Using the Wf-Wrf to Monitor and Forecast Santa Ana Events

Posted on by WeatherFlow Forecaster Posted in Southern California

by Meteorologist, Kerry Challoner Anderson

 

Thousand Oaks Hillsides May 2019

The much anticipated first major Santa Ana wind event has begun.  Strong offshore winds are typical at this time each year when cold Arctic High-pressure systems move into the Great Basin.  This event is very strong.  The Tonopah to Los Angeles gradients dropped this morning to -15mb and stays this low through Friday morning.  However, this event is getting more media attention due to the anticipated pre-planned power outages to lower the risk of wildfires.  Last year’s wetter than normal winter brought stunningly green and lush foliage to the area in May. But that beauty has now turned to be a potential fire hazard after our long dry summer. Adding to the concern is just how low the relative humidity falls when the air descends from the Great Basin and dries due to compressional heating.  Overnight the dewpoint at Opal Mountain sunk from 30 F to – 19 F leaving the relative humidity at an ultra-low 3%.  

While we usually focus the attention of our models on the interaction with the ocean you will find that you can use Weatherflow’s Wf-Wrf model to help follow the winds.  We watch how this model performs carefully to see how it responds to different weather scenarios and our modeling team dials in the forecasting parameters to fine-tune the model for the area.  The Wf-Wrf is run on both a 3 km and a smaller version on a 1 km grid.  The smaller grid allows us to forecast finer features which is vital in an area with such varied topography.  It is interesting to see how vital this finer grid is when forecasting events such as this.  The 12km Nam model (below) gives the general location of the strongest winds beginning first through Palmdale and finding their way through the Oxnard Plain.

12 km NAM forecast for 10 October, 2019

Wf-Wrf forecast for 10 October, 2019

But you can see that the Wf-Wrf forecast (above) for the same time gives greater detail of the location timing and speed of the winds. It also shows the response at the beaches.  These offshore events are particularly difficult to forecast.  You will find us using the phrase “battle between the offshore wind and the ocean winds”.  Due to the topography of the mountains coming right to the shoreline and the canyons that funnel and speed up the offshore winds we can see the winds curve back onshore.  We also find that the valleys warm and sea breezes set up where the mountains shelter the beaches.  Consequently the beach winds will have extreme Up and Down conditions that can be hazardous. Surfer’s Point in Ventura is just one example.  You can see that despite 30 – 40 kt winds driving down the Oxnard Plain, Surfer’s still had an onshore wind in the model, though the model predicts that won’t last.  We will be keeping close tabs on all the beaches and also the valleys and canyons through this event.  You can use the Wf-Wrf and our network of observations to keep track of this event. Stay safe!

West Coast Wind Blog: Huge high pressure creates Diablo, El Norte, Santa Ana & “Rooster” winds

Posted on by WeatherFlow Forecaster Posted in Columbia River Gorge, San Francisco, Southern California

by Mike Godsey, mike@iwindsurf.com

Here is the story of this massive wind event in imagery and animations.

 

West Coast Wind Blog: Why abrupt fade of strong marine surge winds after dawn.

Posted on by WeatherFlow Forecaster Posted in San Francisco

by Mike Godsey, mikeATiwindsurf.com

Did you get wildly excited early this morning when you saw San Francisco’s Point Blunt winds averaging 28 and Berkeley already 22 while Crissy was 23? It looked like the classic Bay Area marine surge end of a heatwave. But by 8AM the wind had faded away at most sites. I forecast a major fade mid morning but not to this extent. What happened?

Watch the animation above from 6:30AM to 9:14 AM. Focus on Crissy and note the amazing drop off of wind from dawn’s 23 knots to 3 knots at 9:14 AM.

Now study this satellite animation and you can see the problem. A normal marine surge after a heatwave is comprised of fog and wind running parallel to the coast due to a N.-S. pressure gradient. And when the surge nears the Bay it is sucked through the Golden Gate and we have strong southerly winds all day.

But today’s marine surge is largely caused by a counter-clockwise spinning low pressure just NW of the Golden Gate and that is promoting large scale SSW to SSE winds. And as you can see in this satellite animation the wind in the morning became too SSE mid-morning to curve into the Bay. So the winds dropped fast at Crissy.

