Crane Point Nature Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crane Point Nature Center clear sky chart from 2005-11-06 to 2025-07-21.

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	5% 4 2 5% 4 5% 5% 5% 8% 12% 45%	119766
	Night	5% 4 2 6% 5% 5% 5% 5% 8% 11% 45%	119354
Transparency	Day	29% 10% 22% 26% 11% 2	123511
	Night	32% 9% 19% 25% 13% 2	123746
Seeing	Day	6% 2 7% 23% 38% 25%	16925
	Night	6% 2 9% 26% 37% 19%	27041

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	6% 4 2 5% 4 4 4 4 8% 14% 44%	4056
	11th to 20th	Day	11% 7% 3 8% 5% 5% 5% 5% 7% 8% 37%	4060
	21st to end	Day	6% 6% 3 7% 5% 6% 6% 4 7% 8% 43%	4859
February	1st to 10th	Day	5% 5% 1 4 3 4 4 6% 7% 10% 51%	2000
	11th to 20th	Day	5% 4 1 4 3 4 3 3 6% 10% 57%	2030
	21st to end	Day	4 3 1 3 2 3 3 3 6% 10% 62%	1815
March	1st to 10th	Day	2 2 1 3 3 4 4 4 7% 11% 59%	4935
	11th to 20th	Day	2 2 1 3 2 3 4 4 6% 10% 64%	4980
	21st to end	Day	5% 3 1 4 4 4 4 4 6% 11% 54%	5465
April	1st to 10th	Day	2 2 1 3 2 4 4 4 6% 12% 59%	2200
	11th to 20th	Day	3 3 1 3 2 3 4 3 7% 11% 60%	2176
	21st to end	Day	4 3 1 4 3 3 4 4 7% 11% 57%	2400
May	1st to 10th	Day	2 1 1 2 2 2 3 3 5% 12% 67%	5405
	11th to 20th	Day	5% 3 1 3 3 3 4 4 6% 10% 59%	5510
	21st to end	Day	3 2 1 3 3 3 4 3 5% 11% 62%	6433
June	1st to 10th	Day	10% 8% 3 9% 6% 6% 6% 6% 9% 11% 27%	2600
	11th to 20th	Day	6% 5% 2 7% 6% 6% 7% 5% 10% 15% 30%	2600
	21st to end	Day	5% 5% 2 6% 6% 7% 6% 6% 10% 14% 32%	2600
July	1st to 10th	Day	3 3 1 5% 4 5% 7% 6% 11% 17% 36%	4250
	11th to 20th	Day	2 3 1 5% 4 6% 6% 7% 12% 17% 35%	4250
	21st to end	Day	2 2 1 3 4 5% 7% 6% 12% 19% 39%	4466
August	1st to 10th	Day	3 3 2 8% 6% 7% 8% 7% 12% 17% 28%	4074
	11th to 20th	Day	2 3 2 8% 7% 7% 7% 7% 10% 15% 33%	3452
	21st to end	Day	3 3 2 5% 6% 7% 8% 8% 12% 17% 29%	3828
September	1st to 10th	Day	5% 4 2 7% 5% 7% 9% 8% 12% 15% 26%	2090
	11th to 20th	Day	5% 5% 3 6% 6% 6% 8% 7% 10% 14% 29%	2090
	21st to end	Day	8% 6% 3 8% 6% 6% 8% 6% 9% 12% 28%	2090
October	1st to 10th	Day	7% 6% 2 7% 6% 6% 7% 6% 9% 14% 29%	2067
	11th to 20th	Day	8% 5% 2 8% 6% 5% 7% 6% 8% 12% 33%	1900
	21st to end	Day	8% 6% 3 6% 4 5% 5% 5% 7% 10% 41%	2090
November	1st to 10th	Day	7% 4 2 5% 5% 3 4 5% 8% 9% 48%	1957
	11th to 20th	Day	7% 6% 2 5% 5% 5% 6% 5% 7% 8% 43%	2000
	21st to end	Day	5% 5% 2 4 4 5% 4 4 6% 9% 51%	2000
December	1st to 10th	Day	6% 3 1 4 3 4 4 3 6% 9% 58%	3199
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 5% 7% 12% 43%	3373
	21st to end	Day	10% 7% 3 8% 6% 5% 6% 5% 8% 9% 33%	4466
January	1st to 10th	Night	5% 4 2 6% 5% 4 5% 5% 8% 11% 45%	5889
	11th to 20th	Night	12% 8% 3 8% 6% 5% 5% 4 7% 7% 35%	5900
	21st to end	Night	8% 6% 2 8% 5% 5% 5% 4 7% 8% 42%	6080
February	1st to 10th	Night	6% 5% 2 5% 4 5% 6% 5% 6% 8% 49%	2400
	11th to 20th	Night	6% 3 2 5% 4 4 4 4 6% 8% 55%	2253
