Weather Theory

steadily from the inflow of relatively warmer air. For the most Symbols for surface fronts and other significant lines part, the dew point remains steady and the pressure levels off. shown on the surface analysis chart After the passage of a warm front, stratocumulus clouds Warm front (red)* predominate and rain showers are possible. The visibility Cold front (blue)* eventually improves, but hazy conditions may exist for a short period after passage. The wind blows from the south- Stationary front (red/blue)* southwest. With warming temperatures, the dew point rises and then levels off. There is generally a slight rise in Occluded front (purple)* barometric pressure, followed by a decrease of barometric * Note: Fronts may be black and white or color depending on their pressure. source. Also, fronts shown in color code do not necessarily show frontal symbols. Flight Toward an Approaching Warm Front Figure 12-24. Common chart symbology to depict weather front By studying a typical warm front, much can be learned location. about the general patterns and atmospheric conditions that exist when a warm front is encountered in flight. Light to moderate precipitation is probable, usually in the Figure 12-25 depicts a warm front advancing eastward from form of rain, sleet, snow, or drizzle, accentuated by poor St. Louis, Missouri, toward Pittsburgh, Pennsylvania during visibility. The wind blows from the south-southeast, and the a flight from Pittsburgh to St. Louis. outside temperature is cool or cold with an increasing dew point. Finally, as the warm front approaches, the barometric At the time of departure from Pittsburgh, the weather is good pressure continues to fall until the front passes completely. VFR with a scattered layer of cirrus clouds at 15,000 feet. As the flight progresses westward to Columbus and closer During the passage of a warm front, stratiform clouds are to the oncoming warm front, the clouds deepen and become visible and drizzle may be falling. The visibility is generally increasingly stratiform in appearance with a ceiling of 6,000 poor, but improves with variable winds. The temperature rises feet. The visibility decreases to six miles in haze with a falling CIRRUS CIRROSTRATUS R AI ALTOSTRATUS M R A W NIMBOSTRATUS COLD AIR Indianapolis Columbus Pittsburgh St. Louis 200 miles 400 miles 600 miles 999 1002 1005 1008 1011 1014 METAR KSTL 1950Z 21018KT 1SM –RA 1017 0VC010 18/18 A2960 999 6 6 5 1 5 10 0 1 2 S 0 0 t. Louis 5 5 9 3 9 20 0 4 6 0 8 5 5 6 6 0 60 1 2 2 6 5 5 1 3 3 0 4 1 1 6 8 6 M E T A R K B I K N N D 0 20 1 950Z 1 1 6 5 0 /1 1 5 2 K T 3 A S 2 M 97 3 RA 1002 Indianapolis Columbus Pittsburgh METAR KCMH 1950Z 13018KT 6SM HZ 0VC060 14/10 A2990 METAR KPIT 1950Z 13012KT 10SM 1005 SCT150 12/01 A3002 1008 1011 1014 1017 Figure 12-25. Warm front cross-section with surface weather chart depiction and associated METAR. 12-19