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5.20.1.4.3 Cumulonimbus Cloud (CB) Forecasts.
CB cloud forecasts are based on an algorithm gives information relating to base, top, and horizontal extent (coverage) of any expected CB clouds. The algorithm is based on Convective rainfall rates.
The horizontal extent component is expressed as a value between 0 and 1, representing the fraction of sky covered by CB cloud within a grid box.
A value of 0.5 implies 50 percent coverage of CB cloud in that grid box (a grid box is 1.25 degrees latitude by 1.25 degrees longitude in size).
Where CB clouds are forecast to exist, a base and a top of the CB cloud is provided, represented by a height that can be converted into a flight level.
CB base and top forecasts are provided in meters above MSL. AWC’s WAFS website provides a display of CB cloud forecasts with the CB tops shown in flight levels (see Figure 5-76, WAFS CB Cloud Forecast—Example).
Figure 5-76. WAFS CB Cloud Forecast—Example
A 6-hour forecast of CB clouds (grey shade) where coverage is more than 0.3, i.e., 30 percent.
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5.20.1.5 Use.
WAFS forecasts are for use in flight planning and flight documentation for international air navigation.
5.21 Additional Products for Icing and Turbulence.
SIGMETs and AIRMETs are produced by NWS forecasters and are the advisory products for turbulence and icing information for aviation users. The NWS also produces icing and turbulence products that are derived from NWP model data with no forecaster modifications. This paragraph provides information on the following icing and turbulence products:
• Current Icing Product (CIP);
• Forecast Icing Product (FIP); and
• Graphical Turbulence Guidance (GTG).
By design, the CIP, FIP, and GTG do not use the intensity level severe. Pilots should always refer to SIGMETs for information on severe icing and severe turbulence.
CIP and FIP products contain a heavy intensity level. Heavy icing has been defined, in part, as the rate of ice accumulation that requires maximum use of ice protection systems to minimize ice accretions on the airframe. Immediate exit from the conditions should be considered. Heavy icing is not an intensity level used in PIREPs.
These icing and turbulence products will continue to evolve over the coming years with increased model resolutions, additional horizontal layers, and improvements to the algorithms and/or data sets used to produce the product. Along with these improvements may come a slight change in references to the product update version (e.g., GTG to GTG2, GTG2 to GTG3). Users can find additional information on these products and any changes on the AWC’s icing and turbulence Web pages.
5.21.1 Current and Forecast Icing Products (CIP/FIP).
The CIP combines sensor and NWP model data to provide an hourly three-dimensional diagnosis of the icing environment. This information is displayed on a suite of graphics available for the CONUS, much of Canada and Mexico, and their respective coastal waters. The FIP provides the same suite of products describing the icing environment in the future and is solely NWP model based. The CIP/FIP product suites are automatically produced with no human modifications. Information on the graphics is determined from NWP model output; observational data, including WSR-88D radar; satellite, PIREPs, and surface weather reports; and lightning network data.
Note: CIP is sometimes referred to as an analysis, but it is actually a 0-hour forecast.
5.21.1.1 Issuance.
The CIP and FIP product suites are issued hourly about 15 minutes after the hour by the AWC. The products are available on their website. Gridded
5-147 versions of these products are also delivered for users who wish to integrate CIP and FIP products with flight-planning systems.
5.21.1.2 Content.
The CIP/FI P product suite as appears on https://www.aviationweather.gov consists of five graphics, including:
• Icing Probability;
• Icing Severity;
• Icing Severity—Probability > 25 percent;
• Icing Severity—Probability > 50 percent; and
• Icing Severity plus Supercooled Large Drop (SLD).
The CIP/FIP products are generated for individual altitudes from 1,000 ft MSL to FL 300 at intervals of 1,000 ft. FIP products are available at 1, 2-, 3-, 6-, 9-, 12-, and 18-hour forecast lead times.
The CIP/FIP products can be viewed at single altitudes and FLs or as a composite of all altitudes from 1,000 ft MSL to FL300, which is referred to as the maximum or max. Single altitudes are referenced to MSL from 1,000 to 17,000 ft and FLs above 17,000 ft. The AWC’s website allows for access to every other altitude (1,000 FT, 3,000 FT, 5,000 FT, etc.). However, vertical cross sections and presentation of all altitudes can be viewed using the Flight Path Tool (see paragraph 6.2) on https://www.av iationweather.gov.
Icing PIREPs are plotted on a single altitude CIP graphic if the PIREP is within 1,000 ft of the selected altitude and has been observed within 75 minutes of the chart’s valid time. Icing PIREPs for all altitudes
(i.e., 1,000 ft MSL to FL300) are displayed, except negative reports are omitted to reduce clutter. The PIREP legend is located on the bottom of each graphic.
