Enzo's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Enzo's Observatory clear sky chart from 2005-11-06 to 2025-09-04.

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	10% 5% 2 5% 3 3 3 3 5% 7% 53%	126128
	Night	10% 5% 2 4 3 3 3 3 4 6% 57%	122860
Transparency	Day	30% 4 10% 25% 23% 9%	129845
	Night	28% 4 9% 23% 25% 12%	127206
Seeing	Day	11% 6% 22% 29% 24% 8%	16317
	Night	12% 6% 27% 37% 17% 1	26111

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 7% 2 5% 3 3 3 2 3 5% 53%	4077
	11th to 20th	Day	7% 4 1 3 2 2 2 3 4 5% 65%	4080
	21st to end	Day	20% 9% 2 5% 2 2 2 2 3 4 49%	4488
February	1st to 10th	Day	15% 6% 2 6% 3 4 4 3 4 5% 49%	1951
	11th to 20th	Day	15% 7% 3 5% 3 3 3 3 4 5% 49%	1949
	21st to end	Day	19% 7% 2 3 3 2 2 2 2 3 55%	1650
March	1st to 10th	Day	14% 5% 2 5% 3 3 3 3 5% 6% 52%	4935
	11th to 20th	Day	12% 4 1 4 3 3 3 3 5% 6% 56%	4980
	21st to end	Day	10% 6% 2 5% 4 3 4 4 6% 6% 50%	5462
April	1st to 10th	Day	12% 6% 2 5% 4 3 4 3 4 7% 50%	2200
	11th to 20th	Day	12% 6% 2 6% 4 4 3 4 5% 6% 49%	2253
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 6% 49%	2589
May	1st to 10th	Day	15% 7% 3 6% 4 3 4 3 5% 7% 42%	5862
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 3 5% 6% 47%	5862
	21st to end	Day	13% 7% 2 7% 5% 5% 5% 4 6% 7% 39%	6434
June	1st to 10th	Day	5% 4 1 5% 4 4 5% 5% 6% 10% 51%	2600
	11th to 20th	Day	5% 3 2 4 4 4 4 4 6% 8% 55%	2600
	21st to end	Day	4 4 1 4 4 4 4 4 5% 8% 58%	2600
July	1st to 10th	Day	7% 6% 3 8% 5% 5% 5% 4 6% 9% 42%	5900
	11th to 20th	Day	3 2 1 3 3 3 3 3 6% 10% 63%	5900
	21st to end	Day	3 3 1 4 3 4 4 4 6% 10% 57%	6422
August	1st to 10th	Day	1 2 3 2 3 3 3 5% 7% 71%	4234
	11th to 20th	Day	4 2 1 3 2 3 4 3 6% 10% 62%	4171
	21st to end	Day	3 2 1 3 3 3 4 4 6% 10% 59%	4162
September	1st to 10th	Day	8% 5% 2 4 3 3 4 3 6% 7% 54%	2123
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 4 6% 6% 48%	2090
	21st to end	Day	8% 3 1 3 3 3 3 3 6% 8% 59%	2090
October	1st to 10th	Day	6% 2 1 4 2 4 3 3 5% 7% 62%	2062
	11th to 20th	Day	10% 4 1 4 2 2 2 3 3 5% 63%	1900
	21st to end	Day	13% 3 2 4 2 3 2 2 3 4 63%	2090
November	1st to 10th	Day	13% 5% 1 4 2 3 2 3 3 5% 57%	1958
	11th to 20th	Day	7% 3 2 4 4 3 3 2 4 5% 63%	1835
	21st to end	Day	14% 6% 2 3 3 3 2 2 4 5% 57%	1800
December	1st to 10th	Day	15% 8% 2 3 3 3 3 2 4 6% 51%	2940
	11th to 20th	Day	16% 6% 3 6% 4 3 4 3 4 4 48%	3391
	21st to end	Day	18% 8% 2 5% 3 2 2 2 3 4 51%	4488
January	1st to 10th	Night	14% 4 2 4 3 3 2 2 3 5% 58%	5888
	11th to 20th	Night	7% 3 1 3 2 1 2 2 3 5% 72%	5900
	21st to end	Night	21% 7% 2 4 3 2 2 2 3 5% 48%	6490
February	1st to 10th	Night	13% 6% 2 6% 3 2 3 2 3 4 54%	2465
	11th to 20th	Night	16% 6% 2 5% 3 3 3 2 4 6% 50%	2338
	21st to end	Night	16% 6% 1 4 3 2 2 2 3 5% 54%	1980
March	1st to 10th	Night	15% 6% 2 5% 3 3 4 3 4 6% 48%	4919
