The Imagery view in WeatherSpork includes the latest automated analyses and forecasts for airframe ice. These are referred to as the Current Icing Product (CIP) and Forecast Icing Product (FIP), respectively. Both the analysis and forecast have three basic components to include probability, severity and supercooled large drop (SLD) icing. Based on WeatherSpork customer feedback, we have recently added the SLD threat to the icing analysis and forecast severity charts like the one shown below.
What is SLD?
SLD stands for supercooled LARGE drop icing. Many pilots like to say it stands for supercooled “liquid” drops. Yes, they are liquid, but they are missing the point. For icing certification standards a large drop environment is one that has a median volumetric diameter (MVD) of greater than 50 microns. This means that if you could line up all of the drops in a cloud by its size and found the median size, that would be the MVD for that environment. Just for reference, the average human hair is 100 microns in diameter. So, just as a drop becomes visible to the naked eye, it’s considered beyond the certification standards of all aircraft.
SLD is shown as a red-hatched overlay on the ADDS icing severity chart like the one shown below. Keep in mind that the SLD analysis or forecast isn’t a calibrated probability. In other words, SLD will be included even when there’s just a 5 percent chance of it occurring. So it’s properly referred to as an SLD “potential” field.
CIP (pronounced “sip”) is an analysis of the current icing situation. This means that it is always valid in the recent past. It is updated hourly and depicts the icing scenario at the top of the most recent hour. It becomes available in WeatherSpork around 25 minutes past each hour. For example, the analysis valid at 1600Z will be available at 1625Z. You will find this SLD analysis in the Imagery view under Icing Analyses::Current Icing Product::ADDS Severity.
If you want to assess the actual likelihood of SLD valid at the top of the most recent hour, WeatherSpork provides a CIP SLD analysis as a separate field. You will find this in the Imagery view under Icing Analyses::Current Icing Product::SLD Potential as shown below. Warm colors such as red and orange represent a greater likelihood of SLD where as cooler colors such as green and blue are indicative of a low likelihood.
FIP, on the other hand, is the forecast counterpart and you will find this in the Imagery view under Icing Forecasts by Altitude::ADDS Severity. You can choose from a lead time of 2, 3, 6, 9, 12, 15 and 18 hours as shown below and it will also have an SLD overlay hatched in red.
“Most pilots are weatherwise, but some are otherwise.”
Weather Systems Engineer