Cedar Springs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Springs Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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	13% 9% 3 8% 6% 5% 5% 4 6% 7% 34%	101069
	Night	13% 10% 4 8% 5% 5% 4 4 5% 7% 34%	97964
Transparency	Day	47% 7% 13% 21% 12% 1	104642
	Night	47% 7% 13% 21% 11% 1	102532
Seeing	Day	17% 15% 32% 23% 10% 3	15540
	Night	18% 12% 32% 27% 10% 1	25123

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	14% 15% 6% 12% 7% 5% 6% 3 5% 5% 21%	2527
	11th to 20th	Day	15% 15% 6% 16% 10% 10% 5% 4 5% 5% 11%	2530
	21st to end	Day	20% 20% 6% 10% 6% 4 4 4 4 6% 15%	2828
February	1st to 10th	Day	12% 13% 5% 11% 8% 7% 6% 5% 4 5% 23%	1710
	11th to 20th	Day	11% 12% 6% 13% 8% 6% 5% 4 5% 5% 24%	1787
	21st to end	Day	12% 14% 5% 10% 7% 6% 6% 3 6% 6% 25%	1570
March	1st to 10th	Day	14% 12% 5% 9% 7% 5% 5% 3 4 6% 31%	3138
	11th to 20th	Day	12% 10% 5% 9% 7% 5% 5% 4 6% 7% 30%	3480
	21st to end	Day	17% 11% 4 9% 6% 6% 5% 3 4 5% 29%	3815
April	1st to 10th	Day	17% 12% 4 8% 5% 4 4 4 5% 6% 31%	2270
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 5% 7% 36%	2404
	21st to end	Day	15% 9% 3 9% 6% 5% 5% 4 5% 6% 34%	2470
May	1st to 10th	Day	13% 9% 3 9% 6% 5% 5% 5% 6% 7% 34%	4082
	11th to 20th	Day	14% 6% 2 6% 4 4 4 5% 7% 8% 40%	4081
	21st to end	Day	10% 6% 2 5% 4 4 4 3 4 8% 48%	4773
June	1st to 10th	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 9% 39%	2850
	11th to 20th	Day	11% 6% 3 6% 5% 4 5% 5% 6% 9% 41%	2850
	21st to end	Day	11% 5% 3 6% 6% 4 6% 5% 7% 9% 38%	2847
July	1st to 10th	Day	10% 6% 3 9% 6% 5% 6% 5% 8% 8% 35%	4440
	11th to 20th	Day	6% 5% 2 6% 4 5% 5% 5% 7% 9% 46%	4440
	21st to end	Day	6% 4 2 7% 5% 6% 7% 5% 7% 9% 41%	4763
August	1st to 10th	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 9% 40%	4104
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 5% 7% 8% 44%	4044
	21st to end	Day	9% 7% 2 7% 5% 5% 5% 4 7% 7% 42%	4474
September	1st to 10th	Day	9% 6% 2 7% 5% 6% 5% 4 6% 9% 41%	2190
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 9% 46%	2090
	21st to end	Day	12% 7% 3 8% 5% 5% 5% 4 5% 9% 37%	2090
October	1st to 10th	Day	15% 7% 2 7% 5% 4 4 4 5% 6% 41%	2050
	11th to 20th	Day	18% 11% 3 9% 5% 5% 5% 3 5% 7% 28%	1881
	21st to end	Day	19% 10% 4 9% 6% 6% 6% 4 6% 7% 23%	1881
November	1st to 10th	Day	11% 10% 3 9% 5% 6% 6% 4 7% 7% 31%	1699
	11th to 20th	Day	13% 13% 4 10% 7% 5% 7% 4 5% 7% 25%	1710
	21st to end	Day	17% 15% 7% 9% 7% 5% 4 4 5% 5% 23%	1538
December	1st to 10th	Day	13% 14% 5% 13% 6% 6% 6% 4 5% 6% 21%	1423
	11th to 20th	Day	14% 16% 5% 10% 6% 5% 4 5% 6% 6% 23%	1675
	21st to end	Day	27% 24% 7% 12% 5% 4 3 2 3 3 10%	2565
January	1st to 10th	Night	14% 14% 6% 12% 5% 5% 5% 3 5% 6% 25%	4428
	11th to 20th	Night	12% 15% 6% 13% 11% 8% 6% 4 5% 5% 15%	4440
	21st to end	Night	17% 19% 7% 12% 6% 4 4 4 5% 5% 17%	4823
