December 1999 2-19 Figure 2-9. Standing Lenticular Altocumulus (ACSL). These clouds are characteristic of the standing or mountain wave. Similar clouds are rotor clouds and standing lenticular cirrocumulus (CCSL). The rotor clouds are usually at a lower altitude than the ACSL. CCSL are whiter and at a higher altitude.
All three cloud types are indicative of possible severe or greater turbulence. (Photo courtesy of Grant Goodge taken at Concord, CA in 1970.)
TEMPERATURE/DEW POINT GROUP METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Temperature/dew point are reported in a two-digit form in whole degrees Celsius separated by a solidus (/). Temperatures below zero are prefixed with M. If the temperature is available but the dew point is missing, the temperature is shown followed by a solidus. If the temperature is missing, the group is omitted from the report.
ALTIMETER METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 The altimeter element follows the temperature/dew point group and is the last element in the body of a METAR or SPECI report. It is reported in a four-digit format representing tens, units, tenths, and hundredths of inches of mercury prefixed with A. The decimal point is not reported or stated.
December 1999 2-20
ALTIMETER REMARKS When the pressure is rising or falling rapidly at the time of observation, Remarks element will show PRESRR or PRESFR respectively.
Some stations also include the sea-level pressure (which is different from altimeter). It is shown in the Remarks element as SLP being the remark identifier followed by the sea-level pressure in hectopascals (h/Pa), a unit of measurement equivalent to millibar (mb).
Example:
SLP982
REMARKS (RMK) (AS REQUIRED) METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Remarks will be included in all observations, when appropriate, in the order as presented in Table 2-6.
The contraction RMK follows the altimeter in the body and precedes the actual remarks. Time entries will be shown as minutes past the hour if the time reported occurs during the same hour the observation is taken. If the hour is different, hours and minutes will be shown. Location of phenomena within 5 statute miles of the point of observation will be reported as at the station. Phenomena between 5 and 10 statute miles will be reported as in the vicinity, VC. Phenomena beyond 10 statute miles will be shown as distant, DSNT. Direction of phenomena will be indicated with the eight points of the compass (i.e., N, NE, E, SE, S, SW, W, NW). Distance remarks are in statute miles except for automated lightning remarks that are in nautical miles. Movement of clouds or weather will be indicated by the direction toward which the phenomenon is moving.
There are two categories of remarks: automated, manual, and plain language; and additive and automated maintenance data.
AUTOMATED, MANUAL, AND PLAIN LANGUAGE REMARKS CATEGORY This group of remarks may be generated from either manual or automated weather reporting stations and generally elaborate on parameters reported in the body of the report. (See Table 2-6.)
December 1999 2-21 Table 2-6 Automated, Manual, and Plain Language Remarks Remarks Examples of Remarks
1. Volcanic Eruptions MT. AUGUSTINE VOLCANO 70 MILES SW ERUPTED 231505 LARGE ASH CLOUD EXTENDING TO APRX 30000 FEET MOVING NE
