Star Parties and Weather
Published on Apr 19, 2009 at 1:27 pm.
3 Comments.
Filed under skywatching.
Last night was my binocular astronomy star party. This was a little different than most of my star parties in that the pre-observing lecture was a little more academic than most. The interpretive ranger at the park had asked for a binocular astronomy program that was sort of like a beginner’s class. Naturally, being a college professor, it is natural for me to do an academic program. The feedback that I got was very positive. There was basic and fun stuff for the kids. There was intermediate level material for the casually interested, and there was more detailed material for the seriously interested who wanted to know what to look for in purchasing binoculars. I was a little worried that I may have been getting too technical, but it seems to have worked out fine. There are lots of different kinds of public astronomy programs and star parties, and I try to fill a niche for those a little more academically minded.
There was quite a bit of doubt, though, about whether or not the star party was going to be going on after all. We got quite a bit of rain on Friday, and some pretty big storms moved through Saturday morning, too. Saturday during the day, it was cloudy. In fact, it was quite cloudy when I left to go to the star party. Some of those who attended said that there was light rain when they left, and others drove through rain to get to the star party. But, I didn’t call off the star party. We went ahead and had it, and the weather cleared up for us. We had very high humidity, and there was some haze, but we still were able to see a variety of things. A number of my students and helpers who said that they were coming didn’t show up, and I think that may have been a result of the weather. Also, many of those who reserved a spot also did not show up. They were probably also deterred by the weather. So, was this just luck on my part, or did I have some reason to go ahead with the star party?
The answer is that I had reason to believe that the weather would do just what it did. I tell my students that you have to always look at the weather before you go to a star party. The weather can change quite quickly almost anywhere. The North Texas area seems to be particularly bad about quick changes and markedly different weather just a few miles apart. There have been many times that I have been doing observations under mostly clear skies at the same time that other outdoor activities have been rained out just a few miles away. Even last night, I got back from the star party to find that it had hailed and stormed at home. It has not been uncommon for me to depart home under cloudy skies and rain, drive 100 miles to hold a star party under clear skies, and then come home to rain and clouds. So, what is that all about?
There are several things going on here. For one thing, much of the weather in this area is generated along the boundaries of air masses. Storms frequently form along frontal boundaries or dry lines. Many of these storms are fairly localized, and they tend to move along the air mass boundaries. So, just a few miles to one side or the other and the weather can be quite different. Secondly, there is a rather pronounced difference in elevation and terrain in just the 100 miles west of here. That means that the air mass moving past that area into the Dallas/Fort Worth area needs to adjust slightly. Fronts often “hang up” near the metropolitan area. Of course, it is ultimately the difference in terrain that accounts for where the cities were built in the first place, so it is not surprising that the weather would be a bit different just a few miles away. The interstate highway system was built to connect major cities, so a couple of major interstates run through the DFW area: Interstate 35 and Interstate 20. It is pretty common for the weather forecast to be such-and-such east of I-35 and such-and-such west of I-35, or sometimes such-and-such north of I-20 and such-and-such south of I-20. The interstates themselves, of course, have no effect on the weather. They simply were conveniently built near where the land changes, and so there are often differences in weather. In addition to any effect that the terrain has on weather, there is also the urban heat island effect going on in the metropolitan area. All of these effects combine to make the weather in rural areas a hour or so way a little different from the weather in the city.
So, how would an amateur astronomer (or even a professional astronomer) know if the weather is going to be OK for observing? That is particularly important if you are going to have to drive to the observing site and you suspect that the weather there may be different from the weather at your starting point. There are several resources that are very useful. I typically look at several of them. Naturally, I look to the National Weather Service. I look not just at the forecast but also at the radar and satellite data. You can get an idea of what is going on by looking at how the storms are moving and how the clouds are moving. I also check Accuweather. Accuweather has a very nice feature in that you can enter a location and get a forecast hour-by-hour. They also have satellite and radar data. I do, of course, listen to the radio and the televisions weather forecasts, but those often seem to be the least reliable. They are OK for a general overview, but most seem to play up the bad weather potential, and they often target the uninformed masses rather than giving detailed data. So, I don’t use them to really make my final decision. Another excellent source of information is the web site called the Clear Sky Clock. The clear sky clock is particularly useful in that it is marketed to astronomers. The clear sky clock gives a graphical representation of the predicted cloud cover, temperature, darkness, and visibility. There is often a bit more specific information here than you get at the other sites. But it is important to remember that all of these sites can’t really tell you what the weather will be, they can only tell you what the weather may be. They are forecasts. They use scientific models to predict the weather, but they are not 100% accurate. The weather is simply far too complicated for total accuracy.
In the end, the observer has to make a judgment call. I look at all of the available forecasts. Typically, they are not all in complete agreement. I look at the radar and the satellite data. I also use my experience. I have lived in this area for over 20 years. I have been watching the sky intently for those two decades. So, I’ve seen storms come in, and I’ve seen storms move out. I’ve seen that the skies to the west of there often clear up before they do in the city. I’ve seen that the skies frequently will clear late in the day and early evening. So, deciding on whether or not the star party is possible eventually comes down to experience. Like everyone else, I sometimes make mistakes. Sometimes I think that it will clear up, and it does not. Sometimes I think that it will not clear up, but it does so anyway. Sometimes I think that the rain will pass by, but instead it storms. So, I can’t fault people for not showing up to the star party, especially given that it was raining in the city (and even hailing!) before, during, and after the star party. It just goes to show how complicated the weather around here can be! I encourage anyone planning a star party, or any amateur astronomer deciding on whether or not to go observing, to learn as much about weather as possible. I am even thinking of suggesting to our Continuing Education division at the college that we may consider offering a couple of non-credit meteorology classes. I know of several people that I would like to ask to teach those classes.
-Astroprof
Image Credit: NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL)
Sili on April 25, 2009 at 12:54 pm: 1
Heh.
A friend of mine is a yachtsman, and he too has a completely different feel for the weather than I do.
When I get a garden, I likely will develop some sense of metereology, too. I hope.
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