Weather Geek: rules to fly by

In a recent blog John Zimmerman quoted from my book, “The Next Hour:”

“One thing is always true of weather…..Regardless of what is reported, what you see is what you get…..we have to always fly with a complete distrust of reported weather conditions.”

John suggested that was my first rule of weather flying. Colleague Pat Luebke jumped on that and wanted to know what my next four or eight or twelve rules might be.

Okay, I’ll give that a try but I’ll warn you that they are all sort of connected to the first rule which I will expand a bit to read “what you see and feel is what you get.”

1. If your destination is in an area covered by fog, be especially distrustful of the timing of a forecast for improvement.

You sure wouldn’t want to be headed for a foggy airport with minimum fuel. Forecasts of fog lifting are pure guesses and several factors can be at work here. For example, if there is a higher overcast, that means the sun won’t be shining on that fog and this can slow down or even preclude improvement. The layer of fog might be thicker than usual which means it will stay around. Or, if it is an upslope condition, where the circulation is moving over rising ground, the fog can persist. There can be huge and lasting areas of fog with a weak east or southeasterly flow over the rising terrain in Oklahoma, Kansas, and Colorado, for example.

2. If the wind aloft forecast is substantially in error then it is likely that other forecasts will also be in error.

A wind aloft that is more southerly and stronger than forecast means that the low pressure system to the west is likely deeper than anticipated. A more southerly wind carries with it a likelihood that the temperature aloft is warmer than forecast and that means it will involve more moisture. The ability of the atmosphere to hold moisture doubles with each 11-degree C. rise in temperature. From that you can gather that the surface weather might well be worse than forecast.

I would add that wind aloft forecasts are a lot better than they used to be. When I first started using computer flight planning programs, the estimated times en route were often pure fiction. Then they got a lot better thanks to programs that look live at actual winds aloft through sensors on airplanes. If an error is made, it can be quickly fixed.

3. Scattered clouds can have the same effect as an overcast on approaches in IMC.

When we are sniffing for asphalt on a low approach we are looking at a slant for the runway. On the ground looking straight up, as an observer or sensor does, clouds might well appear scattered but they might not allow that timely view of the runway if you are atop those clouds at your minimum height. Also, the conditions that lead to low scattered clouds only need to change a little bit for broken clouds or an overcast to form at that level.

4. The nature of turbulence tells us a lot about what is going on in the clouds.

Putting aside what happens when wind flows over mountains, we find two primary kinds of turbulence in clouds.

When the wind changes in velocity or direction over distance or with altitude we have wind shear turbulence. This can make flying (or riding and watching the autopilot fly) a chore but it doesn’t cause any real problems in cruise flight. Wind shear turbulence results in airspeed fluctuation and the airplane responds to this by lurching around. Big fast airplanes are more affected by wind shear than light ones.

Convective turbulence is found in cumulus clouds and is characterized by updrafts near the centers of the clouds. This can make it difficult to hold altitude and airspeed. The ultimate convective turbulence is found as a cumulus cloud morphs into a cumulonimbus, a thunderstorm. There you have strong up and downdrafts and some pretty wildly turbulent air where the up rubs against the down. Please avoid thunderstorms.

5. Nobody gets trapped by weather. There are always signs.

The clearest example of this comes as we fly toward a low or a front. Wishful thinking will not keep the cloud tops from becoming higher. Thus a wise pilot will know the synopsis and be forewarned when flying toward a system.

6. The cloud tops are always 1,000 feet greater than the ceiling of the airplane that you are flying.

Senator (and General) Barry Goldwater, an accomplished pilot, used this line in speeches before aviation audiences and I don’t think anybody ever argued with his observation.

7. If there is a gusty crosswind for takeoff or landing, the most reliable source of information is the old-fashioned windsock.

In general terms the wind will shift in a clockwise direction with an increase in velocity. This needs to be considered if there is what appears to be a direct crosswind. You can watch the windsock for a minute to see which direction will be best for takeoff or landing.

8. If you like to get off to an early start, be aware that there can be a substantial change in the weather at and shortly after sunrise.

It is natural for the temperature to drop a bit just as the sun starts to come up. The dewpoint will stay the same so, if they were close, the temperature and dewpoint might get together with a resulting fog formation. This can also result in the formation of frost on the airplane if the temperature was close to freezing and then drops to or just below freezing at sunrise.

9. If you are flying VFR, the onset of rain is bad news. Not only does it cut visibility but lower clouds often form after it starts raining. Likewise, rain can make flight visibility worse than the visibility that is reported at the surface.

It is not uncommon to have a reported visibility of, say, two or three miles in rain but have an IFR approach requiring a mile flight visibility to actually be below minimums which is the case if you can’t see the runway at the proper time.

10. If, following passage of a cold front, the wind shifts from northwest, to north, then to the northeast, that means the front has stalled and is becoming a stationary front.

Stationary fronts can linger long and while they usually pose no real problem for IFR flying (other than occasional thunderstorms) this condition can preclude VFR flights for long periods of time.

