Deep Springs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deep Springs Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	1 2 1 2 2 2 3 3 4 6% 74%	104947
	Night	1 3 1 3 2 2 3 2 4 6% 73%	102801
Transparency	Day	12% 2 6% 18% 28% 35%	104691
	Night	13% 2 7% 21% 29% 28%	102647
Seeing	Day	4 12% 28% 31% 19% 5%	15156
	Night	3 5% 23% 41% 25% 4	24725

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	1 2 1 3 2 3 3 3 5% 12% 66%	2539
	11th to 20th	Day	3 1 4 3 3 4 4 8% 10% 60%	2540
	21st to end	Day	4 5% 1 3 2 2 4 3 6% 10% 59%	3161
February	1st to 10th	Day	3 2 1 3 2 2 3 2 4 7% 70%	1900
	11th to 20th	Day	2 3 1 2 2 2 3 3 6% 7% 67%	1850
	21st to end	Day	2 4 1 4 2 2 3 3 4 8% 68%	1570
March	1st to 10th	Day	1 3 3 4 3 4 4 4 6% 8% 61%	3138
	11th to 20th	Day	1 3 1 3 2 2 3 3 5% 8% 68%	3258
	21st to end	Day	2 4 1 3 3 3 4 3 6% 8% 63%	4165
April	1st to 10th	Day	1 4 1 2 3 3 3 3 5% 7% 69%	2280
	11th to 20th	Day	2 2 1 2 3 2 3 2 4 6% 72%	2249
	21st to end	Day	1 2 3 2 2 3 3 5% 8% 72%	2280
May	1st to 10th	Day	1 2 1 2 2 2 3 2 4 5% 77%	4103
	11th to 20th	Day	1 2 1 2 3 2 3 3 4 6% 73%	4071
	21st to end	Day	2 2 1 3 2 2 3 2 4 5% 74%	4597
June	1st to 10th	Day	2 2 1 3 3 4 3 3 5% 7% 67%	2660
	11th to 20th	Day	1 1 1 2 2 2 2 3 4 4 78%	2660
	21st to end	Day	1 1 2 2 2 2 2 3 4 80%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 3 3 85%	4420
	11th to 20th	Day	1 2 2 2 2 3 3 4 5% 75%	4420
	21st to end	Day	1 2 1 2 2 2 3 3 5% 6% 73%	4705
August	1st to 10th	Day	2 2 1 2 2 2 2 2 3 3 81%	3800
	11th to 20th	Day	1 1 1 1 1 1 2 3 87%	3724
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	4180
September	1st to 10th	Day	1 1 1 2 2 2 2 2 3 5% 80%	2280
	11th to 20th	Day	1 1 1 2 1 1 2 2 3 5% 82%	2148
	21st to end	Day	1 1 1 1 1 2 2 3 3 85%	2090
October	1st to 10th	Day	1 1 1 1 1 2 2 3 6% 81%	3490
	11th to 20th	Day	1 1 1 1 2 2 2 3 4 84%	3196
	21st to end	Day	1 1 1 2 1 2 1 3 5% 82%	3232
November	1st to 10th	Day	2 1 2 2 2 3 2 3 7% 76%	1710
	11th to 20th	Day	1 1 1 1 1 1 3 2 4 7% 80%	1710
	21st to end	Day	2 2 2 2 2 3 3 6% 5% 73%	1710
December	1st to 10th	Day	2 3 3 1 1 3 3 4 8% 71%	1710
	11th to 20th	Day	3 6% 2 5% 3 3 4 4 5% 9% 55%	1947
	21st to end	Day	2 5% 2 6% 3 3 3 3 6% 9% 57%	2794
January	1st to 10th	Night	1 4 1 4 2 2 2 3 5% 6% 69%	4406
	11th to 20th	Night	3 1 4 3 3 3 3 5% 9% 65%	4420
	21st to end	Night	3 7% 2 3 2 3 3 4 6% 9% 58%	4498
February	1st to 10th	Night	2 4 1 3 2 2 3 3 4 7% 69%	2280
	11th to 20th	Night	1 3 1 3 2 2 3 3 4 6% 71%	2218
	21st to end	Night	1 4 1 4 2 3 2 2 4 8% 69%	1884
March	1st to 10th	Night	1 2 1 4 4 4 4 3 5% 7% 65%	3736
	11th to 20th	Night	1 3 1 4 3 3 4 4 5% 7% 65%	3719
	21st to end	Night	1 4 1 4 3 3 4 3 6% 6% 65%	3488
