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 2024-04-10.

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% 4 8% 7% 4 5% 5% 6% 7% 32%	82746
	Night	14% 10% 4 7% 6% 3 5% 5% 5% 7% 33%	86057
Transparency	Day	49% 8% 13% 19% 10% 1	82449
	Night	49% 8% 13% 20% 10% 1	85875
Seeing	Day	17% 15% 32% 22% 10% 3	14656
	Night	18% 12% 32% 27% 10% 1	24472

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% 14% 7% 11% 8% 5% 5% 5% 5% 6% 21%	2527
	11th to 20th	Day	15% 14% 6% 14% 12% 8% 6% 5% 5% 5% 11%	2530
	21st to end	Day	20% 19% 7% 9% 7% 3 4 4 4 6% 15%	2828
February	1st to 10th	Day	13% 12% 6% 10% 9% 5% 7% 6% 4 5% 23%	1710
	11th to 20th	Day	12% 11% 6% 12% 9% 4 6% 5% 5% 5% 25%	1787
	21st to end	Day	12% 14% 5% 9% 7% 4 7% 4 5% 7% 25%	1570
March	1st to 10th	Day	14% 12% 5% 7% 8% 4 5% 4 4 6% 31%	3138
	11th to 20th	Day	12% 10% 6% 8% 8% 4 5% 5% 6% 7% 30%	3480
	21st to end	Day	17% 11% 5% 8% 7% 5% 6% 4 4 5% 29%	3815
April	1st to 10th	Day	17% 11% 6% 8% 6% 3 4 4 5% 6% 30%	2259
	11th to 20th	Day	17% 10% 3 6% 6% 3 4 4 5% 7% 36%	2276
	21st to end	Day	14% 9% 3 8% 7% 3 6% 5% 6% 6% 33%	2340
May	1st to 10th	Day	15% 7% 3 8% 6% 4 5% 5% 5% 7% 34%	2340
	11th to 20th	Day	16% 6% 3 6% 6% 3 5% 5% 5% 6% 39%	2301
	21st to end	Day	11% 6% 2 5% 5% 4 5% 5% 5% 8% 44%	2689
June	1st to 10th	Day	12% 6% 3 6% 5% 3 5% 6% 6% 9% 40%	2700
	11th to 20th	Day	11% 6% 3 5% 5% 4 4 6% 6% 9% 41%	2700
	21st to end	Day	10% 4 3 6% 6% 3 5% 6% 7% 10% 39%	2698
July	1st to 10th	Day	5% 4 2 5% 5% 4 5% 6% 8% 10% 47%	2520
	11th to 20th	Day	8% 5% 3 6% 5% 4 5% 5% 8% 9% 43%	2520
	21st to end	Day	7% 3 2 6% 6% 4 7% 6% 7% 9% 43%	2719
August	1st to 10th	Day	8% 5% 2 6% 6% 4 5% 7% 7% 9% 40%	2327
	11th to 20th	Day	8% 4 3 6% 6% 3 6% 5% 7% 9% 44%	2303
	21st to end	Day	10% 7% 2 6% 5% 4 5% 4 6% 7% 43%	2544
September	1st to 10th	Day	10% 6% 2 6% 6% 4 5% 5% 6% 9% 40%	2075
	11th to 20th	Day	11% 5% 3 4 5% 3 4 5% 6% 9% 45%	1980
	21st to end	Day	13% 6% 3 7% 6% 3 5% 6% 5% 10% 36%	1980
October	1st to 10th	Day	16% 7% 2 7% 6% 3 4 5% 5% 7% 39%	1943
	11th to 20th	Day	19% 11% 4 8% 7% 4 5% 4 5% 7% 27%	1782
	21st to end	Day	20% 10% 4 8% 7% 4 6% 5% 6% 7% 23%	1782
November	1st to 10th	Day	12% 9% 4 8% 6% 4 7% 5% 7% 7% 31%	1672
	11th to 20th	Day	14% 12% 4 9% 9% 4 6% 6% 5% 7% 25%	1710
	21st to end	Day	17% 14% 7% 7% 8% 3 5% 5% 5% 5% 24%	1538
December	1st to 10th	Day	13% 14% 5% 12% 7% 5% 6% 5% 5% 6% 21%	1423
	11th to 20th	Day	15% 15% 6% 9% 7% 3 5% 6% 6% 6% 23%	1675
	21st to end	Day	27% 22% 7% 11% 6% 3 4 3 3 3 10%	2565
January	1st to 10th	Night	14% 13% 7% 10% 7% 4 5% 4 4 6% 25%	4428
	11th to 20th	Night	13% 14% 6% 11% 13% 6% 6% 5% 5% 5% 15%	4440
	21st to end	Night	17% 18% 8% 10% 7% 3 5% 5% 5% 5% 17%	4823
February	1st to 10th	Night	12% 12% 6% 9% 9% 4 5% 6% 6% 7% 25%	2470
	11th to 20th	Night	13% 12% 5% 8% 7% 4 5% 6% 6% 6% 28%	2276
	21st to end	Night	15% 15% 5% 9% 7% 3 4 4 5% 6% 26%	1884
March	1st to 10th	Night	14% 8% 3 6% 6% 3 5% 4 4 7% 40%	3715
	11th to 20th	Night	10% 8% 4 6% 6% 3 5% 5% 6% 7% 41%	3480
