Oscarness Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oscarness Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	12% 9% 3 8% 5% 4 4 4 5% 7% 39%	138906
	Night	12% 9% 4 8% 5% 5% 4 4 5% 6% 38%	134458
Transparency	Day	44% 5% 12% 26% 12% 1	142483
	Night	45% 5% 12% 24% 13% 1	138960
Seeing	Day	16% 12% 32% 26% 12% 2	18441
	Night	15% 10% 34% 30% 10% 1	28272

By Month

Percentage Cloud Cover SE (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	9% 14% 7% 19% 8% 5% 5% 3 5% 5% 21%	4691
	11th to 20th	Day	5% 12% 7% 13% 6% 7% 8% 8% 8% 5% 21%	4827
	21st to end	Day	4 13% 6% 10% 5% 5% 6% 4 6% 6% 34%	5812
February	1st to 10th	Day	8% 12% 5% 11% 6% 6% 5% 4 6% 6% 31%	1890
	11th to 20th	Day	8% 12% 4 11% 7% 4 4 4 5% 6% 35%	1844
	21st to end	Day	10% 13% 4 9% 5% 5% 5% 4 6% 6% 34%	1612
March	1st to 10th	Day	13% 9% 3 5% 3 3 3 3 6% 7% 44%	4972
	11th to 20th	Day	10% 11% 3 7% 4 4 4 4 5% 8% 40%	5090
	21st to end	Day	22% 11% 4 10% 5% 4 4 3 4 6% 26%	5622
April	1st to 10th	Day	17% 10% 3 8% 5% 3 4 3 5% 6% 35%	2520
	11th to 20th	Day	20% 13% 3 8% 5% 4 4 3 4 6% 32%	2514
	21st to end	Day	22% 11% 3 6% 5% 4 4 4 5% 5% 31%	2730
May	1st to 10th	Day	11% 5% 2 6% 4 4 4 3 5% 6% 50%	7888
	11th to 20th	Day	16% 8% 2 5% 3 3 3 3 5% 7% 45%	8222
	21st to end	Day	16% 7% 3 7% 5% 4 5% 4 5% 7% 38%	9047
June	1st to 10th	Day	11% 6% 2 5% 4 4 5% 4 7% 9% 44%	2940
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 7% 8% 37%	2940
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 5% 7% 9% 39%	2940
July	1st to 10th	Day	9% 5% 2 5% 4 4 5% 4 7% 10% 44%	6500
	11th to 20th	Day	8% 3 2 4 3 3 3 3 5% 7% 58%	6500
	21st to end	Day	7% 4 2 6% 4 4 5% 4 7% 9% 47%	6929
August	1st to 10th	Day	12% 5% 3 6% 4 5% 6% 4 6% 7% 41%	4234
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 7% 8% 43%	4171
	21st to end	Day	10% 6% 3 7% 4 4 4 4 4 7% 48%	4482
September	1st to 10th	Day	11% 7% 2 5% 4 4 4 3 5% 7% 48%	2400
	11th to 20th	Day	12% 6% 1 5% 4 4 4 4 6% 8% 46%	2355
	21st to end	Day	15% 5% 2 5% 4 4 5% 3 4 6% 46%	2113
October	1st to 10th	Day	16% 7% 3 5% 4 4 4 3 4 6% 44%	2000
	11th to 20th	Day	16% 9% 3 6% 4 4 4 3 4 6% 41%	2000
	21st to end	Day	18% 11% 3 6% 4 3 3 3 4 6% 37%	2192
November	1st to 10th	Day	12% 11% 4 9% 4 4 4 4 5% 6% 38%	1721
	11th to 20th	Day	10% 15% 6% 11% 6% 4 3 4 5% 6% 31%	1680
	21st to end	Day	14% 12% 4 9% 5% 4 4 4 5% 7% 34%	1680
December	1st to 10th	Day	7% 12% 3 15% 11% 7% 5% 3 5% 7% 25%	2690
	11th to 20th	Day	10% 16% 6% 10% 7% 5% 5% 3 4 6% 27%	3088
	21st to end	Day	20% 18% 10% 18% 5% 3 3 3 3 4 14%	4070
January	1st to 10th	Night	9% 13% 5% 15% 7% 5% 4 4 5% 6% 27%	8232
	11th to 20th	Night	6% 13% 5% 14% 7% 7% 10% 8% 5% 5% 21%	8160
	21st to end	Night	6% 15% 5% 9% 5% 5% 5% 4 5% 5% 36%	8402
February	1st to 10th	Night	8% 12% 5% 10% 7% 6% 5% 3 5% 6% 33%	2730
	11th to 20th	Night	7% 10% 4 8% 6% 6% 5% 3 5% 7% 39%	2663
