Conner Preserve
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Conner Preserve clear sky chart from 2005-11-06 to 2025-05-11.

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	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 41%	114233
	Night	8% 6% 2 6% 4 5% 5% 4 7% 9% 43%	114718
Transparency	Day	37% 6% 16% 20% 15% 6%	118037
	Night	36% 6% 16% 20% 15% 6%	119053
Seeing	Day	9% 5% 17% 26% 24% 19%	16093
	Night	9% 4 18% 34% 27% 8%	26211

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	8% 6% 2 5% 3 4 4 3 6% 8% 51%	4056
	11th to 20th	Day	20% 10% 3 8% 5% 4 4 4 5% 8% 31%	4060
	21st to end	Day	12% 5% 2 5% 4 3 3 4 7% 10% 46%	4812
February	1st to 10th	Day	13% 5% 3 6% 4 4 5% 3 5% 7% 45%	2000
	11th to 20th	Day	9% 4 2 5% 5% 4 3 3 5% 6% 54%	1948
	21st to end	Day	8% 5% 2 6% 4 4 4 4 6% 8% 50%	1695
March	1st to 10th	Day	7% 5% 2 7% 5% 5% 5% 4 6% 9% 46%	4935
	11th to 20th	Day	6% 4 2 4 3 3 3 3 6% 8% 59%	4980
	21st to end	Day	8% 5% 2 4 4 4 5% 4 6% 8% 51%	5465
April	1st to 10th	Day	7% 4 1 4 4 4 5% 4 7% 9% 50%	2200
	11th to 20th	Day	8% 4 2 5% 5% 5% 6% 4 6% 8% 48%	2176
	21st to end	Day	4 3 1 5% 4 5% 5% 4 6% 8% 54%	2417
May	1st to 10th	Day	3 2 1 4 3 3 5% 4 6% 10% 59%	4212
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 5% 7% 11% 39%	4081
	21st to end	Day	4 3 2 4 3 4 5% 5% 7% 9% 54%	4476
June	1st to 10th	Day	11% 7% 3 8% 7% 6% 7% 6% 7% 10% 27%	2470
	11th to 20th	Day	5% 6% 2 7% 8% 8% 8% 7% 9% 12% 27%	2470
	21st to end	Day	7% 8% 3 7% 8% 6% 8% 6% 8% 10% 28%	2470
July	1st to 10th	Day	6% 5% 3 9% 8% 8% 9% 7% 9% 13% 23%	4120
	11th to 20th	Day	4 5% 2 9% 9% 8% 9% 7% 10% 14% 22%	4120
	21st to end	Day	4 5% 2 9% 8% 8% 9% 8% 11% 13% 22%	4466
August	1st to 10th	Day	8% 5% 2 9% 6% 7% 6% 6% 9% 12% 29%	4104
	11th to 20th	Day	4 5% 3 6% 6% 7% 7% 6% 9% 12% 36%	3732
	21st to end	Day	8% 6% 2 9% 7% 7% 8% 6% 9% 13% 25%	3835
September	1st to 10th	Day	8% 6% 3 10% 8% 8% 8% 7% 9% 10% 21%	2090
	11th to 20th	Day	9% 8% 3 10% 7% 7% 8% 5% 9% 10% 26%	2090
	21st to end	Day	8% 6% 3 8% 7% 7% 8% 6% 8% 9% 32%	2090
October	1st to 10th	Day	11% 6% 3 8% 6% 6% 7% 5% 6% 8% 36%	2090
	11th to 20th	Day	6% 4 2 4 5% 5% 5% 4 6% 8% 51%	1938
	21st to end	Day	6% 5% 2 5% 3 4 4 4 7% 8% 50%	2090
November	1st to 10th	Day	8% 4 2 6% 5% 4 4 4 5% 7% 51%	1957
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 4 5% 8% 48%	2000
	21st to end	Day	8% 6% 2 6% 4 4 5% 5% 5% 9% 46%	1819
December	1st to 10th	Day	4 4 1 4 4 4 4 4 6% 8% 57%	2930
	11th to 20th	Day	8% 6% 3 6% 4 3 4 4 6% 8% 48%	3373
	21st to end	Day	11% 7% 3 9% 5% 5% 5% 4 5% 8% 38%	4466
January	1st to 10th	Night	8% 5% 2 6% 3 4 4 3 5% 8% 52%	5889
	11th to 20th	Night	20% 10% 4 8% 5% 5% 5% 4 6% 8% 27%	5900
	21st to end	Night	15% 6% 2 6% 4 4 4 3 5% 8% 40%	6140
February	1st to 10th	Night	11% 8% 2 5% 4 3 3 4 6% 8% 45%	2400
	11th to 20th	Night	9% 6% 2 6% 4 4 4 4 5% 8% 49%	2338
