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Old 26-05-2014, 17:04   #16
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Re: Bizarre Weather Phenomenon

It can be associated with incoming clouds also, but not necessarily









Happens here more often inland than on sea, in the matter of fact.
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Old 26-05-2014, 17:05   #17
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Re: Bizarre Weather Phenomenon

Ahoi Dockhead,
I guess that Hydra was right with occluded front passing.
It seems that you are sitting between a big north Atlantic High and
some strong Low pressure over northern Russia which will bring you strong
northerlies for at least a couple days.
I think to remember that you like strong breezes or gales, well here you go
Now you could try carstenb's docking technic
Help full link for your area:
Kart – yr.no

Happy sailing
and may there always be a hand breadth of water under your keel.

Martin
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Old 26-05-2014, 17:07   #18
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Re: Bizarre Weather Phenomenon

Quote:
Originally Posted by Dockhead View Post
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:

Was going to first suggest a standard (around South Texas Fall-Spring) frontal system/line. They usually follow a pattern of increasing SE wind flow as a high (cool air) approaches from the N/NW.
As the high nears the gradient may relax to dead calm for a period, then the edge of the front itself (often a wedge shaped pool of cold(er) air) rolls in, sometimes a quite striking wall of dust and moisture (over water just an agitated line on the surface) is visible. Then it hits and the wind acts as you describe, it cools rapidly, and all kinds of things happen.
Secondly (and better fitting your description), it may have been an outflow boundary from a distant thunderstorm (TS) or MCS (Mesoscale Convective System, a complex of TS's).
Outflow boundaries can precede TS/squall lines by quite a distance (think cool breeze before the tropical squall).
They are caused, first, by the normal vertical movements of air within TS's (warm up, cold down), on a small scale around a storm or three.
Secondly, by the collapse of an entire dying MCS system, as a large vertical column of air (formerly mostly warm and rapidly rising) has been cooled, then loses its input warm driving energy (for many reasons, like loss of day heating, but sometimes these MCS's thrive at night), resulting in it falling back to earth and fanning out at surface level on a "meso"scale region.

Can't explain such a 15-20mb pressure drop though, would expect a baro spike with colder air. A mini warm-core low riding atop a cold surface wedge?

We just had another MCS move through here today, as I read this thread, I was watching it approach my boat on the NOAA radar (it was intensifying) and a tornado had formed just 15-20 miles West and was closing on the marina area, yikes. It appears to have eased now before getting there, whew. NWS Corpus Christi TX
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Old 26-05-2014, 17:09   #19
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Re: Bizarre Weather Phenomenon

Does sound like an occluded front given that there was a prediction of it. Not sure if a white squall is so predictable, unless it is essentially a variation on that sort of weather phenomena.
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Old 26-05-2014, 17:09   #20
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Re: Bizarre Weather Phenomenon

If that squally thing can happen on inland waters.... It happened to me in Kupio in Finland in 1992 on a Lake......... lasted 5 or 10 minutes and was gone. winter time. I just thought it was funneled wind but it sure looked like that.
scared witless.
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Old 26-05-2014, 17:10   #21
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Re: Bizarre Weather Phenomenon

The question is, can we anticipate it from a forecast? What is the cause? Is the occlusion related to it?

I only really associate sudden squalls with intense CB activity, either isolated or in a full squall line. This 'white squall' business sounds scary!

The sudden, temporary drop in pressure I suppose is explained by the passing of the occlusion, and perhaps therefore the drop in temperature by a cold occlusion. The squall could be a rapid undercutting of the leading cold air mass by a much colder air mass behind it. So perhaps... watch out for an occluded front with much lower temperatures behind than in front of it?

Can anyone improve on my appalling amateur meteorology?
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Old 26-05-2014, 17:14   #22
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Re: Bizarre Weather Phenomenon

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Originally Posted by DoubleWhisky View Post
It can be associated with incoming clouds also, but not necessarily

Happens here more often inland than on sea, in the matter of fact.
But all those videos look CB related, the rapid darkening and the sudden rain. This isn't that.
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Old 26-05-2014, 17:25   #23
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Re: Bizarre Weather Phenomenon

Quote:
Originally Posted by europaflyer View Post
But all those videos look CB related, the rapid darkening and the sudden rain. This isn't that.

It can be darkening and the sudden rain, it can be not. I just digged these videos in several minutes.
I was three times caught in this on the lakes and happily survived all three. Once with the extreme rainfall, once with sudden hailstorm and once with clear blue sky.

We call it "biały szkwał" (white squall is not perfect translation, may be the white burst would be better) because on the water You see first a white wall of foam/water raised from the surface of the lake/sea.
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Old 26-05-2014, 17:32   #24
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Re: Bizarre Weather Phenomenon

Quote:
Originally Posted by europaflyer View Post
The question is, can we anticipate it from a forecast? What is the cause? Is the occlusion related to it?

I only really associate sudden squalls with intense CB activity, either isolated or in a full squall line. This 'white squall' business sounds scary!

The sudden, temporary drop in pressure I suppose is explained by the passing of the occlusion, and perhaps therefore the drop in temperature by a cold occlusion. The squall could be a rapid undercutting of the leading cold air mass by a much colder air mass behind it. So perhaps... watch out for an occluded front with much lower temperatures behind than in front of it?

