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 2024-03-06.

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 7% 6% 3 4 4 5% 6% 31%	78372
	Night	18% 12% 5% 8% 6% 3 4 4 4 6% 30%	81139
Transparency	Day	53% 7% 11% 18% 10% 1	78077
	Night	55% 6% 11% 17% 9% 1	80968
Seeing	Day	26% 18% 28% 18% 8% 2	13886
	Night	25% 18% 26% 23% 8% 1	23070

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	16% 18% 11% 10% 7% 3 4 4 3 4 21%	2517
	11th to 20th	Day	14% 17% 8% 12% 11% 4 4 4 4 4 19%	2520
	21st to end	Day	19% 19% 10% 9% 7% 2 4 4 3 4 19%	2804
February	1st to 10th	Day	16% 16% 6% 11% 8% 3 4 4 4 5% 22%	1710
	11th to 20th	Day	14% 15% 9% 12% 7% 4 4 4 4 4 24%	1848
	21st to end	Day	18% 14% 5% 12% 7% 3 4 3 4 5% 26%	1570
March	1st to 10th	Day	16% 14% 6% 9% 6% 3 4 5% 4 6% 27%	1847
	11th to 20th	Day	17% 14% 6% 8% 5% 3 4 4 4 5% 30%	1856
	21st to end	Day	19% 13% 4 7% 4 2 4 3 4 5% 34%	2376
April	1st to 10th	Day	21% 13% 4 7% 5% 3 3 3 4 5% 31%	2160
	11th to 20th	Day	16% 12% 3 6% 5% 4 5% 5% 5% 5% 35%	2134
	21st to end	Day	22% 12% 4 5% 6% 3 4 5% 5% 5% 30%	2272
May	1st to 10th	Day	25% 11% 3 6% 5% 3 4 4 4 5% 30%	2353
	11th to 20th	Day	20% 8% 3 6% 4 2 4 4 5% 7% 37%	2478
	21st to end	Day	16% 7% 3 6% 5% 3 4 5% 6% 8% 37%	2725
June	1st to 10th	Day	19% 7% 4 6% 6% 4 5% 6% 6% 9% 27%	2520
	11th to 20th	Day	21% 6% 3 5% 6% 3 5% 5% 6% 10% 31%	2520
	21st to end	Day	20% 7% 2 5% 6% 4 6% 6% 7% 7% 29%	2520
July	1st to 10th	Day	16% 6% 3 6% 5% 3 5% 5% 7% 7% 37%	2520
	11th to 20th	Day	14% 6% 2 6% 6% 3 4 6% 8% 9% 36%	2520
	21st to end	Day	16% 7% 3 6% 5% 4 6% 6% 6% 8% 34%	2744
August	1st to 10th	Day	13% 7% 2 6% 5% 4 6% 7% 6% 9% 36%	2481
	11th to 20th	Day	15% 8% 3 5% 6% 4 6% 6% 7% 9% 32%	2164
	21st to end	Day	16% 5% 2 6% 4 3 5% 6% 6% 9% 38%	2376
September	1st to 10th	Day	16% 6% 2 4 5% 3 5% 5% 5% 8% 41%	2160
	11th to 20th	Day	19% 5% 2 4 4 3 4 3 5% 7% 45%	2057
	21st to end	Day	17% 7% 2 4 5% 3 4 5% 6% 8% 40%	1980
October	1st to 10th	Day	25% 9% 3 5% 5% 3 4 4 4 4 33%	1913
	11th to 20th	Day	17% 10% 4 6% 5% 3 4 5% 5% 6% 35%	1779
	21st to end	Day	26% 13% 3 6% 5% 3 4 5% 4 6% 25%	1782
November	1st to 10th	Day	16% 11% 3 6% 4 2 4 4 4 7% 39%	1671
	11th to 20th	Day	17% 14% 3 8% 5% 2 4 3 4 6% 32%	1710
	21st to end	Day	19% 13% 4 8% 5% 3 4 4 4 5% 28%	1587
December	1st to 10th	Day	19% 19% 7% 11% 5% 3 4 3 4 5% 20%	1520
	11th to 20th	Day	20% 18% 7% 8% 5% 2 3 3 3 4 28%	1906
	21st to end	Day	20% 19% 5% 10% 7% 4 3 3 4 5% 20%	2772
January	1st to 10th	Night	15% 16% 9% 12% 6% 3 3 4 3 4 26%	4429
	11th to 20th	Night	13% 18% 8% 13% 12% 4 4 4 3 5% 16%	4440
	21st to end	Night	22% 16% 6% 12% 8% 5% 4 3 3 3 17%	4850
February	1st to 10th	Night	16% 15% 6% 13% 8% 3 5% 4 5% 4 21%	2469
	11th to 20th	Night	13% 13% 6% 11% 9% 4 5% 4 5% 5% 24%	2218
	21st to end	Night	17% 13% 6% 11% 6% 2 5% 4 5% 5% 27%	1884
