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J shaped cold front

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Louise2
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J shaped cold front

Post by Louise2 »

Hi everyone,
I'm new to here (and basic meteorology). I'll have a couple of dorky questions every now and then .... here goes

As Subject topic above - what are the affects of this shaped cold front as opposed to the usual gradual curve cold front?
I THINK I may have read somewhere that surfers like seeing this cold front with the hook at the bottom.

Also, does a 'DEEP' low pressure system mean that it has really low pressure in the centre?
or
is deeper in the atmosphere than usual? (that probably doesn't make sense? They are all at surface?
or
has the isobars close together so having strong wind?

I don't know what 'DEEP' refers too.

Don't say I didn't warn you! :)
Thanks, Louise
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Rivergirl
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Re: J shaped cold front

Post by Rivergirl »

Hi Louise, welcome to the AWF. I think I know less than you so I will leave it to the experts to answer your queries :)
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Geoff
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Re: J shaped cold front

Post by Geoff »

Welcome Louise, lets see if I can explain clearly enough to help you. Look at this current chart below from the Bureau of Meteorology...
Synoptic Chart.png
Synoptic Chart.png (61.63 KiB) Viewed 13763 times
The cold front crossing the Bight (blue line with blue triangles) has developed a bit of a "J" shape, it is simply being wrapped around the centre of the Low by the clockwise circulating winds near the centre.
This Low pressure system has a central atmospheric pressure of 984 hPa (Hectopascals) and is the "deepest" one on the chart, which simply means it has the lowest central pressure, the lower the pressure the deeper the low.
I hope this helps you, maybe some others on here would like to add more. Feel free to pick our brains on here, we're all here to learn and help! :D
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Louise2
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Re: J shaped cold front

Post by Louise2 »

Thankyou so much Geoff,
I've been feeling 'off' with a bit of a flu virus and haven't been back until now.
So if a low is deepening the air pressure is decreasing ... does that make the clockwise winds stronger (because air would be rushing in faster?)
I'll have to keep an eye out if it is the lower lows have the J shape.
Louise
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Geoff
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Re: J shaped cold front

Post by Geoff »

Louise2 wrote:So if a low is deepening the air pressure is decreasing ... does that make the clockwise winds stronger (because air would be rushing in faster?)
Yes that's right, in almost all cases the lower (deeper) the central pressure the stronger the winds circulating around it will be. This is shown on the weather maps as very tightly packed lines (isobars) around the deep low.
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Louise2
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Re: J shaped cold front

Post by Louise2 »

Thanks again Geoff,
I'm slowly getting there:)
Here's another one ...

The wind of the lows circulate clockwise (in the southern hemisphere).
Where there is a cold front and the wind is heading in the direction shown by the arrows, usually a westerly wind, is it because the frontal wind is strong enough to dampen the clockwise wind direction. Like, if you were south of the centre of the low and in the easterly wind path of the clockwise swirl, you'd still get a westerly wind?

What about when the front passes (still in the same hypothetical position south of the centre of the low), would you then get easterly wind?

Can you understand what I'm talking about? If I have it wrong it's probably confusing to you.

Louise
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Geoff
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Re: J shaped cold front

Post by Geoff »

I think I get your drift. Have a look at this diagram...
winds around an australian low pressure system - Google Search 2013-08-05 17-12-22.png
winds around an australian low pressure system - Google Search 2013-08-05 17-12-22.png (23.94 KiB) Viewed 13742 times
The low pressure system in the Tasman Sea has a lovely "J" shaped cold front. The winds above the low's centre will be blowing from the north ahead of the front and from the west behind it (roughly). Below the low's centre the winds will be easterly (roughly) and the cold front has been bent around the low by these easterly winds. At the same time the whole system will be (usually) moving from west to east.
In the actual centre or "eye" of the low the winds can be from any direction, and are usually termed "variable".
Let me know if I'm on the wrong track!
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Louise2
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Re: J shaped cold front

Post by Louise2 »

That's so good,

It's near to what I thought happened but someone else told me differently ... I was thoroughly confused.
I'll stick to asking here from now on. I'm a bit tired to think at the moment to ask you more.
I'll be baaaaack. I plan to finish a (very basic) meteorology assignment tomorrow.

We had to do it on at least two weather systems that effect the area where we are (South Coast NSW)
I'm only doing two, that's enough of a headache.

I chose ECL's and Cold Fronts, to try and work out the difference between them as it was bugging me.
Any enlightenment would be appreciated :)

cheers
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Louise2
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Re: J shaped cold front

Post by Louise2 »

P.S.

Geoff, where did you get that map from (that includes New Zealand)?
I only know of B.O.M. website and can't see any like that.
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Re: J shaped cold front

Post by Geoff »

For the weather chart with NZ in it just go to the BOM homepage http://www.bom.gov.au/index.php?ref=hdr" onclick="window.open(this.href);return false; and click on the box "Weather Maps", in there you will find "Mean Sea Level Pressure (MSLP) map" - that is the one I used. The other pictures were just found on Google Images. I reccommend you use Google to search for much of the information you need - it's all out there waiting for you, good luck! :D
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Louise2
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Re: J shaped cold front

Post by Louise2 »

Hi Geoff,

Thanks for that Google Images idea, I've had a look, cool!

I've been all over B.O.M. weather maps and their website. They have lots of info to discover.

Your patient help has been great.

Louise

P.S. Doing my cold front screen capture images today from B.O.M. of Satellite, MSLP etc before the cold front hits and lining them up with observations
and forecasts from before and after. (didn't get to it yesterday, NO other chores today please).
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