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 2025-03-27.

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% 4 8% 5% 4 4 4 5% 7% 37%	109290
	Night	12% 10% 4 9% 5% 4 4 4 5% 6% 38%	110279
Transparency	Day	45% 6% 13% 25% 11% 1	112909
	Night	45% 5% 12% 24% 13% 1	114800
Seeing	Day	16% 12% 32% 26% 12% 3	16443
	Night	15% 10% 34% 30% 10% 1	26530

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% 13% 6% 19% 7% 5% 4 3 5% 5% 24%	3617
	11th to 20th	Day	6% 11% 7% 13% 6% 7% 8% 8% 9% 4 21%	3709
	21st to end	Day	6% 17% 7% 13% 5% 4 4 3 4 5% 31%	4488
February	1st to 10th	Day	9% 12% 5% 11% 6% 6% 5% 5% 6% 6% 31%	1800
	11th to 20th	Day	8% 12% 4 11% 7% 4 4 4 5% 6% 34%	1754
	21st to end	Day	10% 12% 4 9% 5% 5% 5% 4 6% 6% 34%	1537
March	1st to 10th	Day	12% 11% 4 7% 4 4 4 3 5% 6% 40%	3500
	11th to 20th	Day	10% 10% 3 8% 4 5% 4 3 4 8% 39%	3590
	21st to end	Day	23% 13% 5% 12% 5% 4 4 2 4 5% 22%	3904
April	1st to 10th	Day	17% 10% 3 7% 5% 3 4 3 5% 6% 35%	2280
	11th to 20th	Day	20% 12% 3 7% 5% 4 4 2 4 6% 32%	2272
	21st to end	Day	22% 12% 3 6% 5% 4 4 4 5% 5% 30%	2470
May	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 5% 7% 40%	4229
	11th to 20th	Day	13% 7% 2 5% 4 4 4 3 6% 7% 45%	4399
	21st to end	Day	18% 7% 3 7% 4 4 5% 4 5% 7% 36%	4824
June	1st to 10th	Day	12% 5% 2 4 4 4 4 4 7% 9% 46%	2660
	11th to 20th	Day	13% 7% 2 7% 5% 5% 5% 4 6% 8% 38%	2660
	21st to end	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 9% 40%	2660
July	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 8% 10% 38%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 3 5% 7% 60%	4440
	21st to end	Day	6% 3 2 6% 5% 4 5% 4 7% 9% 49%	4721
August	1st to 10th	Day	12% 5% 3 6% 4 5% 5% 4 6% 7% 41%	4104
	11th to 20th	Day	13% 6% 2 5% 4 4 5% 4 7% 8% 43%	4041
	21st to end	Day	10% 6% 3 7% 4 4 4 4 4 7% 48%	4345
September	1st to 10th	Day	11% 7% 2 5% 4 4 4 3 5% 6% 49%	2280
	11th to 20th	Day	13% 6% 1 5% 4 4 4 4 5% 8% 47%	2237
	21st to end	Day	15% 6% 2 5% 4 5% 5% 3 5% 7% 44%	2008
October	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 4 6% 44%	1900
	11th to 20th	Day	15% 9% 3 6% 4 4 4 3 4 6% 41%	1900
	21st to end	Day	18% 11% 4 6% 4 3 3 3 4 6% 37%	2083
November	1st to 10th	Day	12% 11% 4 9% 4 4 4 4 5% 5% 38%	1638
	11th to 20th	Day	11% 15% 6% 11% 6% 4 3 4 5% 6% 30%	1600
	21st to end	Day	14% 11% 4 8% 5% 4 4 4 5% 7% 35%	1600
December	1st to 10th	Day	7% 11% 3 15% 10% 7% 5% 3 5% 7% 25%	2610
	11th to 20th	Day	11% 17% 6% 10% 7% 5% 5% 3 4 6% 27%	3008
	21st to end	Day	21% 18% 9% 18% 5% 3 3 3 3 4 14%	3982
January	1st to 10th	Night	7% 12% 5% 16% 8% 5% 4 4 5% 5% 28%	6348
	11th to 20th	Night	7% 11% 5% 13% 7% 7% 9% 8% 6% 5% 21%	6268
	21st to end	Night	8% 19% 6% 9% 5% 5% 4 3 5% 4 33%	6490
February	1st to 10th	Night	8% 12% 5% 10% 7% 6% 5% 3 5% 6% 34%	2600
	11th to 20th	Night	6% 10% 4 8% 6% 6% 5% 3 5% 7% 39%	2533