March	1st to 10th	Night	17% 13% 6% 9% 8% 3 4 4 5% 5% 28%	2217
	11th to 20th	Night	18% 14% 5% 9% 7% 3 4 4 4 4 29%	2101
	21st to end	Night	20% 12% 3 6% 5% 2 4 4 4 4 35%	1980
April	1st to 10th	Night	20% 12% 5% 6% 4 3 4 5% 5% 6% 29%	1800
	11th to 20th	Night	20% 11% 4 5% 4 3 4 5% 5% 6% 33%	1775
	21st to end	Night	21% 12% 4 6% 4 3 3 4 4 5% 32%	1688
May	1st to 10th	Night	24% 12% 3 6% 5% 3 4 4 4 6% 29%	1620
	11th to 20th	Night	20% 8% 3 6% 6% 3 5% 5% 5% 6% 34%	1416
	21st to end	Night	18% 5% 3 7% 5% 3 4 4 7% 7% 37%	1550
June	1st to 10th	Night	21% 7% 3 6% 4 3 5% 4 5% 8% 33%	1440
	11th to 20th	Night	22% 6% 2 4 4 2 4 5% 6% 8% 38%	1440
	21st to end	Night	15% 6% 3 5% 6% 3 5% 5% 7% 8% 39%	1440
July	1st to 10th	Night	15% 7% 2 5% 4 3 6% 5% 6% 7% 39%	1440
	11th to 20th	Night	15% 5% 2 5% 5% 3 6% 6% 5% 10% 37%	1440
	21st to end	Night	14% 6% 2 4 6% 3 5% 5% 5% 9% 42%	1574
August	1st to 10th	Night	13% 6% 2 3 5% 2 4 5% 7% 11% 41%	1439
	11th to 20th	Night	16% 7% 2 5% 5% 4 5% 6% 7% 8% 36%	1732
	21st to end	Night	16% 6% 2 4 4 3 4 4 5% 8% 42%	1980
September	1st to 10th	Night	18% 7% 2 5% 4 3 4 4 5% 5% 43%	1800
	11th to 20th	Night	18% 5% 2 4 5% 2 3 3 4 7% 49%	1903
	21st to end	Night	18% 7% 2 6% 5% 2 4 4 4 6% 42%	1980
October	1st to 10th	Night	24% 8% 3 5% 5% 3 3 4 5% 5% 35%	2044
	11th to 20th	Night	18% 9% 3 5% 5% 3 4 5% 5% 6% 36%	2179
	21st to end	Night	26% 11% 3 6% 5% 4 4 4 5% 6% 26%	2574
November	1st to 10th	Night	16% 11% 3 6% 5% 3 4 4 4 5% 38%	2407
	11th to 20th	Night	18% 12% 4 7% 5% 3 5% 5% 4 5% 32%	2470
	21st to end	Night	16% 15% 5% 7% 5% 3 5% 5% 4 6% 29%	2588
December	1st to 10th	Night	21% 19% 6% 9% 6% 3 4 4 4 4 21%	2660
	11th to 20th	Night	22% 15% 7% 9% 5% 2 4 3 4 4 24%	3288
	21st to end	Night	23% 17% 7% 9% 5% 3 4 4 4 4 20%	4884

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% 8% 16% 4	2518
	11th to 20th	Day	67% 8% 7% 13% 4 1	2520
	21st to end	Day	69% 5% 9% 12% 4 1	2804
February	1st to 10th	Day	65% 5% 9% 14% 6% 1	1710
	11th to 20th	Day	63% 5% 8% 15% 8% 1	1857
	21st to end	Day	61% 6% 9% 14% 9% 1	1570
March	1st to 10th	Day	58% 5% 12% 14% 10% 2	1850
	11th to 20th	Day	56% 5% 11% 11% 13% 3	1856
	21st to end	Day	53% 5% 8% 15% 15% 3	2376
April	1st to 10th	Day	56% 5% 8% 20% 9% 2	2160
	11th to 20th	Day	50% 7% 10% 19% 13% 1	2134
	21st to end	Day	55% 7% 9% 16% 11% 3	2272
May	1st to 10th	Day	56% 5% 9% 17% 11% 1	2353
	11th to 20th	Day	47% 6% 10% 21% 13% 2	2482
	21st to end	Day	44% 8% 16% 21% 10% 1	2725
June	1st to 10th	Day	51% 8% 15% 16% 9%	2520
	11th to 20th	Day	49% 7% 13% 19% 11% 1	2520
	21st to end	Day	51% 8% 12% 19% 9%	2520
July	1st to 10th	Day	43% 8% 12% 22% 13% 1	2450
	11th to 20th	Day	41% 9% 16% 25% 8%	2445
	21st to end	Day	44% 8% 14% 22% 11% 1	2591
August	1st to 10th	Day	42% 10% 16% 22% 9% 1	2467
	11th to 20th	Day	46% 9% 15% 20% 8% 1	2164
	21st to end	Day	41% 9% 14% 25% 11% 1	2376
