🛩 Task C – Weather Information Sources

Objective: To ensure the applicant demonstrates satisfactory knowledge, risk management, and skills associated with obtaining and applying weather information for preflight and inflight planning, in accordance with 14 CFR regulations and FAA guidance.

References: 14 CFR Parts 91 | FAA-H-8083-25 | FAA-H-8083-13 | FAA-H-8083-28 | FAA-H-8083-2 | AviationWeather.gov | AC 00-6B | AC 00-45H | AC 61-23C |

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📘 PA.I.C.K1 – Sources of Weather Data

Pilots must understand and correctly use all available official weather sources before and during flight to ensure safety and compliance with FAA regulations. Weather data is used not only for planning routes but also for determining aircraft performance, alternates, fuel reserves, and risk mitigation.

✅ Primary Sources of Preflight Weather Information

1. Flight Service Station (FSS) – 1-800-WX-BRIEF or 122.2 MHz
   • Provides standard, abbreviated, and outlook briefings
   • Can file flight plans and give inflight updates
   • Best used for: Legal FAA briefing, real-time interaction with a briefer
2. aviationweather.gov (NWS/NOAA)
   • Comprehensive government website for aviation-specific forecasts
   • Access TAFs, METARs, SIGMETs, AIRMETs, GFA, icing charts, and radar
   • Best used for: Self-briefing with full graphical and text data
3. Aviation Digital Data Service (ADDS)
   • Hosted by NOAA/NWS — similar to aviationweather.gov but includes custom visual overlays
   • Best used for: Comparing products like TAFs, PIREPs, convective forecasts on one map
4. Electronic Flight Bags (EFBs) – ForeFlight, Garmin Pilot, WingX, etc.
   • Combine real-time data, route overlays, flight planning, and legal briefings
   • May integrate ADS-B, NOTAMs, TFRs, and weather layers
   • Best used for: Situational awareness, route optimization, and portable cockpit info

✅ Local Weather Observations (Surface Stations)

1. ATIS (Automatic Terminal Information Service)
   • Recorded broadcast at towered airports
   • Includes weather, NOTAMs, runways in use, and remarks
   • Updated hourly or as conditions change
   • Example: “ATIS information Echo… wind 270 at 12… runway 27 in use…”
2. AWOS (Automated Weather Observing System)
   • Provides basic weather: wind, temp, dew point, altimeter, visibility
   • Types: AWOS-A, AWOS-1, AWOS-2, AWOS-3 (each level adds sensors)
   • Common at non-towered airports
3. ASOS (Automated Surface Observing System)
   • More advanced than AWOS; includes precipitation type, lightning, sky cover
   • Found at most towered fields
   • Updates automatically every 60 seconds; issued as METARs/SPECIs

✅ In-Flight Weather Sources

1. HIWAS (Hazardous Inflight Weather Advisory Service)(being phased out)
   • Broadcasts AIRMETs, SIGMETs, Convective SIGMETs over VORs
2. ATC / ARTCC Weather Info
   • ATC provides real-time radar data and weather deviations
   • Helpful for areas not visible to cockpit systems
3. FSS (Inflight) – 122.2 MHz or discrete frequencies
   • Provide PIREPs, inflight advisories, and updated forecasts
   • Can open, amend, or close flight plans
4. EFAS / Flight Watch(consolidated into FSS)
   • Formerly used at 122.0 MHz for enroute weather, now fully integrated into FSS

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📘 PA.I.C.K2 – Acceptable Weather Products

Pilots must be able to identify, obtain, and interpret aviation weather products used to make safe and legal go/no-go decisions.

These products provide both forecast and real-time data across different altitudes and phases of flight. Knowing what each product offers, when it’s updated, and how to apply it can prevent accidents and legal violations.