I expect the fog and winds to pick up later today as the pressure gradient becomes strong enough to curve even SSW winds into the Bay Area.

 

 

West Coast Wind Blog: Wind battle spoils the Isla Vista to Ledbetter winds while Pismo benefits.

Posted on by WeatherFlow Forecaster Posted in San Francisco

by Mike Godsey, mikeATiwindsurf.com

 

Pismo Beach saw strong winds today but Isla Vista to Ledbetter only had weak winds as 3 different wind masses battled over the area this afternoon.

This animation shows the story and an upcoming blog will fill in the details

 

West Coast Wind Blog: Wintry Cold Front advances the stalls over Bay so clearing winds milder than forecast

Posted on by WeatherFlow Forecaster Posted in San Francisco

by Mike Godsey, mikeATiwindsurf.com

The forecast was for scattered showers as a wintry cold front moved over the Bay Area and then broke up. While the afternoon saw upper-teens to maybe 2o clearing winds.

But the actual winds barely reached the upper-teens at some sites and the Waddell did not even reach the mid-teens forecast.

This satellite animation shows the problem.

Notice the well organized cold front in most of the images as is slides over the Bay Area.

Then in the last frames notice how the cold front breaks up and then stalls over the Bay. This stopped the WNW clearing winds from fully reaching many sites.

West Coast Wind Blog: Live: Hurricane Dorian hits Weatherflow HurrNet sensors

Posted on by WeatherFlow Forecaster Posted in Columbia River Gorge, San Francisco, Southern California

by Mike Godsey

Hurricane Dorian is bearing down on our hundred+ hardened weather stations along the eastern seaboard. As you can see in the attached photos these stations are massive and designed to survive at least 140 mph winds.

This sensor mesonet will be providing critical information for the NWS/NOAA during the landfall.

Here is the live link so you can watch our HurrNet sensors that we make public in real-time as Dorian hits the coast. (Some of our critical sensors are not on this page)

https://wx.iwindsurf.com/search/26.261/-78.608/8

Long Beach – When the Heat moves in its either Feast or Famine.

Posted on by WeatherFlow Forecaster Posted in Southern California

by Meteorologist, Kerry Challoner Anderson

For days the Southland has been sitting under a late summer upper-level ridge that has been steadily heating the Los Angeles Basin.  When this happens we watch carefully to see how close that heat comes to the beaches.  Forecasting sea breeze activity is tricky.  The strongest winds develop where we have the steepest temperature gradients.  Due to the topography of the Basin, we have very warm air move close to the shoreline and so we see some of our strongest and most consistent sea breeze activity at Cabrillo beach.  Below is the temperature profile this afternoon.  You can see the heat right up to the beach.  If the heat moves offshore the winds shut down but if we can get a little cooling then we have a steep temperature gradient and strong winds.  I will admit it is a tough forecast because it is either feast or famine.

Today as the I prepared the Midday Update the coast had spent the morning in full sunshine due to a lack of marine clouds.  The temperature profile showed the heat approaching the beach, which will shut down the sea breeze activity.  I backed off from the original forecast of Low 20 winds.  Just after I posted the sea breezes kicked in just enough to start to cool the beach and once that starts unless there is a strong offshore flow this will strengthen the temperature gradients which in turn strengthens the winds, resulting in these low 20s that we are now experiencing.  Enjoy!

 

8/29/10 Thursday Night 9:15PM ET Discussion on Hurricane Dorian

Posted on by WeatherFlow Forecaster Posted in Coastal Georgia, Coastal South Carolina, Southeastern North Carolina

By WeatherFlow Meteorologist Shea Gibson

Discussion viewable on Facebook Live:

8/29/19 Thursday 9:15PM ET Hurricane Dorian Discussion

Posted by Shea Gibson – Meteorologist on Thursday, August 29, 2019

 

Stay safe and cheers from us at WeatherFlow!

Shea Gibson
SE/East Coast Wind Forecasting
New Station Project/ Outreach
Twitter: @WeatherFlowCHAS
Facebook: Shea Gibson – WeatherFlow

West Coast Wind Blog: Bluff Reports and the changing Gorge winds.

