Aviation Weather Sources and Effects on UAS Performance
Reading the products
Two products carry most of the weight. A METAR is an observation issued about once an hour (roughly 50–55 minutes past the hour) describing current conditions; a TAF is a forecast valid 24 or 30 hours, issued four times daily at about 00Z, 06Z, 12Z, and 18Z. Both use UTC, and U.S. reports use statute miles. Decode the pieces: 27015G22KT is wind from 270° at 15 knots gusting 22; 3SM is visibility; BKN020 is a broken ceiling at 2,000 ft. The ceiling is the lowest broken or overcast layer - a scattered layer is not a ceiling. Sources include aviationweather.gov, 1800wxbrief.com, 1-800-WX-BRIEF, and on-site AWOS/ASOS or ATIS.
How weather changes UAS performance
High temperature, high elevation, and high humidity raise density altitude, cutting lift and thrust, degrading climb and endurance, and lengthening takeoff rolls for fixed-wing UAS. Wind changes groundspeed for a given airspeed, which changes range and battery reserve. Gusts, turbulence, and wind shear overwhelm small airframes and gimbals. Cold saps lithium batteries. Visible moisture at freezing temperatures means airframe icing on props and wings. Thunderstorms and microbursts are no-go; a dew point spread under about 5°F hints at fog.
Traps
Students confuse observation with forecast, mix Zulu with local time, or mistake a scattered layer for a ceiling. Remember that Part 107's own minimums - 3 SM visibility and 500/2,000 cloud clearance - are separate from the METAR's flight category.
Rule of thumb
METAR is now, TAF is next; if the numbers cannot support 3 SM and 500/2,000, do not launch.