CVA presents simplified area maps of ceiling, visibility and
flight category as outlined below:
Ceiling estimates are displayed as (i) "Possible Terrain Obscuration" (pale orange) for ceilings less than 200
ft AGL(above ground level), (ii) less than or equal to 1000
ft AGL (pale yellow) from 200 to 999
ft, AGL, and (iii) 1000 ft
AGL or greater (pale blue).
- Visibility estimates are displayed as (i) less than 3 miles (pale yellow), and (ii) 3 miles or greater (pale blue).
- IFR and VFR conditions
are determined according to the criteria given in the table below.
|| Visual Flight Rules
|| ceiling ≥1000 feet
||visibility ≥ 3 statute miles (sm)
||Instrument Flight Rules
||ceiling < 1,000 feet
|| visibility < 3 statute miles
As explained further in help page 4 ,
CVA's ceiling and visibility fields are derived through nearest-neighbor interpolation of METAR data.
This interpolation process, in effect, ‘stretches’ limited-area METAR observations across the broader
domain between stations and accounts for terrain effects on ceiling height. The resulting fields help
to visualize the ‘likely’ conditions at range from METARs. However, the reliability of these fields degrades
as distance from a METAR site increases. Thus, users should apply cautious practical judgment in considering
the representativeness of the product as distance from a METAR site increases.
METAR Station Plots
Each regional display includes station plots showing the current ceiling and visibility observations reported at selected
METAR stations. To avoid overcrowding, the display shows only a
subset of the total number of stations available. Station plot content is shown in the figure below.
Figure 1: Placement and definition of information in the station plots appearing in regional
Figure 2: Guide to coding used in the cloud cover symbol. Further information on station plot coding can be found
Refer to the following links for a complete list of METAR stations and associated station plots:
A complete list of METAR Stations
Station plots by ICAO (International Civil Aviation Organization) station identifier
Viewing CVA Through the HEMS Tool
CVA can also be viewed using the HEMS
(Helicopter Emergency Medical Service) Tool available on Experimental ADDS
(see HEMS tool). The HEMS
tool viewer is approved for use by EMS (Emergency Medical Services) personnel by OpSpec (Operational Specification) A021.