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 Isoheights Isotherms Wind information 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 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 Trough that has short wavelength o Many exist at any given time o Move quickly o 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 SW T Shortwave ridge SWT = shortwave trough

Where are the shortwave and longwave troughs?