Clyde Sachtleben Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Clyde Sachtleben Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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	9% 6% 2 6% 4 4 4 3 5% 7% 50%	105581
	Night	9% 6% 2 5% 3 3 4 3 5% 7% 53%	102182
Transparency	Day	33% 6% 13% 26% 19% 3	105339
	Night	30% 6% 13% 26% 20% 4	102015
Seeing	Day	12% 9% 32% 31% 14% 2	15766
	Night	11% 9% 36% 35% 9% 1	25647

By Month

Percentage Cloud Cover SW (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	6% 14% 4 9% 4 5% 5% 3 5% 6% 38%	2544
	11th to 20th	Day	7% 10% 5% 10% 5% 4 4 4 5% 7% 40%	2850
	21st to end	Day	7% 9% 6% 12% 4 4 3 2 5% 4 44%	3135
February	1st to 10th	Day	9% 11% 3 8% 6% 4 4 4 5% 7% 39%	1710
	11th to 20th	Day	6% 8% 3 7% 4 4 4 3 5% 8% 48%	1844
	21st to end	Day	8% 7% 2 7% 4 4 3 4 4 7% 51%	1570
March	1st to 10th	Day	10% 7% 2 5% 3 3 3 3 4 5% 56%	3223
	11th to 20th	Day	11% 7% 2 5% 3 3 3 2 5% 5% 54%	3480
	21st to end	Day	16% 9% 2 7% 4 3 3 3 5% 7% 39%	3814
April	1st to 10th	Day	11% 6% 2 5% 4 3 3 4 5% 6% 49%	2161
	11th to 20th	Day	13% 7% 2 7% 4 4 4 4 5% 7% 43%	2378
	21st to end	Day	18% 6% 2 6% 3 4 4 3 5% 7% 42%	2470
May	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 7% 43%	4120
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 4 6% 47%	4082
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 7% 43%	4489
June	1st to 10th	Day	5% 4 1 5% 3 4 5% 4 6% 8% 55%	2470
	11th to 20th	Day	8% 4 1 5% 4 3 4 4 7% 8% 51%	2647
	21st to end	Day	6% 4 2 5% 4 4 4 4 7% 9% 53%	2660
July	1st to 10th	Day	10% 5% 2 5% 4 4 5% 3 5% 7% 50%	4430
	11th to 20th	Day	6% 4 2 5% 5% 5% 4 4 6% 9% 51%	4244
	21st to end	Day	5% 3 1 4 3 4 5% 5% 6% 9% 55%	4466
August	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 7% 9% 47%	4103
	11th to 20th	Day	12% 6% 2 6% 4 4 4 4 6% 7% 46%	4041
	21st to end	Day	5% 4 2 5% 3 4 4 3 5% 7% 58%	4412
September	1st to 10th	Day	12% 5% 2 4 4 3 3 2 4 5% 56%	2142
	11th to 20th	Day	9% 4 1 5% 3 3 3 3 5% 6% 57%	2090
	21st to end	Day	8% 4 1 4 3 3 3 3 5% 7% 60%	2090
October	1st to 10th	Day	8% 4 1 3 2 2 2 2 3 4 70%	3417
	11th to 20th	Day	6% 4 1 3 2 2 3 3 4 7% 66%	3140
	21st to end	Day	9% 5% 2 5% 3 3 3 3 4 6% 58%	3255
November	1st to 10th	Day	9% 5% 1 5% 3 3 4 3 5% 7% 56%	1754
	11th to 20th	Day	7% 6% 3 5% 3 3 3 3 5% 5% 57%	1710
	21st to end	Day	9% 9% 3 5% 3 3 4 3 4 7% 51%	1710
December	1st to 10th	Day	6% 7% 3 6% 4 3 3 4 5% 7% 51%	1710
	11th to 20th	Day	7% 8% 3 7% 4 4 4 3 5% 6% 48%	2161
	21st to end	Day	12% 11% 4 11% 5% 5% 4 4 4 5% 36%	3059
January	1st to 10th	Night	6% 12% 4 12% 5% 3 3 3 5% 7% 40%	4387
	11th to 20th	Night	6% 9% 3 6% 4 5% 5% 3 4 5% 50%	4120
	21st to end	Night	8% 10% 4 11% 4 4 3 4 4 5% 42%	4532
February	1st to 10th	Night	9% 10% 4 7% 4 4 4 4 5% 6% 43%	2470
	11th to 20th	Night	6% 8% 3 6% 4 5% 4 4 6% 7% 47%	2237
