Astroknip's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astroknip's Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	16% 10% 3 8% 5% 5% 5% 4 6% 7% 32%	127501
	Night	16% 11% 4 9% 5% 5% 4 4 5% 6% 30%	123508
Transparency	Day	50% 7% 12% 21% 10% 1	130966
	Night	53% 6% 11% 19% 10% 1	128117
Seeing	Day	22% 15% 31% 21% 9% 3	15832
	Night	22% 12% 30% 26% 9% 1	24957

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	14% 17% 6% 15% 7% 5% 5% 4 4 5% 19%	3597
	11th to 20th	Day	13% 14% 7% 14% 7% 6% 5% 3 5% 5% 22%	3570
	21st to end	Day	10% 16% 6% 14% 6% 6% 5% 5% 6% 5% 20%	4126
February	1st to 10th	Day	13% 15% 4 12% 7% 6% 5% 4 4 5% 25%	1800
	11th to 20th	Day	12% 15% 5% 10% 6% 6% 4 4 6% 6% 28%	1758
	21st to end	Day	18% 13% 4 9% 7% 4 5% 5% 6% 5% 25%	1650
March	1st to 10th	Day	18% 12% 5% 11% 6% 5% 5% 4 5% 6% 25%	4476
	11th to 20th	Day	11% 12% 4 9% 5% 5% 6% 5% 6% 7% 30%	4976
	21st to end	Day	17% 11% 4 8% 5% 4 3 3 4 5% 36%	5776
April	1st to 10th	Day	22% 10% 3 7% 4 4 4 3 5% 7% 32%	2400
	11th to 20th	Day	20% 9% 3 7% 5% 4 4 3 4 5% 36%	2374
	21st to end	Day	22% 9% 3 8% 6% 4 4 3 5% 5% 32%	2541
May	1st to 10th	Day	22% 10% 4 8% 5% 5% 5% 4 6% 6% 26%	6346
	11th to 20th	Day	15% 10% 3 9% 6% 5% 5% 4 5% 7% 31%	6318
	21st to end	Day	20% 9% 3 7% 5% 5% 4 3 5% 6% 33%	6949
June	1st to 10th	Day	19% 8% 4 7% 6% 4 5% 5% 5% 7% 30%	2800
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 6% 8% 38%	2800
	21st to end	Day	18% 7% 3 7% 5% 4 6% 5% 7% 7% 32%	2800
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	6360
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 8% 43%	6360
	21st to end	Day	8% 5% 2 5% 4 4 4 4 7% 10% 45%	6926
August	1st to 10th	Day	13% 6% 3 8% 5% 5% 5% 4 7% 8% 37%	4498
	11th to 20th	Day	15% 7% 2 6% 4 4 5% 4 7% 9% 38%	4118
	21st to end	Day	13% 5% 2 6% 5% 5% 5% 4 6% 9% 40%	4312
September	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 7% 43%	2400
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 5% 8% 48%	2400
	21st to end	Day	18% 5% 2 6% 5% 5% 4 3 6% 8% 39%	2133
October	1st to 10th	Day	19% 8% 3 6% 4 4 4 4 6% 6% 37%	2000
	11th to 20th	Day	21% 7% 3 8% 5% 5% 5% 4 6% 7% 30%	2000
	21st to end	Day	25% 9% 3 8% 4 4 5% 4 5% 6% 28%	2038
November	1st to 10th	Day	16% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	1851
	11th to 20th	Day	19% 11% 4 9% 4 5% 5% 4 6% 6% 27%	1686
	21st to end	Day	21% 13% 5% 9% 8% 5% 6% 3 4 5% 20%	1680
December	1st to 10th	Day	20% 20% 5% 10% 6% 5% 5% 5% 5% 6% 14%	2680
	11th to 20th	Day	17% 16% 4 11% 6% 5% 5% 3 4 5% 23%	3042
	21st to end	Day	23% 15% 5% 11% 6% 4 5% 3 4 4 19%	3960
January	1st to 10th	Night	14% 21% 9% 15% 6% 4 3 3 4 4 19%	6349
	11th to 20th	Night	11% 14% 6% 14% 9% 6% 6% 4 4 5% 20%	6315
	21st to end	Night	13% 19% 6% 12% 6% 6% 5% 4 5% 6% 20%	6813
February	1st to 10th	Night	13% 14% 4 13% 7% 6% 5% 4 4 5% 24%	2600
	11th to 20th	Night	13% 13% 5% 11% 7% 6% 4 3 5% 5% 28%	2528
