GFS Evaluation - Part 7

GFS evaluation experiment - Part 7
The outcome of our experiment! The charts show the starting conditions for today's 12z GFS run and so represent actual rather than forecast conditions. Note that the precipitation chart is actually 3 hours ahead due to a data problem we had, but it's near enough to enable a comparison to be made.

12z charts generated on 20/09/2007

Temperature(C)

Rainfall rate (mm/hr)

Wind speed (km/hr) and direction

Finally, here's a link to an image showing the synoptic set up expected.
Chart example

Summary
The general synoptic set up was well forecast at 144 hours ahead by the GFS model. There are some differences in the outcome, notably the flow is more of a south westerly and the air covering southern areas is milder than was forecast. As a result temperatures down at the surface in southern and central regions are a couple of degrees C higher than originally forecast. Wind strengths were generally also well forecast at 144 hours ahead, although the outcome shows an area of stronger winds approaching western Scotland. The precipitation forecast was also quite good in my opinion for 144 hours ahead with rain shown to be affecting the north west of Scotland and the possibility of showers in other areas.

During the last 144 hours the GFS 12z operational run (the one we've been looking at) has generally been consistent and performed well on a daily basis. This goes to show that forecasting at 144 hours ahead is not down to guesswork, although when I'd add that the flow has been a fairly classic and stable one which does tend to result in computer forecasting models generating better results.

Those of you who want to look at the GFS output in more detail can freely do so by using our online chart viewer here.

Issued 21:30, 20/09/2007

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