	21st to end	Night	4 3 1 4 3 4 3 4 5% 8% 60%	1815
March	1st to 10th	Night	3 3 1 6% 4 4 5% 5% 7% 9% 54%	4918
	11th to 20th	Night	2 2 1 4 3 3 4 3 5% 8% 64%	4980
	21st to end	Night	5% 2 1 5% 4 4 5% 4 8% 10% 52%	5467
April	1st to 10th	Night	3 3 1 3 4 4 5% 4 6% 10% 57%	2200
	11th to 20th	Night	5% 4 2 5% 4 3 4 4 6% 11% 53%	2169
	21st to end	Night	4 4 1 4 4 4 5% 4 6% 10% 54%	2000
May	1st to 10th	Night	2 1 1 2 2 2 3 3 6% 11% 68%	4490
	11th to 20th	Night	5% 4 2 6% 4 4 4 3 6% 7% 53%	4409
	21st to end	Night	3 2 1 2 2 2 3 3 5% 10% 65%	4421
June	1st to 10th	Night	11% 10% 3 10% 7% 6% 6% 4 8% 10% 26%	1800
	11th to 20th	Night	6% 5% 2 6% 6% 7% 6% 5% 9% 15% 33%	1800
	21st to end	Night	4 4 2 6% 6% 7% 7% 6% 10% 14% 34%	1800
July	1st to 10th	Night	2 3 1 5% 4 6% 6% 6% 11% 17% 38%	2930
	11th to 20th	Night	2 3 2 5% 4 5% 7% 5% 9% 16% 43%	2930
	21st to end	Night	1 2 1 4 5% 5% 6% 6% 11% 16% 42%	3087
August	1st to 10th	Night	2 3 2 7% 6% 6% 8% 6% 12% 17% 32%	2825
	11th to 20th	Night	2 3 2 5% 6% 6% 7% 6% 11% 17% 37%	3366
	21st to end	Night	3 4 1 5% 5% 7% 8% 8% 14% 18% 27%	3828
September	1st to 10th	Night	5% 3 1 6% 6% 6% 8% 8% 10% 14% 32%	2090
	11th to 20th	Night	4 6% 3 9% 7% 6% 7% 8% 10% 11% 29%	2090
	21st to end	Night	8% 7% 4 8% 6% 8% 8% 5% 9% 11% 27%	2090
October	1st to 10th	Night	7% 7% 2 7% 7% 7% 8% 5% 8% 13% 29%	2110
	11th to 20th	Night	8% 6% 2 8% 5% 5% 7% 6% 10% 13% 30%	2280
	21st to end	Night	10% 7% 3 7% 5% 6% 6% 5% 8% 9% 35%	2508
November	1st to 10th	Night	9% 5% 2 5% 4 5% 5% 4 6% 11% 44%	2341
	11th to 20th	Night	8% 6% 2 6% 5% 5% 6% 4 7% 10% 42%	2400
	21st to end	Night	7% 4 2 5% 5% 4 5% 4 8% 9% 47%	2400
December	1st to 10th	Night	5% 4 2 4 3 3 4 4 6% 8% 57%	3976
	11th to 20th	Night	6% 5% 2 7% 5% 5% 5% 4 7% 10% 44%	4822
	21st to end	Night	9% 7% 3 10% 7% 7% 6% 5% 7% 9% 30%	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	29% 7% 16% 33% 12% 3	4057
	11th to 20th	Day	42% 8% 17% 25% 7% 2	4060
	21st to end	Day	37% 7% 9% 27% 18% 3	4859
February	1st to 10th	Day	28% 7% 12% 31% 19% 3	2000
	11th to 20th	Day	23% 5% 13% 31% 22% 6%	2040
	21st to end	Day	17% 5% 11% 30% 30% 7%	1815
March	1st to 10th	Day	18% 7% 18% 30% 24% 3	4935
	11th to 20th	Day	14% 6% 18% 31% 21% 10%	4980
	21st to end	Day	24% 6% 12% 34% 21% 3	5465
April	1st to 10th	Day	18% 6% 16% 41% 16% 3	2200
	11th to 20th	Day	19% 6% 19% 32% 20% 4	2176
	21st to end	Day	19% 7% 16% 33% 22% 3	2400
May	1st to 10th	Day	10% 5% 18% 45% 19% 2	5437
	11th to 20th	Day	21% 6% 15% 50% 8%	5514
	21st to end	Day	17% 6% 19% 50% 8%	6447
June	1st to 10th	Day	47% 11% 23% 16% 3	2600
	11th to 20th	Day	39% 14% 30% 16% 1	2600
	21st to end	Day	36% 15% 37% 12% 1	2600
July	1st to 10th	Day	29% 15% 39% 17%	4185
	11th to 20th	Day	28% 14% 47% 10%	4181
	21st to end	Day	21% 15% 48% 16% 1	4324
August	1st to 10th	Day	33% 18% 35% 14% 1	4061
