Ceilings
These prognostic charts for 6, 12, 18 and 24 hours (at 0000 and 1200) are produced by the regional run of the Global Environmental Multiscale (GEM) model. Forecast are of low and middle cloud ceilings and are packaged as 4-panel charts as depicted below.
| 6 hour | 12 hour |
|---|---|
| 18 hour | 24 hour |
- Area of coverage for all panels is as follows : North America and Arctic regions, North Atlantic, northern portions of Asia, and North Pacific.
- The transmission identifiers are as follows : CMC784, CMC785.
Sample chart (4-panel)
Low and middle clouds
Fields
- Low cloud
- Depiction: Low clouds with opacity of 6/10 or more of the sky and a base of less than 6500 feet are indicated with a light stippling and a thin dashed line.
- Middle cloud
- Depiction: Middle clouds with opacity of 6/10 or more of the sky and with a base between 6500 and 24000 feet above mean sea level are indicated with a dark stippling and a thick line.
Plotting model
In the stippled areas, the base and top of the low and mid cloud layer are plotted in thousands of feet above mean sea level. The lower number gives the base and the upper number indicates the top of the layer. Tops above 24,000 feet are plotted as 99.