11/14/16 Aviation Weather Services AC 00-45H 5-147 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.
5.19.2.3.1 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.
5.19.2.3.2 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.
5.19.2.4 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 Web site 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.
5.20 Additional Products for Clouds, Visibility, Weather, and Surface Wind Forecasts.
5.20.1 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 5.11) 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.
11/14/16 Aviation Weather Services AC 00-45H 5-148 Aviation Forecast Discussions are available at http://www.aviationweather.gov as well as each NWS WFO Web site.
5.20.1.1 Issuance.
Aviation Forecast Discussions are issued by each NWS WFO for their AOR (see Figure 5-78, 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 5-78. Map of NWS Weather Forecast Office’s Area of Responsibility
5.20.1.2 Format.
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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5.20.1.3 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.
5.20.1.4 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 Web site is the ideal location to access all Aviation Forecast Discussions.
5.20.2 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.
11/14/16 Aviation Weather Services AC 00-45H 5-150 The NDFD graphical products complement the Short-Range Surface Prognostic Charts (see paragraph 5.16), which are also based on the NDFD. The NDFD graphical products can be found on all NWS WFO Web sites. A subset of these products (i.e., sky cover, predominant weather, surface winds) are available on http://www.aviationweather.gov, as well as the Web sites of Flight Service Station (FSS) service providers.
5.20.2.1 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 the NDFD graphical forecasts (i.e., cloud cover, predominant weather, surface winds), valid for three hourly time steps out to 18 hours, is available on http://www.aviationweather.gov, as well as the Web sites of Flight Service Station service providers.
5.20.2.2 Content.
The NDFD graphical product display is a Web-based seamless mosaic of weather forecasts from the NWS.
The NDFD 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 http://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 paragraph will describe the subset of the NDFD graphical forecasts available on http://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 Web site. The areas depicted may be slightly different on http://www.aviationweather.gov, as well as the Web sites of FSS service providers.
5.20.2.2.1 Sky Cover.
The Sky Cover graphic (see Figure 5-79, NDFD Sky Cover Graphic Product—Example, and Figure 5-80, NDFD Sky Cover Graphic Product—Example) is the forecast of the amount of clouds (in percent) covering the sky valid for the indicated hour.
Figure 5-79. NDFD Sky Cover Graphic Product—Example
11/14/16 Aviation Weather Services AC 00-45H Figure 5-80. NDFD Sky Cover Graphic Product-Example 40 50 60 70 80 90 94 hortland lo 100- 39 Concore 98% 100 -100- syracuse 075 Albany: ₩ 9800 Bostop Baffalo 100 Te 00 -100 _Elmira Hartford TOU 98 100F ity
• 13 Pittsburgh 72 _Philadelphi 95 86 68
• Hashime 1% 96* Richnork
• 19 Roanoke Sky Cover (%) For Sat Mar 28 2015 8AM EDT (Sat Mar 28 2015 12Z) National Digital Forecast Database 11z issuance Graphic created-Mar 28 7:19AM EDT
5.20.2.2.2 Weather.
The Weather Graphic Product (see Figure 5-81, NDFD Weather Graphic Product-Example, Figure 5-82, NDFD Weather Graphic Product-Example, Figure 5-84, NDFD Weather Graphic Product-Example, Figure 5-85, NDFD Weather Graphic Product-Example, and Figure 5-86, NDFD Weather Graphic Product-Example) is the forecast predominate weather (precipitating or non-precipitating) valid at the indicated hour. The weather element includes type, intensity, and probability (see Figure 5-83, Legend for NDFD Weather Graphic). Darker shades of precipitation represent probabilities for 55 percent or greater.
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11/14/16 Aviation Weather Services AC 00-45H 5-153 Note: The NDFD graphical products are directed to all users
(e.g., public) and not specifically directed at aviation users. These graphics use weather symbology that differs from that used in Significant Weather (SIGWX) forecasts and METARs.
Figure 5-81. NDFD Weather Graphic Product—Example
The product’s legend will change depending on the forecast weather, e.g., the legend box will have fog only when fog is forecast on the graphic.
