Author Topic: June 2007 East Coast Lows compared to 1950  (Read 4737 times)

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Offline Michael Bath

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June 2007 East Coast Lows compared to 1950
« on: 05 July 2007, 02:10:28 AM »
Anyone care to explain or speculate why June 2007 saw a return to a dominance by East Coast Lows in the weather patterns ?  What overall synoptic features were in place to assist in their formation and what changed so abruptly at the end of May.

The main events:

06 to 10 June
13 to 17 June
23 to 24 June
25 to 29 June

June MSL charts

Michael
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Offline David C

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RE: June 2007 East Coast Lows compared to 1950
« Reply #1 on: 05 July 2007, 04:15:52 AM »
It might be good to look at 500 hPa charts too Michael, as I suspect one of the main factors is that we have seen a prolonged upper level pattern which is favourable for surface cyclogenesis -- this is in contrast to previous years in recent times. Another factor to look at which does change from year to year, would be the temperature gradient associated with the ocean current off the east coast.
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Offline Michael Bath

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RE: June 2007 East Coast Lows compared to 1950
« Reply #2 on: 05 July 2007, 08:24:07 AM »
Yes - plenty of upper cold pools and troughs:

June 500hPa charts

Moisture availability seems different this year. There were several cold pools last year after summer but most failed to produce much other than offshore thunderstorms.

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Offline Jimmy Deguara

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Re: June 2007 East Coast Lows compared to 1950
« Reply #3 on: 12 July 2007, 02:16:51 AM »
Michael,

I know it may be some sort of coincidence but I am wandering why 1950 also saw 4 east coast lows in the same month of June. It is the reason why June can sometimes be seen as a mini peak in the monthly average rainfall graphs. I guess given sufficient moisture with ocean tempteratures relatively warm compared to the impending cooler tempatures aloft, once the upper levels were supportive, we had the makings of an incredible month. Apparently there was a blocking high as well - can anyone confirm this? Perhaps a synoptic chart animation for the whole month could help. I will ask Michael Scollay to assist given he did cover a lot of this in the last Weatherwatch AMOS meeting.

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Re: June 2007 East Coast Lows compared to 1950
« Reply #4 on: 12 July 2007, 02:55:46 PM »
Hi MichaelB,

I have animations of Satpics, MSLP, SSTs and selective radar of these events that are probably too big to upload here. In a nutshell though, La Nina created lifting air-masses in a persistent manner right along our East Coast longitudes. These are easily seen by the Satpic animations. This created a persistent low pressure region that drifted west, then east and so on, that when combined with the cold pools from the south over warm water, set off these ECLs in a sequence. It's the persistence of these features that is of great interest, since that is unrecorded in ECL history.

The highs look like the victims in this sequence as it was the low-pressure regions that dominated with highs flanking adjacent to this feature. They (the highs) are sitting 4 to 6 degrees further north this year but I think this is more a feature of the polar waves combined with cold-SST-pools in the Bight supporting their positioning.

I'm over-simplifying these events since animations do that in one's brain. It appeared obvious from the patterns of air-flow that this sequence of ECLs was inevitable. It also appears that the Earth's over-warming balancing act creates these persistent extremes. We might need to rewrite the texts that describe Hadley Cells and the like since there seems to be other mysterious factors at play.

Finally, a little discussion about the models, in particular GFS. Last year, GFS could hardly get a prediction in June/July correct 3 days out. This year, GFS nailed all ECL events pretty-well, sometimes 6 days out. So GFS modellers appear to understand a warming planet's behavior better! At least in the last 6 weeks or so:-)

Cheers,
Michael Scollay
« Last Edit: 14 July 2007, 10:12:55 AM by Jimmy Deguara »

Offline Michael Bath

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Re: June 2007 East Coast Lows compared to 1950
« Reply #5 on: 14 July 2007, 09:00:17 AM »
Hi MichaelS,

I've probably got the same satpics and radar here, and yes they are a too large to upload. Some of those loops are already in the ECL threads in the other section of the forum.

I notice you said: "La Nina created lifting air-masses in a persistent manner right along our East Coast longitudes" 

This is first reference I've seen indicating La Nina as actually happening, rather then being a forecast of things to come. Also, why and what was the sudden change since May - which was my original question. The thread name was changed to include June 1950 but that was not what I originally wanted to know.

I agree that the models have been very good at forecasting these events many days out.


MB
Location: Mcleans Ridges, NSW Northern Rivers
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