SomeLikeItHot
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56 minutes ago, radiohead said:
However. I have learned that while there is no difference in the southern hemisphere, NCEP have (previously at least) noticed that the 06Z and 18Z tend to score a little worse in the Northern Hemisphere. There is a PowerPoint presentation about it, I can't remember exactly where I found it or what year it is from though.
My memory was that say 72hrs forward 6z and 18z are worse than 12z and 0z, but at the same time, eg 6pm next sunday then 6z is better than 0z and 18z is better than 12z, as the accuracy degrades as you go forward and the accuracy differnce is between the runs is than the accuracy degrades over 6 hrs.
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Only a few days after Sydney copped the wildest storm of the century, an impressive hailstorm in the city late Saturday. Temperature range of 14-26, then a maximum of 17 on Sunday.
Was pretty amazing amount and of hail in some places, sadly only a light shower at my place, despite people snowboarding on the stuff in the next suburb.
Below is a iceflow on the Parramatta river (air temp about 20 degrees at the time)
Also a good show of lighting Apparently 16311 strikes below showing the plot of them in the Sydney region.
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So it looks like most of Sydney region within about 15kms of the coast received around 200-250mm of rain over the last 48 hours, . dropping to around 150mm as you go further west. Rain still on going meant to ease considerably this afternoon but at least the wind has dropped. Some of the Hunter region has recieved over 400mm over the same period of time.Rainfall totals are high but not that unusual (1 in 10 year event?) but combined with two days of severe winds - gusts up to 145kmph for 48 hours is.
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A major weather event for the New South Wales coast, from the mid-north to south of Sydney. The east coast depression has brought sustained gale force winds and very high rainfall totals. There are now reports of casualties. The video is from Dungog, 125 miles to the north of Sydney, this afternoon.
They are reporting the town of Maitland in the Hunter Valley received 246mm of rain between 9am and 1pm, this is on top of the aprox 150mm the region received in the previous 24hrs. The Hunter region has been bearing the brunt of some severe thunderstorms appearing in the system with some extreme preceiptation.
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Its cold, windy and awfully wet if you live in the Sydney - Hunter region. 15c at the moment in Sydney at 1:30pm, down from 27c over the weekend. We are getting close to 150mm in the last 48 hours in many parts of the Sydney region. I think some parts of the Hunter region are closer to 200+mm over the same time period.
Cruise ships stuck outside the harbour in 9+ meter swell.
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Always puzzles me why people make guesses this early?
Given how bad my last minute submissions based on analysis were, I decided that I might as well guess early.
3.2 for me.
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Thanks for posting that graph. I can see why they call it a bell curve...shaped like a bell.
How then is the CET different from other averages? Can anyone explain this to me please?
Averages are good description of the situation where most results are near the middle like in the bell curve above.
But if you get a bi modal distribution (ie outcomes are either higher or lower than the average but rarely near it) then the average is not a good description of what is typical. If you stand with one foot in a bucket of ice and the other in a bucket of near boiling water, you don't feel warm despite what the average temperature may say.
AS for places that have temperatures that switch like that I'm not sure but I'm sure it happens somewhere.
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My method on checking for HLB/MLB trends is looking for yellows and warmer heights in the respective latitude. Looking at the D16 charts there are NO yellows at high latitude on any of the 22 members, and less than 50% greens at high latitude. Where as in the coming week we see plenty of yellows in all models. In the ML not many yellows showing. Not to split hairs but to me that is a sign of trend to a more active PV, i.e. a PV that is moving towards its normal state. Early this year in Jan we have similar charts to the current D16 with the vortex not in its default state, but it was able to produce some horrible wet weather for the UK:
Looking at the CFS AO a move towards a neutral AO as the GEFS are hinting, but short lived:
aoindex.pngThats how I identify a trend but if I am reading it wrong then I stand to be corrected.