	21st to end	Night	14% 10% 4 8% 7% 3 5% 5% 5% 6% 34%	3817
April	1st to 10th	Night	16% 9% 3 8% 6% 3 4 5% 5% 7% 34%	1928
	11th to 20th	Night	18% 7% 3 5% 6% 3 4 4 6% 7% 37%	1633
	21st to end	Night	17% 9% 3 6% 6% 4 4 4 5% 6% 37%	1620
May	1st to 10th	Night	11% 7% 4 7% 6% 4 6% 6% 5% 8% 36%	1620
	11th to 20th	Night	15% 7% 3 5% 5% 3 4 5% 5% 8% 38%	1592
	21st to end	Night	12% 4 2 5% 5% 3 4 4 6% 9% 48%	1579
June	1st to 10th	Night	12% 6% 3 4 4 3 5% 5% 5% 9% 44%	1260
	11th to 20th	Night	10% 4 3 5% 5% 3 5% 5% 6% 9% 46%	1260
	21st to end	Night	7% 5% 2 5% 6% 4 5% 5% 7% 8% 45%	1260
July	1st to 10th	Night	5% 3 2 3 4 2 4 4 7% 8% 57%	1436
	11th to 20th	Night	6% 4 2 4 5% 3 5% 5% 6% 8% 52%	1440
	21st to end	Night	7% 4 2 5% 4 3 4 5% 6% 8% 52%	1597
August	1st to 10th	Night	6% 4 2 4 4 3 4 5% 8% 9% 50%	1611
	11th to 20th	Night	7% 4 2 4 4 2 4 5% 6% 9% 53%	1598
	21st to end	Night	10% 5% 2 3 4 3 4 4 6% 8% 50%	1808
September	1st to 10th	Night	8% 5% 2 5% 5% 3 4 5% 6% 8% 49%	1866
	11th to 20th	Night	10% 4 2 4 4 3 4 4 5% 7% 53%	1980
	21st to end	Night	12% 6% 3 6% 5% 3 4 4 6% 8% 41%	1980
October	1st to 10th	Night	14% 7% 3 5% 4 2 4 5% 5% 8% 43%	2016
	11th to 20th	Night	18% 10% 4 7% 7% 3 5% 4 5% 7% 33%	2176
	21st to end	Night	22% 10% 3 6% 5% 3 5% 4 5% 7% 30%	2574
November	1st to 10th	Night	11% 9% 3 7% 6% 3 4 5% 6% 7% 39%	2406
	11th to 20th	Night	13% 10% 5% 8% 7% 4 6% 6% 6% 8% 27%	2470
	21st to end	Night	17% 12% 5% 9% 6% 4 4 5% 5% 6% 27%	2640
December	1st to 10th	Night	16% 13% 6% 10% 7% 3 5% 6% 4 6% 23%	2755
	11th to 20th	Night	14% 14% 5% 10% 7% 3 5% 6% 6% 7% 22%	3522
	21st to end	Night	26% 22% 6% 9% 6% 3 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	55% 6% 11% 17% 10% 1	2259
	11th to 20th	Day	47% 6% 11% 19% 15% 1	2276
	21st to end	Day	50% 7% 13% 15% 14% 2	2340
May	1st to 10th	Day	47% 8% 9% 22% 12% 2	2340
	11th to 20th	Day	44% 7% 11% 22% 14% 2	2305
	21st to end	Day	38% 7% 16% 23% 15% 1	2689
June	1st to 10th	Day	39% 8% 14% 24% 14% 2	2700
	11th to 20th	Day	37% 8% 12% 23% 17% 2	2700
	21st to end	Day	38% 8% 14% 24% 14% 1	2698
July	1st to 10th	Day	29% 8% 15% 27% 18% 3	2451
	11th to 20th	Day	35% 8% 14% 25% 16% 2	2445
	21st to end	Day	36% 10% 14% 22% 16% 3	2568
August	1st to 10th	Day	38% 10% 15% 24% 12% 1	2314
	11th to 20th	Day	35% 9% 15% 26% 14% 1	2303
	21st to end	Day	38% 8% 13% 26% 13% 2	2544
September	1st to 10th	Day	39% 8% 15% 26% 11% 2	2075
	11th to 20th	Day	35% 7% 17% 29% 12%	1980
	21st to end	Day	43% 8% 14% 25% 9%	1980
October	1st to 10th	Day	45% 7% 11% 25% 12% 1	1943
	11th to 20th	Day	56% 7% 14% 17% 6%	1782
	21st to end	Day	58% 8% 14% 13% 6%	1782
November	1st to 10th	Day	50% 9% 12% 20% 9%	1672
	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% 10% 20% 13% 2	1928
	11th to 20th	Night	44% 6% 10% 21% 16% 2	1633
	21st to end	Night	47% 5% 10% 20% 15% 4	1620
May	1st to 10th	Night	44% 7% 12% 21% 13% 3	1620
	11th to 20th	Night	42% 7% 11% 22% 14% 4	1593
