Sycamore Stars Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sycamore Stars Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	14% 11% 4 9% 5% 4 4 3 5% 7% 33%	126912
	Night	15% 13% 5% 10% 5% 4 4 3 4 6% 31%	124335
Transparency	Day	50% 5% 11% 21% 12% 1	130452
	Night	54% 4 10% 19% 12% 1	128869
Seeing	Day	20% 13% 30% 22% 11% 4	17300
	Night	20% 10% 28% 29% 11% 1	27164

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	12% 21% 9% 21% 6% 4 4 2 4 5% 13%	3617
	11th to 20th	Day	11% 17% 8% 22% 11% 12% 4 2 3 3 6%	3620
	21st to end	Day	18% 21% 7% 17% 6% 3 5% 2 3 4 13%	3982
February	1st to 10th	Day	14% 17% 6% 16% 9% 6% 4 3 3 3 18%	1872
	11th to 20th	Day	14% 15% 7% 16% 9% 5% 4 3 4 5% 19%	1948
	21st to end	Day	16% 18% 5% 12% 5% 5% 5% 3 4 6% 21%	1650
March	1st to 10th	Day	15% 12% 5% 12% 5% 4 4 3 4 6% 29%	4480
	11th to 20th	Day	10% 11% 5% 8% 5% 5% 4 4 6% 8% 35%	4837
	21st to end	Day	18% 16% 7% 8% 5% 4 4 3 4 5% 24%	5679
April	1st to 10th	Day	17% 16% 4 6% 5% 4 4 3 5% 5% 29%	2400
	11th to 20th	Day	17% 12% 3 6% 4 3 3 5% 5% 5% 37%	2422
	21st to end	Day	17% 10% 3 7% 4 5% 4 3 5% 7% 35%	2600
May	1st to 10th	Day	19% 8% 3 6% 4 4 4 3 6% 6% 36%	5862
	11th to 20th	Day	14% 7% 3 7% 5% 4 5% 4 6% 7% 38%	5861
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 43%	6884
June	1st to 10th	Day	10% 6% 2 7% 5% 4 5% 3 6% 8% 44%	2800
	11th to 20th	Day	10% 6% 2 6% 5% 4 4 4 6% 9% 44%	2800
	21st to end	Day	10% 5% 2 7% 5% 5% 5% 4 6% 8% 42%	2800
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 10% 40%	6360
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 6% 10% 45%	6360
	21st to end	Day	8% 6% 2 6% 4 4 5% 4 7% 10% 45%	6924
August	1st to 10th	Day	11% 5% 2 6% 4 4 4 4 6% 8% 44%	4244
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 7% 46%	4174
	21st to end	Day	9% 5% 2 6% 4 4 5% 3 7% 9% 46%	4329
September	1st to 10th	Day	11% 6% 2 7% 4 4 5% 4 6% 9% 42%	2366
	11th to 20th	Day	11% 4 2 5% 3 4 4 3 6% 8% 49%	2200
	21st to end	Day	14% 7% 3 7% 4 5% 5% 4 5% 8% 39%	2200
October	1st to 10th	Day	16% 7% 2 6% 4 4 5% 3 4 5% 44%	2200
	11th to 20th	Day	22% 9% 4 7% 5% 4 5% 4 7% 6% 29%	1961
	21st to end	Day	23% 12% 3 8% 5% 5% 4 4 4 6% 25%	1980
November	1st to 10th	Day	14% 12% 4 7% 4 3 5% 4 5% 6% 36%	1852
	11th to 20th	Day	16% 20% 4 10% 6% 4 5% 4 4 4 24%	1890
	21st to end	Day	20% 18% 8% 11% 5% 4 3 2 4 5% 20%	1890
December	1st to 10th	Day	11% 23% 11% 15% 6% 4 4 3 3 4 15%	2822
	11th to 20th	Day	15% 24% 13% 13% 7% 4 3 2 3 4 12%	3064
	21st to end	Day	24% 23% 7% 14% 5% 3 3 2 3 5% 11%	3982
January	1st to 10th	Night	13% 20% 11% 20% 6% 4 4 2 3 3 13%	6348
	11th to 20th	Night	12% 19% 10% 22% 9% 10% 3 3 3 3 7%	6360
	21st to end	Night	19% 19% 7% 16% 6% 6% 5% 2 3 4 13%	6996
February	1st to 10th	Night	14% 18% 5% 13% 11% 5% 4 3 4 4 20%	2523
	11th to 20th	Night	13% 16% 7% 15% 7% 5% 3 3 4 4 22%	2338
