Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 9-23. GTG Example
9.5.2.2 GTG Composite Analysis and Forecast The GTG Composite products display the maximum intensity of potential turbulence between FL200 and FL450 (Figure 9-19). In other words, at any given location, the displayed value represents the maximum potential turbulence between FL200 and FL450. Single altitude graphics must be examined to determine the altitude of the potential turbulence.
AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-29
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 9-24. GTG Composite Example
9.5.3 Strengths and Limitations The GTG provides an hourly, high resolution analysis and forecast of clear-air turbulence potential at and above FL200. However, the product is only for turbulence associated with upper level fronts and jet streams while other known causes of turbulence are not forecasted.
Strengths
y The product is issued hourly
y Turbulence is plotted to a high resolution.
Limitations
y The accuracy of the analysis is dependent on the number of PIREPs available.
Typically at night fewer pilot reports are received, so the accuracy decreases.
AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-30
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) y For the GTG forecast, the product is only as accurate the computer model output used to create them.
y The product only displays clear air turbulence (CAT) for upper-level fronts and the jet stream. Other known causes of turbulence are not included in the product.
y Data and forecast are only available for FL200 and above.
y It is only approved for use by meteorologists and dispatchers.
9.5.4 Use The Composite product can provide a quick method to determine what the greatest potential of current or forecast turbulence is at a given location. However, to determine the turbulence potential at any given altitude, the individual altitude products must be viewed.
The ADDS web site allows users to overlay turbulence PIREPS on the single altitude graphics.
For the PIREP to be plotted on the single altitude product, it must be located within 1,000 feet vertically of the altitude and have been reported within 90 minutes of the chart time. For example, if a user viewed the FL240 GTG product with a valid time of 1400Z the displayed PIREPS could be located between FL230 and FL250 and reported between 1230Z and 1400Z.
AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-31
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
9.6 Meteorological Impact Statement (MIS) A Meteorological Impact Statement (MIS) is an unscheduled flow control and flight operations planning forecast issued by Center Weather Service Units (CWSUs) (Figures 9-21 and 9-22). It is a forecast and briefing product for personnel at Air Route Traffic Control Centers (ARTCCs), Air Traffic Control System Command Center (ATCSCC), Terminal Radar Approach Control Facilities (TRACONS) and Airport Traffic Control Towers (ATCTs) responsible for making flow control-type decisions.
A MIS may be tailored to meet the unique requirements of the host ARTCC. These special requirements will be coordinated between the host ARTCC and the CWSU.
MISs are available on the Aviation Weather Center (AWC) web site at:
http://aviationweather.gov/products/cwsu/.
9.6.1 Valid Period A MIS is valid up to 12 hours after issuance time and details weather conditions expected to adversely impact air traffic flow in the CWSU area of responsibility. The MIS can be immediately effective for existing conditions when CWSU operations begin or for rapidly deteriorating conditions or be effective up to two hours in advance of expected conditions.
9.6.2 MIS Criteria A MIS enables Air Traffic Control (ATC) facility personnel to include the impact of specific weather conditions in their flow control decision-making. At a minimum, a MIS should be issued when:
• Any of the following conditions occur, are forecast to occur, and, if previously forecast, are no longer expected:
o Conditions meeting convective SIGMET criteria (Section 5.1.8)
o Icing - moderate or greater
o Turbulence - moderate or greater
o Heavy precipitation
o Freezing precipitation
o Conditions at or approaching Low IFR
o Surface winds/gusts >30 knots
o Low Level Wind Shear (surface - 2,000 feet)
o Volcanic ash, dust storms, or sandstorms; and
• In the forecaster's judgment, the conditions listed above, or any others, will adversely impact the flow of air traffic within the ARTCC area of responsibility.
AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-32
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
9.6.3 MIS Issuance MIS phenomena forecasts use the location reference point identifiers depicted on the In-Flight Advisory Plotting Chart (Appendix F), and include the height, extent, and movement of the conditions. MIS product issuances are numbered sequentially beginning at Midnight local time each day. The MIS is disseminated and stored as a "replaceable" product. Therefore, each issuance will contain the details of all pertinent known conditions meeting MIS issuance criteria, including ongoing conditions described in previously issued MISs.
