| Importance of Aviation Weather | | | | whenever possible. |
| Even novice pilots understand that weather | | | | Lightning strikes are actually not the most |
| affects a plane in flight very differently than it | | | | dangerous aspect of thunderstorms. Severe |
| affects a car driving down the freeway. Although | | | | updrafts in a thunderstorm can overstress an |
| weather conditions can compromise your safety | | | | aircraft's airframe, and violent hailstorms often |
| both in the air and on the road, the stakes are | | | | associated with thunderclouds can cause damage |
| higher in flight because you can't pull over to the | | | | to an aircraft's skin and windshield. |
| shoulder if the severity of weather exceeds your | | | | Squall Lines |
| abilities. To better understand the forces that | | | | Thunderstorms can line up along a weather front, |
| weather exerts on planes, it's important to realize | | | | creating a squall line. Aircraft must navigate |
| that the atmosphere is not empty space. Heat | | | | around squall lines, sometimes taking them |
| from the sun and friction from the earth's surface | | | | hundreds of miles off their intended course. Flight |
| act upon the gases and water in the air, creating | | | | Simulator will create squall lines if they currently |
| a variety of weather conditions. | | | | exist when you click on the Real-world weather |
| A number of factors—wind, cloud layers, | | | | option in the Weather dialog box. If you click on |
| temperature, dew point, barometric pressure, and | | | | the Weather themes option, you can also select |
| visibility—affect your Flight Simulator | | | | the Squall Line theme. If you want to create your |
| experience. You've probably heard your local | | | | own squall lines, you'll have to create |
| weather forecaster use these terms, but as a | | | | thunderstorms along a line of weather stations by |
| pilot, it's important that you understand their | | | | clicking on the Customize button under the |
| precise meanings. | | | | User-defined weather option. |
| Wind | | | | Cirrus |
| Wind is one of the basic weather factors | | | | Cirrus clouds are characterized by a wispy |
| affecting flight. Depending on its severity, wind | | | | appearance and very high altitude. Cirrus are |
| can be a nuisance—pushing you off course by | | | | composed of ice crystals. Aircraft don't often fly |
| affecting your heading, airspeed, or altitude—or | | | | at the extreme altitudes at which the cirrus |
| a true hazard, creating dangerous flight conditions. | | | | reside. |
| Wind can also make takeoffs and landings more | | | | Cold and Warm Fronts |
| challenging if it's not aligned with the active | | | | Cold fronts aren't necessarily cold. It's actually just |
| runway. And, although it seems basic, remember | | | | the boundary between a mass of cold air and a |
| that if you're flying into the wind, you're going to | | | | mass of warm air in conditions where the cold air |
| fly slower; flying with the wind will move you | | | | is moving in to replace the warm air. In the |
| along faster. | | | | summer, the "cold" air is just cooler than the |
| Friction on the ground acts as a kind of brake on | | | | warm air and may not seem cold to you at all. |
| the wind. Weather systems don't move in a | | | | Warm fronts are just the opposite; a warm air |
| straight line and often rotate, so wind in one area | | | | mass moving in to replace cooler air. |
| may not be blowing in the same direction as wind | | | | Cold fronts are represented on weather maps |
| in another area nearby. Winds can also change | | | | such as those that you'll find in Flight Simulator's |
| quickly across a weather front. Because there can | | | | Weather dialog box as a blue line with triangles |
| be dramatic differences between the direction | | | | pointing in the direction the front is moving. Warm |
| and velocity of the wind on the ground and at | | | | fronts are represented by red lines. You will only |
| high altitude, aviation weather reports include | | | | see fronts depicted on the map when you use |
| information on both surface winds and winds aloft. | | | | Real-world Weather. As a pilot, you need to be |
| Wind shear refers to situations when the wind | | | | aware of how cold and warm fronts affect the |
| direction and speed are shifting rapidly over a | | | | conditions you'll be flying in. The cloud conditions |
| short distance. Encountering wind shear on final | | | | and weather you'll encounter once the front |
| approach to landing can add unwelcome | | | | passes depend on the stability and moisture |
| excitement to your flight. If the wind shifts | | | | content of the air mass the front is replacing. You |
| dramatically from a headwind to a tailwind, for | | | | won't create fronts using the User-defined |
| example, you may experience severe | | | | weather option, but you'll see fronts (as well as |
| downdrafts. Because a plane's airspeed is already | | | | high and low pressure areas) depicted on the |
| relatively low on approach to landing, wind shear | | | | weather map when using the Real-world weather |
| can create a dangerous situation. | | | | option. |
| You also need to exercise care when taking off | | | | Pressure Changes |
| or landing in crosswinds, and you'll need to adjust | | | | Barometric pressure is important to pilots for two |
| your navigation if wind coming from one side | | | | reasons: it affects how the plane's altimeter |
| blows you off track. If you're flying into a | | | | works and it affects the weather. In order to |
| headwind, you'll need to keep fuel consumption in | | | | measure how high above sea level your aircraft |
| mind so that your plane doesn't run out of fuel | | | | is, its altimeter is set to local barometric pressure. |
| before reaching your destination. | | | | When an air traffic controller says, "Altimeter is |
| Knowing the current conditions of winds aloft can | | | | 2992" she's saying the local barometric pressure is |
| help you plan your route and altitude to either | | | | 29.92 inches of mercury. She's also telling the pilot |
| take advantage of a tailwind or to avoid the | | | | to set the Kollsman window of the altimeter to |
| worst of a headwind. Let's say the wind at an | | | | read 2992. The reading in feet or meters on the |