Posted on by WeatherFlow Forecaster Posted in Columbia River Gorge

by Mike Godsey, mikeATiwindsurf.com

ROUGH DRAFT

There was a recent forum thread on the Gorge Classic iwindsurf.com page asking “are there gustier winds this summer?”

The forum thread had answers ranging from “Obviously!” to “I hear this every year!” How you expereince gusts is impacted by many things like your gear, sail size, years in the Gorge and how good of sailor your are. Moreover, human memory is unreliable and easily biased.

So I have been looking at the Swell City sensor gust lull data. This sensor has its flaws but every one of you looks at that data so it is safe to assume it is somewhat useful.

So I have started analyzing the gust to lull ratio every 60 seconds for the Hatchery for this year vs. 2018 vs. 5 years ago vs. 15 years ago for the month of July. It is a massive amount of data but already the answer is emerging. The gust lull ratio has increased somewhat.

But this is not the real problem with Gorge winds in recent years.

Years ago strong gusty dawn patrol winds were the essence of Gorge windsurfing. All you needed were low compact marine layer clouds filling the western Corridor and a strong pressure gradient. For reasons I will get to that pattern started becoming increasingly less reliable. That is not to say we don’t still get epic days. And this May and August had some great days. But somethings have changed.

Since my windows look down Columbia from the White Salmon Bridge to way past Viento the changes were obvious to me. So about 12 years ago I started doing the Hatch and Swell Bluff report several times each morning. This Bluff Report describes what I am seeing from my house versus what the sensor is reporting.

It was clear to me that in the early morning the winds on the water were frequently either far weaker or stronger than what the sensor was reporting from atop the small cliff at the east end of the Swell City parking lot. This was because of gust and lull bands slowly marching down the corridor in the early morning.

In the early years I would do 2-3 of Bluff Reports until the gust and lull bands subsided and the sensor and the wind on the water were about the same which was typically between 9 and 10 AM. And I would sign off the final report with a “Last report of the day.” which meant I was on my way to the Hatch and there were likely to be solid gusty winds much of the day with perhaps a “mid-day” lull.

But in recent years it became much hardier to do a meaningful Bluff Report. The gust and lull bands west of the Hatch and Swell zone became larger and more numerous and lasted more of the day. This made doing the Bluff Reports way more difficult.

So, for example, I would do a 10 AM Bluff Report saying the sensor and the white caps both agreed that the winds were mid 20’s. But then 15 minutes later I would look out the window and see a lull band moving into the Hatch and Swell area and the winds were only mid-teens.

You can see this issue in my Bluff Reports for yesterday, August 24.

Let me show you what these gust and lull bands look like from my house. This is what I saw at the 11AM report above. Notice the lull band right off Kodak Point at the Hatchery and the second in the “Basement” area between the Hatch and the White Salmon Bridge. Then the 4 lull bands west of Swell City and the large Point east of Drano. And in the far distance, you can see more lull bands. Interspersed between all these lull are strong gust bands.

n the water or at the Hatch or Swell launch sites you can’t see these bands. What you do notice is the wind looking really good and then a while later looking really bad. And if you are on the water when the transition from a gust to lull band passes the wind seems really up and down.

So what causes these gust and lull bands?

The Gorge has always been a gusty place for several reasons.

  1. We are far from the ocean and the marine layer is often breaking up by the time it reaches the Gorge so we lose that wind stabilizing influence. (Unless you get out really early when the land is still cool AND on a day without bands or you go to San Francisco where you are next to the marine layer)
  2. Our wind is often jacked up by strong winds just aloft. These winds hit our topography and become turbulent with lots of up and down motion which randomly transfers momentum to the surface winds. You experience this as abrupt gusts and lulls and even shifts. Can you figure out why the winds are steadier way out east?
  3. There are large points sticking out into the river west of the Hatchery and as the surface wind hits these points turbulence is created causing the bands you see in the photo above.
  4. As the sun beats on these points the land heats the air and parcels of hot air rise this causes gusts as the inbound air accelerates in those spaces. You experience this as patches of stronger and weaker wind on the water. The same thing is happening as the sun bakes the Washington walls of the corridor.
  5. Lastly, the winds are often at an angle to the Gorge creating more turbulence. And more WNW flow favors some sites while WSW flow favors other.

