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Discussion in 'Alpine & Southern' started by TC, Apr 12, 2006.
+29 we should be under water
so wheres the rain????
Today, BOM: http://www.bom.gov.au/climate/enso/#current
"Summary: Pacific remains neutral. Cool phase nearly over
The recent cool phase in the Pacific, which briefly approached La NiÃ±a-like conditions, is showing signs of decay. Sea-surface temperatures have continued to warm in the central to eastern Pacific and are now close to average. More importantly, the large body of cooler than average sub-surface water in the east has contracted considerably during the past month.
Nonetheless, the SOI has continued to rise, with the latest 30-day value being about +18. "
Where did you see +29? The above is:
"CURRENT STATUS as at 12th April 2006"
There is no La Nina, all the talk about it was a beat-up.
SST's in the east pacific are slightly below average, but not by much.
this is good.
Yeah I think people were saying the SOI index at slightly positive is what we're after? More precip, but not so warm?
could the 4 recent TCs in the last few weeks have anything to do with a wildly overstated soi?
These fluctuations are common. The difference in SOI amounts to just a few point difference in the pressures in Tahiti & Darwin:
Date . . . . . . . . Tahiti . . . . . . . Darwin . . . . . . Daily SOI
04-Apr-2006 . . . 1012.39hPa . . . 1004.95hPa . . . 36.40
11-Apr-2006 . . . 1012.83hPa . . . 1009.35hPa . . . 7.80
Churchy, yes the TCs have a significant effect on the SOI. However, TCs this late MAY also be an indication of an approaching La Nina....
i saw the +29 on ABC news a couple of nights ago
Yes, neutral conditions to persist throughout winter looks the go for mine. With the cooling of the SST's in the Bight now, we could well see some big highs blocking for a while. No surprise in late autumn/early winter though. RE SOI, I tend to look at the 30 day running average but its not really a concern at the moment for me.
there is very cold water upwelling at the moment in the east pacific, up to 4C below the average. this could be significant if it continues.
Where'd you see that? Got a link to a chart or something?
For us lay people could you please explain why this could be significant.Thanks
Possible La Nina.
dont put words in my mouth
no, a cooler SST for a prolonged period of time (more than a month or so) does mean the walker circulation should shift further to the west pacific, which is typical of la nina. This is not to say that this will happen because there are other factors involved.
i just said it was encouraging
This can be seen with these two SST anomaly charts one from March 14th and the other April 15th.
falls, you would know this better than me, is this significant? what do u think could possibly be the implications if this continues?
I'm confused, we've been saying a slightly positive SOI is ok, but doesnt that mean its slightly warmer than average nearest Australia during winter? So, wouldnt a strong el-nino be better for our winter, where temps off the east coast are below average?
I have no idea about all this, just wondering, hopefully some of you weather folks can answer
el nino drier but colder generally
la nina warmer and wetter generally but mild ones of but can be good for the australian so season! I think anways.
1. A strong El Nino(SOI of less than about -12) mean very little precipitation, so we DON'T want that. Lower than SSTs (Sea Surface Temperatures) tend towards high pressure, higher than average SSTs tend toward low pressure formation. Look at the SST maps for March/April... it's not all that surprising that there's been tropical cyclones forming this late off NE Australia with all of that warm water in the Coral Sea.
2. SOI SLIGHTLY higher than normal will tend towards more low pressure, and the CHANCE of more snow as well. If the SOI gets too high (+10), then the air temps also climb, so there may be less snow and more rain.
I like to think that a good sustained winter SOI range is between -7 and +3
If anyones intrested I compiled some graphs a few weeks back on SOI vs Snow depth.
SOI Vs Snowdepth
And another graph with same Data but different axis (easier for comparing good seasons and bad ones me thinks)
SOI vs Snow depth graph 2
looking at the graphs that BrentC has, it appears the best ski season came with a SOI of around 8 or 9
Yes, but the 2nd best one came with an SOI of around -5 or -6.
Big seasons with SOI greater than +7(average thru July/Aug) only happened prior to 1982.
Most of the big seasons since 1981 were generally around the -6 to +3 area(Jul/Aug).
SOI measures comparative pressures between Tahiti and Darwin. However it doesn't measure any overall increase in SSTs in the Pacific in the last 25 years.
i would like to see SST's incorporated into these graphs also.
It seems to me that the snow depth is particularly poor in the transition period from a strong El Nino to a strong La Nina which often go in pairs.
My understanding of upwelling along the pacific S American coast is due to strong southerly winds which cause Ekman currents that induce the coastal upwelling.
If this is the case then this implies a strong high pressure system to the west of S America which also implies that there will be strong SE Trades along the central and eastern tropical pacific (south of the equator). If this is so then one would also expect to see a subsequent cooling along the intertropical convergence zone SSTs in this area in the next few weeks. This would reverse the recent warming trend of the SSTs here and thus revert back more towards a La Nina scenario.