	21st to end	Night	11% 9% 4 8% 6% 5% 5% 3 5% 6% 37%	2091
March	1st to 10th	Night	9% 8% 3 7% 4 3 4 3 5% 7% 47%	3602
	11th to 20th	Night	9% 7% 3 7% 5% 5% 5% 4 6% 7% 41%	3590
	21st to end	Night	26% 12% 3 10% 4 3 3 2 3 5% 29%	3864
April	1st to 10th	Night	15% 11% 3 6% 4 3 5% 3 6% 6% 38%	1900
	11th to 20th	Night	20% 9% 4 7% 4 4 4 3 4 6% 35%	1853
	21st to end	Night	18% 9% 3 7% 5% 4 4 4 5% 6% 36%	1710
May	1st to 10th	Night	14% 7% 3 6% 5% 5% 4 4 5% 6% 41%	2673
	11th to 20th	Night	14% 5% 1 5% 3 3 4 3 5% 8% 50%	2506
	21st to end	Night	15% 7% 2 6% 4 4 5% 3 5% 7% 42%	2743
June	1st to 10th	Night	10% 5% 2 4 3 4 4 4 7% 8% 49%	1520
	11th to 20th	Night	9% 5% 2 5% 6% 4 5% 4 6% 9% 45%	1520
	21st to end	Night	8% 4 2 5% 4 4 4 3 6% 9% 53%	1520
July	1st to 10th	Night	11% 4 1 5% 4 5% 4 5% 7% 10% 45%	2530
	11th to 20th	Night	3 3 1 4 4 3 4 4 7% 9% 59%	2530
	21st to end	Night	6% 4 2 4 4 4 4 3 5% 7% 57%	2838
August	1st to 10th	Night	13% 5% 2 5% 4 3 4 4 5% 7% 48%	2836
	11th to 20th	Night	14% 4 2 4 3 3 3 4 5% 7% 52%	2798
	21st to end	Night	10% 6% 3 6% 4 3 4 3 5% 7% 49%	3316
September	1st to 10th	Night	10% 3 2 5% 3 3 4 4 5% 7% 55%	1900
	11th to 20th	Night	10% 4 1 5% 4 4 3 3 5% 8% 53%	1940
	21st to end	Night	13% 5% 2 4 3 3 4 3 4 5% 52%	2152
October	1st to 10th	Night	13% 7% 2 6% 3 3 3 2 4 6% 50%	2280
	11th to 20th	Night	14% 10% 2 6% 4 3 4 3 5% 6% 43%	2280
	21st to end	Night	18% 11% 3 7% 4 4 3 3 5% 6% 37%	2513
November	1st to 10th	Night	13% 9% 3 6% 4 4 4 3 5% 7% 41%	2660
	11th to 20th	Night	12% 12% 4 11% 5% 4 4 3 5% 5% 35%	2800
	21st to end	Night	13% 11% 4 9% 6% 4 4 3 4 6% 37%	2800
December	1st to 10th	Night	6% 9% 4 14% 7% 8% 5% 4 5% 6% 31%	4580
	11th to 20th	Night	10% 17% 7% 13% 7% 4 5% 4 5% 5% 24%	5199
	21st to end	Night	23% 15% 9% 14% 5% 4 4 3 3 4 17%	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	62% 5% 10% 17% 5%	3618
	11th to 20th	Day	59% 5% 8% 17% 10%	3709
	21st to end	Day	55% 5% 15% 17% 7%	4488
February	1st to 10th	Day	53% 5% 14% 18% 9% 1	1800
	11th to 20th	Day	50% 6% 11% 24% 8% 1	1763
	21st to end	Day	50% 6% 13% 19% 11%	1537
March	1st to 10th	Day	44% 5% 13% 26% 11% 1	3500
	11th to 20th	Day	43% 6% 9% 31% 9% 2	3590
	21st to end	Day	65% 5% 8% 16% 5%	3904
April	1st to 10th	Day	49% 6% 11% 22% 12% 1	2280
	11th to 20th	Day	54% 4 10% 19% 12% 2	2272
	21st to end	Day	55% 5% 11% 19% 9% 1	2470
May	1st to 10th	Day	42% 7% 11% 25% 14% 2	4267
	11th to 20th	Day	37% 7% 10% 29% 15% 2	4403
	21st to end	Day	45% 7% 11% 25% 10% 1	4837
June	1st to 10th	Day	33% 7% 14% 31% 13% 2	2660
	11th to 20th	Day	42% 6% 13% 22% 15% 1	2660
	21st to end	Day	36% 9% 16% 26% 11% 2	2660
July	1st to 10th	Day	38% 8% 20% 22% 11% 1	4371
	11th to 20th	Day	22% 5% 16% 35% 19% 2	4365
	21st to end	Day	29% 8% 14% 30% 18% 1	4572
August	1st to 10th	Day	40% 6% 12% 28% 13% 2	4090
	11th to 20th	Day	37% 6% 13% 33% 10%	4080
