The last light of day
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This was taken about 10 minutes before the one below. The sun was just setting and still casting a warm glow on the skyline. You'll notice too that all those great clouds vanished by the time the shot below was made. Just my luck - I wish they had hung around a little longer. They added some nice color and texture to the sky.
I found this vantage point after searching online and got some good pointers from Greg Benz. This is apparently a pretty popular spot from which to shoot. When we arrived here there were 2 other photographers set up and shooting. One guy was using his 10-stop ND to shoot a 10 minute exposure. I'm not sure how good that came out. This is a pedestrian overpass and with traffic passing underneath so close it is susceptible to vibration. I imagine a 10-minute exposure is going to have some sharpness issues. Besides, calculating exposure as the light is changing this rapidly at this time of day sounds like a differential equations problem from hell.
I stuck with shooting shorter exposures.