The old Area Forecast (FA) is going away, and I for one say good riddance. This textual forecast product has plenty of valuable information, but its ALL CAP, coded format is a leftover from a previous era, making it a pain to use. Besides, almost everything in the FA can be found elsewhere these days.
Everything, that is, except cloud top forecasts.
That’s a problem, because cloud tops are an important factor for safe and comfortable flying. Especially in the winter, when ice is a constant concern, knowing if the tops are at 5,000 or 25,000 matters a lot. It’s the difference between flying and canceling for some piston pilots.
The FAA has touted the experimental Graphical Forecasts for Aviation tool as a potential replacement for the Area Forecast, but it’s very much a work in progress. On the good side, it is presented as an interactive, layered map instead of an endless page of text. That’s a major step forward – seeing how radar, satellite, observations and SIGMETs work together is much easier with a color image than with pages of text.
In my opinion, though, the forecast cloud top product is not very accurate for GA pilots, at least not yet. Here’s an example. After going to the GFA tool at AviationWeather.gov, tap, Clouds at the top of the map, then Tops on the left side. I did this recently when a line of storms was moving through Indiana, and saw this.
The forecast map suggests relatively low tops – overcast ceilings about 2000 ft. and tops about 10,000 ft. – with just “CI ABV.” No problem in a turbocharged Cirrus or a TBM, right? Just blast through that layer and you’ll be on top.
Not quite. Look at the radar map in ForeFlight; it tells a very different story. And sure enough, tapping on one of those PIREP symbols reveals tops all that way to FL370. Not a great place to be flying a Cirrus (or anything really).
The cloud top forecast also doesn’t line up with the textual Area Forecast, which is still around (for now). On this day, it showed tops in Indiana as “layered to FL220.”
What’s going on here? For one, the cloud top product seems to be focused in particular on flights below 18,000 ft. But the forecast is also based on a numerical model (RAP), not the skeptical eye of a local forecaster. These models are good at a lot of things, but not estimating tops.
Here’s the Skew-t plot for a station in Indiana. It’s a geeky chart, but you can see the temperature and dewpoint lines converge at the 900mb level (about 2500 ft.) and they diverge again at 700mb (roughly 10,000 ft.). Those numbers match the data shown on the cloud top chart.
While such an observation is a helpful tool for understanding what’s happening in the atmosphere, it’s hardly a precise cloud top predictor.
At this point, it’s best to rely on other tools to determine where the tops really are. One obvious tool is PIREPs. While these aren’t always accurate for icing or turbulence (moderate to a 172 may be light for a Boeing), they are valuable for cloud bases and tops. Seek them out, whether from online weather sources or from ATC, and give them yourself when you’re flying.
Another good option is the color satellite image. This doesn’t show specific cloud altitudes, but it gives you an idea of the relative height – yellow and orange are higher.
The CIP/FIP icing forecast is another great tool, allowing you to see likely icing conditions at different altitudes and times in the future. On this same day, it showed icing at FL190, in clear disagreement with the GFA tool.
And of course the old advice to understand the big picture is probably best. A look at the surface analysis this day makes it clear that the rain and clouds in this area are the result of a fast-moving cold front, with a low pressure area centered on Lake Erie. Knowing that setup, it’s obvious that clouds around the front will be higher than 10,000 ft.
As always with weather, use all available forecast tools to add details, but don’t become a slave to one particular product.
Am I reading the forecast wrong? Anybody have another idea?