Product	Purpose & Contents	Use Case Example	Update Frequency
METAR	Hourly surface observation: wind, visibility, clouds, temperature, dew point, altimeter, remarks	Assess if current conditions meet VFR/IFR minimums for departure and arrival	Issued hourly and amended as needed
SPECI	Special report triggered by visibility, ceiling, wind shift, thunderstorm, precipitation changes, etc.	Detect deteriorating conditions requiring flight delay or alternate plan	As needed during significant changes
TAF	Terminal forecast (5 SM): wind, visibility, clouds, weather trends with FM/TEMPO/PROB30 changes	Determine if ETA meets forecast landing requirements or if alternate is needed	4x daily (valid 24–30 hrs)
PIREPs	Real-time inflight observations from pilots: turbulence, icing, visibility, cloud tops	Adjust route or altitude based on current flight conditions experienced by others	Continuous
GFA	Interactive graphical forecasts for clouds, precip, icing, turbulence, visibility, surface winds	Visualize IFR vs. VFR areas along your route	Continuously updated
Surface Analysis	Frontal systems, isobars, highs/lows for large-scale weather planning	Evaluate impact of cold/warm front on your departure or enroute conditions	Every 3 hours
CVA	Color-coded map from METARs showing VFR, MVFR, IFR ceilings & visibility	Quick overview of weather conditions enroute or near departure field	Every 5 minutes
Winds Aloft (FB)	Forecasted wind direction/speed and temp at altitudes above 3,000 ft	Select optimal cruise altitude to avoid strong headwinds or icing layers	4x daily (valid for 6, 12, 24 hrs)
AIRMETs	Moderate hazards: turbulence (Tango), icing (Zulu), mountain obscuration (Sierra)	Avoid regions not suitable for light aircraft or student pilots	Every 6 hours or as needed
SIGMETs	Severe weather affecting all aircraft: volcanic ash, severe icing, dust storms	Reroute or cancel if area is within flight path	Valid up to 4 hours
Convective SIGMETs	Embedded thunderstorms, squall lines, hail ≥¾ in, tornadoes	Avoid areas completely due to high turbulence and wind shear risk	Hourly + unscheduled as needed

📘 PA.I.C.K2a – METAR / SPECI / PIREP

• METAR: Routine airport weather report issued at 55 minutes past the hour, valid for the airport area (5 SM).
• SPECI: Special METAR issued when significant changes occur, such as:

🔹 Wind direction changes ≥45° with wind ≥10 kt
🔹 Deteriorating visibility
🔹 Sky conditions
🔹 Tornado, funnel cloud, or waterspout observed
🔹 Thunderstorms begin or end
🔹 Change in precipitation type
🔹 Volcanic ash, sandstorm, or duststorm reducing visibility to ≤3 SM
🔹 Aircraft accident occurs at or near the airport

✅ Both METAR and SPECI follow the same coded format and may be automated or manually augmented.

• PIREP: Pilot Report
  • Voluntary report of observed weather conditions
  • Highly valuable for confirming or disputing forecast conditions
  • Types of PIREPs:
    UA = Routine PIREP
    UUA = Urgent PIREP (severe turbulence, icing, low-level wind shear, volcanic ash, etc.)
  • Required Elements Format:

Code	Meaning	Example	Notes
/OV	Location of report	/OV MIA180010	10 NM on 180° radial from MIA VOR
/FL	Altitude / Flight Level	/FL060	Use FLUNKN if unknown
/TP	Aircraft type	/TP C172	ICAO identifier (e.g., B737, PA28)
/SK	Sky cover & cloud tops	/SK BKN045-TOP100	Use MSL for altitudes in PIREPs
/WX	Weather / Visibility	/WX FV02SM RA	FV = flight visibility in SM
/TA	Temperature (°C)	/TA -05	Required in icing reports
/WV	Wind direction & speed	/WV 27035KT	True direction, in knots
/TB	Turbulence	/TB MOD CAT 050-080	Include intensity, type, and altitude
/IC	Icing	/IC RIME 060-080	Include type and altitude range
/RM	Remarks	/RM SMOOTH ABOVE CLOUDS	Optional but recommended for clarity

• 📌 Why PIREPs matter:
  They provide real-time confirmation or contradiction of forecast products and can trigger updates to SIGMETs and AIRMETs.

📘 PA.I.C.K2b – Surface Analysis Chart & Ceiling/Visibility Analysis (CVA)

🗺 Surface Analysis Chart

Issued every 3 hours, this chart gives a visual representation of weather patterns across the U.S. It shows:

Feature	Symbol	Meaning
Cold Front	Blue triangles pointing direction	Advancing cold air, often unstable air, turbulence, T-storms
Warm Front	Red semicircles	Warmer air overtaking cooler air, steady precipitation
Occluded Front	Purple alternating triangles and semicircles	Cold front overtakes warm front; often severe weather
Stationary Front	Red and blue alternating	Neither air mass is advancing; potential prolonged weather
Trough	Orange dashed line	Elongated area of low pressure; lifting, clouds, possible rain
Ridge	Yellow zigzag line	Elongated area of high pressure; usually clear, stable conditions
Dry Line	Orange line with semicircles	Boundary between moist and dry air; common in the plains and often triggers severe weather
Squall Line	Red dashed line like Morse code	Line of thunderstorms, often severe, ahead of a cold front
Isobars	Thin grey lines with pressure labels (e.g., 1016)	Lines of equal pressure; closely spaced = strong winds

📌 High pressure centers marked with a blue “H”
📌 Low pressure centers marked with a red “L”

📉 Ceiling & Visibility Analysis (CVA)

• Replaces older Weather Depiction Charts
• Updated every 5 minutes
• Color-coded station dots:
  • 🟢 Green = VFR
  • 🔵 Blue = MVFR
  • 🔴 Red = IFR
  • 🟣 Purple = LIFR
• Yellow/orange shading highlights terrain-based visibility risks or IFR ceilings

✅ Best used alongside METARs and TAFs for full situational awareness

📘 PA.I.C.K2c – Terminal Aerodrome Forecasts (TAF)

Purpose:
TAFs provide concise weather forecasts within a 5 statute mile (SM) radius of an airport’s runway complex. They are tailored for aviation use and are based on human forecasts (unlike METARs which are automated).

