11/14/16 Aviation Weather Services AC 00-45H Figure 4-19. NWS NCEP Central Operations Model Analyses and Guidance Web Site DOC NOAA NWS NCEP Centers: AWC CPC EMC NCO NHC OPC SPC SWPC WPC NCEP Home ≥ NCO Home ≥ Systems Integration Branch ≥ Model Analyses and Guidance Model Analyses and Guidance Information + Website Check here for the Latest News Select Model Guidance, Observations and Analyses, or Tropical Guidance
MODEL GUIDANCE OBSERVATIONS AND ANALYSES TROPICAL GUIDANCE Upcoming Changes T User's Guide | Frequently Asked Questions | Product Description Document MAG ·3.0.0 NOAA/ National Weather Service Disclaimer Privacy Policy National Centers for Environmental Prediction Credits About Us 5830 University Research Court Glossary Career Opportunities College Park, MD 20740 NCEP Internet Services Team Page last modified: May 20 2013 17:08 PM UTC.
A user's guide, located within Website Information (upper right corner), provides descriptions, details, and examples of the various products.
4.3.1.1 Constant Pressure Analyses.
Constant Pressure Charts (see Figure 4-20, 500 MB Analysis Chart-Example) are being phased out by the NWS in favor of other products (see Figure 4-21, 500 MB Height, Temperature, and Wind, 00-hour Forecast
(i.e., Model's Analyses from the NWS's North American Model [NAM] Example)) available on NCO's Model Analyses and Guidance Web site.
See paragraph 5.15.1 for additional information.
4-21
11/14/16 Aviation Weather Services AC 00-45H 4-22 Figure 4-20. 500 MB Analysis Chart—Example
Figure 4-21. 500 MB Height, Temperature, and Wind, 00-hour Forecast (i.e., Model’s Analyses from the NWS’s North American Model (NAM) Example)
Specific details regarding the content of the product is provided in the Product Description tab on the NCO’s Model Analyses and Guidance Web page.
11/14/16 Aviation Weather Services AC 00-45H 4-23
4.3.1.2 Use.
See paragraph 5.15.1.2.
4.3.2 Radiosonde Observation Analysis.
A common means of analyzing radiosonde observations (see paragraph 3.5.1) is the skew-T diagram (see Figure 4-22, Skew-T Diagram—Example). Skew-T diagrams are primarily intended for, and used by, meteorologists as part of their analyses of the atmosphere. For example, the skew-T diagram can be used to:
• Determine the freezing level (or levels);
• Determine the stability of the atmosphere;
• Determine the potential for severe weather;
• Determine the height and depth of inversions;
• Infer cloud bases, tops, and cloud layers; and
• Determine soaring conditions.
4.3.2.1 Issuance.
Skew-T diagrams are available from the NWS NCO. Their Web site, Model Analyses and Guidance (see Figure 4-19), contains a user’s guide that provides descriptions, details, and examples of the various products, including the skew-T.
4.3.2.2 Format.
The skew-T diagram provided on the NWS NCO Model Analyses and Guidance Web site uses the following format (other weather providers and Web sites may have different formats, especially colors):
• Horizontal axis is temperature in degrees Celsius, skewed to the right, labeled (minus) -20, 0, and 20 (Celsius).
• Vertical axis is pressure levels in millibars, labeled 1,000 (near sea level) to 100 (approximately 53,000 ft MSL).
• Bold solid red line represents the temperature profile over the station taken from the radiosonde observation (weather balloon).
• Bold solid green line represents the dewpoint profile.
• Wind aloft is shown on the far right side.
11/14/16 Aviation Weather Services AC 00-45H 4-24 Figure 4-22. Skew-T Diagram—Example
4.3.2.3 Example.
Two examples are provided: a multiple freezing level example (see Figure 4-23, Skew-T Diagram—Multiple Freezing Level Example) and a cloud top example (see Figure 4-24, Skew-T Diagram—Cloud Top Example).