Those are just a few things to add to the main “what you see and feel is what you get” rule. The VFR pilot actually has the easiest time judging weather because it is always in plain view in the windshield. Either you can see enough to fly visually or you land. It is much more difficult for the pilot flying instruments because on an approach the determination has to be made at the last minute. That determination can’t be based on a surface weather report. It is to be based on what you see. See?


  • The VFR pilot might have the easiest time judging the weather but the hardest time staying legal if he takes too close a look in a changing environment.

  • I support Richard’s rules. Forecasts are never guaranteed. Over the 50+ years I’ve been flying, I’ve learned to put my efforts more into understanding the accuracy of the forecast rather than trying to forecast. I can’t do a better job of forecasting than the experts. I don’t have the skills or the tools. My guess is not worth much. One of my practices is to follow the forecasts for several days before a long flight. If the forecast for my day of interest keeps changing dramatically, that tells me the forecast models are not working well and I need to be prepared for surprises.

  • In regards to rule no. 5, I think it is possible to get trapped in weather by conditions somewhat related to rule no. 1. Fog can form or move in quickly in an unpredictable manner. It has happened to me; admittedly when I was a lot younger and slightly dumber. If it happens, what to do next is important. It used to be that if VFR only, an off airport landing was taught as a real option, and that is not a bad option. Nowdays, it is not encouraged so much and I don’t know if that is a good or bad thing; possibly a topic for discussion. If IFR capable and trapped, a person really must have very good situational awareness and a plan before punching into the clouds; it’s a very dangerous thing to do otherwise.

  • John: Having read your 10 points the only change I would make would be to print in 24 point type, Bold, and what ever else you can come up with. I have experienced each and every example in my 3000 single pilot IFR flying. Keep up the good work.
    Thanks again

  • This is an excellent first step. I have been looking for a practical course/instruction on pilot weather. Most of my flying is from 18,000’ to 25,000’ and I have found few details on how read forecasts, interpret in-cockpit weather, fronts and front propagation, make decisions on penetration vs. avoidance and some of the scientific understanding of cloud types and weather. Nearly all of what is used is based on personal experience and talking the airline pilots. Does anyone have clues on how to meet this need? Thanks

      • Dick, thank you. I have purchased many of these which are valuable. I would really like instruction where there is interaction in a structured environment.

        • John,

          I just completed the ASF Cockpit Weather program and found it quite good. It may be helpful with that aspect of your question.


  • A word on icing: Beware! I blithely took off IFR into forecasted “light to moderate icing” in my Comanche 250. An hour later, I had two-inches of clear ice covering the leading edges and had lost 20 knots of indicated airspeed. It took 20 minutes to climb into warmer air, once ATC cleared me to go higher. And the stall warning kept telling me how close to the edge I’d come. Landed safely but shaking. When I returned to the aircraft the next morning, a small crowd had gathered to marvel at the textbook ice cover and fist-sized ice balls on the VOR antenna.

        • None. But I’d flown through many “light rime icing” episodes with no problems. This was not that kind of episode. Very different from what had been forecast.

          • Let me add that this happened about 25 years ago, and was never repeated. Once is enough for a genuine learning experience.

          • This sounds like it was exactly as forecasted. Remember, trace, light, moderate and severe have to do with the RATE OF ACCUMULATION. If it took an hour to build an inch of ice I would call that light icing at best. For a plane without deice equipment it may be a severe problem but for the rest of the flying world (having deice equipment)your situation would be a non-event and should be reported as trace or light icing.

  • If there is anything I have learned from Mr. Collins books and 30+ years of flying is; always have a way out when the weather gets bad. This includes knowing when to fall back on the exit plan with enough fuel and alternate weather to pull it off.

  • Ellis, I think you’re being a tad harsh on Tom! The first thing I learnt at flying school in N. America and subsequently have been practicing Commercially in Europe and Asia is that no Pilot is perfect and we all make the odd decision which with hindsight and ‘KNOWLEDGE’ will never make again. Forums as these, Incident/accident reports; and for me one of the most important; ‘hangar flying’ with the other chaps teaches us new nuggets of information and at times reminds us of some that fade with the years.

    So in essence Tom, thanks for sharing!

    • Das,…..I appreciate any and all comments concerning a pilot’s skill & experience. I began my flight career in the USAF in 1957, went on to fly Commercially for Shell Oil and subsequently fly now for personal pleasure. It is always better to learn from the mistakes of others rather than make them yourself. This is no truer than in Aviation. Keep the shiny side up.

  • Thanks for these. Mostly they are things I am aware of or make sense, but….

    Can someone please explain number ten to me? I don’t really see why it is true.

  • Weather geeks may not like this but here is one way to visualize where the Lo is…with wind to your back extend your left arm and you’ll be pointing to the Lo. Of course,you’ll need to know the basic synoptic situation to understand what’s happening.

    Hope this hopes.

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