A new Autumn Pattern in Australia??

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A new Autumn Pattern in Australia??

Post  Karl Lijnders on Tue May 19, 2009 4:57 pm

Is it changing literally before our eyes? Am I finding that May has become really really dry now in SE AUS and wet in areas where it should be drying?

I have a feeling that this is now something in concrete. Not suggesting that it will never rain in May in SE Aus but I have that suspicion that now this being a trend over the past few years, it is almost expected.

ECL events have been rather severe as well in the May/June periods over the last decade, but it is normal for this time of year.

Thoughts???
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Re: A new Autumn Pattern in Australia??

Post  droughtbreaker on Tue May 19, 2009 6:55 pm

Ridiculous blocking patterns around this time of year seem to be the culprit. Whatever happened to highs and lows and fronts moving steadily from west to east? It hardly ever happens anymore. We get ridiculously strong highs and lows in blocking pairs continuing for weeks on end. We have had a really cool start to the month and now a ridiculously warm end to it all with almost literally no rain, thanks to the one blocking pattern that hasn't budged all month with the exception of the odd weak system sneaking in. First we are stuck in the southerlies for weeks and now the northerlies for weeks. That's pretty much what is causing the constant heat records we see these days, these blocking patterns allow heat to build up over the continent without any interruption to the pattern and then it gets blasted over us for a week or more in northerlies. That and global warming of course.

The only months where we see good falls these days appears to be around late June-August and November-December. Every other month is a dud. The summer pattern of high domination continues through to early winter, we get affected by the westerlies and significant systems with rain in late winter, by September there is no feed of moisture into the systems because the eastern Indian Ocean is usually anomalously cool and then in late Spring to early Summer it all lines up, moisture and instability and we get more rain. 4 months of rain basically with usually around 100mm each, so we are lucky to get 500mm a year in this new pattern and that's on the ranges, Melbourne CBD is probably lucky to scrape in 300mm by the end of it.

Whilst conceding that this shift to warmer and drier in the far SE of Aus is a permanent one thanks to stronger and slower moving highs, less moisture coming in from the Indian Ocean and the westerlies being forced further polewards with weaker fronts affecting us, I'm still desperately hoping that this is just a particularly bad period and that not every year is like the past couple and 2006. If that's the case our annual average is well on the way to halving.

Shocked

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Re: A new Autumn Pattern in Australia??

Post  Karl Lijnders on Wed May 20, 2009 3:37 pm

Certainly seems that way. But I guess Brisbane was in the same rutt. No rainfall of any substance for a long period. It was probably more accute than this if that is possible with dam levels down to near single figures. Now they are swimming in the rainfall. Could it turn back to some form of old days weather?

It is hard to know whether to place this as a permenant shift!?!
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Re: A new Autumn Pattern in Australia??

Post  hillybilly on Sat May 23, 2009 6:50 pm

An autumn drying trend started in SW Western Australia in the 1970s. It then appeared in the SE in the 1990s and has been dominant since 1996. If you look at Vic we haven't had a well above average autumn since 1989 - 20 years ago. I do remember the 1988/89 summer-autumn - witnessed 4 50mm+ rainday in 5 months and 3 of those were over 70mm. Lots of flash floods...

Autumn used to be very wet in Melbourne's east owing to the warm bay and frequent major lows which would set up cyclonic SW flow. Most of our rain now seems to come from cold outbreaks in autumn which are infrequent and also hit-and-miss.

Would love to see a switch back to the pattens we once had... but a ~40 year trend as seen in SW WA and ~20 year trend in Vic is a long time.

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Re: A new Autumn Pattern in Australia??

Post  hillybilly on Mon Jun 01, 2009 6:14 pm

4th driest May on record for Melbourne with just 10.8mm.

Also worth noting that it's been the 3rd driest start to a year on record for Victoria with just 117.8mm in the first 5 months. The driest start was 1967 with 99.8mm. In Melbourne its the 3rd driest on record (just 3mm ahead of 1967).

Melbourne is a very real chance for having its driest year on record.

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Re: A new Autumn Pattern in Australia??

Post  Karl Lijnders on Thu Jun 04, 2009 9:19 pm

The way it is currently going we are a certainty of receiving that. I have resigned myself to the fact that we will miss out and continue to miss out as long as we have a more Wly flow as opposed to the normal SW shifts behind frontal systems this winter.

It is getting old fast.

Least the sunshine was nice in May Rolling Eyes
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Re: A new Autumn Pattern in Australia??

