An Explanation of the Winds Aloft Chart

The winds aloft chart provides information about cloud cover, temperature and wind speed and direction at various altitudes, plus how it’s changing over time.

Go to Scroll down to “ETA Model UPPER/ALOFT” and click on the star over the closest airport.

Note what this is and ISN’T. This is a pilot’s chart showing weather at altitude, and is only plotted around airports, but PDX weather gives some idea of weather atop Hood.

This is generated by computer model and of course is only as good as the data input and the model so there may be errors.

The vertical scale is in millibars, roughly corresponding to feet (see below).

The horizontal time scale is reverse; now is on the right and each tic mark is 6 hours ahead; ie 11/12 indicates the 11th at 1200 hours

Left scale in millibars
1000mb – sea level (ground level is indicated as brown)
800mb – 5-6000ft
700mb – 10,000ft
600mb – 12,000 ft
500mb – 18,000ft

Head of arrows indicates directions wind is coming from
Each flag indicates 10mph
Triangle on arrow is 50mph

The flags or triangles (carets?) are on the side of the straight line corresponding to the direction from which the wind is coming. That did not come out too clearly – two examples: if the straight line is horizontal and the flags are on its left side, the wind is from the west. If the line is vertical and the flags come off the bottom of the line, the wind is from the south.

A flag indicates a wind speed of 10 mph and a triangle, a wind speed of 50 mph.

Shaded areas on the diagram indicate clouds.

A solid line running across the diagram indicates the freezing level while a dashed line is the zero degree Fahrenheit isotherm.

The colors are moisture in the air in kg/kg (kg H2O/kg air), but there’s no key as to what the colors mean. But in general, the brighter colors are, the more moisture. But you can generally just read them as clouds, and some indication of how low the clouds stop and start, and when clouds are moving in and disappearing.