Over the last decade factors, 1 and 4 and 5 above have changed.

Poiint 1. All along the west coast the average depth of the marine layer has thinned. This has radically changed the windsurfing and kiting for many places. For example, Sherman Island, in the San Francisco Bay Area, used to be renown for steady winds peaking in the early morning and afteroon and often lasting all day. Now with a thinner marine layer it sees those winds less frequently. In the Gorge it means the marine layer clouds do often do move as far inland in the afternoon. And that means a greater gust lull ratio. The reasons for this are complex but basically, for a deep marine layer you need a cooler ocean.

Point 4. The Gorge average summer temp. pattern used to be simple. There were warm days and cool nights with lots of gusty with low to mid 20’s days with a marine layer in the far corridor to  Mt. Defiance that burned back quick. Then several times each summer there would be a 2-3 day heatwave well with temps over 100 and the river was glassy calm and you would see kayaks, waterskis, SUP’s on the water.
Then the heat would end abruptly with the first day having a huge surge of marine layer clouds and  very strong UP AND DOWN winds.
Gradually the pattern of heat has changed. Heatwaves were not as hot, more like low to mid 90’but they lasted 3-5 days then 4-7 days and they became much more common.  Now we 100+ degree heat waves are less common but it was warmer all the time and the evenings did not as cool. The reason for this is increased moisture in the local atmosphere. The average relative humidity has gone up and increased water vapor puts a cap on really hot temps.
All of this was correlated with the increasing gusts and lull patterns and more days with unreliable wind. Why?
The hotter the average temperature and the fewer cooling marine layer clouds the hotter those land points to the west of the Hatch and Swell become. This means more parcels of hot air rising which in turn means larger more frequent gust and lull bands.
It also means in general more rising air which makes the wind pattern you see in this next photo more common. Notice that you not only have gust/lull bands but also lots of lull patches which you see as slicks. I can watch people blasting on a full plane slow and slow as they hit these patches. Unless of course, they are a good enough sailor to immediately turn downwind to ride a swell.
Point 5. Remember the days when you just watched the Maryhill sensor reach 27 (or the Arlington sensor reach 25) and you hit the road with fair confidence that you would get in at least several hours of great winds and swell? As you know that simple wind equation no longer works as well. Too often you get to the Wall or Roos and find most of the wind on the Oregon side of the river. Why?
Because the summer North Pacific High is larger and much further northward than past decades. This means it more likely to be distorted by passing systems and kinks further inland. And this adds more of an NW component to our winds just aloft. And those NW winds interact with our surface winds to make them a bit less WSW and more W to WNW. Look at a relief map and you can easily see what this will do to the Wall and Roosvelt winds. And it even impacts the Hatchery. 
The net result of all this is fewer days with solid winds lasting from dawn to dusk. And the days when you could glance at the sensor and see 25 mph and hit the road knowing you would be sailing for sure are less common.
More later!

 

 

West Coast Wind Blog: Why so many Bay Area eddies this season. Part One

Posted on by WeatherFlow Forecaster Posted in San Francisco

Part one of this blog below is about the smaller eddies mostly in the Bodega to Golden Gate area that have been so common during the 2019 summer season. These eddies often totally or partially die in the afternoon making for extremely difficult forecasts since the southerly eddy wind may die allowing NW wind to curve into Bay.

Part two of the blog, coming soon, covers the huge elongated eddies that have also been common this season. These eddies may span the waters from Pt. Arena to past Big Sur and usually endure all day and throw southerly wind at the Bay Area all day. These huge eddies are easy to forecast.

At this point, if you are a coast or 3rd. Ave. kiter or windsurfer, you are fed up with all these eddies and all the forecast talk about eddy. In feedback, customers have even accused us of just pasting in a boilerplate text about eddies rather than doing original forecasts. And I can understand that thought since time and time again almost exactly the same eddy producing conditions have developed and it is hard to come up with new phrases to describe essentially the same pattern.

