The October annular eclipse is coming up, and the most important requirement will be clear skies. Here’s how to forecast the weather.
With the October annular eclipse now less than two weeks away, it’s time to begin planning for the weather.
The climate statistics on my webpage reveal the probability of seeing sunny skies on October 14th, but you are now rolling the dice with Mother Nature as we move from climatology to reality. Past cloud probabilities are out of date. Planning must now rely on what we call deterministic forecasts — the output from computer models — at least for the time being.
There are a horde of computer model forecasts available online that you can use to look ahead, but if you try them all, you won’t find yourself any wiser than if you confine your look-ahead to just a few. Up to around October 9th, you should use the model outputs for mental “what-if” planning, but I wouldn’t begin canceling hotel reservations before then. After the 9th, the various models should begin to agree on at least the large-scale patterns of cloudiness and other weather elements. Those agreements will gradually coalesce as we approach the eclipse.
If you are an amateur astronomer or a storm chaser, you probably already have a favorite site to go for your weather advice. If not, a search or social media will turn up many model sources, so you might want to explore some of them to find one you like. There are quick links to four of them on my website. The major commercial weather providers that you see on TV also use computer outputs in their forecasts, but they stick to one model, either their own or a government one, and don’t give you a selection from which you can evaluate the reliability of eclipse-day predictions. By going to the internet, you are seeking a second (or even third) opinion before making a change in your plans.
Other eclipse travelers have recommended Windy to me for long-range eclipse planning and though it shows pretty much what any other internet site does, I like it because I can switch quickly between models and make very quick comparisons of individual cloud forecasts. Windy offers three long-range models: the ECMWF, the GFS, and ICON; these have an international flavor, as the models are European, American, and German in origin.
Meteologix is another popular eclipse traveler site that offers 32 models for contemplation, including the Canadian GDPS; it also allows a quick comparison of outputs. Generally speaking, the ECMWF is regarded as the most accurate of all of the models in common use and one that you should put on your list to evaluate.
The mainstream long-range models go out 10 to 15 days, so eclipse day is already in view. However, many sites limit the extended view to only the first 10 days or require a subscription to go farther. To get the full 15-day output, you can go to the College of DuPage site, a favorite of storm chasers.
As eclipse day approaches, a number of short-range models become available. These models typically have higher resolution than the long-range versions, but only make forecasts out to about 84 hours. Two of these, the American NAM and the Canadian RDPS, are readily available online. It’s probably best to avoid the highest-resolution short-range models such as the HRRR and the RAP, as these are designed to help you find your way around thunderstorms rather than find an eclipse.
Whatever model and provider you decide to use, be skeptical until models begin to agree — and until eclipse day is imminent. And on October 13th, be prepared to switch over to satellite photos for your planning — stay tuned for more information on that.