Prog chart
8 min read

The internet and mobile apps have changed life for billions of people around the world, and pilots are certainly no exception. Some call it a technological liberation, others call it a democratization of information, but the end result is the same: all of us have instant access to information that was once either unavailable or jealously guarded by experts.

While this has undeniably been a positive development, it doesn’t come without risks. If we’re not careful, more information can actually lead to less knowledge. Just spend 10 minutes on Twitter if you need proof – everyone there is an expert on politics, economics, sports, science and so much else. This chaos shows that it may be easier to find the right answer online, but it’s also easier to find only the answer you’re looking for. Confirmation bias runs rampant when information is plentiful.

Los Angeles Flight Watch

We don’t have this guy to depend on anymore.

The familiar ritual of a preflight weather briefing can easily fall into the same trap. Where once a preflight weather briefer (in person at a Flight Service Station – how quaint!) sorted through all the information and offered a stern warning that “VFR flight is not recommended,” the go/no-go decision now rests squarely on our shoulders.

I don’t mourn the disappearance of FSS briefings one bit – I’d rather look at a radar picture than have it described to me – but our newfound freedom does demand some significant responsibility. Since most of us don’t have formal weather training, we have to be disciplined about how we collect, organize and analyze preflight information.

Here are 10 lessons I’ve learned in the seven years since I last called Flight Service.

Have a flow. One way to avoid taking in either too little or too much information is to make a plan and have a structured process for preflight weather planning. I like to start with a wide perspective, then get progressively more local and more real time – much the way a standard weather briefing from Flight Service is structured. A good place to begin is with the surface analysis, then consider national forecast charts, then radar/satellite imagery, then local observations. This flow uses a building block approach, so each new piece of data (a METAR, say) fits into a larger theme (widespread marginal VFR conditions due to a surface low).

Prog chart

Start here, then think about METARs and TAFs.

Get the big picture overview. One of the cardinal sins of weather planning is to blindly read METARs and TAFs without considering their context. Instead of being a mindless reader of weather information, think of it as a mystery that you have to solve: why is the weather the way it is? To answer this question, look at the big picture, particularly the location of lows and fronts. Then read the 300mb analysis and get a sense for the ridges and troughs, the highways that move weather around. Once you have this overview in mind, everything else is a matter of filling in details.

Make METARs visual. One of the ways technology has improved weather briefings is by transforming confusing text blocks into simple visual maps, and yet many pilots restrict themselves to raw METARs. Especially for VFR pilots, it’s far better to show those reports as a graphic. Is the low visibility at your airport an isolated event or widespread? With a single glance, you can answer the question. Almost all weather websites and apps have some version of this tool.

Understand the limitations of TAFs. The terminal forecast is an invaluable tool for pilots, whether IFR or VFR, but it’s critical to remember that a TAF is only for the immediate airport area (5 statute miles). If your home airport is in a river valley, a TAF for the big international airport 25 miles away on top of a hill may be just about worthless. Also remember that the age of the TAF says a lot about its accuracy. A four-hour old TAF is worth less than a brand new one. Read and understand the terminal forecast, but don’t give it too much weight – a good option is to read the forecast discussions found in many apps these days, which try to quantify the uncertainty found in most TAFs.

The trend is your friend. This is a basic concept, but it’s so powerful when used consistently. No matter what the actual METAR or TAF says, is it getting better or worse? If the last three METARs have all reported visibility dropping, it doesn’t matter what the TAF says – conditions are clearly worsening. Likewise, if the TAF originally called for clear skies at 8 am tomorrow, then was updated to show 3000 broken at 8 am tomorrow, you should be suspicious. You may wake up to find a 1200-foot overcast, as the developing trend gets ahead of the forecast.

Low visibility in haze

The METAR said 3 miles – it’s legal VFR, right?

Visibility usually matters more than ceilings. Would you rather have ten miles of visibility and 1500 overcast or three miles of visibility in rain under a 5000 foot broken ceiling? There’s no definitive answer, but in most cases I would take the ten miles. That marginal three or four miles can quickly become hard IFR (one or two miles) if precipitation increases, and even three miles is very demanding flying for VFR pilots.

Watch the weather before and after a flight. Plenty of pilots watch the weather well in advance of a flight (sometimes to a fault). While it’s sensible to start reading forecasts a few days before a flight, don’t limit yourself to those situations. There’s a lot to learn by following the weather every week, to get a sense for the patterns at work and to train your eye for common weather signatures. When you fly, watch the weather develop after you land. How did it compare to what you saw in flight? Each of these sessions is a chance to train your own personal weather algorithm.

