2005 08 whether weather to go or not

VINTAGE INSTRUCTOR

THE

DOUG STEWART

Whether/weather to go, or not

T

here I was, driving along the turnpike, looking up at a severe clear cerulean sky, and rather than finding myself ecstatic at that beautiful sight, words that cannot be repeated in this column were forming on my lips. Gosh darn (it was really a lot stronger said than that), the briefer said, “VFR not recommended,” and now instead of being up in that sky where I belong, I am down here, ground bound, driving to my destination.

I know probably every one of us has been in this situation, perhaps more times than we care or choose to remember. As the saying goes, “There are old pilots and bold pilots, but no old, bold pilots.” Many of us are aware that most aviation accidents, when associated with weather, tend to be fatal ones. Thus, if we are not instrument rated and current, or flying an airplane that is not instrument certified, we tend to choose alternative means of transportation when the briefer tells us, “VFR is not recommended.”

But does this always have to be the case? Are there any ways to make those VFR trips possible and still remain safe? Are there any tools we can use to determine if the forecast is holding true, or if it is not? For I think we all, both male and female, would agree that the weather is like the opposite sex—totally fickle and unpredictable. Let’s

take a look at the numerous tools we have for making the go/no-go decision relative to the weather.

To help determine if the forecast is going to hold true I usually first consult the METARS. Check reporting stations along your route.

If you are able, get a history showing the reports over the past three to four hours and see if the reports are corroborating the forecasts.

(DUATS, WSI, and Meteorlogix are all great sources for this information.) What trend do you see in the reports? Is the weather getting better or worse or holding the same? Is it doing what the TAF and FA said it would?

I’m also sure to compare the terminal forecasts (TAF) with the Area Forecast (FA). The TAF covers only a 5-mile radius of the aerodrome, whereas the FA covers an entire area. Keep in mind that cloud bases in the TAF are AGL (above ground), whereas the cloud bases in the FA are MSL (above sea level).

Next I check the PIREPS (pilot reports). Do they substantiate the briefer’s warnings? When checking PIREPS, be sure to take into account where the report was made (threedimensionally), when it was made, and what type of aircraft the reporting pilot was flying. If a 747 reports light chop along my route, I might consider leaving the ropes on my airplane and going to have a frosty one, whereas if it’s a J3 reporting moderate turbulence I might very

well launch on my own flight.

While we are mentioning PIREPS, let’s not forget that (as in all things in life) what goes around comes around. If we are seeking PIREPS in helping us to make the go/no-go decision, we should also consider filing them. It takes only a few moments to file a PIREP, and in doing so you are assisting many other pilots in their flight planning.

These are a few of the tools we can use while still on the ground to determine if the forecast is holding true. But what about when we are already en route? How can we know whether the weather will be as forecast?

Obviously, if the forecast was for severe clear and there are a lot of clouds forming, you do not need to be a rocket scientist or a brain surgeon to know that the forecast is not holding true. But there are many other clues that might not be quite as obvious and that should warn us that the briefer might have been wrong.

If we realize that we are having to fly a heading other than what we had plotted to track our course, or if we are experiencing different ground speeds than what we had expected, we should understand that there is a good chance that the entire forecast might be off. After all, these forecasts are predicated on the expected movement of fronts and pressure zones. When they don’t move as anticipated, the winds aloft

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will be different, thus yielding different headings and groundspeeds than we had planned.

There is something else that can give us a heads-up about the possibility of the forecast going south, and that is the temperatures aloft.

Most aircraft have outside air temperature gauges (OAT), and these can be very useful tools—ones that many pilots ignore. An OAT can be used to corroborate whether the temperatures aloft are as forecast.

(You do remember that the forecast temperatures aloft are included with the winds aloft, don’t you?)

This can give us an understanding of whether the fronts are moving at the speed and direction forecast or if they might be moving slower or faster than expected.

Keeping track of the temperatures as you climb can also help you quickly determine if the lapse rate is stable. Remembering that the stable lapse rate is 2ºC per thousand feet, one can make a note of the temper-

26 AUGUST 2005

ature on the ground prior to takeoff and then check it as you climb. If it is less than 2ºC per thousand, one of the major ingredients in the production of thunderstorms is present, that being an unstable lapse rate. (The other two are moist air and a lifting action of some kind.)

Thus the OAT can be a useful tool in confirming, or refuting, the forecast of thunderstorms.

One could spend a lifetime studying the weather and not get any closer to predicting what it might do. And I can’t do justice to the subject in this short article. However, when it comes to weather I must say that discretion is the better part of valor. There are certainly times when the briefer will give the warning that VFR is not recommended and the day turns out to be beautiful. But there are also times when your beautiful day turns ugly.

Regardless of whether the forecast is for good weather or bad, be sure to have an alternate plan in

place. Remember to run the PAVE and CARE checklists that I wrote about in previous articles to help you make the proper decisions relative to the weather. Using the tools I have mentioned above will help you in checking the enVironment, help in understanding the consequences of the hazards associated with some aspects of the weather, and aid you in assessing the realities of what the weather is really doing.

And when the briefer gives you that dire warning of “VFR not recommended,” keep in mind that it is always much better to be on the ground wishing you were up in the air than up in the air wishing you were on the ground. He might be wrong, and I’ve offered some tools to help determine that, but he very well might be right.

Doug Stewart is the 2004 National CFI of the Year, a Master CFI, and a DPE. He operates DSFI Inc., based at the Columbia County Airport (1B1).