Get full access to Outside Learn, our online education hub featuring in-depth fitness, nutrition, and adventure courses and more than 2,000 instructional videos when you sign up for Outside+ Sign up for Outside+ today.
Lightning over Arches National Park (Photo by Anthony Quintano)
Read the Clouds
The higher the clouds, the better the weather will be. High clouds (in jet territory, above 20,000 feet; thin and wispy) indicate higher atmospheric pressure and dry air, both signs of fair weather. Light breezes are the norm.
Altostratus clouds will grow gray, darken, and thicken when rain is on the way. An easterly wind often develops as well.
Cumulus clouds are the large, white fluffy clouds that develop midday at lower levels of the atmosphere. They indicate fair weather when they’re widely separated. When they come together to form larger, towering cumulonimbus clouds, rain is likely.
Nimbostratus clouds are low blankets of gray or very dark clouds, which often obstruct the horizon and foretell a prolonged rain.
A halo around the sun or moon often indicates an approaching storm, usually 24 to 36 hours away. High-altitude ice particles form this optical phenomenon.
Insects disappear an hour before a storm.
If you see a rainbow in the west in the morning, rain is likely.
Figure Out Fronts
Colliding air masses are known as fronts, and they cause stormy weather. Use your altimeter to determine changes in air pressure and you can predict what will happen. If your altimeter shows a rise in elevation even though you haven’t moved, it means the barometric pressure has fallen. A fall in elevation signals rising barometric pressure
A warm air mass arrives and rises slowly above the cold air ahead.
Signs Low barometric pressure, high humidity, low cloud ceiling
Result Fairly calm winds; steady rain for days.
Fast-moving, unstable cold air pushes under the warm air ahead, forcing it up quickly and cooling it. Signs High barometric pressure, high cloud ceiling, good visibility unless precipitation is present Result Fair weather that can change quickly; strong winds, generally from the north or west; and severe but brief thunderstorms or snow squalls
A fast-moving cold front overtakes a warm front, lifting (occluding) the warm air mass. But then a different, incoming cold front collides with the departing cold air mass. Depending on the temperature differential between the two cold fronts, the incoming front will move either above or below the warm front. Signs Wind direction changes, usually it blows from the north-northwest; falling, then rising barometric pressure Result Storms possible; light to heavy rain followed by dry weather after the front exits.
Become an expert: Get our pocket guide Predicting Weather by Lisa Densmore ($13; falcon.com).