	11th to 20th	Night	10% 4 2 4 3 3 3 3 4 7% 57%	4980
	21st to end	Night	12% 5% 2 5% 3 3 4 3 4 5% 54%	5467
April	1st to 10th	Night	9% 6% 1 4 3 3 4 4 5% 7% 54%	2200
	11th to 20th	Night	12% 5% 2 5% 3 3 3 3 5% 6% 52%	2095
	21st to end	Night	11% 5% 1 4 3 3 3 3 5% 7% 55%	1807
May	1st to 10th	Night	15% 8% 2 6% 4 3 3 3 5% 6% 42%	4053
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 4 5% 7% 49%	4053
	21st to end	Night	11% 5% 2 5% 4 4 4 4 6% 8% 49%	4443
June	1st to 10th	Night	4 3 2 4 3 4 4 3 7% 10% 57%	1800
	11th to 20th	Night	3 2 1 3 3 3 3 3 5% 9% 64%	1800
	21st to end	Night	2 2 1 4 2 4 4 3 7% 10% 62%	1800
July	1st to 10th	Night	6% 5% 2 5% 4 5% 5% 5% 7% 10% 47%	4078
	11th to 20th	Night	2 2 1 3 3 2 3 3 5% 9% 68%	4077
	21st to end	Night	2 2 1 3 3 3 4 3 6% 8% 64%	4449
August	1st to 10th	Night	1 1 1 2 1 1 2 3 5% 8% 75%	2926
	11th to 20th	Night	3 2 1 2 2 2 3 2 6% 10% 67%	2888
	21st to end	Night	2 2 1 3 2 2 4 3 5% 10% 64%	3719
September	1st to 10th	Night	7% 5% 2 4 4 2 3 3 5% 7% 57%	2123
	11th to 20th	Night	10% 5% 2 5% 3 3 4 4 5% 6% 53%	2090
	21st to end	Night	6% 3 1 3 2 2 3 3 6% 8% 63%	2090
October	1st to 10th	Night	6% 3 1 4 3 2 3 2 4 6% 66%	2096
	11th to 20th	Night	9% 3 1 3 3 2 3 2 4 5% 64%	2280
	21st to end	Night	14% 4 1 4 2 2 2 1 3 4 62%	2508
November	1st to 10th	Night	10% 4 2 5% 3 2 3 2 3 4 62%	2340
	11th to 20th	Night	6% 4 1 4 2 3 3 4 5% 5% 63%	2562
	21st to end	Night	14% 5% 2 4 3 3 3 3 4 5% 56%	2600
December	1st to 10th	Night	14% 6% 2 4 3 3 3 3 3 5% 55%	4250
	11th to 20th	Night	15% 6% 2 5% 3 3 3 2 4 5% 52%	4816
	21st to end	Night	14% 8% 2 5% 3 2 2 2 3 4 55%	6490

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	36% 3 5% 27% 24% 5%	4078
	11th to 20th	Day	23% 2 6% 22% 37% 10%	4080
	21st to end	Day	42% 2 4 16% 22% 14%	4488
February	1st to 10th	Day	39% 3 7% 20% 21% 11%	1951
	11th to 20th	Day	39% 3 8% 20% 21% 9%	1959
	21st to end	Day	37% 2 4 15% 26% 15%	1650
March	1st to 10th	Day	33% 3 6% 15% 24% 19%	4935
	11th to 20th	Day	31% 4 8% 17% 17% 23%	4980
	21st to end	Day	33% 5% 11% 23% 21% 7%	5464
April	1st to 10th	Day	35% 4 11% 21% 19% 11%	2200
	11th to 20th	Day	35% 5% 9% 19% 21% 10%	2253
	21st to end	Day	35% 5% 10% 22% 24% 6%	2589
May	1st to 10th	Day	41% 5% 11% 22% 16% 5%	5900
	11th to 20th	Day	39% 5% 9% 20% 24% 5%	5866
	21st to end	Day	41% 7% 11% 24% 12% 5%	6447
June	1st to 10th	Day	26% 8% 15% 29% 18% 3	2600
	11th to 20th	Day	25% 6% 13% 30% 21% 5%	2600
	21st to end	Day	23% 6% 13% 29% 24% 5%	2600
July	1st to 10th	Day	38% 5% 14% 31% 11% 1	5836
	11th to 20th	Day	17% 4 16% 38% 22% 3	5831
	21st to end	Day	21% 5% 15% 34% 24% 2	6240
August	1st to 10th	Day	12% 3 12% 31% 36% 5%	4220
	11th to 20th	Day	18% 5% 15% 39% 22% 2	4210
	21st to end	Day	20% 6% 19% 37% 15% 3	4161