	21st to end	Night	6% 7% 2 6% 5% 4 3 3 5% 5% 54%	1884
March	1st to 10th	Night	10% 6% 2 4 3 3 3 2 4 5% 59%	3638
	11th to 20th	Night	9% 6% 2 4 3 3 3 2 3 6% 59%	3480
	21st to end	Night	15% 8% 2 5% 4 4 4 4 6% 8% 42%	3817
April	1st to 10th	Night	10% 7% 2 5% 4 4 4 3 5% 7% 49%	2016
	11th to 20th	Night	12% 6% 2 5% 4 4 5% 3 6% 7% 46%	1748
	21st to end	Night	12% 5% 3 5% 3 3 3 3 4 9% 49%	1710
May	1st to 10th	Night	21% 7% 2 4 3 3 4 3 5% 5% 44%	2850
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 6% 7% 47%	2823
	21st to end	Night	14% 6% 2 5% 4 4 4 3 6% 9% 41%	3098
June	1st to 10th	Night	5% 3 1 4 4 3 4 4 7% 10% 55%	1710
	11th to 20th	Night	9% 3 2 4 4 3 4 4 6% 8% 54%	1527
	21st to end	Night	3 3 1 4 3 3 5% 4 6% 9% 59%	1520
July	1st to 10th	Night	9% 4 2 5% 3 3 4 3 6% 7% 53%	2540
	11th to 20th	Night	4 3 1 4 3 3 5% 5% 7% 10% 54%	2721
	21st to end	Night	3 3 1 4 3 2 3 3 6% 10% 63%	3097
August	1st to 10th	Night	4 3 2 4 4 4 5% 4 7% 10% 54%	2836
	11th to 20th	Night	11% 5% 2 5% 3 3 4 4 6% 8% 51%	2798
	21st to end	Night	4 3 2 4 4 3 4 4 6% 8% 58%	3252
September	1st to 10th	Night	9% 3 1 2 2 3 3 2 5% 6% 64%	2036
	11th to 20th	Night	8% 3 2 4 3 3 4 3 5% 6% 59%	2090
	21st to end	Night	7% 3 1 4 3 3 3 3 4 7% 61%	2090
October	1st to 10th	Night	8% 2 1 3 2 2 2 2 4 5% 70%	3510
	11th to 20th	Night	6% 3 1 3 2 3 2 2 4 5% 67%	3779
	21st to end	Night	8% 4 2 4 3 3 3 3 4 7% 61%	4295
November	1st to 10th	Night	6% 3 2 4 3 3 3 3 5% 6% 62%	2529
	11th to 20th	Night	7% 5% 1 4 3 3 4 4 5% 6% 58%	2470
	21st to end	Night	8% 6% 2 4 3 3 3 3 5% 7% 57%	2470
December	1st to 10th	Night	6% 6% 2 5% 5% 3 4 3 5% 7% 55%	2470
	11th to 20th	Night	7% 6% 2 6% 3 3 3 3 5% 7% 54%	3036
	21st to end	Night	16% 10% 4 7% 4 4 3 3 4 6% 40%	4596

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	44% 6% 15% 23% 11% 1	2545
	11th to 20th	Day	43% 6% 16% 19% 13% 2	2850
	21st to end	Day	43% 5% 14% 24% 13% 1	3135
February	1st to 10th	Day	44% 6% 15% 22% 10% 3	1710
	11th to 20th	Day	35% 5% 16% 24% 16% 4	1854
	21st to end	Day	32% 5% 14% 26% 16% 6%	1570
March	1st to 10th	Day	30% 5% 10% 23% 27% 4	3223
	11th to 20th	Day	32% 5% 12% 28% 20% 2	3480
	21st to end	Day	42% 7% 23% 21% 5% 1	3814
April	1st to 10th	Day	34% 5% 15% 26% 17% 2	2161
	11th to 20th	Day	40% 6% 13% 23% 15% 3	2381
	21st to end	Day	41% 8% 12% 25% 14% 1	2470
May	1st to 10th	Day	36% 8% 14% 23% 14% 5%	4120
	11th to 20th	Day	37% 7% 12% 28% 15% 1	4086
	21st to end	Day	37% 9% 13% 28% 12% 1	4489
June	1st to 10th	Day	25% 7% 19% 33% 14% 2	2470
	11th to 20th	Day	29% 7% 15% 29% 17% 3	2647
	21st to end	Day	25% 8% 15% 30% 19% 4	2660
July	1st to 10th	Day	34% 5% 11% 26% 22% 2	4361
	11th to 20th	Day	28% 7% 14% 27% 21% 3	4171
	21st to end	Day	23% 8% 14% 23% 25% 7%	4325
August	1st to 10th	Day	32% 7% 16% 23% 17% 4	4090
	11th to 20th	Day	37% 7% 16% 22% 18% 1	4080
	21st to end	Day	25% 6% 14% 24% 23% 8%	4411
