Aviation Weather Information: Reports, Forecasts, and Observations

Weather Information Sources and Platforms

• Primary Information Source: aviationweather.gov     * Preferred for its official status as a .gov website and its exhaustive data.     * Underwent a significant update a few years ago to enhance usability and visual presentation.     * Provides comprehensive weather data necessary for aviation operations.

• Secondary Platforms     * ForeFlight: An electronic flight bag (EFB) used for similar weather data aggregation.     * The core weather services and data types remain the same regardless of the platform used (iPad, computer, or web).

Weather Reports versus Weather Forecasts

• Reports     * Definition: Observations of what is currently happening at the moment.     * Methods: Sourced from human observers or automated sensors/machines.

• Forecasts     * Definition: Predictions of future weather conditions.     * Timeframes: Can cover intervals of $4$, $8$, $12$, $24$, $48$, or $72$ hours.     * Accuracy: As the duration of the forecast increases, the accuracy typically decreases.

Standard Flight Rules and Categories

• General Rule for Categories: If the ceiling and visibility fall into different categories, the more restrictive (lower) category is always the designated flight category.

• VFR (Visual Flight Rules)     * Ceiling: Above 3,000\text{ feet}.     * Visibility: Better than 5\text{ statute miles}.

• Marginal VFR (MVFR)     * Ceiling: $1,000$ to 3,000\text{ feet}.     * Visibility: Between $3$ and 5\text{ statute miles}.

• IFR (Instrument Flight Rules)     * Ceiling: Less than 1,000\text{ feet}.     * Visibility: Less than 3\text{ statute miles}.

• Low IFR (LIFR)     * Ceiling: Less than 500\text{ feet}.     * Visibility: Less than 1\text{ statute mile}.

Service Outlets: Flight Service Stations (FSS)

• Role and Utility     * Provides pre-flight weather briefings giving a complete picture for the entire route of flight.     * Assists in verifying if conditions meet pilot personal minimums and rating minimums.     * Example: If the weather is IFR, a briefer will inform a pilot who does not hold an instrument rating.

• Contact Information     * Phone Line: $1\text{-}800\text{-}WX\text{-}BRIEF$ ($1\text{-}800\text{-}992\text{-}7433$).     * Generic Frequency: 122.2\text{ MHz}.     * Chart Information: Specific frequencies for specific stations are listed on aeronautical charts.

• Additional Services     * In-flight weather updates.     * Weather advisories.     * Current altimeter settings for specific areas.     * Filing flight plans.

• Trends: The FAA is closing many physical flight service stations due to high operation costs and the prevalence of digital information on iPads and computers.

Types of Flight Service Weather Briefings

• Standard Briefing     * The most detailed and complete picture of the weather.     * Includes departure, destination, and en-route weather.     * Recommended for pilots who have not received any weather data earlier in the day and plan to depart within the hour.     * Note: Briefers speak quickly; pilots must have materials ready to record data.

• Abbreviated Briefing     * Used as a supplement to update previously received mass-disseminated data or a prior standard briefing.     * Focuses on changes since the last report.

• Outlook Briefing     * Request this when a flight is planned $6$ or more hours into the future.     * Provides a general picture to help decide if a flight is worth pursuing, as data at this range is less detailed/accurate.

• Pilot Requirements During Call     * Identify as a pilot.     * Provide the planned route and destination.     * Specify if the flight is VFR or IFR.

Surface Aviation Weather Observations

• AWOS (Automated Weather Observation System): Automated sensor reporting.
• ASOS (Automated Surface Observing System): Automated sensor reporting.
• Capability: Sensors measure wind, pressure, precipitation, and sky conditions.
• Coverage: Observations only cover a small area (a few miles) centered on the airport.
• Update Frequency: For automated stations, a new observation is generated frequently (essentially every time the report is re-read over the radio/phone).

METAR (Aviation Routine Weather Report)

• Standardization: International format with minor local variations.