| altitude of 15,000 feet is blowing 360 degrees at | | | | altimeter is known as pressure altitude. |
| 15 knots and the wind at 25,000 feet is blowing | | | | Dew Point |
| 320 degrees at 30 knots. Assume for this | | | | You really don't need to care about dew, unless |
| example that your course for the flight is 340 | | | | you're sleeping under your airplane's wing. But |
| degrees. | | | | when you're planning a flight you should care |
| Assuming further that the aircraft you choose to | | | | about the dew point—the temperature to |
| fly performs well at either altitude, you might | | | | which the air must be cooled to reach saturation. |
| want to plan your flight for 25,000 feet, since | | | | The air around us contains invisible moisture |
| you'll get a speed boost from a quartering tailwind | | | | known as water vapour. The difference between |
| (a quartering wind comes at you from 45 | | | | a location's temperature and its dew point |
| degrees off your tail or nose). If your course was | | | | indicates how well the air can currently hold |
| 160 degrees, you might plan to fly at 15,000 feet | | | | moisture. Because cool air has a harder time |
| to minimize the effect of a quartering headwind. | | | | holding moisture than warm air, pilots use this |
| When using the Real-world weather or Weather | | | | information to determine how likely it is that fog, |
| themes options in Flight Simulator's Weather dialog | | | | clouds, or precipitation will form. |
| box (an option within the Create a Flight dialog | | | | The temperature/dew point spread is usually |
| box), surface winds and winds aloft will be set for | | | | given in terms of a percentage of relative |
| you. You can set surface winds and winds aloft | | | | humidity. For example, if the temperature is 72 F |
| yourself using the User-defined weather option. | | | | (22 C) and the dew point is 52 F (11 C), the |
| Cloud Types | | | | relative humidity is 49 percent. Using this example, |
| Even to the most casual observer, scattered, | | | | the air is 49 percent saturated with moisture. |
| puffy clouds are obviously different than solid | | | | When the air is cooled to a point where it reaches |
| overcast conditions. But there's more to it than | | | | 100 percent saturation, the water vapour |
| simple scenery. Clouds vary in appearance due to | | | | condenses, forming clouds. If the temperature |
| the different atmospheric conditions that cause | | | | falls further, water drops form and fall to the |
| them to form. Understanding the conditions that | | | | ground as rain or, if it's cold enough, ice or snow. |
| create certain cloud types helps pilots determine | | | | The presence of clouds does not guarantee |
| what conditions they may encounter up ahead. | | | | precipitation, but the presence of precipitation |
| Conversely, researching weather conditions ahead | | | | guarantees there are clouds in the area. In Flight |
| of time can give pilots an idea of what kinds of | | | | Simulator, the Automated Terminal Information |
| cloud layers to expect during flight. | | | | Service (ATIS) reports the current temperature |
| Stratus | | | | and the dew point. The closer the dew point is to |
| Because the air in which stratus clouds form is | | | | the current temperature, the more likely you're |
| relatively stable, stratus layers have a flat, even | | | | going to encounter clouds. If you're flying into an |
| appearance and cover much of the sky. Although | | | | area where the temperature is 80 F (29 C) and |
| you will likely enjoy a smooth ride in these | | | | the dew point is 65 F (18 C), you don't need to |
| conditions, visibility is often less clear when the air | | | | worry about a thick layer of clouds blanketing the |
| is stable. Smoke, smog, and moisture can stay | | | | area. If the temperature is 65 F and the dew |
| suspended in stable air, reducing visibility. (You can | | | | point is 60 F (15 C), watch for clouds. |
| use the Visibility setting to determine the visibility | | | | You can set the temperature and dew point for |
| distance; the type of cloud formations alone will | | | | any temperature layer in Flight Simulator. In |
| not affect visibility.). | | | | practical terms, this means you can create |
| Stratus clouds can be high and transparent, or low | | | | conditions where it is more or less likely that |
| and dark grey. The lowest layers of stratus, | | | | clouds will form (although Precipitation is a |
| nimbostratus clouds, are rain clouds. Higher, | | | | separate setting within User-defined weather). Be |
| less-dense stratus layers can produce rain, but it | | | | aware that setting a low cloud layer in Flight |
| tends to be more showery than the drizzle | | | | Simulator weather will not constitute a layer of |
| produced by low stratus layers. | | | | fog. To create fog-like conditions, modify the |
| Cumulus | | | | Visibility settings using the User-defined weather |
| Cumulus clouds are the puffy, pretty ones.They | | | | option. |
| aren't, however, always benign. Cumulus clouds | | | | Density Altitude |
| form in unstable air, which allows them to have | | | | Density altitude is pressure altitude corrected for |
| greater vertical development than stratus clouds. | | | | temperature. When the temperature is high, air is |
| Most frequently they have flat bases and lumpy | | | | less dense. Density altitude affects aircraft |
| tops, and form below 6,000 feet (1,828 meters). | | | | performance: An increase in density altitude |
| The more unstable the atmosphere, the higher | | | | corresponds to a decrease in engine power |
| cumulus can build. | | | | output, propeller efficiency, and aerodynamic lift. |
| Cumulonimbus | | | | Density altitude is normally computed using graphs |
| Cumulonimbus clouds can tower to greater than | | | | in the pilot operating handbook for each aircraft, |
| 50,000 feet (15,240 meters). Cumulonimbus are | | | | but for simplicity's sake, just be aware that if the |
| the clouds that make thunderstorms.Unstable | | | | weather is hot, your aircraft's performance will |
| atmosphere with rapidly rising masses of air | | | | likely suffer. Turbine engine aircraft and |
| creates the conditions necessary for thunder and | | | | turbocharged reciprocating engines suffer less, but |
| lightning. Pilots should avoid these hazards | | | | density altitude is still a factor. |