	21st to end	Day	35% 6% 16% 29% 14% 1	4344
September	1st to 10th	Day	35% 6% 12% 32% 14%	2280
	11th to 20th	Day	34% 6% 17% 34% 9%	2237
	21st to end	Day	40% 5% 12% 32% 11% 1	2008
October	1st to 10th	Day	31% 3 8% 35% 23%	3160
	11th to 20th	Day	39% 4 11% 27% 18% 1	3140
	21st to end	Day	44% 3 14% 30% 9%	3409
November	1st to 10th	Day	47% 5% 14% 20% 13% 3	1638
	11th to 20th	Day	54% 4 13% 18% 10% 1	1600
	21st to end	Day	48% 5% 18% 22% 7% 1	1600
December	1st to 10th	Day	58% 6% 16% 15% 6% 1	2610
	11th to 20th	Day	59% 5% 16% 16% 5%	3005
	21st to end	Day	74% 4 9% 9% 4	3982
January	1st to 10th	Night	57% 5% 10% 21% 7%	6348
	11th to 20th	Night	60% 5% 10% 15% 9%	6268
	21st to end	Night	54% 5% 11% 23% 8%	6490
February	1st to 10th	Night	51% 4 12% 21% 11% 1	2600
	11th to 20th	Night	45% 6% 13% 25% 9% 1	2534
	21st to end	Night	47% 5% 12% 22% 12% 1	2091
March	1st to 10th	Night	37% 5% 12% 28% 17% 1	3602
	11th to 20th	Night	40% 5% 9% 29% 16% 1	3590
	21st to end	Night	59% 4 7% 21% 8% 1	3864
April	1st to 10th	Night	47% 5% 10% 24% 14% 1	1900
	11th to 20th	Night	51% 4 7% 19% 17% 2	1853
	21st to end	Night	48% 6% 9% 21% 14% 2	1710
May	1st to 10th	Night	41% 6% 10% 20% 21% 1	2700
	11th to 20th	Night	33% 6% 10% 26% 20% 5%	2507
	21st to end	Night	39% 7% 10% 26% 16% 1	2751
June	1st to 10th	Night	31% 6% 13% 30% 18% 3	1520
	11th to 20th	Night	34% 7% 15% 23% 18% 3	1520
	21st to end	Night	28% 6% 16% 31% 16% 3	1520
July	1st to 10th	Night	33% 7% 21% 25% 14% 1	2490
	11th to 20th	Night	20% 5% 15% 40% 18% 2	2482
	21st to end	Night	25% 6% 15% 32% 18% 3	2748
August	1st to 10th	Night	36% 6% 12% 28% 14% 4	2826
	11th to 20th	Night	32% 5% 14% 33% 16% 1	2825
	21st to end	Night	34% 6% 17% 27% 14% 2	3316
September	1st to 10th	Night	27% 6% 13% 34% 19% 1	1900
	11th to 20th	Night	28% 6% 16% 32% 18% 1	1940
	21st to end	Night	34% 4 12% 31% 18% 2	2152
October	1st to 10th	Night	23% 3 6% 36% 28% 4	3800
	11th to 20th	Night	32% 4 13% 25% 22% 4	3779
	21st to end	Night	43% 4 12% 28% 13% 1	4137
November	1st to 10th	Night	42% 6% 12% 24% 14% 2	2660
	11th to 20th	Night	51% 5% 11% 20% 12% 1	2800
	21st to end	Night	49% 4 16% 22% 8% 1	2800
December	1st to 10th	Night	52% 6% 18% 19% 5%	4580
	11th to 20th	Night	61% 5% 11% 17% 4 1	5201
	21st to end	Night	71% 4 8% 13% 3	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	13% 12% 34% 30% 8% 3	300
	11th to 20th	Day	15% 15% 40% 26% 4 1	300
	21st to end	Day	16% 12% 39% 24% 8% 2	330
February	1st to 10th	Day	15% 17% 44% 19% 5%	300
	11th to 20th	Day	13% 20% 39% 22% 5% 1	300
	21st to end	Day	16% 15% 45% 21% 3	249
March	1st to 10th	Day	17% 17% 41% 19% 6%	300
	11th to 20th	Day	19% 15% 37% 22% 6% 1	300
	21st to end	Day	26% 18% 27% 21% 6% 2	327
April	1st to 10th	Day	24% 14% 37% 20% 5%	460
	11th to 20th	Day	28% 16% 26% 21% 10% 1	470
	21st to end	Day	25% 15% 30% 21% 8% 1	650