Does this text sound familiar: “The North Pacific High pushes a lobe of high pressure into far Northern California so our ocean wind west of the Farallon Islands turns from NW to NNW. At the same time, low pressure bulges over the coast west of Chico. So we have an eddy in the Bodega to Daly City zone. Meanwhile aloft strong NNW winds aloft create wind shear enhancing the eddy. In the afternoon the eddy probably fades but still enhances north tower to Point Blunt to Pt. Isabel winds while residual SW flow in the Hwy. 92 gap make the winds unreliable at the 3rd. Ave launch site.” If you are a 3rd. Ave kiter those words bring dread while Pt. Isabel windsurfers rejoice.

So where are all these eddy conditions come from and where are our normal NW winds from the North Pacific High?

Short answer: Unusually warm north Pacific encourages North Pacific High to expand northward and southward while El Nino southerly storm track causes NPH to kink inland over far Northern California so our ocean winds turn from NW to NNW while low pressure moves over the north coast and the combo results in eddies.

A Longer but still very simplified answer:

1. El Nino has brought warmer waters to the north Pacific and this encouraged the North Pacific High to move much further northward than normal.

2. This year we are in an exceptionally warm phase of the PDO or Pacific Decadal Oscillation this also encouraged the North Pacific High to move way northward.

3. Arctic warming has continued and Alaska lost all of its sea ice in August. This also encouraged an expansion of the North Pacific High and at times it reached into the Bering Sea and even over Alaska and well into the Arctic. Normally the bulk of the North Pacific High is west of the Gorge by mid-summer.

4. The combo of 1+2+3 above means we often had an NPH wind a weird elongated shape stretching from Alaska into Baja waters.

5. This winter saw an El Nino pattern with the storms taking an unusually southerly track hence the heavy snowfall and even rain in La Ventana, Baja.

6. Then as we moved into summer the storms became less frequent and smaller but they still tracked more southerly than usual bringing unstable convective air over the Pacific Northwest making for less reliable and more up and down Gorge winds.  This is happening even though in the tropics the El Nino is fading to neutral. In the second
image, you can see 2 low-pressure systems and their southerly track and the fragmented nature of the North Pacific High and its  N. and S. expansion.

7. As the storms tracked across the Pacific from West to East they often encountered the greatly distorted N. to S. North Pacific High. Often the North Pacific High was even split into 2 or 3 parts by these storms leaving Northern California with a North Pacific High that was off our coast rather than the Gorge coast.

Compare the second image of the fragmented North Pacific High this July with the third image showing the average shape of  the North Pacific High in July over the period from 1967 to 2010.

So let’s look at how we make the shift from a strong NW pattern like we saw Wednesday, August 21 to the beginning of an eddy pattern today Thursday, August 22. Then in Part 2, we will see how Thursday’s tiny, quickly destroyed eddy turns into a massive elongated eddy Friday, August 23.

NOTE: There are 10 seconds between frames in this animation.

In the first frame, showing Tuesday to late Wednesday, notice how in the first image the North Pacific High’s isobars (in white) are roughly parallel to the coast so strong NW surface winds are along the Bay Area coast.

Then in the next image, for Thursday, the isobars of the North Pacific High begin to move inland into far Northern California while at the same time low pressure bulges over the coast north of the Bay Area. This causes a tiny eddy to develop in the Stinson Beach area just north of the Golden Gate.

This tiny eddy is destroyed later Thursday morning by the strong NW ocean wind.

The next image, for Thursday, shows the very strong winds up at ≈ 18,000 ft. that cause the North Pacific High’s isobars to kink inland over far Northern California setting the stage for an eddy.

The final image shows the very strong winds at NNW to NNE winds at 2000 feet that reinforce the eddy b and end up forming a counter-clockwise spinning mass that causes the eddy to endure all day and to exp

How about the future and eddies?

This El Nino is already fading so that causal factor is gone for a while. Likewise, the PDO should move to a cool phase in a few years. But Artic warming is going to be with us for a long time. So we are unlikely to see as many eddies next year the future is going to see more eddies than we did even 5 years ago. So eddies are going to be a factor in the future.

 

 

 

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