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Old 26-05-2014, 15:23   #1
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Bizarre Weather Phenomenon

I was sailing today along the Eastern coast of Sweden. The weather forecast said that there were supposed to be strong NE winds in the evening. The whole day (we made 72 miles altogether today) was warm and sunny and very calm. I was wearing a short sleeve shirt. We did a bit of motor sailing at one point, but mostly it was motoring in often glassy smooth water.

As evening fell, we pointed the bows landward, and started to pick our way through a miles-long gauntlet of rocks and skerries with lagoons in between -- typical for this part of the world. Because of the weather forecast, we were planning to take tomorrow off, and were going into a good port to do it. But the weather forecast didn't seem to be coming true. I remarked to my crewman -- look at the sea -- this is Beaufort Force 0 -- hardly a ripple on the water. The weather forecast is obviously wrong, so maybe we should just anchor out here rather than going further inland to port. Just second later, my crewman uttered a cry -- look! Towards us across the water was coming something looking like out of a science fiction movie -- some intense agitation of the water's surface flying towards us across the lagoon. Then an intense blast of wind hit us -- 5 knots to 35 knots in half a second. And like that it blew. And the temperature plummeted from 23 degrees to 11 degrees (C obviously) in the same half a second.

I was afraid. I don't mind 35 knots of wind out at sea, but in close quarters with the light failing, trying to pick your way into port -- that's a different matter. We had to go through a so-called "sound", just 20 meters wide! I couldn't have turned around in that! What if the wind was funneled through that bit and intensified, and I lost control?

To make a long story short, we got into port without any big problems other than my trembling legs.

But I'm still wondering about that bizarre wind. Maybe someone on here with some clue about weather (unlike, for example, me) understands what happened? I have experienced sudden, violent, katabatic winds in the Med -- like avalanches of air, when there's a temperature inversion in mountainous terrain. But there are no mountains here! How can such a wind kick up out of nowhere?

Interestingly, the wind prediction on one Finnish weather site, showed something like what we experienced -- windless dead calm with a sharp border to strong winds. Why??? Wind is what happens where there are differences in pressure -- I know that much despite being a semi-ingnoramus what concerns weather. How can such a steep gradation happen? It seems to defy the laws of physics?

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Old 26-05-2014, 15:40   #2
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Re: Bizarre Weather Phenomenon

Sounds like an orographically generated williwaw. Generated basically by Bernoulli induced acceleration of air molecules over an appropriate shape of land mass. These are aggravated by large tidal swings that induce local areas of low pressure.
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Old 26-05-2014, 15:44   #3
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Re: Bizarre Weather Phenomenon

Welcome to New England.

Maybe you should consider going back to using paper charts.
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Old 26-05-2014, 15:47   #4
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Re: Bizarre Weather Phenomenon

According to the UK Met Office forecast chart for 1200UTC today (Met Office: Surface pressure forecast), an occluded front crossed over the Gulf of Bothnia.

This could explain the drop in air temperature.

Alain
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Old 26-05-2014, 15:48   #5
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Re: Bizarre Weather Phenomenon

Don't know how they happen. Have seen the "funny lookiing" stirred up water coming my way. Knew to reduce sail. However, one of those times, it also was predicted.

From this, I suggest you trust the weather broadcast, as it showed itself to be accurate. I suspect the signs are visible in the wx observations, plus experience. Maybe you could telephone the wx bureau, and speak to a meterologist about it. If you do, pls. report back. Maybe we need to pay more attention to the 500mb level.

Ann
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Old 26-05-2014, 15:51   #6
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Re: Bizarre Weather Phenomenon

Quote:
Originally Posted by IdoraKeeper View Post
Sounds like an orographically generated williwaw. Generated basically by Bernoulli induced acceleration of air molecules over an appropriate shape of land mass. These are aggravated by large tidal swings that induce local areas of low pressure.
I don't really think so. There are no tides in the Baltic, and the nearest bit of Estonia is 170 miles away. The blast of air came from the open sea -- nothing katabatic about it.
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Old 26-05-2014, 15:54   #7
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Re: Bizarre Weather Phenomenon

By the way, the barograph shows a huge drop in pressure, to a little over 1000mb, which lasted only 30 minutes, after which pressure popped right back up to 1017mb, and even increased. WTF?? uzzled:
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Old 26-05-2014, 15:59   #8
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Re: Bizarre Weather Phenomenon

Quote:
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I don't really think so. There are no tides in the Baltic, and the nearest bit of Estonia is 170 miles away. The blast of air came from the open sea -- nothing katabatic about it.
Hasnt Madonna turned to katabatic?
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Old 26-05-2014, 16:11   #9
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Re: Bizarre Weather Phenomenon

Dockhead,

I think Hydra has the right of it. The drop of pressure that lasted only 30 min. is consistent with the passage of an occluded front.

Ann
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Old 26-05-2014, 16:12   #10
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Re: Bizarre Weather Phenomenon

Perhaps that warm day impacted an unstable air mass. If the lifted index was the correct value, sort of a reverse dry microburst creating low pressure at the surface that filled in rapidly. I have seen them come up at many thousand ft/min even when wet. Any electrical discharge?

Likely Ann is correct given the temp delta.
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Old 26-05-2014, 16:18   #11
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Re: Bizarre Weather Phenomenon

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Hasnt Madonna turned to katabatic?
No no Weavis, Madonna doesn't wear panties. Especially on Dockheads's boat.
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Old 26-05-2014, 16:24   #12
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Re: Bizarre Weather Phenomenon

Quote:
Originally Posted by IdoraKeeper View Post
Perhaps that warm day impacted an unstable air mass. If the lifted index was the correct value, sort of a reverse dry microburst creating low pressure at the surface that filled in rapidly. I have seen them come up at many thousand ft/min even when wet. Any electrical discharge?

Likely Ann is correct given the temp delta.
Does sound like something microburst related to me. I could not find any mention of clouds, did you see any. Same question about lighting or what IK calls electrical discharge.
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Old 26-05-2014, 16:47   #13
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Re: Bizarre Weather Phenomenon

Welcome to the White Squall
I'm not sure if the nature of it is fully known and understood, but I know that it is extremely difficult to predict. Several years ago Poland was covered by the net of huge weather radars for early warning. They serve well also for warnings about more regular thunderstorms.

If the forecast is for strong wind and the reality is windless, be aware - the later the wind will come, the stronger will be first impact.

Several years ago a tens of boats were lost on the lakes in North East part of Poland, more than ten people drowned, others were killed on land, thousands acres of old forests were wipped out, all in ten or fifteen minutes. Wind jumped from 2 to 11 B in some three or four minutes.
Happily now the warning system is in place.

I believe Finland had the weather info from similar radar system.
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Old 26-05-2014, 16:50   #14
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Re: Bizarre Weather Phenomenon





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Old 26-05-2014, 16:53   #15
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Re: Bizarre Weather Phenomenon

Yes, white squall.

No dark clouds in the sky, and the wind suddenly accelerates from 5-10 kts to 35-40 kts. Had that happen in the Grenadines. Saw it coming only due to the frothing of the surface, approaching fast. I managed to reduce sail in time to head up into the blast and motor through. It was over in 15 minutes or so.

Another reason I really love my mast furling main!
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