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2nd. Video update: Gorge & SoCal gusting to 30 knots.

 
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windfind



Joined: 18 Mar 1997
Posts: 817

PostPosted: Mon Apr 28, 2014 7:52 pm    Post subject: 2nd. Video update: Gorge & SoCal gusting to 30 knots. Reply with quote

Hi Gang,

The winds will be fading away especially Tuesday through Thursday while the temperatures soar.

Go the video blog link below to see some videos that show the upper ridge heating up the west coast and watch the North Pacific High die over the Pacific Northwest and Northern California. Meanwhile a new North Pacific High is created north of Hawaii and moves to the California coast Friday or Saturday.

http://blog.weatherflow.com/upper-ridge-moves-over-california-bringing-heat-and-weak-winds/

Scroll to bottom to see video update.

Mike Godsey
iwindsurf.com



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Last edited by windfind on Tue Apr 29, 2014 10:46 am; edited 1 time in total
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kirk



Joined: 10 Apr 2000
Posts: 158

PostPosted: Tue Apr 29, 2014 9:30 am    Post subject: WRAMS vs iWS Reply with quote

So, why is WRAMS (what does that stand for??) predicting another solid day at Coyote like yesterday while iWS predicts much less wind?

SFO terminal forecast takes the easy way out and predicts the before and after windy periods.
Quote:
Forecasts

San Francisco [SFO] terminal forecast issued 2014/04/29 at 0427 PDT
0427 pdt: wind 000 degrees true at 0 knots, sky clear
0900 pdt: wind 050 degrees true at 5 knots, sky clear
290@15
1500 pdt: wind 290 degrees true at 15 knots, sky clear
2200 pdt: wind 280 degrees true at 9 knots, sky clear
000 pdt: wind 280 degrees true at 5 knots, sky clear
0400 pdt: wind 000 degrees true at 0 knots, sky clear



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Kirk Out
http://bayareawindsurfing.blogspot.com/
http://kirklindstrom.blogspot.com/
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windfind



Joined: 18 Mar 1997
Posts: 817

PostPosted: Tue Apr 29, 2014 10:43 am    Post subject: 30 knot EAST wind Southern California and Gorge. Reply with quote

Hi Kirk,

Looking at video below notice how the North Pacific High has shot a ridge into the Pacific Northwest. Actually parts of the ridge have moved all the way into the Great Basin & the Columbia Basin. So we have high pressure EAST of the coast.

In the AM this high pressure creates the easterly offshore winds you see in the video. Since this East wind in funneled by the walls of the Gorge and the Southern California canyons some sites in those venues are peaking at 30 knots at 8AM this morning. The Bay Area also has easterly winds but the East Bay hills blocks that wind but some hilltops are gusting to 30 knots. This set up also causes the Central Valley thermal low to move to the Bay Area coast hence the limp SFO-SAC pressure gradient.

In the PM today the surface high pressure from the NPH weakens as those basins heats up and the air expands. So in the Gorge and Southern California you will see a major fade of Southern California's Santa Ana and the Gorge's Rooster Rock winds.

For the Bay Area things get really tricky so Benjamin who is on duty is probably sweating bullets. Basically, as the high pressure inland weakens the Central Valley thermal low retracts from the Bay Area coast so the SFO-SAC pressure gradient goes up a bit. At the same time the East Bay temps go up creating a very local low pressure. Then sometime this afternoon as the north ocean wind fades a bit this local pressure gradient will such a bit of with though Golden Gate and San Bruno Gap which provide a Venturi for sites directly downwind. Since the land will be relatively hot this wind will not stick to the surface very well so near the beaches the wind may be light but there is a decent chance of upper teens outside at sites in those venturi areas.

But timing is EVERYTHING in forecasting today's wind. If even one variable of the variables above is delayed then these winds will not materialize. Hence the sweat.

Mike Godsey

PS: Hey, Gorge people who can figure out why the video, which is based upon model output, shows light east winds in the Gorge while in reality Rooster Rock is gusting to 30 knots.



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Last edited by windfind on Tue Apr 29, 2014 11:34 am; edited 1 time in total
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kirk



Joined: 10 Apr 2000
Posts: 158

PostPosted: Tue Apr 29, 2014 11:00 am    Post subject: WRAMS vs iWS Reply with quote

Thanks Mike but I guess I still don't understand why the WRAMS model, which correctly predicted yesterdays blasts above 30 behind SFO, is predicting the same for today while iWS says 19 at best.

[edit 12:30PM]
Does it use a different model or past history?
http://www.weatherflow.com/mesoscale-modeling/weatherflow-weatherflow-rams-wramsrams/
so 1km is grid size for the model... hence more accurate than 8km and I see the iWS forecast now matches the model in matching yesterday's forecast... which even with the gusts, high teens was probably the most accurate as I was comfortable on 6.6.
[/edit]

BTW, I needed more board float yesterday than the graphs would indicate so my guess is the lulls were the wind not sticking to the surface... like the forecast... I went out on 6.6 Hucker and a sinker and had one good run then sank in the jibe attempt (maiden voyage for board so blame me..) and had to mostly slog back in and get my every day, floaty Real Wind (270XL) board... then when it kicked in over 20, I flattened the sail and was still fine but would have been very happy on my 5.6 Hucker.



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Kirk Out
http://bayareawindsurfing.blogspot.com/
http://kirklindstrom.blogspot.com/
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windfind



Joined: 18 Mar 1997
Posts: 817

PostPosted: Tue Apr 29, 2014 5:17 pm    Post subject: Reply with quote

Hi Kirk,

Sorry for the delay getting back to you. Today is a play day so I am not forecasting. I am not sure what you are referring to as the "iWS" do you mean the human forecast?

Forecasting was really tricky yesterday and today. Yesterday the AM saw weak NE winds that faded mid day and were replaced by strong 925mb NW winds that transferred momentum to the surface at times hence the strong gusts and lulls at some sites.

Today there are still, at 3PM, strong NE gusts in the 20-30 knot range on the hilltops while the NW winds aloft are weaker than yesterday. This is keeping the SFO-SAC pressure gradient weak .02 at present. The WRAMS seems convinced that those NE winds will fade in the next hour or so and NW winds will curve into the Bay. I am a bit skeptical and I notice that Ben is still sticking with a solid upper teens at a few sites.

Time will tell.

Mike Godsey
iwindsurf.com
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kirk



Joined: 10 Apr 2000
Posts: 158

PostPosted: Wed Apr 30, 2014 12:03 pm    Post subject: Reply with quote

windfind wrote:
Hi Kirk,
I am not sure what you are referring to as the "iWS" do you mean the human forecast?

Yes, I was trying to figure out what is the difference between different forecasts, models, etc. I think I have a better handle on it now.

I believe the "iWS" human forecast is the human best guess of all the models... something you might try teaching IBM's "Watson" to do... I usually take it a step further and take your models, my local observations and sometimes get an even better forecast for my use. I think what you offer is well worth the money and I urge my friends who bug me for forecasts to pay up as I don't share if I think they can afford it. More paying will keep the costs down and quality improving.

I think I figured out too why WRAMS is more accurate at 1km vs 8km.... grid size for iterations of the model. Obviously, when interesting stuff happens, the program makes a smaller grid so we get the finely resolved model for the Bay. I think it is great.

Thanks for answering our questions.

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Kirk Out
http://bayareawindsurfing.blogspot.com/
http://kirklindstrom.blogspot.com/
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