February	1st to 10th	Night	12% 14% 5% 10% 7% 6% 5% 5% 6% 6% 25%	2470
	11th to 20th	Night	13% 13% 5% 9% 6% 5% 5% 4 7% 6% 27%	2276
	21st to end	Night	15% 16% 4 10% 6% 5% 4 3 5% 7% 26%	1884
March	1st to 10th	Night	14% 9% 3 7% 5% 5% 4 3 4 7% 40%	3715
	11th to 20th	Night	10% 9% 3 7% 5% 4 4 4 6% 7% 41%	3480
	21st to end	Night	14% 11% 4 9% 6% 4 5% 4 5% 6% 34%	3817
April	1st to 10th	Night	16% 10% 3 9% 5% 4 4 4 5% 7% 34%	1928
	11th to 20th	Night	18% 8% 3 6% 5% 5% 4 3 5% 6% 37%	1725
	21st to end	Night	16% 9% 2 7% 5% 5% 4 3 5% 6% 37%	1710
May	1st to 10th	Night	11% 8% 3 7% 6% 5% 5% 4 5% 7% 39%	2813
	11th to 20th	Night	13% 8% 2 6% 4 4 5% 4 6% 9% 39%	2812
	21st to end	Night	12% 6% 2 6% 4 3 3 3 6% 7% 47%	2784
June	1st to 10th	Night	12% 7% 2 6% 3 5% 4 4 5% 8% 43%	1330
	11th to 20th	Night	10% 4 3 6% 4 4 5% 4 7% 9% 46%	1330
	21st to end	Night	8% 5% 2 6% 6% 5% 5% 3 8% 8% 44%	1330
July	1st to 10th	Night	8% 7% 2 7% 5% 4 5% 4 7% 9% 43%	2526
	11th to 20th	Night	6% 4 2 4 5% 4 5% 4 6% 7% 54%	2530
	21st to end	Night	6% 5% 2 7% 4 5% 5% 4 6% 9% 48%	2796
August	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 7% 8% 49%	2825
	11th to 20th	Night	11% 5% 2 5% 3 4 4 3 6% 8% 49%	2785
	21st to end	Night	8% 5% 2 5% 4 4 5% 3 6% 8% 50%	3178
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 8% 50%	1970
	11th to 20th	Night	9% 4 2 5% 3 4 3 3 5% 7% 55%	2090
	21st to end	Night	13% 7% 3 7% 4 4 4 4 6% 8% 41%	2090
October	1st to 10th	Night	14% 6% 2 5% 3 3 4 4 5% 8% 45%	2129
	11th to 20th	Night	17% 10% 3 8% 5% 4 4 3 5% 7% 34%	2297
	21st to end	Night	20% 10% 3 8% 4 4 5% 3 5% 7% 31%	2717
November	1st to 10th	Night	11% 10% 3 8% 5% 4 4 4 6% 7% 38%	2452
	11th to 20th	Night	13% 11% 4 9% 6% 5% 5% 5% 7% 7% 27%	2470
	21st to end	Night	17% 13% 4 10% 5% 5% 4 4 5% 6% 26%	2640
December	1st to 10th	Night	15% 15% 5% 11% 7% 5% 5% 5% 4 5% 23%	2755
	11th to 20th	Night	14% 15% 5% 11% 6% 5% 5% 4 6% 7% 22%	3522
	21st to end	Night	25% 23% 5% 10% 5% 4 4 3 3 4 13%	5097

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	63% 8% 15% 10% 3	2528
	11th to 20th	Day	72% 10% 8% 7% 2	2530
	21st to end	Day	70% 6% 14% 7% 2	2828
February	1st to 10th	Day	61% 7% 10% 16% 5%	1710
	11th to 20th	Day	60% 7% 11% 15% 7% 1	1797
	21st to end	Day	58% 7% 12% 16% 5% 1	1570
March	1st to 10th	Day	53% 6% 12% 21% 7% 1	3138
	11th to 20th	Day	49% 9% 14% 18% 8% 2	3480
	21st to end	Day	56% 7% 9% 16% 11% 1	3815
April	1st to 10th	Day	54% 6% 11% 17% 11% 1	2270
	11th to 20th	Day	47% 6% 11% 20% 15% 1	2404
	21st to end	Day	49% 6% 12% 16% 14% 2	2470
May	1st to 10th	Day	43% 10% 11% 17% 17% 2	4120
	11th to 20th	Day	37% 9% 14% 25% 13% 1	4085
	21st to end	Day	34% 6% 13% 21% 22% 3	4787
June	1st to 10th	Day	39% 8% 14% 24% 13% 2	2850
	11th to 20th	Day	38% 7% 12% 23% 18% 2	2850
	21st to end	Day	40% 8% 14% 24% 14% 1	2847
July	1st to 10th	Day	44% 5% 14% 20% 15% 2	4371
	11th to 20th	Day	33% 5% 14% 30% 17% 1	4365
