Adirondack Public Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Adirondack Public Observatory clear sky chart from 2005-11-06 to 2025-02-21.

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	17% 13% 4 10% 6% 5% 4 4 5% 6% 26%	108616
	Night	16% 15% 6% 13% 6% 5% 4 3 4 5% 24%	109943
Transparency	Day	57% 6% 10% 17% 8% 1	112117
	Night	62% 6% 9% 15% 7% 1	114606
Seeing	Day	28% 18% 28% 16% 8% 2	14903
	Night	27% 18% 26% 21% 8% 1	24103

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	11% 18% 7% 24% 11% 5% 3 2 3 3 11%	3597
	11th to 20th	Day	9% 18% 8% 25% 14% 3 3 2 2 3 12%	3570
	21st to end	Day	11% 20% 8% 15% 7% 8% 6% 3 4 3 14%	4069
February	1st to 10th	Day	13% 20% 7% 18% 8% 5% 4 3 3 3 16%	1800
	11th to 20th	Day	11% 16% 8% 18% 9% 7% 4 3 4 4 17%	1848
	21st to end	Day	15% 18% 7% 14% 8% 6% 4 3 4 4 18%	1570
March	1st to 10th	Day	22% 15% 6% 11% 6% 4 4 2 3 5% 21%	3116
	11th to 20th	Day	11% 25% 8% 11% 6% 4 4 3 3 3 22%	3352
	21st to end	Day	15% 13% 5% 11% 7% 4 3 2 3 5% 32%	4120
April	1st to 10th	Day	20% 18% 5% 8% 4 3 4 3 5% 4 28%	2280
	11th to 20th	Day	20% 14% 3 8% 4 4 3 3 4 5% 32%	2254
	21st to end	Day	24% 14% 3 8% 4 4 3 3 5% 5% 28%	2368
May	1st to 10th	Day	24% 13% 3 7% 5% 4 4 4 5% 6% 26%	4361
	11th to 20th	Day	18% 10% 3 9% 6% 5% 5% 4 5% 7% 28%	4398
	21st to end	Day	16% 8% 2 7% 5% 4 5% 4 6% 8% 35%	4837
June	1st to 10th	Day	24% 8% 3 8% 5% 5% 5% 4 6% 6% 27%	2660
	11th to 20th	Day	20% 8% 3 6% 5% 5% 5% 5% 6% 8% 31%	2660
	21st to end	Day	23% 7% 3 8% 6% 5% 5% 5% 5% 6% 28%	2660
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 10% 33%	4440
	11th to 20th	Day	13% 7% 3 7% 5% 5% 6% 5% 8% 10% 31%	4440
	21st to end	Day	14% 7% 2 7% 5% 5% 6% 5% 7% 9% 34%	4814
August	1st to 10th	Day	18% 9% 3 7% 5% 4 5% 5% 6% 8% 31%	4423
	11th to 20th	Day	16% 7% 3 8% 5% 5% 6% 4 7% 7% 32%	3844
	21st to end	Day	17% 7% 2 6% 4 5% 5% 4 7% 8% 34%	4180
September	1st to 10th	Day	16% 7% 3 6% 5% 4 4 3 6% 7% 38%	2280
	11th to 20th	Day	17% 7% 2 4 4 3 4 3 5% 7% 42%	2226
	21st to end	Day	19% 8% 2 6% 4 4 4 4 6% 7% 35%	2090
October	1st to 10th	Day	24% 11% 3 8% 4 4 4 3 4 5% 29%	1927
	11th to 20th	Day	20% 15% 3 7% 5% 4 4 4 5% 5% 29%	1900
	21st to end	Day	24% 19% 4 6% 4 3 3 3 4 5% 23%	1895
November	1st to 10th	Day	15% 18% 4 9% 5% 5% 4 4 4 5% 26%	1761
	11th to 20th	Day	15% 18% 6% 10% 5% 5% 4 3 4 4 25%	1730
	21st to end	Day	16% 23% 6% 12% 6% 4 4 3 3 5% 18%	1600
December	1st to 10th	Day	13% 26% 9% 21% 8% 4 3 2 2 3 8%	2600
	11th to 20th	Day	16% 19% 8% 18% 5% 4 4 3 4 4 15%	2986
	21st to end	Day	16% 18% 7% 14% 6% 4 4 4 5% 5% 18%	3960
January	1st to 10th	Night	11% 19% 9% 26% 10% 5% 3 2 2 3 11%	6349
	11th to 20th	Night	8% 18% 11% 26% 12% 5% 4 3 2 2 7%	6315
	21st to end	Night	11% 17% 10% 20% 8% 8% 6% 3 3 3 11%	6886
February	1st to 10th	Night	13% 19% 7% 17% 10% 5% 3 3 4 4 15%	2600