2. Tornado, Funnel Cloud, or Waterspout TORNADO B13 6 NE
3. Automated Station Type AO1 or AO2
4. Peak Wind PK WND 28045/15
5. Windshift WSHFT 30 FROPA
6. Tower Visibility or Surface Visibility TWR VIS 1 ½ or SFC VIS 1 ½
7. Variable Prevailing Visibility VIS 1/2V2
8. Sector Visibility VIS NE 2 ½
9. Visibility at Second Site VIS 2 ½ RWY 11
10. Lightning OCNL LTGICCG OHD or FRQ LTGICCCCG W
11. Beginning and Ending of Precipitation RAB05E30SNB20E55
12. Beginning and Ending of Thunderstorm TSB05E30
13. Thunderstorm Locations TS SE MOV NE
14. Hailstone Size GR 1 ¾
15. Virga VIRGA NE (See Figure 2-10.)
16. Variable Ceiling Height CIG 005V010
17. Obscurations FU BKN000
18. Variable Sky Condition BKN014 V OVC
19. Significant Cloud Types CB W MOV E or CBMAM S MOV E or TCU W or ACC NW or ACSL SW-W
20. Ceiling Height at Second Location CIG 002 RWY 11
21. Pressure Rising or Falling Rapidly PRESRR or PRESFR
22. Sea-Level Pressure SLP982
23. Aircraft Mishap (ACFT MSHP)
24. No SPECI Report Taken NOSPECI
25. Snow Increasing Rapidly SNINCR 2/10
26. Other Significant Information Any other information that will impact aviation operations
December 1999 2-22 FIGURE 2-10. Virga. Virga is precipitation falling from a cloud but evaporating before reaching the ground. Virga results when air below the cloud is very dry and is common in the western part of the country. Virga associated with showers suggests strong downdrafts with possible moderate or greater turbulence. (Photo courtesy of Grant Goodge.)
ADDITIVE AND AUTOMATED MAINTENANCE DATA REMARKS CATEGORY Additive data groups are reported only at designated stations. The maintenance data groups are reported only from automated weather reporting stations. The additive data and maintenance groups are not used by the aviation community
December 1999 2-23 EXAMPLES OF METAR REPORTS AND EXPLANATIONS:
METAR KMKL 021250Z 33018KT 290V360 1/2SM R31/2600FT SN BLSN FG VV008 00/M03 A2991 RMK RAESNB42 SLPNO T00111032 METAR aviation routine weather report KMKL Jackson, TN 021250Z date 02, time 1250 UTC 33018KT wind 330 at 18 knots 290V360 wind direction variable between 290 and 360 degrees 1/2SM visibility one-half statute mile R31/2600FT runway 31, RVR 2600 SN moderate snow BLSN FG blowing snow and fog VV008 indefinite ceiling 800 00/M03 temperature 0°C, dew point -3°C A2991 altimeter 2991 RMK remarks RAESNB42 rain ended at four two, snow began at four two SLPNO sea-level pressure not available T00111032 temperature 1.1°C, dew point -3.2°C The following is an example of the phraseology used to relay this report to a pilot. Optional phrases or words are shown in parentheses.
“Jackson (Tennessee), (one two five zero observation), wind three three zero at one eight, wind variable between two niner zero and three six zero, visibility one-half, runway three one RVR, two thousand six hundred, heavy snow, blowing snow, fog, indefinite ceiling eight hundred, temperature zero, dew point minus three, altimeter two niner niner one.”
December 1999 2-24 METAR KSFO 031453Z VRB02KT 7SM MIFG SKC 15/14 A3012 RMK SLP993 6//// T01500139 56012 METAR aviation routine weather report KSFO San Francisco, CA 031453Z date 03, time 1453 UTC VRB02KT wind variable at 2 knots 7SM visibility 7 statute miles MIFG shallow fog SKC clear 15/14 temperature 15°C, dew point 14°C A3012 altimeter 3012 RMK remarks SLP993 sea-level pressure 999.3 hectopascals 6//// an indeterminable amount of precipitation has occurred over the last 3 hours T01500139 temperature 15.0°C, dew point 13.9°C 56012 atmospheric pressure lower since previous 3 hours ago The following is an example of the phraseology used to relay this report to a pilot. Optional phrases or words are shown in parentheses.
“San Francisco (one four five three observation), wind variable at two, visibility seven, shallow fog, clear, temperature one five, dew point one four, altimeter three zero one two.”
SPECI KCVG 312228Z 28024G36KT 3/4SM +TSRA SQ BKN008 OVC020CB 28/23 A3000 RMK TSB24 TS OHD MOV E SPECI aviation selected special weather report KCVG Covington, KY 312228Z date 31, time 2228 UTC 28024G36KT wind 280 at 24, gusts 36 knots 3/4SM visibility three-quarters statute mile +TSRA SQ thunderstorm with heavy rain and squalls BKN008 OVC020CB ceiling 800 broken, 2,000 overcast, cumulonimbus 28/23 temperature 28°C, dew point 23°C A3000 altimeter 3000 RMK remarks TSB24 thunderstorm began at two four TS OHD MOV E thunderstorm overhead moving east The following is an example of the phraseology used to relay this report to a pilot. Optional phrases or words are shown in parentheses.
