Rainy and wet conditions, even in warmer, springlike weather, can cause hypothermia. That's because the body loses heat 25 times faster in water than in air of the same temperature. When working outdoors, particularly in the rainy months of early Spring, it's important to have the proper outerwear to protect from these conditions.
High-quality waterproof and/or windproof outer clothing is a necessity, particularly in the construction industry where workers are exposed to the elements for long periods of time. It is critical that rain gear be put on prior to exposure to wet or damp conditions as wet clothing extracts heat from the body as much as 240 times faster than dry clothing. For this same reason, the best choice of inner clothing to wear is made of polypropylene, which can retain warmth even when wet. Keep in mind that being wet from perspiration is as dangerous and being wet from the elements.
Remember, if you do not have adequate gear to stay warm and dry, terminate your exposure to the elements and get out of the wind and/or rain. Once hypothermia begins to set it, it can cause mental confusion making taking appropriate action more difficult.