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DIY mountain weather forecasting

These ‘rules of thumb’ can help you predict the weather in the mountains. Some of them will not work in other places though, as the weather in the mountains is unique!

Air pressure

If you stand with the upper level wind to you back (check by looking at the high clouds) there is a low (area of low air pressure) to your right and a high (an area of higher air pressure) to your left. Have a look at a weather map in the newspaper or on television, you will see the highs are marked with an H and the lows are marked with an L. Generally a high means good weather and a low means poor weather.

If you have a barometer you can measure the air pressure yourself. If the air pressure is rising it means a high is coming, and if it is dropping it means that a low is coming. So you can use a barometer to help forecast the weather. If the air pressure is falling then some bad weather might be coming (a low). The faster or further the air pressure drops, usually the worse the weather is going to be.

Clouds

Use clouds to see which way the wind is going. Clouds can fool you by looking big and nasty when the weather is okay or by looking small and harmless before a big storm! So clouds are not always good for weather forecasting.
There are some clouds though that warm you that bad weather is coming. Usually they mean that the bad weather is coming in one to two days.
Watch for them when you are at Arthur's Pass.

The first clouds to appear before a storm are Mares Tail clouds (because they look like a horses tail!)
Next come the Cirrus clouds, slowly taking over more and more of the sky.
Lastly, when the winds are very strong, come the hogsback clouds, meaning a good storm is brewing!

Wind direction 

The direction the wind is coming from can tell you a lot about what the weather might be going to do.

North West:
A front is approaching from the Tasman sea, a low is probably passing to the South, Heavy rain and windy in the west and hot and windy in the east,  
          
West-South West:
Maybe clearing.
       
South South West:
Usually good but cool,  high is approaching from the West, watch out though that the wind does not change suddenly to the South.

South:
If the wind changes to the South look out for cold weather with the possibility of snow. Often Southerlies bring sudden cold snaps/snowstorms to the mountains followed quite quickly by clear fine weather with cold frosts.

South East:
There is a high to the south but South East clouds or light rain may cover the eastern mountains.
       
Easterly:
There is a low to the North and a high to the South. The weather depends on the pressure difference between them, usually nothing nasty but light rain possible.

North East:
A low is passing to the North, there is usually a slow deterioration of weather, cloudy with light rain and light winds.
Watch out if the air pressure falls very quickly though, this means a rare and nasty type of low (called a ‘bomb’ by weather forecasters) is forming with heavy snowfall and high winds! (it was a ‘lee cyclogenisis’ storm like this that sank the Wahine ferry).