Why do we get bigger storms at night?

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Postby Fu Manchu » Mon Jun 09, 2008 8:55 pm

on yesterdays weather map there was a front marked, a trough marked and something maybe I should know but ? It was a front with a broken line seperated by crosses? was this a stalled front? A developing front from a trough?

also found this...
Skew-T Log-P diagrams
http://waweathergroup.com/forum/viewtopic.php?t=124
Last edited by Fu Manchu on Tue Jun 17, 2008 9:09 pm, edited 1 time in total.

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Postby Wundo » Thu Jun 12, 2008 4:29 pm

Hi,
I didn't see the graphic but it certainly sounds like a stationary front.

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Postby Wundo » Thu Jun 12, 2008 4:45 pm

RE supercell storms, Bandit was mostly correct though deep layer shear is as important as low level shear in causing an updraft to spin (low level shear is very important in tornado formation). it is also important that the winds increase with height as this too aids rotation. Ideally the strongest winds are at anvil level (a jetstreak) which clears the anvil debris and allows the updraft to be sustained, rather than just pulses. (picture what happens to smoke when u cap a chimney)
Supercell thunderstorms also require lots of CAPE (convective available potential energy) and it helps to have CIN (convective inhibition) initially so the storms don't chew through the CAPE early in the day and get a chance to explode into supercells late afternoon.
Another main difference is that hail from your average garden variety thundery won't potentially cause brain damage if it hits you!
Hope this helps, cheers
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Postby ozzie » Mon Jun 16, 2008 7:21 pm

is there a free weather uploading site from your weather station

I could only find this:
http://www.weather-display.com/features.php

but it costs money, is there one like this that costs nothing?

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Postby hotandstormy2006 » Tue Jun 17, 2008 4:27 am

how do showers develop at night when there isnt any heating from the sun

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Postby Wundo » Sat Jun 28, 2008 5:46 pm

hotandstormy2006 wrote:how do showers develop at night when there isnt any heating from the sun


There are a few mechanisms in place that allow showers to form at night. Erosion of a daytime cap by strengthening upper level winds or an approaching trough. Or some other means of forcing such as air mass boundaries colliding (fronts) or an air mass being forced to rise over higher ground (orographic lifting/forcing) can lead to showers.

Also close to the coast the water at night retains more heat than the atmosphere so often it releases heat and showers form over the ocean at night as they would in the day from normal solar heating, it's known as the diurnal cycle. It's also why we so often get the strongest storms late afternoon/evening when the earth has had the chance to heat all day.

Diagrams are helpful in met, unfortunately I can't draw them here for you.
Hope I helped a bit! Cheers :)
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Postby Vinny » Sun Jun 29, 2008 9:04 pm

I know what a high in the bight at this time of the year means... but what does a 1030hp high to the west of perth mean.?

I saw that situation for next sunday for perth.

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Postby Wundo » Sun Jun 29, 2008 10:04 pm

vinny06 wrote:I know what a high in the bight at this time of the year means... but what does a 1030hp high to the west of perth mean.?

I saw that situation for next sunday for perth.


Hi Vinny, I've been trying to work out just what your question is exactly?
Umm, are u asking what '1030hp high to the west of perth' means OR
are u asking what sort of weather we'll have?
the first part - High Pressure System with strength of 1030 hectopascals will have a centre located west of perth is what it means.. Possibly the same as having a 1030 High in the Bight. If u are not familiar with 'hectopascals' check out

http://en.wikipedia.org/wiki/Pascal_(unit)

and u said u knew what a High in the bight means weatherwise so hope I've helped man.
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what is this ???, is this a fog rainbow

Postby lightning wog » Sat Jul 26, 2008 7:14 pm


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Postby Vinny » Tue Jul 29, 2008 9:27 pm

This may sound like a "dumb question"... but here goes ...

How come Perth receives more rainfall annually , than Adelaide Melbourne and Hobart etc...?

