A successful flight starts long before the tanks are topped off with fuel or the ignition is ever started. It goes back before preflight and past even the restful night before. Today we’ll walk through a decision-making weather scenario that begins several days prior to our scheduled flight. In this scenario, it’s Monday. I’ve just hung up the phone from booking the airplane for a flight this Thursday morning (three days from now) at 10am. I reserved the plane for two hours to kick around the local area and practice some landings at the Thomson-McDuffie Airport (KHQU). Follow along and watch the weather with me as we make the big decision together. To fly or not to fly…THAT is the question.
Three Days Out
Being three days away from our flight, gathering weather information is all about “big picture” analysis. I’ll use a couple of different sources to try to paint the picture of what the weather will be doing over the next few days and how that might affect our flight. Looking at the Wunderground app, the next few days are forecast to be sunny with only a 10% chance of rain. On Thursday (flight day), partly cloudy skies and some wind join the party. There is also a spike in the chance of precipitation between Wednesday night and Thursday morning.
Looking at some weather imagery through DUATS, I find some prognostic charts. Known as “prog charts” by the cool kids, these are maps of things like temperature, wind, precipitation, and this one for frontal movement. Swiping through them, I find one for Wednesay night at 7pm local (0000Z) that shows a cold front with moisture in front of it moving in from west of my location (in Georgia).
I look to the next chart for Thursday at 7am local time (1200Z), just three hours before the flight. I find that the cold front is forecast to have passed our location. Cold fronts tend to bring in clouds and poor weather ahead of the front, followed by clear air with higher winds after the front passes. Well, that explains the rain overnight and the pickup of the wind from our Wunderground forecast.
So what does this all mean? Well, let’s watch out for that cold front in case it moves through slower than forecast. That could leave us with the clouds and precipitation often associated with it. Also, the wind that tends to come after the front might be a little high for my personal minimums. Let’s keep our eyes peeled.
Two Days Out
Checking for any changes from yesterday’s forecasts, we find that the rain still looks to be coming through Wednesday night. Notice that the wind is now forecast to be 12mph instead of the 11mph from yesterday’s forecast. That’s something to keep an eye on.
Looking back at the prog charts, the new forecast for Thursday at 7AM (1200Z) seems to show that the front is moving a little slower than expected. One important thing to keep in mind: a forecast is just a guess. It might be an educated, computer assisted, science backed, history driven guess, but it’s still a guess – not a guarantee. Either way – pick it up, cold front. I’ve got some flying to do.
One Day Out
It’s the day before the flight. This close in, we can get a much better picture of what tomorrow morning will really look like. The cold front is moving along faster than before on the updated 7AM (1200Z) Thursday forecast. That’ll help clear the air of clouds and precipitation.
This close to the flight, a Terminal Aerodrome Forecast (TAF) can start to get us real numbers to work with. The farthest out this TAF goes is to Thursday at 1AM. That’s about 9 hours before the flight and is pretty messy weather. A new TAF comes out every 6 hours, so we’ll have to check back later to see our actual flight time. What helps us here is that we know the big picture. If we hadn’t seen that a cold front was coming through, this TAF might suggest that the weather is simply tanking just hours before our flight. Well, it is, but because we have the big picture, we know the weather will get better. In some ways, at least.
Looking at some different imagery available through Foreflight, I found this MOS Ceiling Height forecast. MOS stands for Model Output Statistics. Sounds fancy. Sciency, even. But this forecast simply shows us the estimated height that the cloud ceilings will begin. This graphic gives me pretty good confidence that we’ll be in that nice strip of clear skies in middle Georgia.
Later in the evening, I check back for the lastest TAF to come out. This one now forecasts out to the time of our flight and beyond. The flight is at 10AM (1500Z). Looking to just an hour before at 1400Z, we can see that the mess of the cold front has moved through as expected. The visibility is good and the clouds are up nice and high at 25000 feet. That wind, though. It might be a better day to take up sailing. 15 knots gusting to 25 knots. That’s certainly higher than the 11-12mph (9-10 knots) that Wunderground originally forecast.
Let’s talk about this wind. It’ll be out of the west at 290, which is good. Thomson Airport has a runway 28, so that’s just 10 degrees of crosswind. Crosswind or not, however, it isn’t looking good for my 10 knot personal minimum. I might go ahead and text one of the instructors at the airport to see if he’s available to fly with me. If the wind is above my personal minimum, I won’t fly alone, but it might be a great day for some instructor guided practice in the wind. After all, that’s the only way to work up that personal minimum. My best bet now is to get a good night’s rest and check again in the morning.
Let’s pour a cup of coffee and open up the iPad to check the latest weather. Now that we’re this close to flight time, looking at big picture imagery isn’t as important as analyzing the numbers in the forecast. Don’t get me wrong – the big picture is important, but we don’t need a map to show us that the front has passed. What we need to analyze is the METAR (current conditions) and the TAF. That will help us see how the big picture trickles down to us. The METAR for the airport actually looks pretty good. The clouds are high, the visibility is good, and the wind is only 6 knots. If it wasn’t for having the big picture and understanding the cold front, we might get our hopes up with this METAR. We might even look no further and hop in the plane.
Looking at the TAF shows us that those METAR conditions are short lived. The forecast is sticking with strong wind – still 15 knots gusting to 25 knots. The next change in the TAF isn’t until 6PM (2300Z), so I’m inclined to think that the wind is here for the day. Top off your coffee and grab a scone. It’s time to look at our options and make a decision.
The decision not fly the local solo practice flight as planned really is made for me. My personal minimum for wind is 10 knots, and the wind will be well beyond that. Our plan B of flying with an instructor is looking pretty good, though. The wind will be almost straight down the runway – gusty crosswind landings might not be so fun. It might be a good time to brush up on some ground reference maneuvers with the wind being so exaggerated. I’ll have a good opportunity to practice positioning my flight controls during taxi with higher winds. My decision is to fly with an instructor. I’ll call Flight Service on the way to the airport to speak with a briefer for a formal weather briefing. That’s a good time to get another professional perspective and see if there is anything I missed. Today the factor was wind, but on other days, it might be thunderstorms in the area. The decision isn’t as black and white as go or no-go. You might think of it more of a “go, adjust, or no-go.” If I were flying to a different airport, for instance, I might learn of marginal weather at my destination only to adjust and select an airport with better weather. Or maybe I would have the ability to push the flight back a few hours, or even move it up a day, as I did on a recent trip to Nashville. Looking at the weather is a big factor, but it’s only ONE factor. Beyond the weather calls are considerations like the IMSAFE checklist (Illness, Medication, Stress, Alcohol, Fatigue, and Eating). The no-go could be made if I woke up feeling a cold coming on. Then there’s mechanical considerations during preflight. The no-go could be made if a critical component isn’t working correctly or has lapsed it’s inspection time. The no-go could be made during the runup if the mag check looks off. The no-go could even be made on the takeoff roll if the engine isn’t in the green. The decision to go or no-go is a continuous one. Every moment is a new decision based on the information and resources you have. And at the end of the day, there is no shame in staying on the ground. Even if you COULD do it, a good decision to fly hinges on building a safe margin for error. Don’t forget – it’s a lot better to be on the ground wishing you were in the air than in the air wishing you were on the ground.
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