The MIS is distributed to ARTCC personnel, including Traffic Management Unit (TMU) personnel.
9.6.4 Format
Figure 9-25. Meteorological Impact Statement (MIS) Decoding Example
Table 9-5. Meteorological Impact Statement (MIS) – Decoding
LINE CONTENT DESCRIPTION 1 ZFW ARTCC Identification MIS Product type 01 Issuance number VALID 190200-191200 Valid period UTC date/time 2 …FOR ATC PLANNING PURPOSES ONLY… Product use statement 3 FROM OKC TO CDS TO GAG TO END TO OKC Phenomenon location 4 LLWS BLO 020 AGL DUE TO LLJ.
CONDS GRDLY IPVG AFT 10Z Phenomenon description
Any remarks such as “SEE CONVECTIVE SIGMET 8W"; "NO UPDATES AVBL AFT 0230Z";
and forecaster initials and/or facility identifier may be placed at the end of the MIS.
If the phenomenon described in a MIS is no longer expected, a cancellation MIS message may be issued. The FAA header does not contain an issuance number. If the phenomenon described in the MIS is expected to continue beyond the operating hours of the CWSU, then the remark "NO UPDATES AFT ttttZ" (where "ttttZ" is the UTC closing time of the CWSU) is added at the text end.
AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-33
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
9.6.5 Examples
ZOA MIS 01 VALID 041415-041900 ...FOR ATC PLANNING PURPOSES ONLY...
FOR SFO BAY AREA BR/FG WITH CEILING BLW 005 AND VIS OCNL BLW 1SM.
ZOA CWSU
Meteorological Impact Statement issued by the Freemont, California CWSU. First MIS issuance of the day, valid from the 4th day of the month at 1415 UTC, to the 4th day of the month at 1900 UTC. For air traffic control planning purposes only. For the San Francisco Bay Area…mist and fog with ceilings below 500 feet MSL and visibility occasionally below 1 statute mile.
ZOA MIS 02 VALID 041650 ...FOR ATC PLANNING PURPOSES ONLY...
FOR SFO BAY AREA CNL ZOA MIS 01. CONDS HAVE IMPRD.
ZOA CWSU
Meteorological Impact Statement issued by the Freemont, California CWSU. The second MIS issuance of the day, valid the 4th day of the month at 1650 UTC. For air traffic control planning purposes only. For the San Francisco Bay Area. Cancel Freemont, California Meteorological Impact Statement number 1. Conditions have improved.
ZID MIS 03 VALID 041200-042330 ...FOR ATC PLANNING PURPOSES ONLY...
FROM IND TO 17WSW APE TO LOZ TO 13NE PXV TO IND TIL 21Z MOD TURB FL310-390 DUE TO JTST WS.
ZID W OF A LINE FM FWA TO BWG AFT 18Z OCNL SEV TSGR TOPS TO FL450. MOV FM 24035KT. MAX SFC WINDS 60KT.
ZID E OF A LINE FM FWA TO 35SE BKW MOD MXD ICE IN CLDS/PRECIPITATION 020-120. CONDS ENDING W OF A 40S CLE TO 20NE BKW LINE BY 19Z.
ZID CWSU
Meteorological Impact Statement issued by the Indianapolis, Indiana CWSU. The third MIS issuance of the day, valid from the 4th day of the month at 1200 UTC to the 4th day of the month at 2130 UTC. For air traffic control planning purposes only. From Indianapolis, Indiana to 17 nautical miles west-southwest of Appleton, Ohio to London, Kentucky to 13 nautical miles northeast of Pocket City, Indiana to Indianapolis, Indiana. Until 21Z, moderate turbulence between flight level 310 and flight level 390 due to jet stream wind shear.