Issued by:
National Weather Service (NWS) forecast offices
⏱ Issued 4 times daily: 0000Z, 0600Z, 1200Z, 1800Z
📍 Available via aviationweather.gov and EFB apps like ForeFlight

✈️ TAF Structure & Components

Section	Description	Example
TAF / TAF AMD / TAF COR	Type of forecast (Routine / Amended / Corrected)	TAF AMD
Station Identifier	4-letter ICAO code	KMIA
Valid Period	Start and end times in Zulu (Z)	2412/2518 = From 12Z on 24th to 18Z on 25th
Wind	Direction (true) and speed in knots	27015KT = 270° at 15 kt
Visibility	In statute miles (SM)	6SM
Weather	Phenomena codes (e.g., RA = rain)	-SHRA = light rain showers
Sky Conditions	Cloud layers and coverage	BKN020 = Broken at 2,000 ft AGL
Optional Elements	Wind shear, icing, probability groups	See below

☁️ Sky Condition Codes

Code	Meaning
SKC	Clear skies
FEW	Few clouds (1-2 oktas)
SCT	Scattered (3-4 oktas)
BKN	Broken (5-7 oktas)
OVC	Overcast (8/8 sky cover)

🔄 Forecast Change Indicators

Code	Meaning
FM	“From” – Rapid, significant change beginning at a specific time
TEMPO	“Temporary” – Conditions expected for <1 hour, and <50% of forecast period
PROB30	30% probability of specified conditions
BCMG	“Becoming” – Gradual change in conditions over time

📘 PA.I.C.K2d – Graphical Forecasts for Aviation (GFA)

Overview:
GFA provides interactive, image-based weather forecasts across the continental U.S., replacing the old Area Forecast (FA). It’s ideal for preflight planning under VFR.

🔗 aviationweather.gov/gfa

🗺️ GFA Layers

• Clouds – Bases, tops, coverage
• Visibility – MVFR, IFR, LIFR shading
• Ceilings – Lowest BKN/OVC layer AGL
• Flight Category – VFR to LIFR color map
• Precipitation – Rain, snow, thunderstorms
• Icing – Intensity and altitude range
• Turbulence – Light to severe, by level
• Winds – Wind barbs at various altitudes

🟩 Flight Category Colors

Color	Category	Meaning
Green	VFR	Ceiling ≥ 3,000 ft & Vis ≥ 5 SM
Blue	MVFR	Ceiling 1,000–3,000 ft or Vis 3–5 SM
Red	IFR	Ceiling 500–1,000 ft or Vis 1–3 SM
Purple	LIFR	Ceiling < 500 ft or Vis < 1 SM

✅ Highlights:

• Forecasts out to 18 hours
• Custom filtering by layer/altitude
• Use with METARs, TAFs, AIRMETs for full picture

📘 PA.I.C.K2e – Winds and Temperatures Aloft (FB)

Purpose:
Forecasts of wind direction, speed, and temperature at various altitudes—used for fuel planning, performance, and altitude selection.

🔗 aviationweather.gov/products/windtemp

⏱ Issued 4× daily (0000Z, 0600Z, 1200Z, 1800Z)

🕐 Valid for 6, 12, or 24 hours

🧾 Text Format Example

750855

• 75 → 250° wind (75 − 50 = 25 × 10)
• 08 → 108 kt wind (08 + 100)
• 55 → Temp = −55°C

Special Codes:

• 9900 = Light & variable winds (<5 kt)
• No winds <1,500′ AGL
• No temps <2,500′ AGL

🌬️ Graphical Format

• Barbs:
  ▸ Short = 5 kt
  ▸ Long = 10 kt
  ▸ Triangle = 50 kt
• Temp: Displayed in °C, above wind barb

📘 PA.I.C.K2f – Convective Outlooks

• Issued by the Storm Prediction Center
• Thunderstorm risk areas:
  • SLGT – Slight
  • MDT – Moderate
  • HIGH – High

📘 PA.I.C.K2g – AIRMETs / SIGMETs / Convective SIGMETs

Purpose:
These advisories alert pilots to in-flight weather hazards that may affect aircraft safety.

