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fxop
Joined: 13 Jun 1998
Posts: 200
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 Posted: Wed May 31, 2023 8:33 am Post subject: Mike -- Palo Alto Prediction 5/30/23 -- How on Earth? |
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Mike/iWindsurf -- how on earth did you guys predict this pathological wind shift *exactly* with the thin blue line on the iWindsurf app? The same pattern was also called exactly on May 25. Yesterday Palo Alto had nice NNW wind early as shown. The whole Bay was SW, but there was a .05 gradient to Bakersfield.
The gradient didn't go away, so why does the NNW get overwhelmed and go W?
Are you doing a special human forecast for Palo Alto or using a robot?
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WNDZRFR
Joined: 28 Mar 2000
Posts: 124
Location: Greater East Bay Area
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| Posted: Thu Jun 01, 2023 1:20 pm Post subject: |
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From what I understand the thin blue line on the older site is a computer model prediction and not human.
I find it more helpful at hard to forecast sites.
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ajmcgraw
Joined: 25 May 2022
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| Posted: Thu Jun 01, 2023 3:06 pm Post subject: |
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| The plot you posted is the previous day's history, not the forecast. The blue line is the recorded mean.
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WNDZRFR
Joined: 28 Mar 2000
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Location: Greater East Bay Area
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| Posted: Thu Jun 01, 2023 10:29 pm Post subject: |
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I meant the thin grey line!
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windfind
Joined: 18 Mar 1997
Posts: 1877
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| Posted: Fri Jun 02, 2023 11:09 am Post subject: Re: Mike -- Palo Alto Prediction 5/30/23 -- How on Earth? |
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| fxop wrote: | Mike/iWindsurf -- how on earth did you guys predict this pathological wind shift *exactly* with the thin blue line on the iWindsurf app? The same pattern was also called exactly on May 25. Yesterday Palo Alto had nice NNW wind early as shown. The whole Bay was SW, but there was a .05 gradient to Bakersfield.
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Hi fxop,
Great question!
For a quick answer to your question, skip to the bottom.
To really understand what is happening, here is some background.
Palo Alto is less prone than 3rd. Ave. to that battle between the "Good" wind and the "Bad wind" that can spoil the winds in the sail/kite/wing area, especially at the launch.
The forces behind the "Good Wind" are:
1. NW to WNW ocean winds which push wind through San Bruno Gap towards 3rd & PA
2. At least a moderate pressure gradient towards Bakersfield via Morgan Hill to Pacheco Pass, which sucks and accelerates the San Bruno Gap winds to the launches at 3rd & PA.
The forces behind the "Bad Wind" are:
1. Anything that promotes southerly ocean winds in the Half Moon Bay to Hwy. 92 Gap area to near 3rd. Ave. or Palo Alto. This includes an eddy, a marine surge, or a very deep marine layer.
2. A pressure gradient towards Stockton via the Altamont and Dresser Passes. This gradient does two things.
A. It tries to curve the wind WNW away from shore at 3rd. Ave., as they turn towards those East Bay, passes.
B. It accelerates the WSW wind in the Hwy. 92 Gap area, so it gets closer or even over Palo Alto and 3rd. Ave. launch areas.
All this means there is sometimes a battle between the NW/WNW "Good Wind" and the WSW "Bad Wind" very close to the launch sites.
If the southerly ocean winds weaken or if the pressure gradient towards Stockton weakens during the afternoon, that battle happens west of Palo Alto and 3rd. Ave., so at the launch sites, all you notice is the "Good Wind."
If the southerly ocean winds weaken or if the pressure gradient towards Stockton weakens during the afternoon, that battle happens west of Palo Alto and 3rd. Ave., so at the launch sites, all you notice is the "Good Wind."
If the southerly ocean winds become stronger or if the pressure gradient towards Stockton builds during the afternoon, that battle between the "Good Winds" and the "Bad Winds" happens right over Palo Alto and 3rd. Ave., so at the launch sites, you notice unreliable changing winds at the launch despite usable winds outside.