“Covington (Kentucky), special report, two eight observation, wind two eight zero at two four, gusts three six, visibility three-quarters, thunderstorm, heavy rain, squall, ceiling eight hundred broken, two thousand overcast, cumulonimbus, temperature two eight, dew point two three, altimeter three zero zero zero, thunderstorm began two four, thunderstorm overhead, moving east.”
More examples without phraseology:
December 1999 2-25 METAR KLAX 140651Z AUTO 00000KT 10SM -RA SCT080 12/05 A2990 RMK AO2 METAR aviation routine weather report KLAX Los Angeles, CA 140651Z date 14, time 0651 UTC AUTO automated site 00000KT calm winds 10SM visibility 10 statute miles -RA light rain SCT080 8,000 scattered 12/05 temperature 12°C, dew point 5°C A2990 altimeter 2990 RMK remarks AO2 automated observation with precipitation discriminator SPECI KDEN 241310Z 09014G35KT 1/4SM +SN FG VV002 01/01 A2975 RMK AO2 TWR VIS ½ RAE08SNB08 SPECI aviation selected special weather report KDEN Denver, CO 241310Z date 24, time 1310 UTC 09014G35KT wind 090 at 14, gusts to 35 knots 1/4SM visibility one-quarter statute mile +SN FG heavy snow and fog VV002 indefinite ceiling 200 01/01 temperature 1°C, dew point 1°C A2975 altimeter 2975 RMK remarks AO2 automated observation with precipitation discriminator TWR VIS 1/2 tower visibility one-half RAE08SNB08 rain ended and snow began at 08 minutes after the hour
December 1999 2-26 METAR KSPS 301656Z 06014KT 020V090 3SM -TSRA FEW040 BKN060CB 12/ A2982 RMK OCNL LTGICCG NE TSB17 TS E MOV NE PRESRR SLP093 METAR aviation routine weather report KSPS Wichita Falls, TX 301656Z date 30, time 1656 UTC 06014KT 020V090 wind 060 at 14 knots varying between 020 and 090 degrees 3SM visibility 3 statute miles -TSRA thunderstorm with light rain FEW040 BKN060CB few clouds at 4,000, ceiling 6,000 broken, cumulonimbus 12/ temperature 12°C (dew point is missing) A2982 altimeter 2982 RMK remarks OCNL LTGICCG NE occasional lightning in cloud, cloud-to-ground northeast TSB17 thunderstorm began 17 TS E MOV NE thunderstorm east moving northeast PRESRR pressure rising rapidly SLP093 sea-level pressure 1009.3 hectopascals SPECI KBOS 051237Z VRB02KT 3/4SM R15R/4000FT BR OVC004 05/05 A2998 RMK AO2 CIG 002V006 SPECI aviation selected special weather report KBOS Boston, MA 051237Z date 5, time 1237 UTC VRB02KT variable wind at 2 knots 3/4SM visibility three-quarters statute mile R15R/4000FT runway visual range on runway 15R 4,000 feet BR mist OVC004 ceiling 400 overcast 05/05 temperature 5°C, dew point 5°C A2998 altimeter 2998 RMK remarks AO2 automated observation with precipitation discriminator CIG 002V006 ceiling variable 200 to 600
December 1999 3-1 Section 3
PILOT AND RADAR REPORTS, SATELLITE PICTURES, AND RADIOSONDE ADDITIONAL DATA (RADATs) The preceding section explained the decoding of METAR reports. However, these “spot” reports are only one facet of the total current weather picture. Pilot and radar reports, satellite pictures, and radiosonde additional data (RADATs) help to fill the gaps between stations.
PILOT WEATHER REPORTS (PIREPs) No observation is more timely than the one made from the flight deck. In fact, aircraft in flight are the only means of observing icing and turbulence. Other pilots welcome pilot weather reports (PIREPs) as well as do the briefers and forecasters. A PIREP always helps someone and becomes part of aviation weather. Pilots should report any observation that may be of concern to other pilots. Also, if conditions were forecasted but were not encountered, a pilot should also provide a PIREP. This will help the NWS to verify forecast products and create accurate products for the aviation community.