April	1st to 10th	Night	2 3 1 3 2 3 3 3 5% 6% 70%	1900
	11th to 20th	Night	1 2 1 2 2 3 2 2 5% 5% 76%	1879
	21st to end	Night	1 3 1 2 2 2 3 3 4 6% 73%	1900
May	1st to 10th	Night	2 2 1 2 2 2 2 2 4 5% 77%	2865
	11th to 20th	Night	3 3 1 3 3 3 3 2 5% 7% 67%	2834
	21st to end	Night	2 3 1 3 2 2 3 2 4 6% 73%	2967
June	1st to 10th	Night	2 3 1 2 3 2 3 4 5% 6% 71%	1520
	11th to 20th	Night	1 1 1 2 2 2 2 4 5% 80%	1520
	21st to end	Night	1 2 2 2 1 2 2 3 4 82%	1520
July	1st to 10th	Night	1 1 2 1 2 3 4 84%	2540
	11th to 20th	Night	2 2 1 3 3 4 4 3 5% 6% 67%	2540
	21st to end	Night	2 2 1 2 2 2 3 2 4 6% 73%	2844
August	1st to 10th	Night	1 2 1 3 2 2 2 3 4 5% 76%	3131
	11th to 20th	Night	1 1 1 1 1 1 2 3 88%	3126
	21st to end	Night	1 1 1 1 1 1 1 2 3 87%	3498
September	1st to 10th	Night	1 1 1 1 2 1 2 3 3 84%	1900
	11th to 20th	Night	1 2 1 2 1 1 2 2 3 3 82%	2030
	21st to end	Night	1 1 1 1 1 1 1 2 4 85%	2090
October	1st to 10th	Night	1 1 1 2 1 2 2 2 3 5% 79%	3490
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 4 86%	3738
	21st to end	Night	1 2 2 2 2 2 3 3 82%	4327
November	1st to 10th	Night	1 1 1 1 1 2 2 3 5% 82%	2469
	11th to 20th	Night	1 2 1 2 1 1 2 2 3 6% 79%	2470
	21st to end	Night	2 2 1 2 2 2 3 2 4 6% 74%	2470
December	1st to 10th	Night	2 3 1 2 2 2 3 3 5% 8% 69%	2470
	11th to 20th	Night	2 9% 1 3 3 2 4 3 6% 11% 57%	3252
	21st to end	Night	2 4 2 4 3 4 4 4 7% 10% 56%	4862

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	12% 2 14% 38% 28% 5%	2539
	11th to 20th	Day	17% 2 22% 29% 23% 7%	2540
	21st to end	Day	20% 2 16% 32% 24% 6%	3161
February	1st to 10th	Day	15% 3 11% 28% 30% 13%	1900
	11th to 20th	Day	13% 3 9% 27% 37% 11%	1860
	21st to end	Day	15% 3 8% 32% 30% 11%	1570
March	1st to 10th	Day	18% 2 5% 31% 30% 14%	3138
	11th to 20th	Day	17% 2 8% 34% 27% 12%	3258
	21st to end	Day	19% 3 7% 28% 31% 12%	4165
April	1st to 10th	Day	14% 3 8% 29% 29% 18%	2280
	11th to 20th	Day	13% 2 7% 21% 35% 23%	2252
	21st to end	Day	11% 2 7% 26% 38% 17%	2280
May	1st to 10th	Day	10% 2 3 17% 42% 26%	4103
	11th to 20th	Day	11% 1 3 14% 39% 32%	4074
	21st to end	Day	12% 2 3 15% 39% 29%	4597
June	1st to 10th	Day	14% 2 5% 15% 31% 33%	2660
	11th to 20th	Day	10% 2 2 8% 27% 51%	2660
	21st to end	Day	9% 1 1 5% 20% 63%	2660
July	1st to 10th	Day	7% 1 2 4 8% 79%	4351
	11th to 20th	Day	11% 3 2 6% 15% 64%	4345
	21st to end	Day	12% 2 3 13% 21% 50%	4556
August	1st to 10th	Day	10% 1 2 6% 23% 57%	3786
	11th to 20th	Day	5% 1 2 4 13% 77%	3760
	21st to end	Day	5% 1 1 4 20% 69%	4179
September	1st to 10th	Day	9% 2 2 8% 19% 60%	2280
	11th to 20th	Day	7% 1 2 11% 31% 48%	2148
	21st to end	Day	5% 1 1 10% 35% 47%	2090
October	1st to 10th	Day	6% 1 2 10% 30% 50%	3490