And if the pressure gradient towards Bakersfield fades, then there are WSW "Bad Winds" both at the launch sites and outside.
All these variables can change during the day, making for a forecasting nightmare.
The imagery below shows some of the above.
So, to answer your question:
We run a custom 1 km version of the WRF model, which is enhanced to capture the Bay Area topography. The forecasters fine-tune the 3rd. Ave. and Palo Alto model forecasts by looking at the reality before the morning and mid-day forecasts. We look at the direction of ocean winds, the actual wind direction and strength in those passes, the actual pressure gradient and the fog flow in those passes. If we have time, we also look at all of our Tempest weather stations between Half Moon Bay and the launch sites. We do this fully aware that all of this can change between the forecast time and your launch time.
Meanwhile, our Denver modeling office is busy developing machine-learning algorithms to incorporate sensor data into the model and human forecast. We can do this because we have over 60,000 of our Tempest weather stations installed and they are all feeding data into our servers in near real-time. The system will take years to become fully operational. But I suspect that that sudden shift you noticed in Kerry's forecast tables from "Good Wind" to the "Bad Wind" was generated by a combo of human pattern recognition and machine learning modifying the forecast table.
I hope all this helps some.
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weatherflow.com
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https://windnotes.smugmug.com
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fxop
Joined: 13 Jun 1998
Posts: 200
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| Posted: Sat Jun 03, 2023 10:30 am Post subject: |
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Thanks Mike! Very impressive!
fxop
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windfind
Joined: 18 Mar 1997
Posts: 1877
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| Posted: Sat Jun 03, 2023 1:23 pm Post subject: |
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| fxop wrote: | Thanks Mike! Very impressive!
fxop |
Thanks, I wish I could forecast all of this 10% as well as I can explain it. Just too many constantly changing variables. The best I can do in 2023 is to forecast generalizations about the "Good" vs. "Bad" winds.
The issue is, mostly, not lack of skill. Google, with Stanford and UC mets nearby, has repeatedly hired me to forecast for projects ranging from Project Loon, Makina Power, The multi masted gaft rigged Google towable Treasure Island store etc. So I must have some skill. But, we need more sensors and higher resolution models.
Mike
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mac
Joined: 07 Mar 1999
Posts: 17609
Location: Berkeley, California
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| Posted: Sat Jun 03, 2023 2:51 pm Post subject: |
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| We also get the north south battle in the bay between Treasure Island-Angel and Berkeley-Pt. Isabel. Makes for up and down winds, which makes it harder to stay lit on smaller sails and wings.
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windfind
Joined: 18 Mar 1997
Posts: 1877
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| Posted: Sat Jun 03, 2023 7:12 pm Post subject: |
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| mac wrote: | | We also get the north south battle in the bay between Treasure Island-Angel and Berkeley-Pt. Isabel. Makes for up and down winds, which makes it harder to stay lit on smaller sails and wings. |
Yes, a similar battle, but easier to forecast since the "Bad" winds are partially coming over water. Plus, we can look at the ≈1000 feet aloft (975MB level) WNW winds over Marin and the East Bay to make a decent guess when the "Bad" winds are likely to reach the zone you describe. Look at the text below the Pt. Isabel and Berkeley tables for words like "WSW winds likely to fade after 4 PM" We are not always right but we do better than our 3rd. Ave. forecast.
Here is a blog about the Treasure Island to Pt. Isabel battle:
https://blog.weatherflow.com/why-did-i-forecast-strong-winds-everywhere-except-pt-isabel-and-berkeley/
Mike
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mac
Joined: 07 Mar 1999
Posts: 17609
Location: Berkeley, California
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| Posted: Sat Jun 03, 2023 7:19 pm Post subject: |
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| Mike—I don’t remember the 25th. But what seems different this year is that you have to go further west from Berkeley, or the yacht club, before you get any steadying of the wind veloocity than any year in my memory. The north south battle is a familiar one, and can sometimes be escaped by going North, or South, or west. But this year the up and down nature has characterized about 2/3 of my 30+ days out. Again today.
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