With WeatherSpork version 4.3.0, we’ve extended the static Imagery to include aviation forecasts from the High Resolution Ensemble Forecast (HREF) model. The HREF is updated four times a day and provides a forecast lead time of 36 hours at one hour time increments. In WeatherSpork you can find these in the Imagery view right below Graphical MOS under HREF Model as shown below.
These six choices provide the probability of a flight category of Marginal VFR (MVFR), IFR and Low IFR (LIFR) as well as the probability of a ceiling below 3,000 ft, 2,000 ft and 1,000 ft AGL. In the sample below, the colors represent probabilities shown on the scale at the bottom of the chart. Colors such as red and purple are indicative of ceilings that are forecast to be less than 3,000 feet as they are in northern Ohio; of course, they could be much less than 3,000 feet in this area. Keep in mind that non-filled areas do not mean clear skies per se. This simply means that there is a very low chance the ceiling will be less than 3,000 feet in these areas. This 21 hr forecast is valid at 1500Z on April 28, 2018.
The probabilistic ceiling forecasts above are additive in nature. In other words if there’s a high probability of a ceiling less than 1,000 feet, there’s also a high probability of a ceiling less than 2,000 feet and 1,000 feet respectively.
Flight category combines both the ceiling and visibility as shown in the table below. These flight categories are sometimes improperly referred to as flight rules in many flight planning apps.
In addition to the probabilistic forecasts for ceiling, the HREF also provides a probabilistic forecast for specific flight categories that include LIFR, IFR and MVFR. The example below has a forecast lead time of 22 hours and is valid at 1600Z on April 28, 2018. Similar to the probabilistic ceiling forecasts above, higher probabilities of a MVFR flight category are shown in red and purple colors like you see in Indiana and Ohio in the example below. Non-filled areas simply mean that the chances of a MVFR flight category are very low. Unlike the probabilistic ceiling forecasts above, these forecasts are not additive. That is, in an area where there’s a high probability of a MVFR ceiling, there may be a very low probability of a LIFR ceiling.
Weather Systems Engineer