	11th to 20th	Night	11% 16% 8% 17% 9% 7% 5% 3 4 4 17%	2437
	21st to end	Night	14% 18% 6% 13% 9% 5% 4 3 4 3 20%	1885
March	1st to 10th	Night	18% 14% 5% 9% 8% 5% 4 3 4 4 26%	3724
	11th to 20th	Night	14% 21% 8% 10% 5% 4 3 3 4 4 25%	3589
	21st to end	Night	16% 16% 5% 10% 5% 4 3 2 4 3 32%	3512
April	1st to 10th	Night	19% 18% 4 10% 3 3 3 3 4 4 29%	1900
	11th to 20th	Night	20% 16% 4 7% 5% 4 4 3 4 5% 29%	1875
	21st to end	Night	20% 12% 4 7% 5% 4 3 2 5% 5% 31%	1810
May	1st to 10th	Night	25% 13% 3 8% 4 4 5% 3 6% 5% 25%	2595
	11th to 20th	Night	20% 12% 3 8% 4 4 4 3 5% 6% 31%	2495
	21st to end	Night	17% 6% 2 7% 5% 4 4 3 6% 8% 37%	2738
June	1st to 10th	Night	22% 8% 2 5% 5% 6% 5% 4 6% 6% 31%	1520
	11th to 20th	Night	20% 6% 2 6% 4 4 3 4 5% 8% 37%	1520
	21st to end	Night	22% 8% 3 5% 6% 4 4 3 6% 8% 33%	1520
July	1st to 10th	Night	14% 7% 2 7% 6% 5% 5% 4 6% 7% 37%	2520
	11th to 20th	Night	14% 8% 3 7% 4 4 5% 4 5% 7% 39%	2520
	21st to end	Night	14% 7% 2 8% 5% 5% 5% 3 5% 8% 39%	2739
August	1st to 10th	Night	20% 9% 2 6% 4 4 4 3 5% 7% 37%	2506
	11th to 20th	Night	17% 8% 3 8% 5% 4 4 4 5% 7% 35%	2949
	21st to end	Night	13% 8% 2 6% 4 5% 5% 3 6% 8% 39%	3476
September	1st to 10th	Night	15% 7% 2 6% 4 4 5% 4 5% 7% 41%	1900
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 5% 6% 46%	1953
	21st to end	Night	20% 7% 1 5% 4 4 4 4 6% 6% 39%	2090
October	1st to 10th	Night	23% 11% 2 6% 4 3 4 4 6% 6% 30%	2251
	11th to 20th	Night	19% 13% 3 8% 5% 5% 4 4 4 6% 30%	2280
	21st to end	Night	25% 18% 4 7% 5% 4 4 3 4 4 22%	2703
November	1st to 10th	Night	17% 17% 5% 8% 5% 4 5% 3 5% 5% 28%	2537
	11th to 20th	Night	17% 17% 6% 9% 6% 4 3 3 4 5% 25%	2665
	21st to end	Night	17% 21% 8% 12% 5% 3 4 3 4 4 18%	2800
December	1st to 10th	Night	13% 26% 13% 21% 6% 3 3 2 3 3 7%	4580
	11th to 20th	Night	16% 21% 8% 15% 6% 4 4 2 3 3 17%	5208
	21st to end	Night	18% 18% 6% 16% 5% 5% 5% 3 5% 4 15%	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	79% 4 5% 9% 3	3598
	11th to 20th	Day	80% 3 4 6% 6% 2	3600
	21st to end	Day	74% 5% 7% 8% 6% 1	4069
February	1st to 10th	Day	75% 4 5% 11% 4 2	1800
	11th to 20th	Day	72% 4 7% 9% 7% 1	1857
	21st to end	Day	70% 4 7% 9% 8% 1	1570
March	1st to 10th	Day	67% 6% 7% 11% 8% 1	3119
	11th to 20th	Day	67% 4 10% 9% 7% 1	3352
	21st to end	Day	57% 3 7% 15% 16% 2	4120
April	1st to 10th	Day	60% 4 8% 16% 10% 2	2280
	11th to 20th	Day	56% 5% 8% 18% 13% 1	2254
	21st to end	Day	59% 5% 8% 14% 11% 3	2368
May	1st to 10th	Day	57% 6% 10% 19% 7% 1	4375
	11th to 20th	Day	53% 10% 11% 18% 7% 1	4402
	21st to end	Day	46% 9% 10% 25% 10% 1	4837
June	1st to 10th	Day	56% 7% 11% 15% 10%	2660
	11th to 20th	Day	50% 8% 11% 21% 8% 1	2660
	21st to end	Day	56% 8% 10% 18% 7% 1	2660
July	1st to 10th	Day	42% 8% 14% 26% 10%	4370
	11th to 20th	Day	44% 10% 15% 27% 5%	4365
	21st to end	Day	45% 9% 12% 27% 7%	4661
