barometric pressure. Approaching Indianapolis, the weather  deteriorates to broken clouds at 2,000 feet with three miles  visibility and rain. With the temperature and dew point the  same, fog is likely to develop. At St. Louis, the sky is overcast  with low clouds and drizzle and the visibility is one mile.  Beyond Indianapolis, the ceiling and visibility are too low  to continue VFR. Therefore, it would be wise to remain in  Indianapolis until the warm front passes, which may take  up to two days.  A cold front occurs when a mass of cold, dense, and stable  air advances and replaces a body of warmer air.  Cold fronts move more rapidly than warm fronts, progressing  at a rate of 25 to 30 mph. However, extreme cold fronts  have been recorded moving at speeds of up to 60 mph.  A typical cold front moves in a manner opposite that of a  warm front. It is so dense, it stays close to the ground and  acts like a snowplow, sliding under the warmer air and  forcing the less dense air aloft. The rapidly ascending air  causes the temperature to decrease suddenly, forcing the  creation of clouds. The type of clouds that form depends  on the stability of the warmer air mass. A cold front in the  Northern Hemisphere is normally oriented in a northeast to  southwest manner and can be several hundred miles long,  encompassing a large area of land.  Prior to the passage of a typical cold front, cirriform or  towering cumulus clouds are present, and cumulonimbus  clouds may develop. Rain showers may also develop due  to the rapid development of clouds. A high dew point and  falling barometric pressure are indicative of imminent cold  front passage.  As the cold front passes, towering cumulus or cumulonimbus  clouds continue to dominate the sky. Depending on the  intensity of the cold front, heavy rain showers form and may  be accompanied by lightning, thunder, and/or hail. More  severe cold fronts can also produce tornadoes. During cold  front passage, the visibility is poor with winds variable and  gusty, and the temperature and dew point drop rapidly. A  quickly falling barometric pressure bottoms out during frontal  passage, then begins a gradual increase.  After frontal passage, the towering cumulus and  cumulonimbus clouds begin to dissipate to cumulus clouds  with a corresponding decrease in the precipitation. Good  visibility eventually prevails with the winds from the west- northwest. Temperatures remain cooler and the barometric  pressure continues to rise.  Warm fronts and cold fronts are very different in nature as are  the hazards associated with each front. They vary in speed,  composition, weather phenomenon, and prediction. Cold fronts,  which move at 20 to 35 mph, travel faster than warm fronts,  which move at only 10 to 25 mph. Cold fronts also possess a  A pilot using sound judgment based on the knowledge of  frontal conditions will likely remain in Indianapolis until the  front has passed. Trying to fly below a line of thunderstorms  or a squall line is hazardous, and flight over the top of or  around the storm is not an option. Thunderstorms can extend  up to well over the capability of small airplanes and can  extend in a line for 300 to 500 miles.  At the time of departure from Pittsburgh, the weather is VFR  with three miles visibility in smoke and a scattered layer of  clouds at 3,500 feet. As the flight progresses westward to  Columbus and closer to the oncoming cold front, the clouds  show signs of vertical development with a broken layer at  2,500 feet. The visibility is six miles in haze with a falling  barometric pressure. Approaching Indianapolis, the weather  has deteriorated to overcast clouds at 1,000 feet and three  miles visibility with thunderstorms and heavy rain showers.  At St. Louis, the weather gets better with scattered clouds at  1,000 feet and a ten mile visibility.  Fast-moving cold fronts are pushed by intense pressure  systems far behind the actual front. The friction between  the ground and the cold front retards the movement of the  front and creates a steeper frontal surface. This results in a  very narrow band of weather, concentrated along the leading  edge of the front. If the warm air being overtaken by the  cold front is relatively stable, overcast skies and rain may  occur for some distance behind the front. If the warm air  is unstable, scattered thunderstorms and rain showers may  form. A continuous line of thunderstorms, or squall line,  may form along or ahead of the front. Squall lines present  a serious hazard to pilots as squall-type thunderstorms are  intense and move quickly. Behind a fast-moving cold front,  the skies usually clear rapidly, and the front leaves behind  gusty, turbulent winds and colder temperatures.  Like warm fronts, not all cold fronts are the same. Examining  a flight toward an approaching cold front, pilots can get a  better understanding of the type of conditions that can be  encountered in flight.  Figure 12-26  depicts a flight from  Pittsburgh, Pennsylvania, toward St. Louis, Missouri.  Fast-Moving Cold Front  Flight Toward an Approaching Cold Front  Cold Front  Comparison of Cold and Warm Fronts  12-20 