	21st to end	Night	11% 9% 4 8% 7% 5% 5% 3 5% 6% 37%	2192
March	1st to 10th	Night	11% 6% 2 7% 4 4 4 3 5% 7% 47%	5131
	11th to 20th	Night	10% 7% 3 6% 5% 5% 5% 4 6% 9% 41%	5090
	21st to end	Night	24% 11% 4 10% 4 4 3 3 4 5% 29%	5548
April	1st to 10th	Night	16% 10% 3 6% 5% 3 5% 3 6% 6% 37%	2100
	11th to 20th	Night	20% 9% 4 7% 4 3 4 3 4 6% 36%	2051
	21st to end	Night	19% 9% 3 7% 5% 4 4 4 4 6% 36%	1890
May	1st to 10th	Night	10% 6% 2 5% 4 4 4 3 5% 6% 52%	4992
	11th to 20th	Night	16% 5% 1 4 3 3 4 3 4 6% 50%	4670
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 7% 38%	5139
June	1st to 10th	Night	11% 5% 2 4 3 4 4 3 6% 8% 48%	1680
	11th to 20th	Night	10% 6% 2 5% 6% 4 5% 4 6% 8% 44%	1680
	21st to end	Night	8% 4 2 5% 4 4 4 3 7% 9% 51%	1680
July	1st to 10th	Night	8% 3 1 4 4 5% 4 5% 7% 9% 49%	3698
	11th to 20th	Night	6% 4 1 4 4 3 4 4 6% 8% 55%	3697
	21st to end	Night	9% 5% 2 5% 4 5% 4 3 6% 7% 50%	4159
August	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 5% 7% 47%	2926
	11th to 20th	Night	14% 4 2 4 3 3 3 4 5% 7% 52%	2888
	21st to end	Night	10% 6% 2 6% 4 3 4 3 5% 7% 49%	3421
September	1st to 10th	Night	9% 4 2 5% 3 3 4 4 5% 7% 53%	2000
	11th to 20th	Night	10% 4 1 5% 4 4 3 4 5% 8% 52%	2042
	21st to end	Night	12% 5% 2 4 3 3 4 3 4 5% 53%	2266
October	1st to 10th	Night	13% 7% 2 6% 3 3 3 2 4 6% 51%	2400
	11th to 20th	Night	14% 9% 3 6% 4 3 4 3 5% 6% 43%	2400
	21st to end	Night	18% 11% 3 7% 4 4 4 3 5% 6% 37%	2646
November	1st to 10th	Night	13% 9% 3 6% 5% 4 4 3 5% 6% 41%	2796
	11th to 20th	Night	12% 12% 4 11% 5% 4 4 3 5% 5% 35%	2940
	21st to end	Night	14% 11% 4 10% 6% 4 4 3 4 6% 36%	2940
December	1st to 10th	Night	6% 9% 4 14% 7% 8% 5% 4 5% 6% 31%	4720
	11th to 20th	Night	10% 17% 6% 13% 7% 5% 5% 4 5% 5% 24%	5339
	21st to end	Night	23% 15% 9% 14% 5% 4 4 3 3 4 17%	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	64% 5% 12% 14% 5%	4692
	11th to 20th	Day	60% 5% 9% 17% 10%	4827
	21st to end	Day	49% 5% 13% 24% 8%	5812
February	1st to 10th	Day	53% 5% 14% 19% 8% 1	1890
	11th to 20th	Day	50% 6% 11% 25% 8%	1853
	21st to end	Day	50% 6% 13% 20% 11%	1612
March	1st to 10th	Day	39% 4 17% 27% 11% 2	4972
	11th to 20th	Day	42% 5% 13% 28% 10% 2	5090
	21st to end	Day	60% 5% 10% 17% 8%	5624
April	1st to 10th	Day	49% 5% 11% 22% 12% 1	2520
	11th to 20th	Day	54% 4 11% 18% 12% 2	2514
	21st to end	Day	54% 5% 11% 20% 9% 1	2730
May	1st to 10th	Day	33% 5% 10% 30% 20% 2	7926
	11th to 20th	Day	39% 5% 7% 25% 20% 5%	8226
	21st to end	Day	45% 6% 9% 29% 11% 1	9061
June	1st to 10th	Day	34% 7% 14% 31% 13% 2	2940
	11th to 20th	Day	43% 6% 13% 22% 14% 1	2940
	21st to end	Day	38% 9% 16% 26% 11% 2	2940
July	1st to 10th	Day	33% 7% 18% 32% 9%	6431
	11th to 20th	Day	26% 5% 15% 37% 17% 1	6425
	21st to end	Day	30% 7% 14% 31% 16% 1	6735
August	1st to 10th	Day	40% 6% 12% 28% 13% 1	4220
	11th to 20th	Day	37% 6% 13% 33% 10%	4210
