Autumn/Winter FI Charts 2012/13

Sponge Bob wrote: »

Both in fact. Even in summer.

The thread is here to stop the forecasting (ie realistic charts up to around a 5-7 day horizon) thread from degenerating into utter lunacy every time certain people discover snow pr0n at 14-20 days.

Anything after 7 days is subject to so many variables that it is fantastical.

After 96 hours at the moment is pretty much FI , good post from NW showing this with the spreads.


These charts may not be something too many are familiar with, but what they show is the sea level pressure mean from the ensembles as the usual contour lines and the colours show the spread, which is the difference between the highest and lowest ensemble run - ie a high spread means a large difference between highest and lowest so less certainty in terms of the outcome.

To put a baseline in, here's the chart for 24 hours and as you can see the spread is virtually all blue and therefore there's good confidence in the pressure pattern (as you'd expect)


By 96 hours, there's a bit more colour coming in there, with an increasing amount of spread surrounding developments of the low pressure system to the northwest of the UK with 5-8hpa 'uncertainty' within parts of that.


Roll it forward to 144 hours and the differences increase with the mid-atlantic, southern tip of Greenland and the east coast of the USA all areas of low confidence, and incidentally all important locations in terms of upstream development for the UK


168 hours and that increases


And by 240 hours, we're talking 10-20hpa of potential swing (on just this run alone) across much of the Atlantic, the UK and the eastern seaboard.


So, what to draw from this? 96 hours is the point to watch in terms of upstream & beyond that there's too much uncertainty to draw any real conclusions at this point.