• Issuance Schedule     * Issued hourly.     * Data is recorded at approximately 50\text{ minutes} past the hour ($H-10$).     * The report is typically officially posted about 15\text{ minutes} after the hour ($H+15$).

• SPECI (Special Issuance): An unscheduled report issued when significant changes in weather occur.

• Accessing METARs     * Phone Text Service: Text $358782$ with the word "METAR" followed by the four-letter airport identifier (e.g., "METAR KPRC").

Decoding METAR Sections

• Airport Identifier: A four-letter code, such as $KPRC$ (Prescott Airport).
• Date and Time Block: Six digits: first two are the date, next four are UTC/Zulu time. Example: $161853Z$ means the $16\text{th}$ day of the current month at 18:53\text{ Zulu}.
• Wind Block     * Format: Direction (3\text{ digits}) followed by speed (2\text{ digits}). Example: $21016G22KT$.     * Definition: Coming from 210\text{ degrees true} ($Written = True, Spoken = Magnetic$) at 16\text{ knots}, gusting to 22\text{ knots}.
• Visibility Block: Reported in statute miles. Example: $10SM$. $P6SM$ means visibility is "plus" or greater than 6\text{ statute miles}.
• Cloud Coverage and Sky Condition     * Codes: $FEW$ (Few), $SCT$ (Scattered), $BKN$ (Broken), $OVC$ (Overcast).     * Altitude: Reported in hundreds of feet AGL (Above Ground Level). Example: $BKN009$ is a broken layer at 900\text{ feet AGL}.     * Ceiling Definitions: Only $BKN$ and $OVC$ layers constitute a "ceiling."     * Clear Sky: $CLR$ (Automated, clear below 12,000\text{ feet}) or $SKC$ (Manual station, sky clear).     * Omissions: If visibility is \ge 5\text{ SM} and ceiling is \ge 5,000\text{ feet}, some reports may exclude these sections.
• Temperature and Dew Point: Reported in degrees Celsius. Example: $19/M15$ means $19^{\circ}\text{C}$ temperature, $-15^{\circ}\text{C}$ dew point. ($M$ prefix stands for Minus/Negative).
• Altimeter Setting: Prefix $A$ followed by a four-digit pressure in inches of mercury. Example: $A3003 = 30.03\text{ inHg}$.

METAR Remarks Section (RMK)

• Station Type: $A02$ means the automated station has a precipitation discriminator (can tell rain from snow, etc.). $A01$ cannot differentiate types.
• SLP (Sea Level Pressure): Reported in millibars (hPa) using last three digits.     * Logic: If the number starts with $0$, $1$, or $2$, add a $10$ in front. If it starts with $8$ or $9$, add a $9$ in front. Add a decimal before the last digit.     * Example: $SLP103 = 1010.3\text{ millibars}$. $SLP933 = 993.3\text{ millibars}$.     * Difference from Altimeter: SLP is used by meteorologists and corrects for station temperature; the altimeter setting ($A$ block) uses a standard temperature profile to calibrate instruments.
• Precise Temp Block ($T$ prefix): Allows for decimal precision. First digit ($0$ for positive, $1$ for negative). Example: $T01891150 = 18.9^{\circ}\text{C}$ temp, $-15.0^{\circ}\text{C}$ dew point.
• Weather Events     * WSHFT1813: Wind shift occurred at $18:13Z$.     * $RAB18$: Rain began at 18\text{ past the hour}.     * $P0018$: Precipitation amount in the last hour was 0.18\text{ inches}.     * \: Maintenance indicator; data may be unreliable.