🔗 View on aviationweather.gov or your EFB

🟡 AIRMET (WA)

For less severe but widespread hazards
✅ Valid up to 6 hrs
Types:

• Sierra – IFR or mountain obscuration
• Tango – Moderate turbulence or surface winds ≥30 kt
• Zulu – Moderate icing or freezing level info

🔴 SIGMET (WS)

For serious hazards affecting all aircraft
✅ Valid up to 4 hrs
Covers:

• Severe turbulence or icing
• Dust/sandstorms
• Volcanic ash

🌩️ Convective SIGMET (WST)

For severe thunderstorm activity
✅ Issued hourly at :55
Covers:

• Embedded/severe T-storms
• Hail ≥ ¾”
• Tornadoes
• Surface winds ≥50 kt

📘 PA.I.C.K3a – Atmospheric Composition & Stability

Atmospheric Composition
78% nitrogen, 21% oxygen, 1% other gases, up to 5% water vapor

Standard Atmosphere (Sea Level)
15°C (59°F), 29.92 inHg (1013.2 hPa)

Standard Lapse Rate
2°C per 1,000 ft (temperature decreases with altitude)

Adiabatic Cooling
Rising air cools as pressure decreases—no external heat loss involved

Temperature Inversion
A reversal of the normal lapse rate—temperature increases with altitude
→ Can trap fog, haze, smoke; reduces visibility and increases icing risk if moisture is present

Stability Comparison

Stable Air	Unstable Air
Poor visibility	Good visibility
Stratiform clouds	Cumuliform clouds
Smooth air	Turbulence
Steady precipitation	Showery precipitation

✅ Stable air = smooth but hazy
✅ Unstable air = bumpy with vertical cloud development

📘 PA.I.C.K3b – Wind

What Causes Wind
Wind is horizontal air movement caused by pressure differences. It’s influenced by:
– Pressure Gradient Force (main driver)
– Coriolis Effect (deflects wind to the right in N. Hemisphere)
– Friction (slows wind near the surface)

Common Wind Types

• Valley Wind – Daytime upslope flow as warm air rises
• Mountain Breeze – Nighttime downslope flow as air cools
• Sea Breeze – Daytime flow from sea to land as land heats faster
• Land Breeze – Nighttime flow from land to sea as land cools
• Katabatic Wind – Cold, dense air draining downhill (often strong)
• Anabatic Wind – Warm, rising air flowing uphill (gentle)

Hazardous Wind Phenomena

• Wind Shear / LLWS – Sudden wind shifts near the surface, dangerous on takeoff/landing
• Mountain Waves – Turbulence and lenticular clouds downwind of mountains
• Mechanical Turbulence – Caused by buildings, terrain disrupting airflow

Jet Stream
High-altitude wind (FL300–FL400), fast-moving (can exceed 100 kt), flowing west to east

✅ Tip: Always consider local terrain and time of day—valley, coastal, and jet stream winds can significantly affect your flight

📘 PA.I.C.K3c – Temperature and Heat Exchange

✅ Temperature Basics

• Affects air density, lift, engine performance, and weather
• Aviation uses Celsius (°C)
• Conversions:
  • °F = (°C × 1.8) + 32
  • °C = (°F − 32) ÷ 1.8
• Boiling point: 100°C (212°F)
• Freezing point: 0°C (32°F)

✅ Standard Atmosphere

• 15°C at sea level, 29.92 inHg pressure
• Standard lapse rate: −2°C per 1,000 ft
• Freezing level: typically around 7,500 ft MSL (varies with actual temperature)

✅ Adiabatic Processes

• Adiabatic cooling: rising air expands and cools
• Adiabatic heating: sinking air compresses and warms
• These drive cloud formation, turbulence, and vertical weather development

✅ Temperature Inversion

• Temperature increases with altitude (reverses normal lapse rate)
• Common on calm, clear nights
• Traps fog, haze, smoke, and pollutants
• Can lead to icing if warm, moist air overlays freezing layers

✅ Pilot Implications

• High temps = reduced performance and longer takeoff roll
• Inversions = poor surface visibility and icing during descent
• Temp/dew point spread <5°C = high fog potential

📌 Tip: Check freezing levels and lapse rates in your preflight weather briefing to anticipate performance issues and icing hazards.

