Aviation Weather Services, Advisory Circular 00-45G, Change 2 (October 2014)
Ceiling and Visibility Analysis (CVA) The Ceiling and Visibility Analysis (CVA) product provides a real-time analysis of current observed and estimated C&V (ceiling and visibility) conditions across the continental United States. The product is primarily intended to help the general aviation pilot (particularly the Visual Flight Rules (VFR)-only pilot) avoid IFR conditions. However, CVA's overview of ceiling and visibility conditions can be useful to others involved in flight planning or weather briefing.
Issuance CVA is issued every five minutes and is available through the Aviation Weather Center’s (AWC) Aviation Digital Data Service (ADDS) Web site at: http://aviationweather.gov/add/cv.
Content CVA presents information via a full-CONUS graphic and 18 regional graphics. Each graphic is rendered on a horizontal grid of 5 km resolution and shows viewer-selectable representations of ceiling height above ground level (AGL), surface visibility in statute miles (sm) and FAA flight category designation.
Each regional display includes an overlay of station plots showing the current ceiling and visibility observations reported at selected METAR stations. To avoid overcrowding, the overlay shows only a subset of the total number of stations available.
CVA Ceiling Analysis The CVA Ceiling Analysis uses observed and estimated ceiling heights as follows:
At display points corresponding to METAR locations, CVA uses the ceiling values observed by the nearest METAR.
At display points between METAR locations (where there are no direct observations), CVA uses estimated ceiling values derived by adjusting the ceiling observation from the nearest METAR to take into account intervening changes in terrain height. When corresponding Geostationary Operational Environmental Satellite (GOES) satellite observations yield an unambiguous indication that no cloud is present, adjusted ceiling observations are reset to indicate clear conditions.
At display points where observed or estimated ceiling height is less than 200 ft. AGL, CVA reports “Possible Terrain Obstruction.”
The CVA Ceiling Analysis graphic is rendered as follows:
• Ceiling less than 1000 ft. AGL – pale yellow.
• Ceiling greater than or equal to 1000 ft. AGL – pale blue.
• Ceiling less than 200 ft. AGL and Possible Terrain Obstruction – orange.
Figure 9-27 shows a CONUS-scale CVA Ceiling Analysis. Figure 9-28 shows a regional-scale Ceiling Analysis.
Section 9: New Generation Weather Products Page 9-35
Aviation Weather Services, Advisory Circular 00-45G, Change 2 (October 2014) Ceiling Caution: This product is intended to aid flight planning and is best used along with other weather products such as METARS, AIRMETS, TAFs and Area Forecasts.
CV-Analysis valid 1315 UTC 01 Oct 2013 /Createj by ADDS ©2013 UCAR Possible Terrain Obscuration Less than 1000 feet 1000 feet or greater Figure 9-27. CONUS Display of CVA Ceiling Analysis Ceiling Caution: This product is intended to aid fright planning and is best used along with other weather products such as METARS, AIRMETs, TAFs and Area Forecasts.
So Analy Mis vald 191517051 0c 2018 2013 * Created by ADDS 62013 U Possible Terrain Obscuration ess than 1000 feet 1000 feet or greater Figure 9-28. Regional Display of CVA Ceiling Analysis Section 9: New Generation Weather Products Page 9-36
Aviation Weather Services, Advisory Circular 00-45G, Change 2 (October 2014)
9.7.2.2 CVA Visibility Analysis The CVA Visibility Analysis (shown as a regional view in Figure 9-29) reports the observed visibility at the nearest METAR. The graphic is rendered as follows:
• Surface visibility less than 3 sm - pale yellow
• Surface visibility greater than or equal to 3 sm - pale blue Visibility Caution: This product is intended to aid flight planning and is best used along with other weather products such as METARs, AIRMETs, TAFs and Area Forecasts.
CV-Analysis valid 1315 So tad is vid 190 1 1 201 2013 UTC 01 * Created.by ADDS ©20 13 UCAT Less than 3 mi 3 mi or greater Figure 9-29. Regional Display of CVA Visibility Analysis
9.7.2.3 CVA Flight Category Analysis The CVA Flight Category Analysis (shown as a regional view in Figure 9-30) uses observed and estimated ceiling and visibility values to report the FAA flight category at each display point. The graphic is rendered as follows:
• VFR - pale blue: Ceiling greater than or equal to 1000 ft. AGL and visibility greater than or equal to 3 sm.
• IFR - pale yellow: Ceiling less than 1000 ft. AGL and/or visibility less than 3 sm.
• Ceiling less than 200 ft. AGL and Possible Terrain Obstruction - orange.
Section 9: New Generation Weather Products Page 9-37
Aviation Weather Services, Advisory Circular 00-45G, Change 2 (October 2014)
Figure 9-30. Regional Display of CVA Flight Category Analysis Areas of possible terrain obscuration (indicated by estimated ceiling less than 200 ft. AGL) are also shown.