Weather Qualifiers and Abbreviations

• Precipitation Types: $RA$ (Rain), $SN$ (Snow), $SG$ (Snow Grains), $GR$ (Hail - from French grêle), $PL$ (Ice Pellets).
• Descriptors: $TS$ (Thunderstorm), $FZ$ (Freezing), $SH$ (Showers), $BL$ (Blowing), $MI$ (Shallow).
• Obscurations: $BR$ (Mist - from French brume), $FU$ (Smoke - from French fumée), $FG$ (Fog), $HZ$ (Haze).
• Intensity: $-$ (Light), No sign (Moderate), $+$ (Heavy).
• Special Clouds: $CB$ (Cumulonimbus), $TCU$ (Towering Cumulus). Always listed at the end of sky condition blocks.
• Lightning Codes     * LTGICCGNW: Occasional lightning in-cloud and cloud-to-ground Northwest of the airport.     * FREQLTGVC: Frequent lightning in the vicinity ($5$-10\text{ miles}).     * DSNTLTGALLQDS: Distant lightning (>10\text{ miles}) in all quadrants.

PIREP (Pilot Report)

• Importance: Provides data ground stations cannot see, such as cloud tops, icing, and turbulence.

• Report Types     * $UA$: Routine pilot report.     * $UUA$: Urgent pilot report.

• Location/Over (OV): Uses a NAVAID followed by a radial and distance. Example: $GGG090025$ means on the 090^{\circ}\text{ radial} (due east) of the $GGG$ station, 25\text{ nautical miles} away.

• Time (TM): Zulu time of observation.

• Altitude (FL): Reported in hundreds of feet MSL. Example: FL060 = 6,000\text{ feet MSL}.

• Aircraft Type (TP): Identifies the source aircraft (e.g., $C182$, $B737$). Crucial for gauging the severity of turbulence/icing relative to aircraft size.

• Turbulence (TB): Categorized by intensity. "Light" causes slight erratic changes in altitude/attitude.

• Weather (WX): Includes items like forward visibility ($FV$) and rain ($RA$).

TAF (Terminal Aerodrome Forecast)

• Scope: Forecasts weather within a 5\text{ statute mile} radius from the center of an airport.

• Validity: Valid for either $24$ or 30\text{ hours}.

• Issuance: Updated four times daily ($0000Z$, $0600Z$, $1200Z$, $1800Z$).

• Forecast Change Groups     * $FM$ (From): Prevailing conditions expected to change significantly in under 1\text{ hour}.     * $TEMPO$: Temporary fluctuations lasting less than 1\text{ hour} and covering less than half the total time period ($probability > 50\%$).     * $PROB30$: A $30\%$ probability of occurrence (typically thunderstorms or precipitation).     * $PROB40$: Used in International (e.g., Canadian) TAFs; indicates a $40\%$ probability.     * $BECMG$ (Becoming): A gradual change occurring over a longer period (usually $2$ or more hours).

Weather Advisories: AIRMET and SIGMET

• AIRMET (G-AIRMET)     * Target: Significant weather for smaller/GA aircraft.     * Issuance: Every 6\text{ hours} starting at 02:45\text{ UTC}.     * Categories:         * SFC Wind: Sustained winds > 30\text{ knots}.         * LLWS: Low-level wind shear below 2,000\text{ feet AGL} yielding airspeed changes \ge 20\text{ knots}.         * Turbulence: Non-convective moderate turbulence.         * FRZLVL: Freezing levels depicted at 4,000\text{ foot} intervals MSL.         * Icing: Non-convective moderate airframe icing.         * MTN OBSC: Mountain obscurations due to clouds, precip, or smoke.         * SigViz IFR: Ceilings < 1,000\text{ feet} or visibility < 3\text{ SM}.

• SIGMET (Significant Weather)     * Target: Serious hazards for all aircraft types.     * Non-Convective SIGMET: Severe turbulence, severe icing, volcanic ash, or severe dust/sand storms. Valid for 4\text{ hours} (6\text{ hours} for hurricanes).     * Convective SIGMET: Thunderstorm activity including lines \ge 60\text{ miles} long, areas covering $40\%$ of a region, tornadoes, winds \ge 50\text{ knots}, or hail \ge \frac{3}{4}\text{ inch}.     * Schedule: Issued hourly at 55\text{ minutes} past the hour and valid for 2\text{ hours}.