Watching the Weather
There are two things that will really mess up your day (and maybe your hair) – wind and rain. When heading bush, what can you do to avoid the worst of the weather?
Over the past 20 years weather forecasting has become more accurate and the amount of data available to you and me is huge. It can be difficult to determine what to look at without being overwhelmed. This explains why there are a number of smartphone apps providing a more user-friendly experience in one place.
Sometimes these apps aren’t available; particularly when you are out in the bush. This makes its important to understand more about the weather systems and what might be coming.
For images, videos and the full Unsealed 4X4 experience, read this in our online magazine.
WEATHER MAPS OR SYNOPTIC CHARTS
Put simply, the lower the air pressure, the worse the weather in terms of wind and rain. When you view a weather map (synoptic chart), it will normally be a mean sea level map – which means the air pressure measurements have been standardised for sea level. This explains why as you drive up a mountain the air pressure will drop; but that doesn’t necessarily mean bad weather.
When air pressure is low and other conditions are present, clouds can grow to much higher depths than normal – therefore producing large amounts of rain. East coast lows and cyclones are good examples of this.
High air pressure will normally limit cloud growth with fog and clear skies often being experienced. On a standard weather map you will see areas labelled as Lows and Highs, meaning areas of low or high air pressure. The lines around these systems are called isobars and they link locations of the same air pressure in much the same way as contours on a topographic map.
In the southern hemisphere winds flow clockwise around a Low and anti-clockwise around a High. The wind direction will be close to parallel to the isobars. The closer the isobars are, the stronger the winds will be. When wind travels over land it will often be dry and warm; and when travelling over water, often moist and cooler.
A good example of hot, dry winds are north-westerlies creating fire hazards in Victoria which are often followed by south-westerlies bringing cooler temperatures with rain. The NW winds have travelled across the hot, dry Outback while the SW winds have travelled over the cool southern ocean. Knowing where the winds are coming from helps a lot in determining what sort of weather might be coming.
The terms ‘troughs’ and ‘ridges’ are also used in weather forecasts. If you think of a trough being low, it is an area of low pressure. The opposite is true for ridges, which are associated with high pressure and better weather. Sometimes you will hear the terms ‘upper level’ troughs and lows which can produce wet weather even though the mean sea level weather chart looks like it should be fine. If upper and lower level troughs and lows combine, there is likely to be a very heavy rain event.
Why is this important? If you see or hear these terms in forecasts for an area that you are about to head for, it might be worth re-considering your plans. This understanding can create a good picture of what the weather might do purely by looking at a synoptic chart.
BORED? SKIP TO HERE!
The Bureau of Meteorology (BoM) keeps providing the general public with more and more tools that are extremely helpful.
One of the more recent innovations by the BoM is MetEye which is a tool to help visualise weather data for a selected area of the country based on current conditions while providing forecasts of different elements. By selecting different layers on the menu, an enhanced picture of what is occurring with the weather can be seen. It is a perfect tool to help with your learning and understanding of weather systems.
BUT WHAT IF I DON’T HAVE INTERNET COVERAGE?
Now this is where it gets interesting. Most of our favourite bush campsites will be out of phone coverage. Smartphones are tremendous tools – so before you go out of range, do a screen grab of the latest forecast weather or charts. This way you can check the forecast each day and if the actual weather varies from what was forecast, you can assume that the next day’s actual weather will vary even more.
One of my favourite charts is the Interactive Weather and Wave Forecast Map. If going bush for more than a few days, I will screen grab one forecast chart per day for the next seven days. By doing this I will have a good idea what may happen, and it will help if forecasts don’t seem to match actuals. There will normally be clues on the forecast charts that will help me make decisions on considering other plans for my trip.
If I was leaving Birdsville to cross the Simpson today (27 August 2016), I would make sure that I was on the other side of the salt lakes by Tuesday 30 as the forecast chart shows a small band of rain moving in from the north-west. The MetEye forecast confirms the forecast for a 60% chance of rain up to 3mm. This is not a lot of rain but if the forecast is wrong and is then updated to 20mm of rain after we head into the desert, we could be in a spot of bother.
SOMETIMES, YOU JUST NEED TO LOOK OUT THE WINDOW
When all else fails, look up into the sky rather than at your screen. By knowing a few different types of cloud, you can predict the future (not the Lotto results, unfortunately). There can be clouds but no rain; but you can’t have rain without clouds.
There are 10 main cloud types and these are broken down into high, middle or low level clouds. High level clouds are cirrus, cirrocumulus or cirrostratus and are made up of ice crystals with no danger of precipitation. They can however warn of a cold front and can appear 12 to 24 hours prior to a front arriving.
The main middle level clouds are known as altocumulus, altostratus and nimbostratus. Altocumulus may produce light showers, altostratus will produce rain, and nimbostratus will produce heavy rain. If cold enough the precipitation could be snow. Generally, the darker the cloud from below, the thicker it is and the more rain it will produce.
Stratocumulus and stratus are low level clouds that will only produce drizzle. Cumulus clouds, which are like fluffy towers with a flat base, will produce showers. Storm clouds known as cumulonimbus produce the most severe weather in terms of lightning, thunder, squalls and localised heavy showers. These stretch from low levels, towering up to 16km high.
FORECASTS VS. ACTUALS VS. LOCAL CONDITIONS
Although the computer modelling is very good these days, forecasts can and do change – so having the most up-to-date forecast is important. Knowing where your last phone coverage is before going bush is crucial if you want to download the latest forecasts.
Actuals will vary from forecast so be prepared for the unexpected; particularly if storms are forecast as they can create localised severe weather. Local conditions can also vary, particularly in the mountains. Having an understanding of how weather systems work and having access to the most up-to-date information will help you make informed decisions and generally make your trip that much more enjoyable.