11/14/16 Aviation Weather Services AC 00-45H 4-25
4.3.2.3.1 Multiple Freezing Level Example.
Figure 4-23. Skew-T Diagram—Multiple Freezing Level Example
Horizontal axis is temperature in degrees Celsius, skewed to the right, labeled -20, 0, and 20 (Celsius).
Vertical axis is pressure levels in millibars, labeled 1000 (near sea level) to 500 (18,000 ft). Bold solid red line represents the temperature profile over the station taken from the radiosonde observation (weather balloon). Bold solid green line represents the dewpoint profile. Note how the temperature profile (bold red line) crosses the 0 degree temperature line (also known as an isotherm) 5 times (near 900 MB, 860 MB, 775 MB, 725 MB, and 675 MB).
4.3.2.3.2 Cloud Top Example.
Figure 4-24 is the radiosonde observation from Vandenberg Air Force Base (VAFB), California, for 1200 UTC for a typical coastal stratus cloud.
Figure 4-24. Skew-T Diagram—Cloud Top Example
At about 950 MB, the temperature profile (bold red line) and dewpoint profile (bold green line) almost touch each other. This is the profile of a cloud top. The temperature and dewpoint quickly diverge, representing a change from the cool, moist air (and associated stratus cloud) to the dry and warmer air (cloud free) above.
4.3.2.4 Use.
Skew-T diagrams are primarily intended for, and used by, meteorologists as part of their analyses of the atmosphere and formulation of various forecasts.
11/14/16 Aviation Weather Services AC 00-45H 5-1 CHAPTER 5. FORECASTS The third distinct type of weather (meteorological) information is forecasts. Chapter 5 will discuss many forecast products, including in-flight advisories, produced by the NWS that are either specific to aviation or are public products of interest to aviation users.
5.1 Significant Meteorological Information (SIGMET).
A SIGMET is a concise description of the occurrence or expected occurrence of specified en route weather phenomena that may affect the safety of aircraft operations. SIGMETs are issued in text format and intended for dissemination to all pilots in flight to enhance safety. SIGMETs are issued as soon as practical to give notice to operators and aircrews of potentially hazardous en route conditions.
• All SIGMETs are available on http://www.aviationweather.gov.
• SIGMETs for Alaska are also available on the Alaska Aviation Weather Unit (AAWU) Web site.
• SIGMETs for Hawaii are also available on the NWS Weather Forecast Office (WFO) Honolulu Web site.
Although the areas where the SIGMETs apply may be shown graphically, a graphical depiction of the SIGMET area is not the entire SIGMET. Additional information regarding the SIGMET may be contained in the text version.
5.1.1 SIGMET Issuance.
SIGMETs are issued from Meteorological Watch Offices (MWO). The United States has three MWOs: the Aviation Weather Center (AWC), the AAWU, and the WFO Honolulu.
Their Areas of Responsibility (AOR) are as follows:
The AWC:
• Twenty domestic air route traffic control center (ARTCC) Flight Information Regions (FIRs) covering the continental United States (CONUS) and adjacent coastal waters. CONUS SIGMETs except for Convective SIGMETs are grouped into six areas (see Figure 5-1, AWC SIGMET Areas of Responsibility—Continental U.S.).
• The New York, Houston, Miami, and San Juan Oceanic FIRs (see Figure 5-2, AWC SIGMET Areas of Responsibility—Atlantic Basin).
• The Oakland Oceanic FIR north of 30 north latitude and the portion east of 140 west longitude, which is between the equator and 30 north latitude (see Figure 5-3, SIGMET Areas of Responsibility—Pacific Basin).
The AAWU is responsible for the Anchorage Continental FIR and Anchorage Oceanic FIR (see Figure 5-3).
WFO Honolulu is responsible for the Oakland Oceanic FIR south of 30 north latitude and between 140 west and 130 east longitude (see Figure 5-3).
11/14/16 Aviation Weather Services AC 00-45H Figure 5-1. AWC SIGMET Areas of Responsibility-Continental U.S.
