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 2026-06-16.

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% 5% 4 5% 6% 26%	137874
	Night	16% 15% 6% 12% 6% 5% 4 3 4 5% 24%	134157
Transparency	Day	58% 6% 10% 17% 8% 1	141329
	Night	62% 6% 9% 15% 7% 1	138791
Seeing	Day	28% 19% 28% 16% 8% 2	16632
	Night	27% 18% 26% 21% 8% 1	25717

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% 8% 24% 11% 6% 4 2 3 3 10%	4661
	11th to 20th	Day	7% 19% 10% 24% 13% 5% 3 2 2 2 12%	4650
	21st to end	Day	9% 17% 8% 16% 10% 11% 7% 3 4 3 13%	5261
February	1st to 10th	Day	12% 19% 7% 18% 8% 6% 5% 3 3 3 16%	1890
	11th to 20th	Day	11% 16% 8% 18% 9% 7% 4 3 4 5% 17%	1943
	21st to end	Day	14% 19% 8% 15% 8% 6% 4 3 4 4 16%	1730
March	1st to 10th	Day	19% 16% 7% 15% 6% 3 4 2 3 4 20%	4576
	11th to 20th	Day	10% 21% 6% 11% 6% 5% 4 3 4 5% 26%	4902
	21st to end	Day	17% 14% 6% 11% 6% 4 4 2 3 4 28%	6026
April	1st to 10th	Day	19% 19% 5% 8% 4 4 4 3 5% 4 26%	2520
	11th to 20th	Day	20% 15% 4 8% 4 4 3 2 4 5% 32%	2494
	21st to end	Day	23% 14% 3 7% 4 4 4 3 4 5% 29%	2618
May	1st to 10th	Day	26% 13% 4 8% 5% 4 5% 4 5% 6% 22%	8116
	11th to 20th	Day	18% 11% 3 9% 6% 5% 5% 4 5% 7% 28%	8221
	21st to end	Day	21% 11% 3 7% 5% 5% 5% 4 5% 6% 28%	9060
June	1st to 10th	Day	23% 8% 3 8% 5% 5% 5% 4 6% 6% 28%	2940
	11th to 20th	Day	19% 8% 3 6% 5% 5% 5% 5% 6% 8% 30%	2870
	21st to end	Day	22% 7% 3 8% 6% 5% 5% 5% 5% 6% 28%	2800
July	1st to 10th	Day	13% 6% 2 7% 5% 6% 6% 5% 7% 10% 33%	6360
	11th to 20th	Day	12% 7% 2 8% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	14% 6% 2 6% 4 4 6% 5% 6% 10% 37%	6926
August	1st to 10th	Day	17% 8% 3 7% 5% 4 5% 4 6% 8% 32%	4563
	11th to 20th	Day	16% 8% 3 8% 5% 5% 6% 4 7% 7% 32%	3968
	21st to end	Day	17% 7% 2 6% 4 5% 5% 5% 8% 8% 34%	4312
September	1st to 10th	Day	16% 7% 3 6% 5% 4 4 3 6% 7% 39%	2400
	11th to 20th	Day	16% 7% 2 4 4 3 4 3 5% 7% 44%	2343
	21st to end	Day	19% 8% 2 6% 4 4 4 4 6% 7% 35%	2200
October	1st to 10th	Day	23% 11% 3 8% 4 4 4 3 4 5% 32%	2028
	11th to 20th	Day	20% 15% 4 7% 4 4 4 4 5% 6% 29%	2000
	21st to end	Day	24% 18% 4 7% 4 3 4 3 4 5% 23%	1995
November	1st to 10th	Day	15% 19% 5% 9% 5% 5% 4 4 4 5% 26%	1851
	11th to 20th	Day	14% 19% 6% 10% 5% 5% 4 3 4 4 24%	1816
	21st to end	Day	16% 24% 6% 12% 6% 4 4 3 3 5% 17%	1680
December	1st to 10th	Day	13% 26% 9% 21% 8% 4 3 2 3 3 8%	2680
	11th to 20th	Day	16% 19% 8% 18% 6% 4 4 3 4 4 15%	3066
	21st to end	Day	16% 18% 7% 14% 6% 4 4 4 5% 5% 17%	4048
January	1st to 10th	Night	11% 20% 8% 24% 10% 5% 3 2 2 3 11%	8234
	11th to 20th	Night	8% 19% 11% 26% 13% 6% 4 2 2 2 7%	8235
	21st to end	Night	10% 15% 8% 19% 11% 10% 7% 4 3 3 10%	8919
February	1st to 10th	Night	13% 18% 7% 18% 10% 6% 3 3 4 4 15%	2730
	11th to 20th	Night	10% 16% 8% 17% 9% 7% 5% 3 4 4 17%	2562