September	1st to 10th	Day	31% 5% 11% 24% 23% 7%	2142
	11th to 20th	Day	27% 5% 12% 30% 23% 3	2090
	21st to end	Day	25% 4 10% 32% 26% 3	2090
October	1st to 10th	Day	20% 3 6% 20% 43% 7%	3417
	11th to 20th	Day	20% 4 10% 36% 21% 9%	3140
	21st to end	Day	29% 3 9% 30% 26% 3	3255
November	1st to 10th	Day	28% 5% 13% 30% 21% 4	1754
	11th to 20th	Day	29% 5% 11% 26% 26% 4	1710
	21st to end	Day	34% 5% 11% 26% 21% 4	1710
December	1st to 10th	Day	33% 4 16% 29% 16% 2	1710
	11th to 20th	Day	36% 5% 15% 31% 13%	2159
	21st to end	Day	49% 6% 11% 20% 13% 1	3059
January	1st to 10th	Night	43% 5% 13% 24% 13% 1	4387
	11th to 20th	Night	35% 5% 14% 27% 18% 1	4120
	21st to end	Night	43% 6% 12% 22% 16% 1	4532
February	1st to 10th	Night	41% 7% 13% 21% 14% 4	2470
	11th to 20th	Night	34% 6% 14% 28% 16% 3	2237
	21st to end	Night	31% 4 13% 21% 23% 8%	1884
March	1st to 10th	Night	28% 4 9% 26% 26% 7%	3638
	11th to 20th	Night	27% 4 10% 27% 28% 4	3480
	21st to end	Night	39% 9% 24% 21% 7% 1	3817
April	1st to 10th	Night	34% 6% 15% 23% 20% 3	2016
	11th to 20th	Night	35% 6% 15% 25% 17% 2	1748
	21st to end	Night	33% 7% 13% 27% 18% 2	1710
May	1st to 10th	Night	40% 6% 11% 25% 15% 3	2850
	11th to 20th	Night	34% 8% 15% 24% 19%	2824
	21st to end	Night	36% 9% 17% 23% 13% 1	3099
June	1st to 10th	Night	22% 9% 19% 31% 18% 2	1710
	11th to 20th	Night	27% 8% 14% 28% 17% 6%	1527
	21st to end	Night	21% 7% 17% 30% 21% 4	1520
July	1st to 10th	Night	29% 7% 14% 27% 20% 3	2500
	11th to 20th	Night	23% 7% 15% 32% 18% 4	2672
	21st to end	Night	16% 7% 16% 28% 25% 8%	2999
August	1st to 10th	Night	25% 7% 18% 26% 20% 5%	2826
	11th to 20th	Night	32% 6% 18% 26% 15% 2	2825
	21st to end	Night	23% 6% 16% 27% 19% 9%	3252
September	1st to 10th	Night	22% 5% 11% 26% 27% 10%	2036
	11th to 20th	Night	25% 5% 10% 30% 25% 5%	2090
	21st to end	Night	24% 5% 10% 28% 29% 5%	2090
October	1st to 10th	Night	19% 3 6% 18% 45% 9%	3510
	11th to 20th	Night	21% 3 9% 29% 26% 11%	3779
	21st to end	Night	25% 3 10% 28% 29% 4	4295
November	1st to 10th	Night	23% 4 11% 29% 25% 7%	2529
	11th to 20th	Night	26% 5% 10% 28% 26% 5%	2470
	21st to end	Night	28% 4 12% 27% 24% 4	2470
December	1st to 10th	Night	30% 5% 14% 30% 19% 2	2470
	11th to 20th	Night	29% 5% 12% 35% 18% 1	3037
	21st to end	Night	44% 6% 11% 26% 11% 2	4596

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	14% 13% 39% 27% 7% 1	270
	11th to 20th	Day	16% 16% 33% 26% 9%	270
	21st to end	Day	13% 9% 43% 26% 8% 1	297
February	1st to 10th	Day	13% 15% 44% 24% 4	270
	11th to 20th	Day	10% 12% 41% 28% 7% 1	270
	21st to end	Day	11% 17% 49% 18% 4	225
March	1st to 10th	Day	13% 14% 45% 22% 5% 1	270
	11th to 20th	Day	23% 10% 35% 23% 9%	270
	21st to end	Day	23% 15% 38% 18% 5%	297
April	1st to 10th	Day	16% 19% 43% 19% 4	341
	11th to 20th	Day	17% 16% 38% 25% 4	579
