Observation Viewer
Here, I show comparisons between what I categorized as undercast, and was was labeled as undercast by the summit observer.
Reading the METAR: the relevant pieces are highlighted — visibility, any layer overhead, and the TPS LWR group giving the coverage and top height of the deck below the 6,288 ft summit. Heights in the body are above the station; TPS LWR heights are above sea level.
The cuts
An observation is called undercast only if it passes every test below. If it fails but clears the looser “ambiguous” bound on every test, it is called ambiguous and left out of training. Anything else is not undercast. Heights are relative to the 6,288 ft summit.
| Test | Undercast | Ambiguous |
|---|---|---|
Deck below the summit (TPS LWR) | BKN or OVC | also SCT |
| Visibility | > 40 SM | > 25 SM |
| Deck top below the summit | ≥ 500 ft | ≥ 250 ft |
| Lowest cloud overhead, any cover (if any) | ≥ 1,000 ft | ≥ 500 ft |
| Lowest BKN/OVC ceiling overhead (if any) | ≥ 5,000 ft | ≥ 3,500 ft |
Photo classification details
The webcam photos come from daily timelapse videos that fade from one day into the next, so some frames show two days blended together. Each date uses a clean frame whose timestamp matches it where one exists. Where none does, the blended frame is shown and marked with an asterisk.
I was fairly generous when labeling undercast days by hand. Parial undercasts (only visible on one camera or partial cloud deck) were generally labeled as undercast/