Summer Forecast 2011 Review

[Paul]

As promised, we have reviewed the 2011 summer forecast to examine where it went wrong, and also where it went right - you can watch the video here:

http://www.netweather.tv/index.cgi?action=summer-review-2011;sess=

[Radiating Dendrite]

Very interesting.

So the eventual pattern he got correct, just the timing was incorrect (by around 2-3 months)?

So with predictions of a cold February, maybe we can expect a cold April/May in reality (PLEASE NOTE THIS IS A JOKE AND NOT A DIG AT GP).

Edited October 26, 2011 by Radiating Dendrite

[johnholmes]

Yes, my thanks also Stewart for standing up and showing with charts why and what went wrong in your view.

No dig this but the summer wrong forecast along with the ;latter end of the last winter one shows just how exceptionally difficult it is to attempt to predict seasonal weather patterns. Keep at it though as experience will be a useful tool in your ability to look at situations and possibly help to interpret the outcome even better than you are able to at the moment.

I'll stick to 1-10 days with attempts limited to maybe 20-25 days ahead. That is difficult enough for me let alone trying to get my head around the links you use with such ease.

Again thanks Stewart and good luck with your winter 2011-12 when you issue it.

[chionomaniac]

I have had one thing that has bugged me all summer about Stewarts summer forecast. When we look at the pressure anomaly prediction map in the forecast it simply does not read shades of 76 to me.

My interpretation is completely different. To me it reads Arctic blocking, low pressure close to the west or over the UK, with the increased pressure around Portugal not significant enough to trust.

If I used that as a basis of my forecast then I would have suggested cool and unsettled towards the Northwest with drier and possibly warmer to the SE. A mixed bag with the trough more likely to dominate than any ridging.

If possible, could Stewart to put up an anomaly chart of what the pressure anomalies actually were for summer (please).

I would be interested to see where the differences lie and if the actual summer chart is similar to the above then surely it is the interpretation of the above chart where the most inaccuracy occured?

If that is the case then I think that Stewart's pre summer analysis was closer than even he may have realised.

[Glacier Point]

Here you go Ed.

The key difference was the position of the mean trough. Not much.but enough to make a big difference.

The majority of guidance was for a similar pattern that we got. However, there was a rump (say 30%) of analogues which suggested that angular momentum would take off during the summer and shift the trough westwards. Having my reasons, I went with this minority against the majority. Wrongly as it transpired, but subsequent events have I believe vindicated to some extent the prediction of the evolution.

[chionomaniac]

Here you go Ed.

The key difference was the position of the mean trough. Not much.but enough to make a big difference.

The majority of guidance was for a similar pattern that we got. However, there was a rump (say 30%) of analogues which suggested that angular momentum would take off during the summer and shift the trough westwards. Having my reasons, I went with this minority against the majority. Wrongly as it transpired, but subsequent events have I believe vindicated to some extent the prediction of the evolution.

Thanks for answering Stewart.

I had wondered whether you had gone for the original chart but with extra GLAAM added, when in fact you should have removed the angular momentum, not added extra. I can see how close the original chart is to making the right call - I bet you have kicked yourself a number of times over the summer. I now realise why that chart bugged me, because the summer you forecast had the westwards shift of the Atlantic trough.

Will you be a little more cautious in future?

Oh and edit - I won't ask to see the anomaly chart for 1976!!

Edited October 26, 2011 by chionomaniac

[johnholmes]

I am sure Stewart has learned from the last 2 outputs from himself, winter 2011-12 and summer 2012. The clever bit, even more so than the suggesting what is likely to be the main effects affecting the forecast, is the intpretation of the data you look at. Its a similar thing whatever the length of the forecast period. Assess what the most likely parameters are to affect the forecast then assess which to use and what weightings to give to each parameter.

Stewart - a question?

you mention 30% of the analogues showing what you went for but that leaves 70% for the other. Can you explain what the reasons were why you chose the smaller sample please? If not for the forum I'd be delighted to chat via pm if that suits you better?

Edited October 26, 2011 by johnholmes

[beng]

Thanks Stewart - very interesting - those 2 anomaly charts for predicted and actual just show how darn hard it is to produce a seasonal forecast for an Island like the UK - there's no real margin for error, because a slight difference in the synoptics can produce big differences on the ground.

[mcweather]

I always enjoy reading GP'S posts and seasonal forecasts especially because he backs them up with his methodology. He has explained how a relatively small movement in the mean trough made a huge difference in the outcome for us weatherwise. It was of course ever thus in weather forecasting especially long term stuff. The difference between a mild southerly and a roaring easterly in winter is often governed by small movements and orientations in a scandi high.

In all I think perhaps the biggest error in the forecast was to raise the ghost of 1976 in the headline. Perhaps 'potential is there for a hot one' might have been a better way of putting it. As soon as the 1976 was mentioned the chances are that GP was on a hiding to nothing bearing in mind the legendary status of that memorable season.

The very best of luck with your winter forecast GP and thanks for the video explaining your early thoughts on the competing factors this time round.

[beng]

I agree with that mcweather, I'm hoping that 1962/63 will be mentioned in the winter forecast though

Edited October 27, 2011 by beng

[mcweather]

I agree with that mcweather, I'm hoping that 1962/63 will be mentioned in the winter forecast though

Preferably with the words 'colder and snowier' than in front of the 62/63 bit

[BLAST FROM THE PAST]

Hi Stew

The one thing that caught my attention was the La Nina hemispheric state even though we were around neutral territory. Looking at solar influence, we are in 'La Nina' dominance perturbation cycle with a predominant -ve PDO. I wonder if that has a part to play in this. Heading same way for winter? Could be.

BFTP

[stewfox]

I cant see the TV screen ? Media training , presentation ?

Clarity and 7 mins my boss would say

[Paul]

The presentation is there for you to use.

[stewfox]

The presentation is there for you to use.

I cant see it but have deleted my post, I respect all long range forecasts