	11th to 20th	Day	7% 1 1 10% 36% 45%	3196
	21st to end	Day	6% 2 2 16% 46% 28%	3232
November	1st to 10th	Day	11% 2 6% 23% 38% 20%	1710
	11th to 20th	Day	7% 1 8% 27% 40% 17%	1710
	21st to end	Day	11% 2 8% 27% 32% 19%	1710
December	1st to 10th	Day	12% 3 13% 30% 28% 14%	1710
	11th to 20th	Day	24% 4 11% 27% 26% 8%	1947
	21st to end	Day	23% 3 16% 30% 21% 7%	2794
January	1st to 10th	Night	17% 2 13% 33% 29% 5%	4406
	11th to 20th	Night	17% 2 17% 37% 19% 7%	4420
	21st to end	Night	23% 2 17% 31% 21% 6%	4498
February	1st to 10th	Night	16% 3 11% 29% 26% 15%	2280
	11th to 20th	Night	15% 2 9% 27% 33% 14%	2219
	21st to end	Night	16% 3 9% 30% 32% 11%	1884
March	1st to 10th	Night	16% 2 6% 30% 36% 10%	3736
	11th to 20th	Night	21% 2 10% 29% 28% 9%	3719
	21st to end	Night	16% 3 6% 35% 32% 7%	3488
April	1st to 10th	Night	16% 2 8% 31% 29% 15%	1900
	11th to 20th	Night	11% 2 7% 26% 35% 19%	1879
	21st to end	Night	12% 3 6% 27% 37% 15%	1900
May	1st to 10th	Night	12% 2 3 19% 43% 22%	2865
	11th to 20th	Night	15% 3 3 16% 39% 24%	2835
	21st to end	Night	12% 2 4 15% 43% 23%	2967
June	1st to 10th	Night	13% 2 5% 15% 31% 33%	1520
	11th to 20th	Night	8% 2 2 13% 28% 47%	1520
	21st to end	Night	8% 2 2 5% 24% 60%	1520
July	1st to 10th	Night	5% 2 2 5% 9% 77%	2500
	11th to 20th	Night	15% 4 3 7% 16% 55%	2492
	21st to end	Night	12% 2 5% 13% 19% 49%	2755
August	1st to 10th	Night	11% 2 2 7% 30% 48%	3122
	11th to 20th	Night	5% 1 2 5% 14% 73%	3156
	21st to end	Night	5% 1 1 6% 20% 67%	3498
September	1st to 10th	Night	8% 1 1 9% 26% 56%	1900
	11th to 20th	Night	9% 2 2 11% 30% 47%	2030
	21st to end	Night	6% 2 2 9% 32% 49%	2090
October	1st to 10th	Night	8% 1 3 10% 29% 48%	3490
	11th to 20th	Night	6% 1 1 10% 35% 47%	3738
	21st to end	Night	8% 1 3 13% 43% 31%	4327
November	1st to 10th	Night	7% 2 7% 26% 38% 21%	2469
	11th to 20th	Night	9% 1 9% 25% 37% 18%	2470
	21st to end	Night	12% 2 8% 23% 37% 17%	2470
December	1st to 10th	Night	14% 4 10% 31% 28% 14%	2470
	11th to 20th	Night	21% 4 14% 30% 24% 7%	3252
	21st to end	Night	22% 3 15% 32% 22% 6%	4862

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	7% 6% 34% 33% 18% 2	180
	11th to 20th	Day	1 11% 28% 34% 19% 8%	180
	21st to end	Day	6% 10% 29% 25% 23% 6%	407
February	1st to 10th	Day	6% 14% 30% 29% 15% 5%	460
	11th to 20th	Day	6% 13% 33% 33% 12% 2	455
	21st to end	Day	4 15% 37% 30% 12% 2	382
March	1st to 10th	Day	5% 15% 40% 28% 11% 2	460
	11th to 20th	Day	7% 17% 31% 28% 15% 2	460
	21st to end	Day	8% 21% 36% 26% 8% 2	506
April	1st to 10th	Day	8% 19% 26% 28% 16% 4	460
	11th to 20th	Day	8% 23% 28% 28% 12% 2	452
	21st to end	Day	6% 17% 35% 24% 13% 5%	460
May	1st to 10th	Day	7% 19% 36% 22% 14% 2	463