	21st to end	Night	16% 13% 5% 8% 6% 5% 5% 4 5% 6% 28%	1980
March	1st to 10th	Night	22% 14% 4 9% 5% 5% 3 3 3 4 28%	5364
	11th to 20th	Night	13% 12% 4 9% 6% 4 4 4 6% 8% 30%	4979
	21st to end	Night	19% 10% 3 8% 5% 4 4 3 5% 6% 33%	5156
April	1st to 10th	Night	20% 11% 3 7% 5% 4 4 4 5% 5% 32%	2000
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 4 5% 36%	1975
	21st to end	Night	21% 8% 4 7% 5% 4 4 3 4 6% 35%	1875
May	1st to 10th	Night	22% 9% 4 8% 5% 5% 6% 5% 6% 7% 24%	3594
	11th to 20th	Night	15% 9% 3 7% 5% 5% 4 4 5% 7% 37%	3575
	21st to end	Night	17% 10% 3 8% 5% 5% 5% 4 6% 6% 31%	3926
June	1st to 10th	Night	15% 7% 2 7% 6% 5% 6% 6% 6% 8% 34%	1600
	11th to 20th	Night	14% 6% 2 7% 4 4 3 3 6% 8% 42%	1600
	21st to end	Night	18% 7% 3 6% 5% 4 5% 4 6% 8% 35%	1600
July	1st to 10th	Night	14% 7% 3 8% 6% 6% 6% 5% 6% 9% 33%	3600
	11th to 20th	Night	11% 6% 2 7% 4 4 5% 5% 6% 8% 42%	3600
	21st to end	Night	8% 6% 2 6% 5% 4 5% 4 6% 8% 46%	3926
August	1st to 10th	Night	11% 7% 3 8% 4 5% 5% 4 5% 9% 39%	2647
	11th to 20th	Night	13% 7% 3 7% 4 5% 4 4 6% 7% 41%	2897
	21st to end	Night	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	3586
September	1st to 10th	Night	11% 5% 2 6% 4 5% 4 4 5% 7% 47%	2000
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 6% 6% 50%	2000
	21st to end	Night	16% 6% 2 7% 4 4 4 3 4 6% 44%	2263
October	1st to 10th	Night	17% 8% 2 7% 4 4 4 4 5% 6% 40%	2400
	11th to 20th	Night	20% 9% 2 7% 6% 5% 5% 3 6% 6% 32%	2400
	21st to end	Night	22% 10% 3 7% 6% 5% 4 4 5% 7% 28%	2800
November	1st to 10th	Night	20% 10% 3 6% 5% 4 4 3 5% 7% 32%	2667
	11th to 20th	Night	18% 11% 3 9% 6% 5% 6% 3 5% 5% 29%	2930
	21st to end	Night	21% 13% 4 10% 6% 5% 4 3 5% 6% 23%	2940
December	1st to 10th	Night	19% 17% 5% 11% 7% 6% 5% 4 5% 6% 16%	4720
	11th to 20th	Night	22% 15% 4 9% 6% 4 4 3 3 6% 24%	5307
	21st to end	Night	26% 18% 4 9% 5% 4 4 3 4 4 19%	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	65% 7% 10% 13% 4 1	3598
	11th to 20th	Day	64% 5% 11% 12% 8%	3600
	21st to end	Day	63% 7% 10% 11% 7% 1	4126
February	1st to 10th	Day	60% 6% 10% 18% 5% 1	1800
	11th to 20th	Day	56% 6% 12% 17% 8% 1	1767
	21st to end	Day	59% 6% 10% 14% 9% 1	1650
March	1st to 10th	Day	58% 5% 9% 14% 12% 3	4479
	11th to 20th	Day	51% 6% 17% 16% 9% 1	4976
	21st to end	Day	49% 5% 6% 20% 17% 2	5776
April	1st to 10th	Day	53% 5% 8% 20% 12% 3	2400
	11th to 20th	Day	51% 4 7% 21% 15% 2	2374
	21st to end	Day	54% 5% 8% 15% 14% 4	2541
May	1st to 10th	Day	56% 7% 9% 18% 8% 2	6357
	11th to 20th	Day	51% 9% 11% 18% 10% 1	6322
	21st to end	Day	50% 6% 11% 21% 11% 1	6949
June	1st to 10th	Day	53% 7% 10% 18% 12% 1	2800
	11th to 20th	Day	41% 8% 11% 25% 13% 2	2800
	21st to end	Day	48% 9% 13% 20% 10% 1	2800
July	1st to 10th	Day	43% 6% 16% 25% 9%	6290
	11th to 20th	Day	36% 7% 14% 30% 13%	6285
	21st to end	Day	32% 7% 16% 36% 10%	6728
