Scopehill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Scopehill Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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% 7% 2 6% 4 4 4 3 5% 7% 46%	101143
	Night	12% 7% 2 5% 4 3 4 3 5% 7% 49%	98707
Transparency	Day	38% 3 11% 27% 18% 3	104793
	Night	36% 2 11% 27% 20% 4	103197
Seeing	Day	14% 7% 26% 28% 19% 5%	15694
	Night	15% 7% 30% 34% 14% 1	25568

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	16% 9% 3 8% 4 3 3 3 4 6% 40%	2847
	11th to 20th	Day	11% 12% 4 6% 6% 4 4 2 4 6% 40%	2850
	21st to end	Day	18% 14% 4 6% 3 3 4 2 3 5% 38%	3135
February	1st to 10th	Day	16% 10% 3 8% 4 4 3 3 3 5% 41%	1710
	11th to 20th	Day	13% 10% 3 7% 5% 4 3 2 3 5% 45%	1665
	21st to end	Day	13% 10% 3 6% 4 4 4 4 5% 6% 40%	1659
March	1st to 10th	Day	15% 8% 3 6% 3 3 3 2 3 6% 49%	3436
	11th to 20th	Day	14% 7% 2 4 3 3 3 3 5% 6% 51%	3480
	21st to end	Day	16% 11% 3 7% 4 4 4 3 5% 6% 37%	3814
April	1st to 10th	Day	12% 8% 2 5% 5% 5% 4 4 5% 7% 44%	2185
	11th to 20th	Day	15% 7% 2 6% 4 4 5% 3 5% 6% 42%	2254
	21st to end	Day	21% 7% 3 7% 5% 4 4 3 5% 5% 37%	2375
May	1st to 10th	Day	19% 9% 3 7% 4 4 4 3 5% 6% 36%	4082
	11th to 20th	Day	14% 7% 2 7% 4 4 4 3 6% 7% 41%	4082
	21st to end	Day	13% 6% 2 6% 5% 4 4 4 6% 9% 41%	4477
June	1st to 10th	Day	6% 5% 2 5% 4 4 5% 5% 7% 10% 47%	2551
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 7% 9% 48%	2654
	21st to end	Day	5% 3 1 3 3 4 5% 4 6% 9% 56%	2470
July	1st to 10th	Day	11% 6% 3 7% 5% 4 5% 4 6% 8% 41%	4120
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 9% 53%	4120
	21st to end	Day	6% 4 2 5% 5% 5% 6% 5% 9% 11% 41%	4465
August	1st to 10th	Day	5% 3 2 5% 4 4 5% 4 6% 10% 54%	4104
	11th to 20th	Day	8% 6% 2 6% 5% 4 5% 4 6% 8% 46%	4041
	21st to end	Day	6% 4 1 5% 3 4 4 4 6% 8% 56%	4226
September	1st to 10th	Day	12% 5% 2 5% 3 4 4 2 4 7% 53%	2280
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 8% 48%	2099
	21st to end	Day	9% 4 1 5% 4 4 4 3 5% 6% 55%	2081
October	1st to 10th	Day	11% 5% 2 5% 3 4 3 3 4 6% 54%	1900
	11th to 20th	Day	12% 5% 2 5% 2 2 2 2 3 6% 58%	1900
	21st to end	Day	18% 6% 2 5% 2 3 3 3 4 4 49%	2090
November	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 5% 56%	1958
	11th to 20th	Day	15% 6% 1 4 3 3 3 3 4 6% 52%	1846
	21st to end	Day	16% 7% 3 6% 3 2 2 2 4 5% 51%	1605
December	1st to 10th	Day	12% 7% 3 7% 4 3 4 3 4 5% 48%	1584
	11th to 20th	Day	14% 9% 3 6% 4 4 4 2 4 5% 45%	1918
	21st to end	Day	19% 16% 5% 7% 4 4 3 3 4 6% 29%	3080
January	1st to 10th	Night	12% 8% 3 9% 5% 4 3 3 4 5% 45%	4108
	11th to 20th	Night	11% 7% 3 7% 5% 5% 6% 4 4 5% 41%	4120
	21st to end	Night	21% 11% 3 6% 3 3 3 2 3 5% 40%	4532
February	1st to 10th	Night	13% 12% 3 6% 4 3 4 3 5% 6% 41%	2470
	11th to 20th	Night	13% 8% 3 6% 3 4 3 3 5% 6% 45%	2403
