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Private pilot · ACS PA.I.C · lesson pack

Weather Information

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Why this one matters

Weather is behind a large share of fatal general aviation accidents, especially VFR flight into instrument conditions. Most of those flights started with a briefing that showed the risk. This task is about turning weather information into a clear decision, and having the discipline to stick to it in the air.

1 · Know these cold

  • •Before every flight, become familiar with all available information. For any flight that includes runway lengths and takeoff and landing distance data; for IFR or a flight not in the vicinity of an airport it also includes weather reports and forecasts, fuel requirements, alternatives, and known ATC delays.(14 CFR 91.103(a)-(b))
  • •Brief from FAA and NWS products: call Flight Service (1-800-WX-BRIEF), or self-brief through 1800wxbrief.com, aviationweather.gov or an EFB showing those products, in the standard-briefing order. Noting the time and source of your briefing is good practice.(AC 91-92; AIM 7-1-4)
  • •Observations tell you what is (METAR, SPECI, PIREPs); forecasts tell you what's expected (TAF, GFA, winds aloft, convective outlook).(Aviation Weather Handbook (FAA-H-8083-28))
  • •AIRMETs warn of conditions hazardous mostly to light aircraft (Sierra: IFR and mountain obscuration; Tango: turbulence, strong surface winds, low-level wind shear; Zulu: icing and freezing level). SIGMETs and Convective SIGMETs warn of more severe hazards.(Aviation Weather Handbook (FAA-H-8083-28))
  • •Thunderstorms need moisture, unstable air and a lifting force. Avoid any thunderstorm identified as severe, or giving an intense radar echo, by at least 20 miles, and treat every thunderstorm as hazardous.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services; AIM 7-1-27)
  • •Datalinked radar in the cockpit can be many minutes old: use it to stay far away from storms, never to pick a path through them.(AIM chapter 7, Meteorology)
  • •Set personal minimums before you look at the weather, and decide in advance what would make you divert.(Risk Management Handbook (FAA-H-8083-2A))