11/14/16 Aviation Weather Services AC 00-45H Figure 5-82. NDFD Weather Graphic Product-Example None Rain Snou Portland
- SH SH- SH- concors -SH- Syracuse Hibany 05-5 - Boston 1SH-/F Buffalo SH- Elnira Hartfol → SH- S- SH THeu YI SHE Pittsburgh SH- _Phi delphi • SH- SH- Hashinetor SH- sy- Richmonde Roanoke Predominant Weather For Sat Mar 28 2015 8AM EDT (Sat Mar 28 2015 12Z) National Digital Forecast Database 11z issuance Graphic created-Mar 28 7:09AM EDT Forecast valid for day 1 at 8 a.m. EDT (i.e., 12Z or 1200 UTC). Snow showers are forecast to extend from Virginia up to and across New England. Mixed precipitation (combination of rain and snow, rain and sleet, or snow and sleet) is forecast over portions or North Carolina and southern Virginia as well as off the coast of New England. Darker shades indicate 55 percent or greater probability.
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11/14/16 Aviation Weather Services AC 00-45H Figure 5-83. Legend for NDFD Weather Graphic National Digital Forecast Database Graphical Forecast Weather Legend None Rain L, R, FW, T Drizzle, Rain, Rain Showers, Thunderstorms Severe T+ Severe Thunderstorms Wintry Mix RIS Rain / Snow Mix Ice IP, ZL, ZR Sleet, Freezing Drizzle, Freezing Rain Snow SW, S Snow Showers, Snow Obstructions To Vision F Fog H Haze K Smoke BS, BD Blowing Snow, Blowing Dust Weather Intensity: - Light + Heavy Weather Probability: Darker shades indicate higher probability 5-155
11/14/16 Aviation Weather Services AC 00-45H Figure 5-84. NDFD Weather Graphic Product-Example None Rain Fog Poplar bluff Tulsa Nashville Jonesbora RH- Little Rock Temphis • T/RH Huntsville Tupelo ° RH/T Texal Tana - Birningham
• T/RH- T/RH- © RH - RH/T Shreveport Jackson TARH øȚ/RH—¢ Lufkin PREP Nobile.
Lake Charles a New Orie Housto Predominant Weather For Mon Mar 30 2015 8AM EDT (Mon Mar 30 2015 12Z) National Digital Forecast Database 17z issuance Graphic created-Mar 28 1:10PM EDT Forecast valid for day 3 at 8 a.m. EDT (i.e., 12Z or 1200 UTC). Thunderstorms and light rain showers are forecast from Texas and Oklahoma to across the southeastern United States. Darker shades indicate 55 percent or greater probability. Fog is forecast across southern Mississippi and eastern Louisiana.
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11/14/16 Aviation Weather Services AC 00-45H Figure 5-85. NDFD Weather Graphic Product-Example None Rain Snou Fog TRH-
• RH- \Kalispel Havre © RH- Spokani Glasgow Minot o RH- Missoula Butte Bismarck Billings Yelloustone Rapid City Pierre Twin Falls Riverton Douglas Elko Predominant Weather For Sat Mar 28 2015 Salt Lake City North Platte SAM EDT (Sat Mar 28 2015 12Z) National Digital Forecast Database 11z issuance Graphic created-Mar 28 7:18AM EDT Forecast valid for day 1 at 8 a.m. EDT (i.e., 122 or 1200 UTC). Fog from North Dakota into South Dakota and light rain showers across the Northern Rockies. Darker shades indicate 55 percent or greater probability.
Figure 5-86. NDFD Weather Graphic Product-Example None Rain Snou Chicar South Bend Des Moines Fort Hayne Peoria Springfield Indianapolis
• 5- Cincinnati
- Columbia dusville R-/S- aducah R-/S- plar Bluffr Nashville Jonesbor a Little Rock temphis Huntsville TiDeln ° R-15- Predominant Weather For Sat Mar 28 2015 8AM EDT (Sat Mar 28 2015 12Z) National Digital Forecast Database 11z issuance Graphic created-Mar 28 7:18AM EDT Forecast valid for day 1 at 8 a.m. EDT (i.e., 12Z or 1200 UTC). Light snow is forecast from southern Iowa into central Missouri; a mix of precipitation (combination of rain and snow, rain and sleet, or snow and sleet) is forecast from western Missouri to northern Mississippi, along with light rain over most of Arkansas.
Darker shades indicate 55 percent or greater probability.
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5.20.2.2.3 Wind.
Wind is provided in two graphics, one for surface wind speed and direction (see Figure 5-87, NDFD Surface Wind Speed and Direction—Example) and one for wind gusts (see Figure 5-89, NDFD Surface Wind Gust Graphic—Example). Symbols for wind speed and direction (see Figure 5-88, NDFD Wind Speed and Direction Graphic Product Plot Model) are plotted on the graphic. Wind speed and gust speed are also depicted using a color.
Both wind speed and gusts are in knots.
Figure 5-87. NDFD Surface Wind Speed and Direction—Example