	21st to end	Day	20% 14% 35% 19% 9% 2	650
May	1st to 10th	Day	14% 13% 33% 30% 9% 1	653
	11th to 20th	Day	17% 9% 33% 25% 13% 2	675
	21st to end	Day	16% 10% 31% 27% 14% 2	734
June	1st to 10th	Day	5% 6% 27% 36% 20% 6%	680
	11th to 20th	Day	9% 7% 36% 32% 15% 1	680
	21st to end	Day	7% 7% 34% 33% 16% 2	680
July	1st to 10th	Day	8% 3 20% 38% 26% 5%	671
	11th to 20th	Day	4 3 19% 45% 24% 5%	668
	21st to end	Day	8% 2 18% 41% 25% 6%	739
August	1st to 10th	Day	9% 3 18% 42% 24% 4	676
	11th to 20th	Day	7% 2 23% 41% 25% 2	665
	21st to end	Day	9% 2 23% 40% 21% 5%	680
September	1st to 10th	Day	13% 4 24% 39% 16% 5%	352
	11th to 20th	Day	6% 5% 29% 39% 17% 5%	300
	21st to end	Day	12% 9% 31% 27% 17% 5%	300
October	1st to 10th	Day	21% 6% 23% 30% 16% 4	300
	11th to 20th	Day	8% 14% 42% 23% 11% 1	300
	21st to end	Day	16% 17% 34% 24% 8% 1	330
November	1st to 10th	Day	12% 16% 35% 26% 8% 2	297
	11th to 20th	Day	9% 17% 44% 21% 9%	270
	21st to end	Day	20% 13% 34% 22% 10% 1	270
December	1st to 10th	Day	7% 10% 44% 27% 10% 1	270
	11th to 20th	Day	15% 9% 40% 29% 6%	270
	21st to end	Day	18% 13% 45% 22% 2	297
January	1st to 10th	Night	11% 11% 38% 32% 6% 1	950
	11th to 20th	Night	11% 11% 39% 31% 7% 1	950
	21st to end	Night	10% 10% 42% 30% 7%	1045
February	1st to 10th	Night	14% 11% 43% 28% 4	950
	11th to 20th	Night	10% 10% 44% 32% 4	763
	21st to end	Night	11% 13% 45% 27% 4	628
March	1st to 10th	Night	12% 13% 43% 29% 3 1	703
	11th to 20th	Night	15% 11% 41% 27% 5% 1	570
	21st to end	Night	17% 13% 43% 22% 5%	627
April	1st to 10th	Night	14% 14% 42% 27% 3	570
	11th to 20th	Night	15% 14% 42% 25% 4	563
	21st to end	Night	14% 12% 36% 31% 6% 1	570
May	1st to 10th	Night	18% 9% 35% 31% 6%	570
	11th to 20th	Night	15% 8% 35% 33% 7% 1	561
	21st to end	Night	16% 9% 31% 33% 11%	617
June	1st to 10th	Night	7% 6% 26% 46% 14% 2	570
	11th to 20th	Night	8% 5% 38% 38% 11%	570
	21st to end	Night	4 5% 36% 43% 11%	570
July	1st to 10th	Night	7% 3 21% 44% 25%	555
	11th to 20th	Night	3 2 21% 53% 20% 1	552
	21st to end	Night	3 1 16% 55% 24% 1	624
August	1st to 10th	Night	5% 2 19% 52% 19% 2	567
	11th to 20th	Night	8% 2 23% 49% 16% 1	564
	21st to end	Night	7% 2 24% 44% 22% 1	627
September	1st to 10th	Night	11% 3 25% 45% 16% 1	570
	11th to 20th	Night	9% 3 35% 37% 15% 1	570
	21st to end	Night	8% 6% 35% 36% 14% 1	570
October	1st to 10th	Night	15% 7% 33% 32% 13%	587
	11th to 20th	Night	13% 9% 38% 31% 8%	760
	21st to end	Night	14% 12% 32% 32% 10%	936
November	1st to 10th	Night	8% 10% 36% 38% 7%	973
	11th to 20th	Night	10% 11% 41% 30% 7%	950
	21st to end	Night	11% 11% 34% 32% 11% 1	950
December	1st to 10th	Night	10% 10% 43% 33% 4 1	950
	11th to 20th	Night	13% 10% 39% 30% 7%	950
	21st to end	Night	16% 11% 38% 31% 5%	1045

Page generated at 2024-11-07 05:55:48. Version ac07

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