	21st to end	Night	13% 19% 6% 14% 9% 5% 4 3 4 3 20%	2076
March	1st to 10th	Night	17% 16% 5% 12% 7% 6% 4 3 3 4 22%	5484
	11th to 20th	Night	12% 17% 7% 9% 5% 4 4 3 5% 6% 28%	5259
	21st to end	Night	18% 17% 6% 12% 6% 4 3 2 3 3 25%	5148
April	1st to 10th	Night	20% 18% 4 10% 3 3 3 3 4 5% 28%	2100
	11th to 20th	Night	21% 17% 4 7% 5% 4 3 3 4 5% 28%	2075
	21st to end	Night	19% 13% 4 7% 5% 4 4 2 5% 5% 32%	2000
May	1st to 10th	Night	27% 15% 3 8% 4 4 4 2 5% 5% 21%	4825
	11th to 20th	Night	20% 11% 3 7% 4 4 4 3 5% 8% 30%	4639
	21st to end	Night	20% 11% 3 8% 5% 4 5% 3 5% 8% 29%	5114
June	1st to 10th	Night	22% 8% 3 5% 5% 5% 5% 4 6% 7% 33%	1680
	11th to 20th	Night	20% 7% 2 6% 4 4 3 4 5% 8% 37%	1640
	21st to end	Night	21% 8% 3 6% 5% 4 4 3 6% 7% 33%	1600
July	1st to 10th	Night	13% 6% 2 7% 5% 5% 5% 4 7% 9% 36%	3600
	11th to 20th	Night	16% 7% 2 7% 4 4 5% 3 5% 7% 40%	3600
	21st to end	Night	12% 7% 2 7% 4 4 4 3 5% 8% 45%	3926
August	1st to 10th	Night	20% 9% 2 6% 4 4 4 3 5% 7% 38%	2586
	11th to 20th	Night	17% 8% 3 8% 5% 4 4 4 5% 7% 35%	3044
	21st to end	Night	13% 8% 3 6% 4 5% 5% 3 6% 8% 39%	3586
September	1st to 10th	Night	15% 7% 2 6% 4 4 5% 4 5% 6% 42%	2000
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 5% 6% 47%	2056
	21st to end	Night	20% 8% 1 5% 4 4 4 4 6% 6% 39%	2200
October	1st to 10th	Night	22% 11% 2 6% 4 3 4 4 6% 6% 32%	2370
	11th to 20th	Night	18% 13% 3 8% 5% 5% 4 4 5% 6% 31%	2400
	21st to end	Night	24% 18% 4 7% 5% 4 4 3 4 4 23%	2845
November	1st to 10th	Night	18% 18% 5% 8% 4 4 4 3 4 5% 27%	2667
	11th to 20th	Night	16% 17% 7% 10% 6% 4 3 3 4 5% 25%	2799
	21st to end	Night	17% 21% 8% 13% 5% 3 4 3 4 4 18%	2940
December	1st to 10th	Night	13% 25% 13% 21% 6% 3 3 2 3 3 8%	4720
	11th to 20th	Night	16% 20% 8% 16% 7% 5% 4 2 3 3 17%	5348
	21st to end	Night	18% 18% 6% 16% 5% 5% 5% 3 5% 4 14%	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	80% 4 5% 8% 2	4662
	11th to 20th	Day	81% 3 3 5% 7% 2	4680
	21st to end	Day	76% 4 6% 8% 6% 1	5261
February	1st to 10th	Day	75% 3 5% 12% 4 2	1890
	11th to 20th	Day	71% 4 7% 10% 7% 1	1952
	21st to end	Day	72% 4 7% 9% 7% 1	1730
March	1st to 10th	Day	69% 5% 7% 9% 8% 3	4579
	11th to 20th	Day	61% 4 13% 12% 7% 3	4902
	21st to end	Day	61% 4 6% 12% 16% 2	6026
April	1st to 10th	Day	61% 4 8% 16% 10% 1	2520
	11th to 20th	Day	57% 4 7% 17% 13% 1	2494
	21st to end	Day	58% 5% 8% 15% 12% 3	2618
May	1st to 10th	Day	63% 6% 8% 15% 8% 1	8128
	11th to 20th	Day	54% 8% 11% 19% 7%	8225
	21st to end	Day	55% 7% 8% 22% 7%	9061
June	1st to 10th	Day	55% 7% 11% 16% 11% 1	2940
	11th to 20th	Day	50% 8% 11% 22% 8% 1	2870
	21st to end	Day	55% 8% 10% 18% 8% 1	2800
July	1st to 10th	Day	43% 8% 15% 23% 10%	6290
	11th to 20th	Day	42% 9% 13% 25% 9%	6285
	21st to end	Day	40% 8% 12% 33% 6%	6728
August	1st to 10th	Day	48% 9% 13% 20% 9%	4549
