Backcountry Weather Forecasting
The Sun, Wind and Clouds Provide crucial Information
Learn to assess weather in backcountry field settings to minimize the risk of encountering a storm unprepared. These five things will help you better understand weather.
Predicting weather gets harder the further away we try to predict, but there are several things that can help a backcountry traveler to better understand weather. Exposure is the leading cause of death in the mountains. In the backcountry you aren’t going to get a daily weather forecast, you must become your own forecaster. Being able to assess current conditions can help you to determine if what you see will be a short passing front or a long lasting storm and can mean the difference between a wondrous trip and a horrible one.
Forces that Create Weather
Air movement, in part created by temperature variations due to the sun is the catalyst of weather. Horizontal air movement or wind, can rise and descend. Cooler air is denser and sinks; when air warms it becomes less dense and rises. Warm air is associated with low pressure and cooler air with high pressure. Air moving from high to low pressure, heading upwards, carries moisture with it and when that air cools the moisture condenses into clouds or fog, often resulting in precipitation.
There are infinite variables in how air is moved around the earth as it turns. Bodies of water, ice, and mountains all influence cold dry air to slide south, forcing some warmer air to rise. The zone where cold air is replacing warm air is referred to as a cold front, and warm air replacing cold air is a warm front. Both types of fronts are marked by different cloud types.
Clouds
Backcountry travelers can distinguish one type of front from another by looking to the skies. Clouds seen in conjunction with a cold front include puffy clouds such as cumulus, altocumulus, cumulonimbus and stratocumulus. Clouds seen in conjunction with a warm front include halos, lenticular, stratus, cirrocumulus, cirrostratus, altostratus and nimbostratus.
According to Gavin Pretor-Pinney’s Cloud Spotter’s Guide, there are 10 genera of clouds. However, the ones which bring the worst tidings are the cumulonimbus or thunderclouds, nimbostratus which bring long lasting rain and altocumulus also known as lenticular clouds which indicate speedy winds and are commonly mistaken for UFO’s.
Winds
Since winds are altered by specific landforms such as mountains it is important to understand localized patterns. Pay attention to trends that may be recurring in your area of wilderness travel. Winds can often travel twice as fast through gaps such as mountain passes. Vegetation is also an indicator of winds common to the area. Shorter and sparser vegetation indicates the terrain is frequented by harsh winds. Winds will commonly reach their maximum during the hours of midnight to early morning according to the 7th edition of Mountaineering, Freedom of the Hills, when the land cools and air flows down slope in a gravity wind.
Storm Indicators
Approaching storms may give a variety of clues to the keen observer, but changes in cloud cover, wind direction and speed and changes in air pressure are key factors. If you carry a barometer, which measures air pressure, you will have a great warning as to the pressure systems approaching. Generally low pressure systems are the ones to look out for, though rapidly building high pressure can bring strong winds.
Plan and Prepare
Be checking the positions of high and low pressure systems, and fronts before you set out into the backcountry. Websites such as www.noaa.gov are an excellent source. More importantly once you have collected information and learned a bit about how weather works, how you use that knowledge is more important. Pack your layers and equipment accordingly as well, weather is only bad if you aren't equipped for it.
