Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1,032.0 mb and 992 signify 992.0 mb.
METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required.
5.1.3.4.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and typhoons (See Figure 5-15) are low-pressure systems with their names and central pressures denoted.
A trough or an elongated area of low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of high atmospheric pressure is denoted with saw-toothed symbols. Ridges are rarely denoted on charts produced by the HPC.
5.1.3.4.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-15. The symbols on the front indicate the type of front and point in the direction toward which the front is moving.
Two short lines across a front indicate a change in front type.
5.1.4 TPC Surface Analysis Charts The Tropical Prediction Center (TPC) in Miami, Florida is responsible for the tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude. The surface analysis chart is located at:
• http://www.nhc.noaa.gov/marine_forecasts.shtml
5.1.4.1 Issuance The Tropical Prediction Center (TPC) issues Surface Analysis Charts for tropical regions of the western hemisphere south of 30oN latitude and east of 160oE longitude four times a day (Table 5-3).
Table 5-3. TPC Surface Analysis Charts Issuance Schedule Valid Time (UTC) 00 06 12 18
5.1.4.2 Analysis Symbols Figure 5-17 shows analysis symbols used on TPC surface analysis charts.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-14
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) H1024 CENTER OF HIGH PRES
ITH PRES IN MILLIBARS TRPCL × 999 WITH PRES IN MILLIBARS TRPCL DEPRESSION CENTER OF LOW PRES STORM (IS) L 10 KI 5 KT COLD FRONT • HURRICANE (HRON) L L 15 KT 20 KT Ш 25 КТ WARM FRONT P CONVECTION We- 35 KT
GALE OR TRPCL STORM STATIONARY FRONT TRPCL - 50 KT STORM WAVE Ale 74 KT HRCN
OCCLUDED FRONT TEXT ABBREVIATIONS M 105 KT DRY LN KT KNOTS 24 HR HIGH PRES
FT FEET MOVEMENT
SQUALL LN NM NAUTICAL MILES
GI GUSTS
TROF LN HRCN - HURRICANE TRPCI- TROPICAL 24 HR LOW PRES
PRES - PRESSURE MOVEMENT
RIDGE AXIS TROF - TROUGH LINE
MOV MOVING
STNR - STATIONARY Figure 5-17. TPC Surface Analysis Chart Symbols SON 04 1026 1826-21 STHRY 3ON 20 TROF 1016 20 08 12
21.4N 11. IPC PSN *120KT 994 OITEZ- N 35. 34 0900 T MOYE 1955КГ 6 5k 5N los .
16 14025 . 130W 120W . 110W. 100W . 90W. SOW 16 10y 16 GOH 50W 3OW 20W 20;4!
06Z TROPICAL SURFACE ANALYSIS 2004 TROPICAL PREDICTION CENTER ISSUED: 17 SCALLOP LINES MIAMI, THUNDERSTORMS: COLLABORATING CENTERS: TAFB ANALYST: FORMOSA TPC OPC НРС HF0 Figure 5-18. TPC Tropical Surface Analysis Chart Example
5.1.4.2.1 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is in "true" degrees and is depicted by a stem (line) pointed in the direction from which the wind is blowing. The wind speed is determined by adding up the value of the flags (50 kts), lines (10 kts), and half-lines (5 kts), each of which has the following individual values:
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-15
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
A single circle over the station with no wind symbol indicates a calm wind.
Figure 5-19 shows some sample wind symbols:
Figure 5-19: TPC Surface Analysis Chart Wind Plotting Model
5.1.4.3 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on the surface analysis charts.
5.1.4.3.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns.
On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1,032.0 mb and 992 signify 992.0 mb.
METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required.
5.1.4.3.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-16
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) typhoons (See Figure 5-17) are low-pressure systems with their names and central pressures denoted.
A trough or an elongated area of low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of high atmospheric pressure is denoted by saw-toothed symbols. Ridges are rarely denoted on charts produced by the TPC.
5.1.4.3.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-17. The symbols on the front indicate the type of front and point in the direction toward which the front is moving.
Two short lines across a front indicate a change in front type.
5.1.5 Unified Surface Analysis Chart The Unified Surface Analysis Chart is a composite of all the surface analysis charts produced by HPC, OPC, TPC and WFO Honolulu. It contains an analysis of isobars, pressure systems and fronts.