	11th to 20th	Day	7% 14% 27% 30% 16% 5%	488
	21st to end	Day	6% 13% 25% 32% 19% 5%	529
June	1st to 10th	Day	5% 11% 26% 28% 23% 6%	490
	11th to 20th	Day	4 12% 32% 29% 19% 5%	490
	21st to end	Day	1 9% 30% 32% 24% 4	490
July	1st to 10th	Day	2 8% 24% 36% 23% 6%	486
	11th to 20th	Day	3 5% 19% 39% 24% 11%	484
	21st to end	Day	4 4 25% 35% 24% 9%	531
August	1st to 10th	Day	3 8% 30% 36% 17% 6%	487
	11th to 20th	Day	2 11% 24% 29% 24% 10%	477
	21st to end	Day	1 7% 26% 32% 24% 8%	539
September	1st to 10th	Day	2 10% 22% 35% 22% 9%	490
	11th to 20th	Day	2 11% 30% 32% 21% 3	490
	21st to end	Day	2 9% 27% 36% 23% 3	490
October	1st to 10th	Day	3 11% 27% 31% 23% 6%	490
	11th to 20th	Day	4 10% 25% 34% 22% 5%	490
	21st to end	Day	2 10% 27% 34% 19% 8%	411
November	1st to 10th	Day	3 7% 21% 35% 29% 5%	282
	11th to 20th	Day	1 8% 24% 35% 21% 11%	270
	21st to end	Day	3 7% 24% 31% 28% 6%	270
December	1st to 10th	Day	3 7% 29% 36% 20% 6%	270
	11th to 20th	Day	3 8% 28% 32% 21% 8%	189
	21st to end	Day	4 14% 30% 26% 24% 3	198
January	1st to 10th	Night	4 6% 24% 37% 22% 6%	760
	11th to 20th	Night	2 4 31% 41% 17% 6%	760
	21st to end	Night	6% 6% 28% 35% 20% 5%	836
February	1st to 10th	Night	4 8% 27% 38% 19% 4	760
	11th to 20th	Night	3 7% 28% 39% 21% 2	744
	21st to end	Night	4 6% 34% 41% 13% 2	628
March	1st to 10th	Night	2 6% 32% 44% 13% 3	760
	11th to 20th	Night	2 7% 28% 37% 22% 3	760
	21st to end	Night	4 11% 31% 39% 14% 2	836
April	1st to 10th	Night	3 9% 30% 39% 18% 2	760
	11th to 20th	Night	3 12% 31% 36% 15% 3	751
	21st to end	Night	2 7% 32% 36% 20% 3	760
May	1st to 10th	Night	3 10% 32% 39% 13% 2	575
	11th to 20th	Night	3 7% 28% 38% 22% 1	561
	21st to end	Night	5% 9% 25% 36% 23% 1	539
June	1st to 10th	Night	1 5% 21% 45% 26% 2	380
	11th to 20th	Night	1 5% 22% 47% 25% 1	380
	21st to end	Night	1 2 16% 54% 25% 2	380
July	1st to 10th	Night	1 8% 54% 35% 2	370
	11th to 20th	Night	2 1 7% 50% 36% 4	368
	21st to end	Night	4 1 9% 44% 40% 2	463
August	1st to 10th	Night	2 2 16% 48% 30% 3	734
	11th to 20th	Night	1 1 15% 42% 38% 3	752
	21st to end	Night	2 1 11% 44% 39% 4	836
September	1st to 10th	Night	1 1 13% 43% 37% 4	760
	11th to 20th	Night	2 3 13% 45% 33% 4	760
	21st to end	Night	1 3 17% 38% 38% 5%	760
October	1st to 10th	Night	2 3 20% 40% 29% 5%	760
	11th to 20th	Night	3 4 17% 42% 28% 6%	760
	21st to end	Night	1 6% 20% 33% 31% 8%	836
November	1st to 10th	Night	2 3 20% 38% 29% 8%	760
	11th to 20th	Night	1 4 21% 43% 24% 6%	760
	21st to end	Night	3 4 24% 38% 27% 5%	760
December	1st to 10th	Night	4 5% 26% 43% 19% 4	760
	11th to 20th	Night	4 4 28% 42% 18% 4	760
	21st to end	Night	4 6% 31% 39% 19% 2	836

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