August	1st to 10th	Day	49% 9% 13% 19% 9%	4409
	11th to 20th	Day	48% 9% 16% 22% 5%	3883
	21st to end	Day	43% 9% 16% 22% 9%	4180
September	1st to 10th	Day	44% 7% 11% 26% 11% 1	2280
	11th to 20th	Day	41% 5% 11% 28% 15% 1	2226
	21st to end	Day	47% 7% 12% 21% 11% 1	2090
October	1st to 10th	Day	48% 6% 11% 24% 11%	3200
	11th to 20th	Day	50% 5% 13% 18% 13%	3140
	21st to end	Day	50% 5% 15% 24% 5% 1	3095
November	1st to 10th	Day	60% 7% 10% 15% 8%	1761
	11th to 20th	Day	63% 5% 9% 12% 8% 4	1730
	21st to end	Day	70% 5% 10% 10% 4	1600
December	1st to 10th	Day	83% 4 5% 6% 1	2600
	11th to 20th	Day	72% 6% 7% 11% 4	2986
	21st to end	Day	68% 5% 6% 9% 11% 1	3960
January	1st to 10th	Night	82% 3 5% 6% 3	6349
	11th to 20th	Night	84% 5% 4 4 3 1	6360
	21st to end	Night	79% 4 5% 7% 5% 1	6886
February	1st to 10th	Night	75% 5% 6% 8% 6% 1	2600
	11th to 20th	Night	72% 5% 5% 11% 7%	2439
	21st to end	Night	69% 5% 6% 12% 7% 1	1885
March	1st to 10th	Night	61% 7% 8% 14% 10% 1	3734
	11th to 20th	Night	64% 4 11% 13% 7% 1	3590
	21st to end	Night	59% 3 6% 16% 14% 2	3512
April	1st to 10th	Night	61% 5% 8% 16% 10% 1	1900
	11th to 20th	Night	58% 5% 9% 16% 11%	1875
	21st to end	Night	56% 6% 8% 16% 12% 2	1810
May	1st to 10th	Night	59% 6% 10% 15% 8% 1	2601
	11th to 20th	Night	53% 8% 10% 19% 8% 1	2496
	21st to end	Night	45% 8% 12% 21% 14% 1	2739
June	1st to 10th	Night	51% 8% 13% 20% 8% 1	1520
	11th to 20th	Night	46% 5% 15% 21% 12% 1	1520
	21st to end	Night	51% 8% 12% 20% 9%	1520
July	1st to 10th	Night	45% 7% 13% 22% 12% 1	2480
	11th to 20th	Night	42% 9% 14% 28% 6%	2472
	21st to end	Night	44% 8% 14% 26% 8% 1	2651
August	1st to 10th	Night	48% 7% 15% 22% 7%	2496
	11th to 20th	Night	48% 9% 16% 20% 6%	2976
	21st to end	Night	39% 9% 15% 27% 8% 1	3476
September	1st to 10th	Night	42% 8% 13% 26% 10% 1	1900
	11th to 20th	Night	38% 6% 13% 32% 11%	1953
	21st to end	Night	44% 8% 11% 25% 12% 1	2090
October	1st to 10th	Night	52% 8% 11% 21% 8%	3758
	11th to 20th	Night	50% 7% 12% 18% 10% 2	3779
	21st to end	Night	56% 6% 13% 19% 5% 1	4453
November	1st to 10th	Night	59% 6% 11% 13% 8% 2	2537
	11th to 20th	Night	62% 6% 8% 13% 8% 3	2665
	21st to end	Night	70% 6% 8% 11% 4 1	2800
December	1st to 10th	Night	85% 3 5% 5% 2	4580
	11th to 20th	Night	74% 5% 5% 10% 6%	5208
	21st to end	Night	73% 4 5% 8% 8% 2	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	26% 25% 34% 11% 5% 1	200
	11th to 20th	Day	30% 27% 34% 8% 2 1	200
	21st to end	Day	26% 27% 34% 11% 2	243
February	1st to 10th	Day	39% 31% 24% 6%	300
	11th to 20th	Day	35% 29% 29% 7% 1	395
	21st to end	Day	34% 26% 28% 9% 3	382
March	1st to 10th	Day	33% 21% 30% 14% 3	460
	11th to 20th	Day	32% 23% 29% 12% 3 1	460
	21st to end	Day	34% 26% 21% 11% 6% 1	506
April	1st to 10th	Day	36% 21% 25% 11% 6% 1	460
	11th to 20th	Day	38% 18% 21% 14% 7% 2	452
	21st to end	Day	36% 19% 28% 9% 6% 2	460
