December 1999 DAY 2 CONVECTIVE OUTLOOK 0800Z 040498 ISSUED: 12002 040498 FROM: 1200Z 040598 UNTIL: FORECASTER: HART Figure 12-1. Severe Weather Outlook Chart.
DAY 1 CONVECTIVE OUTLOOK ISSUED: 0623Z 04/03/98 FROM: 1200Z 04/03/98 1200Z 040498 HART UNTIL: FORECASTER:
12-3
December 1999 13-1 Section 13
VOLCANIC ASH ADVISORY CENTER (VAAC) PRODUCTS The Volcanic Ash Advisory Center (VAAC) may issue two products when there is a volcanic eruption:
the Volcanic Ash Advisory Statement (VAAS) and forecast charts of ash dispersion. The U.S. VAACs are the AAWU in Anchorage, Alaska, and the Washington, D.C. VAAC located in Camp Springs, Maryland. Other international centers contribute to the tracking of volcanic ash events. The VAACs do not issue routine products but create and issue them when a volcanic eruption occurs. The products are based on information from PIREPs, MWO SIGMETs, satellite observations, and volcanic observatory reports. Since the products are triggered by the occurrence of an eruption, pilot reports concerning volcanic activity are extremely important.
VOLCANIC ASH ADVISORY STATEMENT (VAAS) Usually the first VAAC product to be issued is the Volcanic Ash Advisory Statement(VAAS). The VAAS is required to be issued within 6 hours of an eruption and every 6 hours after that. However, it can be issued more frequently if new information about the eruption is received. The VAAS summarizes the currently known information about the eruption. It may include the location of the volcano, height of the volcano summit, height of the ash plume, a latitude/longitude box of the ash dispersion cloud, and a forecast of ash dispersion. The height of the ash cloud is estimated by meteorologists analyzing satellite imagery and satellite cloud drift winds combined with any pilot reports, volcano observatory reports, and upper-air wind reports. The VAASs are transmitted to users via the Global Telecommunications System (GTS), the World Area Forecast System (WAFS), the Aeronautical Fixed Telecommunications Network (AFTN), the FAA communications system (WMWCR), and the NWS Family of Services. In addition, VAASs are available on several Internet sites listed on the last page of this document.
December 1999 13-2 Example of a VAAS:
FVAK20 PANC 190323
VOLCANIC ASH ADVISORY - ALERT
ALASKA AVIATION WEATHER UNIT
NATIONAL WEATHER SERVICE ANCHORAGE AK ISSUED 0300 UTC SUNDAY JULY 19 1998 BY ANCHORAGE VAAC VOLCANO: KARYMSKY (1000-13) 98-01 KAMCHATKA 54.05N 159.43E 1486 M 4875 FT SOURCES OF INFORMATION: PILOT REPORT ERUPTION DETAILS: ERUPTION TO FL100 REPORTED BY PILOT REPORT AT 19/0200 UTC VIA WASHINGTON DC VAAC.
ASH CLOUD DESCRIPTION: N/A ASH CLOUD TRAJECTORY: NE 10 KT.
12 HOUR OUTLOOK: IF ASH PERSISTS ALOFT AT 12 HOURS THE FORECAST AREA FROM THE PUFF MODEL BELOW 15000FT IS 56N 161E, 55N 166E, 54N 165E, 55N 162E.
ADDITIONAL INFORMATION: NO ERUPTION VISIBLE ON SATELLITE IMAGERY DUE TO CLOUD IN AREA.
THIS WILL BE THE ONLY ADVISORY ISSUED FOR THIS EVENT.
DAC JUL98 AAWU
VOLCANIC ASH FORECAST TRANSPORT AND DISPERSION (VAFTAD) CHART The Volcanic Ash Forecast Transport and Dispersion (VAFTAD) Chart, Figures 13-1 and 13-2, is generated by a three-dimensional time-dependent dispersion model developed by the National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory (ARL). The VAFTAD model focuses on hazards to aircraft flight operations caused by a volcanic eruption with an emphasis on the ash cloud location in time and space. It uses National Centers for Environmental Prediction (NCEP) forecast data to determine the location of ash concentrations over 6-hour and 12-hour intervals, with valid times beginning 6, 12, 24, and 36 hours following a volcanic eruption. This computer-prepared chart is not issued on a routine basis, but only as volcanic eruptions are reported. Since the VAFTAD chart is triggered by the occurrence of volcanic eruption, PIREPs concerning volcanic activity are very important. Initial input to the VAFTAD model run and the resulting chart include: geographic region, volcano name, volcano latitude and longitude, eruption date and time, and initial ash cloud height.
