Most fronts are preceded by a variety of higher altitude cloud types. Those types of clouds can be used by pilots to determine what the macro level weather pattern may suggest for the coming hours or days.
Mare’s tails: Thin, white to light-gray streamer clouds high in the sky (cirrus clouds). Iso- lated mare's tails aren't a strong portent of bad weather to come, but dense and wide- spread mare's tails can indicate the approach of a front from as far as 24 to 48 hours away.
Cirrostratus: Uniform, featureless, white or gray clouds at high altitude covering most or all of the sky. These clouds usually mean that a significant amount of moisture is moving into the area. They aren't spectacular, but they are important. Monitor the sky for a change in the weather.
Halos: Rings of light around the sun or moon caused by light refracted through high altitude ice crystals. The old adage about halos preceding storms by 24 to 48 hours generally holds true in the wetter regions of the United States, but sometimes in drier climates halos can pass with no ill weather side effects.
Altostratus: Gray, water-droplet clouds at medium altitude. A solid coverage of these gunmetal-gray clouds usually precedes major weather systems by less than ten hours.
Nimbostratus: A layer of dark clouds with noticeable blurring below the cloud bases. These clouds bring rain or snow, and in the warmer months can develop into thunder- storms. Typically associated with the arrival of a front. The weather is likely to stay bad for 24 hours.