Stickney Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stickney Observatory clear sky chart from 2005-11-06 to 2026-09-29.

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	18% 11% 4 9% 5% 4 4 4 5% 7% 30%	149283
	Night	18% 13% 5% 10% 5% 4 4 3 4 6% 28%	142127
Transparency	Day	52% 6% 11% 19% 9% 1	152778
	Night	56% 6% 11% 17% 10% 1	146721
Seeing	Day	27% 19% 28% 18% 7% 2	17269
	Night	26% 17% 26% 23% 7% 1	26210

By Month

Percentage Cloud Cover NE (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	13% 16% 9% 24% 7% 3 4 2 3 3 15%	4661
	11th to 20th	Day	10% 15% 8% 18% 8% 6% 3 4 4 4 19%	4650
	21st to end	Day	13% 16% 8% 10% 8% 5% 4 3 3 4 25%	5184
February	1st to 10th	Day	15% 17% 5% 13% 7% 4 5% 4 4 5% 22%	1890
	11th to 20th	Day	14% 15% 8% 13% 7% 5% 4 2 4 4 23%	2048
	21st to end	Day	17% 16% 4 14% 6% 4 4 3 3 5% 25%	1730
March	1st to 10th	Day	20% 16% 6% 12% 4 4 3 3 4 4 24%	4576
	11th to 20th	Day	15% 17% 5% 9% 4 4 3 3 4 5% 31%	4777
	21st to end	Day	22% 12% 4 9% 5% 4 4 3 4 5% 29%	6102
April	1st to 10th	Day	21% 15% 3 7% 5% 4 3 3 5% 5% 30%	2520
	11th to 20th	Day	16% 14% 3 7% 4 5% 4 4 5% 5% 33%	2494
	21st to end	Day	21% 12% 3 6% 5% 4 4 3 5% 5% 31%	2651
May	1st to 10th	Day	29% 12% 3 8% 5% 4 4 4 5% 6% 21%	7693
	11th to 20th	Day	20% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	8221
	21st to end	Day	23% 10% 3 7% 4 4 4 4 6% 7% 28%	9060
June	1st to 10th	Day	19% 8% 3 7% 5% 5% 5% 4 6% 9% 28%	2940
	11th to 20th	Day	21% 6% 2 7% 5% 5% 5% 4 6% 9% 30%	2940
	21st to end	Day	20% 8% 2 7% 5% 5% 6% 4 6% 7% 29%	2940
July	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 5% 7% 9% 31%	8280
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 4 7% 10% 38%	8280
	21st to end	Day	17% 7% 3 6% 4 4 4 4 6% 7% 37%	8993
August	1st to 10th	Day	18% 9% 3 8% 5% 5% 5% 5% 6% 8% 29%	6415
	11th to 20th	Day	15% 7% 2 7% 4 5% 5% 4 6% 9% 34%	5582
	21st to end	Day	15% 6% 2 7% 5% 5% 6% 5% 7% 9% 35%	6080
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 7% 42%	2520
	11th to 20th	Day	17% 4 2 5% 3 4 3 3 5% 7% 46%	2399
	21st to end	Day	17% 7% 2 5% 4 4 5% 4 6% 8% 38%	2288
October	1st to 10th	Day	23% 9% 3 6% 4 4 4 3 4 4 35%	2125
	11th to 20th	Day	17% 11% 3 7% 4 3 3 4 5% 6% 36%	1976
	21st to end	Day	24% 13% 3 7% 4 4 4 4 4 6% 28%	1980
November	1st to 10th	Day	15% 13% 3 7% 4 3 4 3 4 6% 38%	1851
	11th to 20th	Day	16% 16% 3 9% 4 3 3 3 4 5% 32%	1890