	21st to end	Night	34% 6% 14% 28% 14% 4	1580
June	1st to 10th	Night	36% 7% 12% 25% 17% 2	1260
	11th to 20th	Night	33% 8% 16% 22% 18% 2	1260
	21st to end	Night	34% 10% 12% 26% 16% 3	1260
July	1st to 10th	Night	23% 7% 14% 32% 21% 3	1396
	11th to 20th	Night	29% 6% 16% 30% 18% 1	1392
	21st to end	Night	29% 8% 17% 27% 18% 2	1508
August	1st to 10th	Night	27% 9% 19% 31% 13% 1	1600
	11th to 20th	Night	27% 8% 15% 32% 16% 1	1598
	21st to end	Night	31% 7% 15% 29% 17% 1	1808
September	1st to 10th	Night	32% 7% 13% 28% 18% 1	1866
	11th to 20th	Night	30% 6% 14% 37% 13%	1980
	21st to end	Night	40% 7% 15% 29% 9% 1	1980
October	1st to 10th	Night	38% 7% 14% 27% 12% 2	2016
	11th to 20th	Night	50% 7% 12% 21% 8% 1	2176
	21st to end	Night	53% 7% 12% 19% 8%	2574
November	1st to 10th	Night	42% 8% 15% 25% 10% 1	2406
	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% 20% 32% 19% 5%	457
	11th to 20th	Day	26% 20% 29% 14% 8% 2	412
	21st to end	Day	23% 16% 30% 22% 7% 2	420
May	1st to 10th	Day	19% 19% 35% 15% 8% 3	423
	11th to 20th	Day	18% 14% 35% 20% 9% 4	447
	21st to end	Day	14% 13% 31% 27% 11% 4	630
June	1st to 10th	Day	14% 13% 37% 25% 8% 3	630
	11th to 20th	Day	13% 13% 36% 24% 10% 4	630
	21st to end	Day	12% 9% 37% 29% 10% 3	630
July	1st to 10th	Day	5% 7% 34% 30% 18% 5%	621
	11th to 20th	Day	9% 11% 33% 29% 12% 6%	618
	21st to end	Day	9% 6% 34% 33% 13% 5%	660
August	1st to 10th	Day	9% 6% 27% 29% 19% 9%	446
	11th to 20th	Day	9% 6% 22% 33% 19% 11%	439
	21st to end	Day	13% 9% 24% 32% 17% 6%	495
September	1st to 10th	Day	14% 8% 27% 27% 15% 8%	450
	11th to 20th	Day	10% 8% 24% 28% 21% 8%	450
	21st to end	Day	20% 11% 23% 24% 15% 6%	450
October	1st to 10th	Day	20% 16% 29% 21% 13% 2	450
	11th to 20th	Day	22% 22% 32% 19% 4 1	432
	21st to end	Day	27% 22% 35% 12% 3 1	297
November	1st to 10th	Day	20% 20% 38% 15% 6% 1	270
	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	21% 12% 33% 24% 8% 2	533
	21st to end	Night	20% 9% 29% 32% 8%	540
May	1st to 10th	Night	12% 9% 37% 32% 9% 1	540
	11th to 20th	Night	16% 9% 28% 34% 12% 1	531
	21st to end	Night	16% 4 28% 32% 19% 1	566
June	1st to 10th	Night	14% 6% 32% 37% 12%	360
	11th to 20th	Night	13% 5% 32% 35% 16%	360
	21st to end	Night	8% 5% 32% 34% 19% 2	360
July	1st to 10th	Night	6% 3 23% 45% 22% 2	521
	11th to 20th	Night	7% 4 23% 40% 22% 4	522
	21st to end	Night	9% 2 25% 42% 20% 1	591
August	1st to 10th	Night	9% 2 23% 41% 23% 2	537
	11th to 20th	Night	9% 3 20% 35% 29% 4	534
	21st to end	Night	10% 5% 22% 38% 23% 2	594
September	1st to 10th	Night	10% 5% 25% 34% 21% 4	606
	11th to 20th	Night	12% 7% 22% 36% 20% 4	720
	21st to end	Night	17% 8% 24% 29% 18% 4	720
October	1st to 10th	Night	18% 11% 28% 27% 16% 1	720
	11th to 20th	Night	22% 15% 33% 23% 6%	720
	21st to end	Night	26% 15% 32% 22% 5% 1	792
November	1st to 10th	Night	16% 14% 37% 21% 10% 1	740
	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 2024-04-07 09:28:09. Version ac07

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