August	1st to 10th	Day	44% 7% 16% 24% 9%	4484
	11th to 20th	Day	42% 7% 15% 27% 8% 1	4157
	21st to end	Day	39% 6% 17% 26% 11%	4312
September	1st to 10th	Day	38% 7% 15% 29% 11%	2400
	11th to 20th	Day	34% 7% 13% 32% 13% 1	2400
	21st to end	Day	43% 7% 15% 25% 11%	2133
October	1st to 10th	Day	45% 5% 12% 29% 7%	3260
	11th to 20th	Day	45% 7% 15% 24% 8% 1	3240
	21st to end	Day	49% 6% 18% 20% 7%	3263
November	1st to 10th	Day	48% 8% 15% 21% 6% 1	1851
	11th to 20th	Day	57% 6% 13% 15% 8% 1	1686
	21st to end	Day	65% 7% 12% 9% 6%	1680
December	1st to 10th	Day	70% 6% 12% 10% 2	2680
	11th to 20th	Day	63% 7% 10% 14% 7%	3042
	21st to end	Day	67% 6% 8% 14% 4	3960
January	1st to 10th	Night	68% 5% 11% 12% 4	6349
	11th to 20th	Night	64% 7% 11% 13% 5%	6360
	21st to end	Night	64% 6% 8% 10% 10% 1	6813
February	1st to 10th	Night	61% 5% 10% 16% 7% 1	2600
	11th to 20th	Night	57% 5% 11% 18% 8% 1	2530
	21st to end	Night	56% 6% 9% 19% 9% 1	1980
March	1st to 10th	Night	60% 4 7% 15% 12% 3	5374
	11th to 20th	Night	51% 6% 17% 16% 8% 3	4980
	21st to end	Night	50% 5% 7% 22% 13% 2	5156
April	1st to 10th	Night	53% 6% 8% 18% 13% 2	2000
	11th to 20th	Night	50% 6% 7% 21% 15% 1	1975
	21st to end	Night	51% 5% 9% 17% 15% 3	1875
May	1st to 10th	Night	55% 9% 9% 17% 8% 2	3600
	11th to 20th	Night	44% 7% 14% 19% 14% 1	3576
	21st to end	Night	49% 7% 12% 16% 14% 1	3927
June	1st to 10th	Night	47% 8% 12% 22% 10% 2	1600
	11th to 20th	Night	39% 7% 11% 24% 16% 2	1600
	21st to end	Night	46% 8% 12% 20% 13% 1	1600
July	1st to 10th	Night	46% 6% 16% 19% 12% 1	3560
	11th to 20th	Night	37% 7% 15% 30% 11%	3552
	21st to end	Night	36% 6% 13% 29% 15%	3809
August	1st to 10th	Night	40% 9% 15% 24% 11% 1	2637
	11th to 20th	Night	40% 7% 16% 28% 8%	2924
	21st to end	Night	39% 8% 15% 25% 12% 2	3586
September	1st to 10th	Night	36% 7% 11% 30% 15% 1	2000
	11th to 20th	Night	33% 7% 13% 35% 11% 1	2000
	21st to end	Night	41% 6% 12% 28% 13%	2263
October	1st to 10th	Night	40% 6% 13% 28% 12% 1	3920
	11th to 20th	Night	45% 6% 15% 24% 9%	3899
	21st to end	Night	48% 6% 17% 20% 8%	4512
November	1st to 10th	Night	52% 6% 14% 21% 8% 1	2667
	11th to 20th	Night	55% 6% 12% 17% 9% 1	2930
	21st to end	Night	61% 7% 13% 15% 5%	2940
December	1st to 10th	Night	67% 6% 12% 12% 2	4720
	11th to 20th	Night	63% 5% 7% 14% 10% 1	5307
	21st to end	Night	68% 4 6% 13% 9%	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	23% 20% 34% 20% 4	200
	11th to 20th	Day	27% 17% 38% 14% 4 1	200
	21st to end	Day	20% 18% 37% 20% 4	257
February	1st to 10th	Day	30% 22% 33% 14% 2	300
	11th to 20th	Day	26% 26% 38% 10% 1	305
	21st to end	Day	28% 21% 33% 16% 2	414
March	1st to 10th	Day	26% 17% 34% 18% 5%	500
	11th to 20th	Day	24% 18% 36% 18% 3 1	500
	21st to end	Day	29% 22% 27% 14% 7% 1	550
April	1st to 10th	Day	29% 21% 29% 15% 5% 1	500
	11th to 20th	Day	31% 20% 24% 14% 10% 2	492