I thought they (hobart etc)were further south (like nz ) and therefore would be closer to the cold fronts from the southern ocean etc..

or is it nothing to do with that.

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Postby ozzie » Tue Jul 29, 2008 9:48 pm

i think it is because of the amount of strong fronts we get, also i think the cold fronts weaken before they hit adelaide and melbourne, i am not sure though!

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Postby davo » Tue Jul 29, 2008 11:22 pm

I'd say for Melbourne and Adelaide the NW winds which get lifted and provide most of the moisture for a frontal band dry out alot as they have to pass over land (as opposed to Perth where they come from thousands of km of Indian Ocean and a bit of extra boost from the warm Leeuwin current), that's why they do better precipitation-wise from the big southerly bursts.

Hobart is on the east coast of Tassie so suffers from the rain shadow effect (in regard to fronts) where the west side gets most of the rain due to orographic lifting (air forced to rise over land/mountains causing it to cool therefore it's moisture condenses and rains out), leaving very little for the Hobartians...oops, hope I can call them that!

Hope that is not too confusing!

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Postby Super Choc Bear » Wed Jul 30, 2008 3:46 pm

this one has always stumped me...why do places like bickley and all those on the hills get more rain? Is it because of a higher altitude?

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Postby Tim S » Wed Jul 30, 2008 3:55 pm

The answer is Oragraphic Lifting SCB, as the moist air passes over the ranges it is forced upwards causing the airmass to cool and consequently condense beyond the air's dewpoint meaning that excess moisture falls out of the cloud as rain.

Better explanation here: http://en.wikipedia.org/wiki/Orographic_lift
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Postby Vinny » Wed Jul 30, 2008 4:05 pm

Super Choc Bear wrote:this one has always stumped me...why do places like bickley and all those on the hills get more rain? Is it because of a higher altitude?


lol... i was just gonna post the same question and you beat me to it !

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Postby Vinny » Wed Jul 30, 2008 4:07 pm

ok then..regarding bickley etc...

how come in winter the max temp is usually 4 or more degrees less than perth.

In short... why is it colder there during the day there in winter?

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Postby peterperthh » Wed Jul 30, 2008 4:13 pm

I think in most orographic lifting in the world the zone of high rainfall
declines because of the rain shadow effect (when the air warms and dries
on the other side of the mountain or hill) but the in perth the darling hills
are actually an escarpment which means they go up and dont go back
down on the other side.

So I presume thats why a decent area in the 'hills' gets higher rainfall.
The point where rainfall starts declining much further inland in our case is
due to the clouds basically raining themselves out and not having a good moisture feed anymore.

The following diagram shows the orographic effect on rainfall:


Image

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Postby peterperthh » Wed Jul 30, 2008 4:15 pm

vinny06 wrote:ok then..regarding bickley etc...

how come in winter the max temp is usually 4 or more degrees less than perth.

In short... why is it colder there during the day there in winter?


1) its higher altitude so the air is generally more cold
2) because the previously explained extra clouds and rainfall there allow
less heating from the sun during the day

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Postby Vinny » Wed Jul 30, 2008 4:20 pm

so if the hills get more rainfall then, has the hills rainfall been declining much since the 1970's.

or is it much the same.?

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Postby peterperthh » Wed Jul 30, 2008 4:33 pm

Do you really think that climate change can effect perth but not the hills just down the road from it?
If we get less, the hills get less, If we get more the hills get more.
They are the same weather systems that go over us...

And on the idea that rainfall has slowly declined since 1970, the IOCI
(indian ocean climate initiative) found that it was basically a sharp drop of
rainfall in about 1970 and its stayed there since. (thanks Fu Manchu for
the link http://www.ioci.org.au/publications/pdf ... eries2.pdf )
which they found was basically the same time that there was a shift in
global atmospheric circulation.

Which I find interesting so I might go and find out what that change was and how they knew it occured..

Perhaps pain yourself to do some research now and then yourself vinny

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