Ceiling and Visibility Plot Help

CVA Plots

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 the overview section , 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.

cva station plot description
Figure 1: Station plots for CVA displays.
cva cloud symbols description
Figure 2: Cloud cover symbols.

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

URL Options

Here is a list of the URL options:

  • region=region - This selects the specific region to display. The regions are:
    • ina - CONUS US
    • alb - Albany NY
    • bwi - Baltimore MD
    • clt - Charlotte NC
    • tpa - Tampa FL
    • dtw - Detroit MI
    • evv - Evansville IN
    • mgm - Montgomery AL
    • msp - Minneapolis MN
    • lit - Little Rock AR
    • pir - Pierre SD
    • ict - Wichita KS
    • aus - Austin TX
    • cod - Cody WY
    • den - Denver CO
    • abq - Albuquerque NM
    • lws - Lewiston ID
    • wmc - Winnemuca NV
    • las - Las Vegas NV
  • type={fltcat|ceil|vis} - This selects the type of plot. The default is fltcat.
  • date=yyyymmddhhnn - This selects a specific date and time to display. ADDS creates images every 5 minutes. The default is current.