CHAPTER 4

Chapter 26
26.2 SIGMET

SIGMET
Significant Meteorological Information
Disseminated to all pilots
Issued from the Aviation Weather Center (AWC)
The AWC issues for 6 regions

SIGMET
Sigmets are issued with a unique ID.
Continental US are N thru Y except for S and T
S and T are used for Airmets
Each wx event is assigned a number indicating continuation
Example: November 1, November 2, November 3

SIGMET
All heights are MSL
Lat and Long in whole degrees and minutes
Some messages may be abbreviated and or contractions may be used

SIGMET
In order to be issued the wx event has to cover at least 3,000 sq mi
May be issued if the wx event may significantly impact aircraft safety

SIGMET
Things that make up a SIGMET:
Severe or greater turbulence (SEV TURB)
Severe Icing (SEV ICE)
Widespread Duststorm (WDSPR DS)
Widespread Sandstorm (WDSPR SS)
Volcanic Ash (VA)

SIGMET
Good for up to 4 hours
Issued whenever currently needed
Issued whenever conditions are forecasted in the next 4 hours

SIGMET
Content:
Series name and number
Beginning and ending time
Affected states
Location of phenomena
Phenomena description
Vertical extent
Movement
Intensity change
Indication that phenomena

SIGMET
(Line 1) SIGMET ROMEO series issued for the San Francisco Area at 0130 UTC on the 10th day of the month.
(Line 2) This is the first issuance of the SIGMET ROMEO series and is valid until the 10th day of the month at 0530 UTC.
(Line 3) The affected states within the SFO area are Oregon and Washington.
(Line 4) From Seattle, WA; to Pendleton, OR; to Eugene, OR; to Seattle, WA;
(Line 5) Occasional moderate or greater clear air turbulence between Flight Level 280 and Flight Level 350, expected due to jet stream. Conditions beginning after 0200Z continuing beyond 0530Z and spreading over central Idaho by 0400Z.

SIGMET
Cancelled when the event is over
Amendments not issued – a new SIGMET is issued using the next issue number
Corrections are indicated with a COR

CHAPTER 26
26.2.4.2 Convective SIGMET

CONVECTIVE SIGMET
What are these for?
Convective activity (Thunderstorms)
Severe or greater turbulence
Severe icing
Low level windshear

CONVECTIVE SIGMET
Normally issued for:
Line of T-storms 60 miles long for 40% of its length
Area of T-storms affecting 3,000 sq. miles covering 40%
Embedded or severe T-storms lasting 30 min or more

CONVECTIVE SIGMET
Special issuance for:
Tornado
Hail ¾ inch or bigger
Wind gusts 50kts or greater
Rapidly changing conditions

CONVECTIVE SIGMET
Come out H+55
Valid for 2 hours
May have a 2-6 hour outlook at the end

CONVECTIVE SIGMET
Format:
Series # and region letter E,W or C
Ending time
States affected
Location of phenomena
Movement
Cloud tops
Remarks

CONVECTIVE SIGMET
20th SIGMET of the year
CONVECTIVE SIGMET
Can access these off aviationweather.gov or through normal briefing
WSUS32 KKCI 262355
SIGC
CONVECTIVE SIGMET 11C
VALID UNTIL 0155Z
LA AND CSTL WTRS
FROM 40SW BTR-90SE LCH-140S LCH LINE EMBD TS 30 NM WIDE MOV FROM 27030KT. TOPS TO FL290.
OUTLOOK VALID 270155-270555
FROM AEX-SJI-130ESE LEV-120SSW LCH-AEX WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS.
ICAO Identifier
Outlook is good for 2 to 6 hours as stated

SIGMET Outside CONUS
Items effecting greater than 3,000 sq mi
Thunderstorm—of type below*
Obscured (OBSC TS)
Embedded (EMBD TS)
Widespread (WDSPR TS)
Squall line (SQL TS)
Isolated severe (ISOL SEV TS)
Severe turbulence (SEV TURB)
Severe icing (SEV ICE)
With freezing rain (SEV ICE (FZRA))
Widespread duststorm (WDSPR DS)
Widespread sandstorm (WDSPR SS)
Volcanic ash (VA)
Tropical cyclone (TC)
Radioactive cloud (RDOACT CLD)