	21st to end	Night	7% 6% 3 6% 5% 5% 4 3 6% 8% 49%	1932
March	1st to 10th	Night	11% 7% 2 7% 4 4 4 4 5% 6% 45%	4918
	11th to 20th	Night	5% 4 2 3 3 3 3 4 6% 10% 57%	4980
	21st to end	Night	8% 6% 2 6% 4 3 4 4 6% 7% 49%	5467
April	1st to 10th	Night	6% 4 1 5% 4 4 3 5% 7% 10% 52%	2200
	11th to 20th	Night	5% 5% 2 6% 3 4 4 4 6% 8% 52%	2173
	21st to end	Night	6% 3 1 4 3 4 4 3 5% 7% 59%	1994
May	1st to 10th	Night	4 3 1 4 3 3 4 4 5% 9% 59%	2903
	11th to 20th	Night	7% 5% 2 6% 4 5% 5% 4 7% 10% 47%	2818
	21st to end	Night	4 3 1 4 3 3 3 4 5% 9% 61%	3079
June	1st to 10th	Night	9% 5% 3 7% 5% 5% 5% 5% 7% 10% 39%	1710
	11th to 20th	Night	5% 5% 2 6% 5% 6% 6% 6% 9% 14% 37%	1710
	21st to end	Night	6% 6% 2 8% 6% 5% 8% 5% 11% 12% 33%	1710
July	1st to 10th	Night	6% 6% 3 11% 8% 6% 8% 7% 10% 12% 24%	2840
	11th to 20th	Night	3 5% 2 7% 7% 7% 8% 7% 12% 14% 27%	2840
	21st to end	Night	5% 7% 4 10% 8% 11% 9% 7% 10% 11% 19%	3087
August	1st to 10th	Night	5% 5% 2 7% 6% 7% 7% 5% 9% 13% 34%	2825
	11th to 20th	Night	4 4 2 5% 4 5% 6% 6% 9% 17% 38%	3092
	21st to end	Night	6% 6% 2 8% 6% 6% 7% 6% 10% 12% 28%	3786
September	1st to 10th	Night	7% 6% 2 7% 7% 7% 7% 7% 10% 14% 28%	2090
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 8% 11% 29%	2090
	21st to end	Night	7% 6% 3 8% 5% 6% 6% 4 9% 10% 36%	2090
October	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 5% 7% 8% 38%	2090
	11th to 20th	Night	6% 5% 2 5% 4 3 4 4 6% 9% 54%	2239
	21st to end	Night	7% 5% 2 6% 3 4 4 3 5% 9% 50%	2508
November	1st to 10th	Night	8% 4 2 5% 4 3 4 4 5% 8% 53%	2341
	11th to 20th	Night	8% 6% 2 7% 4 4 4 5% 4 7% 50%	2400
	21st to end	Night	8% 6% 3 6% 5% 4 4 4 5% 9% 47%	2577
December	1st to 10th	Night	5% 3 1 4 3 3 4 3 6% 7% 60%	4250
	11th to 20th	Night	9% 6% 3 5% 4 4 4 3 5% 6% 51%	4822
	21st to end	Night	13% 9% 3 7% 5% 4 4 4 6% 8% 37%	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	31% 3 8% 17% 27% 13%	4057
	11th to 20th	Day	53% 3 4 18% 15% 7%	4060
	21st to end	Day	35% 3 8% 27% 20% 7%	4812
February	1st to 10th	Day	37% 6% 8% 18% 19% 12%	2000
	11th to 20th	Day	31% 3 8% 21% 25% 11%	1958
	21st to end	Day	32% 5% 10% 19% 22% 11%	1695
March	1st to 10th	Day	35% 4 12% 22% 20% 8%	4935
	11th to 20th	Day	24% 3 9% 24% 22% 18%	4980
	21st to end	Day	31% 3 8% 30% 20% 8%	5465
April	1st to 10th	Day	29% 5% 15% 22% 21% 8%	2200
	11th to 20th	Day	32% 6% 11% 18% 23% 10%	2176
	21st to end	Day	27% 5% 10% 25% 27% 7%	2417
May	1st to 10th	Day	19% 5% 16% 35% 19% 6%	4250
	11th to 20th	Day	37% 6% 19% 23% 14% 2	4085
	21st to end	Day	24% 6% 13% 34% 21% 2	4489
June	1st to 10th	Day	49% 7% 19% 19% 6%	2470
	11th to 20th	Day	45% 8% 23% 19% 4	2470
	21st to end	Day	47% 10% 25% 13% 4	2470
July	1st to 10th	Day	49% 8% 35% 7% 1	4055
	11th to 20th	Day	48% 11% 35% 6% 1	4051
	21st to end	Day	46% 15% 30% 9% 1	4324
August	1st to 10th	Day	45% 8% 30% 14% 3	4091