For the Indianapolis ARTCC airspace west of a line from Fort Wayne, Indiana to Bowling Green, Kentucky. After 18Z, occasional severe thunderstorms, hail, tops to flight level 450. Moving from 240 degrees at 35 knots. Maximum surface winds 60 knots.
For the Indianapolis, Indiana ARTCC airspace east of a line from Fort Wayne, Indiana to 35 nautical miles southeast of Beckley, West Virginia. Moderate mixed icing in clouds and precipitation between 2,000 feet to 12,000 feet MSL. Conditions ending west of a line from 40 AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-34
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) nautical miles south of Cleveland, Ohio to 20 nautical miles northeast of Beckley, West Virginia by 19002.
Anchorage CWSU Seattle Chi/S U Minneapolis CI/SU evelar Salt Lake Dir CIrsU Dakland Denver Ci/SU Chicago C/SU * D.C.
Los Ang * Memphis C/SU Abuquerque Chi/S U * Fort Worth Chi:
Honclulu CYSU * Houston CISU Figure 9-26. Center Weather Service Unit (CWSU) Areas of Responsibility - CONUS Figure 9-27. CWSU Anchorage, AK (PAZA) Area of Responsibility AC 00-45F, CHG 2 Section 9: Supplementary Products Page 9-35
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 10 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 provided.
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 necessary.
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.
AC 00-45F, CHG 2 Appendix A: Definition of Common Terms Used In… Page 10-1
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) AC 00-45F, CHG 2 Appendix A: Definition of Common Terms Used In… Page 10-2 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 validity.
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 necessary.
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 are identified.
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
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) 11 APPENDIX B: CONTRACTIONS AND ACRONYMS
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 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 AC 00-45F, CHG 2 Appendix B: Contractions and Acronyms Page 11-1
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
AP
Airport or anomalous propagation APCH Approach APCHG Approaching 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 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 AC 00-45F, CHG 2 Appendix B: Contractions and Acronyms Page 11-2
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Potential Energy CARIB Caribbean CASCDS Cascades CAT Category or Clear air turbulence CAVO Visibility, cloud and present weather better than prescribed values or conditions CB Cumulonimbus CC Cirrocumulus CCA (or CCB, CCC…etc., in sequence) Corrected meteorological message CCLDS Clear of clouds CC Counterclockwise CCSL Cirrocumulus Standing Lenticular CDFNT Cold front CDN Coordination CFP Cold front passage CHC Chance CHCS Chances CHG Modification (message type designator) CHGD Changed CHGG Changing CHGS Changes CHSPK Chesapeake CI Cirrus CIG Ceiling CIGS Ceilings CIT Near or over large towns CLA Clear type of ice formation CLD Cloud CLDNS Cloudiness CLDS Clouds CLKWS Clockwise CLR Clear(s) or cleared to…or clearance CLRG Clearing CLRS Clears CLSD Close or closed or closing CM Centimeter CMPLX Complex CNL Cancel or cancelled CNDN Canadian CNTR Center CNTRD Centered CNTRL Central CNTY County CNTYS Counties CNVG Converge CNVGG Converging CNVGNC Convergence CNVTN Convection CNVTV Convective CNVTVLY Convectively CONFDC Confidence CO Colorado COMPR Compare COMPRG Comparing COMPRD Compared COMPRS Compares COND Condition CONS Continuous CONT Continue(s) or continued CONTLY Continually CONTG Continuing CONTRAILS Condensation trails CONTDVD Continental Divide CONUS Continental U.S.
COORD Coordinates COR Correct or correction or corrected (used to indicate corrected meteorological message; message type designator COT At the coast COV Cover or covered or covering CPBL Capable CPC Climate Prediction Center CRLC Circulate CRLN Circulation CRNR Corner CRNRS Corners CRS Course CS Cirrostratus CSDR Consider CSDRBL Considerable CST Coast CSTL Coastal CT Connecticut CTSKLS Catskills CU Cumulus CUFRA Cumulus Fractus COV Cover or covered or covering CWSU Center Weather Service Unit AC 00-45F, CHG 2 Appendix B: Contractions and Acronyms Page 11-3