Part 107 Weather Minimums - Memorize These
All three must be met simultaneously. These are legal minimums - good aeronautical decision-making (ADM) means often staying well above them, especially for commercial operations over populated areas or equipment with limited safety margins.
Important: Visibility is measured from your control station, not necessarily from the drone's position. If you can only see the drone but visibility in the operating area is below 3 SM, you do not meet the minimum.
How to Decode a METAR
A METAR (Meteorological Aerodrome Report) is issued hourly by weather stations at airports. Reading a METAR is a core skill for the Part 107 exam. Here is a sample METAR and a field-by-field decode:
Operational analysis of this METAR: Visibility is 7 SM (above 3 SM minimum Correct:). Ceiling is broken at 3,500 ft. If flying below 3,000 ft (500 ft below the 3,500 ft ceiling), cloud clearance is met Correct:. Rain is light. Gusty winds at 22 knots may be near or over some drones' wind limits. Overall: likely flyable within Part 107 minimums, but the pilot must verify the drone's wind rating and whether the ceiling interpretation is correct for the intended operation altitude.
Sky Condition Coverage Codes
| Code | Meaning | Cloud Coverage |
|---|---|---|
| SKC / CLR | Sky clear / Clear below 12,000 ft | 0/8 sky coverage |
| FEW | Few clouds | 1/8 to 2/8 coverage |
| SCT | Scattered | 3/8 to 4/8 coverage |
| BKN | Broken - this IS a ceiling | 5/8 to 7/8 coverage |
| OVC | Overcast - this IS a ceiling | 8/8 (complete) coverage |
| VV | Vertical visibility - reported when sky is obscured (fog, smoke, etc.) | Sky obscured |
Ceiling definition: The lowest broken (BKN) or overcast (OVC) layer, or vertical visibility (VV), is the ceiling. FEW and SCT layers are NOT ceilings. For Part 107, the ceiling determines whether you can maintain 500 ft of vertical clearance below clouds.
How to Read a TAF
A TAF (Terminal Aerodrome Forecast) is a weather forecast for a specific airport, valid for 24-30 hours and issued four times per day. TAFs use the same coded elements as METARs but include change group indicators:
| TAF Change Indicator | Meaning |
|---|---|
| FM (From) | A complete change in conditions starting at the specified time; replaces previous forecast |
| BECMG (Becoming) | Conditions gradually changing to the forecast value during the specified period |
| TEMPO (Temporary) | Fluctuating conditions expected to last less than 1 hour at a time and less than half the period |
| PROB30 / PROB40 | 30% or 40% probability of the following conditions occurring during the specified period |
TAF study tip: For exam questions, identify the valid period of the TAF, locate the relevant time window for your planned flight, and read the forecast conditions (including any TEMPO or BECMG changes) that apply during that window.
Density Altitude and UAS Performance
Density altitude is pressure altitude corrected for non-standard temperature. When density altitude is high, the air is thinner - which reduces lift and motor thrust, shortening flight times and slowing climb rates.
Factors that increase density altitude (and reduce performance):
- High elevation: Less air pressure at higher airports or terrain
- High temperature: Hot air is less dense than cold air
- High humidity: Water vapor displaces denser air molecules
- Low atmospheric pressure: Below-standard pressure reduces air density
Exam rule of thumb: "HHHL" - High elevation, High temperature, High humidity, Low pressure = High density altitude = Reduced performance.
For drone pilots, high density altitude means the aircraft may require more battery power to maintain hover, may have a lower maximum payload, and will have reduced emergency performance margins. For a deeper review of payload, battery, and weight-and-balance effects, see the Performance & Loading Guide. Always check manufacturer performance charts for high-altitude operations.
