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 2025-05-26.

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% 6% 30%	113813
	Night	18% 13% 5% 10% 5% 4 4 3 4 5% 28%	115434
Transparency	Day	53% 7% 11% 19% 10% 1	117354
	Night	56% 6% 11% 16% 10% 1	120057
Seeing	Day	27% 19% 27% 18% 8% 2	15487
	Night	25% 18% 26% 23% 8% 1	24604

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% 25% 6% 3 3 2 3 3 18%	3597
	11th to 20th	Day	11% 15% 7% 18% 9% 5% 3 3 4 4 20%	3570
	21st to end	Day	16% 17% 9% 11% 6% 4 4 3 3 4 23%	4006
February	1st to 10th	Day	15% 17% 5% 13% 8% 4 4 4 4 5% 22%	1800
	11th to 20th	Day	14% 15% 8% 13% 7% 5% 4 3 4 5% 23%	1948
	21st to end	Day	18% 15% 4 14% 6% 3 4 3 3 5% 25%	1650
March	1st to 10th	Day	20% 16% 6% 12% 4 4 3 3 4 4 24%	4476
	11th to 20th	Day	15% 16% 5% 9% 4 4 3 3 4 5% 32%	4674
	21st to end	Day	22% 12% 4 9% 4 4 4 3 4 5% 29%	5970
April	1st to 10th	Day	21% 15% 3 8% 5% 4 3 3 4 5% 30%	2400
	11th to 20th	Day	16% 14% 3 7% 5% 4 4 4 5% 5% 34%	2374
	21st to end	Day	21% 12% 3 6% 5% 4 4 3 5% 5% 31%	2525
May	1st to 10th	Day	28% 11% 3 7% 4 4 4 3 5% 6% 26%	4264
	11th to 20th	Day	19% 9% 3 7% 5% 4 5% 4 6% 7% 30%	4538
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 6% 8% 38%	4907
June	1st to 10th	Day	19% 8% 3 7% 6% 5% 5% 5% 6% 9% 28%	2660
	11th to 20th	Day	20% 6% 2 6% 5% 4 5% 4 6% 10% 31%	2660
	21st to end	Day	20% 8% 2 6% 6% 5% 6% 4 7% 7% 28%	2660
July	1st to 10th	Day	14% 7% 3 7% 4 5% 6% 5% 7% 10% 33%	4440
	11th to 20th	Day	13% 7% 2 7% 6% 5% 5% 5% 8% 9% 33%	4440
	21st to end	Day	17% 8% 3 7% 5% 5% 5% 4 7% 8% 32%	4814
August	1st to 10th	Day	18% 8% 3 7% 4 5% 5% 5% 5% 8% 31%	4371
	11th to 20th	Day	15% 8% 3 8% 5% 5% 6% 4 7% 9% 30%	3794
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 6% 9% 39%	4180
September	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	18% 5% 2 5% 3 4 3 3 5% 6% 46%	2171
	21st to end	Day	17% 7% 2 5% 4 4 4 4 6% 8% 39%	2090
October	1st to 10th	Day	24% 9% 3 7% 4 4 4 3 4 5% 33%	2019
	11th to 20th	Day	17% 11% 3 7% 4 3 3 4 5% 6% 36%	1877
	21st to end	Day	24% 13% 3 7% 4 4 4 4 4 6% 27%	1881
November	1st to 10th	Day	15% 12% 3 7% 4 2 4 3 4 6% 39%	1761
	11th to 20th	Day	17% 15% 3 9% 5% 3 4 3 4 5% 33%	1800
	21st to end	Day	20% 14% 4 9% 5% 4 4 3 4 5% 28%	1670
December	1st to 10th	Day	15% 22% 6% 14% 5% 4 4 3 4 5% 19%	2600
	11th to 20th	Day	19% 18% 8% 12% 4 3 3 2 2 4 25%	2986
	21st to end	Day	19% 18% 4 10% 5% 4 3 3 4 6% 24%	3960
January	1st to 10th	Night	12% 14% 10% 22% 6% 3 3 3 3 4 20%	6349
	11th to 20th	Night	10% 18% 9% 20% 9% 5% 4 3 3 5% 14%	6315
	21st to end	Night	16% 14% 6% 15% 7% 6% 5% 3 4 5% 20%	6934
February	1st to 10th	Night	16% 17% 5% 14% 7% 4 4 4 5% 4 21%	2598
	11th to 20th	Night	13% 14% 5% 12% 9% 5% 5% 3 5% 5% 23%	2338
	21st to end	Night	16% 15% 5% 12% 5% 4 5% 3 5% 5% 26%	1980