San Francisco Salt Lake City Chicago Boston Dallas/Fort Worth Miami Figure 5-2. AWC SIGMET Areas of Responsibility-Atlantic Basin 40
NEW YORK OCEANIC FIR 30
HOUSTON MIAMI,
OCEANIC OCEANIC Q I MIAMI
FIR FIR OCEANIC EIR
SAN JUAN → FIR -90 - 80 ·260 - 50 -40 5-2
11/14/16 Aviation Weather Services AC 00-45H 5-3 Figure 5-3. SIGMET Areas of Responsibility—Pacific Basin
Note that KKCI refers to the AWC that is in Kansas City, MO.
5.1.1.1 SIGMET Identification.
U.S. SIGMETs (other than Convective SIGMETs) are assigned a series identifier:
• AWC for CONUS:
o NOVEMBER, OSCAR, PAPA, QUEBEC, ROMEO, UNIFORM, VICTOR, WHISKEY, XRAY and YANKEE. Note that SIERRA and TANGO are excluded.
• AWC for Oakland Oceanic FIR:
o ALFA, BRAVO, CHARLIE, DELTA, ECHO, FOXTROT, GOLF and HOTEL.
• Honolulu MWO for Oakland Oceanic FIR:
o NOVEMBER, OSCAR, PAPA, QUEBEC, ROMEO, SIERRA,
TANGO, UNIFORM, VICTOR, WHISKEY, XRAY, YANKEE and ZULU.
11/14/16 Aviation Weather Services AC 00-45H 5-4
• AAWU for Anchorage FIR:
o INDIA, JULIET, KILO, LIMA and MIKE.
A number is assigned sequentially with each issuance until the phenomenon ends. At 0000 Coordinated Universal Time (UTC) each day, all continuing SIGMETs are renumbered to 1 regardless of a continuation of the phenomena
(e.g., YANKEE 1, YANKEE 2, YANKEE 3).
5.1.2 SIGMET Standardization.
SIGMETs follow these standards:
• All heights or altitudes are referenced to above Mean Sea Level (MSL), unless otherwise noted, and annotated using the height in hundreds of feet, consisting of three digits (e.g., 040). For heights at or above 18,000 ft, the level is preceded by flight levels (FL) (e.g., FL180).
• References to latitude and longitude are in whole degrees and minutes following the model: Nddmm or Sddmm, Wdddmm, or Edddmm with a space between latitude and longitude and a hyphen between successive points. Example: N3106 W07118— N3011 W7209.
• Messages are prepared in abbreviated plain language using contractions from the current edition of FAA Order JO 7340.2, ICAO Abbreviations and Codes, for domestic products and International Civil Aviation Organization (ICAO) document 8400 for international products issued for Oceanic FIRs. A limited number of non-abbreviated words, geographical names, and numerical values of a self-explanatory nature may also be used.
5.1.3 SIGMET (Non-Convective)—CONUS.
5.1.3.1 SIGMET (Non-Convective) Issuance Criteria—CONUS.
A SIGMET may be issued in the CONUS when any of the following conditions are affecting or, in the judgment of the forecaster, are expected to affect an area of at least 3,000 square miles (m2) or an area judged to have a significant impact on the safety of aircraft operations:
• Severe or greater turbulence (SEV TURB).
• Severe icing (SEV ICE).
• Widespread duststorm (WDSPR DS).
• Widespread sandstorm (WDSPR SS).
• Volcanic ash (VA).
5.1.3.2 SIGMET (Non-Convective) Issuance Time and Valid Period—CONUS.
A SIGMET is an unscheduled product issued any time conditions reaching SIGMET criteria are occurring or expected to occur within a 4-hour period. A SIGMET can have a valid period up to, but not exceeding, 4 hours. SIGMETs
11/14/16 Aviation Weather Services AC 00-45H 5-5 for continuing phenomena will be reissued at least every 4 hours as long as SIGMET conditions continue to occur in the AOR.
5.1.3.3 SIGMET (Non-Convective) Format and Example—CONUS.
The content and order of elements in the SIGMET are as follows:
• Series name and number.
