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-   -   wind predictions (http://www.sailnet.com/forums/general-discussion-sailing-related/47342-wind-predictions.html)

xort 09-22-2008 09:52 AM

wind predictions
 
I looked at 'Passage Weather' (PassageWeather - Wind, Wave and Weather Forecasts for Sailors and Adventurers) Saturday and they predicted 5k winds for Sunday. Went out sailing Sunday and the least we saw was 15k, mostly lower 20's and a gust to 30k. I looked again today and Passage Weather will go back in time and they still have 5k showing and the wrong wind angle too.
This is for the open waters of Lake St Clair.
Is decent wind prediction 24 hours in advance or even 12 hours in advance immpossible?

BTW, had a great time doing 7.5k close reaching in 22k winds but the gust to 30 with full sails was a bit much so we reefed the main by 2/3 and did 6.5 when the wind calmed down to 18k or so. Need to remember to set the genoa track car BEFORE trying to reach!!

Classic30 09-22-2008 08:43 PM

It's a neat tool and not one I'd seen before - thanks! :)

Quote:

Originally Posted by xort (Post 372514)
...
Is decent wind prediction 24 hours in advance or even 12 hours in advance immpossible?

Pretty much. The note at the bottom of their pages says "Our forecast charts are derived from the GFS and WaveWatch III weather models, the same weather models that produce the GRIB files used by modern electronic navigation software and weather routing software."

The biggest issue is that none of these models take into account local weather alteration caused by actual cloud cover, topography (mountains, hills, valleys, ..trees!) changing wind direction and strength or by man-made alterations to the surrounding landscape (eg. large suburban areas cause localised ground heating, hence thermals, hence localised barometric pressure changes) changing wind strength (and direction to a smaller extent) for miles around.

The best use of these models is to tell you when the local situation might change, but the most accurate forecast you'll get will be the one you make yourself by looking out of the companion-way first thing in the morning. ;)

Cameron.

eMKay 09-22-2008 08:57 PM

The forecast is never right here at the other end of the big lake. It's frustrating in a small boat that has a small wind speed window.

J36ZT 09-22-2008 10:20 PM

I don't trust weather "observers" or "predictors" anymore. A few years back, I bought my boat in Southern California and sailed her North. We picked up fuel, about mid-day at the Dana Point harbor. While there, I could see dark clouds out to sea. I listened to NOAA Marine Weather and they predicted light winds and calm seas for the afternoon. Based on the forecast, we headed out and I was thinking to myself it would really suck to be sailing in the rain. Winds started out at about 5 knots and seas were 1-2 feet. It wasn't long before the boat picked up speed and started heeling past 15-degrees. I was just considering reefing the main when the winds increased to 25+. The seas began to build as well. Just as I began to call for the crew (I was the only one on deck), the boat performed an accidental tack. I quickly released one jib sheet and drew tight the other while I steered the boat. We needed to tack soon anyway, the boat was moving nicely, and I didn't see the need for the crew to rush. Within two minutes, she performed another accidental tack. I decided when she did the third, a minute later, to heave-to and assess what was going on. I left the jib sheet tight on the upwind side and turned the rudder hard-over to point into the wind. Within two seconds, the boat laid over with 45+ degrees of heel, started moving backwards, and water was coming over the side into the cockpit. The crew looked bewildered from the companionway. There wasn't much else to do but start the engine, nose into the wind, and bring down the sails. By the time the sails were secured, we were in 30+ knots of wind and 5-6 foot swells. Needless to say, we motored to our next port. The weather had gone from 5 knot winds and 1-2 foot swells to 30+ knot winds and 5-6 foot seas in the space of about ten minutes or less. So, NO...I don't trust weather forecasters anymore.

At the time, I was rather inexperienced both at sailing and with the boat.

When we made it to Santa Barbara, we learned at least one sailboat had been demasted by that same storm.

Skipper, J/36 "Zero Tolerance"

Valiente 09-23-2008 02:06 AM

Local is local. If the wind is coming from west to south to east, there's a bay here at the mouth of the Humber River called "Slumber Bay", because the wind just cacks. Swing it to the north west, however, and the valley funnels it two or three miles out into the lake, and you get a four-mile "fan" of accelerated (sometimes strongly) winds. Throw in a geographical feature like a big island around which a current runs or winds can bend and either die or speed up, and you learn they are predicting for the airport, not the shore, because that is far too dynamic to be predicted until you are out there.

SEMIJim 09-23-2008 01:31 PM

I use SailFlow. They were off for Lk. St. Clair Sunday, but not that far off. And, IIRC, they had the direction right. (I use the St. Clair buoy data, mostly.)

We took friends out Sunday. Perfect day for a sail out there! :) Put the #3 up and a reef in the main. With 1' seas it was a very pleasant ride. Later on, as our guests became more comfortable with the idea of heeling and the wind dropped from about 15 kts down to 12 kts or so, I shook out the reef.

Jim

honeybear 09-24-2008 10:59 AM

I have tried bouyweather.com and have reasonable information for local weather as it is based on the bouy reading in my area here in Fort Lauderdale. I would be open to checking that against any other site. Our city nickname is "Venice of America" yet most forecasts for weather on TV will give very sketchy info if at all.

CharlieCobra 09-24-2008 12:33 PM

I find that up here in the PNW, all you can trust is what ya see at the time on the water. Too many variables around here to get an accurate forecast.

SEMIJim 09-24-2008 01:33 PM

Dunno as it could be much worse than the lake we've been talking about, Charlie. The sailors here-abouts call it "Lake St. Stupid" because of its frequently erratic, unpredictable and undependable wind patterns.

We were in a race a couple Saturdays ago, up in the bay. We won the pickle boat award :p. One of the reasons is we hit every freakin' hole in the lake. I mean every hole. There'd be boats not 100 yards off in one direction or the other from us sailing, and we'd be dead in the water, or darn near. That's Lk. St. Stupid for ya.

Jim

Boasun 09-24-2008 02:17 PM

What you see on TV the night before and on the morning news and sometimes from Noaa Radio on VHF may or may not be the same as what you are experiencing while sailing.
Take the weather reports as advisories and not fact. :rolleyes:
Fact is what you are sailing in once you get underway. :eek:


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