March	1st to 10th	Night	20% 11% 6% 11% 6% 4 4 4 5% 5% 24%	5364
	11th to 20th	Night	17% 15% 4 8% 4 4 3 2 4 6% 30%	5269
	21st to end	Night	25% 15% 5% 10% 4 3 3 3 3 3 26%	4962
April	1st to 10th	Night	21% 14% 4 7% 4 3 5% 3 6% 6% 28%	2000
	11th to 20th	Night	20% 13% 3 6% 4 4 4 4 5% 6% 32%	1975
	21st to end	Night	21% 13% 4 6% 4 3 4 3 4 5% 33%	1874
May	1st to 10th	Night	28% 10% 2 7% 4 4 4 4 4 6% 26%	2924
	11th to 20th	Night	17% 10% 3 9% 6% 5% 5% 4 5% 6% 29%	2576
	21st to end	Night	18% 7% 3 7% 5% 5% 4 3 7% 7% 35%	2784
June	1st to 10th	Night	20% 8% 3 6% 4 4 4 3 5% 8% 33%	1520
	11th to 20th	Night	21% 6% 1 5% 4 4 4 3 6% 8% 38%	1520
	21st to end	Night	15% 7% 3 5% 5% 4 5% 4 7% 7% 38%	1520
July	1st to 10th	Night	14% 9% 3 7% 5% 5% 6% 4 6% 7% 35%	2520
	11th to 20th	Night	20% 9% 3 7% 5% 4 4 3 5% 7% 34%	2520
	21st to end	Night	17% 8% 3 7% 5% 4 5% 4 5% 8% 35%	2739
August	1st to 10th	Night	27% 8% 2 5% 3 3 3 3 5% 7% 32%	2527
	11th to 20th	Night	17% 9% 3 7% 4 5% 4 4 6% 7% 34%	3029
	21st to end	Night	13% 7% 2 5% 3 4 4 4 5% 9% 44%	3476
September	1st to 10th	Night	17% 7% 2 6% 3 4 4 3 5% 5% 43%	1900
	11th to 20th	Night	17% 5% 2 5% 4 3 3 2 4 7% 49%	2009
	21st to end	Night	17% 7% 2 6% 5% 4 4 3 4 6% 42%	2090
October	1st to 10th	Night	23% 9% 3 6% 4 4 3 4 5% 5% 34%	2158
	11th to 20th	Night	17% 11% 3 6% 4 4 4 4 5% 6% 37%	2301
	21st to end	Night	24% 11% 3 7% 4 5% 3 3 5% 5% 27%	2717
November	1st to 10th	Night	16% 12% 3 7% 4 4 3 3 5% 5% 38%	2537
	11th to 20th	Night	18% 12% 3 8% 5% 4 5% 4 5% 5% 32%	2600
	21st to end	Night	15% 17% 4 8% 5% 4 5% 3 5% 5% 29%	2725
December	1st to 10th	Night	17% 23% 9% 16% 4 3 4 2 3 3 15%	4580
	11th to 20th	Night	23% 17% 7% 11% 5% 3 3 2 3 3 23%	5208
	21st to end	Night	19% 19% 6% 9% 4 4 4 3 4 4 24%	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	70% 6% 6% 14% 4	3598
	11th to 20th	Day	66% 7% 6% 10% 9% 2	3600
	21st to end	Day	65% 4 7% 14% 8% 2	4006
February	1st to 10th	Day	65% 5% 9% 14% 6% 1	1800
	11th to 20th	Day	64% 5% 8% 15% 8% 1	1957
	21st to end	Day	62% 6% 9% 14% 9% 1	1650
March	1st to 10th	Day	65% 4 10% 10% 8% 3	4479
	11th to 20th	Day	52% 6% 15% 16% 8% 3	4674
	21st to end	Day	57% 5% 7% 12% 17% 3	5970
April	1st to 10th	Day	57% 5% 8% 19% 9% 2	2400
	11th to 20th	Day	51% 7% 10% 18% 13% 1	2374
	21st to end	Day	54% 7% 9% 17% 11% 3	2525
May	1st to 10th	Day	58% 6% 11% 16% 9% 1	4278
	11th to 20th	Day	51% 8% 15% 18% 7% 1	4542
	21st to end	Day	40% 8% 14% 25% 12% 1	4907
June	1st to 10th	Day	50% 8% 15% 17% 9%	2660
	11th to 20th	Day	48% 7% 13% 20% 11% 1	2660
	21st to end	Day	52% 8% 12% 19% 8%	2660
July	1st to 10th	Day	44% 8% 12% 23% 12% 1	4370
	11th to 20th	Day	43% 9% 15% 23% 9%	4365
	21st to end	Day	47% 8% 15% 21% 10%	4661
August	1st to 10th	Day	49% 8% 14% 20% 8%	4357
	11th to 20th	Day	47% 8% 16% 23% 5% 1	3832
	21st to end	Day	40% 8% 14% 29% 9% 1	4180