Utilizing the NCEP meteorological forecast guidance, volcanic ash particle transport and dispersion are depicted horizontally and vertically through representative atmospheric layers. The charts from an actual eruption will be labeled with ALERT. Another possible reason to generate a chart could be for potential volcanic eruption. This chart would be labeled WATCH as shown on Figure 13-1.
December 1999 13-3
VAFTAD PRODUCT The VAFTAD product presents the relative concentrations of ash following a volcanic eruption for three layers of the atmosphere in addition to a composite of ash concentration through the atmosphere.
Atmospheric layers depicted are: surface to flight level (FL) 200, surface to FL550 (composite), FL200 to FL350, and FL350 to FL550. Figure 13-1 shows 8 panels of ash cloud relative concentrations for 12 to 24 hours; and Figure 13-2 shows 18 to 24 hours after a volcanic eruption. Note that the first 6 hours after the volcanic eruption are not depicted. An appropriate SIGMET will be issued by an MWO for that period concerning the volcanic eruption and the area affected by the ash cloud. The four panels in any column are valid for the same time interval (specified and located below the third panel). The top three panels in each column provide the ash location and relative concentrations for an atmospheric layer, identified by top and bottom flight levels. The highest layer is at the top of the chart. Volcano eruption information is given in the legend at the lower left (see Figure 13-1) which includes the volcano name (with location symbol), latitude and longitude, eruption date and time, duration, and ash column height.
USING THE CHART The VAFTAD chart is strictly for advanced flight planning purposes. It is not intended to take the place of SIGMETs regarding volcanic eruptions and ash.
December 1999 TERLAT= 17. CENTERLON= 62,-RADIUS=30.) PPER HAL HART
WATCH WATCH -L55 1351 FL200 -L20
SURFACI _ EQ VALID 06Z 24 OCT 97 (ERUPTION+12H) { § VALID 18Z 24 OCT 97 (ERUPTION+24H) FL550
SURFACE (COMPOSITE) WATCH CHART 1 WATCH
LOWER HALF
NOAA/ARL VOLCANIC ASH FORECAST TRANSPORT AND DISPERSION (VAFTAD) ISSUED BY NWS/NCEP/NCO I SOUFRIERE-HILLS16.7N 62.2W AVN FORECAST CYCL SUMMIT 3000 FT 27 23 OCT 9 ERUPTION 18Z 23 OCT 97 ASH COLUMN FL400 DURATION SEE CURRENT SIGMET
FOR WARNING AREA Figure 13-1. Volcanic Ash Forecast Chart.
13-4
December 1999
17. CENTERLON= 62, RADIUS-30. CHART 2
JPPER HAL WATCH. WATCH
•L55 • 1 351 Hing FL250 im® SURFACE __-EQ EQ VALID 12Z 24 OCT 97 (ERUPTION+18H) { • VALID 18Z 24 OCT 97 (ERUPTION+24H) -L55
SURFACI (COMPOSITE.)
WATCH CHART 2 WATCH
LOWER HALF
NOAA/ARL VOLCANIC ASH FORECAST TRANSPORT AND DISPERSION (VAFTAD)
AVN FORECAST CYCL ERUPTION 18Z 3000 FT 23 OCT 97 "- ALERT " ******** 2Z 23 OC ASH COLUMN HE400 DURATION NATCH SEE CURRENT SIGMET FOR WARNING AREA Figure 13-2. Volcanic Ash Forecast Chart.
13-5
December 1999 14-1 Section 14
TURBULENCE LOCATIONS, CONVERSION AND DENSITY ALTITUDE TABLES,
CONTRACTIONS AND ACRONYMS, SCHEDULE OF PRODUCTS, NATIONAL WEATHER SERVICE STATION IDENTIFIERS, WSR-88D SITES, AND INTERNET ADDRESSES This section provides text, graphs, and tables that can be used by the pilot to further understand the weather. Information included covers:
1. Locations of probable turbulence
2. Standard conversions table
3. Density altitude and chart
4. Contractions and acronyms
5. Scheduled issuance and valid times of forecast products
6. National Weather Service station identifiers and WSR-88D sites
7. Internet addresses
LOCATIONS OF PROBABLE TURBULENCE Turbulence occurs due to either terrain features or weather phenomenon which can produce intensities from light to extreme. The type and intensity of the turbulence will depend on the situations as described in the following paragraphs.
LIGHT TURBULENCE Light turbulence can be caused by obstruction of the wind in hilly or mountainous terrain. Even with light winds, there can be enough displacement of the wind to produce small-scale eddies or turbulence.