Strengths and Limitations CVA Strengths
• CVA’s area-wide graphics highlight observed and estimated IFR, VFR, and possible ground obscuration conditions, enabling a user’s quick recognition of ceiling and visibility hazards, as represented by existing observational tools.
• CVA is issued every 5 minutes using the most current METAR and GOES satellite observations available. These rapid updates enhance recognition of trends when conditions are changing. CVA incorporates “special” METAR observations as they are issued.
• CVA fills a gap in existing presentation of C&V information. No other NWS product provides analyzed C&V guidance with comparable spatial and temporal resolution.
Section 9: New Generation Weather Products Page 9-38
Aviation Weather Services, Advisory Circular 00-45G, Change 2 (October 2014)
CVA Limitations
• CVA is an analysis of estimated real-time conditions only. It is not a forecast and cannot be used in place of a forecast.
• CVA must only be used with products such as METARs, TAFs, AIRMETs, and Area Forecasts.
• CVA’s representation of ceiling and visibility conditions in regions between METARS (where direct observations are unavailable) can be significantly in error.
As distance from the nearest METAR increases, the uncertainty in represented conditions increases.
• Impacted ceiling and visibility conditions can be highly localized and smaller in scale than the 5 km grid used to convey CVA information. Thus, small-scale variations in C&V conditions may not be represented by CVA, even in regions close to observing stations.
Use General aviation pilots, weather briefers and others involved in flight planning can use CVA as a companion to METARS, TAFs, AIRMETs, and Area Forecasts to help them recognize and avoid IFR conditions. Along with the foregoing weather information sources, CVA can aid IFR avoidance and escape for the en route pilot who inadvertently encounters IFR conditions.
Airmen and flight planners must exercise judgment when using CVA information, as it is based in recent weather information and calculated estimations. Degrading conditions are more likely as the distance and time increase from the station's reported weather.
Section 9: New Generation Weather Products Page 9-39
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) APPENDIX A: DEFINITION OF COMMON TERMS USED IN
EN ROUTE FORECASTS AND ADVISORIES Table A-1. Definition of Common Terms Used in En Route Forecasts and Advisories (FA, SIGMET, AIRMET, TCA, VAA, ROFOR) Contraction Translation Definition EMBD Embedded thunderstorms or cumulonimbus Thunderstorms or cumulonimbus (CB) clouds that are embedded in cloud layers or concealed by haze.
EXTREME TURB Extreme Turbulence Turbulence in which aircraft is violently tossed about and is practically impossible to control. It may cause structural damage.
FIR Flight Information Region An airspace of defined dimensions within which flight information service and alerting service are FL Flight Level A surface of constant atmospheric pressure which is related to a specific pressure datum, 1013.2 hectopascals (hPa), and is separated from other such surfaces by specific pressure intervals.
FRQ Frequent thunderstorms or cumulonimbus Consisting of elements with little or no separation between adjacent thunderstorms with a maximum spatial coverage greater than 75 percent of the area affected by the phenomena at a fixed time or during the period of validity.
IMC Instrument Meteorological Conditions Ceiling greater than or equal to 500 feet to less than 1,000 feet and/or visibility greater than or equal to 1 to less than 3 miles. LIMC is a sub-category of IMC, thus, IMC conditions are ceiling less than 1,000 feet and /or visibility less than 3 miles.
ISOL Isolated thunderstorms or cumulonimbus Consisting of individual features affecting an area with a maximum spatial coverage less than 50 percent of the area affected by the phenomena at a fixed time or during the period of validity.
LINE TS Line (of thunderstorms) A line of thunderstorms being at least 60 miles long with thunderstorms affecting at least 40 percent of its length LIMC Low Instrument Meteorological Conditions Ceiling less than 500 feet and/or visibility less than 1 SM. LIMC is a sub-category of Instrument Meteorological Conditions.
MVMC Marginal Visual Meteorological Conditions Ceiling greater than or equal to 1,000 feet to less than or equal to 3,000 feet and/or visibility greater than or equal to 3 to less than or equal to 5 miles.
MOD ICE Moderate Icing The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is MOD TURB Moderate Turbulence Turbulence that causes changes in attitude (pitch, roll, yaw) and/or altitude, but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed.
Appendix A: Definition of Common Terms Page 10-1
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Contraction Translation Definition MT OBSC Mountain Obscuration Conditions over significant portions of mountainous geographical areas are such that pilots in flight should not expect to maintain visual meteorological conditions or visual contact with mountains or mountain ridges near their route of flight.
OBSC Obscured thunderstorm or cumulonimbus Obscured by haze, smoke or cloud or cannot be readily seen due to darkness.
OCNL Occasional thunderstorms or cumulonimbus An area with a maximum spatial coverage between 50 and 75 percent of the area affected by the phenomena at a fixed time of during the period of SCT Scattered 25 to 50 percent of area affected.
SEV ICE Severe Icing The rate of accumulation is such that normal deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is SEV TURB Severe Turbulence Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control.
VMC Visual Meteorological Conditions Ceiling greater than 3,000 feet and visibility greater than 5 miles.