Use new weather tools. The last 5-10 years have seen some great weather forecast products come on the scene. If your weather toolbox doesn’t include these new ones, you’re missing out on some valuable information. My favorites address three of our most consistent concerns in general aviation: thunderstorms, icing and turbulence. The CCFP and ECFP offer graphical depictions of convective weather, extending four to five days out, and really help plan a summer cross country. The CIP/FIP charts show forecast icing conditions at various altitudes and times in the future. It’s not flawless, but it’s becoming very good, and when combined with a big picture overview it can help you avoid the worst icing. Like the icing forecast, the GTG chart shows forecast turbulence at different altitudes and times. This was previously only available for high altitudes, but it now goes all the way to 1000 ft.

Ice on wing

The best way to avoid the white stuff on your wing is to find the tops.

Find the tops if ice is around. For instrument pilots in piston aircraft, in-flight icing is one of the most serious threats from Mother Nature. The charts mentioned above are the best tool, but there’s more to consider. One of the best approaches is to aggressively search out reports of cloud tops, whether from PIREPs, area forecasts, forecast discussions or even satellite imagery. Combine all of these products with your knowledge of the big picture (hint: east of a strong low is a bad place to be). And remember: a lack of PIREPs does not mean it’s safe.

More isn’t always better. Being a weather geek can be fun, but some pilots suffer from analysis paralysis. If you have a good idea of the big picture, a feel for the trend, and all the supporting weather reports, it’s probably time to make the go/no-go decision. Reviewing Skew-t log(p) plots for every station along your route or devouring pages of coded MOS forecasts is interesting, but it probably won’t help you make a safe decision. You’ll either get confused by all the additional information or you’ll search for the one report that tells you it’s OK to launch – that confirmation bias coming back into play. Instead, make a plan, then follow it.

Technology has taken a lot of the mystery out of weather forecasting, filling in the gaps with more precise, more accurate and more comprehensive information. Given the abundance of weather products, it’s tempting to simply consume weather reports without thinking about them: “the TAF says it’ll be good, so we’re going!” That’s a dangerous mindset. A good pilot is still his own weather forecaster, suspiciously evaluating all the reports and forecasts he comes across and fitting them into a theory of what the atmosphere is doing at the moment of departure. A good pilot is also not afraid to use all the tools at his disposal.

John Zimmerman
7 replies
  1. Duane
    Duane says:


    Nice summary of the current state of the art in aviation flight self-briefings. The “less is more” is especially apt, given the much increased array of sources available conveniently online.

    Let me add another guideline for consideration in self-briefings:

    It’s much less important to accurately forecast the weather – which no matter how thoroughly and professionally we analyze it, the actual weather we fly in often doesn’t match the forecast – than it is to be able to use the weather info to plan “escape routes” for when the weather doesn’t cooperate.

    This means not only looking at macro weather phenomena like frontal systems, temperatures, winds, etc., but also micro weather as it might apply to the specific terrain and obstacles we plan to fly over, and to the alternate routes, airspace, and airports that we might need to use to escape unhelpful weather or equipment malfunctions. Make robust alternative flight planning a standard tactic and template for all flight planning activities.

  2. Scott Dennstaedt
    Scott Dennstaedt says:

    John – overall a very thoughtful write-up. As you say the big picture weather (or what meteorologists refer to as the synoptic overview) and trends are often more important than most pilots think or want to believe. Diving into the details right away is by far the worst thing to do…it’s like driving down the road looking through a straw. In fact, I had a customer of mine make a trip yesterday from NYC to MIA. He and I did an online session together to review the weather and what we saw at the synoptic level was extremely important for making the very best decision for the safest route. Essentially, a slow moving cold front into the SE became stalled over the mountains. This left the Southeast U.S. in very unstable conditions. The heating of the day allowed convection to develop over a good portion of the region to the southeast of the front – *over land.* However, without a front “pushing” the convection eastward, the cooler waters over the Atlantic would keep the areas off the coast free of any convection. Any convection that moved out over the water would likely dissipate quickly. This meant a coastal route would be the safest. He had a raft (eventually headed to Jamaica) so he was comfortable deviating as necessary if there were a few cells in his path right along the coastline. Worked out great with only one significant deviation along the entire route.

    Couple of other points. You say, “Also remember that the age of the TAF says a lot about its accuracy. A four-hour old TAF is worth less than a brand new one.” Not sure this holds any truth. In fact, it may be just the opposite. TAFs get routinely issued every 6 hours at 00Z, 06Z, 12Z and 18Z (every three or even two at some high impact airports – although the non-standard issuances are labeled as AMD at these airports). Sure, a brand new TAF or amended TAF is likely more up to date with changes in the weather or forecast. But that doesn’t mean a 4 hour old TAF isn’t going to be as up to date since TAFs are watched carefully when the exceed amendment criteria. A TAF that is four hours old might be one where the meteorologist has nailed the forecast and doesn’t need an amendment. In fact, that kind of situation makes me feel the forecaster has a great handle on the weather and can be trusted. Versus one that is amended every couple of hours due to a tough forecast and changeable weather where the meteorologist is having a tough time. I wouldn’t be so quick to say the latter is a better situation.