September	1st to 10th	Day	41% 8% 12% 26% 13% 1	2160
	11th to 20th	Day	39% 5% 11% 25% 19% 1	2057
	21st to end	Day	41% 6% 13% 25% 14% 2	1980
October	1st to 10th	Day	54% 6% 9% 18% 11% 2	1913
	11th to 20th	Day	48% 7% 14% 22% 7% 1	1779
	21st to end	Day	61% 5% 11% 13% 8% 2	1782
November	1st to 10th	Day	45% 6% 14% 21% 13% 1	1671
	11th to 20th	Day	53% 6% 11% 16% 12% 1	1710
	21st to end	Day	56% 5% 16% 15% 7% 1	1587
December	1st to 10th	Day	67% 6% 9% 11% 6% 1	1520
	11th to 20th	Day	62% 4 11% 16% 6% 1	1906
	21st to end	Day	66% 7% 10% 11% 7%	2772
January	1st to 10th	Night	61% 6% 12% 13% 7% 1	4429
	11th to 20th	Night	67% 8% 9% 10% 5% 1	4440
	21st to end	Night	71% 5% 8% 10% 5% 1	4850
February	1st to 10th	Night	65% 6% 9% 13% 5% 1	2469
	11th to 20th	Night	60% 7% 10% 13% 9% 1	2220
	21st to end	Night	58% 6% 11% 16% 8% 2	1884
March	1st to 10th	Night	58% 6% 9% 18% 8% 1	2227
	11th to 20th	Night	58% 5% 10% 17% 9% 2	2102
	21st to end	Night	52% 5% 8% 16% 15% 4	1980
April	1st to 10th	Night	54% 6% 12% 17% 9% 1	1800
	11th to 20th	Night	51% 7% 10% 20% 12% 1	1775
	21st to end	Night	54% 5% 10% 16% 12% 3	1688
May	1st to 10th	Night	57% 6% 8% 14% 13% 2	1620
	11th to 20th	Night	49% 7% 12% 17% 12% 2	1417
	21st to end	Night	44% 9% 12% 22% 11% 2	1551
June	1st to 10th	Night	48% 6% 14% 21% 10%	1440
	11th to 20th	Night	44% 7% 16% 22% 11%	1440
	21st to end	Night	42% 8% 15% 24% 10% 1	1440
July	1st to 10th	Night	41% 9% 14% 21% 14% 1	1400
	11th to 20th	Night	41% 8% 16% 26% 9%	1392
	21st to end	Night	38% 8% 15% 26% 12% 1	1486
August	1st to 10th	Night	35% 10% 18% 26% 11% 1	1429
	11th to 20th	Night	42% 10% 15% 23% 10%	1732
	21st to end	Night	39% 6% 14% 27% 13% 1	1980
September	1st to 10th	Night	42% 7% 12% 26% 13% 1	1800
	11th to 20th	Night	37% 5% 11% 27% 18% 1	1903
	21st to end	Night	43% 6% 10% 24% 15% 2	1980
October	1st to 10th	Night	50% 6% 11% 21% 10% 2	2044
	11th to 20th	Night	48% 6% 16% 20% 9% 1	2179
	21st to end	Night	59% 6% 11% 15% 8% 1	2574
November	1st to 10th	Night	49% 5% 11% 19% 14% 2	2407
	11th to 20th	Night	52% 7% 11% 16% 11% 2	2470
	21st to end	Night	55% 7% 14% 17% 7%	2588
December	1st to 10th	Night	66% 7% 11% 11% 5%	2660
	11th to 20th	Night	63% 7% 11% 10% 8%	3288
	21st to end	Night	68% 5% 9% 13% 5%	4884

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	30% 29% 24% 14% 3	180
	11th to 20th	Day	32% 28% 28% 9% 1 1	180
	21st to end	Day	26% 29% 31% 9% 5%	207
February	1st to 10th	Day	36% 34% 23% 5% 1	270
	11th to 20th	Day	30% 33% 26% 10% 2	456
	21st to end	Day	34% 25% 26% 12% 2	382
March	1st to 10th	Day	31% 25% 26% 16% 2	440
	11th to 20th	Day	32% 26% 28% 11% 3	420
	21st to end	Day	34% 25% 22% 12% 6% 2	462
April	1st to 10th	Day	36% 20% 24% 12% 7% 1	420
	11th to 20th	Day	29% 25% 25% 12% 7% 2	412
	21st to end	Day	34% 17% 29% 13% 4 2	420