There is definitely a warm pool in the western tropical Pacific and as far as I am concerned this is not going anywhere in a hurry. So I favour a La Nina side of neutral this winter, but not extreme. If Sandy's stats are right then this must favour a better than average snow season.
Having said that there have been some disturbing side shows which temper my enthusiasm. One being how much snow that Mammoth Mountain got and continues to get at the moment. The last time this amount of snowfall fell was in the northern winter of 92-93 and we know how much snow Australia got in 1993.
the soi continues to rise to record highs ...but still no rain
No rain? All I've seen for about a week is rain! I've found mushrooms growing in the parks near my house, havent seen them grow since 2004, last year was bone dry all through winter
(this is melbourne i'm talking about by the way)
chief ill agree with you. as far as i know all parts of the state east of melbourne have already recieved their monthly average rainfall.
some of these changes take a while to get through TC. Recall that the maximum summer temperatures are towards the end of Jan/early Feb due to lag. SOI has a similar lag.
Also, have a look up north, cairns is having record rainfall, so did katherine not long ago and most of the top end, the monsoon is kicking royal ass up there.
And with the fronts due to come through in the next few weeks, it looks like plenty more rain is on the way.
unfortunately im in sydney
I miss my melb
The SOI should take a HUGE spike into the positives in the next couple of days.....
My guess would be +100 or more......
ahh monica my darling
but that wont be sustained because its a running 30 day average
Isn't that what "spike" means??
but but but....ahhh
well whats happening
well the SOI is around 15 if i remember correctly, or maybe 12, and SST's are still cool in the upwelling region in the east pacific. Look at April's rainfall and you'll see that more than 50% of the country had above average rainfall. with the fronts lining up like they are for the SE it looks like we'll be above average again this month if it goes to plan.
The next update from BOM should come out tomorrow, well... today... should be interesting!
The Current SOI is +2.3
30 day average is +11.24
90 day average is +8.05
"Fronts lining up" do not generally give us much better than average rainfall in the SE, it's cut off lows that provide the elevated levels of rain. Why? Generally, if we have one front after another before winter, we have lower than average temperatures (April was one degree lower than average in Melbourne) but the fronts are weak and the pressure remains higher.
For example in Melbourne, we two episodes of "fronts lining up" in April, 11th & 14th(with rain on 14,15,16th of 15mm), again on 18th, 20th, 21st & 23rd(with rain on 20,21,22nd of 11.8mm). The pressures dropped to 1005.5hPa on the 11th and 1008.9hPa on the 19th. These pressures don't provide the "whack" for sustantially higher levels of monthly rain.
If you look at December on the other hand, Melbourne had 38% more rainfall than average.
This was mainly made up of a series of cut off lows. There was 38.2mm with a pressure of 995.7hPa around 3rd-4th, 33.2mm with a pressure of 1001.5hPa around 6th-7th, and 6.2mm with a pressure of 999.3hPa around 12-13th.
At 44.8mm Melbourne had 13% less than its average rainfall for April.
At 46mm Hobart had slightly above average rainfall for April. (+7%)
At 9.8mm Sydney had 91% less than its average rainfall for April.
So I'd hardly say "looks like we'll be above average again this month", since we haven't really had above average rain LAST month.
The SOI figures for March/April have been skewed to a large extent due to the number of tropical cyclones in QLD/NT/WA. This drops the SOI sharply, although briefly. The late TC season may be indicative of warming off NE Australia, however. Now that the TC season is "over", I'd look at the daily SOI for the next few weeks, and at the SST maps.
Here is the SST anomoly chart for 2nd May. It shows why we've had a few TCs form in the Coral Sea.
You can also see the current cooling off Chile & Peru.
i wasnt just talking about melbourne and tassie, australia is bigger than that
"At 9.8mm Sydney had 91% less than its average rainfall for April."
Conditions in NSW generally are starting to look really dire again. Made a trip out west of the Blue Mountains a week or so ago and it's parched. East of the Blue Mountains isn't much better.
You said "with the fronts lining up like they are for the SE it looks like we'll be above average again"
Its been updated!
se australia looks good
yeah SOI looks good for a nice fall in late May I reckon.
thanks misses frog
So frog's wife is doing forecasts now
the SOI has nose dived to +7
SOI can often change quite a lot from day to day. Here's the last 10 days(oldest to newest)
30 day average is +4.9
90 day average is +8.64
SOI graph for 2004-2006 Trending towards the low + values:
whats causing such fluctuations
or is that normal so the avg smooth out the fluctuations
SOI measures the difference in pressure between Darwin and Tahiti (in Standard Deviations, I think) if you get a spike in the pressure in either place, it changes quite a lot.