The long range weather forecasts are once again teasing us with snow on the horizon, starting on or around the 6th Feb.
For those geeks amongst us, it is quite useful to keep checking back to this chart:
Although to the untrained eye, this looks like a kid has gone mad with a colouring pen, in reality it is a useful chart for snow prediction.
There are two sets of lines in these forecast graphs;
1) The top set represents temperatures at 850 Hpa (approx 1450 m altitude)
There are quite a few lines, each one telling us one possibility of the GFS forecast model. The closer together they are, the more certain the prediction.
The thick red line is the 30-year average.
The thick blue line is the most probable model run.
The grey line is the average of all the model runs.
The scale up the left hand side gives temperature in degree celsius.
2) The lower set of lines represents precipitation, following the same arrangement as the temperatures. The total precipitation at a given location is proportional to the area bounded by each line. The scale on the right marks precipitation in mm (for rain) or cm (for snow).
The more in the future a prediction, the less reliable it is.
The forecasts are run four times a day and are known as “00z”, “06z”, “12z” and “18z”. They are generally available on about a 6 hour delay, so you can see the 00z until around midday, when it will change to the 06z and so on… The data input into the forecasts changes on each run as follows:
00z – Weather buoy, satellite data, shipping data, country data, NOAA data
06Z – Weather buoy, satellite data, shipping data
12Z – Shipping data, Satellite data ONLY
18Z – Weather buoy, satellite data, shipping data, country data, NOAA data
So there you have it – we can all easily become amateur meteorologists!