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Blog: NW clearing winds... not!

 
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windfind



Joined: 18 Mar 1997
Posts: 1440

PostPosted: Wed Apr 11, 2018 10:21 am    Post subject: Blog: NW clearing winds... not! Reply with quote

Hi Gang,

Looking at the Bay Area ocean buoys winds today you would think that NW clearing winds are ramping up. But you would be thinking wrong.

But thinking right if you launch along the Central California coast, Southern California or Baja!

Check out this blog for the back story:

http://blog.weatherflow.com/west-coast-wind-blog-fast-moving-cold-fronts/

Mike Godsey
iwindsurf.com/ikitesurf.com
Weatheflow.com



NPHcoldFrontNW2SW.gif
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NPHcoldFrontNW2SW.gif


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loopy



Joined: 21 May 2004
Posts: 59

PostPosted: Wed Apr 11, 2018 1:08 pm    Post subject: Reply with quote

hi mike,

i have a couple of questions about the graphics: are the isobars and the wind visualization for the same altitude? are they at sea level?

also, do lateral winds flow in the same direction as the isobars or across them from higher to lower pressure?

thanks

alex
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windfind



Joined: 18 Mar 1997
Posts: 1440

PostPosted: Wed Apr 11, 2018 2:07 pm    Post subject: Reply with quote

Hi Alex,

Both the isobars and the winds in the animation are at sea level over the ocean.

Surface winds blow roughly "parallel" to the isobars but actually at an angle to the surface isobars as a general rule.

More precisely at the surface the wind direction crosses the isobars towards lower pressure at about a 30-degree angle due to friction. The angle is determined by the roughness of the terrain so over the ocean the angle is less but the angle is more over mountains. The California coast range and gaps in that range can radically change the direction of the wind.

Also, the isobars in this imagery are from a low-resolution global model so at best they are a rough approximation of the actual distribution of low and high-pressure zones especially over land.

Models at this low resolution are great for forecasting future overall wind patterns but not very useful for forecasting wind at specific sites where topogrpahy comes into play.

Mike
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loopy



Joined: 21 May 2004
Posts: 59

PostPosted: Wed Apr 11, 2018 3:07 pm    Post subject: Reply with quote

hi mike,

thanks for the quick reply and clear explanations!
learned something new today!

for clarification, the isobars should also be changing over time right,
and presumably only the 1st time frame was displayed?

alex
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windfind



Joined: 18 Mar 1997
Posts: 1440

PostPosted: Wed Apr 11, 2018 4:36 pm    Post subject: Reply with quote

for clarification, the isobars should also be changing over time right,
and presumably, only the 1st time frame was displayed?


Actually, if you look carefully the isobars are changing with most time slots.

Look even more carefully in the last 2 time slots and you can see a hint of the NPH's isobars beginning to lean into California. This is the beginning of the ridge of high pressure that will bring less favorable NNW ocean winds to the Bay Area and AM offshore winds to Southern California this coming Friday.

Watch for it!

Mike
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