The 500mb Chart and
Shortwave vs. Longwave
Troughs
Information on the Chart
• Isoheights
o Lines of constant height
o Dark solid lines
o Analogous to lines on a topographic
map
• Isotherms
o Lines of constant temperature
o Dashed red lines
• Wind speed and direction
o Blue barbs and flags
• Dew Point
o Green numbers
Wind symbol convention
Information on the Chart
Wind
information
Isoheights
Isotherms
Dew point
Uses
• Starting point for making a forecast
o See general patterns in the atmosphere
• Identify troughs and ridges
• Trough
o Area of lower heights
o As you go into the trough, heights decrease
o Analogous to a valley on a topographic map
• Ridge
o Area of higher heights
o As you go into the ridge, heights increase
o Analogous to a mountain on a topographic map
Troughs and Ridges
Trough
Ridge
Trough
Note height labels to determine if heights are increasing or decreasing
Shortwave Trough vs.
Longwave Trough
• Longwave trough
o Trough that has long wavelength
o Only about 3-7 in the entire Northern Hemisphere at any given
time
o Move slowly
• Shortwave trough
o
o
o
o
Trough that has short wavelength
Many exist at any given time
Move quickly
Can be stand alone, or embedded within longwave troughs or
ridges
• If embedded, look for little “kinks” in the isoheights
Examples
Longwave trough stretching over much of the U.S.
Longwave
troughs
Shortwave trough over Ohio and Tennessee Valley, another
entering southern California (and there are more)
Longwave trough
Shortwave trough
SWT = shortwave trough
Longwave trough
SW
T
SWT
SW
T
SWT
Where are the shortwave and longwave troughs?