Meteorology #3

• Topics for Tonight
• Aviation Routine Weather Reports (METARs)
• Terminal Aerodrome Forecasts (TAFs)
• Graphic Area Forecasts (GFAs)
• Upper Wind Forecasts (FDs)
• PIREPs
• Significant Weather Bulletins (SIGMETs)
• General Weather Wisdom
• Readings
• From the Ground Up, pages 158-172
• AIM – Meteorology (MET), pages 119 - 176

1

✈

METARs

• Aviation routine weather report.
• Human observer, or
• Automated weather observation stations (AWOS).
• Normally taken on the hour.
• SPECI is the code for a special weather report.
• Computer encodes the information into a METAR.

HUMAN OBSERVER

Looks cloudy!

It’s raining!

Oh shoot...

2

✈

What They Indicate

• Current weather conditions in the vicinity of the aerodrome or the observation station.
• Winds
• Visibility
• Cloud Conditions
• Temperature
• Dewpoint
• Altimeter Setting
• Weather Conditions in General
• Remarks

This Sort of Stuff...

3

✈

Example of a METAR

• MEANS:
• METAR for Saskatoon issued on the 29th day of the month at 2000Z;
• Winds 300 degrees true at 15 gusting to 25 knots;
• Visibility 2 statute miles in light snow;
• Sky condition, 800 feet AGL broken, 4000 feet AGL overcast;
• Temperature minus 5, dewpoint minus 8;
• Altimeter 29.92” Hg;
• Remarks:
• Stratus Fractus clouds in 5 oktas, stratocumulus clouds in 3 oktas;
• Visibility 1/2 statute mile to the northwest;
• The sun is dimly visible;
• Sea level pressure is 1013.4 hectopascals (hPa).

METAR CYXE 292000Z CCA 30015G25KT 2SM -SN BKN008 OVC040 M05/M08 A2992 RMK SF5SC3 VIS 1/2 TO NW SUN DMLY VSBL SLP134

4

✈

Decoding METARs

• Report Type
• METAR is given in first line of text.
• SPECI (special) reports are issued only if significant weather changes occur off the hour.
• Station Indicator
• Airport ICAO identifier, e.g. CYOW, CYYZ, CYVR, CYYC.
• Stations normally located within 3 km of geometric centre of the runway complex (1.6 miles).
• Date/Time of Observation
• Day of the month is included.
• UTC used (Zulu/Greenwich Mean Time).
• Report Modifier
• AUTO means automated weather observation system.
• “CC” means correction; CCA is first, CCB is second, etc.

5

✈

More on Decoding...

• Winds
• 2-minute mean wind direction and speed, including gusts.
• Wind direction rounded off to nearest 10 degrees true.
• Wind speed is two digits (three if required).
• Wind Gusts
• Included if gusts exceed average wind speed by 5 knots+, and
• Gusts exceed 15 knots.
• Example: 30015G25KT
• Variation in Direction
• Direction varies by 60 degrees or more, mean speed 3 knots+.
• Example: 30015G25KT 260V340

6

✈

Decoding Continued

• Prevailing Visibility
• Reported in statute miles and fractions.
• No upper limit to visibility.
• Lower visibilities that are half or less of the prevailing are reported in remarks at the end of the METAR.
• May include Runway Visual Range (reported visibility at touchdown on the runways), designated by “R” and the runway number, reported in hundreds of feet.
• RVR trend: “U” -- upwards, improving; “D” -- downwards.
• Example: R06L/1000V2400FT/U

7

✈

Present Weather Phenomena

• Intensity
• - Light
• Moderate has no qualifier
• + Heavy
• VC Vicinity of
• Qualifier
• MI Shallow
• BC Patches
• PR Partial
• DR Drifting
• BL Blowing
• SH Showers
• TS Thunderstorm
• FZ Freezing

• Precipitation
• DZ Drizzle
• RA Rain
• SN Snow
• SG Snow Grains
• IC Ice Crystals
• PL Ice Pellets
• GR Hail
• GS Snow Pellets
• UP Unknown Precipitation
• AWOS only

8

✈

Present Weather Phenomena

• Obscuration
• BR Mist
• Visibility greater than or equal to 5/8 statute miles.
• FG Fog
• Visibility less than 5/8 statute miles.
• FU Smoke
• Visibility 6 statute miles or less.
• DU Dust
• Visibility 6 statute miles or less.
• SA Sand
• Visibility 6 statute miles or less.
• HZ Haze
• Visibility 6 statute miles or less.