	21st to end	Day	35% 6% 16% 29% 14% 1	4481
September	1st to 10th	Day	36% 6% 13% 31% 14%	2400
	11th to 20th	Day	34% 6% 18% 33% 9%	2355
	21st to end	Day	39% 5% 11% 32% 12% 1	2113
October	1st to 10th	Day	30% 3 8% 35% 23%	3260
	11th to 20th	Day	40% 4 10% 26% 19% 1	3240
	21st to end	Day	44% 3 14% 29% 10%	3518
November	1st to 10th	Day	46% 5% 14% 19% 13% 2	1721
	11th to 20th	Day	54% 4 13% 19% 10% 1	1680
	21st to end	Day	49% 4 17% 21% 7% 1	1680
December	1st to 10th	Day	58% 6% 15% 15% 6% 1	2690
	11th to 20th	Day	59% 5% 16% 16% 5%	3085
	21st to end	Day	74% 4 9% 9% 4	4070
January	1st to 10th	Night	57% 5% 14% 18% 6%	8233
	11th to 20th	Night	62% 5% 9% 15% 8%	8160
	21st to end	Night	49% 5% 11% 26% 10%	8402
February	1st to 10th	Night	51% 4 13% 21% 10% 1	2730
	11th to 20th	Night	45% 5% 13% 26% 9% 1	2664
	21st to end	Night	47% 4 12% 23% 12% 1	2192
March	1st to 10th	Night	37% 5% 12% 28% 16% 2	5131
	11th to 20th	Night	39% 4 13% 28% 14% 1	5090
	21st to end	Night	59% 4 9% 18% 10% 1	5548
April	1st to 10th	Night	47% 5% 10% 23% 14% 1	2100
	11th to 20th	Night	49% 4 8% 20% 16% 2	2051
	21st to end	Night	49% 6% 8% 21% 14% 2	1890
May	1st to 10th	Night	31% 5% 9% 32% 21% 2	5019
	11th to 20th	Night	35% 5% 8% 21% 24% 7%	4671
	21st to end	Night	44% 5% 9% 27% 12% 2	5149
June	1st to 10th	Night	31% 5% 13% 30% 18% 2	1680
	11th to 20th	Night	35% 7% 15% 23% 18% 3	1680
	21st to end	Night	29% 6% 16% 30% 16% 3	1680
July	1st to 10th	Night	29% 6% 20% 30% 14% 1	3660
	11th to 20th	Night	25% 5% 14% 39% 15% 2	3652
	21st to end	Night	32% 6% 15% 29% 16% 2	4042
August	1st to 10th	Night	36% 6% 12% 28% 13% 4	2916
	11th to 20th	Night	32% 5% 14% 32% 16% 1	2915
	21st to end	Night	33% 6% 17% 28% 14% 2	3421
September	1st to 10th	Night	28% 6% 13% 34% 18% 1	2000
	11th to 20th	Night	29% 6% 16% 31% 17%	2042
	21st to end	Night	33% 4 11% 31% 19% 2	2266
October	1st to 10th	Night	23% 3 6% 36% 28% 5%	3920
	11th to 20th	Night	33% 4 12% 25% 22% 4	3899
	21st to end	Night	43% 4 11% 28% 13% 1	4270
November	1st to 10th	Night	42% 6% 12% 24% 14% 2	2796
	11th to 20th	Night	51% 5% 11% 20% 12% 1	2940
	21st to end	Night	50% 4 15% 22% 8% 1	2940
December	1st to 10th	Night	53% 6% 18% 19% 5%	4720
	11th to 20th	Night	61% 6% 11% 17% 4 1	5341
	21st to end	Night	71% 4 9% 13% 3	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	15% 12% 34% 29% 8% 3	330
	11th to 20th	Day	15% 15% 41% 24% 4 1	330
	21st to end	Day	16% 13% 38% 24% 7% 1	363
February	1st to 10th	Day	16% 17% 44% 18% 5% 1	330
	11th to 20th	Day	13% 19% 38% 23% 6% 1	330
	21st to end	Day	17% 16% 43% 20% 4	273
March	1st to 10th	Day	18% 18% 41% 19% 5%	330
	11th to 20th	Day	21% 15% 37% 21% 6% 1	330
	21st to end	Day	27% 19% 28% 19% 6% 2	377
April	1st to 10th	Day	25% 15% 36% 19% 5%	540
	11th to 20th	Day	28% 17% 26% 20% 9% 1	552
	21st to end	Day	25% 15% 31% 20% 8% 1	750
