Received: from hplms26.hpl.hp.com by opus.hpl.hp.com with SMTP (1.37.109.8/15.5+ECS 3.3+HPL1.1) id AA04682; Tue, 11 Jul 1995 08:31:47 -0700 Return-Path: <WindFinder@aol.com-DeleteThis> Received: from mail06.mail.aol.com by hplms26.hpl.hp.com with ESMTP ($Revision: 1.36.108.11 $/15.5+ECS 3.3+HPL1.1S) id AA005556731; Tue, 11 Jul 1995 08:32:13 -0700 Received: by mail06.mail.aol.com (1.37.109.11/16.2) id AA067186479; Tue, 11 Jul 1995 11:27:59 -0400 Date: Tue, 11 Jul 1995 11:27:59 -0400 From: WindFinder@aol.com-DeleteThis Message-Id: <950711112758_112392920@aol.com-DeleteThis> To: wind_talk@opus.hpl.hp.com-DeleteThis Subject: Re: Windsight/Wind_after/CotW Whatsup?
Ed Scott says
"Kudos to Windsight and their prediction for Crissy yesterday. It was
dead on the mark. They reported up and down winds with an early
shutdown, which seemed to coincide with the start of the flood. I had
switched to my 5.5 by the end of the day (185#), and was sufficiently
powered to make it back to the launch. Unfortunately, my friend Jim M.
on his 4.5 did a tour of the Yacht Club.
So what phenomenon causes it to
blow like stink on shore, but yet, die completely about 200 yds out?
That was a real trap for the unwary."
Mike Godsey replies
The answer to this question is really complex and even this brief version is
long winded so if you are not into weather dump this now. To forecast wind at
Crissy and to make sense of the sensor report you have to plug in the
following variables:
1. Atmospheric stability 2. The marine layer thickness or the absense of an
inversion (obtained daily from the Oakland radio beacon sounding 3. Marine
layer penetration and direction (we have 4 guys who are in high buildings
overlooking different parts of the Bay who phone in several reports daily.)
4. On-shore or offshore marine push. 5 And sometime the position of a
jetstreak aloft.
When the atmosphere is stable with a clear inversion, with fog and an onshore
push the Crissy sensor will give you an idea of what the wind is like towards
the north tower of the Golden Gate Bridge. But the wind will be light, even
unsailable, at the beach. The risk is low since you can see that you will
have problems getting out and back and rig accordingly. The only problem is
you may have driven to Crissy only to find that it is too light to get to the
windline. This is why we have Justin, Jeff, Jim, John, Mike and myself doing
phone reports from the beach at Crissy to report the actual sail sizes being
rigged.
When the trend is towards the opposite of the above the sensor will read high
but there will still be strong winds the first half of the Bay but the wind
will fade out towards the N. tower. Again no problem for an experience
sailor.
The problem arises when the atmospheric is unstable and there is some
jetstream activity overhead. Depending upon the direction of the jet the wind
will be either epic and gusty or patchy on and off periods. In these
conditions big areas of the bay especailly near shore may die for a period
especially late in the day. Usually we can forecast this and put out a
warning.
Ed Scott continues
"OK, so I got the new Windsight SW, and the 3:00 pm report for today says
Crissy at 36. COTW is only reporting 20, and Ken's report was yet another
number.
Mike replies
The basic problem is that ALL of the current sensors at Crissy are poorly
sited. SInce the wind is slightly offshore the sensors have to be mounted
high to avoid wind shadows. Unfortuntly this means that in many wind patterns
they pick up much stronger winds that you will find on the beach. Genneraly
you can trust the sensors most when there are NW winds on the coast and least
when there is fog in the Bay. The Windsight and the SFBA sensors are atop the
St. Francis Yacht Club just east of the launch site. Unfortuntly SFBA sensor
is located where a nearby tile roof sends a stream of air right at the cups.
The Windsight sensor has a slighlty better location but still often
mis-reads. The Call of the Wind sensor is located far from the sailing area
at the GG yacht club on the Marina Green. This area is often a wind hole.
Remember that all of the sensors sample the wind over different time periods
so the readings will be different. (Please skip the following promotional
plug) Because of all these problems Windsight's on site verbal reports giving
sail sizes and wind conditons and the noon forecast are currently the best
bet for Crissy. When our Smart Pager comes our next season it will have
sensor reports, on-site text reports and custom forecasts for all the
sailing sites on the pager. And if things go right we may finally have the
perfect Crissy sensor next season.
Mike Godsey
1-800-685-WIND
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