September	1st to 10th	Day	28% 5% 9% 23% 24% 11%	2123
	11th to 20th	Day	36% 6% 10% 19% 22% 7%	2090
	21st to end	Day	23% 4 8% 23% 29% 13%	2090
October	1st to 10th	Day	13% 3 7% 15% 36% 27%	3426
	11th to 20th	Day	17% 3 5% 21% 35% 19%	3140
	21st to end	Day	23% 2 5% 29% 30% 11%	3428
November	1st to 10th	Day	31% 4 7% 21% 26% 11%	1958
	11th to 20th	Day	24% 3 8% 21% 30% 13%	1835
	21st to end	Day	33% 2 5% 21% 27% 11%	1800
December	1st to 10th	Day	36% 3 5% 27% 23% 5%	2940
	11th to 20th	Day	41% 3 6% 11% 28% 12%	3389
	21st to end	Day	39% 2 4 25% 21% 9%	4488
January	1st to 10th	Night	31% 2 6% 26% 27% 8%	5888
	11th to 20th	Night	19% 2 6% 19% 38% 17%	5900
	21st to end	Night	42% 3 4 14% 23% 15%	6490
February	1st to 10th	Night	35% 3 7% 18% 23% 14%	2465
	11th to 20th	Night	37% 2 8% 17% 25% 11%	2338
	21st to end	Night	35% 2 7% 16% 23% 17%	1980
March	1st to 10th	Night	37% 4 5% 14% 22% 18%	4919
	11th to 20th	Night	29% 3 8% 18% 18% 24%	4980
	21st to end	Night	34% 4 7% 18% 30% 7%	5467
April	1st to 10th	Night	28% 6% 10% 21% 21% 15%	2200
	11th to 20th	Night	32% 4 9% 19% 21% 14%	2095
	21st to end	Night	29% 5% 10% 22% 27% 6%	1807
May	1st to 10th	Night	41% 5% 11% 23% 14% 5%	4080
	11th to 20th	Night	34% 6% 13% 18% 23% 7%	4054
	21st to end	Night	32% 6% 14% 27% 12% 9%	4452
June	1st to 10th	Night	22% 6% 15% 31% 20% 5%	1800
	11th to 20th	Night	18% 6% 13% 34% 23% 8%	1800
	21st to end	Night	18% 6% 14% 27% 28% 7%	1800
July	1st to 10th	Night	32% 5% 15% 33% 13% 2	4035
	11th to 20th	Night	14% 4 14% 38% 26% 4	4026
	21st to end	Night	18% 4 16% 34% 26% 2	4320
August	1st to 10th	Night	8% 4 9% 32% 42% 6%	2916
	11th to 20th	Night	13% 4 13% 38% 26% 6%	2915
	21st to end	Night	17% 5% 20% 35% 20% 3	3719
September	1st to 10th	Night	26% 5% 9% 23% 25% 11%	2123
	11th to 20th	Night	30% 6% 10% 20% 22% 11%	2090
	21st to end	Night	20% 4 8% 24% 28% 17%	2090
October	1st to 10th	Night	12% 2 5% 16% 30% 36%	3499
	11th to 20th	Night	15% 2 5% 20% 32% 25%	3779
	21st to end	Night	24% 2 3 23% 32% 15%	4120
November	1st to 10th	Night	28% 3 6% 20% 26% 16%	2340
	11th to 20th	Night	22% 4 7% 22% 29% 16%	2562
	21st to end	Night	33% 3 7% 18% 27% 13%	2600
December	1st to 10th	Night	35% 3 5% 22% 26% 10%	4250
	11th to 20th	Night	37% 2 6% 15% 26% 15%	4817
	21st to end	Night	35% 2 6% 20% 26% 11%	6490

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	21% 12% 34% 26% 7%	300
	11th to 20th	Day	18% 11% 37% 24% 10%	300
	21st to end	Day	20% 11% 39% 21% 9% 1	330
February	1st to 10th	Day	19% 11% 37% 25% 7% 1	300
	11th to 20th	Day	20% 15% 40% 19% 5% 1	300
	21st to end	Day	25% 12% 40% 19% 4	249
March	1st to 10th	Day	20% 16% 34% 24% 6%	300
	11th to 20th	Day	18% 17% 39% 21% 5% 1	300
	21st to end	Day	12% 14% 45% 21% 7% 1	330
April	1st to 10th	Day	17% 13% 37% 24% 8% 2	300
	11th to 20th	Day	17% 13% 37% 25% 8%	371
