Weather Flashcards
What are the standard temperature and pressure at sea level?
15°C temperature and 29.92 inches of mercury pressure
The standard atmosphere serves as a reference point for aviation, with temperature starting at 15°C at sea level and decreasing by 2°C per 1000 feet in the troposphere (up to 36,090 ft). Pressure begins at 29.92 inches of mercury and decreases by approximately 1 inch per 1000 feet. These standard values are crucial for aircraft performance calculations and altimeter settings.
What forces influence wind movement and how do they interact?
Pressure gradient, Coriolis effect, and friction
Wind movement results from the interaction of three main forces. The pressure gradient force moves air from high to low pressure (like air escaping a soda bottle). The Coriolis effect deflects moving air to the right in the Northern Hemisphere due to Earth’s rotation. Friction affects wind near the surface, causing it to move at an angle to isobars rather than parallel to them as at higher altitudes.
What are the main types of clouds and what do they indicate?
Stratus (stable, layer-like) and Cumulus (unstable, buildups)
Stratus clouds appear as smooth layers or blankets, indicating stable air conditions. Cumulus clouds are characterized by vertical development and indicate unstable, turbulent air. Cumulonimbus (CB) clouds are thunderstorm clouds that can grow extremely tall (over 60,000 ft) and present multiple aviation hazards including turbulence, downdrafts, and icing.
What are the essential components for thunderstorm formation?
Moisture, instability, and lift
Thunderstorms require three key ingredients to form: moisture (water vapor in the air), instability (unstable air mass that promotes vertical motion), and lift (a forcing mechanism to push air upward). When these three elements combine, they can create powerful storms that pilots must avoid due to multiple hazards including turbulence, windshear, microbursts, icing, and lightning.
How do METARs and TAFs differ, and what information do they provide?
METARs report current conditions, TAFs forecast future conditions
METARs (Meteorological Aerodrome Reports) provide current weather observations including winds, visibility, clouds, temperature, and pressure. They’re typically issued hourly with special updates (SPECIs) as needed. TAFs (Terminal Area Forecasts) predict weather conditions over a specified period, usually 24-30 hours, helping pilots plan future flights.
What is wind shear and why is it significant?
Sudden changes in wind direction or speed that can significantly affect aircraft performance
Wind shear is particularly dangerous because unlike steady winds, which don’t affect airspeed, sudden changes in wind direction or speed can dramatically impact aircraft performance. This is especially critical during takeoff and landing phases when aircraft are operating at lower speeds and altitudes with less time to recover from unexpected changes.
What constitutes a ceiling?
The lowest BKN (broken) or OVC (overcast) cloud layer
Cloud coverage is reported using specific terms: FEW (1/8-2/8), SCT (3/8-4/8), BKN (5/8-7/8), and OVC (8/8). Only broken (BKN) or overcast (OVC) layers constitute a ceiling, which is crucial for determining if conditions meet VFR requirements. While scattered clouds at low altitudes might make flying challenging, they don’t technically create a ceiling.
What is dew point and why is it important for aviation?
Temperature at which air becomes saturated and condensation begins
Dew point indicates when air becomes fully saturated with moisture, leading to condensation in the form of dew, fog, or clouds. Understanding dew point is crucial because when temperature approaches dew point, especially on moist days, conditions can quickly deteriorate with fog formation. This relationship between temperature and dew point helps pilots anticipate potential visibility issues.
How do winds flow around pressure systems?
High pressure: clockwise, Low pressure: counterclockwise (in Northern Hemisphere)
Like opening a soda bottle, air moves from high pressure to low pressure. However, due to the Earth’s rotation (Coriolis effect) and friction, the winds flow clockwise around high pressure systems and counterclockwise around low pressure systems in the Northern Hemisphere. At high altitudes, winds flow nearly parallel to the isobars (lines of equal pressure), while near the surface, friction causes winds to cross the isobars at an angle toward lower pressure. Understanding these patterns helps pilots predict likely wind conditions along their route.
How would you decode this METAR: KJFK 121651Z 18010KT 10SM SCT020 20/15 A2992
JFK airport, 12th at 1651Z, wind 180° at 10kts, 10 mile visibility, scattered clouds at 2000ft, temp 20°C dew point 15°C, altimeter 29.92
This standard METAR format shows current conditions at JFK. Breaking it down: KJFK is the identifier, 121651Z gives the day (12th) and time (1651 UTC/Zulu), wind is from 180° at 10 knots, visibility is 10 statute miles, clouds are scattered at 2,000 feet above ground level, temperature is 20°C with a dew point of 15°C, and altimeter setting is 29.92 inches of mercury.