📘 PA.I.C.K3d – Moisture and Precipitation

✅ Key Concepts

• Water in the atmosphere appears as vapor, liquid, or ice, and plays a major role in weather formation
• Moisture impacts visibility, airframe icing, and air density
• Moisture enters the atmosphere through evaporation and sublimation, and leaves through condensation and precipitation

✅ Relative Humidity & Dew Point

• Relative Humidity: percentage of air’s moisture saturation
• Dew Point: temperature at which air becomes fully saturated
• Temperature–Dew Point Spread:
  • Small spread (<5°C) = high likelihood of fog, low clouds, or precipitation

✅ Precipitation Formation

• Requires saturation and vertical motion (lifting)
• Two main processes:
  • Coalescence: water droplets collide and grow (warmer clouds)
  • Bergeron Process: ice crystals grow by absorbing water vapor (colder clouds)
• Thick clouds (4,000+ ft) = heavier precipitation

✅ Types of Precipitation

• Drizzle: small droplets, light intensity
• Rain: larger droplets, may be light or heavy
• Snow: frozen ice crystals
• Freezing Rain/Drizzle: liquid falls and freezes on contact—very hazardous
• Sleet: frozen raindrops
• Hail: formed in strong updrafts; common in thunderstorms

✅ Supercooled Water & Icing

• Supercooled water exists as liquid below 0°C
• Freezes instantly on contact with airframes, causing clear icing
• Most hazardous between 0°C and −15°C

✅ Pilot Implications

• Precipitation can reduce visibility, increase weight, and impact control surfaces
• Expect structural icing if flying in visible moisture at or below freezing temperatures
• Heavy precipitation may signal strong updrafts, turbulence, and thunderstorm activity

📌 Tip: Always check for freezing levels, precipitation types, and dew point spread during preflight. Avoid visible moisture in freezing conditions.

📘 PA.I.C.K3e – Weather Systems and Fronts

✅ Air Masses and Fronts

• Weather systems form when large air masses with different temperatures and moisture levels interact
• The boundary between two air masses is called a front
• Fronts are a major source of lift and weather changes

✅ Types of Fronts

• Cold Front: Cold air undercuts warm air, forcing it upward
  • Brings turbulence, cumuliform clouds, showery precipitation, and rapid changes
• Warm Front: Warm air slides over cooler air
  • Brings stratiform clouds, steady rain, poor visibility, and potential icing
• Stationary Front: Air masses remain in place
  • Prolonged periods of low ceilings and light precipitation
• Occluded Front: A cold front overtakes a warm front
  • Often produces widespread and severe weather
• Dry Line: Boundary between moist and dry air
  • Common trigger for thunderstorms in the plains

✅ Frontal Weather Clues

• Wind shift at surface and aloft
• Temperature change
• Drop or rise in pressure
• Cloud development and type transition
• Changes in visibility and precipitation

✅ Pilot Implications

• Plan for turbulence, wind shear, and convective activity near cold fronts
• Expect IFR conditions, fog, and icing risks with warm fronts
• Monitor occluded fronts for intense weather systems
• Always check surface analysis and forecast charts to identify frontal boundaries

📌 Tip: Avoid frontal passage times during takeoff or landing, and build in alternate options when fronts are along your route.

📘 PA.I.C.K3f – Clouds

✅ What Are Clouds?

• Clouds form when rising air cools to its dew point, causing water vapor to condense on microscopic particles
• Cloud type indicates stability, moisture content, and potential weather hazards

✅ Cloud Classifications

Clouds are classified by altitude and appearance

• Low Clouds (Surface to 6,500 ft AGL)
  • Stratus (ST): Uniform gray layers, drizzle or mist
  • Stratocumulus (SC): Low, lumpy clouds; light rain possible
  • Nimbostratus (NS): Thick, dark layers with steady rain or snow
• Middle Clouds (6,500 to 20,000 ft AGL)
  • Altostratus (AS): Gray or blue layers; precede warm fronts
  • Altocumulus (AC): White/gray patches; possible turbulence
• High Clouds (20,000 ft AGL and above)
  • Cirrus (CI): Thin, wispy ice-crystal clouds
  • Cirrostratus (CS): Transparent veil; may cause halos
  • Cirrocumulus (CC): Small, patchy, ripple-like patterns
• Vertically Developed Clouds
  • Cumulus (CU): Puffy clouds; fair weather or early convection
  • Towering Cumulus (TCU): Strong vertical growth; indicates instability
  • Cumulonimbus (CB): Thunderstorm clouds; heavy rain, turbulence, hail, and lightning

✅ Cloud Prefixes & Suffixes

• “Strato–” = layered
• “Cumulo–” = heaped
• “Nimbo–” / “–nimbus” = precipitation-producing
• “Alto–” = mid-level
• “Cirro–” = high-level, ice-based

✅ Pilot Implications

• Low clouds = reduced visibility, potential for IMC
• Middle clouds may signal incoming warm fronts
• High clouds often indicate upper-level moisture or jet stream proximity
• Cumulonimbus = avoid at all costs due to turbulence, wind shear, and icing
• Towering cumulus = potential thunderstorm development

📌 Tip: Vertically developed clouds often signal unstable air. Avoid CBs by at least 20 NM.

✅ What is Turbulence?