May	1st to 10th	Day	18% 15% 34% 23% 8% 2	753
	11th to 20th	Day	20% 13% 28% 23% 13% 3	775
	21st to end	Day	18% 10% 28% 29% 12% 2	844
June	1st to 10th	Day	10% 9% 29% 32% 17% 3	780
	11th to 20th	Day	17% 10% 37% 25% 9% 2	780
	21st to end	Day	13% 11% 32% 26% 15% 3	780
July	1st to 10th	Day	10% 4 24% 31% 22% 8%	771
	11th to 20th	Day	8% 8% 27% 32% 19% 5%	768
	21st to end	Day	5% 7% 28% 39% 17% 4	845
August	1st to 10th	Day	9% 5% 27% 34% 21% 4	726
	11th to 20th	Day	14% 5% 24% 30% 22% 5%	715
	21st to end	Day	10% 7% 27% 35% 16% 5%	688
September	1st to 10th	Day	15% 10% 27% 28% 16% 4	530
	11th to 20th	Day	14% 6% 27% 32% 18% 3	485
	21st to end	Day	15% 13% 30% 19% 18% 5%	330
October	1st to 10th	Day	17% 12% 31% 27% 11% 3	330
	11th to 20th	Day	18% 22% 35% 20% 4 1	330
	21st to end	Day	25% 16% 34% 17% 7% 1	363
November	1st to 10th	Day	21% 18% 35% 17% 8% 1	330
	11th to 20th	Day	16% 21% 42% 19% 2	330
	21st to end	Day	22% 15% 42% 18% 3	330
December	1st to 10th	Day	14% 14% 40% 25% 6%	330
	11th to 20th	Day	22% 16% 37% 23% 3	330
	21st to end	Day	27% 15% 40% 13% 4	363
January	1st to 10th	Night	12% 13% 39% 29% 7% 1	1050
	11th to 20th	Night	16% 14% 37% 27% 5% 1	1050
	21st to end	Night	17% 11% 38% 28% 5%	1155
February	1st to 10th	Night	14% 14% 39% 27% 6%	1050
	11th to 20th	Night	12% 13% 42% 27% 5% 1	1029
	21st to end	Night	15% 14% 38% 26% 7% 1	808
March	1st to 10th	Night	16% 11% 39% 27% 7% 1	684
	11th to 20th	Night	18% 12% 40% 24% 6%	630
	21st to end	Night	22% 12% 31% 24% 10% 1	693
April	1st to 10th	Night	21% 14% 34% 26% 5%	630
	11th to 20th	Night	24% 12% 30% 28% 6%	623
	21st to end	Night	22% 10% 34% 25% 8% 1	630
May	1st to 10th	Night	17% 11% 33% 31% 7% 1	630
	11th to 20th	Night	16% 10% 32% 31% 11%	621
	21st to end	Night	16% 9% 26% 35% 13%	683
June	1st to 10th	Night	12% 6% 30% 40% 12%	630
	11th to 20th	Night	10% 7% 34% 42% 8%	630
	21st to end	Night	9% 5% 27% 44% 14% 1	630
July	1st to 10th	Night	6% 2 25% 39% 26% 2	615
	11th to 20th	Night	6% 4 28% 44% 17% 2	612
	21st to end	Night	5% 3 26% 48% 17% 2	687
August	1st to 10th	Night	7% 4 20% 46% 21% 1	597
	11th to 20th	Night	12% 3 20% 39% 23% 3	594
	21st to end	Night	7% 5% 28% 35% 23% 2	660
September	1st to 10th	Night	10% 6% 25% 38% 18% 3	600
	11th to 20th	Night	12% 5% 34% 31% 16% 2	600
	21st to end	Night	12% 10% 32% 30% 16% 1	666
October	1st to 10th	Night	17% 11% 30% 29% 13%	800
	11th to 20th	Night	19% 13% 35% 26% 7% 1	800
	21st to end	Night	24% 12% 30% 28% 6%	880
November	1st to 10th	Night	18% 13% 35% 27% 7% 1	950
	11th to 20th	Night	18% 14% 37% 24% 6% 1	1050
	21st to end	Night	17% 16% 38% 23% 6%	1050
December	1st to 10th	Night	15% 11% 40% 27% 7%	1050
	11th to 20th	Night	19% 12% 38% 25% 6% 1	1050
	21st to end	Night	25% 12% 33% 25% 4	1155

Page generated at 2026-07-28 02:25:23. Version ac07

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