myiW Current Conditions and Forecasts Community Forums Windsurfing Videos Buy and Sell Services
 
Hi guest · myAccount · Log in
 SearchSearch   ProfileProfile   Log in to check your private messagesLog in to check your private messages   RegisterRegister 
Today forecast imagery: A Sherman Island puzzle for you
Goto page 1, 2  Next
 
Post new topic   Reply to topic    iWindsurf Community Forum Index -> Southwest USA, Hawaii, Mexico
View previous topic :: View next topic  
Author Message
windfind



Joined: 18 Mar 1997
Posts: 803

PostPosted: Sun Aug 03, 2014 11:58 am    Post subject: Today forecast imagery: A Sherman Island puzzle for you Reply with quote

Hey Gang,

Recently on days like this when I am not forecasting and there is no wind, I sometimes work on a blog about weirdness of Sherman Island winds.

Today is a good example. The sensors at dawn were solid low 20's.

Looking at the imagery from about 8:30 today (along with some highlighted hints.) Take your shot at why today....

1. The Sherman Island winds were so much stronger than the SFO-SAC pressure gradient of .07 in. would cause.

2. Why the winds are so much stronger at Sherman Island than at nearby sensors that receive the same inbound wind.

3. Why were the readings from M10 vs. M14 fairly close while many days they are very different.

4. And the $64K questions:
a. Why are the winds likely to fade some mid day and then pick up in the afternoon?

b. Why does Sherman Island blow strong in the morning like the Gorge but unlike any other site in the Bay Area.

c. Looking carefully at the top image guess why the winds at the Powerlines are often modest and up and down for long stretches. Yet sometimes the Powerlines blow strong for several days during a marine surge.

If you rather not guess you can just wait until the movie version comes out later this summer in a video blog near you.

Mike Godsey
iwindsurf.com



ShermanStrongDawn.jpg
 Description:
 Filesize:  389.08 KB
 Viewed:  1172 Time(s)

ShermanStrongDawn.jpg


Back to top
View user's profile Send private message
waitinSD



Joined: 28 Dec 2010
Posts: 39

PostPosted: Mon Aug 04, 2014 12:44 am    Post subject: Reply with quote

Mike
Thanks for the great info- again. Help me understand how the lower pressure gradient number = higher wind speeds, e.g. todayís highest winds at S.I., as well as lowest pressure gradients, were in the early a.m. I thought more always = more better. What did the gradients look like when the wind dropped for the rest of the day? Is Bay area gradient data available? Thanks again for all the extra info, Iíve learned a lot from your posts and blogs.
Back to top
View user's profile Send private message
windmaddness



Joined: 09 Oct 2010
Posts: 36

PostPosted: Mon Aug 04, 2014 11:58 am    Post subject: Reply with quote

Here's my personal interpretation:

1-the spinning counter clock wise winds at 5000ft helped Sherman wind despite the low pressure gradient .7

2-the winds at sherman island increase in speed due the Venturi effect caused by the hills.

3-depending on the wind direction, if the winds are more to the west or wnw M14 gets less wind than M10. Today the spinning winds aloft helped the SW flow above sherman island resulting in close reading between M10 and M14.

4-a- sherman island is the PASSAGE of the cold air from the ocean to the hot boiling Valey. In the morning the cool air line is just west of sherman and the valley is still hot resulting in strong wind accentuated by the topography as mentioned in -2-
Around midday sherman warms up almost matching the valley temperature in the same time the marine layer starts receding to the gate causing the PASSAGE to temporarily move west. As the valley continues to heat up and the marine layer sattles at the gate, the pressure gradient continues to build. If sherman gets as hot as the valley wind will pick up at the bay and be modest at sherman and if sherman keeps it's midday temperature (which is less than the valley's by 20 degrees) as it's highest wind will pick up again and increases as the bay cools off more with the marine layer moves eastward and the sherman become the passage again.

b-sherman sits righ in the middle of 2 extreme climates. Very hot in the valley and cold by the ocean. When the marine layer is over the east bay hills and the valley been baking for many days, the temperates in the valley stay high even at night that means the hot air is constantly rising. There is tremendous need in cool air to replace the vacuum and sherman happened to be sitting in That passage.

c-the powerline is blocked by the hills on the west side. Unless the wind is SW it only gets gusty turbulent wind.
Back to top
View user's profile Send private message
spennie



Joined: 13 Oct 1995
Posts: 829
Location: Thousand Oaks, CA

PostPosted: Mon Aug 04, 2014 12:52 pm    Post subject: Reply with quote

Question 4d. Why does the wind at Shermant quite often peak at 4 AM, when there's no sun to energize the atmosphere?