Weather conditions that can cause light turbulence are associated with clear-air convective currents over a heated surface or near and in small cumulus clouds. Weak wind shear in the vicinity of troughs aloft, lows aloft, jet streams, or the tropopause can cause light turbulence. Also in the lower 5,000 feet of the atmosphere, light turbulence can occur when winds are near 15 knots or where the air is colder than the underlying surfaces.
MODERATE TURBULENCE Moderate turbulence will be reported in mountainous areas with a wind component of 25 to 50 knots perpendicular to and near the level of the ridge. The turbulence will be located at all levels from the surface to 5,000 feet above the tropopause. The areas most likely to have moderate turbulence is within 5,000 feet of the ridge level, at the base of relatively stable layers below the base of the tropopause, or within the tropopause layer. The turbulence will extend downstream from the lee of the ridge for 150 to 300 miles.
Also, moderate turbulence can be encountered in and near towering cumuliform clouds and thunderstorms (in the dissipating stage).
Moderate turbulence can occur in the lower 5,000 feet of the troposphere when surface winds are 30 knots or more, where heating of the underlying surface is unusually strong, where there is an invasion of very cold air, or in fronts aloft.
December 1999 14-2 Wind shear in the vertical direction that exceeds 6 knots per 1,000 feet and/or horizontal wind shear that exceeds 18 knots per 150 miles will produce moderate turbulence.
SEVERE TURBULENCE Severe turbulence is likely in mountainous areas with a wind component exceeding 50 knots perpendicular to and near the level of the ridge. The location of the severe turbulence will be in 5,000- foot layers at and below the ridge level in rotor clouds or rotor action, at the tropopause, and sometimes at the base of other stable layers below the tropopause. The severe turbulence will extend downstream from the lee of the ridge for 50 to 150 miles.
Severe turbulence can be encountered in and near growing and mature thunderstorms and occasionally in other towering cumuliform clouds.
Severe turbulence will also occur 50 to 100 miles on the cold side of the center of the jet stream, in troughs aloft, and in lows aloft where vertical wind shear exceeds 10 knots per 1,000 feet, and horizontal wind shear exceeds 40 knots per 150 miles.
EXTREME TURBULENCE Extreme turbulence will be found in mountain wave situations. The turbulence will be located in and below the level of well-developed rotor clouds. Sometimes the turbulence extends to the ground.
Besides mountain wave situations, extreme turbulence will occur in severe thunderstorms. A severe thunderstorm is indicated by large hailstones (diameter ¾ inch or greater), strong radar echoes, or continuous lightning.
December 1999
STANDARD CONVERSION TABLE This table can be used as a quick reference for conversion between metric and English units.
Speed - Distance Temperature Pressure - Altitude Altimeter Setting M/H KTS KM/H -100 120 °F °c 50 INS. MBS./hPas. FT* 100'S 28.5 INS. MBS./hPas. 965 110 -180 12 400 - -230 970 90 -170 110 40 13 220 210 100 -160 100 14 -200 980
• 190
- 500 - 29.0 80 -150 90 15 -180 90 30 - 170 -140 80 16 - 160 - 990 80 70 - 130 17 -150 -120 70 20 18 600 - 130 - 140 29.5 - 1000 70 60 -110 60 19 • 120 100 50 10 20 - 1010 60 700 50 90 40 21 30.0 22 50 80 30 • 1020 40 23 70 20 800 40 60 -10 24 • 1030 30 10 25 30.5 30 50 26 40 -20 - 900 • 1040 20 27 20 -10 30 28 -20 31.0 1050 10 -30 29 10 -1000 10 -30 30
• 1060 o 0 -40• -40 31 -1050 M/H KTS KM/H °F INS. MBS./hPas. FT* 100'S 31.5 1065 *Standard Atmosphere INS. MBS./hPas.
Figure 14-1. Standard Conversion Table.
14-3
December 1999 14-4
DENSITY ALTITUDE Density altitude can affect the takeoff, climb, and landing performance of any aircraft. The distance required to take off and land and the rate of climb are affected by density altitude.
Aircraft will perform better in low density altitude conditions. Low density altitude conditions exist when the air is dense. This occurs when the temperature is cold combined with a high pressure system.
The air is the most dense in this situation and the aircraft will perform as if it were at a lower altitude.
For example, a plane is at an airport with a station elevation of 7,000 feet MSL. The atmospheric conditions at that airport indicate a low density altitude situation. The density altitude is calculated to be 5,500 feet MSL. The plane will perform as if it were at 5,500 feet MSL instead of 7,000 feet MSL. This low density altitude situation will decrease takeoff and landing roll while increasing the initial rate of climb.
