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Memorize this: Here's your Spring!
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windfind



Joined: 18 Mar 1997
Posts: 1559

PostPosted: Wed Apr 21, 2010 6:37 pm    Post subject: Memorize this: Here's your Spring! Reply with quote

Hi Gang,

Today was a rare set up as wind in the 30 knot range rocked Southern California, Hawaii, the S. F. Bay Area, the Oregon coast and the Gorge.

Memorize the pattern in the image below. It is a meteorologist dream. Notice the huge North Pacific High lording over the pacific from the west coast to Hawaii. This high is a massive dome of clockwise spinning air centered today about a 1000 miles west of the Golden Gate. On the west coast it is creating powerful NW wind. In Hawaii it creates blasting ENE trade winds.

Meanwhile a massive surface low extending from the Columbia River Basin to the desert SW is sucking the NW flow through gaps in the Cascades and the California coast range making those venues rip with westerly wind.

The North Pacific High and the low acting in concert are forming a huge pressure gradient represented by the tight isobars along the west coast and over the Gorge.

Why is this pattern a meteorologist dream? If is so easy to forecast that you can do the forecast in 15 minutes and actually get to sail or kite.

Mike Godsey
iwindsurf.com/ikitesurf.com



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windsass01



Joined: 09 Jun 2005
Posts: 26

PostPosted: Wed Apr 21, 2010 7:30 pm    Post subject: Reply with quote

Figures, it was windy everywhere on the west coast except Sherman.
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chibichibi



Joined: 26 Jun 2006
Posts: 275

PostPosted: Wed Apr 21, 2010 8:38 pm    Post subject: Reply with quote

no wind in the east bay today though! Rolling Eyes Sad Twisted Evil
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windfind



Joined: 18 Mar 1997
Posts: 1559

PostPosted: Thu Apr 22, 2010 9:08 am    Post subject: Why so strong on the coast and weak inside the bay Reply with quote

When the wind is so powerfully NW like yesterday the wind never has a chance to curve into the Bay and head over the East Bay to Rio and towards the Central Valley. So sites like Crissy, Sherman, Berkeley, Pt. Isabel etc that have topography upwind barely got any wind. The NW wind simply hits the ridges near the coast and lifts way above the water.

So in this pattern head to sites that have nothing upwind to the NW. Best bets are Waddell, Bodega, Tomales or way outside at 3rd. and you will find LOTS of GUSTY wind.

Mike Godsey
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rigatoni



Joined: 25 Feb 1999
Posts: 423

PostPosted: Thu Apr 22, 2010 9:13 am    Post subject: Reply with quote

OK Mike but Crissy is weird in that respect. Sometimes that great NW buoy spring winds make for epic days at Crissy and sometimes like yesterday-marginal. The angle of the wind is obviously critical but sometimes we have great spring days at Crissy even without a favorable WNW bend to the wind. Could you give me an explanation?
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windfind



Joined: 18 Mar 1997
Posts: 1559

PostPosted: Thu Apr 22, 2010 12:41 pm    Post subject: NW ocean wind and Crissy in the Spring Reply with quote

You are right. Sometimes NW wind on the coast translates in to great WSW wind starting at the beach at Crissy. Other times, like yesterday, NW wind means very marginal wind at Crissy. Here is a somewhat oversimplified explanation:

Good NW wind: Good spring NW days at Crissy need a NW ocean wind that is mild to moderate wind. They also need the wind to be mostly at the surface and require a decent SFO-SAC pressure gradient (ie the Central Valley is relatively warm). With this setup the NW wind is funneled along the coast range of Marin and sweeps southward towards the Gate. Once it arrives at the Golden Gate the SFO-SAC pressure gradient causes the wind to curve into the bay as WSW to W wind and Crissy has a great day with the wind starting at the beach. And Treasure Island and Berkeley also have good days.

Bad NW wind: If the ocean NW wind is very strong there is likely to also be very strong NW wind just aloft. This wind just aloft tends carry some of the surface wind OVER the Marin coast range where it's turbulent flow may hit the East Bay shoreline sporadically. This flow deprives Crissy of some of the wind energy. If in addition the SFO-SAC pressure gradient is weak much of the NW wind DOES NOT curve into the Golden Gate but rathers continues down the coast. This leaves Crissy partially in the wind shadow of the Marin headlands and also partially deprived of the wind that normally heads towards Blunt Point. So Crissy has a relatively weak day. If you think about it you will realize that this pattern would favor Ocean Beach.

Does that make some sense. Of course in reality there are not just 2 NW patterns. Rather there is a continuum which makes the forecast very tricky. And worse the variables change during the day. Worse yet none of the computer models are aware of this process.

Mike G.
iwindsurf.com
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chibichibi



Joined: 26 Jun 2006
Posts: 275

PostPosted: Thu Apr 22, 2010 3:44 pm    Post subject: Reply with quote

thanks for the details, mike.
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girsang



Joined: 16 Jun 2000
Posts: 52
Location: San Francisco

PostPosted: Thu Apr 22, 2010 4:40 pm    Post subject: Crissy Reply with quote

So why didn't the meteorologist include that in the Crissy forecast? The strong wind aloft was known and the weak SFO-SAC gradient was known.

The other factor was the flood. It wasn't working at Crissy. And it wasn't working at 3rd even though it is not blocked to the north.
This too would be mentioned in the forecast, if the meteorologist had local knowledge.

I also checked OB, but the waves were 13@10 and I wasn't ready to take that on with only 1 session so far this year.
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windfind



Joined: 18 Mar 1997
Posts: 1559

PostPosted: Thu Apr 22, 2010 4:48 pm    Post subject: well.... Reply with quote

The fact that the forecaster on duty yesterday did not mention it is probably my fault even though I was not forecasting. Part of my job is to convey that info. to the other forecasters.

It takes many years to get that local knowledge so they have pick it up from me AND from you as you mail us nuggets of insight.

Plus it is hard to remember all that info. on the spur of the moment for the may dozens of sites we are forecasting each day across the USA. We have a conference call for an hour every week where the 10 forecasters share this type of knowledge that is not picked up by any model. This allows us to very slowly improve the forecasts. 15 years ago the forecasts were a joke now they are somewhere between the amusing to useful range. Wink

Mike G.
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rigatoni



Joined: 25 Feb 1999
Posts: 423

PostPosted: Fri Apr 23, 2010 1:20 pm    Post subject: Reply with quote

Sometimes Crissy blows on a NW without a pressure gradient particularly if the ocean winds are really, really strong. But sometimes not. Usually we get good wind on the first day of a NW pattern but then the wind angle starts getting too north. But sometimes not. I can't quite figure it all out.

Usually May and June are more consistent at Crissy because you are still seeing coastal winds but SAC is heating up as well. I get that.
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