	21st to end	Night	17% 14% 5% 11% 5% 4 4 4 5% 5% 27%	1980
March	1st to 10th	Night	15% 11% 4 10% 5% 4 4 3 5% 7% 34%	5373
	11th to 20th	Night	11% 9% 3 7% 4 3 4 3 5% 7% 44%	5122
	21st to end	Night	18% 13% 5% 9% 4 4 4 3 4 6% 30%	5294
April	1st to 10th	Night	15% 12% 3 6% 4 4 5% 4 5% 6% 35%	2000
	11th to 20th	Night	19% 11% 2 6% 4 4 4 3 4 6% 36%	1926
	21st to end	Night	17% 9% 2 6% 5% 4 4 3 5% 7% 38%	1800
May	1st to 10th	Night	17% 11% 3 7% 4 4 4 3 5% 6% 34%	4033
	11th to 20th	Night	16% 8% 2 6% 4 4 3 3 4 7% 42%	4032
	21st to end	Night	16% 7% 3 6% 4 4 4 3 5% 6% 42%	3987
June	1st to 10th	Night	11% 5% 2 4 4 4 4 4 7% 9% 47%	1600
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 7% 8% 43%	1600
	21st to end	Night	10% 4 2 4 5% 5% 5% 5% 5% 10% 45%	1600
July	1st to 10th	Night	9% 5% 2 6% 5% 4 5% 4 7% 9% 44%	3618
	11th to 20th	Night	8% 5% 2 6% 5% 4 4 3 5% 8% 51%	3617
	21st to end	Night	10% 6% 2 6% 4 4 4 3 6% 9% 46%	3947
August	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 7% 9% 47%	2905
	11th to 20th	Night	11% 6% 2 6% 3 4 4 3 6% 7% 47%	2875
	21st to end	Night	9% 5% 3 7% 5% 4 4 4 5% 7% 46%	3553
September	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 8% 50%	2013
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 5% 7% 55%	2200
	21st to end	Night	13% 8% 3 6% 4 4 4 4 5% 6% 43%	2200
October	1st to 10th	Night	15% 6% 2 6% 3 4 4 3 4 7% 47%	2200
	11th to 20th	Night	19% 10% 3 8% 5% 4 4 3 3 6% 36%	2434
	21st to end	Night	24% 10% 3 7% 3 3 3 3 5% 6% 33%	2860
November	1st to 10th	Night	15% 13% 3 8% 4 4 4 3 5% 5% 37%	2666
	11th to 20th	Night	14% 18% 5% 10% 5% 4 4 4 4 6% 25%	2730
	21st to end	Night	19% 18% 6% 9% 5% 4 4 3 4 5% 23%	2730
December	1st to 10th	Night	13% 22% 10% 15% 6% 5% 4 3 4 4 15%	4581
	11th to 20th	Night	16% 25% 10% 15% 7% 4 3 2 3 4 12%	5298
	21st to end	Night	24% 22% 7% 11% 5% 4 3 3 4 5% 11%	6996

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	75% 4 9% 10% 1	3618
	11th to 20th	Day	86% 3 7% 3 1	3620
	21st to end	Day	77% 3 10% 8% 2	3982
February	1st to 10th	Day	72% 4 8% 11% 5%	1872
	11th to 20th	Day	69% 4 8% 12% 7%	1958
	21st to end	Day	65% 4 11% 13% 6% 1	1650
March	1st to 10th	Day	56% 4 12% 19% 9%	4480
	11th to 20th	Day	47% 5% 16% 24% 8% 1	4837
	21st to end	Day	63% 3 8% 16% 9% 1	5681
April	1st to 10th	Day	56% 5% 9% 18% 12%	2400
	11th to 20th	Day	47% 5% 9% 22% 14% 2	2422
	21st to end	Day	49% 4 12% 19% 15% 2	2600
May	1st to 10th	Day	47% 5% 10% 21% 15% 2	5897
	11th to 20th	Day	43% 6% 12% 22% 15% 2	5865
	21st to end	Day	39% 5% 10% 26% 18% 2	6898
June	1st to 10th	Day	36% 6% 11% 27% 18% 2	2800
	11th to 20th	Day	36% 5% 13% 25% 19% 2	2800
	21st to end	Day	39% 6% 13% 22% 17% 3	2800
July	1st to 10th	Day	39% 5% 12% 25% 16% 2	6291
	11th to 20th	Day	34% 5% 13% 29% 18% 1	6285
	21st to end	Day	33% 6% 15% 25% 19% 2	6728
August	1st to 10th	Day	35% 7% 12% 28% 16% 1	4230