• Turbulence is irregular or violent air movement that disrupts an aircraft’s flight path
• It can be caused by terrain, weather systems, temperature gradients, jet streams, or other aircraft
• Varies in intensity and frequency—from mild bumps to extreme forces that affect control

✅ Types of Turbulence

• Mechanical Turbulence: Wind flowing over terrain, trees, or buildings; common near mountains and airports
• Thermal (Convective) Turbulence: Rising warm air due to surface heating, often in the afternoon
• Frontal Turbulence: Occurs along cold fronts as dense air displaces warmer air
• Wind Shear Turbulence: Sudden wind speed/direction changes—found near inversions, frontal zones, or jet streams
• Clear Air Turbulence (CAT): High altitude, no visible clouds, often near the jet stream
• Wake Turbulence: Created by wingtip vortices behind aircraft—especially heavy, clean, and slow-flying aircraft
  • Strongest when the generating aircraft is heavy, clean, and slow
  • Vortices sink and drift with the wind
  • Greatest risk during takeoff, landing, or parallel approaches

✅ Turbulence Intensity Levels

Intensity	Description	Turbulence	Chop
Light	Slight, brief changes in pitch, roll, or altitude	Slight, erratic changes	Rhythmic bumpiness without altitude changes
Moderate	Definite changes; control maintained	More pronounced than light; occupants feel strain	Similar to moderate turbulence but more regular
Severe	Large, abrupt changes; temporary control loss	Occupants forcibly thrown; unsecured items displaced	“Chop” rarely used at this level
Extreme	Aircraft violently tossed; control may be lost	Structural damage possible	“Chop” not applicable—this is pure turbulence

✅ Pilot Implications

• Reduce airspeed to VA to avoid structural damage
• Anticipate wake turbulence when behind large aircraft—stay above their glide path and land beyond their touchdown point
• Use PIREPs, SIGMETs, AIRMETs, and ATC reports to avoid known turbulent areas
• Always submit turbulence reports to improve safety for others

📌 Tip: “Chop” feels like vibration; “turbulence” involves real control changes. Wake turbulence is invisible but predictable—spacing and awareness are key.

📘 PA.I.C.K3h – Thunderstorms and Microbursts

✅ Thunderstorm Basics

• Thunderstorms form when warm, moist, unstable air is lifted and cools to form towering cumulonimbus (CB) clouds
• Key ingredients:
  • Moisture
  • Unstable air
  • Lifting action (fronts, terrain, convection)

✅ Thunderstorm Life Cycle

• Cumulus Stage: Strong updrafts build the cloud vertically; no precipitation yet
• Mature Stage: Updrafts + downdrafts; heavy rain, lightning, turbulence, hail
• Dissipating Stage: Downdrafts dominate; storm weakens but can still be dangerous

📌 Tip: A thunderstorm is most violent during the mature stage

✅ Thunderstorm Hazards

• Severe turbulence
• Lightning
• Hail (can occur miles from the storm)
• Wind shear and microbursts
• Low visibility, heavy rain, IFR conditions
• Icing (especially in the 0°C to −15°C range inside CBs)

✅ Microbursts

• Powerful localized downdrafts (up to 6,000 ft/min descent rate)
• Occur during or near thunderstorms, typically within 5 NM of the cell
• Duration: Usually less than 15 minutes, but extremely dangerous
• Horizontal wind speeds can exceed 100 knots

🛑 Often undetectable visually — especially during wet microbursts, which are masked by precipitation

✅ Pilot Implications

• Avoid CBs by at least 20 NM
• Never attempt to fly under or through a thunderstorm
• Use ATC, Radar, GFA, and PIREPs to monitor convective activity
• If wind shear or microburst alert is issued—delay departure or go around
• Be alert for Virga (precipitation that evaporates before hitting the ground)—often a sign of potential microbursts

📌 Tip: No aircraft is certified to fly through a thunderstorm. Avoidance is the only safe strategy.

📘 PA.I.C.K3i – Icing and Freezing Level Information

✅ What Is Aircraft Icing?

• Icing occurs when supercooled water droplets strike a surface below 0°C and freeze on contact
• Ice increases weight, reduces lift, adds drag, and can severely degrade aircraft performance
• Just a trace can reduce lift by 30% or more

✅ Conditions for Icing

• Visible moisture (clouds, rain, fog)
• Air temperature between 0°C and −20°C
• Aircraft surface must be below freezing
• Most common in stratus layers, freezing rain, and wave clouds