CHAPTER 26
26.3 AIRMETS

AIRMET
These are aimed at light aircraft
HOWEVER AIRMETs are intended for dissemination to all pilots in flight to enhance safety and are of particular concern to operators and pilots of aircraft sensitive to the phenomena described and to pilots without instrument ratings
Enroute Wx phenomena which may effect safety but at a lower intensity than a SIGMET
6 separate regions

AIRMET
Issued for:
Ceilings less than 1000 & 3 miles vis
Mountain obscurations
Moderate turbulence
Surface winds 30kts or greater
Moderate icing
Non convective low-level wind shear below 2,000 feet AGL

AIRMET
Altitudes are msl
Normal abbreviations are used
Good for 6 hours
Unlike SIGMETS these may be amended (coded AMD)
Issued every 6 hours

AIRMET
3 different types of AIRMETS:
Sierra for IFR and mountain obscuration
Tango for moderate turbulence
Zulu for moderate icing

AIRMET

AIRMET
SFOS WA 262045
AIRMET SIERRA UPDT 3 FOR IFR AND MTN OBSCN VALID UNTIL 270300
NO SGFNT IFR EXP OUTSIDE OF CNVTV ACT
AIRMET MTN OBSCN…WA OR CA
FROM 70WSW YXC TO 50NE BKE TO 60SE REO TO 40SE LKV TO 40SSW FMG TO 20SE RZS TO 40W RZS TO 30W ENI TO 90SW EUG TO ONP TO 20SSE HQM TO TOU TO HUH TO 70WSW YXC MTNS OBSC BY CLDS/PCPN/BR. CONDS CONTG BYD 03Z THRU 09Z
OTLK VALID 0300-0900Z AREA 1…IFR CA BOUNDED BY 20NNW FMG-40S FMG-50NE MOD-20NE CZQ-30NE EHF-40WSW EHF-RZS-40W RZS-40ESE SNS-40ESE ENI-20NNW FMG CIG BLW 010/VIS BLW 3SM PCPN/BR/FG. CONDS DVLPG 03-06Z. CONDS CONTG THRU 09Z.

CHAPTER 26
Section 26.3.4 Graphical Airman’s Meteorological Advisory (G-AIRMET)

G-AIRMET
Issuance Schedule

G-AIRMET snapshots are graphical forecasts of en route weather hazards valid at discrete times no more than 3 hours apart for a period of up to 12 hours into the future (00, 03, 06, 09, and 12 hours)
00 hour represents the initial conditions, and the subsequent 3-hourly graphics depict the area affected by the particular hazard at that valid time.

G-AIRMET
Forecast of en-route weather hazards
Issued 4 times daily, every 6 hrs, updated as necessary
Valid at discrete times every 3 hrs, for a total of 12 hrs
8 products available:
IFR Ceiling and Visibility
Mountain Obscuration
Icing
Freezing Level
Turbulence High Level
Turbulence Low Level
Low Level Wind Shear
Strong Surface Winds

Ceiling and Visibility
Bases less than 1000 AGL, Vis less than 3sm
Visibility causes are denoted:
PCPN, FU, HZ, BR, FG, BLSN

Mountain Obscuration
VMC cannot be maintained
Obscuring phenomena:
CLDS, PCPN, FU, HZ, BR, FG

Icing
Areas of airframe icing including bases and tops
Note: this is non-convective caused icing
Altitude variations in the bases may be denoted by more than one layer
E.g.: “030/010” suggests the icing layer starts at between 1000 and 3000 msl

Freezing Level
Lowest freezing level above the ground or at the surface
4000 foot intervals in msl
Multiple freezing levels are denoted by base and top labels
Over Florida:
Freezing at 7000 and again at 12,000
Zig zag indicates freezing level at the surface

Turbulence High Level
Areas of moderate turbulence
Bases and tops denoted
Non-convective

Turbulence Low Level
Areas of moderate turbulence
Bases and tops denoted
Non-convective

Low Level Wind Shear
Wind shear below 2000 AGL
Defined as exceeding 10kts per 100 feet
Non-convective

Surface Winds
Surface winds greater than 30 kts

The new format
https://aviationweather.gov/gfa/#gairmet

G-AIRMET
Using the G-AIRMET
When using the G-AIRMET, users must keep in mind that if a 00-hour forecast shows no significant weather and a 03-hour forecast shows hazardous weather, they must assume a change is occurring during the period between the two forecasts
It should be taken into consideration that the hazardous weather starts immediately after the 00-hour forecast unless there is a defined initiation or ending time for the hazardous weather
The same would apply after the 03-hour forecast. The user should assume the hazardous weather condition is occurring between the snapshots unless informed otherwise.