5.1.5.1 Issuance The chart is issued four times daily by the OPC (see Table 5-4).
Table 5-4. Unified Surface Analysis Chart Issuance Schedule Valid Time (UTC) 00 06 12 18
Figure 5-20. Unified Surface Analysis Chart Example
5.1.5.2 Analysis Symbols Figure 5-21 shows analysis symbols used on the Unified Surface Analysis charts.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-17
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 5-21. Unified Surface Analysis Chart Symbols
5.1.5.3 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on the surface analysis charts.
5.1.5.3.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns.
On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1032.0 mb and 992 signify 992.0 mb.
METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required.
5.1.5.3.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmospheric pressure while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low -- the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center. Tropical storms, hurricanes, and typhoons (See Figure 5-21) are low-pressure systems with their names and central pressures denoted.
On a Surface Analysis Chart, a trough is an elongated area of relatively low atmospheric pressure, while a ridge is an elongated area of relatively high atmospheric pressure. Troughs are denoted by dashed lines and identified with the word TROF. Ridges are denoted by sawtoothed symbols. Ridges are rarely denoted on charts produced by the HPC.
5.1.5.3.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-21. The symbols on the front indicate the type of front and point in the direction toward which the front is moving.
Two short lines across a front indicate a change in front type.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-18
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
5.1.6 AAWU Surface Charts The Alaskan Aviation Weather Unit (AAWU) in Anchorage, Alaska is responsible for the state of Alaska. The surface analysis chart is located at:
• http://aawu.arh.noaa.gov/surtace.php
5.1.6.1 Issuance The AAWU issues Surface Analysis Charts 4 times daily for the state of Alaska. The valid times are shown in Table 5-5.
Table 5-5. AAWU Surface Analysis Issuance Schedule Valid Time 00 06 12 18 (UTC)
5.1.6.2 Analysis Symbols The symbols (Figure 5-22) used on the Alaskan Surface Analysis Chart are similar to those found on the HPC Surface Analysis chart. However, since the Alaskan Surface Analysis chart is in black and white all of the symbols are black and white as well.
A Key to Symbols used on the AAWU Graphic Products
- Cold Front H 1032 - High Pressure Center Pressure in millibars
- Warm Front L 988 - Low Pressure Center
- Occluded Front Pressure in millibars
- Stationary Front
- Occasional or greater
- Trough Precipitation
- Ridge
- Fog - Freezing Rain * - Mixed Rain/Snow
- Haze - Freezing Drizzle - Rain Showers
- Smoke - Light Icing - Snow Showers ‡→ - Drifting Snow - Moderate Icing - Rain/Snow Showers
- Sandstorm - Severe Icing K - Thunderstorm
• - Drizzle * - Snow A - Light Turbulence
• - Rain › - Ice Crystals A - Moderate Turbulence A - Ice Pellets A - Severe Turbulence Figure 5-22. AAWU Surface Analysis Chart Symbols AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-19
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 5-23. AAWU Alaskan Surface Chart Example
5.1.6.3 Station Plot Models Land, ship, buoy, and C-MAN stations are plotted on the chart to aid in analyzing and interpreting the surface weather features. These plotted observations are referred to as station models. Some stations may not be plotted due to space limitations. However, all reporting stations are used in the analysis.
Figures 5-24 and 5-25 show the most commonly used station plot models used in surface analysis charts.
Figure 5-24. AAWU Surface Analysis Chart Station Plot Model
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-20
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 5-25. AAWU Surface Analysis Chart Ship/buoy Plot Model
5.1.6.3.1 Station Identifier The format of the station identifier depends on the observing platform.
• Ship -- Typically 4 or 5 characters. If 5 characters, then the fifth will usually be a digit.
• Buoy -- Whether drifting or stationary, a buoy will have a 5-digit identifier. The first digit will always be a 4.
• C-MAN -- Stands for Coastal-Marine Automated Network, and are usually close to coastal areas. Their identifier will appear like a 5-character ship identifier, however the 4th character will identify off which state the platform is located.
• Land -- Land stations will always be 3 characters, making them easily distinguishable from ship, buoy, and C-MAN observations.
5.1.6.3.2 Temperature Air temperature is plotted in whole degrees Celsius on large-scale charts. Hourly surface charts may have temperatures using whole degrees Fahrenheit.
5.1.6.3.3 Dew Point Dew point temperature is plotted in whole degrees Celsius on large-scale charts. Hourly surface charts may have dew point temperatures using whole degrees Fahrenheit.
5.1.6.3.4 Wind Wind is plotted in increments of 5 knots (kts). The wind direction is in “true” degrees and is depicted by a stem (line) pointed in the direction from which the wind is blowing. Wind speed is determined by adding the values of the flags (50 kts), barbs (10kts), and half barbs (5 kts) found on the stem.
