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Old 24-10-2012, 11:38   #1
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Clear Sky Squalls

Just wondering what other folks' experiences with these are. Had another one a few days ago. I read Richard Henry Dana's book and he commented that the scariest weather for him was off the Southern California coast where cloudless squalls would blow through with no warning, taking 10 knots to 30 for an hour then residing. Nothing to foretell it, no real rhyme or reason.

Do folks see these everywhere? I'm guessing they might be low pressure troughs moving through. Not enough of a frontal system for the clouds but still tons of wind. And can come from any direction, not necessarily backing like in a low pressure system.
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Old 24-10-2012, 11:47   #2
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Re: clear sky squalls

Was delivering a Santa Cruz 40 from Marina Del Rey to SF 2 weeks ago. Crystal clear day. We were off Channel Islands harbor about noon, and for no apparent reason the winds went from 10-12 kts to 25++ sustained for about 2 hours. By 1400 hrs all was quiet again. Wierd indeed!
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Old 24-10-2012, 11:51   #3
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Re: clear sky squalls

I was on a trip from Tampa to Destin, 30 mises off the coast of Appalaciola, clear skies, about 12 kn of wind all day, suddenly, no clousds, severe winds, steep choppy seas, maybe 4 to 6 ft waves, white caps, for about 45 minutes. tore my sails and had to turn in to port, travelled the icw on to destinn. could not figure it out. nothing on my radar to indicate this. glad it did not happen at night.
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Old 24-10-2012, 12:00   #4
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Re: clear sky squalls

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Originally Posted by Captain Jeffry View Post
Was delivering a Santa Cruz 40 from Marina Del Rey to SF 2 weeks ago. Crystal clear day. We were off Channel Islands harbor about noon, and for no apparent reason the winds went from 10-12 kts to 25++ sustained for about 2 hours. By 1400 hrs all was quiet again. Wierd indeed!
That sounds like a katabatic wind to me, cold air tumbling down the Channel Islands mountains. Do I guess right - the wind came from the direction of the land?

The Meltemi in the Aegean blows out of a clear sky. A creepy, scalding hot, dry wind, which often blows at more than 40 knots.
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Old 24-10-2012, 12:10   #5
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Re: clear sky squalls

Had something like that on the Chesapeake a few years back. Coming out of the Wye river on a beautiful autumn day , winds maybe 10 kts. Then, with the only warning the sudden white caps on the eastern bay, we were hit by a 180 degree winds shift and winds 25-30 kts. Fortunately we had only the main up and no damage was done. The wind shift put the wind from the starboard bow to the port quarter. In about a hour (seemed longer) the wind died down and shifted back.
Was really scary when it happened and really uncomfortable,thebay is shallow and a 30kt wind stirs up a nasty chop.
Also , it was a white squall that did in the Pride of Baltimore back in the mid-80s in the Caribbean. The Pride was replica of the 182 Baltimore Clippers about 100 feet on deck. Crew who were rescued (3 were lost) said that the squall came out of a clear blue sky with winds up to 80 kts laid the ship over so it filled with water through the open companionway and sank.
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Old 24-10-2012, 12:16   #6
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Re: clear sky squalls

Wind actually did not change direction much. Did clock a bit: Before about 265 mag, during 280 mag. Went back to 265 after and stayed thru the night until we got to Conception where it died completely! Sweet delivery!

ps- We were about 6nm off Channel Islands harbor.
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Old 24-10-2012, 12:24   #7
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Re: clear sky squalls

I go with Dockheads analysis.

I've experienced katabatic winds in the Aegean (Cyclades). Wind went from 12kts to 40+. quite an interesting experience with an inexperioenced crew. nearly flattened us but back in control quickly. Lasted about an 45 mins. Cold air displaced from high ground comes spilling down - you don't know it's there til it hits you.
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Old 24-10-2012, 13:33   #8
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I think Dockhead is onto something.

The only substantial katabatic wind in SoCal are the Santa Anas.

They can also form sudden squall like gusts near the shore as they are forming and dissipating and then coastal winds are trying to assert themselves. It can even happen during the height of a given Santa Ana.

If it is as the high is forming inland and the air is just starting to shift to that classic dry off shore breeze you can still have very calm to no wind conditons off the coast with sudden gusts of wind up to 30knots or more, you can even have stiff onshore conditions in the 15knot range with the wind suddenly dropping and then a fierce sustained gust from shore.