But how many were seeing the current forecast set up later this week at 16days? I doubt many if any. Even my relatively limited (ie 3 years) experience of model watching shows that blocks once established get shifted faster in the models than reality. Today's UKMO 12Z and GFS at 96 bares a lot more similarity to the ECM 12Z +144 on the 7th than their own efforts at the same time.
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Interesting the drop in mean daily temperatures from 12th to 13th November.
Even in the full history from 1772 there is an observable steeper decline in the average across this period. With the 11th to 17th of Nov average daily temperature decline averaging twice the monthly average of temperature decline per day. Not sure if its statistically significant though.
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Mean, Mode, and Median are all measures of central tendency. The median is always useful since it less affected by outliers, whilst the mean can be really affected by outliers.
Yes but what median are you using? Based on the daily CET or Monthly?
ie is your median just the average CET of the middle of the three months?
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Winter was traditionally winter solstice (21st of Dec) as it was relatively easily observable even in pre-historic times and is reasonably close to the coldest period (10th of Dec to 10th of March) as Roger says above. There is no real reason other than convinience we should define winter as a fixed set of calendar months.
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To complete this for the actual winter months.
Running correlation and regression on Feb gives a correlation of 0.48. The regression line puts a -2.2 OPI (if that the final OPI figure) giving around a 2.8 +/- 1.6 (1 StDev) for a Feb CET (vs 4.3 for the 1976-2013 avg) so pretty wide range but on the cold side.
The winter (DJF) CET Mean correlation is 0.68 actually higher than for any individual winter month, regressing forecasts that a -2.2 OPI gives a CET 3.0 +/- 0.9.
So based on the small data set we have it would appear to be forecasting a below average winter. Past performance is no guarantee of future returns.
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If you got the data, I can do the analysis.
It's unlikely we will see step change behaviour, although it is possible.
NDJ. February isn't winter. It could well be that the restrictions of the UK definition of winter holds up analysis here.
Since when did Febuary stop being Winter and November start being winter?
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Am I looking at the same charts with the GFS as it looks like a transitory Azores ridge to me?
Current GFS is a transitory azores ridge, but the parrallel GFS (I think this is the upgrade being tested) is much more similar to the UKMO which is what he was saying.
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Well temperature is not simple either. It's a combination of billions of measurements of the kinetic energy of billions and billions molecules.
OPI is a specific value, temperature is a specific value and that's what matters when we do correlation tests. The validity of the results and the hidden variables behind is another issue.
Temperature is a measure chosen for another purpose, if the october CET anomaly correlated with the winter CET anomaly then it would be interesting to measure the significance.
However if I took the last 24 months of CET data and combined it in such a way that it would have a 80% correlation with the next winter CET anomaly calibrated over the last 30 years. a significance test wouldn't really tell me much only a testing going forward (or using historical data its not calibrated to) would determine whether there was something there. The second situation is closer to the OPI in my opinion.
Which brings something to mind/ Is it possible to reconstruct OPI figures (and winter AOs) from earlier dates than the 30years the index was developed on. Isn't there reanalysis that goes back for a much longer period?
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I have made a simple calculation about the correlation between October's OPI and the average temperature of following winter in the 850 hPa level for a big portion of UK. (I provide the values i used in the end of this post)
So i took the October's OPI value and the following winter's average temperatures in degrees Celcius in the 850 hPa level for december+january+february, for the area that is defined by 5° W to 0° E and 50° N to 55° N (that contains most of England and Wales) and have calculated Pearson's r correlation coefficient and Kendall's tau.
The values of temperatures have been acquired from NOAA and the values for OPI from a post here.
So the calculated values between October's OPI compared to following December+January+February average temperature in 850 hPa were:
Pearson's r = 0.76
Kendall's tau = 0.55
2-sided p-value = 0.0000014
Pearson's r value is relatively high and shows that something might going on with this OPI thing.