Mike, I think you're leaving an important element out of your calculations, the FM factor.

It's Fucking Magic.

_________________
Spennie the Wind Junkie
www.WindJunkie.net
Back to top
View user's profile Send private message Visit poster's website
windfind



Joined: 18 Mar 1997
Posts: 803

PostPosted: Mon Aug 04, 2014 2:11 pm    Post subject: Reply with quote

Hi Gang!

windmaddness: great job! Your meteorology is a bit off but your concepts are perfect!

Spennie: Great Question 4d (how can Sherman blow at 4AM when the there is no sun to heat the Central Valley.

The graphic below about today's AM Sherman Island winds and windmaddness's answer 4a will answer your question.

More later, gotta sail!

Mike Godsey
iwindsurf.com



Sherman IslandAM.jpg
 Description:
 Filesize:  356.37 KB
 Viewed:  901 Time(s)

Sherman IslandAM.jpg


Back to top
View user's profile Send private message
jroberts



Joined: 10 Feb 1997
Posts: 18

PostPosted: Mon Aug 04, 2014 9:33 pm    Post subject: Reply with quote

katabatic flow for early morning winds
Back to top
View user's profile Send private message
spennie



Joined: 13 Oct 1995
Posts: 829
Location: Thousand Oaks, CA

PostPosted: Wed Aug 06, 2014 10:43 am    Post subject: Reply with quote

Katabatic wind (from the Greek: katabaino - to go down) is the generic term for downslope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys or planes below.

Probably not katabatic wind, no tall mountains close enough to create that much wind for so many hours.

_________________
Spennie the Wind Junkie
www.WindJunkie.net
Back to top
View user's profile Send private message Visit poster's website
jroberts



Joined: 10 Feb 1997
Posts: 18

PostPosted: Wed Aug 06, 2014 7:25 pm    Post subject: Reply with quote

It is katabatic flow from the coast range. They cool off fast and then it just goes downhill--like most things in life.

spennie wrote:
Katabatic wind (from the Greek: katabaino - to go down) is the generic term for downslope winds flowing from high elevations of mountains, plateaus, and hills down their slopes to the valleys or planes below.

Probably not katabatic wind, no tall mountains close enough to create that much wind for so many hours.
Back to top
View user's profile Send private message
beallmd



Joined: 10 May 1998
Posts: 1074

PostPosted: Fri Aug 08, 2014 4:49 pm    Post subject: Reply with quote

It was called "hand waving" in med school when a prof would get up there and discuss something like the immune system which is incredibly complex and poorly, if really at all, understood. Note; the immune system is at least as complicated as the brain, probably more so. In the book Even Cowgirls Get the Blues Robbins writes; "Isn't it interesting that the brain decided it is the most interesting organ in the body!" I digress, but I think much like our professors, the explanation for AM Rio wind involves a lot of bits of information thrown out there, along with a lot of hand waving, as a way of looking like one understands it. I don't see where there is a good workable theory. Search quotes from that book, very funny stuff. Not everything from the hippie days was a loss.
Back to top
View user's profile Send private message
gregnwind



Joined: 11 Apr 2004
Posts: 8

PostPosted: Fri Aug 08, 2014 6:16 pm    Post subject: A Sherman Island puzzle for you Reply with quote

No answers from here...but a question/observation.
I've sailed Shermine Is for the past 20+ years & have given up at the power lines (my old favorite) since all the windmills have gone up. It seems they've changed the wind flow on the water from this launch site.
I remember the big PG&E fiasco near Benicia with their huge windmill that was too high & above the winds, so it flopped. They eventually tore it down. It really showed how our Delta Breeze is focused close to the ground.
Any calcs been done on the effect of these windmills for winds on the water?
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    iWindsurf Community Forum Index -> Southwest USA, Hawaii, Mexico All times are GMT - 5 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum

myiW | Weather | Community | Membership | Support | Log in
like us on facebook
© Copyright 1999-2007 WeatherFlow, Inc Contact Us Ad Marketplace

Powered by phpBB © 2001, 2005 phpBB Group