Global weather drivers
Discover what influences global weather and why it can complicate weather forecasting, particularly in the UK.
What global systems impact the weather forecast?
At any time, there are many weather systems weaving around the globe. The worlds’ weather is interconnected, and it is often the case that no single driver will determine a weather forecast, so multiple factors need to be considered.
El Niño and La Niña
'El Niño' is the warming of sea surface temperature that occurs every few years in the tropical Pacific. 'La Niña' means 'opposite episodes with cooler-than-normal sea surface'. These episodes alternate in an irregular interannual cycle called the ENSO.
ENSO affects global temperatures
El Niño raises and La Niña reduces global temperature slightly, with any increases a few tenths of a degree - much smaller than the current level of global warming of around 1.2 degrees accrued due to climate change. But, it can be a significant driver in setting new records.
North Atlantic Oscillation (NAO)
NAO describes differences in the usual pressure patterns over the North Atlantic – with positive and negative phases.
Changes in local weather patterns such as temperature, rainfall and wind strength/direction are strongly influenced by changing local pressure patterns.
Forecasting weather impacts from NAO
A Met Office Hadley Centre breakthrough in climate prediction capability means forecasts can allow more time to prepare for likelihood of NAO associated weather events, such as damaging winter storms, high near surface wind-speeds and extreme temperatures.
Madden-Julian Oscillation (MJO)
Characterised by an eastward spread of large regions of enhanced and suppressed tropical rainfall, mainly observed over the Indian and Pacific Ocean.
How does MJO impact global weather?
It creates favourable conditions for tropical cyclone activity, making MJO important to monitor during Atlantic hurricane season. The enhanced rainfall phase of the MJO can also bring the onset of Monsoon seasons. It can also influence El Nino and La Nina, and the onset of SSW.
Sudden stratospheric warming (SSW)
SSW describes an event when rapid warming occurs high up in the stratosphere. However, it can lead to changes in our weather at the surface.
Why it is called a warming if it leads to cold conditions?
SSW is observed in the stratosphere - rapid warming up to about 50 °C in just a few days, high above the earth’s surface. We don’t feel the ‘warming’ ourselves, but a few weeks later, we can start to see knock-on effects on the jet stream effecting our weather lower down.
What is the jet stream and how does it affect our weather?
The jet stream is a core of strong winds around 5 to 7 miles above the Earth’s surface, blowing from west to east. It causes changes in the wind and pressure at that level, which affects things such as areas of high and low pressure, and therefore helps shape the weather we see.