May	1st to 10th	Day	32% 18% 29% 11% 7% 3	463
	11th to 20th	Day	25% 17% 29% 21% 7% 1	487
	21st to end	Day	23% 19% 29% 19% 10% 1	529
June	1st to 10th	Day	30% 16% 27% 20% 4 2	490
	11th to 20th	Day	24% 16% 29% 21% 8% 2	490
	21st to end	Day	29% 17% 28% 18% 6% 2	490
July	1st to 10th	Day	17% 12% 32% 25% 12% 2	485
	11th to 20th	Day	17% 12% 35% 24% 10% 2	484
	21st to end	Day	16% 14% 37% 24% 8% 2	532
August	1st to 10th	Day	19% 11% 30% 22% 15% 4	486
	11th to 20th	Day	19% 10% 29% 24% 13% 6%	479
	21st to end	Day	16% 16% 28% 23% 12% 5%	539
September	1st to 10th	Day	22% 11% 29% 18% 13% 7%	490
	11th to 20th	Day	18% 12% 21% 18% 20% 10%	490
	21st to end	Day	20% 14% 26% 21% 14% 4	490
October	1st to 10th	Day	29% 16% 22% 15% 12% 4	490
	11th to 20th	Day	30% 19% 24% 18% 7% 1	490
	21st to end	Day	37% 18% 24% 17% 4	436
November	1st to 10th	Day	36% 14% 27% 15% 7% 1	395
	11th to 20th	Day	36% 22% 25% 9% 6% 1	330
	21st to end	Day	35% 24% 30% 10% 1	200
December	1st to 10th	Day	37% 18% 31% 13% 2 1	200
	11th to 20th	Day	36% 27% 31% 5% 2 1	200
	21st to end	Day	35% 20% 34% 8% 3 1	220
January	1st to 10th	Night	28% 27% 30% 13% 2	800
	11th to 20th	Night	30% 24% 31% 12% 3	800
	21st to end	Night	21% 26% 32% 17% 4	880
February	1st to 10th	Night	29% 26% 30% 14% 1	800
	11th to 20th	Night	28% 26% 31% 14% 2	783
	21st to end	Night	27% 23% 32% 15% 3	629
March	1st to 10th	Night	28% 23% 30% 18% 2	760
	11th to 20th	Night	30% 23% 28% 15% 3 1	760
	21st to end	Night	27% 22% 27% 18% 5% 1	836
April	1st to 10th	Night	32% 19% 27% 18% 3	760
	11th to 20th	Night	32% 20% 24% 18% 6%	751
	21st to end	Night	32% 17% 24% 20% 7%	670
May	1st to 10th	Night	31% 12% 25% 22% 9% 1	435
	11th to 20th	Night	19% 12% 30% 31% 8% 1	374
	21st to end	Night	17% 14% 27% 29% 13%	411
June	1st to 10th	Night	26% 9% 26% 28% 11% 1	380
	11th to 20th	Night	23% 5% 24% 34% 13%	380
	21st to end	Night	23% 10% 27% 31% 9%	380
July	1st to 10th	Night	12% 6% 28% 38% 16%	370
	11th to 20th	Night	13% 4 27% 38% 17% 1	368
	21st to end	Night	15% 6% 25% 41% 12% 1	416
August	1st to 10th	Night	19% 6% 21% 37% 16% 1	378
	11th to 20th	Night	20% 7% 20% 30% 21% 2	650
	21st to end	Night	19% 7% 24% 33% 17% 1	836
September	1st to 10th	Night	19% 11% 24% 28% 16% 2	760
	11th to 20th	Night	20% 7% 19% 28% 22% 4	760
	21st to end	Night	24% 11% 23% 21% 19% 2	760
October	1st to 10th	Night	30% 14% 21% 19% 14% 2	760
	11th to 20th	Night	30% 14% 24% 24% 7% 1	760
	21st to end	Night	37% 18% 23% 19% 3	836
November	1st to 10th	Night	32% 16% 27% 18% 7%	780
	11th to 20th	Night	30% 20% 27% 14% 8% 1	800
	21st to end	Night	33% 23% 24% 15% 5%	800
December	1st to 10th	Night	33% 26% 25% 14% 3	800
	11th to 20th	Night	30% 24% 27% 15% 3 1	800
	21st to end	Night	32% 26% 26% 12% 3	880

Page generated at 2025-02-18 03:26:28. Version ac07

Copyright © 2025 Attilla Danko.