic zones at the ocean surface and just below).
At this point, we’re just watching for upper shear to relax enough to allow for vertical stacking and deeper convection. The next name on the list is “Franklin”.

Stay safe and have a plan!

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

Sources: WeatherBell Analytics, NHC, UNISYS, NOAA GOES-EAST

 

Posted in Cape Cod, Chesapeake Bay, Coastal Georgia, Coastal South Carolina, Delmarva, Long Island/SE New York, Long Island/SE NY, Massachusetts North Coast, New Jersey, Outer Banks of North Carolina, SouthEastern North Carolina, Tidewater Virginia

West Coast Wind Blog: Major Bay Area eddy event…

Surface eddy and low pressure aloft maintain southerly winds.

by Mike Godsey,

Mike AT iwindsurf.com
Today, Saturday July 29 things start with a small surface eddy near the coast.

Then tomorrow a Bodega eddy, much like the one you see in my banner animation above, forms at the surface.

Then low pressure systems develop above the surface eddy cause it to grow much longer and to endure for several days.

Notice in the first animation how the North Pacific High’s surface NW winds turn more NNW as it pushes a ridge towards the Pacific Northwest.

Then notice how a small surface eddy forms west of the Golden Gate in response to the NNW winds. In recent years this eddy formation has gone from being a rare event to being a very common event. The reasons are complex and near global causation and are way beyond this blog’s scope.

But this building surface eddy is more complex than most eddies. As you can see in the 2nd. animation NNE winds develop aloft and a massive counter-clockwise spinning low pressure develop above the surface eddy. This causes the surface eddy to enlarge and endure for days. And the  combo of all the southerly flow from these circulations pushes a deep marine layer far into the Bay Area.

 

 

More later….

Posted in San Francisco

West Coast Wind Blog: The Wall: Wind direction and 2 Venturi’s…

They determine if the The Wall is Great or Hate!

by Mike Godsey, mike@iwindsurf.com

Take a look at the swell near The Wall in my banner above. Notice how the big swell is uniform reflecting solid WSW wind from Oregon to Washington on an epic Wall day. This VIDEO  link shows the sort of action you see at The Wall on this type of day.

The image on the right shows the perfect set up for The Wall. Since the Columbia River runs overall from East to West there is a tendency to think this is true all along the river like it is at The Hatchery.

However at The Wall the river is actually running from NNE to WSW. This means that the best set up for The Wall is WSW winds.

Looking at this image notice how the vertical cliffs on either side of the river SW of Maryhill act to funnel (pink dashed linesWSW wind into the waters of The Wall. Also notice how the constriction of the cliffs in this zone make a venturi effect accelerating the winds as they pass by the Maryhill Bridge on the way to the Washington side of the river.

Next notice the location of the sensors on the Oregon side of the river. Note how the Maryhill sensor (just west of the Bridge on the Oregon side) and and “The Wall marker 40” sensor (just west of the actual Wall zone on the Oregon side) These sensors are will sited for the winds on the Oregon side of the  river but can not pick up the winds on the Washington side of the  river.

Having 2 sensors so close to a launch site is a treat for our customers and reflects the importance weatherflow places on The Wall as a customer destination.

But paradoxically the complex curving course of the  river and the tortuous cliff topography makes the winds do some really strange things in The Wall zone. This means that sometimes these 2 sensors show upper 20’s or even low 30’s wind from the SW but when you arrive at the Washington launch sites you either find almost NO wind at the launch sites or WNW wind that blast on the Oregon side but are on and off at the launch sites. This is especially frustrating since most of us sometimes drive around a hour or more with the expectation of strong wind only to find barely useful wind.

The next 2 photographs show such a day. In the top image I have zoomed in on the waters around the Wall M40 sensor near the Oregon side. Clearly the winds are ripping at the sensor and the wind graph at the sensor reflects this with upper 20’s or stronger wind from the SW. So sitting at the Hatch and seeing that wind graph you would probably hit the road expecting and Wall day.

But now look at the zoomed out version of the same photograph. You can still see the raging winds over on the Oregon side but note the near glassy slick and weak winds on the Washington launch side. You all know the sinking feeling as you drive onto the gravel road and see that slick.

Personally I take the Stonehedge road overlooking the entrance of The Wall so I can reroute to a different launch site if the slick is large.

So what often causes weird powerful sensor readings at Maryhill and M40 when the river is actually weak at the launch sites?

The answer to this question is complex but has to do with variations in the overall wind direction. In the very top image we saw that the best overall wind direction for The Wall is usually WSW. But often the overall wind is NOT WSW with W. being the most common. So let’s look at a graphic showing what west winds do to The Wall.