Pilots should help themselves, the aviation public, and the aviation weather forecasters by providing PIREPs.
A PIREP is transmitted in a prescribed format (see Table 3-1). Required elements for all PIREPs are type of report, location, time, flight level, aircraft type, and at least one weather element encountered.
When not required, elements without reported data are omitted. All altitude references are mean sea level (MSL) unless otherwise noted. Distance for visibility is in statute miles and all other distances are in nautical miles. Time is in universal coordinated time (UTC).
Table 3-1 PIREP Format PIREP Format UUA/UA Type of report OV Location TM Time FL Altitude/Flight level TP Aircraft type SK Sky cover WX Flight visibility and weather TA Temperature WV Wind TB Turbulence IC Icing RM Remarks
December 1999 3-2 Table 3-2 Encoding PIREPs UUA/UA Type of report:
URGENT (UUA) - Any PIREP that contains any of the following weather phenomena: tornadoes, funnel clouds, or waterspouts; severe or extreme turbulence, including clear air turbulence (CAT); severe icing; hail;
volcanic ash: low-level wind shear (LLWS) (pilot reports air speed fluctuations of 10 knots or more within 2,000 feet of the surface); any other weather phenomena reported which are considered by the controller to be hazardous, or potentially hazardous, to flight operations.
ROUTINE (UA) - Any PIREP that contains weather phenomena not listed above, including low-level wind shear reports with air speed fluctuations of less than 10 knots.
/OV Location: Use VHF NAVAID(s) or an airport using the three- or four-letter location identifier. Position can be over a site, at some location relative to a site, or along a route. Ex: /OV ABC; /OV KFSM090025; /OV OKC045020- DFW; /OV KABR-KFSD /TM Time: Four digits in UTC. Ex: /TM 0915 /FL Altitude/Flight level: Three digits for hundreds of feet with no space between FL and altitude. If not known, use UNKN. Ex: /FL095; /FL310; /FLUNKN /TP Aircraft type: Four digits maximum; if not known, use UNKN. Ex: /TP L329;
/TP B737; /TP UNKN /SK Sky cover: Describes cloud amount, height of cloud bases, and height of cloud tops. If unknown, use UNKN. Ex: /SK SCT040-TOP080;
/SK BKNUNKN-TOP075; /SK BKN-OVC050-TOPUNKN;
/SK SCT030-TOP060/OVC120; /SK FEW030; /SK SKC /WX Flight visibility and weather: Flight visibility (FV) reported first in standard METAR weather symbols. Intensity (- for light, no qualifier for moderate, and + for heavy) shall be coded for all precipitation types except ice crystals and hail. Ex: /WX FV05SM -RA; /WX FV01SM SN BR; /WX RA /TA Temperature (Celsius): If below zero, prefix with an “M.” Temperature shall also be reported if icing is reported. Ex: /TA 15; /TA M06 /WV Wind: Direction from which the wind is blowing coded in tens of degrees using three digits. Directions of less than 100 degrees shall be preceded by a zero.
The wind speed shall be entered as a two- or three-digit group immediately following the direction, coded in whole knots using the hundreds, tens, and units digits.
Ex: /WV 27045KT; /WV 280110KT /TB Turbulence: Use standard contractions for intensity and type (CAT or CHOP when appropriate). Include altitude only if different from FL. (See Table 3-3.)
Ex: /TB EXTRM; /TB OCNL LGT-MOD BLW 090;
/TB MOD-SEV CHOP 080-110 /IC Icing: Describe using standard intensity and type contractions. Include altitude only if different from FL. (See Table 3-4.) Ex: /IC LGT-MOD RIME;
/IC SEV CLR 028-045 /RM Remarks: Use free form to clarify the report putting hazardous elements first.
