It might be the MJO signal in the case of GEFS  - wants to go to phase 1 for August. You can add the JMA and CMA to the list that MVH tweeted. The MJO has not been well forecasted this summer so I would be wary of that particular strand. The fact that all models are predicting a trough over W Europe for August must be based on a broader signal - I'm of the opinion that switch in PDO to positive has moved overall wave pattern in our favour so far - what is forecast for that in month ahead?

It's true what Tim says - seen the chart on Netweather:

http://www.weatherxchange.com/unzippedmonth/Coleshill_monthts_Tmean_18072013_D+XX.png

http://www.weatherxchange.com/unzippedmonth/Coleshill_monthts_Rain_18072013_D+XX.png

The temperatures remain reasonable and the mean only takes rainfall above average for the period 21st-29th July.

IMO the main signal there is for us to remain on the warmer side of the trough. GFS actually went that way in early FI but gradually pushed things east thereafter... which might just be typical progressiveness.

As for what's causing the shift, seasonal wavelength changes combined with increasing activity in the tropics look to be the main drivers (according to Chionomaniac on NW). So it really is a case of whether the models are overdoing the shift or not.

My own suspicion is that we will be close to the unsettled/settled boundary. Obviously that opinion is subject to change based on the next week of model output...

Interesting points Nouska - anybody know of a PDO outlook publicly available? tia

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I'll risk the chart - the control is not good but you would not base your forecast on that alone.

if u look not much action in jet on ecm mean on now tk thinking hopeful as other members form her that its being over played.

 

http://www.wetterzentrale.de/topkarten/fsecmeur.html

Thanks so is it a capital i ? Or a small L ?

Cheers
VSC

1) For the models, it's a case of different algorithms, different levels of computing power, different number of inputs. There can also be a difference in interpretation between forecasters, but this is often marginal at the close range.

2) It's FI, it means Fantasy Island, and defines the period of model output that may as well be written on the floor in childrens crayon. When FI starts varies on the set-up. Stable high pressure scenarios (particulalrly with a sw-ne orientation) tend to have an FI of around 7-8 days. If there is a channel low on the charts in January, FI starts at T+24!

3) I think (though am not sure) that it stands for Zulu, as in the international baseline for time. The same time as it is in the UK between October and March.

4) Who knows? It looks to be potentially thundery in the next week or so, but focussed more on the south and west I think, if it even occurs.

5) Not that I know of. Is there a particular output you are having trouble with?

Thanks very much thats the one

If August turns out poor and a big if, than at least we're had the best July since July summer 06 now thats got to count for something compared to our run of poor summer since 07.

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perhaps the jap run has it right it did last time was first to switch back

http://www.meteociel.fr/modeles/jma.php?ech=144&mode=1

As was said last night anything can happen more or less in such slackness.

going to be very intresting none the less

 

GFS 6z again looks to be bringing forward the breakdown with the cut off low heading nearer to the UK.

1) Weather models are just computer programs. You put in the current conditions (temperature, pressure, etc. at lots of points all over the world) and ask the program to guess what happens next. Sometimes the answer is obvious, so the models will agree. Sometimes, slight differences in the data will lead to great differences down the line. The agreement or disagreement is a useful way of deciding how likely a particular outcome is. Of course, they could all be wrong.

2) "FI" stands for "Fantasy Island". http://www.youtube.com/watch?v=9yrxsuMGdDY

This is not a technical term. If you said this at the Met Office, you would get blank looks. Back in the early days of TWO forum (about 10 years ago), people would comment on the far end of the GFS run, and being as the likelihood of what that showed occurring was so remote, people were calling it fantasy land, or Fantasy Island. The term stuck, and is now normally referred to as "FI" for short. It's nothing to do with Formula 1!

After a while, as well as referring to the far out charts as "FI", people state when they think "FI" starts; i.e. the point at which the model output is unreliable or unlikely to happen. So you'll hear people say things like "FI is at T72", which means that the charts after 72 hours ahead diverge enough from each other to be considered unreliable. This goes back to question 1. In recent days, the models have been reliably predicting high pressure for up to 10 days. In the winter with an Easterly flow, things are very much less certain, for example.

You may see FI mentioned on other weather forums such as Netweather or UKWW. This is because lots of TWO members also use those forums, or migrated there, and so that particular term and others have spread there. In the early days, TWO was the only weather forum of note, so we invented a lot of the terminology which gets used in UK weather forums.

3) Already answered; this refers to "Zulu Time" which is a fancy way of saying GMT. This is a recognised official term, i.e. it's not a TWO invention.