	11th to 20th	Day	37% 9% 26% 24% 3	3768
	21st to end	Day	48% 10% 26% 16% 1	3835
September	1st to 10th	Day	52% 13% 21% 11% 3	2090
	11th to 20th	Day	50% 10% 22% 14% 4	2090
	21st to end	Day	44% 9% 15% 19% 10% 3	2090
October	1st to 10th	Day	58% 9% 11% 11% 8% 5%	3480
	11th to 20th	Day	25% 4 7% 23% 35% 7%	3204
	21st to end	Day	27% 4 7% 24% 30% 7%	3428
November	1st to 10th	Day	32% 5% 10% 24% 19% 11%	1957
	11th to 20th	Day	34% 5% 9% 20% 21% 10%	2000
	21st to end	Day	34% 4 9% 22% 20% 10%	1819
December	1st to 10th	Day	25% 3 15% 28% 20% 10%	2930
	11th to 20th	Day	35% 4 10% 20% 20% 11%	3370
	21st to end	Day	43% 4 10% 22% 16% 5%	4466
January	1st to 10th	Night	32% 3 8% 18% 30% 10%	5889
	11th to 20th	Night	56% 3 8% 15% 14% 4	5900
	21st to end	Night	43% 4 9% 20% 17% 8%	6140
February	1st to 10th	Night	36% 5% 10% 19% 19% 11%	2400
	11th to 20th	Night	33% 5% 10% 20% 23% 9%	2339
	21st to end	Night	34% 5% 11% 20% 22% 8%	1932
March	1st to 10th	Night	40% 4 11% 18% 18% 9%	4918
	11th to 20th	Night	23% 4 16% 21% 18% 18%	4980
	21st to end	Night	33% 4 9% 28% 20% 6%	5467
April	1st to 10th	Night	27% 5% 18% 26% 18% 6%	2200
	11th to 20th	Night	28% 5% 13% 24% 22% 8%	2173
	21st to end	Night	25% 4 13% 28% 24% 6%	1994
May	1st to 10th	Night	21% 6% 18% 34% 16% 5%	2930
	11th to 20th	Night	31% 7% 23% 25% 13% 1	2819
	21st to end	Night	19% 6% 15% 40% 18% 1	3087
June	1st to 10th	Night	38% 8% 24% 24% 7%	1710
	11th to 20th	Night	34% 11% 30% 22% 3	1710
	21st to end	Night	39% 14% 25% 16% 5%	1710
July	1st to 10th	Night	50% 12% 31% 6% 1	2795
	11th to 20th	Night	42% 15% 38% 6%	2786
	21st to end	Night	54% 13% 25% 7%	2988
August	1st to 10th	Night	39% 11% 34% 12% 3	2814
	11th to 20th	Night	30% 11% 33% 24% 2	3122
	21st to end	Night	44% 12% 29% 12% 3	3786
September	1st to 10th	Night	43% 15% 27% 12% 3	2090
	11th to 20th	Night	46% 11% 23% 17% 3 1	2090
	21st to end	Night	39% 9% 18% 21% 10% 2	2090
October	1st to 10th	Night	57% 8% 11% 12% 7% 4	3480
	11th to 20th	Night	23% 4 8% 26% 33% 5%	3712
	21st to end	Night	31% 4 8% 21% 30% 6%	4120
November	1st to 10th	Night	29% 4 13% 23% 21% 11%	2341
	11th to 20th	Night	34% 4 9% 22% 22% 9%	2400
	21st to end	Night	34% 4 10% 24% 19% 9%	2577
December	1st to 10th	Night	23% 3 16% 28% 16% 13%	4250
	11th to 20th	Night	34% 4 12% 23% 18% 10%	4824
	21st to end	Night	45% 4 12% 20% 15% 4	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	10% 12% 45% 22% 10%	300
	11th to 20th	Day	10% 14% 33% 30% 10% 3	300
	21st to end	Day	17% 14% 39% 24% 6%	330
February	1st to 10th	Day	14% 7% 31% 31% 14% 3	300
	11th to 20th	Day	12% 7% 35% 30% 13% 4	300
	21st to end	Day	8% 12% 30% 31% 18% 2	294
March	1st to 10th	Day	8% 10% 36% 32% 13% 1	500
	11th to 20th	Day	11% 8% 29% 30% 20% 2	500
	21st to end	Day	6% 7% 33% 33% 19% 3	550
April	1st to 10th	Day	10% 8% 29% 32% 19% 3	500
