I've never seen a night launch of the Shuttle (or any large launch vehicle--the biggest I've ever seen was a Delta II out of Vandenberg, from a motel in Lompoc). But there's only a forty percent chance of flying tonight, due to concerns about low-level clouds with a front moving in. I have to decide by six or so if it's worth the drive up to the Cape, or risk having to watch from a hundred fifty miles away on the beach down here. If it doesn't go tonight, the next most likely success would be on Sunday night, due to forecast of high winds on Friday and Saturday. Of course, if it slips long enough (well into next week) the window will have slid backward enough that it's no longer a night launch.

[Update at 2:30 PM EST]

Weather's getting worse:

Kennedy Space Center already is overcast and getting worse by the hour. The satellite imagery indicates that the cloud cover that was feared as a potential launch show-stopper is going to intensify.

All three of the Transoceanic Abort Landing sites in Spain and France are experiencing unacceptable weather conditions in case an unprecedented emergency landing were attempted because of some problem during the early stages of flight.

There are low clouds and showers within 20 miles of the landing sites in Zaragosa and Moron in Spain. At the French emergency site in Istris, winds are forecast to be too strong to land.

No probability of launch update, though. I have to think it's dropping below forty percent. This is the MMT's bane--having to make a decision to send the crew out to lie on their backs for a couple hours, and hoping for the best against long odds. It's looking less and less likely that we'll make the drive up.

[3:15 PM Update]

They're still saying a sixty percent chance of clouds preventing launch. But what's the joint probability of having good weather at the Cape, and at all the abort landing sites? I have to think it's a lot less than forty percent at this point. It's going to be really hard to motivate myself to make the drive.

You've seen it launch in daytime, right? Stay home, pull out the binoculars and get a different view.

From here in central NJ, if it isn't too low, we get to see the last minute before MECO and tank separation. There is a series of bright flashes, which we also saw in the video from the ET tank, as some plasma cloud or something surrounds the shuttle. Do you know what causes that?

From here in central NJ, if it isn't too low, we get to see the last minute before MECO and tank separation.

That's because it launches to the north. From where we are in south Florida, we'd be way too far away to see it at MECO.

There is a series of bright flashes, which we also saw in the video from the ET tank, as some plasma cloud or something surrounds the shuttle. Do you know what causes that?

Probably the explosions from the pyrotechnic charges that separate the ET from the Orbiter.

You've seen it launch in daytime, right? Stay home, pull out the binoculars and get a different view.

Also, there's a world of difference between a day and a night launch. At night, it lights the area like broad daylight. We wouldn't get that effect down here.

Probably the explosions from the pyrotechnic charges that separate the ET from the Orbiter.

No, that isn't it. In the video, it looks like there is burning going on just out of camera range while the engines are still firing, and it gets more pronounced as engine cut-off approaches. It is as if the engine exhaust plume is coming forward and enveloping the shuttle. I think there are flashes even at this point, but I don't remember.

After tank separation, as the shuttle pulls away and out of the camera frame, there are repeated flashes of light. If you catch the video again you'll see what I mean.

But what's the joint probability of having good weather at the Cape, and at all the abort landing sites?

On any given day of the year, I can't imagine that this combined percentage is very high, would it be? How is it that we have ever actually launched a shuttle, given the confluence of such a great number of scrub-worthy variables, (not counting all of the new scrub-worthy variables from foam)?

Ignoring, of course, the unproven possibility of actually being able to abort and land at any of those sites...