	21st to end	Night	15% 9% 3 5% 4 3 3 3 4 6% 46%	1809
March	1st to 10th	Night	14% 8% 2 5% 3 3 3 3 4 6% 49%	3419
	11th to 20th	Night	10% 6% 2 5% 3 4 3 3 4 6% 54%	3480
	21st to end	Night	14% 7% 3 6% 5% 5% 4 3 5% 6% 41%	3817
April	1st to 10th	Night	11% 6% 2 6% 4 3 4 3 4 7% 50%	1993
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 4 5% 49%	1875
	21st to end	Night	17% 7% 2 7% 5% 3 4 3 5% 5% 44%	1800
May	1st to 10th	Night	15% 8% 3 6% 4 4 4 4 5% 6% 42%	2823
	11th to 20th	Night	14% 7% 3 6% 4 3 4 4 6% 6% 43%	2823
	21st to end	Night	11% 5% 2 4 4 3 4 3 5% 8% 52%	3090
June	1st to 10th	Night	6% 3 2 4 4 4 4 4 7% 10% 52%	1615
	11th to 20th	Night	4 3 1 4 4 4 5% 4 8% 11% 52%	1520
	21st to end	Night	5% 3 1 4 3 4 3 4 6% 7% 60%	1701
July	1st to 10th	Night	9% 6% 3 6% 4 4 3 4 5% 8% 48%	2850
	11th to 20th	Night	3 2 1 4 4 4 4 4 6% 10% 58%	2850
	21st to end	Night	7% 4 2 4 4 4 5% 4 8% 12% 48%	3098
August	1st to 10th	Night	3 2 1 4 3 3 4 3 6% 9% 62%	2836
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2798
	21st to end	Night	3 3 1 4 3 3 3 3 5% 9% 63%	3431
September	1st to 10th	Night	10% 5% 2 4 2 3 3 3 4 7% 57%	1900
	11th to 20th	Night	10% 4 1 4 4 4 4 4 5% 7% 53%	2078
	21st to end	Night	7% 4 2 5% 3 3 3 3 5% 7% 58%	2090
October	1st to 10th	Night	8% 4 1 4 2 3 3 2 5% 6% 61%	2270
	11th to 20th	Night	13% 4 2 4 2 3 2 2 4 5% 58%	2280
	21st to end	Night	15% 6% 2 5% 3 3 3 2 3 5% 53%	2508
November	1st to 10th	Night	11% 6% 1 3 3 2 2 2 3 5% 62%	2340
	11th to 20th	Night	11% 6% 2 6% 3 3 3 3 4 6% 53%	2550
	21st to end	Night	16% 7% 2 4 3 2 2 2 4 5% 53%	2790
December	1st to 10th	Night	12% 8% 2 5% 3 3 3 3 6% 7% 48%	2779
	11th to 20th	Night	13% 8% 2 6% 4 3 4 3 5% 5% 46%	3279
	21st to end	Night	19% 14% 5% 7% 4 3 4 3 4 5% 33%	4582

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	48% 1 8% 27% 15% 1	2848
	11th to 20th	Day	49% 1 11% 25% 12% 1	2850
	21st to end	Day	52% 2 9% 20% 17% 1	3135
February	1st to 10th	Day	49% 3 9% 26% 10% 2	1710
	11th to 20th	Day	45% 2 12% 23% 16% 3	1674
	21st to end	Day	44% 2 8% 25% 15% 6%	1659
March	1st to 10th	Day	41% 1 7% 24% 23% 4	3436
	11th to 20th	Day	36% 1 11% 30% 17% 4	3480
	21st to end	Day	50% 2 17% 23% 7% 1	3814
April	1st to 10th	Day	40% 3 12% 24% 17% 3	2185
	11th to 20th	Day	43% 3 11% 24% 16% 2	2254
	21st to end	Day	50% 2 11% 25% 11% 1	2375
May	1st to 10th	Day	51% 2 10% 20% 15% 2	4120
	11th to 20th	Day	43% 3 14% 26% 14%	4086
	21st to end	Day	43% 3 12% 28% 13% 1	4489
June	1st to 10th	Day	31% 4 18% 29% 17% 2	2551
	11th to 20th	Day	31% 4 14% 33% 16% 2	2654
	21st to end	Day	24% 4 16% 34% 19% 3	2470
July	1st to 10th	Day	40% 4 12% 22% 18% 4	4056
	11th to 20th	Day	29% 4 12% 37% 17% 2	4051
	21st to end	Day	31% 6% 20% 30% 12%	4325
August	1st to 10th	Day	26% 4 17% 26% 24% 3	4090
	11th to 20th	Day	36% 5% 15% 28% 15% 1	4080
	21st to end	Day	26% 4 12% 40% 14% 4	4225
