Topic: Is the jet done and dusted for the remainder of 2007?

[David C]

Focusing on eastern Australia:

What I am seeing now with respect to the upper level pattern reminds me of one of the late 90's / early '00 chase season's, except (and very importantly) we're seeing better moisture than was the case then. I remember plotting AVN back in the day and looking at generous CAPE and 5-knot 500 winds day-after-day. Atm, the jet stream is way down south and I wonder whether we might be stuck in this pattern until the 'second season' next year - certainly GFS out to 14 days is trending that way! Compare this with, for example, 2004/2005, a year during where we seemed to get numerous upper level waves coming through and multiple severe storm / supercell events. Each year is proving to be very different and it's an ongoing education for chasers really.

While it does not look like this will be a great period for classic supercells, as long as the moisture is getting in, things will happen, as was the case over the last week. Interesting times ahead I think with the potential for an ongoing unsettled period............we'll see!

Any thoughts?
 

[Jimmy Deguara]

David,

Obviously this is a very interesting discussion as it seems the jet has evaded us. Though would you say the late 1990's was anywhere near in comparison to these conditions? You are correct far more moisture and very much atypical of a La Nina pattern. I would have thought the year you were refering to was the 1997 to 1998 summer. I would look more into a similar year where La Nina was in place during the November period - 1988? Heatwaves during October and then November fired with rainfall and storms. Of course we had a system that lasted a week that year and was obviously more ideal with supercell a plenty.

There is a difference once again though - with the real intense La Nina pattern setting in during the late summer to autumn that year. Obviously what we have hear is a closed tiled system that is breaking down. Will there be a few pulse as a result of differential heating or is this set to go all the way to South Australia and possibly Western Australia?

Time will tell. As Rune always said, the good thing about the weather is that you simply never know - anticipation.

Regards,

Jimmy Deguara

[Michael Bath]

I can't comment on previous seasons as I just can't recall the setups well enough - too old I guess !

One question though - can someone please explain what a 'closed tiled system' is ?

regards, Michael

[Jimmy Deguara]

Hi Michael,

Perhaps I incorrectly used the term closed but it was a hint of what a tiled system really is. It is completely cut off from other circulations but there is an upper level low 'tiled' virtually vertically rather than tilted forward or lagging so to speak.

What a moving 'tilted' low pressure system allows is for destabilsation to occur as the surface heats and cold air aloft overrides this warmth. It is a way the cap can be broken almost certainly - sometimes explosively as we see often in the US situations. In the case of the above mention 'tiled' low pressure system, the shear is mismatched and the heating takes place away from the cooling. The temperatures are 700hPa for instance were too low, the cap weak and this allowed for numerous storms to erupt.

I hope this helps differentiate and define the less ideal and more ideal cases.

Regards,

Jimmy Deguara

[David C]

Yes the uncertainty for us humans is one of the great things about the global weather system. Just looking at the latest runs, very good mid-level flow becomes established as early as next week.