9

✈

More Decoding

• Sky Conditions
• Reported in oktas.
• SKC (CLR if AWOS).
• FEW, SCT, BKN, OVC.
• Temperature and Dewpoint
• Degrees Celsius.
• Altimeter
• In inches of mercury.
• Add a decimal point after the second digit to interpret.
• Example: A3000 = 30.00” Hg.
• Recent Weather
• Recent weather that occurred but is not occurring at the time of observation.
• Example: RERA = “recent rain.”

10

✈

Last METAR Decoding Remarks

• Wind Shear
• “WS” reported along takeoff/departure path of runways.
• Remarks
• Preface “RMK.”
• Cloud types and oktas that they cover are reported.
• Sea level pressure in hectopascals is reported.
• Additional remarks are noted (usually shorthand form).

MOON DMLY VSBL!

11

✈

Terminal Aerodrome Forecasts

• Are forecasts for weather within 5 nautical miles of the centre of the runway complex.
• Use similar codes to METARs.
• Critical for flight planning departure and arrival, occasionally some enroute stuff...

12

✈

Decoding TAFs

• TAF for Ottawa issued on the 21st day of the month at 1452Z;
• Valid on the 21st from 1500Z to 1500Z the next day (24 hours);
• Winds 220 degrees true, 10 gusting 20 knots;
• Visibility greater than 6 miles, few 3000’ AGL, scattered 5000’ AGL, broken 7000’ AGL;
• From 2100Z, winds 200 degrees true at 12 gusting 22 knots, visibility 4 statute miles in light rain showers, 800’ AGL scattered, 2000’ AGL broken, 5000’ AGL overcast;
• Temporarily between 2200Z and 0200Z, visibility 2 statute miles in light rain showers and mist, 500’ AGL broken, 1500’ AGL overcast;
• 30% probability between 2200Z and 0200Z of 1 statute mile visibility in thunderstorms and rain with the ceiling 1000’ AGL overcast, cumulonimbus;
• Next forecast by 1800Z.

TAF CYOW 211452Z 211515 22010G20KT P6SM FEW030 SCT050 BKN070 FM2100Z 20012G22KT 4SM -SHRA BR SCT008 BKN020 OVC050 TEMPO 2202 2SM SHRA BR BKN005 OVC015 PROB30 2202 1SM TSRA OVC010CB. RMK NXT FCST BY 18Z=

13

✈

Interpreting the TAFs

• Report Type and Station Indicator
• TAF used to indicate Terminal Aerodrome Forecast.
• AMD indicates that the TAF was amended.
• Four-letter ICAO identifier used.
• Issue Time
• Issued as infrequently as 6 hours, as often as 3 hours.
• Validity Period
• Varies.
• It is listed with the TAF.
• Winds
• Forecast in degrees true and knots.
• Same system as a METAR.
• Use these for takeoff/landing calculations in flight planning.

14

✈

More Stuff on Interpreting TAFs

• Low Level Wind Shear
• Strong non-convective windshear may be forecast.
• “WS” indicates windshear likely.
• Visibility
• Horizontal prevailing visibility is forecast.
• Fractions and statute miles up to 3 miles.
• Whole miles up to 6 statute miles, then P6SM.
• Significant Weather
• Same coding as METARs.
• Sky Conditions
• Same as METARs.
• Cumulonimbus layers are the only types that are identified.
• Example: OVC020CB

15

✈

Change Groups in TAFs

• Multiple elements within a weather and/or sky condition group are considered single entities for the purpose of revising them.
• Example: SCT030 BKN050 OVC080
• Followed by a change indicator, then: BKN050
• Indicates other two layers no longer exist!
• FM
• “From.”
• Used for a permanent change that occurs rapidly.
• BECMG
• “Becoming.”
• Gradual changes evolving over a period of 2-4 hours.
• Example: BECMG 1113 3SM -SHRA BR OVC009

16

✈

Other Change Groups

• TEMPO
• “Temporarily.”
• Transitory change group.
• Temporary fluctuation occurring for not more than 1 hour duration at a time, and covering not more than 1/2 of the period.
• At ending of significant weather, “NSW” is used.
• PROB
• Probability (30% or 40%)
• Will include, but is not limited to,
• thunderstorms,
• freezing precipitation,
• low level windshear below 1500’ AGL.
• Probability of less than 30% does not justify including it.

17

✈

Last Comment on TAF Decoding...