While low density altitude increases aircraft performance, high density altitude can lead to an aircraft accident. High density altitude situations are more prevalent at higher elevations. High temperatures combined with a low pressure system will produce a high density altitude situation. (The air is least dense in this situation.) Airports in mountainous terrain are more susceptible to high density altitude situations because they already have a high station elevation. The combination of a high station elevation, high temperatures, and low pressure will produce a very high density altitude situation. For example, a plane is at an airport with a station elevation of 7,000 feet MSL. Using the values of station elevation, temperature, and pressure, the density altitude is calculated to be 12,000 feet MSL. Any aircraft taking off or landing at that airport will perform as if it were at an airport with a station elevation of 12,000 MSL. For some aircraft, a high density altitude situation will indicate an altitude higher than the service ceiling of that specific aircraft. In that case, if a pilot attempts to take off during a high density situation, the aircraft will not be able to gain altitude but stay in ground effect and possibly crash.
Use Figure 14-2 to find density altitude either on the ground or aloft. Set the aircraft’s altimeter at 29.92 inches. The altimeter will indicate pressure altitude. Read the outside air temperature. Enter the graph at the pressure altitude value and move horizontally to the temperature value. Read the density altitude from the sloping lines.
Examples:
Density altitude in flight: Pressure altitude is 9,500 feet and the temperature is -8 degrees C. Find 9,500 feet on the left of the chart and move to -8 degrees C. Density altitude is 9,000 feet. See dot on the chart that is labeled number 1.
Density altitude for takeoff: Pressure altitude is 4,950 feet and the temperature is 97 degrees F. Enter the graph at 4,950 feet and move across to 97 degrees F. Density altitude is 8,200 feet. See dot on the chart that is labeled number 2.
December 1999 20,000
STMOSARERE PRESSURE ALTITUDE - FEET 15,000 DENSITY ALTITUDE
- T 10,000 5,000 - 10,000- 5,000+ ,000 + ZERO + 5,000 -50-40 -30 -20 -10 0°% 10 20 30 40 50 TEMPERATURE °C -50-40-20 00F ' 20 40 60 80 100 120
TEMPERATURE OF Figure 14-2. Density Altitude Computation Chart.
14-5
December 1999 14-6
CONTRACTIONS AND ACRONYMS Contractions and acronyms are used extensively in surface reports, pilot reports, and forecasts.
A AAWU – Alaskan Aviation Weather Unit ABNDT - Abundant ABNML - Abnormal ABT - About ABV - Above AC - Convective outlook or altocumulus ACC - Altocumulus castellanus ACCUM - Accumulate ACFT - Aircraft ACLT - Accelerate ACLTD - Accelerated ACLTG - Accelerating ACLTS - Accelerates ACPY - Accompany ACRS - Across ACSL - Altocumulus standing lenticular ACTV - Active ACTVTY - Activity ACYC - Anticyclone ADJ - Adjacent ADL - Additional ADQT - Adequate ADQTLY - Adequately ADRNDCK - Adirondack ADVCT - Advect ADVCTD - Advected ADVCTG - Advecting ADVCTN - Advection ADVCTS - Advects ADVN - Advance ADVNG - Advancing ADVY - Advisory ADVYS - Advisories AFCT - Affect AFCTD - Affected AFCTG - Affecting AFDK - After dark AFOS - Automated Field Operations System AFSS - Automated Flight Service Station AFT - After AFTN - Afternoon AGL - Above ground level AGN - Again AGRD - Agreed AGRS - Agrees AGRMT - Agreement AHD - Ahead AK - Alaska AL - Alabama ALF - Aloft ALG - Along ALGHNY - Allegheny ALQDS - All quadrants ALSTG - Altimeter setting ALT - Altitude ALTA - Alberta ALTHO - Although ALTM - Altimeter ALUTN - Aleutian AMD - Amend AMDD - Amended AMDG - Amending AMDT - Amendment AMP - Amplify AMPG - Amplifying AMPLTD - Amplitude AMS - Air mass AMT - Amount ANLYS - Analysis ANS - Answer AOA - At or above AOB - At or below AP - Anomalous Propagation APCH - Approach APCHG - Approaching APCHS - Approaches APLCN - Appalachian APLCNS - Appalachians APPR - Appear APPRG - Appearing APPRS - Appears APRNT - Apparent APRNTLY - Apparently APRX - Approximate APRXLY - Approximately AR - Arkansas ARL – Air Resources Lab ARND - Around ARPT - Airport