	11th to 20th	Day	32% 14% 40% 13% 1	3486
	21st to end	Day	34% 19% 38% 9% 1	3828
September	1st to 10th	Day	36% 19% 30% 14% 1	2090
	11th to 20th	Day	39% 16% 29% 14% 2	2090
	21st to end	Day	43% 14% 24% 15% 4	2090
October	1st to 10th	Day	40% 11% 25% 18% 4 1	3431
	11th to 20th	Day	47% 13% 18% 14% 7% 1	3140
	21st to end	Day	37% 7% 12% 28% 13% 2	3428
November	1st to 10th	Day	31% 8% 13% 23% 21% 4	1957
	11th to 20th	Day	36% 8% 11% 23% 18% 4	2000
	21st to end	Day	30% 8% 13% 22% 24% 3	2000
December	1st to 10th	Day	24% 6% 11% 35% 22% 2	3199
	11th to 20th	Day	33% 9% 13% 25% 16% 4	3370
	21st to end	Day	45% 10% 14% 16% 15% 1	4466
January	1st to 10th	Night	30% 7% 13% 32% 15% 2	5889
	11th to 20th	Night	45% 8% 14% 23% 9% 1	5900
	21st to end	Night	39% 6% 9% 27% 18% 2	6080
February	1st to 10th	Night	32% 7% 12% 27% 19% 3	2400
	11th to 20th	Night	27% 5% 12% 25% 24% 7%	2254
	21st to end	Night	24% 4 12% 24% 28% 9%	1815
March	1st to 10th	Night	25% 8% 12% 27% 25% 4	4918
	11th to 20th	Night	19% 6% 15% 30% 20% 11%	4980
	21st to end	Night	24% 6% 12% 29% 23% 5%	5467
April	1st to 10th	Night	21% 6% 16% 37% 17% 2	2200
	11th to 20th	Night	27% 7% 15% 28% 20% 4	2169
	21st to end	Night	26% 7% 12% 32% 22% 2	2000
May	1st to 10th	Night	11% 5% 16% 50% 17% 2	4520
	11th to 20th	Night	29% 7% 11% 36% 16%	4410
	21st to end	Night	16% 6% 20% 46% 12%	4429
June	1st to 10th	Night	51% 10% 20% 15% 3	1800
	11th to 20th	Night	37% 15% 30% 16% 3	1800
	21st to end	Night	34% 15% 35% 15% 1	1800
July	1st to 10th	Night	26% 14% 42% 17%	2885
	11th to 20th	Night	25% 14% 49% 13%	2876
	21st to end	Night	22% 13% 43% 21% 1	2988
August	1st to 10th	Night	32% 14% 36% 16% 1	2814
	11th to 20th	Night	27% 12% 44% 16% 1	3398
	21st to end	Night	33% 21% 36% 10%	3828
September	1st to 10th	Night	34% 16% 35% 14% 1	2090
	11th to 20th	Night	43% 15% 28% 13% 2	2090
	21st to end	Night	46% 13% 22% 14% 5%	2090
October	1st to 10th	Night	42% 11% 22% 19% 5% 1	3526
	11th to 20th	Night	49% 13% 18% 13% 6% 1	3779
	21st to end	Night	43% 8% 10% 25% 12% 2	4120
November	1st to 10th	Night	35% 8% 13% 24% 17% 3	2341
	11th to 20th	Night	36% 8% 12% 24% 17% 3	2400
	21st to end	Night	33% 8% 12% 22% 21% 4	2400
December	1st to 10th	Night	25% 6% 11% 37% 18% 3	3976
	11th to 20th	Night	34% 8% 14% 26% 14% 4	4824
	21st to end	Night	48% 9% 13% 17% 13% 1	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	8% 4 17% 35% 33% 3	300
	11th to 20th	Day	10% 5% 17% 41% 23% 4	300
	21st to end	Day	9% 4 21% 40% 24% 2	330
February	1st to 10th	Day	3 4 13% 36% 39% 6%	300
	11th to 20th	Day	4 3 10% 33% 44% 6%	382
	21st to end	Day	5% 1 14% 32% 42% 7%	414
March	1st to 10th	Day	4 2 14% 43% 33% 3	500
	11th to 20th	Day	5% 1 14% 37% 37% 5%	500
	21st to end	Day	4 3 12% 36% 42% 3	550
April	1st to 10th	Day	2 1 9% 41% 44% 3	500