CHAPTER 26
Section 26.4 Center Weather Advisory

CENTER WEATHER ADVISORY
Meets the same criteria as the AIRMET, SIGMET or CONVECTIVE SIGMET
Useful for anticipating adverse conditions in the enroute structure
Is primarily used for aircrews to anticipate and avoid adverse weather conditions
May augment AIRMET/SIGMET information
Are usually written out in plain text

CENTER WEATHER ADVISORY
Valid for 2 hours
May be issued hourly for convective activity

CENTER WEATHER ADVISORY
Issued for the following reasons:
There is no existing AWC or AAWU advisory in effect
Any of the following conditions:
Conditions meeting Convective SIGMET criteria.
Icing—moderate or greater.
Turbulence—moderate or greater.
Heavy and extreme precipitation.
Freezing precipitation.
Conditions at or approaching low IFR.
Surface wind gust at or above 30 kts.
LLWS (surface to 2,000 ft.)
Volcanic ash, dust storms or sandstorms

CENTER WEATHER ADVISORY
Issued for the following reasons: (continued)
When a hazard has grown significantly outside of the boundary defined by the AWC or the AAWU advisory.
To upgrade a thunderstorm advisory to include severe thunderstorms.
To upgrade an AIRMET to include isolated severe turbulence or icing. If greater than isolated severe turbulence or icing is occurring, then a new CWA should be issued.
To define a line of thunderstorms within a larger area covered by the AWC or the AAWU advisory.
To better define hazards expected at a major terminal already within an AWC or an AAWU advisory.
Anything that in the judgment of the CWSU forecaster will add value to an existing advisory.
If in the forecaster’s judgment the conditions listed above, or any others, may adversely impact the safe flow of air traffic.

CENTER WEATHER ADVISORY

CENTER WEATHER ADVISORY
ZME1 CWA 081300
ZME CWA 101 VALID TIL 081500
FROM MEM TO JAN TO LIT TO MEM
OCNL TS MOV FM 26025KT. TOPS TO FL450.
Center Weather Advisory issued for the Memphis, Tennessee ARTCC on the 8th day of the month at 1300 UTC. The 1 after the ZME in the first line denotes this CWA has been issued for the first weather phenomenon to occur for the local calendar day. The 101 in the second line denotes the phenomenon number again (1) and the issuance number (01) for this phenomenon. The CWA is valid until the 8th of the month at 1500 UTC. From Memphis, Tennessee to Jackson, Mississippi to Little Rock, Arkansas to Memphis, Tennessee. Occasional thunderstorms moving from 260 degrees at 25 knots. Tops to flight level 450

Chapter 26
Section 26.5 Volcanic Ash Advisory

VOLCANIC ASH ADVISORY
Comes from the Volcanic Ash Advisory Center (VAAC)
Predict the lateral and vertical extent of eruption clouds
Issued within 6hrs of an eruption and every 6hrs after
Location, height of volcano, height of ash plume, lat and long of ash dispersion cloud, and a forecast of where it’s going

VOLCANIC ASH ADVISORY
FVXX23 KNES 031808
VA ADVISORY
DTG: 20150303/1808Z

VAAC: WASHINGTON

VOLCANO: COLIMA 341040
PSN: N1930 W10337

AREA: MEXICO

SUMMIT ELEV: 12631 FT (3850 M)

ADVISORY NR: 2015/135

INFO SOURCE: GOES-EAST. GFS WINDS. VOLCANO WEB
CAMERA.

ERUPTION DETAILS: EMISSION AT 03/1448Z

OBS VA DTG: 03/1745Z

OBS VA CLD: SFC/FL200 N2120 W10236 – N2120 W10216
– N2056 W10216 – N2056 W10237 – N2120 W10236 MOV
NE 30KT

FCST VA CLD +6HR: 04/0000Z SFC/FL200 NO ASH EXP

FCST VA CLD +12HR: 04/0600Z SFC/FL NO ASH EXP

FCST VA CLD +18HR: 04/1200Z NO ASH EXP

RMK: VA FROM THIS EMISSION IS 105 NMI NNE FROM
THE SUMMIT. WEBCAMERA AND IMAGERY HAS NOT SHOWN
ANY ADDITIONAL VA EMISSIONS BUT EMISSIONS OF
GASES WITH POSSIBLE LIGHT VA CONTINUE …SCHWARTZ