May	1st to 10th	Day	19% 16% 35% 22% 7% 1	653
	11th to 20th	Day	19% 12% 29% 24% 14% 3	675
	21st to end	Day	18% 11% 27% 29% 12% 3	734
June	1st to 10th	Day	10% 8% 29% 33% 16% 3	680
	11th to 20th	Day	15% 8% 38% 27% 9% 2	680
	21st to end	Day	12% 11% 31% 27% 16% 3	680
July	1st to 10th	Day	10% 4 25% 31% 22% 8%	671
	11th to 20th	Day	8% 8% 28% 31% 20% 5%	668
	21st to end	Day	6% 5% 27% 39% 18% 5%	739
August	1st to 10th	Day	9% 5% 26% 34% 22% 3	676
	11th to 20th	Day	14% 4 24% 31% 21% 5%	665
	21st to end	Day	10% 7% 28% 34% 15% 5%	639
September	1st to 10th	Day	14% 10% 28% 29% 16% 4	490
	11th to 20th	Day	15% 6% 28% 31% 18% 3	447
	21st to end	Day	16% 14% 32% 18% 16% 4	300
October	1st to 10th	Day	19% 11% 29% 27% 11% 3	300
	11th to 20th	Day	15% 22% 36% 21% 5% 1	300
	21st to end	Day	24% 17% 35% 16% 7% 1	330
November	1st to 10th	Day	20% 16% 37% 17% 9% 1	300
	11th to 20th	Day	16% 20% 42% 19% 2	300
	21st to end	Day	22% 14% 45% 17% 3	300
December	1st to 10th	Day	14% 13% 41% 25% 6%	300
	11th to 20th	Day	20% 16% 37% 23% 3	300
	21st to end	Day	28% 14% 39% 14% 4	330
January	1st to 10th	Night	11% 13% 39% 29% 8% 1	1000
	11th to 20th	Night	16% 13% 37% 28% 5% 1	1000
	21st to end	Night	18% 11% 38% 27% 5%	1100
February	1st to 10th	Night	14% 13% 38% 28% 6%	1000
	11th to 20th	Night	11% 13% 43% 27% 6% 1	979
	21st to end	Night	15% 14% 37% 26% 7% 1	771
March	1st to 10th	Night	15% 10% 40% 27% 7% 1	651
	11th to 20th	Night	16% 12% 41% 25% 6%	600
	21st to end	Night	22% 12% 30% 24% 11% 2	647
April	1st to 10th	Night	19% 14% 35% 26% 5%	570
	11th to 20th	Night	24% 12% 30% 28% 6%	563
	21st to end	Night	21% 9% 34% 26% 8% 1	570
May	1st to 10th	Night	18% 11% 34% 31% 6% 1	570
	11th to 20th	Night	15% 9% 32% 32% 11% 1	561
	21st to end	Night	16% 9% 26% 35% 14%	617
June	1st to 10th	Night	11% 5% 31% 39% 13%	570
	11th to 20th	Night	10% 5% 33% 43% 8%	570
	21st to end	Night	9% 4 26% 45% 15% 1	570
July	1st to 10th	Night	6% 2 26% 38% 26% 2	555
	11th to 20th	Night	6% 4 29% 44% 16% 1	552
	21st to end	Night	5% 2 25% 47% 18% 2	624
August	1st to 10th	Night	7% 4 20% 47% 20% 1	567
	11th to 20th	Night	12% 3 20% 39% 23% 3	564
	21st to end	Night	7% 4 29% 35% 23% 2	627
September	1st to 10th	Night	10% 5% 25% 40% 17% 3	570
	11th to 20th	Night	12% 5% 34% 31% 16% 2	570
	21st to end	Night	12% 10% 33% 29% 15% 1	632
October	1st to 10th	Night	17% 11% 30% 29% 14%	760
	11th to 20th	Night	18% 13% 35% 26% 8% 1	760
	21st to end	Night	23% 12% 30% 28% 6%	836
November	1st to 10th	Night	18% 12% 35% 27% 7% 1	904
	11th to 20th	Night	18% 14% 38% 24% 6% 1	1000
	21st to end	Night	17% 16% 38% 24% 6%	1000
December	1st to 10th	Night	15% 11% 40% 28% 7% 1	1000
	11th to 20th	Night	19% 11% 39% 25% 6% 1	1000
	21st to end	Night	25% 13% 33% 25% 4	1100

Page generated at 2025-03-24 08:04:27. Version ac07

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