	21st to end	Day	38% 6% 15% 20% 20% 1	4613
August	1st to 10th	Day	39% 7% 12% 27% 14% 1	4091
	11th to 20th	Day	38% 5% 14% 30% 12% 1	4083
	21st to end	Day	40% 6% 14% 27% 12% 1	4473
September	1st to 10th	Day	38% 7% 14% 27% 12% 2	2190
	11th to 20th	Day	34% 7% 16% 29% 13% 1	2090
	21st to end	Day	43% 8% 13% 25% 11%	2090
October	1st to 10th	Day	33% 4 9% 33% 18% 3	3401
	11th to 20th	Day	46% 4 12% 25% 13%	3109
	21st to end	Day	55% 5% 12% 19% 9%	3081
November	1st to 10th	Day	50% 9% 12% 20% 9%	1699
	11th to 20th	Day	55% 9% 16% 12% 7%	1710
	21st to end	Day	62% 8% 12% 13% 4 1	1538
December	1st to 10th	Day	61% 9% 13% 14% 2	1423
	11th to 20th	Day	60% 9% 15% 13% 4 1	1671
	21st to end	Day	80% 5% 7% 6% 2	2565
January	1st to 10th	Night	58% 9% 12% 14% 6% 1	4428
	11th to 20th	Night	69% 9% 10% 9% 3	4440
	21st to end	Night	68% 7% 11% 10% 3	4823
February	1st to 10th	Night	57% 8% 10% 17% 8% 1	2470
	11th to 20th	Night	54% 7% 12% 19% 7% 1	2277
	21st to end	Night	57% 7% 11% 17% 7% 1	1884
March	1st to 10th	Night	44% 7% 16% 25% 8% 1	3715
	11th to 20th	Night	39% 8% 17% 22% 13% 2	3480
	21st to end	Night	48% 9% 14% 18% 9% 1	3817
April	1st to 10th	Night	49% 6% 9% 20% 13% 2	1928
	11th to 20th	Night	45% 6% 9% 21% 16% 2	1725
	21st to end	Night	47% 5% 10% 20% 15% 4	1710
May	1st to 10th	Night	40% 8% 13% 19% 17% 3	2840
	11th to 20th	Night	37% 8% 13% 27% 13% 2	2813
	21st to end	Night	36% 6% 13% 23% 16% 6%	2791
June	1st to 10th	Night	37% 7% 12% 25% 18% 2	1330
	11th to 20th	Night	33% 8% 16% 22% 19% 2	1330
	21st to end	Night	35% 9% 12% 26% 16% 3	1330
July	1st to 10th	Night	37% 4 14% 25% 14% 5%	2486
	11th to 20th	Night	29% 4 13% 39% 15% 1	2482
	21st to end	Night	34% 5% 18% 23% 18% 1	2707
August	1st to 10th	Night	33% 6% 15% 31% 15% 1	2814
	11th to 20th	Night	33% 5% 16% 31% 14% 1	2812
	21st to end	Night	31% 5% 15% 32% 16% 1	3178
September	1st to 10th	Night	32% 7% 13% 29% 18% 1	1970
	11th to 20th	Night	29% 5% 14% 37% 16%	2090
	21st to end	Night	40% 6% 15% 28% 10% 1	2090
October	1st to 10th	Night	29% 4 12% 35% 19% 1	3558
	11th to 20th	Night	43% 4 12% 26% 15%	3808
	21st to end	Night	47% 4 12% 27% 9%	4467
November	1st to 10th	Night	42% 8% 15% 24% 9% 1	2452
	11th to 20th	Night	53% 9% 15% 17% 6%	2470
	21st to end	Night	58% 8% 15% 14% 4	2640
December	1st to 10th	Night	61% 8% 12% 15% 5%	2755
	11th to 20th	Night	59% 9% 14% 11% 6% 1	3525
	21st to end	Night	75% 7% 7% 8% 3	5097

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	20% 21% 38% 16% 4 1	270
	11th to 20th	Day	23% 20% 39% 16% 3	270
	21st to end	Day	23% 18% 36% 19% 4 1	297
February	1st to 10th	Day	19% 29% 35% 14% 2 1	270
	11th to 20th	Day	19% 28% 39% 11% 2	270
	21st to end	Day	24% 32% 35% 8% 1	225
March	1st to 10th	Day	24% 27% 39% 10% 1	275
	11th to 20th	Day	22% 17% 34% 20% 7% 1	460
	21st to end	Day	26% 16% 33% 19% 5% 1	506
April	1st to 10th	Day	23% 21% 32% 19% 5%	460
	11th to 20th	Day	27% 22% 28% 14% 7% 2	452
