Sunday, July 10, 2011

Crepuscule with Nellie

Before we had METARs, we had SAs. If I remember correctly, SA stood for Sequence Advisory; by the same token, a PIREP was a UA, or Unsolicited Advisory. SAs appeared on yellow paper on a teletype machine at the Flight Service Station (that's an honest teletype, not the new-fangled KSR-33). They came up in order: Pittsburgh, Harrisburg, Wilkes-Barre, Philadelphia, and so on; you could watch a cold front move across the country.

When we switched to METARs the RMK field became more formalized, and human weather observers lost the ability to put CREPUSCULAR RAYS in the comment section. Presumably the machines don't notice.


Crepuscule means twilight. I didn't learn the word "crepuscule" from a sequence report; it comes from this song by Thelonius Monk. Here Monk and John Coltrane perform Crepuscule with Nellie at Carnegie Hall. The song combines dissonance with poignancy.



My made-up explanation for crepuscular rays is highly humid air, which glows red at crepuscule, and towering cumulus to the west blocking some of the sun's rays. So the rays are actually the absence of the Sun's rays.

Seeing that remark in the SA reminded me of every evening I ever spent outdoors in the South or Plains. Crepuscular rays meant spitting watermelon seeds, fireflies, an AM radio in the distance tuned to a minor league baseball game, and maybe holding hands with a new girl.

And besides inducing nostalgia for my Taylorcraft, crepuscular rays meant something about the weather. Towering cumulus to the West in the mid-latitudes of the Northern hemisphere usually come your way, and seeing them at sunset, when things should be calming down for the day, means that those CU have lots of energy. Crepuscular rays are a poison flower, pretty to look at but...

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