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.
Figure 5-83. GTG Max Intensity Example CAT+MWT All Levels Aircraft: Heavy • Plot: Combined * Vertical level: max Forecast time: Ohr - 15Z 03 Nov GTG - Max combined intensity (1000 ft. MSL to FL500) 00 hr forecast valid 1500 UTC Tue 03 Nov 2015 ADDE Eddy Dissipation Rate (EDR) _ Mod 10 20 30 40 50 60 70 80 90 Turb PIREP Symbols - - Smooth-Light @ Smooth A Light A Light-Moderate _A Moderate A Moderate-Sevara _M Severe * Extreme 5-157
Figure 5-84. CAT+MWT Low Levels Example (GA Users) Aircraft: Heavy • Plot: Combined • Vertical level: 5,000 Forecast time: 0hr - 15Z 03 Nov GTG - Combined CAT+MTW at 5000 ft. MSL 00 hr forecast valid 1500 UTC Tue 03 Nov 2015 Crestad by;
ADDE ' Eddy Dissipation Rate (EDR) terroin Mad Sev JE 10 20 30 40 50 60 70 80 90 Turb PIREP Symbols - - Smooth-Light @ Smooth A Light A Light-Moderate _A Moderate A Moderate-Savera A Severe * Extreme 5-158
Figure 5-85. Explicit MWT Forecasts Example Aircraft: Heavy • Plot: Mtn Wave • Vertical level: max Forecast time: Ohr - 152 03 Nov GTG - Max mountain wave (1000 ft. MSL to FL500) 00 hr forecast valid 1500 UTC Tue 03 Nov 2015 Eddy Dissipation Rate (EDR) Igt| _ Mod Sei 10 20 30 40 50 60 70 80 90 Turb PIREP Symbols - - Smooth-Light O Smooth A Light A Light-Moderate _A Moderate A Moderote-Savera _^ Severe * Extreme
5.21.2.3 Strengths and Limitations.
The GTG provides an hourly, high-resolution product of EDR at and above 10,000 ft MSL in 1,000-ft intervals. The product is based on an ensemble of 5-159
5-160 turbulence indicators and, therefore, can capture more diverse sources of turbulence and provide a more reliable forecast than can be provided by a single indicator. However, it does not specifically predict turbulence associated with Convective clouds, or small-scale terrain features, but does predict turbulence associated with upper-level clear and mountain wave sources.
5.21.2.3.1 Strengths.
• The product is issued hourly out to a maximum 18-hour lead time.
• Turbulence is plotted to a high resolution.
• The product is based on an ensemble of turbulence indicators and, therefore, can capture more diverse sources of turbulence and provide a more reliable forecast than can be provided by a single indicator.
5.21.2.3.2 Limitations.
• The accuracy of the product depends on the accuracy of the computer model output used to create them.
• The product does not specifically predict turbulence associated with Convective clouds or small-scale local terrain features.
5.21.2.4 Use.
The maximum product can provide a quick method to determine what the greatest potential of turbulence is at a given location. However, to determine the turbulence potential at any given altitude, the individual altitude output must be viewed.
The AWC’s website overlays 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 ft vertically of the displayed 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.
5.22 Additional Products for Clouds, Visibility, Weather, and Surface Wind Forecasts.
5.22.1 NWS Aviation Forecast Discussion.
Aviation Forecast Discussions describe the weather conditions within a multistate or substate sized area. They also may:
• Describe the weather conditions as they relate to a specific TAF (see paragraph 5.13) or group of TAFs; and
• Provide additional aviation weather-related issues that cannot be encoded into the TAF, such as the reasoning behind the forecast.
5-161 Aviati on Forecast Discussions are available at https://www.aviationweather.gov as well as each NWS WFO website.
5.22.1.1 Issuance.
Aviation Forecast Discussions are issued by each NWS WFO for their AOR (see Figure 5-86, Map of NWS Weather Forecast Office’s Area of Responsibility). They are issued roughly every 6 hours and correspond to the issuance of TAFs from the respective NWS WFO.
Figure 5-86. Map of NWS Weather Forecast Office’s Area of Responsibility
5.22.1.2 F ormat.
Aviation Forecast Discussions are a free-form plain language text product.
Common or well-known aviation weather contractions are used as well as local or regional geographic names, such as valleys, mountain ranges, and bodies of water. Each NWS office may tailor the format to meet the needs of their local aviation users.
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5.22.1.3 Examples.
