PPL – Weather Questions and Answers Graded A+

PPL – Weather Questions and Answers Graded A+ General characteristics of air flows around high/low pressure systems in the Northern Hemisphere Low Pressure - inward, upward, and counterclockwise High Pressure - outward, downward, and clockwise What is a trough? An elongated area of relatively low atmospheric pressure. At the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground; it must go upward. Therefore, a low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather. What is a ridge? An elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather. Standard temperature and pressure at sea level? 29.92 inches of mercury, 1013.2 millibars, 15 degrees Celsius/59 degrees Fahrenheit What are isobars? An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure. Isobars are lines labeled in millibars used to plot pressure readings on weather maps and connect points of equal pressure. The pattern reveals the pressure gradient (change in pressure over a distance). Also help to identify pressure systems. If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide? The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds. A shallow pressure gradient (isobars not close together) usually means wind speeds will be less. What causes winds aloft to flow parallel to the isobars? The Coriolis force (caused by Earth's rotation) Why do surface winds generally flow across the isobars at an angle? Surface friction For every 1000' you climb, the pressure drops by: 1 inch Hg What is a dew point? The temperature to which air must be cooled to become saturated. When temperature and dew point are close together (within 5 degrees), what type of weather is likely? Visible moisture in the form