ADDS - Aviation Digital Data Service

ADDS - C&V Help Page (3 of 5)
Back to C&V Page or C&V help page 2 or C&V help page 4.


Using CVA

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.

Flight Category Formulation
VFR Visual Flight Rules ceiling ≥1000 feet and visibility ≥ 3 statute miles (sm)
IFR Instrument Flight Rules ceiling < 1,000 feet and/or 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 CVA displays.
cva station plot description
Figure 2: Guide to coding used in the cloud cover symbol. Further information on station plot coding can be found here .
cva cloud symbols description

Refer to the following links for a complete list of METAR stations and associated station plots:

  1. A complete list of METAR Stations
  2. 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.