Table 4-1.—Common Contour Names, Standard Values, and Intervals
ISOLINE
NAME
Isobar
Isoheight
Isotherm
Isotach
DRAWN FOR
BASIC
VALUES OF
CONTOUR
EQUAL...
VALUE
Pressure
04 (1004 hPa)
Altitude
147 (1470 m)
306 (3060 m)
558 (5580 m)
720 (7200 m)
912 (9120 m)
176 (11760 m)
Wave height
3 A
Temperature 0°C
0°C
Wind speed
10 kts
STANDARD
CONTOUR
INTERVAL
4 hPa
30 m
30 m
60 m
60 m
120 m
120 m
3 ft
5°C
2°C
20 kts,
50 kts
EXAMPLE OF CHART
USED ON
SFC PRES
850-hPa HT
700-hPa HT
500-hPa HT
400-hPa HT
300-hPa HT
200-hPa HT
Wave HT
850-hPa to 200-hPa TEMP
SST
300-hPa & 200-hPa
Isallobar—lines of equal pressure change
Isallohypse—lines of equal height change
Isallotherm—lines of equal temperature change
Q25.
What is the standard contour interval used for
wave heights?
Q26.
What term is used to indicate lines of equal dew-
point temperature?
REVIEW QUESTIONS
Q27.
Lines of equal pressure change are defined what
term?
Q17.
What is the difference between an outlook and a
forecast?
STANDARD DEPICTION OF
Q18. Define a briefing aid as it pertains to weather
OBSERVATION REPORTS
forecasting?
Q19.
What color is used to mark only one set of history
on a chart?
Q20.
What colors are used to indicate (a) an occluded
front and (b) a shear line, on a surface pressure
chart?
Q21. What color is used to indicate a divergent
asymptote on a streamline analysis?
Q22. What color is used to indicate (a) clear air
turbulence (CAT) and (b) nonconvective
continuous frozen precipitation on a horizontal
weather depiction analysis?
In addition to contour lines and weather system
depictions, many charts also show plotted wind speeds
or plotted observation reports. Standard plotting
models are used to guide the placement of information.
Plotting models vary slightly by application. There are
two synoptic surface observation plotting models: the
surface synoptic land observation model and the surface
synoptic ship observation model. There is also a
synoptic upper-air observation plotting model used to
plot reports on all constant pressure level charts.
Additionally, there is a METAR observation plotting
model, which is a slight variation from the synoptic
models and is occasionally used to plot hourly aviation
observations.
Q23.
What is the standard contour interval used for
isobars?
Observation reports plotted by computers or
manually by people use the same plotting models but
Q24.
What is the standard contour interval used for
with one important difference. When a chart is plotted
isoheights at 300-hPa?
manually, all data in the observation are routinely
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