CVA (Ceiling and Visibility Analysis) is a real-time analysis of current C&V (ceiling and visibility) conditions across the continental U.S. The product is primarily intended to help the general aviation pilot (particularly the VFR-only pilot) avoid IFR conditions. However, CVA's quick-glance overview of ceiling and visibility conditions can be useful to others involved in flight planning or weather briefing. To remain current in rapidly changing conditions, CVA is updated every five minutes. The overview provided by CVA should be followed by further examination of METARs, TAFs, AIRMETs, Area Forecasts and other weather information.
The product makes use of real-time METAR observations to establish C&V (Ceiling & Visibility) conditions at approximately 2000 observing points.
At display points between METAR locations (where there are no direct observations), CVA ceiling values are derived as follows:
Visibility values at display points are taken as the visibility observed at the nearest METAR site and are displayed as (i) less than 3 miles (pale yellow), and (ii) 3 miles or greater (pale blue).
Flight category values are derived from ceiling and visibility display values according to the official definition, as given in the table below.
|VFR (Visual Flight Rules)||Visual Flight Rules||ceiling ≥1000 feet||and||visibility ≥ 3 statute miles (sm)|
|IFR (Instrument Flight Rules)||Instrument Flight Rules||ceiling < 1,000 feet||and/or||visibility < 3 sm (statute miles)|
While CVA provides an accurate representation of observed conditions at METAR locations, only estimated conditions are available at regions between METAR sites, and these estimates are subject to error.
NOAA carried out a study comparing CVA ceiling and visibility estimates with actual observations. Understanding the results of the study can improve a user's understanding of how to best use the CVA product. The study is entitled, NCVA_D4_SUB_REGION_ENHANCEMENT_FINAL.pdf
CVA grids are made available by the NWS (National Weather Service) as GRIB2 (GRIdded Binary) files for distribution and archive via NOAAPORT (for subscribers) and via FTP (File Transfer Protocol) from the NWSTG (National Weather Service Telecommunications Gateway).
By FAA policy, CVA is a Supplementary Weather Product for enhanced situational awareness only. CVA must only be used with primary products such as METARs, TAFs and AIRMETs.
See the Supplementary Weather Product Description page for a definition of these terms. Also see AIM Section 7-1-3 for requirements regarding use of aviation weather products.