Rising altitudes and falling temperatures
Anyone who is a regular hill walker will know that mountain weather conditions can change dramatically from one hour to the next.
For example, in just a few minutes a thunderstorm can roll in when the sky had previously been perfectly clear.
In just a few hours the temperature can drop from quite mild with the sun on your face, to temperatures that are below freezing with rain, hailstones and squally winds.
The main differences in the climate of mountains are temperature and moisture.
Mountains tend to have much wetter climates than the surrounding flat land, which means they will receive larger falls of both rain and snow.
The temperature on mountains becomes colder the higher the altitude gets.
That is important at this time of year as it can mean the difference between rain or snow.
And sometimes as little as three or four hundred feet can be enough height for the temperature to drop low enough for rain to turn to snow.
That is why it can be raining in the centre of Belfast, but snowing in the hills that surround the city.
Also the higher up a mountain we climb, the colder and windier it usually gets so that the wind chill factor increases.
For example, in the Mournes it can be at least 5C (9F) cooler near the top of Slieve Donard in comparison to the valley bottom.
If the temperature at Newcastle beach is 6C (43F) the temperature at the top of Slieve Donard, if it is covered in cloud with snow, will be below 0C (32F) and depending on the strength of the wind it may feel more like -5C (23F) to -10C (14F) on bare skin.
This weekend will feel more like winter at times rather than spring.
Sunday will be a cold day across Northern Ireland with strong and gusty westerly winds.
The Met Office has issued a yellow warning for snow and ice across Northern Ireland between 02:00 GMT and 11:00 GMT on Sunday.
It will be bright at times with sunshine and great visibility but there will also be fast-moving showers, which will fall as hail, sleet and snow.
Winds will be stronger still over the mountains with severe gales possible combined with much lower temperatures and heavy snow showers.
Temporary blizzard conditions can be expected and winds on the summits may gust to over 50mph (80kph).