September	1st to 10th	Day	40% 8% 12% 27% 13% 1	2280
	11th to 20th	Day	38% 6% 11% 25% 19% 1	2171
	21st to end	Day	42% 6% 13% 24% 13% 2	2090
October	1st to 10th	Day	52% 6% 8% 20% 13% 1	3357
	11th to 20th	Day	45% 4 13% 23% 14% 1	3093
	21st to end	Day	42% 6% 12% 27% 10% 2	3081
November	1st to 10th	Day	45% 6% 14% 21% 13% 1	1761
	11th to 20th	Day	52% 6% 10% 17% 14% 2	1800
	21st to end	Day	57% 5% 15% 15% 6% 1	1670
December	1st to 10th	Day	67% 5% 11% 13% 4	2600
	11th to 20th	Day	64% 4 8% 16% 7% 1	2986
	21st to end	Day	61% 5% 8% 12% 11% 3	3960
January	1st to 10th	Night	68% 5% 10% 11% 6% 1	6349
	11th to 20th	Night	71% 7% 8% 9% 5% 1	6360
	21st to end	Night	65% 5% 8% 9% 10% 2	6934
February	1st to 10th	Night	65% 6% 9% 13% 5% 1	2598
	11th to 20th	Night	61% 6% 11% 13% 9% 1	2340
	21st to end	Night	59% 6% 11% 16% 7% 2	1980
March	1st to 10th	Night	60% 6% 11% 13% 10% 1	5374
	11th to 20th	Night	52% 6% 17% 15% 7% 2	5270
	21st to end	Night	62% 5% 4 11% 15% 2	4962
April	1st to 10th	Night	56% 6% 11% 17% 9% 1	2000
	11th to 20th	Night	53% 6% 10% 19% 12% 1	1975
	21st to end	Night	52% 6% 9% 17% 13% 3	1874
May	1st to 10th	Night	58% 7% 10% 15% 9% 1	2930
	11th to 20th	Night	53% 9% 15% 15% 7% 1	2577
	21st to end	Night	45% 9% 12% 20% 13% 2	2785
June	1st to 10th	Night	48% 6% 15% 21% 10%	1520
	11th to 20th	Night	43% 7% 17% 23% 11%	1520
	21st to end	Night	43% 8% 15% 23% 11% 1	1520
July	1st to 10th	Night	47% 7% 13% 18% 14%	2480
	11th to 20th	Night	49% 6% 12% 23% 10%	2472
	21st to end	Night	46% 7% 12% 24% 10% 1	2651
August	1st to 10th	Night	51% 7% 13% 20% 8%	2517
	11th to 20th	Night	47% 7% 16% 21% 8%	3057
	21st to end	Night	37% 6% 17% 29% 11%	3476
September	1st to 10th	Night	42% 7% 11% 26% 14% 1	1900
	11th to 20th	Night	36% 5% 12% 28% 18% 1	2009
	21st to end	Night	44% 6% 10% 25% 14% 2	2090
October	1st to 10th	Night	55% 6% 12% 18% 9% 1	3600
	11th to 20th	Night	44% 4 13% 20% 17% 2	3824
	21st to end	Night	47% 5% 11% 28% 8% 1	4467
November	1st to 10th	Night	48% 5% 11% 20% 14% 2	2537
	11th to 20th	Night	52% 7% 11% 16% 12% 2	2600
	21st to end	Night	55% 7% 14% 17% 6%	2725
December	1st to 10th	Night	74% 6% 8% 9% 3	4580
	11th to 20th	Night	65% 6% 9% 10% 10%	5208
	21st to end	Night	63% 5% 7% 12% 9% 4	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	31% 32% 23% 13% 3	200
	11th to 20th	Day	32% 28% 29% 10% 1 1	200
	21st to end	Day	29% 28% 30% 8% 5%	230
February	1st to 10th	Day	38% 35% 22% 5% 1	300
	11th to 20th	Day	32% 33% 24% 9% 1	496
	21st to end	Day	34% 25% 27% 12% 2	414
March	1st to 10th	Day	34% 25% 25% 15% 2	500
	11th to 20th	Day	33% 26% 27% 11% 3	500
	21st to end	Day	33% 27% 22% 11% 5% 1	550
April	1st to 10th	Day	39% 21% 22% 11% 6% 1	500
	11th to 20th	Day	35% 24% 23% 11% 6% 1	492
	21st to end	Day	32% 19% 29% 13% 5% 2	500
May	1st to 10th	Day	35% 21% 25% 12% 5% 2	503