✅ Types of Icing

• Clear Ice
  • Temperature Range: 0°C to −10°C
  • Large droplets freeze slowly and spread, forming smooth, hard ice
  • Found in cumulus clouds and freezing rain
  • Hard to detect and difficult to remove
• Rime Ice
  • Temperature Range: −10°C to −20°C
  • Small droplets freeze quickly on contact
  • Rough, opaque, brittle texture
  • Found in stratus clouds or stable layers
• Mixed Ice
  • Combines features of clear and rime ice
  • Uneven accumulation; most unpredictable and dangerous
• Frost
  • Forms on surfaces below 0°C on clear, calm nights
  • Disrupts airflow and must be completely removed before flight

✅ Freezing Level

• The lowest altitude at which air temperature is 0°C
• Can have multiple layers in unstable conditions or frontal zones
• Freezing levels are reported in winds aloft (FB), AIRMET Zulu, and graphical forecasts (GFA)

📌 Tip: A quick rule of thumb—if OAT is <0°C and you’re in visible moisture, there’s a risk of icing.

✅ Pilot Implications

• Avoid areas of forecast or reported icing if not certified for it
• Exit icing layers promptly by climbing, descending, or turning
• Monitor PIREPs, AIRMETs, and weather radar for known icing conditions
• Use anti-ice systems early: pitot heat, carb heat, windshield defog, etc.
• Always ensure frost is fully removed before takeoff—even a thin layer reduces performance

🛑 No aircraft is certified for severe icing. Avoidance is the only truly safe option.

📘 PA.I.C.K3j – Fog and Mist

✅ What Is Fog?

• Fog is a surface-based cloud made of tiny water droplets that reduces visibility to less than 5/8 statute mile
• Occurs when air becomes saturated—temperature equals dew point
• Dangerous for VFR flight, especially during takeoff and landing

✅ Fog Formation Requirements

• High humidity (temp/dew point spread ≤ 5°C)
• Calm to light winds
• Cooling to dew point by various mechanisms

✅ Types of Fog – Use the acronym “I.F.S.U.P.R.A.”

Each letter represents a distinct fog type:

• I – Ice Fog
  • Forms in very cold temps (below −25°C)
  • Moisture sublimates into ice crystals
  • Common in Arctic or polar regions
• F – Frontal Fog(aka Precipitation-Induced Fog)
  • Warm rain falls into cooler air near the surface
  • Evaporation increases humidity until fog forms
  • Common along frontal boundaries
• S – Steam Fog
  • Cold air moves over warmer water
  • Water evaporates then condenses in the cold air
  • Often seen over lakes or rivers; turbulent and localized
• U – Upslope Fog
  • Moist air is pushed up terrain, cools adiabatically
  • Common along foothills and mountainous terrain
• P – Precipitation Fog(alternate for Frontal Fog)
  • Overlaps with “F”; results from evaporation during rain
  • Enhances saturation at low levels
• R – Radiation Fog
  • Clear, calm nights with ground cooling
  • Air near the surface chills to dew point
  • Forms just before sunrise and dissipates after
• A – Advection Fog
  • Warm, moist air moves over cooler ground or water
  • Common in coastal areas (e.g., San Francisco)
  • Can last for days if winds are steady

✅ Mist (BR)

• Like fog, but with visibility 5/8 SM to 6 SM
• Reported in METARs as “BR”
• Can still be problematic for VFR, especially at night

✅ Pilot Implications

• Fog can form rapidly, especially near dawn or after rainfall
• Monitor temperature/dew point spread, especially during calm, humid conditions
• Use TAFs, METARs, and PIREPs to anticipate fog before flight
• Plan alternates and delay VFR departures when fog is forecasted

📌 Tip: If temp and dew point are within 2°C overnight, fog formation is likely.

📘 PA.I.C.K3k – Frost

✅ What Is Frost?

• Frost is ice crystal formation on a surface when the surface temperature is below freezing and the surrounding air contains enough moisture
• Forms when dew point is below 0°C and the surface cools below both the ambient temperature and dew point
• Typically appears on calm, clear nights due to radiational cooling

✅ Conditions for Frost Formation

• Clear skies (promotes heat loss via radiation)
• Calm or very light winds (prevents mixing of warmer air)
• High humidity near the surface
• Surface temperature ≤ freezing point (0°C / 32°F)

✅ Why Frost Is Dangerous

• Disrupts smooth airflow over wings, reducing lift
• Increases drag and stall speed
• Just 1/16 inch of frost can reduce lift by up to 30% and increase drag by up to 40%
• Can prevent takeoff altogether or significantly degrade climb performance

✅ FAA Regulations

• §91.527 prohibits takeoff when frost, snow, or ice is adhering to wings, propellers, or control surfaces
• Even thin or “frost-like” contamination on critical surfaces (like leading edges) must be removed
• “Cold-soaked fuel frost” on the top of the wing may require special handling if permitted by aircraft limitations

✅ Pilot Actions

• Always perform a visual preflight inspection
• Remove all frost before departure—use approved methods (deicing fluid, warm air, mechanical removal)
• Check METARs, TAFs, and temp/dew point spreads on clear, calm mornings for frost potential
• Consider delaying departure until frost naturally dissipates if removal is not possible

📌 Tip: If you can write your name in the frost on the wing, the aircraft is not airworthy until it’s removed.

