On Monday 13.09, the EC46 (or EC42 as it is named in Open Charts) came up with the weather regime classification below, suggesting a really strong blocking episode, similar to the one we had seen beginning and end of July. And that forecast was quite a change from the seasonal forecast that was released only 1 week earlier, suggesting increased chances for westerly flow towards Europe in October.
 

Then, on Thursday 16.09, the updated EC46 came up with the solution below. A big jump in the +NAO chances for following two weeks. 

I wonder if this volatility is related to the intense Atlantic activity at the moment and what would be the best strategy for a forecaster to follow at such situations.

5 Comments

  1. Rebecca Emerton

    Thanks Vasilis Pappasfor this interesting post. We've had some discussion on this topic this week, and this jumpiness / uncertainty is potentially due to the combination of a few factors - as you mention, the Atlantic activity and the predictability, alongside the requirement for this product to classify the forecast into these discrete categories, and possibly some influence from the time of year in terms of the transition from warm to cold regime structures. There is some interesting discussion on this in a recent newsletter article on weather regimes in extended-range predictions, and we discussed that another product that can be useful alongside these regime bar charts, to visualise these shifts and the uncertainty, is the 2D PDFs / NAO-BLO phase space diagrams. 

  2. Vasilis Pappas

    Thank you Rebecca Emerton for your reply. I am grateful as I have already learned two things (at least (smile)): that during the transition period (October and April) such issues might appear in the EC42 and that there is a very promising new product, the 7WR, that I am hoping to be able to see and test soon. Whilst I always try to combine in my forecast the regime bar charts with the 2D PDFs, I find it often difficult to use the latter even in a probabilistic way. 

    1. Rebecca Emerton

      Thanks Vasilis Pappas- glad to hear this could be useful! Indeed, we're not aware of any systematic issues with the product in the transition periods, but a combination of factors related to the predictability in this case. The 7WR is an interesting product, we'll try to keep this page updated if there is any news or other updates in regards to this. 

  3. Robin Locatelli

    Hello

    When do you think we could have the 7 WR product available ? Any deadline?
    Also, do you think that historical forecasts of 4 WR are available ? On the ECMWF server, I only find 1 year of history.

    Thanks.


    1. Rebecca Emerton

      Hi Robin Locatelli- the latest update I have is that the 7WR product is something that's under consideration / investigation, but there isn't any timeline or definitive answer as to whether / when this will be released. We'll try to keep this post updated if there are more updates on this. 

      I've now checked with some colleagues regarding your second question, and while the forecast values for the 4WR product are made available on the ftp server, they haven't been run retrospectively for any past dates beyond the introduction of this product, so I believe the history that you already have found is everything that is available.