	11th to 20th	Day	27% 17% 33% 17% 5% 1	527
	21st to end	Day	24% 15% 29% 22% 8% 3	549
June	1st to 10th	Day	19% 15% 34% 21% 10% 1	490
	11th to 20th	Day	22% 12% 32% 24% 9% 1	490
	21st to end	Day	23% 18% 29% 20% 8% 2	490
July	1st to 10th	Day	17% 10% 32% 25% 14% 2	485
	11th to 20th	Day	15% 7% 36% 29% 11% 2	484
	21st to end	Day	15% 13% 37% 23% 11% 1	532
August	1st to 10th	Day	15% 12% 28% 29% 13% 5%	486
	11th to 20th	Day	17% 10% 31% 23% 13% 6%	479
	21st to end	Day	17% 11% 28% 26% 13% 5%	539
September	1st to 10th	Day	18% 12% 23% 26% 14% 6%	490
	11th to 20th	Day	17% 13% 23% 21% 17% 9%	490
	21st to end	Day	19% 13% 29% 20% 12% 7%	490
October	1st to 10th	Day	30% 12% 23% 18% 13% 3	490
	11th to 20th	Day	25% 19% 25% 20% 9% 1	477
	21st to end	Day	33% 15% 29% 19% 4	429
November	1st to 10th	Day	28% 21% 22% 19% 9% 1	395
	11th to 20th	Day	29% 26% 24% 16% 5% 1	400
	21st to end	Day	34% 25% 24% 14% 3	270
December	1st to 10th	Day	37% 25% 25% 11% 4	200
	11th to 20th	Day	42% 24% 24% 9% 2	200
	21st to end	Day	39% 20% 26% 12% 3	220
January	1st to 10th	Night	26% 29% 31% 13% 2	800
	11th to 20th	Night	30% 24% 26% 17% 3	800
	21st to end	Night	22% 26% 31% 18% 3	880
February	1st to 10th	Night	27% 28% 31% 14% 1	800
	11th to 20th	Night	27% 27% 30% 13% 2	783
	21st to end	Night	28% 25% 28% 17% 2	660
March	1st to 10th	Night	29% 22% 29% 18% 2	800
	11th to 20th	Night	29% 25% 27% 17% 3	800
	21st to end	Night	30% 23% 23% 17% 6%	880
April	1st to 10th	Night	30% 21% 27% 19% 3	800
	11th to 20th	Night	29% 20% 26% 18% 7%	791
	21st to end	Night	30% 16% 28% 20% 5% 1	674
May	1st to 10th	Night	30% 16% 24% 23% 7% 1	600
	11th to 20th	Night	24% 12% 29% 31% 4	395
	21st to end	Night	19% 9% 26% 33% 11% 1	423
June	1st to 10th	Night	22% 9% 25% 31% 12% 1	380
	11th to 20th	Night	21% 7% 23% 39% 10%	380
	21st to end	Night	17% 7% 27% 37% 11% 1	380
July	1st to 10th	Night	15% 5% 21% 44% 15% 1	370
	11th to 20th	Night	17% 5% 21% 39% 17% 1	368
	21st to end	Night	16% 5% 23% 41% 14% 1	416
August	1st to 10th	Night	16% 5% 19% 41% 18% 1	386
	11th to 20th	Night	19% 4 20% 34% 19% 4	706
	21st to end	Night	17% 6% 21% 33% 20% 1	836
September	1st to 10th	Night	20% 7% 25% 31% 16% 2	760
	11th to 20th	Night	19% 7% 19% 30% 20% 5%	760
	21st to end	Night	20% 12% 23% 29% 14% 3	760
October	1st to 10th	Night	28% 11% 20% 26% 13% 2	760
	11th to 20th	Night	24% 13% 27% 26% 10%	760
	21st to end	Night	32% 17% 26% 21% 4	836
November	1st to 10th	Night	25% 19% 26% 24% 6%	780
	11th to 20th	Night	25% 21% 29% 17% 7% 1	800
	21st to end	Night	28% 21% 29% 16% 5% 1	800
December	1st to 10th	Night	33% 25% 24% 14% 4	800
	11th to 20th	Night	31% 24% 26% 16% 3	800
	21st to end	Night	31% 25% 26% 15% 3	880

Page generated at 2025-05-23 09:21:03. Version ac07

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