May	1st to 10th	Day	34% 20% 25% 13% 6% 2	423
	11th to 20th	Day	26% 17% 34% 18% 4 2	447
	21st to end	Day	22% 15% 29% 21% 9% 3	485
June	1st to 10th	Day	19% 15% 34% 20% 10% 1	450
	11th to 20th	Day	23% 11% 31% 24% 8% 2	450
	21st to end	Day	21% 18% 29% 21% 8% 2	450
July	1st to 10th	Day	18% 9% 30% 25% 14% 2	445
	11th to 20th	Day	16% 7% 34% 30% 11% 2	444
	21st to end	Day	15% 12% 37% 23% 11% 1	488
August	1st to 10th	Day	13% 11% 28% 30% 13% 5%	446
	11th to 20th	Day	17% 10% 31% 23% 13% 6%	439
	21st to end	Day	17% 11% 28% 26% 12% 5%	495
September	1st to 10th	Day	18% 12% 23% 26% 14% 6%	450
	11th to 20th	Day	19% 14% 25% 19% 15% 9%	450
	21st to end	Day	19% 13% 29% 20% 12% 7%	450
October	1st to 10th	Day	31% 12% 23% 18% 13% 4	450
	11th to 20th	Day	24% 20% 25% 20% 9% 1	439
	21st to end	Day	34% 14% 29% 19% 3 1	396
November	1st to 10th	Day	26% 21% 22% 20% 10% 1	365
	11th to 20th	Day	29% 28% 22% 15% 5% 1	370
	21st to end	Day	31% 25% 26% 15% 3	247
December	1st to 10th	Day	36% 25% 26% 9% 3	180
	11th to 20th	Day	41% 25% 24% 9% 2	180
	21st to end	Day	39% 23% 25% 11% 3	198
January	1st to 10th	Night	26% 28% 31% 13% 2	760
	11th to 20th	Night	29% 25% 26% 18% 2	760
	21st to end	Night	22% 26% 31% 18% 3	836
February	1st to 10th	Night	26% 28% 31% 15% 1	760
	11th to 20th	Night	25% 28% 30% 14% 2	743
	21st to end	Night	28% 25% 27% 17% 2	628
March	1st to 10th	Night	28% 22% 29% 18% 3	743
	11th to 20th	Night	28% 26% 26% 17% 3	720
	21st to end	Night	28% 23% 23% 18% 7% 1	792
April	1st to 10th	Night	29% 21% 27% 20% 4	720
	11th to 20th	Night	27% 19% 26% 19% 8%	711
	21st to end	Night	29% 16% 27% 21% 6% 1	608
May	1st to 10th	Night	27% 17% 24% 24% 7% 1	540
	11th to 20th	Night	25% 12% 28% 31% 4	355
	21st to end	Night	18% 10% 25% 34% 12% 1	389
June	1st to 10th	Night	23% 8% 25% 31% 13% 1	360
	11th to 20th	Night	21% 6% 23% 39% 10%	360
	21st to end	Night	16% 6% 26% 39% 12% 1	360
July	1st to 10th	Night	16% 5% 20% 43% 15% 1	350
	11th to 20th	Night	16% 5% 22% 39% 17% 1	348
	21st to end	Night	16% 5% 23% 41% 14% 1	394
August	1st to 10th	Night	14% 5% 20% 42% 19% 1	365
	11th to 20th	Night	19% 4 20% 35% 18% 4	668
	21st to end	Night	17% 6% 22% 33% 20% 2	792
September	1st to 10th	Night	20% 7% 25% 32% 15% 2	720
	11th to 20th	Night	20% 8% 20% 29% 18% 5%	720
	21st to end	Night	20% 12% 23% 28% 14% 3	720
October	1st to 10th	Night	28% 11% 20% 26% 13% 2	720
	11th to 20th	Night	23% 13% 28% 26% 9%	720
	21st to end	Night	33% 17% 25% 21% 4	792
November	1st to 10th	Night	25% 19% 25% 24% 6%	740
	11th to 20th	Night	25% 22% 28% 16% 7% 1	760
	21st to end	Night	27% 21% 29% 17% 6% 1	760
December	1st to 10th	Night	33% 26% 24% 13% 4	760
	11th to 20th	Night	30% 24% 26% 16% 3	760
	21st to end	Night	32% 26% 26% 14% 2	836

Page generated at 2024-03-03 06:28:56. Version ac07

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