Can anyone improve on my appalling amateur meteorology?
Only I can tell this is in Poland always associated with the moment when Atlantic weather system meet over our heads with the continental weather system coming from over the Russia. And the warning is often very late, so it is probably difficult to predict. Happily it happens rarely - once, twice a year.
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Old 26-05-2014, 17:35   #25
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Re: Bizarre Weather Phenomenon

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Originally Posted by DoubleWhisky View Post
It can be darkening and the sudden rain, it can be not. I just digged these videos in several minutes.
I was three times caught in this on the lakes and happily survived all three. Once with the extreme rainfall, once with sudden hailstorm and once with clear blue sky.

We call it "biały szkwał" (white squall is not perfect translation, may be the white burst would be better) because on the water You see first a white wall of foam/water raised from the surface of the lake/sea.
Different phenomena then? Black squall I know, white squall is new. Extreme rainfall and sudden hailstorm is what I would associate with intense CB activity, and the squall in that case would be more of a classic microbust. What we seem to be talking about here is a squall not necessarily related to intense convection.

https://en.wikipedia.org/wiki/White_squall

Not very helpful unfortunately, googling further impeded by a film called 'white squall'.
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Old 26-05-2014, 17:48   #26
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Re: Bizarre Weather Phenomenon

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Originally Posted by europaflyer View Post
Different phenomena then?
I really do not know. What we care about here is to see the wind a lot under the forecast. Most disturbing is, when the forecast is for really strong wind, and in reality there is no, or almost no wind. When it finally arrive, it is stronger, when You longer waited for it. And it is always wet all over - clouds or not. You do not need a rain, enough water is taken into the air from the surface to reduce the visbility a lot. I'm not sure if there was much rainfall on the videos, may be not at all.
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Old 26-05-2014, 17:52   #27
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Re: Bizarre Weather Phenomenon

One more thing - the patch of the burst is often narrow, even very narrow.
Sometime several kilometers, sometime several hundred meters.
I watched once the wall of water passing my boat by two or three hundred meters, and putting the boats flat. I was in about Force 4 - 5 at the moment.
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Old 26-05-2014, 18:16   #28
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Re: Bizarre Weather Phenomenon

Let me let NOAA explain what these phenomenon are (most likely), an outflow boundary, downburst, micro-burst, white squall, shear line; they differ mostly in scale and can do significant damage (micro-bursts take down aircraft):
(a NOAA search on "outflow boundary")-- outflow boundary - NOAA.gov Search Results
.

Quote first link, have a look at others:
"
Outflow Boundary A storm-scale or mesoscale boundary separating thunderstorm-cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature. Outflow boundaries may persist for 24 hours or more after the thunderstorms that generated them dissipate, and may travel hundreds of miles from their area of origin.

New thunderstorms often develop along outflow boundaries, especially near the point of intersection with another boundary (cold front, dry line, another outflow boundary, etc.; see triple point)."

We had one here at home 5-6 years ago. A clear calm sky, no sign of trouble.
A dying MCS 1-200 miles West, on the edge of the Mexican Sierra Madre's, caused a West wind line (dry squall) to rapidly built to over 100mph in minutes, and did tremendous straight line damage all over the county. Utility poles down and bent over at 45 degrees, buildings destroyed, etc.
My very solid house shook like I've never experienced before (I live on a fairly exposed ridgeline).
I later found lead roof flashings on the West side peeled back from the roof tiles (the flashings are aprx 1/4"-3/8" thick, 12-16" wide, feet/yards long pure lead, partially under tiles or boards, the exposed edge peeled up and over.
My open 'shed' (placed E-W, 20' x 20', 2" square steel tubing, metal roof panels, w/ground anchors) was neatly lifted up and 'flown' 300-400 yards due East after 5 minutes of extreme up and down bucking gyrations. Disintegrating as it went along at 'flight level 20 feet' (I was watching it, couldn't do a thing, the scream of tearing metal was awesome). The two vehicles it sheltered were untouched by the liftoff.
The whole thing lasted about thirty minutes, I thought my house might get it but there wasn't too much damage to it.
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Old 26-05-2014, 23:11   #29
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Re: Bizarre Weather Phenomenon

If you would make the gods laugh, tell them your plans.
If you would make the weather gods laugh, predict their behavior.
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Old 27-05-2014, 04:15   #30
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Re: Bizarre Weather Phenomenon

Very interesting and useful discussion.

It has moved on a lot from my own particular experience (which is natural), but FWIW, here are more details about what happened to me yesterday:

1. It was not a microburst -- it influenced the sea as far as I could see, and I think it was a large-scale phenomenon.

2. It was not unpredicted -- you can actually see it in one of the Passageweather GFS grib files -- F7 or F8 on one side of a hard line, and F0 or F1 on the other. Bizarre.

3. It was not a "white squall" of the violence we read about -- I don't think I saw 40 knots, at least not for long. It was not actually dangerous; there were no walls of water. It was just very strange and very frightening, coming with such suddenness after a dead calm.

4. There were clouds involved, but no rain. We saw some really strange, really low clouds, which looked like they were just a couple hundred meters above the see, flying across.

5. Huge drop in temperature and pressure. The pressure drop was temporary; temperature not. It is now 9 degrees C; yesterday before this happened it was 20+.

6. It lasted probably 30 - 40 minutes, after which it did not become calm again. Rather, blustery and gusty, 10 knots of wind with 20 knot gusts. In fact even now that is what my wind graph says -- average 10 knots with gusts to 21 during the last hour as I write this.
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