Let’s review some basic concepts in meteorological reports for Pilots.
Cloud cover: measured in oktas, or out of eighths of the sky coverage:
- SKC – sky clear of cloud
- Few 1-2 out of 8
- Scattered 3-4 out of 8
- Broken 5-7 out of 8
- Overcast 8 out of 8 – full sky coverage
METAR: Aviation routine weather reports are coded weather observations that are taken each hour at over 200 aerodromes and other locations in Canada.
SPECI: Special Weather Reports – these amend METAR observations, whenever weather conditions fluctuate or are below criteria. What are these criteria?
- Sky condition: (1) the cloud ceiling height changes either up or down from 1500 feet, 1000 feet, 500 feet, 300 feet or 100 feet, or to the published IFR limits for that aerodrome. Also, (2) the first occurrence of cloud under 1000 feet is noted.
- Temperature: if above 20 degrees, an increase of 5 degrees; or if the temperature decreases to 2 degrees or colder.
- Visibility: up or down any of these thresholds: 3 SM, 1.5 SM, 1 SM, 3/4 SM, 1/2 SM, or the limits for the aerodrome.
- Wind: Wind doubles to exceed 30 knots, or shifts.
- Severe weather: thunderstorm, tornado, funnel cloud.
- Other: these can be incidents at the aerodrome, such as an accident or a special request from a weather forecast office, or if the weather observer feels it’s just to take initiative to issue this alert.
TAF: Terminal area forecast. Limited to aerodromes where METARS and SPECIs are published. There are about 180 TAFs in Canada. Generally prepared four times daily with up to 30 hour validity.
GFA: Graphical Area Forecast. There are seven GFA areas in Canada, these weather charts depict the most probable weather conditions expected to occour on the ground up to FL240 (flight level 24,000 feet). There are six charts prepared for every period, issued daily at 2330, 0530, 1130 and 1730 UTC, valid from 0000, 0600, 1200 and 1800 UTC respectively. Each chart has 12 hours of forecasting plus a 12 hour IFR outook, giving us a total of 24 hours of forecasting. Of the six GFAs listed for each forecast period, three contain cloud and weather information and three contain icing, turbulence and freezing levels.
The GFA can also be amended by AIRMETs or SIGMETs. AIRMETs are short term weather advisory for aircraft in flight, alerting pilots to possible hazardous flying conditions, but not severe enough to require a SIGMET. SIGMETS are short term warnings of certain potential hazardous weather phenomena, and are limited to more serious hazards which are important to all types of aircraft.
FDs – These provide upper level wind forecasts. They are provided for seven specific regions in Canada, and are further broken down for specific areas. Forecast for the 3000, 6000, 9000, 12,000 and 18,000 foot levels are provided, and these are the low-level FDs. They are also given for flight levels above 18,000 feet (FL180).
Radar: Radar is provided on the Environment Canada webpage. It will show you developing precipitation. It is very accurate.
Satellite: Satellite is shown on the AWWS webpage, and is useful for long term weather forecasting and planning. You can use it to find low and high pressure systems. Recall that air rotates clockwise around a high and counterclockwise around a low.
PIREP: Pilot reports can be filed at any time. They should be regularly checked for your region. In fact, one that I received from a controller at Calgary terminal saved me from going into an area of severe turbulence.
RVR Index: Another great tool is the RVR index. The Runway Visual Range shows real time the current wind speed and direction at your chosen aerodrome. It is so accurate I often check it when I am already at the airport getting ready for a flight. The image on the left it shows a sample of what you will see. The wind speed and direction is displayed according to the magnetic compass. Here the wind is blowing from 130 at 9 knots. The wind direction is overlayed with the actual runways to get a sense of where exactly the wind is coming from, and if we can expect a crosswind. In fact the cross wind component for each runway is calculated in a table next to the image. Wind given is the average for each minute.
It is important to understand how to read these reports and understand how they are created. After awhile, it becomes second nature. Pilots after all, are lifetime students of weather.