    You say, “More isn’t often better.” Yes, it will come to a point where getting more information isn’t going to add any value to your decision. In fact, when you start seeing the same message as you look at more info, that’s a good thing…it tells you there’s consistency in the data. However, I encourage my students not to confuse this with being complete in your analysis. I find too many pilots often are not complete in their analysis. I’ve fallen victim to this as well. I remember a trip where I was ultra-concerned about being able to get on top of an icing layer and staying on top. Both the climb and descent would be in clear air. In all of that focus, I totally missed the 35 knot crosswind that was expected for my destination airport (and I didn’t factor that into my fuel requirements if I need to find an alternate). I had no issues staying on top, but that landing was indeed challenging.

    I usually spend at least one hour looking at the weather for a single leg trip (even if the flight is only an hour in duration). Usually in the first 15 minutes I can get a sense of whether or not I can make a safe flight. The rest of the time is spent refining the timing, route and altitude and most importantly, spending time looking at alternates. TAFs (and MOS) are very good for alternate selection. They are point forecasts and shouldn’t be used as an en route forecast. But you should always say, “if things go bad, which airports make a good alternate.” In other words, use TAFs (and MOS) as “if I had to go there, what is the expected weather at the time of my arrival.” As opposed to, “well it looks like the TAFs along my route look fine, so I should be okay to make the flight.” The latter will eventually lead you to en route surprises.

    Lastly, I do like your statement to “train your own personal weather algorithm.” I hear way too many pilots tell other pilots, “don’t beat yourself up when you decide not to make a flight and the weather turned out fine.” Or, my favorite is, “don’t second-guess yourself.” Neither of these attitudes are healthy when it comes to weather. No, I don’t beat myself up for deciding to stay, but I learn from it if I’ve made poor decision. I don’t put it behind me and lose the opportunity to learn If you make a “poor” decision to stay, what’s the likelihood you make a poor decision to go? You can’t have your cake and eat it too. It goes both ways. Learn from your no-go mistakes and seek out formal training in weather. This will help you make more confident decisions in the future.

    • John Zimmerman
      John Zimmerman says:

      Great analysis as always, Scott. I love looking at MOS and lots of other weather products, but the key is to make sure you’re doing it with the right motivation. I see some pilots, when confronted with bad weather, start searching out any weather product they can that will give them hope of flying that day. That’s dangerous to me.

  3. Richard
    Richard says:


    A great discussion on a topic near and dear to all pilots. I am somewhat a weather geek, so I appreciate you letting me be a vouyer into your thoughts.

  4. Steve Kuemmerle
    Steve Kuemmerle says:

    Great essay and comments. I have only about 800 hrs., but a couple of Wx habits I have found useful are: 1) I print a mini-report consisting of 5-6 METAR/TAF reports along the route, winds aloft and area forecast (soon to go; sigh). That way I can see how conditions may be changing as I check ahead during the flight. And, 2) for any x-country trip, I do an on-line Wx review before talking to a LMFS briefer. The on-line / live combo seems to work well for me.


  5. Larry Olson
    Larry Olson says:

    John and Scott,
    Good comments from both of you. Lots to think about, and a LOT depends on the particular day of flight.

    I will rarely spend an hour briefing for a one hour flight… it rapidly defeats the purpose, if the flight is to save time and convenience, which is often the case. Now, in some cases… perhaps. Like if I need to have the plane there for a later flight that’s equally important. But if the briefing gets a lot over an hour, one could make the argument to just drive, delay or divert.

    But, at times, I’ve spend 2 or 3 hours in briefing, with an initial brief, then a few updates, and the last one just before launching.

    However, what is more important, is to constantly up date weather and decisions enroute. For a long trip, this would be several times, and perhaps adjusting the route accordingly.

    And also, always have a plan b, and perhaps a plan c, and those might change.

    Fortunately the vast majority of flight are uneventful and very few adjustments for weather. For a lot of us, this is 95% of our flying. And only 2 or 3 % is a challenge and the rest is a no go (or divert).

    Now, I’m more of a “deviate or divert” as necessary, especially with fast moving or changing wx. Occasionally, we’ll check the wx several times in the several hours before the flight, and it changes with every briefing. I would probably just launch and just update and decide along the way, especially with convective stuff we see on the east side of this country.

    Now having said the above, I can say that it has worked well for me for my ~27k hours. Never been in a mature thunderstorm, never in severe ice, and never had a severe weather emergency. Yes, I’ve had a few uncomfortable rides.

    Minor point about vis….. I’ll take ceilings over vis, just to get them above mins. If you’re still in the clouds at mins, ya ain’t gonna land, but if you are below the clouds, even at 200 feet, with a 1/4 mile, you “could” land.

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