	11th to 20th	Day	36% 6% 13% 29% 15% 1	4213
	21st to end	Day	33% 5% 13% 28% 18% 2	4328
September	1st to 10th	Day	37% 6% 13% 27% 15% 3	2366
	11th to 20th	Day	32% 5% 11% 31% 19% 2	2200
	21st to end	Day	42% 6% 11% 24% 17% 1	2200
October	1st to 10th	Day	30% 3 7% 39% 19% 1	3590
	11th to 20th	Day	41% 4 12% 25% 18%	3164
	21st to end	Day	50% 3 11% 24% 10% 1	3180
November	1st to 10th	Day	49% 5% 11% 22% 13% 1	1852
	11th to 20th	Day	64% 4 9% 16% 6% 1	1890
	21st to end	Day	68% 4 12% 13% 3	1890
December	1st to 10th	Day	73% 6% 11% 8% 2	2822
	11th to 20th	Day	78% 3 9% 8% 1	3061
	21st to end	Day	78% 4 7% 9% 2	3982
January	1st to 10th	Night	77% 4 6% 9% 3 1	6348
	11th to 20th	Night	83% 4 6% 4 3	6360
	21st to end	Night	76% 3 11% 7% 2	6996
February	1st to 10th	Night	69% 4 9% 12% 6%	2523
	11th to 20th	Night	66% 4 7% 16% 7%	2339
	21st to end	Night	59% 4 13% 16% 7% 2	1980
March	1st to 10th	Night	52% 3 13% 24% 7% 1	5373
	11th to 20th	Night	40% 5% 12% 29% 12% 2	5122
	21st to end	Night	56% 4 10% 17% 12% 1	5294
April	1st to 10th	Night	48% 5% 11% 22% 13% 1	2000
	11th to 20th	Night	49% 4 8% 19% 17% 3	1926
	21st to end	Night	45% 6% 11% 21% 16% 2	1800
May	1st to 10th	Night	51% 5% 10% 18% 13% 4	4060
	11th to 20th	Night	43% 5% 10% 22% 17% 3	4033
	21st to end	Night	43% 5% 9% 23% 19% 2	3995
June	1st to 10th	Night	32% 5% 12% 30% 17% 3	1600
	11th to 20th	Night	36% 8% 13% 23% 19% 2	1600
	21st to end	Night	34% 6% 16% 25% 16% 3	1600
July	1st to 10th	Night	35% 4 13% 28% 15% 5%	3580
	11th to 20th	Night	32% 5% 13% 26% 22% 2	3572
	21st to end	Night	35% 5% 13% 21% 24% 2	3832
August	1st to 10th	Night	34% 5% 14% 30% 16% 1	2895
	11th to 20th	Night	35% 5% 11% 32% 16% 1	2902
	21st to end	Night	36% 6% 9% 28% 18% 2	3553
September	1st to 10th	Night	32% 5% 12% 29% 19% 3	2013
	11th to 20th	Night	30% 5% 8% 33% 23% 2	2200
	21st to end	Night	41% 5% 11% 24% 17% 1	2200
October	1st to 10th	Night	28% 4 9% 35% 23% 1	3590
	11th to 20th	Night	42% 3 11% 23% 21%	3970
	21st to end	Night	43% 3 8% 28% 17%	4610
November	1st to 10th	Night	49% 5% 9% 23% 13% 1	2666
	11th to 20th	Night	61% 4 11% 16% 7% 1	2730
	21st to end	Night	64% 4 12% 17% 3	2730
December	1st to 10th	Night	73% 5% 10% 9% 3	4581
	11th to 20th	Night	79% 3 8% 7% 2	5300
	21st to end	Night	76% 4 9% 8% 3	6996

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	22% 18% 35% 19% 6%	300
	11th to 20th	Day	26% 20% 38% 13% 3 1	300
	21st to end	Day	27% 20% 32% 16% 3	330
February	1st to 10th	Day	28% 21% 32% 15% 3 1	300
	11th to 20th	Day	29% 23% 34% 12% 3	300
	21st to end	Day	28% 31% 29% 9% 2 1	249
March	1st to 10th	Day	23% 28% 34% 12% 3	300
	11th to 20th	Day	27% 17% 30% 20% 5% 1	435
	21st to end	Day	32% 18% 28% 17% 4 1	550
April	1st to 10th	Day	30% 15% 32% 17% 5%	500
	11th to 20th	Day	29% 20% 27% 15% 6% 2	492
	21st to end	Day	27% 16% 29% 19% 7% 1	500
