The EZWxBrief progressive app provides the capability to see a depiction of clouds on the Route Profile and Airport Wx Meteogram views. For ease of discussion, both of these views utilize the same technique in how the presence or absence of clouds are determined. But for the sake of brevity, we'll only consider the Route Profile view.
First and foremost, determining the presence of clouds along a proposed route of flight is incredibly difficult if not fundamentally impossible at times. So a probabilistic approach using multiple numerical weather prediction models is required. Many of the heavyweight aviation apps on the market that also employ a route profile view will determine if clouds exist by utilizing a rudimentary relativity humidity scheme from a single model source. In general, this is a horrible and scientifically invalid approach to determine the presence of absence of clouds. Moreover it is unreliable especially for cold clouds (clouds at temperatures below -12°C). EZWxBrief, on the other hand, utilizes what is referred to as "cloud fractions" that are specifically blended from several forecast models to determine the presence or absence of clouds along the proposed route.
Without getting into the weeds of the complex algorithm employed by EZWxBrief, here's a high level view of how it is done. Once each hour, the EZWxBrief data server pulls a fresh new version of the numerical weather prediction forecasts from several high resolution models. When a user activates a route, it will do a georeferenced lookup and pull all necessary model data that is within a 50 mile corridor along the route (25 miles on each side). Essentially, at the departure airport and every 2.5 km along the route up to the destination airport, it attempts to find at most four primary cloud layers aloft using the cloud fractions scheme mentioned above while employing an inverse-distance weighting methodology. It may find no cloud layers or up to four layers accordingly.
Using the cloud fractions scheme along with the icing and ceiling algorithm (for consistency) it determines if the sky is clear or if there is indeed some cloud coverage up to 45,000 feet. If there are no cloud layers found, the sky is shown to be clear above that point. If there's a single cloud layer, then it will determine the cloud coverage (few, scattered, broken or overcast) and depth and plot that on the route profile as a white or gray rectangle at that location and altitude in the main viewport. White is used for broken or overcast coverage and gray is for few or scattered cloud coverage. Taller rectangles means the clouds have a greater depth.
The same is done when there are multiple cloud layers detected. Once a broken or overcast cloud layer is detected, any layers above that are also deemed to be broken or overcast. This approach may sometimes be overkill for those higher cloud layers but when deeper weather systems are present, it's very difficult to determine the sky coverage for those layers, especially when the area has a high likelihood of deep, moist convection occurring.
Lastly, the flight category bar along the route is rendered below the main viewport area and depicts the flight category forecast along the proposed route. This forecast has a 2.5 km resolution. If you hover your mouse over the bar as shown above (tap on it using a touch screen device), it will depict in tabular form the height of the lowest cloud layer(s) and the surface visibility. That height in the tabular display depicts height above the terrain. In the image above there are two layers above the proximity airport KFVX (about 2/3rds along the route). The lowest layer is scattered at 12,000 feet (gray rectangle) and there's a broken layer at 14,000 feet (bright white rectangle). This column of clouds extends up to 28,000 feet MSL.
Most pilots are weatherwise, but some are otherwise™
Dr. Scott Dennstaedt
Weather Systems Engineer
Founder, EZWxBrief™
CFI & former NWS meteorologist
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