It is relatively uncommon but can be unnerving, especially as the humidity level can noticeably change in an instant as well.
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Old 24-10-2012, 13:50   #9
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Re: clear sky squalls

Sounds like a breeze acceleration zone - the overall wind pattern locally accelerated by air movements caused by uneven heating of land / water masses. May change from day to day but once you see the pattern, you are on the safe side.

Experienced similar things inshore but never in the open water.

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Old 24-10-2012, 18:03   #10
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Re: clear sky squalls

Would this be what you are experiencing?
Death From Clear Blue Sky Extreme Non-Convective High Winds | Earthzine
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Old 24-10-2012, 18:16   #11
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Re: clear sky squalls

rebel heart--you will find these winds all down the baja coast and also down mexico.
some have names--the chubasco and papagayos. at the tehuantepec venturi, there is a notorious wind coming thru occasionally.
they happen day and night when they come--our 60 kt wind north of cabo was 0400. wicked and fun sailing. be aware. i reefed early--out of necessity due to tears and tatters and clew hardware unstitching .. but we still hit 8.4 kts...was fun!!

deepfrz--some could be that--san diego is in correct geographical zone for those--there are also the mountains down baja and along mexico--sierra madres--to influence winds and cause winds of strange origin and description.
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Old 24-10-2012, 18:20   #12
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Re: clear sky squalls

Quote:
Originally Posted by skipperr100 View Post
I was on a trip from Tampa to Destin, 30 mises off the coast of Appalaciola, clear skies, about 12 kn of wind all day, suddenly, no clousds, severe winds, steep choppy seas, maybe 4 to 6 ft waves, white caps, for about 45 minutes. tore my sails and had to turn in to port, travelled the icw on to destinn. could not figure it out. nothing on my radar to indicate this. glad it did not happen at night.
Good it did not happen to you as you were getting close to the Destin inlet....one of the most treacherous inlets I've ever seen especially with a strong onshore wind!
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Old 24-10-2012, 18:22   #13
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Re: clear sky squalls

I have experienced such winds at times, but they have been explainable by temperature differences and/or altitude differences, like the katabatic winds. Down in the San Blas Islands off of Panama we were hit several times by what they call a chocosana wind. The first warning was a sudden decrease in temperature followed by a rapid shift in the wind coming off the high mountains. The first one that hit us was up to 56 knots and came in so fast from the opposite direction to the prevailing wind that our boat didn't really rotate at anchor--we sailed downwind on the chocosana until we reached the end of the anchor rode and flipped around with a strong jerk. Out of 10 boats in the anchorage 8 dragged, and one went up on the reef. I've seen a similar thing, though only up to gale force when anchored in Buzzards Bay on a summer night. Around midnight, or a bit after, there was a sudden shift of the wind to the north, coming off the hot mainland, and a rapid increase as hot air from the land poured offshore--with the weather radio still reporting light onshore breezes throughout. Sometimes this hot middle of the night blast lasts for an hour or so with a clear starry sky, and then peters out. Catches a lot of boaters anchored on short scope by surprise.
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Old 24-10-2012, 18:35   #14
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Re: clear sky squalls

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Originally Posted by rebel heart View Post
Just wondering what other folks' experiences with these are. Had another one a few days ago. I read Richard Henry Dana's book and he commented that the scariest weather for him was off the Southern California coast where cloudless squalls would blow through with no warning, taking 10 knots to 30 for an hour then residing. Nothing to foretell it, no real rhyme or reason.

Do folks see these everywhere? I'm guessing they might be low pressure troughs moving through. Not enough of a frontal system for the clouds but still tons of wind. And can come from any direction, not necessarily backing like in a low pressure system.

I don't recall what the overall weather pattern was, but we had this in suburban St. Louis once, out of nowhere, a clear sky, nice day, not extremely hot, not winter ... and 70 mph winds.

There are no mountains in St. Louis, either, so that doesn't explain it.
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Old 24-10-2012, 18:37   #15
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Re: clear sky squalls

Some of the reasons that Southern California is the soaring capital of the world is large unstable airmasses in summer - due to a giant desert and convective updrafts, and giant mountains when combined with frontal convergence creates huge topographical lift in the winter.

This instability bleeds though the passes and creates a lot of regional wind and weather phenomena.
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