פורסם עם: General Aviation
SPECIAL WEATHER
Sometimes the tip-off that something unexpected is happening with the weather isn't a detail in a weather report, but the type of report itself. A pilot who can spot differences between routine and special information will be on the alert when deciding whether to fly or how to continue a flight.
How can you tell? Weather briefings contain reports on surface conditions at your departure point, destination, and airports en route. As explained in Chapter 11 of the Pilot's Handbook of Aeronautical Knowledge, make note of whether you are reading a routine report (a METAR) or a special observation. "The first is the routine METAR report that is transmitted every hour. The second is the aviation selected special weather report (SPECI). This is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information."
Forecasts differ too. Suppose your terminal aerodrome forecast, or TAF, is coded "TAF AMD." This means that the forecast was amended. Timing of reports also signals departure from the routine. Convective sigmets are presented at 55 minutes past the hour but can be "issued during the interim for any reason." Radar reports are issued every 35 minutes but also "special as needed."
An alert pilot inquired about unusual coding of a pilot report (UUA instead of UA) as addressed in the Aug. 15, 2008, AOPA ePilot: "A message will be coded as UA for a routine pirep. It will be coded as UUA when the information is considered urgent. Information is considered urgent when a pirep contains any of the following weather phenomena: tornadoes, funnel clouds, or waterspouts; severe or extreme turbulence, including clear air turbulence; severe icing; hail; volcanic ash; low-level wind shear (pilot reports airspeed fluctuations of 10 knots or more within 2,000 feet of the surface); or any other weather phenomena reported that are considered by the controller to be hazardous, or potentially hazardous, to flig! ht operations."
An urgent pilot report on headwinds or an amended forecast might have saved a flight instructor and student in Virginia from a tense diversion at night as recounted in this account from "Never Again Online."
Know when special conditions exist, and be ready to take action