The 500mb Chart and Shortwave vs.

Longwave Troughs

Information on the Chart• Isoheights

o Lines of constant heighto Dark solid lineso Analogous to lines on a topographic

map

• Isothermso Lines of constant temperature o Dashed red lines

• Wind speed and directiono Blue barbs and flags

• Dew Pointo Green numbers

Wind symbol convention

Information on the Chart

Isoheights

Isotherms

Wind information

Dew point

Uses• Starting point for making a forecast

o See general patterns in the atmosphere

• Identify troughs and ridges

• Trougho Area of lower heightso As you go into the trough, heights decreaseo Analogous to a valley on a topographic map

• Ridgeo Area of higher heightso As you go into the ridge, heights increaseo Analogous to a mountain on a topographic map

Troughs and Ridges

Ridge

Trough

Trough

Note height labels to determine if heights are increasing or decreasing

Shortwave Trough vs. Longwave Trough

• Longwave trougho Trough that has long wavelengtho Only about 3-7 in the entire Northern Hemisphere at any given

timeo Move slowly

• Shortwave trougho Trough that has short wavelengtho Many exist at any given timeo Move quicklyo 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

Longwave trough

SWT

SWT

SWT

SWT Shortwa

ve ridge

SWT = shortwave trough

Where are the shortwave and longwave

troughs?