4) Bracknell, 6 miles down the road from me, had a big thunderstorm on Wednesday night; one spot recorded an inch of rain. At home it stayed dry. I didn't know if that storm was going to hit us until about 15 minutes before it changed course and died.

Given this fact, if you seriously think anyone can tell you for sure if your back yard will get a proper thunderstorm, then think again!  It could be that Loughborough gets a huge storm and Leicester gets nothing. Actually, that's more likely. Move in with Charmhills and you should see one.

5) Ooh, tricky. Ask specific questions about certain symbols and I'm sure you'll get a response.

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Hi all,

Here's todays video update;

A Very Different August On The Way?

http://www.gavsweathervids.com/

Models look concerning, but note I am NOT forecasting a poor August at this stage - Just perhaps not as good as July.

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I'm surprised no-one has commented on this particular chart from the 6z GFS run for next Wednesday evening. I can imagine that generating some interest should it occur...

http://www.wetterzentrale.de/pics/Rmgfs1323.gif

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http://www.wetterzentrale.de/pics/MT8_London_ens.png

Possible u-turn as some members want to stay in the hot side after mid-week but likely the ECM set-up to be the one that will happen as GFS are too progressive all year around on 06z runs.

Most believe it will occur on later in the week like ECM did as GFS went too progressive early so to discount it as there no support. 

Looking through the different ensembles sets it seems that after a transition period through next week a return to cooler more unsettled conditions is quite likely. Hopefully it's a transient one! 

Hadn't seen that . I think GFS is bringing in the trough a bit soon but when it does make inroads there could well be some fireworks!

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Come to daddy. But indeed, it seems to have been brought forward on yesterday (my original thought was that it wouldn't arrive here until Thursday morning at the earliest, now its looking likely to be a Wednesday feature). Assuming if it comes off as I'm sure the models will continue to change their minds more often than a woman wondering what to wear before going out for the evening.

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Hi Gav, top video as always, but I must admit I'm  not sure we're going to see a poor August either.

My rationale behind this is very simple. Patterns such as the one we are in at present have a tendancy to rinse and repeat (as we often see in cold winters as well).

I think that as most models are based on NWP and probabilities, this somewhat skews the longer range models.

The reason for this is because the starting data for these longer range models will be factoring in the prolonged dry spell we are experiencing, and therefore, the PROBABILITY is that we will see a breakdown to a poor August.

But probabilities are not definitive. In a normal English summer, it's probable that this pattern will break, of course, but equally, there is just as much a chance that we will see a rinse and repeat.

I'm also not sure that the models have got the breakdown sorted yet, and I always think that until we see this breakdown, the models will continue to skew the longer-range prospects.

It's similar in late summer when the hurricane season is in full flow and models (all models) just can't get a grip of the pattern going forwards.

My opinion (for what it's worth), is it is highly likely we will see a spell of cooler unsettled weather next week and a spell of thunderstorms before hand.

But this does not necessarily mean a poor August will follow - it's just the NWP probability that August won't be as good as July.

The fact is, nobody knows, and no range of models will accurately predict what we are going to see.

Personally, I think August willl be a fine month, although clearly not likely to be as hot as July!

 

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Not so sure about the rinse and repeat thing, after the scorching July 2006 August 2006 was the coolest August since 1999 it was also the dullest since 1986! But who knows August might give us some continued heat.

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Agree, but hence why I mentioned probabilities.

Also, after so many rough Augusts in recent years, the probability is that at some stage, August will buck the trend and deliver.

Incidentally, the 12z UKMO is showing signs of the thundery trough pushing north quickly and re-establishing the Azores High, which seems to be nudging back in at T+144. A long way off of course, but just another option on the table.

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There's lots of talk on the weather forecasts about things becoming more oppressive and humid during next week. Would on e of the experts on here explain why this should be the case? Is it down to subtle repositioning of the HP?

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I'm not remotely an expert, but the reason is the southerly plume drawing up moist air.

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It's to do with low pressure positioning itself to the SW of the UK and developing. Apart from increasing humidity, it will draw up hot air on southerly winds ahead of it.If you look at the upper temperatures early next week, they exceed 16'C hPa which is very warm and would translate to maxes of 32'C+ if we get sufficient sunshine

http://www.wetterzentrale.de/pics/Rtavn7817.png

http://www.wetterzentrale.de/pics/Rtavn10217.png

http://www.wetterzentrale.de/pics/Rtavn12617.png

Last 3 hot days of this spell

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