	11th to 20th	Day	10% 6% 24% 34% 21% 5%	492
	21st to end	Day	5% 3 20% 37% 25% 10%	500
May	1st to 10th	Day	5% 4 22% 31% 25% 13%	503
	11th to 20th	Day	9% 2 16% 30% 27% 17%	487
	21st to end	Day	8% 2 9% 24% 30% 28%	529
June	1st to 10th	Day	13% 2 6% 22% 31% 25%	490
	11th to 20th	Day	7% 2 7% 22% 30% 32%	490
	21st to end	Day	7% 2 3 16% 30% 43%	490
July	1st to 10th	Day	7% 1 2 11% 28% 51%	485
	11th to 20th	Day	7% 1 1 12% 27% 52%	484
	21st to end	Day	9% 3 2 15% 27% 45%	532
August	1st to 10th	Day	9% 2 4 13% 29% 43%	486
	11th to 20th	Day	7% 3 1 12% 27% 51%	479
	21st to end	Day	8% 2 5% 15% 33% 36%	539
September	1st to 10th	Day	9% 2 4 14% 34% 37%	490
	11th to 20th	Day	11% 2 3 22% 34% 28%	490
	21st to end	Day	10% 2 6% 20% 37% 24%	490
October	1st to 10th	Day	13% 3 14% 33% 29% 8%	490
	11th to 20th	Day	7% 3 17% 32% 29% 12%	490
	21st to end	Day	7% 3 19% 40% 26% 5%	539
November	1st to 10th	Day	11% 4 20% 34% 25% 7%	495
	11th to 20th	Day	12% 4 22% 38% 19% 5%	500
	21st to end	Day	11% 6% 28% 32% 18% 4	319
December	1st to 10th	Day	5% 10% 35% 30% 15% 5%	300
	11th to 20th	Day	14% 7% 34% 27% 15% 2	300
	21st to end	Day	10% 9% 30% 35% 14% 2	330
January	1st to 10th	Night	11% 7% 32% 36% 14%	800
	11th to 20th	Night	12% 7% 26% 40% 15% 1	800
	21st to end	Night	16% 7% 32% 37% 8%	880
February	1st to 10th	Night	16% 5% 28% 38% 14%	800
	11th to 20th	Night	11% 7% 27% 41% 13% 1	783
	21st to end	Night	9% 5% 29% 46% 11%	660
March	1st to 10th	Night	8% 5% 35% 41% 10% 1	800
	11th to 20th	Night	9% 6% 28% 40% 16% 1	800
	21st to end	Night	9% 5% 28% 43% 15%	880
April	1st to 10th	Night	8% 4 29% 42% 16% 1	800
	11th to 20th	Night	8% 5% 29% 43% 15% 1	791
	21st to end	Night	7% 3 23% 45% 22% 1	762
May	1st to 10th	Night	5% 2 13% 49% 30% 3	600
	11th to 20th	Night	6% 2 13% 41% 34% 4	563
	21st to end	Night	6% 2 8% 36% 41% 8%	617
June	1st to 10th	Night	10% 2 5% 28% 44% 12%	570
	11th to 20th	Night	7% 2 3 18% 46% 23%	570
	21st to end	Night	7% 3 2 14% 47% 27%	570
July	1st to 10th	Night	6% 2 1 9% 48% 35%	555
	11th to 20th	Night	5% 2 7% 44% 42%	552
	21st to end	Night	5% 2 1 8% 50% 33%	624
August	1st to 10th	Night	7% 3 2 8% 52% 29%	567
	11th to 20th	Night	6% 2 1 8% 44% 39%	564
	21st to end	Night	11% 4 3 19% 42% 22%	807
September	1st to 10th	Night	9% 2 5% 19% 44% 20%	760
	11th to 20th	Night	12% 2 5% 26% 41% 14%	760
	21st to end	Night	10% 2 6% 30% 41% 11%	760
October	1st to 10th	Night	14% 2 13% 41% 26% 5%	760
	11th to 20th	Night	7% 3 15% 39% 33% 3	760
	21st to end	Night	9% 3 18% 41% 26% 2	836
November	1st to 10th	Night	9% 2 23% 42% 21% 3	780
	11th to 20th	Night	11% 3 22% 43% 20% 2	800
	21st to end	Night	10% 4 24% 45% 16% 1	800
December	1st to 10th	Night	10% 4 25% 40% 21% 1	800
	11th to 20th	Night	10% 5% 25% 42% 17% 1	800
	21st to end	Night	10% 6% 27% 38% 18% 1	880

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