Incidentally the next graphic summarizes the about 3 years of research. Each time I found crappy wind at The Wall despite great sensor readings I drove around all the roads on both sides of the river with image stabilize binoculars watching ripples, swell, wind turbine direction and even the wind patterns on grassy fields. But the biggest break though happened several years ago when there was a fire to the west which sent smoke down the river. Voila! A natural wind tunnel with smoke as streamlines. Watching the smoke really gave me insight about the weird way wind funnels around The Wall. And since it was a Wall bad day with weak wind at the launch sites I could see the smoke hugging the Oregon side of the river despite great sensor readings from our sensors. I also have a wind tunnel app that I have run over a simplified version of The Wall and it provided additional support for my reasoning below.

So looking at the image below of a “Bad” day at The Wall notice that the overall wind flow is West over the eastern Gorge. At the Hatch this works well since the river runs rough E. to W. but remember that the river runs NNE to WSW in the Wall area.

First note how the cliffs at the top of the image act to funnel (yellow dashed line) the West winds so they turn WNW in The Wall zone. This is especially true in the boat ramp area but impacts all the launch sites. At the launch sites you notice this as gusty WNW winds blowing slightly offshore or from your back as you face the river. This WNW flow is usually very gusty and is going at an angle across the river.

Now notice how the cliffs west of Maryhill make a funnel (pink dashed line) that tends to turn the West wind more WSW to SW near the Maryhill Bridge.

As these two winds interact the WNW flow coming down the yellow funnel tends to intermittently push the SW to WSW wind towards the Oregon side where the sensors are located leaving the Washington launch sites with weak or even intermittently calm wind. Can you guess where the best launch site is in the area in this pattern?

This next image shows you what happens when the overall winds in The Wall area are WNW. If you are at Rufus the winds seem like they are coming across the river from the turbines. Yet the Maryhill and M40 sensors are showing strong SW winds. Making the long drive in this situation is a real fail.

So how do you tell when The Wall is going to have a good or a bad day? First read the forecast carefully looking for any mention of WSW flow. Next take a look at the black insert in the image above.

The more nearby sensors you see that are showing WSW wind like those in the red diamonds the more likely there will be WSW winds entering the Pink funnel and the less likely there will west wind entering the Yellow funnel.

So put the new iwindsurf or ikitesurf web site in the terrain mode like you see below and look at all the sensors within 20 miles of The Wall before you make the drive.

Here is a link for that overall view of The Wall zone using your regular iwindsurf or ikitesurf account: The Wall overall winds

Unfortunately the wind often shifts from WSW to more West during the day so even this technique is not full proof. Lastly, the stronger the winds the less the impact of the yellow funnel so when the sensors are into the low 30’s there is so much wind on the river that you are likely to have an epic day especially at The Cove and The Marker.

So the further increases your chances of success use a web site that allows you to easily step through hours of the day while watching the overall wind direction.

Still, I have to confess that I find sailing The Wall so addicting that I find the melody of the Pink Floyd music in my head irresistible and make the long drive despite an abundance of contrary evidence.

 

 

 

 

 

Posted in Columbia River Gorge

Using Medium Range Computer Models for Guidance

By WeatherFlow meteorologist Shea Gibson

Check out the GFS (American model) short to medium range forecast for the North Atlantic Ocean out to 384 hours (16 days). Notice the “H” bouncing around out there. This is the Bermuda-Azores High that waxes and wanes back and forth almost all summer long (and much the year). This is known as a “blocking pattern” and provides Easterly trade winds through the Windwards, Antilles, Caribbean islands, Bahamas and the Keys. For us locally along the Southeast/East Coast, when it builds further west and we get a stronger Bermuda High presence, we generally see stronger Southerly winds help to build our afternoon Sea Breezes. Conversely, the further east it fades, the weaker those Southerly winds and associated Sea Breezes become. It also is a steering mechanism for tropical waves and tropical cyclones. But also notice that there are no areas of concern right now, for the short or medium term forecast.

Typically beyond 3-5 days, these models become very erroneous (with the exception of the EURO at times to a certain extent), but ok to watch for a few guidances. Even with all of the super computing we have in today’s technology, the actual “skill” is only around 6 days, but barely that. Just remember when looking at them, and even in our WeatherFlow products, that they are just a numerical/computer forecast opinion of what the winds and weather will do.