• Remarks:
• Remarks will be included on Canadian TAFs.
• Include next forecast period, etc.
• Important Things to Remember
• TAFs do not forecast temperature and pressure changes.
• TAFs only forecast the area within 5 nautical miles of the centre of the runway complex.
• Winds are in degrees true and knots.
• Ceilings are in feet AGL.
• Visibility is in statute miles.
• Use TAFs for planning weather at point of arrival, departure, and alternates, and enroute airports if they are within 5 nautical miles of the track you intend to fly.

18

✈

Getting Weather Information

• Call a Flight Service Station
• 1-866-WX-BRIEF.
• Use this for weather briefing, filing a flight plan before doing a cross-country flight.
• Check the Internet
• http://www.flightplanning.navcanada.ca

​

• AWWS– Aviation Weather Web Site
• CFPS – Collaborative Flight Planning Service

​

​

19

✈

Graphic Area Forecasts

• Designed to meet pre-flight planning for enroute portions of flight in Canada.
• A series of weather charts compiled to depict probable meteorological conditions over a wide area.
• Valid for below 400 mb level (24 000 feet ASL).
• Each GFA consists of six charts
• Two GFA chart types: Clouds and Weather, Icing & Turbulence.
• Near-term forecast.
• 6-hour forecast.
• 12-hour forecast.
• 12-hour Clouds and Weather forecast includes an IFR outlook for an additional 12 hours.

​

20

✈

Terms Used for GFAs

• Issued every 6 hours, valid at 0000Z, 0600Z, 1200Z, 1800Z.
• Winds
• Included if steady at 20 knots+ or gusts to 30 knots+.
• Wind direction shown by wind barbs.
• Visibility
• Measured in statute miles.
• Ceilings/Clouds
• Heights in hundreds of feet ASL.
• Heights AGL where stated.
• Cloud types stated as necessary.
• Cloud tops indicated as well!

2-5SM

BKN AC

100

70

21

✈

GFA Symbols

Warm Front

Cold Front

Trowal

Thunderstorms

Freezing Rain

Tropical Storm

Volcanic Activity

Sandstorm or Dust Storm

Occlusion

Quasi-Stationary Front

Trough Line

Upper Trough

Ice Pellets

Freezing Drizzle

22

✈

More GFA Symbols

Showery Precipitation

Steady Precipitation

Moderate Turbulence

Severe Turbulence

Moderate Icing

Severe Icing

Freezing Levels

Isobars

Highs

Lows

23

✈

Comments Section on GFAs

• Watch them very carefully!
• Outlook Forecast
• IFR
• Ceiling less than 1000’ AGL and/or
• visibility less than 3 statute miles.
• MVFR
• Means “Marginal VFR.”
• Ceiling between 1000’ and 3000’ AGL and/or
• visibility between 3 and 5 statute miles.
• VFR
• Ceiling above 3000’ AGL and visibility greater than 5 statute miles.

24

✈

Viewing a GFA -- Clouds and Weather

25

✈

Viewing a GFA -- Icing, Turbulence

26

✈

Upper Wind Forecasts

• Derived from
• Isobars/weather charts,
• Weather balloons, and
• Reports from aircraft.
• Use them for flight planning!
• Issued every 3000’ increment starting at 3000’ ASL.
• Temperatures issued starting at 6000’ ASL.
• 3000’ ASL can easily be affected by daytime heating.
• 6000’ ASL is generally too high to be affected by heating.

Upper Level Tailwind

Whoa!

27

✈

Upper Wind Forecasts

• Known as “FDs.”
• Wind direction is forecast in degrees true.
• Wind speed is forecast in knots.
• Temperature is forecast in degrees Celsius.
• Example:
• 1530+06
• Means 150 degrees at 30 knots, temperature plus 6 degrees C.
• 2010+00
• Means 200 degrees at 10 knots, temperature 0 degrees C.
• 3422-10
• Means 340 degrees at 22 knots, temperature -10 degrees C.

28

✈

More On Upper Winds

• If the wind speed is greater than 100 knots, 50 is added to the direction digits, and 100 is subtracted from the wind speed.
• Example: 8310+00
• Means winds are 330 degrees true at 110 knots, temperature 0 degrees C.
• Above 24 000’ ASL, temperatures are all negative, so they are not listed as plus or minus.
• Example: 795144
• Means winds are 290 degrees at 151 knots, temperature -44 degrees Celsius.
• If winds are light and variable, they will read:
• 9900 (and the temperature indicator).

29

✈

PIREPs

• Are reports of adverse weather conditions submitted by an in-flight observer.
• Coded by “UA.”
• Think “Unreliable Airman.”
• Include date and time of issue, location of the observation, time of the observation, type and altitude of the observing aircraft, and the conditions observed.

#%!&*$%!

