The winds aloft at about 500 mb (18,000 ft) play a key role in the winds we ultimately feel on the surface. The relationship is discussed in our textbook Modern Marine Weather. In short, the direction of the winds aloft tell us which way the surface Lows will approach us, and the speed of the winds aloft are a measure of the speed of the surface Lows (about 30 to 50% of the winds aloft speeds) as well as the severity of the surface winds we can expect.  The seminal explanation of the practical relation between winds aloft and surface winds is by Joe Sienkiewicz and Lee Chesneau.

Short of having an actual map of the winds aloft (which is easy to come by if we have wireless connections), we can gage both speed and direction from visual observations. Again, I refer to our text for details, but one way to spot direction is to note that the winds make waves in high cirrus clouds, much as wind makes waves in water. These waves show up as fine ripples in cirrocumulus clouds, called mackerel sky. The direction of the winds are, as is the case with water waves, perpendicular to the waves,  inline with the motion of the waves.

The speed of the winds aloft can be judged from other cirrus cloud patterns, such as prominent mare’s tails. The very existence of a prominent and persistent wave pattern is some indication of at least a well defined wind pattern, but a more positive sign is the topic at hand. Namely, if you can actually see the high cirrus clouds moving, then the winds must be fast.  We mention this in several books, but this is not a very common observation, although we do indeed often see cirrocumulus in neat wave patterns…. as if waves in sand—as opposed to the much broader and more common patterns seen in altocumulus waves.

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