Fax Charts

[chionomaniac]

I have another question for the experts who kindly helped me in the past.

I know the Fax charts are the version that the professionals produce once they have interpreted their own supercomputers model output. But what does Fax actually stand for?

And (I hope this works) how do the met office forecasters get from this:

http://www.netweather.tv/models/meto/20071...ages/met.72.png

to this?

http://212.100.247.145/fax/PPVK89.png

thanks

[Rustynailer]

Thats an interesting question, I am going to read the results here with interest too

Russ

[chionomaniac]

Charts have updated since but I originally chose UKMO 0z for 20/11 for demo purposes as I still haven't worked out how to upload the charts!! I'm sure I'll soon work this out!! Any help on this gratefully received.

[johnholmes]

remind me again tomorrow evening when I'll have some free time and I'll try and explain

[BrickFielder]

They will have a number of charts to look at including :

Vorticity charts which at low levels will tend to indicate frontal systems and at higher levels cold air troughs.

Theta E charts which will show where moisture is and how it is moving.

Thickness charts which can be used to see boundaries , whether it wil rain or snow.

Temperature charts including the zero degree isotherm( where snow and ice begins to turn to rain as it falls)

Dewpoint charts show misture.

Wind charts show strength and direction of winds and also can be used to locate frontal boundaries and weather severity.

Taking all these together the forecasters then make a judgement on how well the models have done and use their experience to come up with a likely scenario.

[chionomaniac]

Thats a lot of information to sift through to produce 10 fax charts every 12 hours!

[Paul]

They also use the ecmwf ensemble data as part of their considerations as well I believe.

[chionomaniac]

Thanks for the replies guys. Does anyone know why they are called fax charts? Is it something as simple as this:

"Fax (short for facsimile, from Latin fac simile, "make similar", i.e. "make a copy") is a telecommunications technology used to transfer copies (facsimiles) of documents, especially using affordable devices operating over the telephone network."

(courtesy of wikipedia)

so that the info could be shared quickly - or is there a hidden meteorological meaning?

Edited November 19, 2007 by chionomaniac

[Rustynailer]

They will have a number of charts to look at including :

Vorticity charts which at low levels will tend to indicate frontal systems and at higher levels cold air troughs.

Theta E charts which will show where moisture is and how it is moving.

Thickness charts which can be used to see boundaries , whether it wil rain or snow.

Temperature charts including the zero degree isotherm( where snow and ice begins to turn to rain as it falls)

Dewpoint charts show misture.

Wind charts show strength and direction of winds and also can be used to locate frontal boundaries and weather severity.

Taking all these together the forecasters then make a judgement on how well the models have done and use their experience to come up with a likely scenario.

Thank you Brickfielder.

Do they just use the meto and ECM(thanks Paul ) models or do they look at the others aswell like GFS and its sisters? even others we can not get?

Regards,

Russ

[Essan]

Thanks for the replies guys. Does anyone know why they are called fax charts? Is it something as simple as this:

"Fax (short for facsimile, from Latin fac simile, "make similar", i.e. "make a copy") is a telecommunications technology used to transfer copies (facsimiles) of documents, especially using affordable devices operating over the telephone network."

(courtesy of wikipedia)

so that the info could be shared quickly - or is there a hidden meteorological meaning?

Yep. Fax is short for facsimile. And that's always why these charts are in black & white - because you can't (or couldn't) send colour faxes. In pre internet days this was the quickest way of sending documents.

Faxing documents (sending a copy via a phone line) was state of the art technology in the late 80 and early 90s .....

[chionomaniac]

Thanks Essan, sometimes the answer is so obvious that you dont think its right!

[chionomaniac]

After discussing how the met office position troughs on fax charts from t24 with John Holmes in a separate thread I subsequently emailed the met office

Hi

I wonder if anyone could possibly assist an interested novice

meteorologist. I have been keenly studying the models and charts for a

number of years now, and have wondered how on the fax charts the

positioning and timing of troughs is ascertained. I know that areas of

vorticity, lift, convergence zones at/near the surface can give some

guidance in the short term but from 24 hours out are there other factors

taken into consideration?

Many thanks in anticipation,

and here is their reply:

Sorry for the delay in replying to your email.

As far as I know, there is no difference in forecasting troughs to that

of the other meteorological features. Please excuse me if you already

know how this is achieved.

The basics of forecasting are the hourly observations which are then

plotted on the relevant chart, and the chart analysed adding the fronts,

centres and isobars. A sequence of charts are then compared to see the

speed and direction with which these features are moving, and a forecast

chart is produced with the estimated position of each shown in the

expected position at a given time in the future. Without having a

previous chart, I think the isobars and centres are the easier to drawn,

then the fronts can be found by looking at where there might be

precipitation ar sudden temperature/humidity changes. Other sudden kinks

to the isobars or bands of cloud might be other identifying features.

So whether it is a front (warm, cold or occlusion) or a trough, the

method of forecasting would be the same.

Producing forecast charts is obviously more complicated than the above,

which knowledge would be taught during our in-house courses, plus a

forecaster's experience, but I have tried to explain the basic method.

Forecast charts are now routinely produced by computer, rather than the

'man', with the necessary equations having been included into the

program used by the computer. This program is continually being updated.

I hope this answers your question.

Apologies for the questionnaire, but we have been asked to include the

below with our emails.

Regards

Graham

Its a bit of a general answer but I hope I am right in assuming that forecast=fax charts rather than the model output.

If that is right and fax charts are computer generated how does that account for the times when the metoffice produce fax charts that go against what their own models produce?

c

[johnholmes]

Met O Fax charts are the ideal in a sense in that the charts are generated by the model, the Fax charts are then modified by the senior forecaster on duty. They take all the data into account, models, from various sources, their own plotted and hand analysed charts(alongside the computer generated ones) surface and upper air, satellite data, radar data(at short time scales), they then create their Fax chart, so put simply its a mix of model and man, which is why they will sometimes not appear to be following their own Fax charts.

hope that helps

Edited November 26, 2007 by johnholmes