Even more, in the Kendall's calculation, we see a smaller correlation but a very interesting p-value, since the almost zero 2-sided p-value shows that assuming(the null hypothesis) October OPI and average temperature of DJF are independent, we have an extremely small chance of obtaining this 0.55 correlation if October OPI and average temperature of DJF are independent.
So we must assume they are dependent with a +0.55 (positive) correlation.
Positiv emeans that when the value of October OPI is large(get's larger) the average temperature of DJF is large(get's larger) also and when the values of October OPI decrease, the value of average temperature of DJF decrease also.
So all in all there is something interesting with this OPI.
And it seems to suggest that a correlation with your winter's temperature lies between them. A positive OPI brings warmer winter and a negative colder. With the aforementioned correlations of course. This is NOT a strict 1 to 1 rule of course.
Interesting post however the independence tests don't really work when you have selected specific data and combined them in a particular way to match the historical series which is what has been done here. Its not like the OPI is say a relatively simple temperature or pressure measurement at one point.
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I suspect that even the core 3 winter months would have managed at least 1 17c+ CET daily maximum.
Since I had the data to hand.
Largest daily maximums by month. (Data since 1878 - which is the earliest CET data for max & min).
Jan 13.7
Feb 16.4
Mar 22.1
Apr 25
May 29
Jun 30.3
Jul 33.2
Aug 33.2
Sep 31.3
Oct 27.1
Nov 18.7
Dec 14.7
So it apears not for the 3 winter months,
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An article on Storm Chasing in the SMH. I think the paywall only kicks in after 10 articles a month so you should be able to view it and the images.
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One thing puzzles me with the OPI, the first calculation, so is it geopotential height anomalies? In which case, why is the heading 'elypticization' not a real word I don't think but implies shape (as in egg) more than a pressure anomaly to me
Could be a poor translation from italian. I presume they meant a quantity like eccentricity, but perhaps not defined in exactly the same way.
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The OPI manages above 0.9 fitted to historical data, though to quote John von Neumann - "With four parameters I can fit an elephant, and with five I can make him wiggle his trunk"
Good Quote. OPI has 7 parameters doesn't it? Presumably with 7 he could make it dance.
Edit: Actually I think it has 5 the other two t are derived from the 5 inputs.
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65.8% accuracy over 38 data points vs 50% by random chance. 0.279 correlation. A weak correlation indeed. Considering 38 data points - that's possibly within the margin of error if there was no correlation. There's probably something to the OPI but these numbers don't suggest a holy grail of long range forecasting. It's never going to be that easy. If something sounds too good to be true...
No to mention the fact that a -AO winter does not in any way guarantee cold snowy weather... I don't understand why some are putting so much weight and importance on what the OPI figure will be? Maybe I'm missing something.
0.279 is the october AO - winter AO correlation. NOT the OPI winter AO correlation.
October AO is but one factor in the OPI, The OPI has a 90% correlation with winter AO - , albeit based on the data set it was presumably calibrated on.
So far we have had one test of the OPI last year. The AO predicted was the right sign but less positive than may have been expected from the the OPI. This year we will get a second test and if it is a strong negative (as it looks to be) it should be a good test of the model.
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Going to recycle my october guess. 9.0 for me.
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That's what I thought. So how have you come to a positive OPI output for October? Quote your post 'Moreover I tell you that currently the OPI is abaut +1/+1.5, so the winter will be probably a AO++ winter."
??
The quote was for October 2013 last year so "currently" is for october last year which was a positive OPI.
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-3.04 on the 0z so still strong negative.
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Australian Weather
in Weather Around The World
Posted
In Sydney my local area has had 335mm since 10pm Thursday to 7pm Sunday and its still going at about 10mm per hour - about 135 since 9am today, Although the radar is now looking like it will ease back to showers in a few hours hopefully. Generally the whole region has 100-150mms since 9am. They are saying its the biggest rainfall event in NSW region since 1998, and yes there won't be many fires left burning in the wake of that - although its sure to miss some parts.