5.21.1.2.1 Icing Probability.
The icing probability product displays the probability of icing at any level of intensity. Probabilities range from 0 percent (no icing expected) to 85 percent or greater (nearly certain icing). The product is available on https://www.aviationweather.gov in single altitudes, e.g., 3,000 ft MSL (see Figure 5-77, CIP/FIP Icing Probability (3,000 Feet MSL)—Example), or a composite of all altitudes from 1,000 ft MSL to FL300, i.e., max level (see Figure 5-78, CIP/FIP Icing Probability—Max Example).
Figure 5-77. CIP/FIP Icing Probability (3,000 Feet MSL)-Example Probability of icing at 3000 ft. MSL Analysis valid 1500 UTC Mon 27 Nov 2006 terrain 15 25 35 45 55 65 75 es Negative Y/ Trace-Light W| Light-Moderate W Moderate-Severa (percent) cing PIREP Symbols W Trace Lyl Light / Moderate Y! Severa "Cool" colors (e.g., blue and green) represent low probabilities and "warm" colors (orange and red) represent higher probabilities. Probabilities do not reach 100 percent because the data used to determine the probability of icing cannot diagnose, with absolute certainty, the presence of icing conditions at any location and altitude. White regions indicate where no probability of icing exists. Brown regions indicate where higher-elevation terrain extends above the altitude of the particular graphic.
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5-149 Figure 5-78. CIP/FIP Icing Probability—Max Example
5.21.1.2.2 Icing Severity.
The Icing Severity product depicts the icing intensity likelihood at locations where the icing probability product depicts possible icing. Icing intensity is displayed using icing intensity categories: trace, light, moderate, and heavy.
The product is available on https://www.aviationweather.gov in single altitudes, e.g., 3,000 ft MSL (se e Figure 5-79, CIP/FIP Icing Severity (3,000 Feet MSL)—Example), or a composite of all altitudes from 1,000 ft MSL to FL300, i.e., max level (see Figure 5-80, CIP/FIP Icing Severity—Max Example).
Figure 5-79. CIP/FIP Icing Severity (3,000 Feet MSL)-Example Icing severity at 3000 It. MSL Analysis valid 1500 UTC Mon 27 Nov 2006 terrain None Trace Light Moderate Heavy ø Negative WJ Trace-Light \ Light-Moderate I Moderate-Savere Icing PIREP Symbols W Trace Lyl Light / Moderate I/ Sevare The lightest blue color represents trace icing. As the blue-color shades become darker, the icing intensity increases. The darkest blue color represents heavy icing. White regions indicate where no probability of icing exists. Brown regions indicate where higher-elevation terrain extends above the altitude of the particular graphic.
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5-151 Figure 5-80. CIP/FIP Icing Severity—Max Example
5.21.1.2.3 Icing Severity—Probability > 25 Percent.
The Icing Severity—Probability > 25 percent product depicts where at least a 26 percent probability exists for the indicated icing intensity. Icing intensity is displayed using icing intensity categories: trace, light, moderate, and heavy.
The product is available on https://www.aviationweather.gov in single altitudes, e.g., 3,000 ft MSL, or a composite of all altitudes from 1,000 ft MSL to FL300, i.e., max level.
The lightest blue color represents trace icing. As the blue color shades become darker, the icing intensity increases. The darkest blue color represents heavy icing. White regions indicate where no probability of icing exists. Brown regions indicate higher-elevation terrain extending above the altitude of the particular graphic. A gray color is used to mask the intensity pixels where the probability of icing is 25 percent or less.
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5.21.1.2.4 Icing Severity—Probability > 50 Percent.
The Icing Severity—Probability > 50 percent product depicts where the probability of the indicated icing intensity is at least 51 percent. Icing intensity is displayed using icing intensity categories: trace, light, moderate, and heavy.
The product is available on https://www.aviationweather.gov in single altitudes, e.g., 3,000 ft MSL, or a composite of all altitudes from 1,000 ft MSL to FL300, i.e., max level.
The lightest blue color represents trace icing. As the blue color shades become darker, the icing intensity increases. The darkest blue color represents heavy icing. White regions indicate where no probability of icing exists and, therefore, no intensity is necessary. Brown regions indicate where higher-elevation terrain extends above the altitude of the particular graphic.
A gray color is used to mask the intensity pixels where the probability of icing is 50 percent or less.
5.21.1.2.5 Icing Severity Plus Supercooled Large Drops (SLD).
The Icing Severity plus SLD product depicts the intensity of icing expected as well as locations where a threat for SLD exists. The product is available on https://www.aviationweather.gov in single altitudes, e.g., 3,000 ft MSL (see Figure 5-81, CIP/FIP Icing Severity Plus Supercooled Large Drops (SLD)—Example), or a composite of all altitudes from 1,000 ft MSL to F L300, i.e., max level (see Figure 5-82, CIP/FIP Icing Severity Plus Supercooled Large Droplets (SLD)—M ax Example).
SLD is defined as supercooled water droplets larger than 50 micrometers in diameter. These size droplets include freezing drizzle and/or freezing rain aloft. SLD, which are outside the icing certification envelopes (14 CFR part 25 a ppendix C), can be particularly hazardous to some aircraft.