• Valid beginning and ending time (UTC).
• List of states affected by the phenomena.
• Location of phenomena delineated by high-altitude Very High Frequency Omni-Directional Range (VOR) coordinates covering the affected area during the SIGMET valid time.
• Phenomena description (e.g., SEV ICE).
• Vertical extent (base and top), if appropriate.
• Movement, if appropriate.
• Intensity change (INTSF—intensifying, WKN—weakening, NC—no change).
• Indication that the weather condition will continue during the 4 hours beyond the valid time of the SIGMET.
Figure 5-4. SIGMET for the Continental U.S.—Example SFOR UWS 100130 SIGMET ROMEO 1 VALID UNTIL 100530 OR WA
FROM SEA TO PDT TO EUG TO SEA SEV TURB BTN FL280 AND FL350. CONDS CONTG BYD 0530Z.
11/14/16 Aviation Weather Services AC 00-45H 5-6 Table 5-1. Decoding a SIGMET (Non-Convective) for the Continental U.S.
Line 1 Content SFO Description SIGMET area identifier R SIGMET series WS Product identifier 100130 Issuance date/time UTC 2 SIGMET Product type ROMEO SIGMET series name 1 Series issuance number VALID UNTIL 100530 Ending valid date/time UTC 3 OR WA Phenomenon location (states) 4 FROM SEA TO PDT TO EUG TO SEA Phenomenon location (high-altitude VOR coordinates) 5 SEV TURB BTN FL280 AND FL350. CONDS CONTG BYD 1000Z Phenomenon description The SIGMET in Figure 5-4, SIGMET for the Continental U.S.—Example, is decoded as the following:
(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) Severe turbulence between Flight Level 280 and Flight Level 350.
Conditions continuing beyond 0530Z.
11/14/16 Aviation Weather Services AC 00-45H 5-7
5.1.3.4 SIGMET (Non-Convective) Cancellations—CONUS.
A CONUS Non-Convective SIGMET is canceled when the phenomena is no longer occurring or no longer expected to occur or has moved out of the AOR.
5.1.3.5 SIGMET (Non-Convective) Amendments—CONUS.
Amendments to CONUS Non-Convective SIGMETs are not issued. Instead, a new SIGMET is issued using the next series number.
5.1.3.6 SIGMET (Non-Convective) Corrections—CONUS.
Corrections to CONUS Non-Convective SIGMETs are issued as necessary.
The corrected SIGMET is identified by a “COR” located at the end of the first line after the issuance UTC date/time.
5.1.4 Convective SIGMET.
Convective SIGMETs are issued for the CONUS instead of SIGMETs for thunderstorms.
Any Convective SIGMET implies severe or greater turbulence, severe icing, and low-level wind shear.
Although the areas where the Convective SIGMETs apply may be shown graphically, a graphical depiction of the Convective SIGMET area is not the entire Convective SIGMET. Information regarding the Convective SIGMET identified by graphic depiction should be referred to for further information.
5.1.4.1 Convective SIGMET—Routine Issuance Criteria.
A Convective SIGMET will be issued when any of the following conditions are occurring or, in the judgment of the forecaster, are expected to occur:
• A line of thunderstorms at least 60 miles (mi) long with thunderstorms affecting at least 40 percent of its length.
• An area of active thunderstorms affecting at least 3,000 mi2 covering at least 40 percent of the area concerned and exhibiting a very strong radar reflectivity intensity or a significant satellite or lightning signature.
• Embedded or severe thunderstorm(s) expected to occur for more than 30 minutes during the valid period regardless of the size of the area.
5.1.4.2 Convective SIGMET—Special Issuance Criteria.
A special Convective SIGMET may be issued when any of the following criteria are occurring or, in the judgment of the forecaster, are expected to occur for more than 30 minutes of the valid period.
• Tornado, hail greater than or equal to ¾ inch (in) (at the surface), or wind gusts greater than or equal to 50 knots (kts) (at the surface) are reported.