Weather update – 22.02.07

More snow forecast for this weekend:

Weak high cell 1016 hpa over Switzerland, weakening. Complex low area 962-972 hpa far northwest of the British Isles, drifting east. Linked disturbance expected to reach the Alps by Saturday
Fairly sunny – cold in the morning – mild on sunny slopes later
SKY CONDITIONS (cloud – sunshine) : clear or partly cloudy – high cloud coming in from the west towards the evening – period of sunshine close to 90%.
WIND  ground level : variable light.
  mid mountain : SSW light to moderate.
  high mountain : variable -> SW light to moderate.
TEMPERATURE : min -3°C – max +11°C.
ISOTHERM 0°C :  1800 -> 2000 m.
ISOTHERM -10°C :  3800 m.
SKY CONDITIONS (cloud) : cloudy – partly cloudy at times.
WIND  aloft : SW light.
Changeable – scattered cloud crossing over – slight evening precipitation risk
SKY CONDITIONS (cloud – sunshine) : partly cloudy in the morning – becoming cloudy – high cloud coming in from the west in the afternoon, fairly thick at times – period of sunshine close to 50%.
PRECIPITATION : slight late afternoon shower risk
WIND  aloft : SW light to moderate.
TEMPERATURE :  min -4°C – max +9°C.
Mainly cloudy – rain in the afternoon
SKY CONDITIONS (cloud – sunshine) : mostly cloudy – cloudy at times in the morning with fleeting sunny spell – overcast in the afternoon – period of sunshine close to 100%.
PRECIPITATION : starting up towards the middle of the day – light at first – moderate at times towards the evening – rain-snow limit towards 1300 m.
WIND  aloft : SW moderate -> NW strong.
TEMPERATURE :  dropping highs.
Sunday : gloomy – light to moderate precipitation – rain-snow limit dropping towards 1000 m. Monday : changeable and cold – morning snow showers – sunny spells spreading out in the afternoon. Tuesday : changeable – slight shower risk – getting milder.
Forecast reliability : fairly good until Sunday – poor thereafter.



Weather data

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!