Manned weather observation sites now report SKC (sky clear) when no clouds are observed, and automated sites report CLR (clear) when no clouds are observed below 12,000 feet. A total obscuration and its indefinite ceiling are reported as VVxxx: VV001 indicates a total obscuration with a vertical visibility of 100 feet.
Partial obscurations caused by fog, mist, haze, or smoke are reported as FEW (few), SCT (scattered), or BKN (broken) followed by three zeros. BKN000 in a METAR (routine meteorological report) indicates a five-eighths to seven-eighths obscuration, SCT000 indicates a three-eighths to one-half (four-eighths) obscuration, and FEW000 indicates that up to one-quarter (two-eighths) of the sky is obscured.
Students frequently ask why sky cover and obscurations are reported in octas rather than tenths. The four cardinal points of the compass (N, E, W, S) and the four intercardinal points (NE, NW, SE, SW) divide the compass into eight sectors. Cloud cover and obscurations are easy to evaluate if you observe the conditions that exist in each of the eight sectors and base your report on how many sectors that condition occupies.
Actual weather is usually somewhere between WOXOF and CAVU, and you must determine whether or not it is flyable based on your certification level, experience, and the airplane you'll be flying. That's what makes flying a challenge. Conditions are often various shades of gray, not black and white like WOXOF and CAVU.
How do you deal with gray skies? Extreme winds, fast-moving frontal systems, thunderstorms, icing conditions, and reduced surface visibilities with small temperature-dew point spreads and the possibility of cooler temperatures or upslope movement are obviously no place for VFR or IFR pilots flying light airplanes.
When gray skies exist, you must ask yourself, "If I start this flight and conditions deteriorate, do I have a clear-cut out - an option that I know will ensure the safety of my flight?" If you do, then go. Reaching your destination, however, must not be mandatory. That obsession has killed many pilots. And do take extra cash and a credit card because you may spend one or more nights at a diversion airport.
After you take off and reach cruise altitude, your first priority is a groundspeed check in order to validate the wind forecast on which you based your flight plan. Hopefully your groundspeed is equal to or faster than that planned. If not, you must recompute your en route and estimated arrival times, fuel consumption, and fuel reserves.
Your next priority is to validate the weather forecast that you used for flight planning. Are the en route and terminal weather performing as forecast, or is the weather deteriorating or improving? You must monitor weather trends in order to make logical decisions regarding the outcome of your flight.
I call the FAA flight service system's En route Flight Advisory Service (Flight Watch) on 122.0 MHz at five minutes past each hour - when the latest weather reports should be on file - to get the current en route and destination weather. If conditions are marginal, I'll call at 30 minutes past each hour to see if a SPECI (special weather observation) has been issued. If the original forecast is not holding up and conditions are becoming questionable, I divert to an alternate airport. I never wait until further flight becomes impossible.
Flight Watch is available from approximately 6 a.m. to 10 p.m., and reception is guaranteed if you are at or above 5,000 feet agl. For specific times refer to the inside back cover of the applicable Airport/Facility Directory. If you can't contact flight watch because of low ceilings, contact a flight service station using one of their many remote communication outlets.
You must always have safe options when flying. Don't expect the weather or winds to be as forecast or expect the aircraft's systems and your flashlight batteries to perform when needed. And, if you fly an unfamiliar airplane, never expect the actual fuel tank capacity or fuel consumption to be that which is listed in the airplane flight manual.
Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying for 43 years and has 25,000 hours in both fixed- and rotary-wing aircraft. Visit his Web site ( www.skyroamers.com ).
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