30

✈

Decoding a PIREP

• PIREP issued by Toronto FSS on the 15th of the month at 2352Z for weather conditions within the Toronto Flight Information Region.
• A pilot report over the Ottawa VOR 270 degree radial at 25 miles distance (25 DME to be accurate) at 8500’ ASL.
• Aircraft type was a Cessna 172.
• Sky condition is overcast at 9000’ ASL.
• Air temperature is +10 degrees Celsius.
• Conditions: 3 statute miles visibility in light rain showers.

UACN10 CYYZ 152352

YZ

UA/OV YOW 270025 2347 FL085 /TP C172 /SK OVC 090 /TA +10 /VIS 3SM -SHRA

31

✈

SIGMETs and AIRMETs

• Are short-term warnings of potentially hazardous weather conditions.
• SIGMETs are broadcast on appropriate frequencies when received.
• SIGMETs are issued for things like
• Thunderstorms,
• Hail storms,
• Severe turbulence,
• Severe icing,
• Mountain wave effects,
• Hurricanes,
• Sandstorms, Dust storms,
• Volcanic Ash,
• Low Level Wind Shear.

32

✈

Decoding a SIGMET

• SIGMET issued by the Winnipeg Weather Office on the 22nd of the month at 1215 Zulu.
• SIGMET B3 (supersedes its predecessor, B2) valid from the 22nd of the month at 1215Z to the 22nd of the month at 2215Z.
• Within 40 nautical miles of a line from Dauphin to Brandon to Winnipeg, thunderstorms with the maximum tops at 37 000’ ASL have been observed on Doppler Radar. The line is moving eastward at 15 knots. There is little change in intensity.

WSCN32 CYWG 221215

SIGMET B3 VALID 221215/222215 CYWG

WTN 40 NM OF LN DAUPHIN/BRANDON/ WINNIPEG. TS MAX TOPS 370 OBSD ON DOPPLER RADAR. LN MOVG EWD AT 15 KT. LTL CHG IN INTSTY.

33

✈

AIRMETs

• Similar to SIGMETs, but for less severe conditions that are not described in current GFAs or SIGMETs.
• IFR conditions,
• Freezing precipitation (not requiring a SIGMET),
• Moderate icing and/or turbulence,
• Isolated thunderstorms,
• Surface mean wind over a large area is 20 kts+ or gusts to 30 kts+ where not forecast,
• Difference between forecast and observed wind is 60 degrees or more.
• Ensures that pilots receive important info prior to departure and that the conditions get included in the GFAs.
• AIRMET valid until it is updated or cancelled.

34

✈

General Weather Wisdom

• Watch for small temperature/dewpoint spreads.
• Possibility of fog and poor visibility.
• Night makes it difficult to see clouds.
• Check GFAs and TAFs thoroughly.
• Don’t fly above scattered layers at night.
• Watch both the TAFs and the GFAs.
• GFAs give you weather over a general area.
• Specific observed conditions may spring up in small areas before GFAs can be revised.
• Never trust a dark cloud (especially a green cloud).
• Think ACCs, TCUs, CBs.
• Watch GFAs for frontal and convective activity.
• Avoid cold fronts, trowals and unstable warm fronts.
• Expect deteriorating conditions at warm fronts.

35

✈

General Weather Wisdom

• Thunderstorms:
• Don’t fly anywhere near them.
• Divert well around their possible paths.
• Land if you see one ASAP.
• Icing Conditions:
• Stay out of known or forecast icing conditions.
• Get to warmer temperatures or on the ground ASAP if you suspect icing.
• Check struts, fairings, tires, handles and tubes for build-up.
• Marginal VFR Weather:
• Stay close to home.
• When planning a trip, leave yourself lots of time to get there and back.

36

✈

Final Word on Weather

• If it’s not screaming VFR, get a comprehensive weather briefing from FSS.
• Don’t just check the Internet.
• NEVER push on and hope for better weather.
• DON’T PUSH YOUR LUCK!
• If advised of adverse weather, think long and hard.
• “It’s better to be on the ground wishing that you were in the air than in the air wishing that you were on the ground.” -- Aviation Proverb.

“If you crash because of weather, your funeral will be held on a sunny day.”

37

✈

Next Class

• MID-TERM EXAM
• 1.5 hour, 69 questions.
• Answers taken up in class.
• Does not count towards any final mark.
• Subject Areas
• Theory of Flight
• Air Law and Airspace
• Engines and Instruments
• Meteorology
• READINGS
• Everything previously covered in the course: in class, in the handouts, in the assignments, and in the readings.

38

✈