Post  Walrus on Fri Jun 12, 2009 7:07 pm

Interesting figures seem to show a definite reduction in autumn rainfall in this area. Whether it is sustained or cyclic is the 64 dollar question


Rainfall recorded at RUTHERGLEN (RESEARCH)
Historical monthly rainfall (mm)


Year Mar Apr May Total
1913 100 3 60 163
1914 51 40 55 146
1915 5 12 89 106
1916 9 30 21 60
1917 14 15 66 95
1918 39 38 136 213
1919 17 38 54 109
1920 16 10 15 41
1921 26 39 97 162
1922 0 12 38 50
1923 0 6 51 57
1924 50 55 27 132
1925 15 10 33 58
1926 54 100 81 235
1927 5 1 50 56
1928 119 40 43 202
1929 46 62 25 133
1930 7 37 45 89
1931 112 81 128 321
1932 66 118 7 191
1933 18 15 52 85
1934 21 81 0 102
1935 33 104 10 147
1936 13 52 21 86
1937 29 9 34 72
1938 3 37 15 55
1939 200 162 19 381
1940 0 89 26 115
1941 102 9 2 113
1942 21 23 94 138
1943 8 49 12 69
1944 21 46 64 131
1945 4 9 15 28
1946 69 41 32 142
1947 71 25 17 113
1948 0 28 54 82
1949 73 19 38 130
1950 101 29 50 180
1951 4 62 82 148
1952 39 95 106 240
1953 2 32 71 105
1954 4 43 38 85
1955 63 6 73 142
1956 227 101 118 446
1957 70 20 15 105
1958 33 13 78 124
1959 34 70 21 125
1960 14 42 115 171
1961 54 59 11 124
1962 24 38 80 142
1963 45 17 111 173
1964 9 56 24 89
1965 5 27 47 79
1966 43 12 51 106
1967 32 3 24 59
1968 17 48 122 187
1969 68 88 72 228
1970 88 90 28 206
1971 13 62 47 122
1972 9 25 22 56
1973 72 106 49 227
1974 23 150 135 308
1975 31 17 52 100
1976 13 7 14 34
1977 32 18 72 122
1978 76 44 130 250
1979 8 40 66 114
1980 18 35 26 79
1981 36 6 42 84
1982 74 16 40 130
1983 59 65 117 241
1984 26 27 10 63
1985 44 46 44 134
1986 3 31 65 99
1987 15 54 45 114
1988 40 33 173 246
1989 94 88 98 280
1990 15 66 90 171
1991 10 12 4 26
1992 20 55 66 141
1993 55 3 25 83
1994 28 9 13 50
1995 0 35 93 128
1996 25 24 35 84
1997 37 5 76 118
1998 1 73 5 79
1999 55 26 67 148
2000 58 20 88 166
2001 35 16 15 66
2002 55 18 16 89
2003 5 48 38 91
2004 3 22 32 57
2005 12 5 6 23
2006 17 36 13 66
2007 31 26 79 136
2008 35 13 23 71

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Re: A new Autumn Pattern in Australia??

Post  Luken on Sat Jun 13, 2009 11:51 am

Interesing stats Walrus.

Just looking at them quickley. I calculated total rainfall from 1913, to 1923 was 1202mm (avg 120.1mm)

Then 1998 to 2008 was 992mm (99.2mm avg)

Difference = -210mm

I just picked the first 10 years of the study as a random sample. But looking at the whole list it also seems it was a bit drier than normal. But not a massive difference to what we have had in the last 10 years.

Don't really have a point to it all, just interested.
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Re: A new Autumn Pattern in Australia??

Post  droughtbreaker on Sun Jun 14, 2009 5:44 pm

So many systems these days only affect specific parts of the state, I literally cannot remember the last time the entire state saw good rain from the one system. In the 'good ol' days' of my childhood we used to see widespread rain areas with fronts and lows in late autumn through to spring where the entire Melbourne radar would be filled in with rain echoes. That simply never happens anymore. It is either only SW VIC, or only W VIC or only NE VIC or only central ranges, or only Melbourne, or only eastern Melbourne and the rest of the state misses out.

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Re: A new Autumn Pattern in Australia??

Post  Johnno on Sun Jun 14, 2009 9:51 pm

I think the Mid December low affected the whole state last year but your right Andrew it happens very sparesly these days

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Re: A new Autumn Pattern in Australia??

Post  tizza on Fri Jun 19, 2009 12:11 pm

It's not looking good at all yet again. One thing I've noticed over the years is that the high pressure systems should be starting to drift north by now. Sitting over the mid north coast of NSW and by the end of June into July they should be over sitting over NE/NSW-SE/QLD allowing the cold fronts to do their thing. The highs are still just too far south, stuck in that blocking pattern the resembles summer heatwaves, leaving central Vic to get clipped by a front or nothing at all. The lows either get pushed south or if they cut off, most (not all) go north of the ranges which is just weird. Who knows, maybe Melbourne and it's surrounds, nestled in it's little valley has actually been built on a micro desert climate. It's just something I've been thinking about over the last few years, we really haven't resided in this part of the world for that long. It's just something I wanted to put out there. I loved June weather, cold nights, sunny days, mainly calm with loads of fog, getting us ready for the really horrid windy July/August part of winter. Anyway, nothing new in there except me feeling free to express my thoughts without ridicule, but please debate and teach me!!