A single circle over the station with no wind symbol indicates a calm wind.
Figure 5-26 shows some sample wind symbols.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-21
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
Figure 5-26: AAWU Surface Analysis Chart Wind Plotting Model
5.1.6.3.5 Ceiling Ceiling is plotted in hundreds of feet above ground level.
5.1.6.3.6 Visibility Surface visibility is plotted in whole statute miles.
5.1.6.3.7 Pressure Sea-level pressure is plotted in tenths of millibars (mb), with the first two digits omitted (generally a 10 or 9). For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values:
410: 1041.0 mb 103: 1010.3 mb 987: 998.7 mb 872: 987.2 mb
5.1.6.3.8 Pressure Trend The pressure trend has two components, a number and symbol, to indicate how the sea-level pressure has changed during the past three hours. The number provides the 3-hour change in tenths of millibars, while the symbol provides a graphic illustration of how this change occurred.
Figure 5-27 shows the meanings of the pressure trend symbols.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-22
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) Continuously falling Continuously rising Falling, then steady Rising, then steady Falling before a lesser rise Falling before a greater rise 1 Rising before a greater fall Rising before a lesser fall Steady Figure 5-27. AAWU Surface Analysis Chart Pressure Trends
5.1.6.3.9 Sky Cover The approximate amount of sky cover can be determined by the circle at the center of the station plot. The amount the circle is filled reflects the amount of sky covered by clouds. Figure 5-28 shows the common cloud cover depictions:
Clear Scattered cloud:
(approximately 25% cloud cover (apply sinatly 50% cloud cover) (apst xinately 75% cloud cover) Overcast Sky Obscured Sky Cover Missing Figure 5-28. AAWU Surface Analysis Chart Sky Cover Symbols
5.1.6.3.10 Water Temperature Water temperature is plotted in whole degrees Fahrenheit.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-23
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009)
5.1.6.3.11 Swell Information Swell direction, period, and height are represented in the surface observations by a 6-digit code.
The first two digits represent the swell direction, the middle digits describe the swell period (in seconds), and the last two digits are the swell's height (in half meters).
090703 09 - The swell direction is from 90 degrees (i.e. it is coming from due east).
07 - The period of the swell is 7 seconds.
03 - The height of the swell is 3 half meters.
271006 27 - The swell direction is from 270 degrees (due west).
10 - The period is 10 seconds.
06 - The height of the swell is 6 half meters.
5.1.6.3.12 Wave Information The period and height of waves are represented by a 5-digit code. The first digit is always 1.
The second and third digits describe the wave period (in seconds), and the final two digits give the wave height (in half meters). Below are two examples:
10603 1 - A group identifier. The first digit will always be 1.
06 - The wave period is 6 seconds.
03 - The wave height is 3 half meters.
10515 1 - The group identifier again.
05 - The wave period is 5 seconds.
15 - Wave height is 15 half meters.
5.1.6.4 Analyses Isobars, pressure systems, and fronts are the most common analyses depicted on surface analysis charts.
5.1.6.4.1 Isobars An isobar is a line of equal or constant pressure commonly used to analyze pressure patterns.
On a Surface Analysis Chart, isobars are solid lines usually spaced at intervals of 4 millibars (mb). Each isobar is labeled. For example, 1032 signifies 1032.0 mb and 992 signify 992.0 mb.
METAR/SPECI (Section 2.1) reports pressure in hectopascals. However, one millibar is equivalent to one hectopascal, so no conversion is required.
5.1.6.4.2 Pressure Systems On a Surface Analysis Chart, a High (H) is a maximum of atmosphere pressure, while a Low (L) is a minimum of atmospheric pressure. Central pressure is the atmospheric pressure at the center of a High or Low – the highest pressure in a High and the lowest pressure in a Low. The central pressure is denoted near each pressure center.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-24
Aviation Weather Services, Advisory Circular 00-45F, Change 2 (March 2009) A trough or an elongated area of relatively low atmospheric pressure is denoted by dashed lines and identified with the word TROF. A ridge or an elongated area of relatively high atmospheric pressure is denoted by saw-toothed symbols. Ridges are rarely denoted on charts produced by the AAWU.
5.1.6.4.3 Fronts The analysis shows positions and types of fronts by the symbols in Figure 5-22. The symbols on the front indicate the type of front and point in the direction toward which the front is moving.
Two short lines across a front indicate a change in front type.
AC 00-45F, CHG 2 Section 5: Graphical Observations and Derived Products Page 5-25