	21st to end	Day	20% 16% 4 9% 5% 4 4 3 4 5% 27%	1753
December	1st to 10th	Day	15% 21% 7% 14% 5% 4 4 3 4 5% 20%	2680
	11th to 20th	Day	19% 17% 8% 12% 4 3 3 2 3 4 25%	3066
	21st to end	Day	19% 18% 4 11% 5% 4 3 3 4 6% 24%	4048
January	1st to 10th	Night	14% 16% 9% 20% 6% 3 3 3 3 4 19%	8234
	11th to 20th	Night	10% 19% 9% 20% 10% 5% 4 3 3 4 13%	8235
	21st to end	Night	13% 12% 5% 14% 9% 8% 5% 3 4 5% 21%	8981
February	1st to 10th	Night	16% 16% 5% 14% 7% 5% 4 4 5% 4 22%	2728
	11th to 20th	Night	13% 14% 6% 13% 9% 5% 5% 3 5% 5% 23%	2458
	21st to end	Night	16% 16% 5% 12% 5% 4 4 3 5% 5% 26%	2076
March	1st to 10th	Night	20% 11% 6% 10% 6% 4 4 3 5% 5% 24%	5484
	11th to 20th	Night	17% 15% 5% 9% 4 4 3 2 4 6% 30%	5386
	21st to end	Night	25% 15% 5% 10% 4 3 3 3 3 3 26%	5072
April	1st to 10th	Night	21% 14% 4 7% 3 3 5% 3 5% 6% 28%	2100
	11th to 20th	Night	21% 13% 3 6% 4 4 3 4 4 5% 32%	2075
	21st to end	Night	20% 12% 4 6% 4 3 4 3 4 5% 34%	1968
May	1st to 10th	Night	31% 12% 2 7% 4 4 4 3 4 5% 23%	5259
	11th to 20th	Night	19% 10% 3 9% 5% 5% 5% 4 6% 7% 27%	4640
	21st to end	Night	26% 9% 3 7% 5% 4 4 3 5% 6% 27%	5114
June	1st to 10th	Night	20% 8% 3 6% 4 4 4 3 5% 8% 35%	1680
	11th to 20th	Night	22% 7% 1 6% 4 4 4 3 6% 8% 36%	1680
	21st to end	Night	16% 7% 2 6% 5% 3 5% 4 7% 8% 38%	1680
July	1st to 10th	Night	16% 9% 3 7% 4 5% 5% 4 6% 8% 34%	4680
	11th to 20th	Night	18% 7% 3 7% 5% 4 4 3 5% 7% 39%	4680
	21st to end	Night	14% 7% 3 7% 4 4 4 3 5% 8% 41%	5084
August	1st to 10th	Night	26% 9% 3 6% 3 3 3 3 5% 7% 30%	3688
	11th to 20th	Night	20% 9% 3 7% 4 4 4 3 5% 7% 33%	4459
	21st to end	Night	17% 8% 3 6% 4 4 4 4 6% 8% 36%	5045
September	1st to 10th	Night	18% 8% 2 6% 3 4 4 3 5% 5% 43%	2100
	11th to 20th	Night	16% 5% 2 5% 4 3 3 3 4 7% 49%	2221
	21st to end	Night	18% 8% 2 6% 5% 4 4 3 4 6% 41%	2289
October	1st to 10th	Night	23% 8% 3 6% 4 4 3 4 5% 6% 36%	2272
	11th to 20th	Night	17% 11% 3 6% 4 4 4 4 5% 6% 37%	2422
	21st to end	Night	24% 11% 3 7% 4 5% 3 3 5% 5% 28%	2860
November	1st to 10th	Night	17% 12% 3 6% 4 4 3 3 4 5% 38%	2667
	11th to 20th	Night	18% 14% 4 8% 5% 4 5% 3 5% 5% 31%	2730
	21st to end	Night	16% 17% 5% 8% 5% 4 5% 3 5% 5% 28%	2862
December	1st to 10th	Night	17% 23% 9% 16% 4 3 4 2 3 3 15%	4720
	11th to 20th	Night	22% 17% 7% 11% 5% 3 3 2 3 3 23%	5348
	21st to end	Night	19% 18% 6% 10% 4 4 4 3 4 4 24%	7150