Correct me if I'm wrong but when is El Nino usually announced? 1st of July or later? The SOI is not looking good at all but then again we have just had our driest start to the year during a La Nina! I just can't figure it out. One thing I did hear on 774 the other day was that if this doesn't stop, 09/10 fire season is going to make 80/09 look like play school, which is a terrifying thought.
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Re: A new Autumn Pattern in Australia??

Post  droughtbreaker on Sat Jun 20, 2009 3:50 pm

I reckon it is the abundance of cut off lows and destabilising upper levels that are forcing the highs south. The latest EC progs are really ramping up the lows coming through from the west and wants to form a massive area of low pressure originating from, but sheared off from the westerlies. It was hinting at this general pattern on previous runs as well. IMO we will see larger and more widespread falls across the SE from one of these potential systems coming through than just standard frontal and LWT passages as the former systems will stick around for longer and draw unseasonal moisture down from the tropics whereas the LWT brings in colder drier air and ends up benefiting the ranges in the northerlies ahead of the system and mountains and hills east of Melbourne in SW stream, other places miss out.

Good signs I reckon, this is what we used to see in June when we got big falls here, these huge cut off lows and cradled by highs way down south. In July the pattern would break and we would get the highs shifting way north and our regular westerly dominance associated more with mid to late winter. Already in the latest EC prog you can see an attempt of the high pressure ridge to establish north of the area of low pressure which seems to be splitting the subtropical high belt to the south and north generally. In July I reckon we should see the highs shift permanently north (well until mid spring anyway).

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Re: A new Autumn Pattern in Australia??

Post  hillybilly on Sun Jun 21, 2009 5:56 am

Have a good friend who has been studying the drying trend for ~5 years - he's just written an update which is not pretty reading - it is now the worst drought on record interms of dryness and duration. The up-shot is that nearly all the drying can be put down to the simple fact that pressures are on average getting higher across southern Australia. This means that we get more highs/less lows, strong highs and weaker lows. You can see this really clearly in the big increase in the number of highs at http://www.bom.gov.au/cgi-bin/climate/change/trendmaps.cgi?map=high_density&area=aus&season=0112&period=1970

What is really odd with this long drought is that it effects all of southern Australia which gets rainfall from westerlies (only Tasmania seems to be spared a bit). Apart from the Nov-Feb period which seems not to have changed a whole lot, it seems we only get to average rainfall in the other months if we get a freak (or few freak) weather events. The days of shower weather piling on rain for days as happen before this drought seem long gone.

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Re: A new Autumn Pattern in Australia??

Post  droughtbreaker on Sun Jun 21, 2009 12:54 pm

Yep, larger highs, stronger highs and slower moving blocking out advancing cold fronts and low pressure systems to the west. This has been the pattern of the last 12 years and in particular the last 5 years with no signs of anything improving.

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Re: A new Autumn Pattern in Australia??

Post  Anthony Violi on Thu Jul 30, 2009 2:30 pm

Need to bookmark this thread..as i would like to know the cause of the next record rainfall we set in the autumn..

Weather = cycles.

Logic....use it.
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Re: A new Autumn Pattern in Australia??

Post  Karl Lijnders on Thu Jul 30, 2009 4:44 pm

LOL!!! Oh dear, well it needs to cycle a little faster then!!!
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Re: A new Autumn Pattern in Australia??

Post  hillybilly on Thu Jul 30, 2009 5:39 pm

Need to bookmark this thread..as i would like to know the cause of the next record rainfall we set in the autumn.

Last wet autumn for Vic was 1989. We are certainly overdue, but I've given up hoping...

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Re: A new Autumn Pattern in Australia??

Post  Anthony Violi on Thu Jul 30, 2009 5:57 pm

Keep the faith guys..we all thought SE QLD was screwed as well, in 18 months they made up 10 years worth..its only a matter of when. The question is...4 months? 3 years? 27 years?

We all have no idea..
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Re: A new Autumn Pattern in Australia??

Post  hillybilly on Tue Aug 18, 2009 5:46 am

Anthony we haven't had a wet autumn (Tercile 3) in Victoria since 1989. That's 20 years which means we are over due for 6 wet autumns. We may - one day - get a wet autumn (every year I hope...) but that won't change the fact that they have reduced starkly in number. When we get 6 wet autumns then statistically we can claim a return to normal, but 1 wet autumn would indicate nothing.

The research I've seen shows that the autumn drying is a global scale phenomena due to an increase in pressure in the subtropics. This pattern of change first impacts SW WA in the 1970s and spread to Victoria in the 1990s.

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Re: A new Autumn Pattern in Australia??

Post  windyrob on Wed Aug 19, 2009 6:04 am

well I do have an idea (a wacky one) that overcomes some of the possible shortcomings common to both AGW and Solar that would be caused by possible negative feedback and short response times in the oceans. This is not the thread for it but I could start another if people are interested. I would especially like hillbilly's input since i have a physical science background rather than meterological.
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