LancairTalk

With the winter season approaching rapidly I thought I’d write about some of the tools that I use for winter flying decision making with
a focus on icing conditions. Most of the details of these weather models I learned at Scott Dennstaedt’s “Under The Weather” seminar.

There are 4 main things I look at. First of all the forecast icing potential on aviationweather.gov. Unfortunately it doesn’t tell you about how serious the icing is, just the likelihood. One thing I’m looking for is any SLD (Supercooled Large Drop) predictions- if I see that, I’m going to avoid it at all costs. But mostly it gives me a picture of what levels to expect icing at.

The second thing I look for is a chart with the ‘lifted index’ from one of the weather models. Icing is pretty dependent on lifting happening in the atmosphere. As I understand it, without lifting when the temps are less than 0C, you are just going to get already frozen ice particles / snow which is no big deal. With lifting little bits of liquid water go up where they get colder but they don’t necessarily actually freeze until they hit your wing.

The third thing is a skew-T diagram. Skew-T will give you much better predications of where the cloud tops and layers are than the stuff you will find on aviationweather.gov. For example the cloud-top predications there I find are usually way higher than the real cloud tops. If you look at the skew-T and see the temperature and dew points are almost equal for a big stretch of altitudes, thats a pretty nasty thing to climb through. If they just briefly touch, thats probably a good sign. Plus the skew-t can show you inversions and other things to watch out for (freezing rain is really bad).

The last is of course PIREPs. These are often not so useful but I try anyway, and there is nothing like actual reports of icing (and lack thereof) and/or tops to do some good planning. If I really can’t tell I’ve been known to ask an arriving or departing jet to report tops- most of the time these guys have been super helpful although they often aren’t paying attention to the tops level unless you ask ahead of time.

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