This GFS .gif loop is courtesy of Tropical Tidbits / www.tropicaltidbits.com

Cheers and stay safe

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

Posted in Cape Cod, Chesapeake Bay, Coastal Georgia, Coastal South Carolina, Delmarva, Long Island/SE New York, Long Island/SE NY, Massachusetts North Coast, New Jersey, Outer Banks of North Carolina, Rhode Island, SouthEastern North Carolina, Tidewater Virginia

West Coast Wind Blog: West Coast “Eddy” vertical analysis of the wind



by Mike Godsey, mike AT iwindsurf.com

 

 

Looking at the top animation of the surface winds from Sunday through Monday it looks like we transition into an unusual wind event for the Bay Area to Southern California regions starting tomorrow.

At first glance if looks like a just a huge surface Golden Gate “eddy” for the Bay Area and a huge surface “Catalina Eddy” for Southern California.

But as you can see in the animation below its cause is much more complex and clearly involves a elongated mid level low just off the California coast.

And this in turn appears to either cause or at least greatly enhance the surface eddies.

But the cause of this mid level low pressure  is somewhat mysterious at least to me.

So take a look at the animation below for 6AM July 1.

Especially notice the the wind patterns from the surface to 500mb in the animation.

 

Posted in Los Angeles, San Diego, San Francisco

West Coast Wind Blog: Heat bubble expands over Belmont to Seal so up and down winds but…

Leo and Cabrillo are spared for different reasons.

Hey Mike,
 Long time no talk. Hope all is well and you’re having a great summer. I thought I’d share a weather thought from today’s very strong winds for Leo Carrillo.
I’m not at the beach today (too much weekend madness for my tastes), but checking the graphs I find it really interesting to have intensive heat at the nearby ridge tops in Malibu, perhaps record breaking, yet no heat bubble at Leo. I’ve never seen this happen before that I can recall.  Attached is the mesowest region map from 3:45pm 06/25. History always shows that when temps go over 100 in this zone, the beach is impacted by the heat expanding to the coast, yet the coast is still 73deg at the NWS sensor and 65deg at the iWS sensor. Maybe it will still happen later in the afternoon, but it sure seems strange and inconsistent to past personal observations.
It’s always a guessing game for me in trying to figure this out.
 Thanks for listening – stay well!
Mitch K 
by Mike Godsey, Mike AT iwindsurf.com
Hi Mitch,
Good to hear from you and thanks for the informative mail.
It is rare for me to forecast such strong winds at Leo. Pre dawn I was watching the temperature forecasts for inland valley sites near Leo that suggested that the heat bubble would be an issue for parts of the coast. In the image below notice how the isobars from the thermal low expanded over the Belmont to Seal area. In reality the pressures probably flow back and forth over the beaches in that area as the cooling ocean wind and the land heat interact. You can see that in the Belmont to Seal wind graphs where the impact of the heat bubble is indicated by the green arrows.
But I know from experience that in most thermal trough (aka “heat bubble”) situations Cabrillo is somewhat protected since the Palos Verdes Peninsula is surrounded by cooling water on 3 sides. So its wind graph looks much better.
 As your images shows 104 is clearly in the range that would could the heat bubble over Leo. But I reasoned that:
1.  The ridges behind the Leo area will slow the expansion of the heat bubble to the beaches so it might not close down the wind until very late afternoon.
2. With such strong winds at Leo the heat bubble would have a hard time getting the last mile to the beach.
3. The forecast inland winds were more W. and not pushing the heat bubble towards Leo
So I gambled and forecast Leo to have very strong wind without a heat bubble effect until evening when the fading winds would allow the bubble to cover the beach. You can see in the Leo wind graph this is pretty much what happened.
Win some, lose some… but this was a win!
Mike
Posted in Los Angeles, San Diego

West Coast Wind Blog: Low pressure off California…

Battles with subsidence from crushing high pressure heat wave.

by Mike Godsey, mike AT iwindsurf.com

A marine surge is arriving either tomorrow Friday or Saturday AM at the latest. These animations show some of the variables involved.

 

Posted in Los Angeles, San Diego, San Francisco

West Coast Wind Blog: Unusual Bay Area wind pattern likely Sunday June 18…

Makes forecasting very iffy

by Mike Godsey, mike AT iwindsurf.com

Take a look at the extended forecast for the Bay Area tomorrow. So what is going on?

As you may have noticed Bay Area wind patterns keep changing in last 10-20 years. They are very very different than the stable spring and summer pattern that prevailed for decades or longer.

And Sunday we will see a pretty crazy pattern. I will let the 2nd. graphic below speak for itself. Take a look at all the different wind patterns I have to deal with in trying to forecast this mess.

At the surface there will be NW, NNW, W, WSW, SW, S and even NE winds around the Bay Area while just aloft strong NNW winds prevail.

And the reality will be far more complex than this simplified computer output. So take tomorrows forecast with more than the usual grain of salt.

Posted in San Francisco
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