	11th to 20th	Day	2 1 10% 44% 38% 4	492
	21st to end	Day	5% 1 4 39% 48% 4	500
May	1st to 10th	Day	4 4 30% 52% 11%	503
	11th to 20th	Day	9% 2 4 28% 46% 12%	527
	21st to end	Day	9% 1 3 14% 50% 23%	573
June	1st to 10th	Day	11% 2 4 16% 38% 29%	530
	11th to 20th	Day	6% 2 3 12% 35% 42%	530
	21st to end	Day	4 1 1 5% 31% 58%	530
July	1st to 10th	Day	4 1 1 3 31% 60%	525
	11th to 20th	Day	3 1 2 3 31% 60%	524
	21st to end	Day	5% 1 1 4 32% 58%	532
August	1st to 10th	Day	4 1 4 36% 54%	486
	11th to 20th	Day	2 1 4 33% 59%	479
	21st to end	Day	5% 1 4 8% 35% 47%	539
September	1st to 10th	Day	7% 1 1 6% 30% 56%	490
	11th to 20th	Day	5% 1 2 6% 26% 60%	490
	21st to end	Day	8% 2 5% 10% 31% 44%	490
October	1st to 10th	Day	6% 1 4 18% 51% 20%	490
	11th to 20th	Day	11% 2 6% 21% 40% 21%	490
	21st to end	Day	9% 3 11% 25% 40% 13%	539
November	1st to 10th	Day	6% 3 12% 27% 40% 11%	495
	11th to 20th	Day	7% 3 14% 28% 38% 11%	500
	21st to end	Day	6% 2 14% 32% 37% 9%	500
December	1st to 10th	Day	9% 3 11% 29% 41% 8%	465
	11th to 20th	Day	6% 3 12% 28% 40% 11%	300
	21st to end	Day	9% 3 12% 30% 38% 7%	330
January	1st to 10th	Night	7% 3 14% 35% 35% 6%	800
	11th to 20th	Night	10% 3 19% 35% 30% 3	800
	21st to end	Night	7% 6% 21% 33% 31% 2	880
February	1st to 10th	Night	6% 4 15% 35% 37% 3	800
	11th to 20th	Night	6% 2 17% 36% 35% 4	783
	21st to end	Night	4 2 12% 34% 42% 6%	660
March	1st to 10th	Night	3 2 16% 43% 32% 4	800
	11th to 20th	Night	3 1 13% 40% 39% 4	800
	21st to end	Night	4 2 16% 38% 36% 3	880
April	1st to 10th	Night	3 1 9% 43% 41% 3	800
	11th to 20th	Night	6% 3 11% 41% 36% 3	791
	21st to end	Night	4 1 9% 43% 40% 3	800
May	1st to 10th	Night	3 1 6% 34% 46% 10%	800
	11th to 20th	Night	9% 2 7% 29% 45% 8%	760
	21st to end	Night	8% 1 6% 17% 52% 16%	650
June	1st to 10th	Night	14% 3 7% 18% 41% 18%	600
	11th to 20th	Night	7% 1 3 11% 42% 37%	600
	21st to end	Night	4 1 1 9% 35% 52%	600
July	1st to 10th	Night	2 2 5% 34% 57%	585
	11th to 20th	Night	3 1 1 6% 37% 52%	582
	21st to end	Night	3 2 5% 32% 57%	624
August	1st to 10th	Night	3 1 1 6% 40% 49%	567
	11th to 20th	Night	3 1 1 6% 33% 56%	747
	21st to end	Night	7% 1 3 9% 36% 44%	836
September	1st to 10th	Night	6% 1 2 6% 35% 51%	760
	11th to 20th	Night	7% 3 9% 29% 52%	760
	21st to end	Night	10% 1 5% 10% 35% 39%	760
October	1st to 10th	Night	8% 1 6% 19% 46% 20%	760
	11th to 20th	Night	9% 2 6% 19% 43% 21%	760
	21st to end	Night	13% 1 9% 30% 33% 13%	836
November	1st to 10th	Night	11% 3 14% 28% 36% 8%	780
	11th to 20th	Night	8% 2 10% 29% 41% 10%	800
	21st to end	Night	6% 2 14% 35% 36% 7%	800
December	1st to 10th	Night	7% 3 11% 32% 38% 8%	800
	11th to 20th	Night	8% 4 13% 31% 38% 6%	800
	21st to end	Night	7% 4 14% 33% 34% 8%	880

Page generated at 2025-07-18 01:09:57. Version ac07

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