NWS Boise, ID COLD FRONT CURRENTLY OVER SW IDAHO WEST OF THE MAGIC VALLEY. IFR IN
HEAVIER RAIN/SNOW SHOWERS BEHIND THE FRONT MOSTLY IN THE MTNS UNTIL THIS EVENING. OTHERWISE LOW VFR THROUGH TOMORROW WITH ISOLATED SHOWERS INTO THE EVENING. SURFACE WINDS...W TO NW WITH GUSTS 20-30 KTS...BECOMING 35-45 KTS IN THE UPPER TREASURE AND MAGIC VALLEYS FOR A FEW HOURS THIS AFTERNOON...DROPPING DOWN TO 20-30 KTS OVERNIGHT INTO THE MORNING IN THE MAGIC VALLEY AND 5-10 KTS ELSEWHERE. WINDS ALOFT NEAR 10K FT MSL...NW 30-40 KTS...40-50 KTS OVER THE UPPER TREASURE AND MAGIC VALLEYS OVERNIGHT...BECOMING 20-30 KTS BY 15/12Z.
NWS Buffalo, NY
EXPECT LIMITED LAKE EFFECT CLOUDS TO LINGER SOUTHEAST OF LAKE ONTARIO INTO THIS EVENING. EVEN SO...CONDITIONS SHOULD BE MAINLY VFR WITH CLOUD BASES JUST ABOVE 3K FT. AFTER THIS...SKIES WILL CLEAR OUT
WITH A PROLONGED PERIOD OF VFR CONDITIONS LIKELY TO LAST THROUGH SUNDAY.
OUTLOOK...
SUNDAY NIGHT THROUGH TUESDAY...AREAS OF MVFR IN RAIN/SNOW SHOWERS.
WEDNESDAY...VFR.
THURSDAY...VFR/MVFR. A CHANCE OF RAIN.
NWS Chicago, IL ORD AND MDW CONCERNS...UPDATED 20Z...
* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS OVER 30 KT.
5.22.1.4 Use.
Aviation Forecast Discussions provide the aviation weather user with additional information regarding the weather affecting airports with TAF service as well as weather features affecting NWS WFO’s AOR.
The AWC’s website is the ideal location to access all Aviation Forecast Discussions.
5.22.2 NWS National Digital Forecast Database Graphic Products.
The NWS’s NDFD graphical products are a seamless mosaic of weather forecasts from NWS WFOs and the NWS’s NCEP. The NDFD graphic products are derived from a prescribed set of data contained within the NWS’s NDFD. The NDFD is NWS’s official database of the 7-day public and select other forecasts for the 50 states, Guam, and Puerto Rico.
5-163 The NDFD graphi cal products complement the Short-Range Surface Prognostic Charts (see paragraph 5.18), which are also based on the NDFD. The NDFD graphical products can be found on all NWS WFO websites. A subset of these products (i.e., sky cover, predominant weat her, surface winds) are available on https://www.aviationweather.gov, as well as the websites of Flight Service Station (FSS) service providers.
5.22.2.1 Issuance.
NWS offices and centers routinely update NDFD graphical products. NDFD graphical forecasts for days 1, 2, and 3 are provided for the following times:
0000, 0300, 0600, 0900, 1200, 1500, 1800, and 2100 UTC. NDFD graphical forecasts for days 4 through 7 are provided for 0000 and 1200 UTC. Proposals to provide day 1 and 2 NDFD graphical products at 1-hour time intervals are being considered by the NWS.
A subset of t he NDFD graphical forecasts (i.e., cloud cover, predominant weather, surface winds), valid for three hourly time steps out to 18 hours, is available on https://www.aviationweather.gov, as well as the websites of Flight Service Station service providers.
5.22.2.2 Content.
The NDFD graphical product display is a Web-based seamless mosaic of weather forecasts from the NWS.
The NDF D graphical products can be displayed on a national display, regional display, and sub-regional display. A subset of the NDFD graphical forecasts
(i.e., sky cover, predominant weather, surface winds) is available on https://www.aviationweather.gov in a CONUS projection as well as select regional projections.
NDFD graphical products are divided into the following categories: public, marine , fire weather, tropical, and hazardous. The NDFD public graphic products are available for the following:
• Maximum and minimum temperature;
• Temperature;
• Dewpoint;
• Relative humidity;
• Sky cover;
• Weather;
• Hazards;
• Probability of precipitation;
• Amount of precipitation;
• Snow amount;
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• Snow level;
• Ice accumulation;
• Sky cover; and
• Surface wind direction, speed, and gusts.
The paragrap h will describe the subset of the NDFD graphical forecasts available on https://www.aviationweather.gov in a CONUS projection as well as select regional projections. These subset products are sky cover, predominant weather, and surface winds.
Note: The regional examples shown in this paragraph are from the NWS’s NDFD website. The areas depicted may be slightly different on https://www.aviationweather.gov, as well as the websites of FSS service providers.
5.22.2.2.1 Sky Cover.
The Sky Cover graphic (see Figure 5-87, NDFD Sky Cover Graphic Product—Example, and Figure 5-88, NDFD Sky Cover Graphic Product—Example) is the forecast of the amount of clouds (in percent) coveri ng the sky valid for the indicated hour.
Figure 5-87. NDFD Sky Cover Graphic Product—Example