Aviation Weather Hazards for Drone Operations
| Hazard | What It Is | Risk to Small UAS |
|---|---|---|
| Thunderstorms | Convective storms with lightning, heavy rain, hail, and severe turbulence | Extreme - never fly within or near a thunderstorm. Rapid wind changes and downdrafts can exceed any drone's limits. |
| Microbursts | Intense, localized downdraft from a thunderstorm lasting 1-5 minutes | Extreme - can push a drone into the ground within seconds. Downdraft winds can exceed 100 knots. |
| Wind shear | Sudden change in wind speed or direction over a short distance | High - can cause sudden loss of altitude or control, especially on approach or departure. |
| Low ceilings / fog | Reduced or zero visibility due to clouds near the surface or fog | High - if ceiling drops to drone altitude, visual line of sight and cloud clearance minimums are violated. |
| Icing | Ice accumulation on rotors, wings, or sensors | High - most consumer drones have no anti-icing capability. Icing degrades lift and can cause failure. |
| High surface winds | Sustained winds or gusts exceeding drone limits | Moderate to high - check the manufacturer's rated wind resistance; gusts are the main risk. |
| Density altitude | Thin air at high elevation or temperature | Moderate - reduced performance and shorter flight times. |
| Temperature inversions | Warm air layer over cool air, trapping pollutants and reducing visibility | Moderate - can create low visibility layers and unusual wind patterns. |
Other FAA Weather Products to Know
- PIREP (Pilot Report): Reports from pilots of actual conditions encountered - turbulence, icing, visibility. Coded as UA (routine) or UUA (urgent).
- SIGMET (Significant Meteorological Information): Warns of severe weather: hurricanes, severe or extreme turbulence, severe icing, or widespread dust/sandstorms.
- AIRMET (Airmen's Meteorological Information): Less severe than SIGMETs; warns of moderate icing (AIRMET Sierra), moderate turbulence (AIRMET Tango), or IFR conditions / low visibility (AIRMET Sierra).
- Winds Aloft Forecasts (FB): Forecast wind speed, direction, and temperature at various altitudes - useful for flight planning at any altitude.
- Prog Charts: Forecast surface analysis charts showing fronts, pressure systems, and forecast precipitation.
Weather Fronts and UAS Implications
| Front Type | Characteristics | Associated Weather |
|---|---|---|
| Cold Front | Cold air advancing, pushing warm air up steeply | Thunderstorms, heavy precipitation, rapid visibility changes, gusty winds. Often the most hazardous front for drone ops. |
| Warm Front | Warm air advancing over colder air, more gradual slope | Extended low ceilings, widespread fog, drizzle, and poor visibility over a large area. |
| Stationary Front | Front not moving significantly | Persistent bad weather: fog, low ceilings, and precipitation in the same area for extended periods. |
| Occluded Front | Cold front catches and lifts warm front | Complex, mixed weather with precipitation, moderate to poor visibility. |
Weather FAQ
What are the Part 107 weather minimums?
3 statute miles flight visibility from the control station, at least 500 ft below clouds, and at least 2,000 ft horizontally from clouds - all three must be met simultaneously.
What is a METAR?
A METAR is a Meteorological Aerodrome Report - a standardized coded weather observation issued hourly at airports. It reports wind, visibility, sky conditions, temperature, dew point, and altimeter setting.
What is a TAF?
A TAF (Terminal Aerodrome Forecast) is a 24-30-hour weather forecast for a specific airport, issued four times per day. It uses the same coded format as METARs plus change indicators (FM, BECMG, TEMPO, PROB30/40).
What does BKN mean in a METAR?
BKN stands for Broken - 5/8 to 7/8 sky coverage. A BKN layer IS a ceiling. The number after it (e.g., BKN035) is the height in hundreds of feet MSL - so BKN035 means a broken ceiling at 3,500 ft MSL.
What increases density altitude?
High elevation, high temperature, high humidity, and low atmospheric pressure all increase density altitude, reducing drone performance (less thrust, shorter flight times). The Performance & Loading Guide explains this as the HHHL shortcut.
Can I fly a drone if it's raining?
Legally, you may fly in rain as long as Part 107 weather minimums are met. Operationally, most drones are not waterproof, and rain reduces sensor performance and can cause equipment damage. The remote pilot-in-command must determine whether conditions are safe regardless of minimums.
More Part 107 Study Resources
Disclaimer: Launch107 is an independent study resource, not affiliated with or endorsed by the FAA. Always check official FAA weather sources and apply sound aeronautical decision-making before every flight. Verify current Part 107 rules at FAA.gov/uas.