	21st to end	Day	15% 10% 40% 26% 8% 1	689
May	1st to 10th	Day	15% 8% 35% 32% 9% 1	703
	11th to 20th	Day	16% 5% 29% 34% 13% 3	725
	21st to end	Day	13% 6% 26% 32% 18% 4	789
June	1st to 10th	Day	7% 2 13% 40% 28% 9%	730
	11th to 20th	Day	6% 2 15% 41% 29% 7%	730
	21st to end	Day	3 1 12% 33% 38% 12%	730
July	1st to 10th	Day	6% 2 5% 34% 38% 16%	721
	11th to 20th	Day	2 1 5% 31% 45% 15%	718
	21st to end	Day	3 2 4 29% 44% 19%	794
August	1st to 10th	Day	2 1 4 28% 50% 15%	726
	11th to 20th	Day	7% 1 4 28% 46% 14%	715
	21st to end	Day	4 1 3 24% 40% 27%	498
September	1st to 10th	Day	7% 2 5% 18% 39% 29%	309
	11th to 20th	Day	6% 1 3 26% 43% 22%	300
	21st to end	Day	12% 2 6% 23% 36% 21%	300
October	1st to 10th	Day	2 1 16% 30% 36% 15%	300
	11th to 20th	Day	9% 5% 28% 32% 22% 4	300
	21st to end	Day	21% 8% 24% 26% 18% 4	330
November	1st to 10th	Day	20% 6% 30% 25% 15% 4	300
	11th to 20th	Day	11% 8% 30% 30% 17% 4	300
	21st to end	Day	16% 11% 38% 20% 12% 2	300
December	1st to 10th	Day	18% 7% 30% 31% 11% 4	300
	11th to 20th	Day	19% 7% 36% 29% 9%	300
	21st to end	Day	23% 8% 35% 26% 8%	330
January	1st to 10th	Night	14% 7% 35% 34% 9%	1000
	11th to 20th	Night	15% 11% 32% 36% 6%	1000
	21st to end	Night	15% 10% 36% 32% 7%	1100
February	1st to 10th	Night	17% 9% 37% 30% 5% 1	865
	11th to 20th	Night	18% 12% 38% 29% 4	784
	21st to end	Night	22% 11% 41% 24% 2	660
March	1st to 10th	Night	18% 10% 37% 31% 5%	600
	11th to 20th	Night	15% 8% 40% 32% 5%	600
	21st to end	Night	11% 10% 42% 32% 5%	660
April	1st to 10th	Night	11% 13% 40% 31% 5%	600
	11th to 20th	Night	14% 10% 41% 31% 5%	593
	21st to end	Night	13% 8% 42% 30% 7% 1	600
May	1st to 10th	Night	11% 6% 39% 36% 7% 1	600
	11th to 20th	Night	11% 4 33% 38% 13% 1	591
	21st to end	Night	9% 3 31% 40% 16% 1	650
June	1st to 10th	Night	5% 2 15% 52% 25% 2	600
	11th to 20th	Night	4 2 20% 55% 19% 1	600
	21st to end	Night	2 1 13% 47% 33% 4	600
July	1st to 10th	Night	4 2 8% 43% 39% 5%	585
	11th to 20th	Night	3 1 7% 46% 41% 3	582
	21st to end	Night	1 1 4 44% 47% 3	657
August	1st to 10th	Night	2 1 4 45% 46% 3	597
	11th to 20th	Night	6% 1 5% 41% 43% 5%	594
	21st to end	Night	5% 1 2 42% 44% 7%	660
September	1st to 10th	Night	8% 2 5% 41% 39% 5%	579
	11th to 20th	Night	13% 1 5% 40% 37% 4	570
	21st to end	Night	8% 1 11% 42% 34% 4	570
October	1st to 10th	Night	7% 1 17% 43% 28% 3	576
	11th to 20th	Night	10% 5% 25% 41% 17% 2	760
	21st to end	Night	16% 7% 28% 31% 17%	836
November	1st to 10th	Night	12% 3 27% 41% 16% 1	780
	11th to 20th	Night	8% 7% 31% 38% 14% 1	962
	21st to end	Night	17% 9% 34% 30% 10%	1000
December	1st to 10th	Night	14% 8% 35% 36% 7%	1000
	11th to 20th	Night	18% 7% 32% 36% 6%	1000
	21st to end	Night	18% 8% 34% 33% 6%	1100

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