Chapter 26
Section 26.6 Aviation Tropical Cyclone Advisory

AVIATION TROPICAL CYCLONE ADVISORY (TCA)
Provides short term tropical cyclone forecast guidance
National Hurricane Center NHC takes care of the Atlantic and Eastern Pacific
Central Pacific Hurricane Center takes care of the Central Pacific
TCAs are issued at 0300, 0900, 1500, and 2100
Gives:
Current position
Motion and intensity
12, 18 and 24 hr forecast positions
GMZ013 Zone Forecast
GMZ013-040315- N CENTRAL GULF INCLUDING FLOWER GARDEN BANKS MARINE SANCTUARY- 1012 AM EST TUE MAR 3 2015 …GALE CONDITIONS POSSIBLE THU… .TODAY…SE WINDS 10 TO 15 KT. SEAS 3 TO 5 FT. .TONIGHT…SE TO S WINDS 10 TO 15 KT. SEAS 4 TO 5 FT. .WED…SE TO S WINDS 10 TO 15 KT. SEAS 4 TO 5 FT. .WED NIGHT…S WINDS 10 TO 15 KT. SEAS 4 TO 5 FT. .THU…N OF 27N W OF 92W NE WINDS 30 TO 35 KT DIMINISHING TO 25 TO 30 KT. SEAS 8 TO 10 FT BUILDING TO 11 TO 13 FT. ELSEWHERE W OF FRONT N TO NE WINDS 26 TO 30 KT. SEAS 6 TO 9 FT BUILDING TO 8 TO 10 FT. E OF FRONT SW WINDS 5 TO 10 FT BECOMING N TO NE WINDS 25 TO 30 KT. SEAS 3 TO 5 FT BUILDING TO 8 TO 10 FT. .THU NIGHT…N TO NE WINDS 25 TO 30 KT…BECOMING NE 20 TO 25 KT LATE. SEAS 9 TO 13 FT. .FRI…NE WINDS 20 TO 25 KT. SEAS 7 TO 10 FT. .FRI NIGHT…NE TO E WINDS 15 TO 20 KT. SEAS 6 TO 8 FT. .SAT…NE TO E WINDS 15 TO 20 KT. SEAS 4 TO 6 FT. .SAT NIGHT…NE WINDS 20 TO 25 KT…DIMINISHING TO 15 TO 20 KT LATE. SEAS 3 TO 5 FT.

TROPICAL CYCLONE PUBLIC ADVISORY (TCP)
Issuance of warnings and watches when needed
Tropical depression up to 33 kts
Tropical storm 34-63 kts
Hurricane/Typhoon in excess of 64 kts

Chapter 26
Section 26.7 Space Weather Advisory

Issuance
Born under star date 2019
Consortium of four global space weather centers
Mainly focused on alerting of GPS and communication degradation
Issued in 6, 12, 18 and 24 hour forecasts

Space Weather
Space Wx scales for 3 events
Geomagnetic storms
Solar radiation storms
Radio blackouts
Space Wx messages include
Watch messages are issued with long lead times for the majority of all space weather activity predictions.
Warning messages are issued when some condition is expected. The messages contain a warning period and other information of interest.
Alert messages are issued when an event threshold is crossed and contain information that is available at the time of issue.
Summary messages are issued after the event ends and contains additional information that was not available at the time of issue.

Space Weather
Forecast Discussion is issued every 12 hours
Has a summary and a forecast
3 day forecast issued every 12 hours
Looks at the observed and forecast space wx
There are others…
https://www.swpc.noaa.gov/

Space Weather Prediction Center (SWPC)
https://www.swpc.noaa.gov/

Chapter 26
Section 26.8 Low-Level Wind Shear (LLWS)/Microburst Advisories

Low-Level Wind Shear (LLWS)/Microburst Advisories
ATC alerting for LLWS after detection from
PIREP
Terminal Weather System
LLWS Alert System
TDWR Terminal Doppler Weather Radar
Alerts remain in place over ATIS or verbally from Tower for 20 minutes

Chapter 26
Section 26.9 Airport Weather Warning (AWW)

Airport Weather Warning
Mainly for ground personnel at airports
Issued for
Strong surface winds
Freezing rain
Heavy snow
Lightning within 5 miles of the airport
watches
Meteorological discussion
Technical information for the aviation community

Use this thing to see where the worst T-storms are