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, (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 sm
As explained further in Inside CVA – How it Works,
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.
The opening view presents a broad-scale survey of conditions across the continental U.S.
Placing the cursor over the map display opens a moveable “magnifier” that provides a more detailed look at the display region
underneath. The magnifier can also be useful in reading text on the display.
Any one of 18 regional-scale views may be selected for closer inspection using the “Region” drop-down menu or the
“Picker” button to its right. The magnifier can be used on these displays as well. The
METAR station plots appearing on regional displays are described
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
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 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 personnel by OpSpec