	11th to 20th	Day	48% 9% 15% 22% 6%	4007
	21st to end	Day	43% 9% 16% 22% 9%	4312
September	1st to 10th	Day	43% 7% 11% 28% 11% 1	2400
	11th to 20th	Day	40% 5% 10% 29% 15% 1	2343
	21st to end	Day	47% 8% 12% 22% 11% 1	2200
October	1st to 10th	Day	47% 6% 11% 24% 12%	3301
	11th to 20th	Day	50% 5% 13% 19% 13% 1	3240
	21st to end	Day	51% 5% 15% 24% 5% 1	3195
November	1st to 10th	Day	61% 7% 10% 15% 8%	1851
	11th to 20th	Day	64% 4 8% 12% 8% 3	1816
	21st to end	Day	71% 5% 10% 10% 4	1680
December	1st to 10th	Day	83% 4 5% 6% 2	2680
	11th to 20th	Day	71% 6% 7% 11% 5%	3066
	21st to end	Day	68% 5% 6% 9% 11% 1	4048
January	1st to 10th	Night	81% 3 6% 7% 3	8234
	11th to 20th	Night	85% 4 3 4 3 1	8280
	21st to end	Night	80% 4 4 6% 5% 1	8919
February	1st to 10th	Night	74% 5% 6% 8% 6% 1	2730
	11th to 20th	Night	71% 5% 6% 11% 6%	2564
	21st to end	Night	69% 5% 7% 12% 6% 1	2076
March	1st to 10th	Night	66% 5% 6% 11% 10% 1	5494
	11th to 20th	Night	57% 5% 15% 13% 7% 3	5260
	21st to end	Night	65% 4 4 14% 11% 1	5148
April	1st to 10th	Night	60% 4 8% 16% 10% 1	2100
	11th to 20th	Night	59% 5% 8% 16% 11%	2075
	21st to end	Night	55% 6% 8% 17% 12% 2	2000
May	1st to 10th	Night	64% 6% 8% 14% 8% 1	4831
	11th to 20th	Night	52% 7% 11% 21% 9% 1	4640
	21st to end	Night	54% 7% 9% 20% 9%	5115
June	1st to 10th	Night	50% 7% 12% 20% 9% 1	1680
	11th to 20th	Night	47% 5% 15% 20% 12% 1	1640
	21st to end	Night	51% 8% 12% 21% 9%	1600
July	1st to 10th	Night	42% 8% 18% 22% 10%	3560
	11th to 20th	Night	43% 8% 13% 26% 10%	3552
	21st to end	Night	38% 7% 14% 32% 9%	3809
August	1st to 10th	Night	47% 7% 15% 23% 8%	2576
	11th to 20th	Night	48% 9% 16% 20% 7%	3071
	21st to end	Night	40% 9% 15% 27% 8% 1	3586
September	1st to 10th	Night	42% 8% 12% 27% 11% 1	2000
	11th to 20th	Night	38% 6% 12% 32% 12%	2056
	21st to end	Night	44% 8% 10% 24% 13% 1	2200
October	1st to 10th	Night	51% 7% 11% 21% 9% 1	3877
	11th to 20th	Night	50% 7% 12% 19% 11% 2	3899
	21st to end	Night	56% 6% 13% 19% 5% 1	4595
November	1st to 10th	Night	60% 6% 11% 13% 8% 2	2667
	11th to 20th	Night	63% 6% 8% 13% 8% 3	2799
	21st to end	Night	71% 6% 8% 11% 4 1	2940
December	1st to 10th	Night	84% 3 5% 5% 2	4720
	11th to 20th	Night	74% 5% 5% 10% 6%	5348
	21st to end	Night	73% 4 5% 8% 8% 2	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	26% 25% 35% 10% 4	220
	11th to 20th	Day	32% 27% 32% 7% 1	220
	21st to end	Day	25% 27% 34% 10% 2	267
February	1st to 10th	Day	36% 29% 26% 7% 1	330
	11th to 20th	Day	34% 28% 30% 6% 1	430
	21st to end	Day	33% 27% 29% 9% 3	446
March	1st to 10th	Day	33% 22% 29% 13% 3	540
	11th to 20th	Day	34% 24% 28% 12% 3 1	540
	21st to end	Day	35% 28% 21% 10% 5% 1	594
April	1st to 10th	Day	37% 22% 24% 10% 5% 1	540
	11th to 20th	Day	39% 19% 22% 13% 6% 2	532
	21st to end	Day	35% 19% 29% 9% 6% 2	540
May	1st to 10th	Day	34% 20% 29% 10% 6% 2	543