May	1st to 10th	Day	25% 17% 29% 21% 7% 2	503
	11th to 20th	Day	21% 10% 30% 24% 11% 4	527
	21st to end	Day	16% 12% 29% 26% 12% 4	764
June	1st to 10th	Day	15% 11% 36% 24% 10% 4	730
	11th to 20th	Day	14% 11% 33% 27% 13% 2	730
	21st to end	Day	14% 10% 35% 27% 12% 3	730
July	1st to 10th	Day	8% 6% 29% 31% 16% 10%	721
	11th to 20th	Day	13% 6% 32% 27% 16% 7%	718
	21st to end	Day	9% 5% 30% 29% 20% 7%	794
August	1st to 10th	Day	10% 4 21% 28% 24% 13%	536
	11th to 20th	Day	12% 5% 24% 29% 22% 8%	519
	21st to end	Day	13% 5% 21% 29% 25% 8%	583
September	1st to 10th	Day	15% 8% 22% 26% 21% 8%	530
	11th to 20th	Day	9% 4 20% 29% 28% 10%	530
	21st to end	Day	20% 11% 21% 25% 16% 7%	530
October	1st to 10th	Day	18% 10% 27% 26% 16% 3	530
	11th to 20th	Day	26% 16% 30% 23% 5%	435
	21st to end	Day	32% 18% 32% 15% 2 1	363
November	1st to 10th	Day	26% 18% 32% 19% 5% 1	330
	11th to 20th	Day	31% 24% 28% 14% 3	330
	21st to end	Day	32% 18% 38% 9% 3	330
December	1st to 10th	Day	30% 24% 27% 14% 5%	330
	11th to 20th	Day	23% 26% 36% 13% 2	321
	21st to end	Day	27% 24% 33% 12% 2 1	330
January	1st to 10th	Night	24% 16% 33% 19% 7%	1000
	11th to 20th	Night	26% 15% 34% 21% 4 1	1000
	21st to end	Night	23% 12% 32% 28% 3	1100
February	1st to 10th	Night	23% 15% 36% 23% 4	810
	11th to 20th	Night	21% 17% 32% 25% 4	783
	21st to end	Night	25% 16% 37% 18% 4	660
March	1st to 10th	Night	22% 14% 32% 25% 7% 1	800
	11th to 20th	Night	18% 15% 35% 25% 6% 1	800
	21st to end	Night	25% 12% 31% 25% 7%	810
April	1st to 10th	Night	19% 14% 33% 28% 6% 1	600
	11th to 20th	Night	25% 11% 33% 23% 7% 1	593
	21st to end	Night	23% 9% 33% 28% 7% 1	600
May	1st to 10th	Night	20% 8% 35% 28% 8% 1	600
	11th to 20th	Night	21% 7% 26% 35% 10%	591
	21st to end	Night	16% 5% 29% 33% 16% 1	650
June	1st to 10th	Night	12% 6% 28% 40% 14% 1	600
	11th to 20th	Night	14% 5% 25% 41% 16%	600
	21st to end	Night	12% 3 24% 38% 22% 2	600
July	1st to 10th	Night	10% 2 18% 41% 26% 3	585
	11th to 20th	Night	10% 2 17% 45% 22% 4	582
	21st to end	Night	9% 2 16% 44% 27% 1	657
August	1st to 10th	Night	10% 2 13% 45% 26% 4	597
	11th to 20th	Night	11% 1 14% 42% 27% 4	594
	21st to end	Night	11% 3 17% 36% 31% 3	660
September	1st to 10th	Night	11% 4 16% 38% 26% 4	613
	11th to 20th	Night	10% 5% 17% 38% 27% 4	800
	21st to end	Night	17% 7% 23% 31% 19% 4	800
October	1st to 10th	Night	18% 7% 22% 34% 18% 2	800
	11th to 20th	Night	24% 12% 26% 28% 8% 1	800
	21st to end	Night	30% 13% 29% 22% 6%	880
November	1st to 10th	Night	22% 14% 30% 24% 9% 1	820
	11th to 20th	Night	25% 16% 32% 22% 5% 1	840
	21st to end	Night	29% 12% 32% 23% 4	840
December	1st to 10th	Night	26% 16% 31% 22% 5%	963
	11th to 20th	Night	27% 15% 34% 21% 3	1036
	21st to end	Night	34% 14% 32% 18% 2	1100

Page generated at 2025-12-15 01:13:52. Version ac07

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