What does the wind tell me?
The isobars on a weather map provide general wind directions. However, local conditions can produce winds quite different from those expected. In open areas where isobaric wind flow is expected, you can often work out the location of a low pressure by facing the wind. In Australia, the low will be on your left. If you face north into the wind, the low is to your left and hence to the west, so worsening weather should be planned for. If the wind is from the south, the low pressure is to your left and moving eastward, and the weather is likely to be improving. Winds getting stronger, particularly from the north, indicate that the low is approaching. Isobars are normally closer together around low-pressure systems. Understand how the wind changes direction as a front moves through. A northerly wind will shift back to a westerly then to a southwesterly.
In the outdoors there are many practical situations where an accurate prediction of weather can make conditions more comfortable and safe. Some examples include:
- Having observed the imminent arrival of a front, in what direction do you face the door of your tent?
- Where do you place your tent with respect to a campfire?
- Your party camped in unpleasant conditions the night before. A thunderstorm forced meals to be cooked in tents. This morning, there is a light scattering of snow and the previous day’s northerly wind has been replaced by a cold southerly. You tell your party to rug up and smile, because the weather is getting better. The low is now to the east and a high pressure system is approaching.
- With a cloudless sky on a windless late afternoon, a snow-covered clearing is considered for a campsite. Some of your party members do not have very warm sleeping bags. There is a high probability of very low temperatures during the night, as the earth cools down due to radiative cooling. You might advise your party to seek additional shelter by camping under tree cover. Water bottles should be kept in the tent to prevent freezing.
- Another hot, windless day and your party has a relatively short walk along the beach at a coastal park. Is it better to walk in the morning or midday or afternoon? You might decide to wait for a sea breeze. During summer days, the land heats up more than the water. By midday there may be a strong rising current of air above the land, which is replaced by a cool breeze blowing in from the sea—a pleasant walking environment.
- You are to meet your party early on the first day of a walk at a carpark at the top of a river system. The weather is fine with the high pressure centred overhead. The forecast is for a calm cloudless night. Do you drive up the river valleys to the meeting point the evening before or early in the morning? A still cloudless night leads to frosts and fogs, particularly in river valleys. You might choose an evening trip.
- Noting the morning fog, you know that the night has been clear and windless. The high pressure has not moved on and the day is likely to be fine and sunny.