September	1st to 10th	Day	33% 3 11% 28% 18% 8%	2280
	11th to 20th	Day	33% 3 9% 26% 26% 2	2099
	21st to end	Day	31% 3 8% 27% 26% 5%	2081
October	1st to 10th	Day	20% 1 6% 20% 41% 13%	3160
	11th to 20th	Day	19% 1 4 28% 38% 10%	3140
	21st to end	Day	32% 3 7% 27% 27% 4	3428
November	1st to 10th	Day	32% 2 9% 30% 22% 5%	1958
	11th to 20th	Day	35% 2 7% 26% 24% 5%	1846
	21st to end	Day	39% 2 9% 29% 20% 1	1605
December	1st to 10th	Day	39% 2 9% 35% 13% 1	1584
	11th to 20th	Day	44% 1 9% 26% 17% 2	1915
	21st to end	Day	59% 2 9% 21% 8% 2	3080
January	1st to 10th	Night	44% 2 12% 26% 14% 2	4108
	11th to 20th	Night	48% 1 10% 26% 14% 1	4120
	21st to end	Night	50% 1 11% 22% 13% 2	4532
February	1st to 10th	Night	46% 2 10% 25% 15% 2	2470
	11th to 20th	Night	41% 2 10% 27% 17% 3	2404
	21st to end	Night	41% 2 8% 23% 19% 7%	1809
March	1st to 10th	Night	39% 1 9% 24% 21% 5%	3419
	11th to 20th	Night	34% 2 8% 27% 27% 3	3480
	21st to end	Night	46% 2 15% 26% 11% 1	3817
April	1st to 10th	Night	36% 3 9% 23% 23% 5%	1993
	11th to 20th	Night	39% 3 8% 25% 20% 4	1875
	21st to end	Night	45% 2 10% 25% 16% 2	1800
May	1st to 10th	Night	45% 3 13% 21% 15% 3	2850
	11th to 20th	Night	43% 2 13% 29% 12% 1	2824
	21st to end	Night	32% 3 13% 31% 20% 1	3099
June	1st to 10th	Night	26% 3 19% 31% 18% 3	1615
	11th to 20th	Night	25% 4 17% 31% 21% 2	1520
	21st to end	Night	23% 3 14% 35% 22% 4	1701
July	1st to 10th	Night	35% 4 13% 25% 20% 4	2805
	11th to 20th	Night	21% 4 11% 39% 22% 2	2796
	21st to end	Night	28% 5% 20% 31% 15% 1	2999
August	1st to 10th	Night	18% 4 17% 34% 20% 7%	2826
	11th to 20th	Night	33% 4 13% 30% 19% 2	2825
	21st to end	Night	21% 4 13% 40% 18% 4	3431
September	1st to 10th	Night	28% 3 11% 27% 22% 9%	1900
	11th to 20th	Night	30% 4 9% 25% 27% 5%	2078
	21st to end	Night	28% 3 7% 28% 30% 4	2090
October	1st to 10th	Night	16% 2 6% 20% 43% 14%	3790
	11th to 20th	Night	22% 2 5% 23% 34% 16%	3779
	21st to end	Night	31% 2 6% 30% 26% 5%	4120
November	1st to 10th	Night	28% 2 10% 29% 24% 6%	2340
	11th to 20th	Night	35% 2 6% 26% 27% 5%	2550
	21st to end	Night	37% 2 8% 27% 23% 3	2790
December	1st to 10th	Night	36% 3 12% 29% 19% 1	2779
	11th to 20th	Night	41% 2 8% 28% 19% 2	3281
	21st to end	Night	57% 2 8% 20% 11% 2	4582

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	21% 11% 33% 24% 10% 1	270
	11th to 20th	Day	26% 15% 33% 23% 2	270
	21st to end	Day	17% 11% 43% 21% 7%	297
February	1st to 10th	Day	23% 17% 33% 22% 5%	270
	11th to 20th	Day	19% 17% 41% 19% 4 1	270
	21st to end	Day	21% 21% 41% 14% 3	225
March	1st to 10th	Day	21% 14% 36% 24% 3	270
	11th to 20th	Day	25% 11% 35% 22% 7%	270
	21st to end	Day	30% 12% 39% 15% 2 2	297
April	1st to 10th	Day	17% 18% 36% 22% 7% 1	365
	11th to 20th	Day	19% 13% 37% 24% 8%	452
	21st to end	Day	24% 12% 32% 22% 10%	555
