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WW: Elders, and Why You Should Ignore It
Submitted by Juffy on Wed, 07/21/2010 - 12:04
(This started off as a reply in this thread, but it got a bit long so I've moved it to its own post under my secret identity as the Wandering Weatherman.)
Elders is useless as a forecast model.
You can see it from the issue notes on the right-hand side of the calendar, talking about hemispherical wave patterns - it's basically an assumption that we have a set of high- and low-pressure systems trundling around the Antarctic, and we can predict rainfall based on when the next low system is due past. When I first learned to read surface charts, watching ABC news in B&W with presenters who actually knew their stuff (come back John Colwill, all is forgiven), that's what I remember as Perth's winter weather.
I've lost count of the number of times I've seen "The hemispheric long wave pattern has been relatively slow moving in recent weeks." at the top of their issue notes. Why is it slow? Relative to what?
My belief is that it's relative to their historical records, and it's slow relative to those records because of the bogeyman no one wants to mention in Descent season - climate change. IMO this is why Elders so often disagrees with BoM and the GFS forecast model. Elders are the only weather service I know of that goes 28 days (672 hours) in advance. The extended GFS goes out to about 360 and it's completely unreliable at half that.
The best long-range prediction models I know of are actually BoM's 3-month forecasts, and even then you have to think about what they're actually telling you. I linked to some climate denialist's blog a few weeks ago. He wrote that BoM had predicted 30% of average rainfall for a certain period, they got a big storm and 120% of average, therefore BoM was clearly a waste of money and should be shut down. What BoM actually predicted was a 30% chance *of exceeding average rainfall*, and that's based on the best macro-predictors we have - the El Nino/La Nina indicators and the Indian Ocean dipole.
At the start of this season Phantom posted up the BoM 3-month rainfall prediction for May-July, which was pretty dire - 40% chance of above median rain across the entire catchment.
The one for June-August is even worse, with 30-35% across the catchment, but we all quietly ignored it and kept hoping. Sure enough we're having one of the 70% years where we get stuff-all rain, and how good the Descent is will come down to the last week - as it always does.
Good luck, everyone.
Where to get a goat?
Anyone got a goat?
Goat Boat
Will a 'goat boat' do the trick.
sundries
My friend Pete and I are considering entering sundries with an inflatable boat. We will put it in a backpack and run the majority of the race, then inflate it for the final 30km.
We may very well take line honours, as our boat will survive the valley while a lot of others won't. We can also run faster than most of you can drag your boats so we should be in front after the day 2 ti-trees.
;-)
Grumpy much?
you need to get out paddling Juffy.
God will provide
Yeah Juffy be nice. Just 'cos you're probably right doesn't allow you to deny hope to the masses. Delusion is quite healthy at times. If I sat and contemplated going from Northam to Toodyay in 3cm of water, dragging across sandbanks and watching wafer thin teenagers float past me I'd get all grouchy about the whole thing.
Instead I'm going to welcome whatever comes! Might do an article on that!!
"Probably" right?
I'd almost take that as an insult. :)
In other news, has anyone else been watching that dimple in the isobars around the 25-28th which has been slowly strengthening into something interesting? Lovely bit of onshore flow coming in behind it, too.
The lead-up week is still looking promising on the GFS, if a little less so than before. Standing by my 0.5 prediction for now.
Can't float a boat on hope
Hope? Faith? Positive thinking? Why not go all out - sit back, pop your skirt, clasp your hands around your paddle and chant "God will provide"?
Maybe we should sacrifice a goat too, just in case our "positive thinking" doesn't get the attention of the rain pixies.
gotta have hope
It's all about having some hope. We could have all decided in 2008 that the outlook for rainfall exceeding the median was 35% across the entire SW land division.
The rainfall was below average that year (I don't have the median figures) - but we all did some positive thinking, and entered the race when the only rain forecast was on the pie-in-the-sky 28 day chart.
And those who were dissappointed were those who didn't enter the race. The faithful were rewarded with a bumber crop of rain at the perfect time and an awesome race.
Maybe we should be out spruiking the need for attention on climate change to the powerboat crews...
Stopped clocks
...and all that.
I can predict that we'll have rain every day in July, and according to the long-term averages I'll be right about half the time - and that'll make me a damn sight more accurate than Elders - but would anyone listen? Of course not. A forecast you can't rely on is one you might as well not have.
And you've completely missed my point about the 3-month outlooks.
Easy does it
The 28 day rain chart is a handy tool, and has picked many a front on the nose from 3-4 weeks out.
Back in 2006, it accurately predicted the unfortunately timed cold front that landed on the Sunday of the race, from well before it was on the 14 day precip chart.
It's not always right, particularly when we have blocking highs. But it does help to tell when the good stuff will be coming around past South Africa - even if it can't provide certainty - it does indicate times of increased probability.
I'm not sure whether a long range outlook from 2 months ago is much use at this stage.
I won't comment on the weather, since I believe that this can cause it not to happen (not that I can prove this). I suspect there are many people in this boat.
This is what makes the high years all the more sweet - although it's not a done-deal just yet.
I just hope everyone doesn't take 2 boats to scrutineering !!
Boggled
Thanks Juffster. The Phantom never set out to be an actual meteorologist, and has thus just read this post very slowly, using a dictionary for the big words. It helps me understand why I stopped some time ago using the Elders 28 day thing - I never found any congruence with what happened in real life, so the tool resulted in some red herrings coming from me.