Three hikers go for a short hike on a sunny day in July. There's no snow in sight, and they're only planning on a few hours out in the daylight. Temperature forecasts tell them that it will reach a high of 30°C, so they wear shorts, and bring lots of water. Why should they worry about being cold?

Several events can happen that would make the above scenario involve hypothermia.

What the weather forecast did not tell them is this:the high predicted was for sea level in Vancouver, and they were hiking on the north side of a mountain. The north side is shady, and the altitude decreases the temperature. More exposure to wind also cools the air. The cooler air causes warm air from lower altitudes to condense, and fog or drizzle can happen.

The hike goes on longer that planned, and it gets dark, since the hikers have not brought a flashlight they continue in the dark, and one of them sprains her evening gets cooler and it begins to drizzle. Dressed in tshirts and shorts, and moving slowly, all three quickly begin to shiver. In the dark, and feeling desperate, they call for help.

1 hour later when SAR members arrive on scene, they find three slightly hypothermic patients. What started as a simple sprained ankle is now three patients, none of whom can walk out on their own. SAR members spend the evening rewarming the patients, and walk them out the next day.

Things to remember about Hypothermia:

rain, wind, elevation and terrain have a significant effect on the temperature. Dress for the current conditions but remember the forecast is for the urban areas, and the wilderness can be very different, even very close to town.
the amount of food or water you've eaten affects your body's ability to maintain it's temperature.
a person can become hypothermic in very mild temperatures, even just 1 or 2 degrees below room temperature. Wind and rain magnify the effects of colder air.

slurred speech
apathy, lack of energy
stiff limbs

stay dry, remove and replace wet clothes
stay hydrated and well fed, calories keep you warm
wear a hat
be prepared