May	1st to 10th	Day	21% 9% 34% 25% 10% 1	653
	11th to 20th	Day	19% 6% 28% 30% 13% 4	675
	21st to end	Day	16% 5% 27% 27% 18% 7%	734
June	1st to 10th	Day	6% 2 16% 36% 28% 10%	680
	11th to 20th	Day	8% 3 21% 39% 23% 7%	680
	21st to end	Day	7% 4 27% 35% 22% 4	680
July	1st to 10th	Day	11% 3 13% 29% 30% 13%	671
	11th to 20th	Day	5% 1 13% 36% 36% 9%	668
	21st to end	Day	9% 1 10% 32% 35% 14%	739
August	1st to 10th	Day	9% 2 12% 37% 33% 8%	676
	11th to 20th	Day	8% 2 14% 33% 36% 8%	665
	21st to end	Day	8% 2 9% 28% 37% 16%	572
September	1st to 10th	Day	13% 3 12% 30% 34% 9%	490
	11th to 20th	Day	5% 1 16% 38% 31% 10%	309
	21st to end	Day	13% 2 20% 36% 23% 7%	300
October	1st to 10th	Day	13% 6% 26% 27% 19% 10%	300
	11th to 20th	Day	12% 9% 37% 29% 10% 2	300
	21st to end	Day	25% 10% 33% 23% 8% 1	330
November	1st to 10th	Day	16% 9% 34% 26% 11% 4	300
	11th to 20th	Day	17% 10% 35% 24% 13% 1	300
	21st to end	Day	21% 12% 33% 25% 7% 2	300
December	1st to 10th	Day	13% 12% 42% 22% 9% 3	294
	11th to 20th	Day	17% 11% 35% 29% 7% 1	270
	21st to end	Day	20% 17% 41% 21% 1	297
January	1st to 10th	Night	15% 11% 38% 29% 6%	950
	11th to 20th	Night	17% 12% 39% 26% 5%	950
	21st to end	Night	15% 11% 38% 32% 4	1045
February	1st to 10th	Night	19% 11% 39% 27% 4	950
	11th to 20th	Night	17% 11% 40% 29% 3	929
	21st to end	Night	21% 13% 38% 25% 3	553
March	1st to 10th	Night	18% 9% 38% 32% 4	570
	11th to 20th	Night	21% 8% 33% 32% 5% 1	570
	21st to end	Night	22% 11% 37% 27% 4	627
April	1st to 10th	Night	13% 10% 39% 30% 7%	570
	11th to 20th	Night	18% 11% 34% 31% 6%	563
	21st to end	Night	21% 6% 38% 27% 8%	570
May	1st to 10th	Night	17% 6% 32% 36% 9%	570
	11th to 20th	Night	17% 3 26% 37% 16% 1	561
	21st to end	Night	13% 5% 24% 35% 19% 3	617
June	1st to 10th	Night	6% 4 14% 43% 32% 1	570
	11th to 20th	Night	5% 1 22% 49% 21% 1	570
	21st to end	Night	6% 1 24% 49% 18% 1	570
July	1st to 10th	Night	8% 2 11% 42% 34% 4	555
	11th to 20th	Night	3 1 11% 47% 35% 2	552
	21st to end	Night	8% 1 9% 39% 40% 2	624
August	1st to 10th	Night	6% 2 11% 44% 35% 2	567
	11th to 20th	Night	9% 1 9% 46% 31% 2	564
	21st to end	Night	6% 1 8% 38% 42% 4	627
September	1st to 10th	Night	12% 2 11% 44% 28% 4	570
	11th to 20th	Night	11% 2 14% 39% 29% 5%	570
	21st to end	Night	10% 1 20% 42% 23% 3	570
October	1st to 10th	Night	11% 2 24% 37% 23% 2	750
	11th to 20th	Night	14% 6% 36% 35% 10%	760
	21st to end	Night	18% 9% 32% 31% 9% 1	836
November	1st to 10th	Night	14% 6% 36% 32% 11% 1	780
	11th to 20th	Night	16% 9% 36% 29% 9%	950
	21st to end	Night	20% 9% 35% 28% 8%	1000
December	1st to 10th	Night	17% 7% 39% 30% 6%	993
	11th to 20th	Night	22% 7% 34% 32% 5%	950
	21st to end	Night	20% 12% 36% 28% 4	1045

Page generated at 2024-12-06 02:54:49. Version ac07

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