2 · The lesson

Where weather comes from
  • The National Weather Service produces the observations and forecasts; the Aviation Weather Center (aviationweather.gov) publishes the aviation products.(Aviation Weather Handbook (FAA-H-8083-28))
  • Choose the briefing type: a standard briefing when you have no earlier briefing (normally within about 6 hours of departure); an abbreviated briefing to update one you already have or answer one or two items (say when and where you got the first); an outlook briefing when departure is 6 or more hours away, for planning only, followed later by a standard or abbreviated one.(AIM 7-1-5; AC 91-92)
  • If a briefer says "VFR flight not recommended", treat it as a strong no-go signal and re-plan.(AIM 7-1-5)
  • A complete self-briefing from FAA/NWS products, on a website or an EFB, can meet 91.103; Flight Service is there to consult, not the only legal route. Know where your app's data comes from and how old it is.(AC 91-92; AIM 7-1-4)
The products
  • METAR: a routine hourly observation at an airport. SPECI: a special observation when conditions change significantly.(Aviation Weather Handbook (FAA-H-8083-28))
  • PIREP: what pilots actually encountered (turbulence, icing, cloud tops). Often the best information you'll get; give them too.(Aviation Weather Handbook (FAA-H-8083-28))
  • TAF: the forecast for 5 statute miles around an airport, usually for 24 or 30 hours.(Aviation Weather Handbook (FAA-H-8083-28))
  • Graphical Forecasts for Aviation (GFA): the set of observations and forecasts for the contiguous U.S. (clouds, weather, icing, turbulence and winds) that replaced the old text area forecast.(Aviation Weather Handbook (FAA-H-8083-28); AIM 7-1-7)
  • The SPC Convective Outlook forecasts the risk of severe thunderstorms by category (general thunderstorms, marginal, slight, enhanced, moderate, high) for Day 1, with Day 2 and 3 outlooks; it isn't just a chance of any thunderstorm.(AIM 7-1-7; SPC)
  • Surface analysis: fronts and pressure systems. Ceiling and visibility (CVA): current ceilings and visibility over an area.(Aviation Weather Handbook (FAA-H-8083-28))
  • Winds and temperatures aloft (FB): forecast winds and temperatures at set altitudes. No winds are forecast within 1,500 feet of the station elevation, no temperatures within 2,500 feet, and no temperature at the 3,000-foot level. A blank group means not forecast, not calm.(Aviation Weather Handbook (FAA-H-8083-28))
  • Convective outlook: the chance of thunderstorms over the next days. AIRMETs, SIGMETs and Convective SIGMETs: in-flight advisories for hazards.(Aviation Weather Handbook (FAA-H-8083-28))
  • Every product has limits: TAFs cover only near the airport, forecasts can be wrong, and observations are a snapshot. Cross-check them.(Aviation Weather Handbook (FAA-H-8083-28))
The weather itself
  • Stable air: stratiform clouds, smooth air, poor visibility in haze or fog. Unstable air: cumuliform clouds, turbulence, good visibility outside showers.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
  • Fronts mark boundaries between air masses; expect wind shifts, clouds and precipitation as one passes.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
  • Fog forms when temperature and dew point come together (it seldom forms with a spread over about 2°C): radiation fog on clear calm nights; advection fog when moist air moves over a cooler surface; upslope fog when air is pushed uphill; steam fog (sea smoke) when cold air moves over warm water; precipitation-induced fog when rain evaporates into cool air, common ahead of warm fronts; and ice fog in very cold air. It is reported as fog below 5/8 statute mile visibility, as mist (BR) above that.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services; Aviation Weather Handbook (FAA-H-8083-28))
  • Thunderstorms bring turbulence, hail, lightning, wind shear and microbursts. A microburst's downdraft and outflow can exceed an airplane's climb performance.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services; AIM chapter 7, Meteorology)
  • Structural icing needs visible moisture and temperatures at or below freezing. Light airplanes are usually not certified for icing: avoid it.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
  • Frost on the wings disrupts airflow and raises the stall speed: remove it all before takeoff.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
  • Mountain wave and strong winds over terrain cause severe turbulence and downdrafts on the lee side.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
Weather in the cockpit
  • ADS-B (FIS-B, 978 MHz UAT) and satellite weather show radar, METARs and TAFs in the cockpit. The age shown on NEXRAD is the age of the mosaic, and the weather in it can be 15 to 20 minutes older than that. Use it for strategic decisions 20 or more minutes ahead, never to thread between cells.(AIM 7-1-10, 7-1-11; NTSB Safety Alert SA-017)
  • In flight you also have Flight Service by radio for updates and hazardous weather, ATC hazardous-weather broadcasts, and ATIS, ASOS and AWOS at airports along the way.(AIM 7-1-5, 7-1-18)
  • Use cockpit weather for strategic decisions (stay far away, divert early), not tactical ones (picking a gap between cells).(AIM chapter 7, Meteorology)
Making the decision
  • Set personal minimums (ceiling, visibility, wind, crosswind) before checking the weather, based on your real experience.(Risk Management Handbook (FAA-H-8083-2A))
  • Decide in advance what would make you turn back or divert: lowering ceilings, a forecast that isn't verifying, a PIREP of icing or turbulence.(Risk Management Handbook (FAA-H-8083-2A))
  • Hazards like forecast icing or turbulence aloft, thunderstorms on the route, or marginal VFR at the destination are no-go or wait signals for a VFR pilot.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
  • Have an out: an alternate airport and enough fuel to use it.(PHAK (FAA-H-8083-25C), Weather Theory and Aviation Weather Services)
Reading METARs and TAFs
  • The ceiling is the lowest broken (BKN) or overcast (OVC) layer, or vertical visibility (VV) into an obscuration. Scattered (SCT) is not a ceiling.(AIM 7-1-30; PHAK (FAA-H-8083-25C), Ch. 13)
  • A TAF covers the area within 5 statute miles of the runway complex, is issued four times a day and is valid 24 hours (30 at some large airports). Read it by the change group in effect when you arrive: FM (a rapid change to new conditions), BECMG (a gradual change), TEMPO (temporary changes, each under an hour and in total less than half the period), PROB30/40 (a probability).(AIM 7-1-31; PHAK (FAA-H-8083-25C), Ch. 13)
  • A SPECI is an unscheduled METAR issued for a significant change, such as a ceiling or visibility crossing a threshold, a wind shift, or a thunderstorm beginning or ending.(AIM 7-1-29)
Advisories and when they apply
  • AIRMET Sierra: widespread ceilings below 1,000 feet and/or visibility below 3 miles, and mountain obscuration. Tango: moderate turbulence, sustained surface winds of 30 knots or more, and nonconvective low-level wind shear. Zulu: moderate icing and freezing levels.(AIM 7-1-6)
  • SIGMET: severe icing, severe or extreme turbulence, dust or sandstorms, or volcanic ash, hazardous to all aircraft. Convective SIGMET: severe thunderstorms (surface winds 50 knots or more, hail 3/4 inch or more, or tornadoes), embedded thunderstorms, lines of thunderstorms, or widespread thunderstorms with heavy precipitation; it implies severe turbulence, severe icing and low-level wind shear.(AIM 7-1-6)
Weather theory you apply
  • Thunderstorm life cycle: cumulus (updrafts only), mature (updrafts and downdrafts, precipitation begins, the most violent stage), dissipating (downdrafts dominate).(PHAK (FAA-H-8083-25C), Ch. 12; Aviation Weather Handbook, Ch. 22)
  • Thunderstorm avoidance in full: at least 20 miles from a severe storm or intense echo, especially under the anvil (hail falls in clear air); tops at or above 35,000 feet are extremely hazardous; don't fly between echoes less than 40 miles apart, don't fly under a thunderstorm, and go around areas with 6/10 or more coverage.(AIM 7-1-27; AC 00-24)
  • Fronts by type. Cold front: cumuliform clouds, showers and thunderstorms (sometimes a squall line ahead), turbulence, a sharp wind shift and temperature drop, good visibility behind. Warm front: widespread stratiform clouds, steady precipitation, poor visibility, smooth air, and possibly embedded thunderstorms. Stationary fronts bring long periods of the same weather; occluded fronts combine both, often with embedded storms.(PHAK (FAA-H-8083-25C), Ch. 12; Aviation Weather Handbook, Chs. 10-11)
  • Air masses take on the character of where they formed (cold or warm, dry or moist), and their stability decides the weather. Reading the surface analysis for air masses and fronts lets you predict what you'll fly into.(PHAK (FAA-H-8083-25C), Ch. 12)
  • Temperature and inversions: temperature normally drops about 2°C per 1,000 feet; an inversion (warm air over cold) traps haze, smoke and fog below it, gives smooth air above, and can bring low-level wind shear. A small temperature/dew point spread warns of fog and low cloud bases.(PHAK (FAA-H-8083-25C), Ch. 12)
  • Clouds by family: high (cirrus types), middle (alto-), low (stratus, stratocumulus, nimbostratus), and clouds of vertical development (towering cumulus and cumulonimbus, with turbulence, icing and thunderstorms). Precipitation types include rain, drizzle, snow, freezing rain and hail; freezing rain means warmer air above you.(PHAK (FAA-H-8083-25C), Ch. 12; Aviation Weather Handbook)
  • Obstructions to visibility: fog and mist (BR), haze, smoke, smog, dust and sand, spray, and volcanic ash, which also damages engines and airframes.(PHAK (FAA-H-8083-25C), Ch. 12; Aviation Weather Handbook)