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	72% 6% 7% 12% 3	4662
	11th to 20th	Day	66% 6% 7% 9% 9% 2	4680
	21st to end	Day	63% 4 7% 18% 7% 1	5184
February	1st to 10th	Day	64% 5% 9% 14% 7% 1	1890
	11th to 20th	Day	64% 5% 8% 15% 7% 1	2057
	21st to end	Day	62% 6% 9% 14% 9% 1	1730
March	1st to 10th	Day	64% 4 10% 11% 8% 3	4579
	11th to 20th	Day	53% 6% 15% 15% 8% 3	4777
	21st to end	Day	57% 5% 7% 12% 17% 3	6102
April	1st to 10th	Day	57% 5% 8% 19% 9% 2	2520
	11th to 20th	Day	51% 7% 10% 18% 13% 1	2494
	21st to end	Day	53% 6% 8% 17% 12% 3	2651
May	1st to 10th	Day	62% 7% 9% 14% 7%	7705
	11th to 20th	Day	52% 7% 14% 20% 8% 1	8225
	21st to end	Day	53% 7% 11% 22% 7%	9061
June	1st to 10th	Day	50% 8% 14% 18% 10%	2940
	11th to 20th	Day	49% 7% 12% 20% 11% 1	2940
	21st to end	Day	51% 8% 13% 19% 9%	2940
July	1st to 10th	Day	47% 7% 14% 22% 10%	8210
	11th to 20th	Day	38% 8% 16% 27% 11% 1	8205
	21st to end	Day	44% 6% 13% 26% 11%	8795
August	1st to 10th	Day	51% 8% 14% 17% 9%	6401
	11th to 20th	Day	44% 8% 19% 24% 5%	5620
	21st to end	Day	42% 9% 14% 27% 8% 1	6080
September	1st to 10th	Day	39% 8% 11% 28% 13% 1	2520
	11th to 20th	Day	38% 5% 11% 26% 19% 2	2399
	21st to end	Day	42% 6% 12% 24% 13% 2	2288
October	1st to 10th	Day	51% 6% 8% 21% 14% 1	3463
	11th to 20th	Day	45% 4 13% 23% 14% 1	3192
	21st to end	Day	42% 6% 12% 27% 10% 2	3180
November	1st to 10th	Day	46% 6% 14% 21% 12% 1	1851
	11th to 20th	Day	53% 6% 10% 17% 13% 2	1890
	21st to end	Day	59% 5% 15% 15% 6% 1	1753
December	1st to 10th	Day	67% 5% 10% 13% 4	2680
	11th to 20th	Day	64% 4 8% 16% 7% 1	3066
	21st to end	Day	61% 5% 7% 12% 11% 3	4048
January	1st to 10th	Night	68% 5% 10% 11% 6% 1	8234
	11th to 20th	Night	73% 6% 8% 7% 5% 1	8280
	21st to end	Night	64% 5% 8% 11% 10% 2	8981
February	1st to 10th	Night	64% 6% 9% 15% 6% 1	2728
	11th to 20th	Night	61% 6% 10% 13% 8% 1	2460
	21st to end	Night	59% 6% 10% 16% 7% 2	2076
March	1st to 10th	Night	60% 6% 11% 13% 10% 1	5494
	11th to 20th	Night	53% 6% 17% 15% 7% 2	5387
	21st to end	Night	63% 5% 4 11% 15% 2	5072
April	1st to 10th	Night	56% 6% 11% 16% 10% 1	2100
	11th to 20th	Night	53% 6% 9% 19% 12% 1	2075
	21st to end	Night	51% 6% 9% 17% 14% 3	1968
May	1st to 10th	Night	61% 6% 10% 12% 10% 1	5265
	11th to 20th	Night	54% 8% 12% 18% 7% 1	4641
	21st to end	Night	57% 7% 9% 20% 8% 1	5115
June	1st to 10th	Night	47% 6% 13% 22% 11%	1680
	11th to 20th	Night	46% 7% 16% 22% 10%	1680
	21st to end	Night	43% 7% 15% 24% 10% 1	1680
July	1st to 10th	Night	46% 7% 15% 21% 11%	4640
	11th to 20th	Night	45% 6% 10% 24% 14% 1	4632
	21st to end	Night	41% 6% 15% 26% 11%	4967
August	1st to 10th	Night	53% 7% 13% 18% 9% 1	3678
	11th to 20th	Night	49% 7% 16% 21% 6%	4487
	21st to end	Night	45% 6% 16% 24% 9%	5045
September	1st to 10th	Night	42% 7% 11% 26% 14% 1	2100
	11th to 20th	Night	36% 5% 11% 28% 19% 1	2221
	21st to end	Night	45% 6% 9% 24% 15% 2	2289
October	1st to 10th	Night	53% 6% 11% 18% 10% 1	3714
	11th to 20th	Night	44% 4 13% 20% 17% 2	3945
	21st to end	Night	47% 5% 11% 28% 8% 1	4610
November	1st to 10th	Night	49% 5% 11% 20% 13% 2	2667
	11th to 20th	Night	53% 7% 11% 16% 12% 2	2730
	21st to end	Night	56% 7% 14% 17% 6%	2862
December	1st to 10th	Night	73% 6% 8% 10% 3	4720
	11th to 20th	Night	65% 6% 9% 10% 10%	5348
	21st to end	Night	63% 5% 7% 12% 9% 3	7150