Ex: /RM LLWS -15 KT SFC-030 DURC RWY22 JFK Icing and turbulence reports state intensities using standard terminology when possible. To lessen the chance of misinterpretation, report icing and turbulence in standard terminology. If a PIREP stated,
December 1999 3-3 “...PRETTY ROUGH AT 6,500, SMOOTH AT 8,500 PA24...,” there could be many interpretations of the strength of the turbulence at 6,500 feet. A report of “light,” “moderate,” or “severe” turbulence at 6,500 feet would have been more concise and understandable. If a pilot’s description of an icing or turbulence encounter cannot readily be translated into standard terminology, the pilot’s description should be transmitted verbatim.
TURBULENCE The following table classifies each turbulence intensity according to its effect on aircraft control, structural integrity, and articles and occupants within the aircraft.
Pilots should report location(s), time (UTC), altitude, aircraft type, whether in or near clouds, intensity, and when applicable, type (CHOP/clear air turbulence [CAT]), and duration of turbulence. Duration may be based on the time the pilot is flying between two locations or over a single location.
High-level turbulence (normally above 15,000 feet AGL) that is not associated with cumuliform clouds (including thunderstorms) shall be reported as CAT.
Table 3-3 Turbulence Reporting Criteria Intensity Aircraft Reaction Reaction Inside Aircraft Light Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw). Report as light turbulence or light CAT.
or Turbulence that causes slight, rapid and somewhat rhythmic bumpiness without appreciable changes in altitude or attitude. Report as light CHOP.
Occupants may feel a slight strain against belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking.
Moderat e Turbulence that causes changes in altitude and/or attitude occurs but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed. Report as moderate turbulence or moderate CAT.
or Turbulence that is similar to light CHOP but of greater intensity. It causes rapid bumps or jolts without appreciable changes in aircraft or attitude.
Report as moderate CHOP.
Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.
Severe 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. Report as severe turbulence or severe CAT.
Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food service and walking are impossible.
Extreme Turbulence in which the aircraft is violently tossed about and is practically impossible to control.
It may cause structural damage.
Report as extreme turbulence or extreme CAT.
December 1999 3-4 ICING The following table classifies each icing intensity according to its operational effects on aircraft.
Pilots should report location(s), time (UTC), altitude, aircraft type, temperature, and icing intensity and type (rime, clear, or mixed). Rime ice is rough, milky, opaque ice formed by the instantaneous freezing of small supercooled water droplets. Clear ice is a glossy, clear, or translucent ice formed by the relatively slow freezing of large supercooled water droplets. Mixed ice is a combination of rime and clear ice.
Table 3-4 Icing Intensities, Airframe Ice Accumulation, and Pilot Report Intensity Airframe Ice Accumulation Pilot Report Trace Ice becomes perceptible. Rate of accumulation slightly greater than rate of sublimation. It is not hazardous even though deicing/anti-icing equipment is not used unless encountered for an extended period of time (over 1 hour).
Location, time, altitude/FL, aircraft type, temperature, and icing intensity and type Light The rate of accumulation may create a problem if flight is prolonged in this environment (over 1 hour). Occasional use of deicing/anti-icing equipment removes/prevents accumulation. It does not present a problem if the deicing/anti-icing equipment is used.
Location, time, altitude/FL, aircraft type, temperature, and icing intensity and type Moderate The rate of accumulation is such that even short encounters become potentially hazardous and use of deicing/anti-icing equipment or diversion is necessary.
Location, time, altitude/FL, aircraft type, temperature, and icing intensity and type Severe The rate of accumulation is such that deicing/anti-icing equipment fails to reduce or control the hazard. Immediate diversion is necessary.
Location, time, altitude/FL, aircraft type, temperature, and icing intensity and type EXAMPLES AND EXPLANATIONS (REFER TO TABLE 3-2):
UUA /OV ORD/TM 1235/FLUNKN/TP B727/TB MOD/RM LLWS +/- 20KT BLW 003 DURD RWY27L Urgent UA over Chicago O’Hare Airport, Chicago, IL, at 1235Z. Flight level is unknown but the information is from a Boeing 727. Turbulence was moderate and on descent to runway 27 left, lowlevel wind shear was detected below 300 feet. Airspeed fluctuations were plus and minus 20 knots.