	11th to 20th	Day	26% 19% 29% 19% 7% 1	567
	21st to end	Day	25% 19% 29% 17% 9% 1	617
June	1st to 10th	Day	28% 16% 28% 21% 5% 2	570
	11th to 20th	Day	24% 17% 30% 20% 7% 2	550
	21st to end	Day	29% 17% 29% 18% 6% 2	530
July	1st to 10th	Day	17% 12% 33% 25% 11% 2	525
	11th to 20th	Day	16% 12% 35% 25% 10% 2	524
	21st to end	Day	15% 14% 38% 24% 8% 2	576
August	1st to 10th	Day	17% 10% 29% 23% 17% 4	526
	11th to 20th	Day	18% 9% 29% 24% 13% 7%	519
	21st to end	Day	16% 16% 28% 22% 13% 4	583
September	1st to 10th	Day	21% 11% 29% 18% 15% 6%	530
	11th to 20th	Day	17% 12% 21% 19% 21% 11%	530
	21st to end	Day	20% 15% 27% 20% 14% 4	530
October	1st to 10th	Day	28% 16% 23% 16% 13% 5%	530
	11th to 20th	Day	31% 19% 24% 18% 7% 1	530
	21st to end	Day	36% 19% 24% 17% 4	470
November	1st to 10th	Day	37% 15% 26% 14% 7% 1	425
	11th to 20th	Day	35% 23% 25% 10% 6% 1	356
	21st to end	Day	36% 24% 30% 9% 1	220
December	1st to 10th	Day	35% 19% 31% 12% 2	220
	11th to 20th	Day	35% 28% 30% 4 2	220
	21st to end	Day	35% 21% 33% 8% 3 1	242
January	1st to 10th	Night	28% 27% 30% 13% 2	840
	11th to 20th	Night	31% 24% 30% 12% 2	840
	21st to end	Night	21% 27% 31% 17% 4	924
February	1st to 10th	Night	28% 25% 30% 16% 2	840
	11th to 20th	Night	27% 25% 32% 13% 2	823
	21st to end	Night	27% 22% 32% 16% 2	692
March	1st to 10th	Night	28% 23% 30% 17% 2	840
	11th to 20th	Night	30% 23% 29% 14% 3	840
	21st to end	Night	29% 22% 27% 17% 4 1	924
April	1st to 10th	Night	33% 19% 27% 18% 3	840
	11th to 20th	Night	33% 20% 23% 18% 6%	831
	21st to end	Night	31% 17% 26% 20% 7%	740
May	1st to 10th	Night	32% 13% 25% 21% 8% 1	481
	11th to 20th	Night	20% 12% 30% 30% 8%	414
	21st to end	Night	19% 14% 28% 28% 11%	455
June	1st to 10th	Night	26% 9% 26% 28% 11% 1	420
	11th to 20th	Night	24% 7% 24% 33% 12%	410
	21st to end	Night	23% 11% 27% 31% 9%	400
July	1st to 10th	Night	11% 6% 29% 38% 15%	390
	11th to 20th	Night	13% 4 26% 39% 16% 1	388
	21st to end	Night	15% 6% 25% 41% 11% 1	438
August	1st to 10th	Night	18% 6% 20% 38% 16% 1	398
	11th to 20th	Night	19% 7% 20% 30% 22% 2	685
	21st to end	Night	19% 8% 24% 32% 17% 1	880
September	1st to 10th	Night	19% 11% 24% 29% 16% 2	800
	11th to 20th	Night	19% 7% 18% 28% 23% 4	800
	21st to end	Night	25% 11% 23% 21% 19% 2	800
October	1st to 10th	Night	29% 14% 21% 20% 15% 2	800
	11th to 20th	Night	29% 15% 25% 24% 7% 1	800
	21st to end	Night	36% 18% 23% 20% 3	880
November	1st to 10th	Night	33% 15% 26% 18% 6%	820
	11th to 20th	Night	30% 20% 27% 13% 8% 1	840
	21st to end	Night	33% 24% 24% 15% 4	840
December	1st to 10th	Night	33% 26% 25% 14% 3	840
	11th to 20th	Night	30% 25% 27% 14% 3 1	840
	21st to end	Night	33% 26% 26% 12% 3	924

Page generated at 2026-06-13 02:31:39. Version ac07

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