Icing intensity is displayed using icing intensity categories: trace, light, moderate, and heavy.
Figure 5-81. CIP/FIP Icing Severity Plus Supercooled Large Drops (SLD)-Example Icing severity at 3000 ft. MSL Analysis valid 1800 UTC Mon 27 Nov 2006 SLD threat terrain None Trace Light Moderate Hedyy es Negative L Trace-Light 1] Light-Moderate I Moderate-Severe cing PIREP Symbals W Trace Lyl Light ' Moderate '/ Severe The lightest blue color represents trace icing. As the blue color shades become darker, the icing intensity increases. The darkest blue color represents heavy icing. White regions indicate where no probability of icing exists. Brown regions indicate where higher-elevation terrain extends above the altitude of the particular graphic. Locations where a threat for SLD exists are depicted with red hatching.
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5-154 Figure 5-82. CIP/FIP Icing Severity Plus Supercooled Large Droplets (SLD)—Max Example
5.21.1.3 St rengths and Limitations.
5.21.1.3.1 Strengths.
The CIP product suite is updated hourly and provides a diagnostic tool to assist in determining the probability for icing, the intensity of icing, and the threat for SLD.
5.21.1.3.2 Limitations.
Actual icing severity may be different than what is depicted on the CIP graphics and plotted PIREPS because:
• Different aircraft types experience different severities of icing in the same atmospheric environments. Severity definitions are currently pilot based and thus are a function of the aircraft type, flight phase (takeoff/landing,
5-155 cruise, etc.), aircraft configuration, as well as the pilot’s experience and perception of the icing hazard.
• Assessing the amount and drop size of Supercooled Liquid Water (SLW) in the atmosphere is difficult.
• The Icing Severity products depict the severity of the meteorological icing environment and not the resultant icing that may occur on the aircraft.
5.21.1.4 Uses.
The CIP/FIP Icing Probability product can be used to identify the current and forecast three-dimensional probability of icing. The CIP/FIP should be used in conjunction with the report and forecast information contained in an AIRMET and SIGMET.
The CIP/FIP Icing Severity product can be used to determine the intensity of icing. The CIP/FIP Icing Severity—Probability > 25 percent or Probability > 50 percent depicts the probability of a given intensity of icing occurring.
Finally, the Icing Severity plus SLD product can help in determining the threat of SLD, which is particularly hazardous to some aircraft.
Icing PIREPs are plotted on single altitude graphics if the PIREP is within 1,000 ft of the graphic’s altitude and has been observed within 75 minutes of the chart’s valid time. On CIP/FIP max level product, PIREPs for all altitudes
(i.e., 1,000 feet MSL to FL300) are displayed except negative reports do not appear to reduce clutter. The PIREP legend is located on the bottom of each graphic.
5.21.2 Graphical Turbulence Guidance (GTG).
The GTG product suite provides a four-dimensional diagnosis and forecast of Non-Convective turbulence intensity (as indicated by the estimated energy dissipation to the 1/3 power–EDR in units of m2/3 s-1). GTG3 does not specifically predict turbulence associated with Convective clouds, or small-scale local terrain features, but does predict turbulence associated with upper-level clear and mountain wave sources.
Note: GTG3 is the third generation of the GTG product. Whereas the graphic examples in this paragraph state GTG3, this paragraph uses the general name of GTG in the description of the product.
The GTG is created using a combination of derived turbulence indicators from NCEP’s Weather Research and Forecasting (WRF) Rapid Refresh (RAP) NWP model. The GTG product suite, which consists of 0-, 1-, 2- 3-, 6-, 9-, 12-, and 18-hour forecasts, is automatically generated with no human modifications. It should be used in conjunction with the report and forecast information contained in an AIRMET and SIGMET. The GTG is available for the CONUS, much of Canada and Mexico, and their respective coastal waters.
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5.21.2.1 Issuance.
The GTG pr oduct suite is issued and updated every hour by the AWC and is available through https://www.aviationweather.gov.
5.21.2.2 Content.
The GTG product (see Figure 5-83, GTG—Max Intensity Example CAT+MWT All Levels) can be viewed at single altitudes and FLs or as a composite of all altitudes from 10,000 ft MSL to FL450, which is referred to as a maximum or max (see Figure 5-84, CAT+MWT Low Levels Example (GA Users)). Single altitudes are referenced to MSL from 10,000 to 17,000 ft and FLs above 17,000 ft.
The AWC’s website allows for access to every other altitude (11,000 FT, 13,000 FT, 15,000 FT, etc.). However, vertical cross sections and presentation of all altitudes can be viewed using the Flight Path Tool (see paragraph 6.2) on https://www.aviationweather.gov. Gridded versions of these products are also delivered for users who wish to integrate GTG with flight pla nning systems or to view the output in their own graphical display systems.