VOLCANIC
ERUPTION Volcanic Eruption A volcano eruption has occurred when an eruption report is received from a volcano observatory. A volcanic eruption is also considered to have occurred regardless of volcano observatory notification if reported by PIREP, or ground observer, or if remote sensing data indicates that an eruption has occurred based on satellite imagery or WSR-88D radar data or any other reliable sources
VOLCANIC ASH Volcanic Ash Any ash that can be seen by any one or more of the following: satellite imagery (visible, IR, multi-channel or TOMS), PIREPs, ground observations, radar and VAFTAD (In the event volcanic ash is entrained in clouds, the volcanic ash will be treated as visible using the VAFTAD as guidance).
WDLY SCT Widely Scattered Less than 25 percent of area affected WDSPR Widespread 50 percent or greater of the area affected
Appendix A: Definition of Common Terms Page 10-2
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) APPENDIX B: CONTRACTIONS AND ACRONYMS Table B-1. Contractions and Acronyms Contraction or Acronym Subject Defined A AAA (or AAB, AAC…etc., in sequence) Amended meteorological message (message type designator) AAWU Alaskan Aviation Weather Unit ABNDT Abundant ABNML Abnormal ABT About ABV Above AC Altocumulus or Convective Outlook ACARS Aircraft communication and addressing system ACC Altocumulus Castellanus ACCID Notification of an aircraft accident ACCUM Accumulate ACFT Aircraft ACPY Accompany ACRS Across ACSL Altocumulus Standing Lenticular ACT Active or activated or activity ACYC Anticyclone ADA Advisory area ADDN Addition or additional ADJ Adjacent ADQT Adequate ADQTLY Adequately ADRNDCK Adirondack ADVCT Advect ADVCTD Advected ADVCTG Advecting ADVCTN Advection ADVCTS Advects ADVN Advance ADVNG Advancing ADVY Advisory ADVYS Advisories AFCT Affect AFCTD Affected AFCTG Affecting Appendix B: Contractions and Acronyms Page 11-2
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Contraction or Acronym Subject Defined AFT After…(time or place) AFTN Afternoon AFSS Automated Flight Service Station AGL Above ground level AGN Again AGRD Agreed AGRS Agrees AGRMT Agreement AHD Ahead AIREP Air-report AIRMET Airman’s Meteorological Information (Information concerning en-route weather phenomena which may affect the safety of low-level aircraft operations) AK Alaska AL Alabama ALF Aloft ALG Along ALGHNY Allegheny ALQDS All quadrants ALSTG Altimeter setting ALT Altitude ALTA Alberta ALTHO Although ALTM Altimeter ALUTN Aleutian AMD Amend or amended (used to indicate amended meteorological message; message type designator) AMDG Amending AMDT Amendment AMP Amplify AMPG Amplifying AMPLTD Amplitude AMS AMSL Above mean sea level AMT Amount ANLYS Analysis ANS Answer AOA At or above AOB At or below AP Airport or anomalous propagation APCH Approach APCHG Approaching Appendix B: Contractions and Acronyms Page 11-3
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Contraction or Acronym Subject Defined APCHS Approaches APLCN Appalachian APLCNS Appalachians APPR Appear APPRG Appearing APPRS Appears APR April APRNT Apparent APRX Approximate or approximately AR Arkansas ARFOR Area Forecast (in aeronautical meteorological code) ARND Around AS Altostratus ASC Ascend to or ascending to ASSOCD Associated ASSOCN Association AT… At (followed by time at which weather change is forecast to occur) ATLC Atlantic ATP At…(time or place) ATTM At this time ATTN Attention AUG August AVBL Available or availability AVG Average AWC Aviation Weather Center AWT Awaiting AZ Arizona AZM Azimuth B BACLIN Baroclinic BAJA Baja, California BASE Cloud base BATROP Barotropic BC British Columbia BCFG Fog patches BCH Beach BCKG Backing BDA Bermuda BDRY Boundary BECMG Becoming Appendix B: Contractions and Acronyms Page 11-4
Aviation Weather Services, Advisory Circular 00-45G, Change 1 (July 2010) Contraction or Acronym Subject Defined BFR Before BGN Begin BGNG Beginning BGN Begins BHND Behind BINOVC Breaks in overcast BKN Broken BL… Blowing (followed by DU = dust, SA = sand or SN = snow) BLD Build BLDG Building BLDUP Buildup BLKHLS Black Hills BLKT Blanket BLKTG Blanketing BLKTS Blankets BLO Below clouds BLW Below… BLZD Blizzard BND Bound BNTH Beneath BR Mist BRF Brief BRK Break BRKG Breaking BRKHIC Breaks in higher clouds BRKS Breaks BRKSHR Berkshire BRM Barometer BLDU Blowing Dust BLSA Blowing Sand BLSN Blowing Snow BTL Between layers BTN Between BYD Beyond C C Degrees Celsius (Centigrade) or centre (runway identification) CA California CAA Cold air advection CAPE Convective Available Potential Energy CARIB Caribbean Appendix B: Contractions and Acronyms Page 11-5