How high are the cloud tops?

Cloud top heights have always been hard to find. We have lots of information about cloud bases: METARs, AWOS, TAFs, and Pilot Reports. When the weather's low, it's fairly easy to identify the cloud bases. But when icing's a concern, we're more focused on cloud tops, and those are hard to predict.

We used to have the Area Forecast, which was far from perfect. But it did forecast cloud layers and tops, and it had a meteorologist involved. That's gone away in favor of the Graphical Area Forecast, which has some advantages. But it isn't always as accurate with cloud tops.

We also have the Color IR Satellite picture, which is pretty accurate, with one major limitation. We have Pilot Reports. They're our favorite, but often, they're hard to come by. And finally, we have icing forecasts, which will come into play on this flight.

The Flight

Since the best way to show this is with a real flight, the video at the top of this article is our trip from Rocky Mountain Metro, KBJC, to Santa Fe, New Mexico, KSAF.

There's warm front extending from a low in west-central Colorado, extending to the New Mexico border. Our route flies over IFR ceilings all the way to the Colorado-New Mexico border, when the ceilings clear up.

We'll need to fly a departure on our way out of Broomfield, and the Pikes One lines up with our route to the southwest. We have two transition options. The Alamosa transition keeps us on a more direct route towards Santa Fe, but takes us west of Pikes Peak and over higher terrain. That usually leads to higher cloud tops and more ice.

The Pueblo transition keeps us further east, over lower terrain, and gives us the option of crossing the Sangre De Christo Range further south where the weather is better, with lower clouds and less ice. So to start, let's get an idea of where those tops are.

1) The Graphical Area Forecast

With the Area Forecast out of production, we'll look at its replacement: the Graphical Area Forecast. It uses the NOAA Rapid Refresh data model to forecast cloud coverage, bases, and tops. And it's entirely autonomous - meteorologists don't intervene in the forecast output. In our opinion, it's not very accurate, especially with cumuliform clouds and thunderstorms, But it seems to do better with large scale stratiform clouds. Either way, we'll take the forecast with a grain of salt.

ForeFlight includes this under the Forecasts tab, under "Cloud Coverage." It shows overcast coverage along our route, with bases at seven thousand feet MSL and tops at twelve thousand feet MSL. And those tops lower as we head south. The tops are higher to the west over the mountains, reaching Flight Level Two Two Zero in spots, and lower over the eastern plains, which makes sense. The higher terrain lifts the air mass and cloud layers.

2) Color IR Satellite

We often have a more accurate picture of what's going on with the Color IR Satellite overlay. This isn't a forecast, it's a picture of what's happening now. And, while it shows the cloud coverage, it doesn't directly show the height of the tops. But it does show the temperature at the cloud tops.

Combine that with the winds aloft temperatures, and you can estimate the cloud tops.

The clouds in the Denver fade from light blue to green. Checking the Foreflight weather guide, that ranges from -32C to -24C.

Comparing that to the Denver winds aloft forecast, where the temperature at 24,000' is forecast at -24C, the tops are somewhere above 24,000'.

Of course, the green drops off to orange south by Colorado Springs, which could be -12C or warmer. That matches the 15,000' forecast. So, do the clouds around Denver reach up above 24,000'? This points out the biggest issue with satellite estimated cloud tops. They can only see the highest layer, and there's no way to tell if there are layers of clouds (or clear skies) below.

3) Pilot Reports

Pilot reports are often the most accurate, but many pilots don't report cloud tops, only bases. Luckily we have quite a few pilot reports today, with some top heights.

An Embraer 175 reported cloud tops at 12,500' MSL, with light rime ice between 9,500' and 11,500', which matches the Graphical Area Forecast. The report is a bit old though, at almost two hours.

A Citation 525A, CJ2, reported 2.5SM of visibility in light freezing drizzle and mist at Centennial, with light rime between 9,000' and 6,400' MSL. It's also kind of old, at an hour and a half.

An Embraer 145 reported a light mix of ice from the surface to 10,500' MSL. And, a Boeing 717-200 reported moderate to heavy rime between 10,000' and 6,400' MSL, 6 miles south of Denver. Heavy isn't an icing severity, but we'd assume the crew meant severe.

Avoiding Ice

Our Cirrus SR-22 turbo is equipped with a TKS deicing system, and it's certified for flight into moderate known icing. The system protects the wing from the root to the tip, as well as the elevators and horns, and the vertical stabilizer.

Fluid also slings out onto the prop, and some of that sprays back to the windshield, though we have windshield jets if we need them. But, defrost normally does the job. The pitot tube and stall warning vanes are heated, as well.

Of course, the best anti-ice system is clear air, and that's our goal today. Climb through the clouds up to the top.

Putting Everything Together For A Safe Flight

Icing layers are notoriously hard to predict. And cloud tops are just as difficult to forecast.

While pilot reports are one of our best sources, the tops usually go unreported. But, by combining the Graphical Area Forecast, Color IR Satellite, Pilot Reports, and the CIP and FIP icing products, you can build a pretty good plan.

Today, we found part of what we expected. Tops of a layer at 10,500' MSL, close to the GFA, with another higher layer at 14,500' MSL, which matches our 15,000' satellite estimate south of the metro area.

And, as always, you need to have a couple of good outs. After all, if you can't find the cloud tops, you don't want to use your anti-icing system long.