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GRIB Data Warning...Great Example

Posted: Fri Oct 23, 2009 3:34 pm
by weatherman
Hi again ,

A deep area of low pressure (~980mb) is going to be crossing Scotland this weekend. By 6am Sunday morning it is expected to be off northern Scotland...

Image


Now, given this area of low pressure, it's depth, development and track, wind speeds across outhern and western Scotland as the feature passes through, can be expected to be around 35-45kt (F 8 -F9) gusting in excess of 60kt (F10-F11) over exposed coasts and hills.

Many of you will have access to GRIB data and can check the speeds predicted by the models. This data will be the same as the chart below...

Image

Notice how the mean wind speeds from the GRIB data shown here are of the order of 20-25kt (although the orange colours in the far NW of the chart indicated mean speeds of 30kt).

This is a good example of how GRIB data will smooth out wind speeds and, although very useful, GRIB is only a tool in the forecasting box, especially in potentially dangerous situations.

Thought you might be interested.

Simon

Re: GRIB Data Warning...Great Example

Posted: Fri Oct 23, 2009 9:10 pm
by tcm
well, um, the two maps don't match - the first is over atlantic, second centred on europe. And as you say, the one over scotland shows the 30something knots which we all know means add a bit in open sea. Anyway, i see the point.

The "gusting 60knots" should cover it, you weather forecasters eh?...

Re: GRIB Data Warning...Great Example

Posted: Sat Oct 24, 2009 3:19 pm
by sahona
Well, something just 'flipped' in the Clyde, we've gone from brisk Easterlies to strong Southwesterlies in the last 1/2 hour (with rain) .
Looks like PSC cancelled their dinghy racing , but still the golfers plod their weary way among the gorse.
That's where all the hard men have gone
(everybody-) long time passing....




Ramble over

Re: GRIB Data Warning...Great Example

Posted: Sun Oct 25, 2009 9:42 pm
by Silkie
Simon has linked to actual forecasts unfortunately rather than saving the ones in question and linking to them as jpgs. I am currently seeing 48hr forecasts valid for 1200 Tuesday 27/10 and for quite different areas as tcm has said.