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	31% 32% 22% 13% 2	220
	11th to 20th	Day	33% 28% 28% 9% 1 1	220
	21st to end	Day	30% 29% 30% 8% 4	253
February	1st to 10th	Day	35% 34% 23% 7% 1	330
	11th to 20th	Day	32% 32% 26% 10% 1	536
	21st to end	Day	34% 26% 27% 11% 2	446
March	1st to 10th	Day	34% 24% 26% 14% 1	540
	11th to 20th	Day	34% 26% 26% 11% 2	540
	21st to end	Day	34% 28% 21% 10% 5% 1	594
April	1st to 10th	Day	41% 20% 22% 11% 5% 1	540
	11th to 20th	Day	35% 24% 24% 11% 6% 1	532
	21st to end	Day	32% 19% 29% 13% 5% 2	540
May	1st to 10th	Day	37% 21% 24% 11% 5% 2	543
	11th to 20th	Day	27% 17% 33% 17% 5% 1	567
	21st to end	Day	25% 15% 30% 20% 8% 2	617
June	1st to 10th	Day	21% 14% 33% 22% 10% 1	570
	11th to 20th	Day	25% 12% 32% 22% 8% 1	570
	21st to end	Day	22% 18% 31% 20% 7% 2	570
July	1st to 10th	Day	17% 11% 34% 24% 12% 2	565
	11th to 20th	Day	16% 8% 35% 28% 10% 2	564
	21st to end	Day	16% 13% 36% 23% 10% 2	620
August	1st to 10th	Day	15% 11% 27% 30% 13% 4	566
	11th to 20th	Day	16% 11% 31% 23% 13% 5%	559
	21st to end	Day	16% 12% 29% 26% 12% 5%	627
September	1st to 10th	Day	19% 13% 25% 24% 14% 6%	570
	11th to 20th	Day	16% 12% 25% 22% 16% 9%	570
	21st to end	Day	20% 13% 29% 20% 12% 6%	562
October	1st to 10th	Day	29% 12% 23% 19% 14% 4	530
	11th to 20th	Day	26% 20% 25% 20% 9% 1	516
	21st to end	Day	32% 15% 30% 18% 4	462
November	1st to 10th	Day	30% 21% 21% 18% 9% 1	425
	11th to 20th	Day	29% 26% 23% 16% 5% 1	430
	21st to end	Day	37% 25% 23% 13% 3	293
December	1st to 10th	Day	37% 25% 25% 10% 3	220
	11th to 20th	Day	43% 24% 24% 8% 2	220
	21st to end	Day	40% 21% 24% 12% 2	242
January	1st to 10th	Night	26% 28% 31% 13% 2	840
	11th to 20th	Night	30% 25% 25% 17% 2	840
	21st to end	Night	23% 26% 31% 17% 3	924
February	1st to 10th	Night	26% 27% 31% 16% 1	840
	11th to 20th	Night	27% 26% 31% 13% 2	823
	21st to end	Night	28% 25% 28% 17% 2	692
March	1st to 10th	Night	29% 22% 30% 17% 2	840
	11th to 20th	Night	30% 25% 26% 16% 3	840
	21st to end	Night	31% 22% 24% 17% 6%	924
April	1st to 10th	Night	31% 21% 27% 18% 3	840
	11th to 20th	Night	30% 20% 26% 18% 7%	831
	21st to end	Night	29% 16% 29% 20% 5% 1	708
May	1st to 10th	Night	30% 16% 25% 22% 6%	630
	11th to 20th	Night	24% 12% 30% 31% 4	415
	21st to end	Night	20% 9% 28% 32% 10% 1	455
June	1st to 10th	Night	21% 9% 25% 32% 12%	420
	11th to 20th	Night	23% 7% 25% 37% 10%	420
	21st to end	Night	17% 6% 28% 37% 11%	420
July	1st to 10th	Night	16% 5% 21% 44% 14%	410
	11th to 20th	Night	16% 6% 24% 38% 15% 1	408
	21st to end	Night	15% 5% 25% 41% 13% 1	460
August	1st to 10th	Night	16% 5% 18% 43% 18% 1	427
	11th to 20th	Night	19% 4 20% 35% 18% 3	782
	21st to end	Night	18% 7% 22% 34% 19% 1	924
September	1st to 10th	Night	21% 7% 23% 33% 15% 1	840
	11th to 20th	Night	19% 7% 19% 32% 19% 4	840
	21st to end	Night	20% 11% 23% 30% 13% 3	833
October	1st to 10th	Night	27% 11% 20% 27% 14% 2	800
	11th to 20th	Night	24% 13% 28% 25% 9%	800
	21st to end	Night	31% 17% 26% 21% 4	880
November	1st to 10th	Night	26% 19% 26% 23% 6%	820
	11th to 20th	Night	26% 21% 28% 17% 6% 1	840
	21st to end	Night	28% 21% 29% 16% 5% 1	840
December	1st to 10th	Night	33% 25% 25% 14% 4	840
	11th to 20th	Night	32% 24% 26% 15% 3	840
	21st to end	Night	32% 25% 26% 14% 3	924

Page generated at 2026-09-26 04:18:41. Version ac07

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