Cima
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cima clear sky chart from 2003-08-01 to 2005-11-07.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	6% 67%	8674
	Night	8% 65%	8495
Transparency	Day	5% 5% 14% 28% 45%	7143
	Night	5% 6% 18% 29% 38%	6886
Seeing	Day	14% 30% 39% 15%	571
	Night	8% 19% 32% 34%	2924

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	10% 5% 5% 6% 51%	560
	Night	13% 6% 5% 48%	793
February	Day	21% 5% 6% 6% 36%	561
	Night	24% 5% 5% 42%	684
March	Day	7% 5% 66%	659
	Night	7% 5% 65%	703
April	Day	75%	730
	Night	5% 6% 65%	589
May	Day	76%	806
	Night	5% 78%	558
June	Day	90%	780
	Night	90%	537
July	Day	74%	795
	Night	5% 6% 68%	558
August	Day	8% 6% 5% 6% 58%	1139
	Night	8% 5% 5% 5% 60%	904
September	Day	84%	985
	Night	83%	960
October	Day	5% 70%	642
	Night	71%	721
November	Day	10% 5% 6% 54%	468
	Night	10% 61%	698
December	Day	10% 7% 56%	549
	Night	16% 53%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	7% 12% 32% 37% 10%	353
	Night	10% 10% 29% 35% 14%	499
February	Day	20% 12% 29% 29% 8%	291
	Night	14% 16% 33% 23% 12%	350
March	Day	5% 8% 23% 32% 28%	494
	Night	5% 10% 21% 30% 31%	507
April	Day	5% 6% 15% 40% 32%	594
	Night	7% 8% 15% 31% 36%	477
May	Day	6% 13% 28% 49%	685
	Night	9% 15% 27% 43%	492
June	Day	6% 27% 65%	742
	Night	11% 43% 40%	513
July	Day	6% 18% 70%	663
	Night	10% 18% 66%	445
August	Day	8% 6% 15% 23% 46%	859
	Night	9% 6% 18% 25% 39%	696
September	Day	22% 71%	900
	Night	7% 23% 65%	885
October	Day	6% 15% 28% 46%	819
	Night	6% 19% 22% 47%	898
November	Day	11% 9% 29% 35% 14%	386
	Night	7% 10% 29% 34% 18%	598
December	Day	6% 17% 45% 28%	357
	Night	7% 23% 45% 19%	526

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Day	18% 45% 36%	11
	Night	16% 21% 30% 26%	232
February	Day	28% 40% 17% 13%	45
	Night	20% 30% 28% 16%	189
March	Day	21% 27% 27% 23%	55
	Night	11% 22% 34% 26% 5%	233
April	Day	30% 28% 34% 5%	52
	Night	17% 22% 29% 28%	221
May	Day	18% 40% 33% 6%	59
	Night	10% 23% 40% 22%	184
June	Day	8% 40% 45% 6%	60
	Night	18% 32% 43%	180
July	Day	20% 59% 17%	62
	Night	31% 58%	185
August	Day	24% 47% 24%	86
	Night	6% 28% 53% 9%	328
September	Day	9% 32% 40% 17%	86
	Night	14% 33% 43%	356
October	Day	16% 23% 40% 20%	55
	Night	6% 18% 31% 36% 7%	364
November	Night	8% 29% 36% 22%	235
December	Night	10% 25% 39% 18% 6%	217

Page generated at 2008-08-27 04:51:49. Version ab11