Meteorology and Weather Products
The Weather Chain
A dispatcher assembles a picture from observations (METAR/SPECI), forecasts (TAF), and remote or supplemental data: PIREPs, radar, satellite, winds and temperatures aloft, AIRMETs, SIGMETs, and convective outlooks. Memorize the METAR/TAF syntax cold, because exam questions hinge on decoding rather than interpretation.
AIRMETs cover moderate hazards: Sierra (IFR conditions and mountain obscuration), Tango (moderate turbulence and strong surface winds), Zulu (moderate icing and freezing level). SIGMETs cover severe or extreme conditions; convective SIGMETs address thunderstorms and related hazards.
Ceiling is the lowest broken or overcast layer, or vertical visibility into an obscuration - few and scattered layers are not ceilings. Distinguish prevailing visibility from RVR. Winds in METAR/TAF are referenced to true north; surface winds passed by tower/ATIS are magnetic - a classic trap.
Standard Atmosphere
Sea level 29.92 inHg and 15 °C, with a lapse rate near 2 °C per 1,000 ft. Pressure altitude = (29.92 − altimeter setting) × 1,000 + field elevation. Density altitude climbs with heat, humidity, and low pressure, and degrades every performance number in the release.
Worked Example
KJFK 121851Z 24015G25KT 2SM +RA BR BKN008 OVC015 18/17 A2985. Translation: wind 240° at 15 gusting 25, 2 SM visibility in heavy rain and mist, ceiling 800 ft overcast 1,500 ft. With a 500-ft field elevation, pressure altitude is (29.92 − 29.85) × 1,000 + 500 ≈ 570 ft - low, but the 800-ft ceiling is what threatens the alternate requirement.