Last year, it was cloudy from the end of the first week of February, through about mid March. There were small handful of partially clear nights (literally, five total), mostly near the end of April, and every one of them landed on a bright gibbous our dead full moon. Every other night was cloudy...basically cloudy for months strait from Feb through April. The only times it ever seemed to clear up was during the day.
The year before that, it was cloudy from late January through March, then March through June.
And, of course, once the long stretches of cloudy nights are past, you still only get a few clear nights here and there each month, and late fall/early winter is usually also a month or two of mostly solid clouds.
The key is to be prepared for the one clear night that comes, and to make the best use of it possible. After the cloudy first half of the year, I had some nights in August, a few in Sept, a couple in Oct, and a couple more in Nov. Despite there just being a few clear nights each month, when the entire night is clear, you can image the whole night long if you are automated. You can then acquire data on many objects concurrently, a few hours per object each night for anywhere from 6 to 12 (maybe even 14, depending on how far north you are) hours each night. Over several months, you can acquire tens of hours of data per object, and end up with tens of hours per object for many objects.
I've been working through my backlog since 7/31 last year (which is when I finally got my Mach 1 set up and running, after waiting 7 months to get it!! I guess I pre-paid my cloudy night dues on that one. ) It turns out I ended up getting data on quite a few objects. Some just a few hours, but several I've got tens of hours on, despite the relatively sparse clear nights. So my multiple targets per night strategy seems to be working out pretty well.
I built my observatory in 2013. 2016 was my best year so far, 151hrs imaging. 2017: 79.6 hrs. Last year I managed about 5 hrs one one target, 2 nights this year. What I'm wondering is, is this cloudy weather a short term blip or a long term trend?
What do you consider long term?
I've been studying longer-ish and long term weather patterns for a while now. What I've come to learn is that there are ~18-19 year weather cycles, and they largely follow the 18.6 year lunar cycle. You can generally expect weather patterns within this cycle to follow a fairly consistent pattern...however, it is, after all...18-19 years which is a pretty long time, and it is not always exact...it might be 17, might be 21. Within this cycle, there are periods where cloudcover is higher, periods where it is lower. Periods that are wetter, periods that are drier.
Problem is, these cycles are overlaid on much longer cycles, spanning decades to tens of decades to hundreds of years. These follow longer term solar cycles (the solar cycle is actually 22 years, with overlapping sets of sun spots that persist for about 11 years on average, but can range anywhere from 8 to 15 years long). The even longer term cycles follow planetary orbits, particularly Jupiter followed by Saturn, and these cycles cover 200/400 year periods or so.
From what I can tell, we are falling into the trough of one of the very long cycles, where we enter Maunder Minimum. This is a period of almost non-existent solar sunspot activity, which can have a rather dramatic impact on global climate, particularly cloud cover.
So...long term? As in...a few years? We may see cloud cover levels change with the lunar cycle. But, if we are indeed entering a Maunder Minimum period of solar activity...that could have a more significant effect on cloud cover that overpowers the 18.6 year lunar cycle. In that case, we may indeed be in for some very LONG term heavier cloud cover patterns...