	21st to end	Day	23% 16% 30% 21% 7% 2	460
May	1st to 10th	Day	19% 19% 36% 15% 8% 3	463
	11th to 20th	Day	17% 15% 34% 21% 10% 4	487
	21st to end	Day	14% 13% 31% 28% 11% 3	683
June	1st to 10th	Day	14% 14% 37% 25% 8% 3	680
	11th to 20th	Day	13% 14% 37% 24% 9% 3	680
	21st to end	Day	13% 10% 37% 28% 9% 3	680
July	1st to 10th	Day	6% 8% 34% 30% 17% 5%	671
	11th to 20th	Day	9% 11% 33% 30% 12% 6%	668
	21st to end	Day	9% 6% 33% 33% 14% 5%	713
August	1st to 10th	Day	10% 7% 27% 29% 19% 8%	486
	11th to 20th	Day	9% 6% 22% 34% 19% 10%	479
	21st to end	Day	12% 8% 24% 33% 16% 6%	539
September	1st to 10th	Day	13% 9% 28% 26% 16% 8%	490
	11th to 20th	Day	10% 8% 23% 28% 22% 10%	490
	21st to end	Day	19% 10% 24% 26% 14% 6%	490
October	1st to 10th	Day	19% 16% 29% 21% 13% 2	490
	11th to 20th	Day	21% 21% 32% 20% 5% 1	471
	21st to end	Day	27% 22% 35% 13% 3 1	330
November	1st to 10th	Day	21% 20% 37% 16% 5% 1	279
	11th to 20th	Day	20% 25% 35% 14% 6%	270
	21st to end	Day	22% 26% 34% 15% 3	188
December	1st to 10th	Day	23% 21% 38% 12% 4 1	180
	11th to 20th	Day	22% 29% 35% 13% 1	180
	21st to end	Day	29% 27% 30% 12% 2	238
January	1st to 10th	Night	19% 17% 36% 22% 5% 1	950
	11th to 20th	Night	21% 16% 35% 21% 6%	950
	21st to end	Night	18% 11% 35% 30% 6%	1010
February	1st to 10th	Night	18% 17% 39% 23% 3	760
	11th to 20th	Night	21% 17% 36% 22% 4	743
	21st to end	Night	25% 16% 36% 20% 3	628
March	1st to 10th	Night	17% 13% 40% 24% 7%	760
	11th to 20th	Night	18% 16% 36% 24% 5% 1	760
	21st to end	Night	22% 14% 32% 26% 4 1	836
April	1st to 10th	Night	21% 14% 35% 24% 6% 1	598
	11th to 20th	Night	22% 13% 33% 23% 7% 2	563
	21st to end	Night	21% 10% 29% 32% 8%	570
May	1st to 10th	Night	12% 9% 36% 33% 9% 1	570
	11th to 20th	Night	16% 9% 28% 35% 12% 1	561
	21st to end	Night	15% 5% 28% 31% 19% 1	598
June	1st to 10th	Night	14% 6% 32% 37% 11%	380
	11th to 20th	Night	12% 5% 32% 36% 15%	380
	21st to end	Night	10% 5% 32% 34% 18% 2	380
July	1st to 10th	Night	6% 3 24% 44% 21% 2	551
	11th to 20th	Night	7% 4 23% 40% 21% 4	552
	21st to end	Night	10% 2 24% 41% 21% 1	624
August	1st to 10th	Night	8% 2 24% 41% 23% 2	567
	11th to 20th	Night	9% 3 20% 36% 28% 3	564
	21st to end	Night	10% 5% 22% 39% 23% 1	627
September	1st to 10th	Night	10% 6% 26% 33% 22% 4	640
	11th to 20th	Night	11% 6% 21% 35% 22% 4	760
	21st to end	Night	17% 8% 24% 29% 18% 4	760
October	1st to 10th	Night	17% 11% 29% 27% 16% 1	760
	11th to 20th	Night	21% 14% 33% 24% 7%	760
	21st to end	Night	25% 15% 32% 23% 5% 1	836
November	1st to 10th	Night	16% 14% 37% 21% 10% 1	755
	11th to 20th	Night	19% 18% 38% 19% 6%	760
	21st to end	Night	23% 14% 38% 20% 4	760
December	1st to 10th	Night	23% 16% 35% 21% 4	855
	11th to 20th	Night	23% 16% 38% 18% 4	950
	21st to end	Night	28% 16% 34% 20% 2	1045

Page generated at 2024-11-01 22:47:48. Version ac07

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