	21st to end	Day	31% 19% 29% 14% 6% 1	500
May	1st to 10th	Day	24% 16% 32% 20% 6% 2	503
	11th to 20th	Day	17% 17% 35% 20% 8% 2	527
	21st to end	Day	19% 15% 31% 23% 11% 1	573
June	1st to 10th	Day	24% 11% 32% 22% 9% 2	530
	11th to 20th	Day	16% 14% 32% 26% 10% 3	530
	21st to end	Day	18% 15% 33% 22% 9% 2	530
July	1st to 10th	Day	12% 9% 30% 32% 14% 3	525
	11th to 20th	Day	12% 8% 33% 29% 15% 3	524
	21st to end	Day	12% 8% 32% 30% 15% 4	576
August	1st to 10th	Day	14% 6% 26% 32% 17% 4	526
	11th to 20th	Day	13% 8% 25% 28% 18% 8%	519
	21st to end	Day	14% 11% 29% 26% 13% 7%	583
September	1st to 10th	Day	15% 11% 30% 19% 15% 9%	530
	11th to 20th	Day	11% 8% 24% 25% 20% 13%	530
	21st to end	Day	18% 10% 30% 22% 14% 5%	530
October	1st to 10th	Day	23% 13% 25% 22% 12% 5%	530
	11th to 20th	Day	24% 19% 31% 19% 6% 1	530
	21st to end	Day	29% 14% 29% 22% 6%	493
November	1st to 10th	Day	25% 18% 32% 18% 6% 1	425
	11th to 20th	Day	27% 20% 33% 12% 7% 1	226
	21st to end	Day	31% 17% 36% 13% 3 1	220
December	1st to 10th	Day	30% 15% 35% 17% 3	220
	11th to 20th	Day	28% 26% 32% 11% 2 1	214
	21st to end	Day	30% 18% 33% 14% 4 1	220
January	1st to 10th	Night	25% 16% 34% 21% 3	800
	11th to 20th	Night	25% 18% 31% 21% 5% 1	800
	21st to end	Night	19% 13% 38% 26% 5%	880
February	1st to 10th	Night	23% 14% 37% 22% 3	800
	11th to 20th	Night	21% 18% 38% 19% 4	783
	21st to end	Night	24% 18% 29% 25% 4	660
March	1st to 10th	Night	24% 15% 36% 22% 4	800
	11th to 20th	Night	22% 19% 32% 21% 5%	800
	21st to end	Night	24% 17% 27% 25% 7%	880
April	1st to 10th	Night	27% 14% 31% 23% 5%	800
	11th to 20th	Night	25% 16% 29% 22% 8%	791
	21st to end	Night	26% 14% 29% 23% 7% 1	675
May	1st to 10th	Night	23% 9% 31% 28% 8% 1	400
	11th to 20th	Night	21% 11% 28% 31% 9%	394
	21st to end	Night	15% 7% 39% 26% 12%	433
June	1st to 10th	Night	18% 5% 32% 36% 9%	400
	11th to 20th	Night	15% 8% 30% 34% 12% 1	400
	21st to end	Night	21% 5% 32% 29% 13% 1	400
July	1st to 10th	Night	10% 6% 29% 42% 14%	390
	11th to 20th	Night	12% 5% 26% 42% 14% 1	388
	21st to end	Night	9% 4 28% 43% 14% 2	438
August	1st to 10th	Night	11% 3 24% 41% 21% 1	433
	11th to 20th	Night	13% 3 21% 36% 24% 2	603
	21st to end	Night	13% 7% 26% 34% 18% 2	880
September	1st to 10th	Night	14% 6% 29% 32% 18% 1	800
	11th to 20th	Night	15% 7% 20% 32% 23% 4	800
	21st to end	Night	18% 9% 25% 26% 20% 2	800
October	1st to 10th	Night	20% 9% 28% 27% 15% 1	800
	11th to 20th	Night	24% 13% 30% 26% 8% 1	800
	21st to end	Night	26% 14% 28% 26% 6%	880
November	1st to 10th	Night	27% 14% 28% 23% 8% 1	820
	11th to 20th	Night	23% 16% 34% 17% 9% 1	840
	21st to end	Night	29% 17% 27% 22% 6%	840
December	1st to 10th	Night	30% 15% 30% 21% 4	840
	11th to 20th	Night	28% 15% 31% 20% 4 1	829
	21st to end	Night	33% 15% 29% 18% 4	880

Page generated at 2025-12-15 01:13:49. Version ac07

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