📘 PA.I.C.K3l – Obstructions to Visibility

✅ What Are Obstructions to Visibility?

• Obstructions to visibility are atmospheric phenomena (other than fog or precipitation) that reduce flight visibility
• Often reported in METARs, especially under “WX” (weather) field using standard codes
• May significantly impact VFR operations, particularly during takeoff, landing, and low-level navigation

✅ Common Obstructions – METAR Codes

These may occur alone or in combination with other weather phenomena:

• BR – Mist
  • Visibility: 5/8 to 6 SM
  • Similar to fog but less dense
• HZ – Haze
  • Caused by fine dust, smoke, or salt particles
  • Reduces slant-range and horizontal visibility
  • Common in humid, stagnant air
• FU – Smoke
  • Result of wildfires, agricultural burning, or industrial activity
  • Can severely reduce visibility, especially near the surface
• DU – Dust
  • Dry soil particles suspended in the air
  • Can cause widespread haze or dust storms (DS) if winds are strong
• SA – Sand
  • Suspended sand particles
  • Most common in desert regions; often reported with blowing sand (BLSA)
• VA – Volcanic Ash
  • Extremely hazardous to aircraft (can melt and fuse in engines)
  • Very fine particles; usually spreads across wide areas
  • Aircraft should avoid any area with reported VA
• BLDU / BLSA / BLSN – Blowing Dust, Sand, or Snow
  • Reported when particles are raised by surface winds to ≥ 6 feet
  • Can reduce visibility to <3 SM or lower
  • BLSN (Blowing Snow) is particularly hazardous during winter operations
• PO – Dust/Sand Whirls
  • Short-lived, rotating columns of dust (mini-tornadoes)
  • Generally less than 50 feet in diameter and height

✅ Pilot Implications

• Know the METAR codes and interpret their impact on visibility
• Consider delays, alternate airports, or IFR when obstructions persist
• In VFR flight, maintain increased awareness of terrain, traffic, and landmarks
• Use synthetic vision, EFB moving maps, or VOR navigation when visibility is marginal

📌 Tip: Even with VFR legal minimums, reduced visibility can create practical IMC—don’t press into poor conditions.

📘 PA.I.C.K4 – Flight Deck Instrument Displays of Digital Weather and Aeronautical Information

✅ Overview

Modern cockpits increasingly feature digital flight displays (glass cockpits) and Electronic Flight Bags (EFBs) that present real-time weather and aeronautical information. Pilots must understand what these systems display, how to interpret the information, and their limitations.

✅ Common Sources of Digital Weather & Aero Info

• ADS-B IN (Automatic Dependent Surveillance–Broadcast)
  • Provides FIS-B weather: METARs, TAFs, radar, lightning, NOTAMs, TFRs
  • Data is not real-time—may be delayed up to 15 minutes
  • Requires ADS-B IN capability (portable or panel-mounted)
• SiriusXM Weather (subscription-based)
  • Satellite-based weather feed
  • No coverage gaps like ADS-B at low altitudes
  • Provides high-resolution radar, METARs, TAFs, winds aloft, lightning, icing forecasts
• EFIS / MFD (Electronic Flight Instrument System / Multi-Function Display)
  • Often found in G1000, Avidyne, and other glass cockpit platforms
  • Displays NEXRAD, METARs, TAFs, winds, traffic, terrain, and more
  • Integrated with GPS and aircraft systems
• EFBs (Electronic Flight Bags) – e.g., ForeFlight, Garmin Pilot
  • Consolidate weather, airspace, NOTAMs, charts, and traffic overlays
  • Allow pilots to layer information and plan more effectively
  • Many provide legal briefings and ADS-B weather integration

✅ Limitations and Risks

• Data Latency: Radar and METAR info via ADS-B or satellite may be 5–15 minutes old
• Coverage Gaps: ADS-B weather requires ground station reception
• Misinterpretation: Pilots may mistake delayed radar as real-time; always cross-check with visual cues and ATC
• System Failures: Always carry backup sources (paper charts, alternate briefing tools)

✅ Pilot Responsibilities

• Understand which systems are installed and how to operate them
• Know the refresh rates and data sources (ADS-B vs. SiriusXM vs. Wi-Fi)
• Maintain proficiency in traditional weather interpretation
• Use EFBs for preflight planning but never as the sole source of inflight weather decision-making

📌 Tip: Always verify that weather and NOTAMs are current and complete. Combine multiple sources—FSS, ADS-B, and ATC—for the full picture.

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