Want it all on one page, with scenarios? Read the full lesson.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

  1. Remember Recall it

    “What does a TAF cover?”

  2. Understand Explain why

    “Why is a PIREP often more useful than a forecast?”

  3. Apply Use it on a flight

    “Your destination TAF shows a ceiling dropping to 1,500 broken by your arrival time, and your personal minimum is 2,500. What do you do?”

4 · Common mistakes

  • Looking at the weather and then deciding what your minimums are.

    Get-there-itis will lower them every time.

    Instead: Write your personal minimums down beforehand, and go by them.

  • Using cockpit radar to thread between storms.

    The picture can be many minutes old.

    Instead: Use it to stay far away and divert early.

  • Checking only the destination TAF.

    Hazards en route (icing, turbulence, convection) and the departure and alternate matter too.

    Instead: Get a full briefing: observations, forecasts, advisories and PIREPs along the whole route.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

  1. 1. What is the difference between a METAR and a SPECI?

  2. 2. What three things does a thunderstorm need?

  3. 3. Which AIRMET covers icing?

  4. 4. What conditions are needed for structural icing?

  5. Scenario5. A PIREP at your destination reports a 15-knot loss of airspeed on final near a rain shower. What might be happening, and what do you do?

  6. 6. Does the winds aloft forecast include winds within 1,500 feet of the station elevation?

Trained it? Now prove it: practice weather information out loud with our examiner.

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Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Preflight Preparation

A July afternoon. You plan a 90 NM trip from a 2,800-foot runway at 1,500 feet elevation; it's 33 °C. The destination TAF has a TEMPO for thunderstorms starting about when you'd arrive.

How do the weather, the airplane's performance and your fuel plan change one another, and what do you decide? Decide, then see the worked answer

Work the density altitude first. Standard temperature at 1,500 feet is about 12 °C, so 33 °C is about ISA +21 °C and the density altitude is roughly 4,000 feet (more if the pressure is low). Enter the POH takeoff and climb charts at the actual pressure altitude and temperature, never the field elevation, and compare the ground roll, the distance over a 50-foot obstacle and the climb with the 2,800 feet and the obstacles, with a margin. If it's tight, cut payload and baggage first. Never cut fuel below trip fuel plus fuel to divert to an alternate plus the 91.151(a)(1) day VFR reserve of 30 minutes at normal cruise. After any load change, recompute the weight and balance and the CG, and check the landing distance at the destination too. The TEMPO puts thunderstorms over the destination at your arrival. Don't plan to beat the TEMPO window or to divert closely around cells: avoid thunderstorms with severe or intense radar echoes by at least 20 miles, never take off or land in the face of an approaching thunderstorm, and wait storms out on the ground. With thin performance margins and storms at the far end, the better answer is the cooler, calmer morning.

PHAK (FAA-H-8083-25C), Aircraft Performance and Weather Theory; AC 00-24C, Thunderstorms; 14 CFR 91.103, 91.151

Brings together: Weather Information · Cross-Country Flight Planning · Performance and Limitations

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Aviation Weather Handbook (FAA-H-8083-28); Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); AIM; AC 91-92; 14 CFR 91.103; Risk Management Handbook (FAA-H-8083-2A). Checked against current sources 2026-11-12.