DarkSights Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DarkSights Observatory clear sky chart from 2005-11-06 to 2024-11-28.

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	6% 5% 2 5% 3 3 3 3 4 6% 60%	105262
	Night	8% 7% 3 7% 4 4 4 3 4 6% 50%	103021
Transparency	Day	23% 5% 8% 18% 24% 22%	105019
	Night	29% 6% 9% 17% 20% 18%	102853
Seeing	Day	9% 11% 27% 32% 17% 4	15456
	Night	10% 5% 15% 36% 28% 6%	24799

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	16% 10% 3 6% 4 4 4 4 6% 6% 36%	2671
	11th to 20th	Day	15% 10% 5% 10% 6% 5% 4 3 4 5% 33%	2860
	21st to end	Day	21% 10% 3 8% 5% 4 4 4 6% 6% 28%	3146
February	1st to 10th	Day	16% 8% 2 6% 4 3 3 3 6% 6% 44%	1710
	11th to 20th	Day	12% 8% 3 6% 4 5% 4 3 5% 7% 42%	1759
	21st to end	Day	13% 7% 2 6% 4 3 3 3 4 6% 47%	1570
March	1st to 10th	Day	12% 11% 5% 12% 6% 5% 6% 4 6% 6% 27%	3367
	11th to 20th	Day	9% 6% 2 5% 4 4 3 3 5% 6% 54%	3490
	21st to end	Day	11% 8% 3 7% 6% 6% 6% 5% 7% 7% 34%	3903
April	1st to 10th	Day	12% 8% 2 5% 5% 4 4 3 5% 7% 44%	2280
	11th to 20th	Day	9% 6% 2 5% 3 3 4 3 4 6% 55%	2249
	21st to end	Day	4 5% 1 4 3 3 3 3 5% 9% 58%	2280
May	1st to 10th	Day	5% 3 1 3 2 2 2 2 3 6% 71%	3909
	11th to 20th	Day	3 2 2 3 2 2 2 2 3 6% 73%	4192
	21st to end	Day	2 4 3 5% 3 2 3 2 3 6% 68%	4813
June	1st to 10th	Day	3 5% 2 4 3 3 3 3 6% 7% 61%	2660
	11th to 20th	Day	1 2 1 2 2 2 2 2 5% 6% 74%	2660
	21st to end	Day	2 2 1 3 2 2 2 2 3 5% 74%	2660
July	1st to 10th	Day	1 1 2 2 2 2 1 2 4 83%	4420
	11th to 20th	Day	1 2 1 3 2 2 3 2 4 6% 75%	4178
	21st to end	Day	2 1 3 2 1 2 2 4 5% 77%	4455
August	1st to 10th	Day	1 2 1 3 3 3 4 3 5% 8% 66%	4091
	11th to 20th	Day	1 1 3 2 2 3 2 3 5% 78%	3816
	21st to end	Day	1 2 1 4 3 3 2 2 4 5% 74%	4180
September	1st to 10th	Day	1 2 1 3 1 2 1 2 3 4 79%	2280
	11th to 20th	Day	2 4 2 5% 3 3 3 3 4 6% 65%	2280
	21st to end	Day	2 2 1 3 2 2 2 2 4 6% 75%	2023
October	1st to 10th	Day	2 2 1 3 2 2 2 2 4 7% 73%	3180
	11th to 20th	Day	3 3 3 5% 3 3 3 2 4 6% 67%	3161
	21st to end	Day	4 4 2 4 3 3 4 3 5% 7% 60%	3448
November	1st to 10th	Day	7% 4 2 5% 2 3 4 4 5% 9% 55%	1903
	11th to 20th	Day	8% 8% 2 7% 5% 4 4 3 4 7% 50%	1800
	21st to end	Day	12% 6% 2 5% 2 3 3 3 5% 7% 52%	1626
December	1st to 10th	Day	12% 8% 3 6% 4 4 4 4 5% 6% 45%	1520
	11th to 20th	Day	22% 11% 3 8% 4 5% 3 3 5% 5% 30%	1928
	21st to end	Day	16% 11% 4 7% 5% 4 5% 4 5% 7% 34%	2794
January	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 6% 44%	4274
	11th to 20th	Night	16% 11% 4 8% 6% 5% 5% 3 5% 6% 31%	4110
	21st to end	Night	20% 15% 4 7% 4 4 4 3 3 5% 31%	4521
February	1st to 10th	Night	15% 8% 2 4 3 3 3 3 5% 5% 49%	2470
	11th to 20th	Night	11% 7% 3 7% 5% 4 4 4 4 8% 44%	2307
	21st to end	Night	11% 8% 2 5% 4 3 3 3 4 7% 51%	1884
March	1st to 10th	Night	15% 13% 5% 9% 5% 5% 4 4 4 5% 32%	3504
	11th to 20th	Night	10% 7% 3 8% 4 4 3 3 4 5% 50%	3490
	21st to end	Night	13% 14% 4 8% 4 4 4 4 4 6% 34%	3750
April	1st to 10th	Night	9% 8% 3 5% 5% 3 4 3 6% 7% 46%	1900
	11th to 20th	Night	8% 7% 3 6% 3 3 3 3 5% 6% 53%	1879
	21st to end	Night	5% 4 2 4 4 4 3 4 6% 9% 57%	1900
May	1st to 10th	Night	4 6% 2 5% 3 2 2 2 4 5% 65%	3064
	11th to 20th	Night	2 4 2 8% 7% 5% 5% 3 4 6% 55%	2689
	21st to end	Night	2 6% 4 9% 4 3 3 2 3 5% 59%	2762
June	1st to 10th	Night	5% 6% 2 5% 3 3 3 3 6% 7% 56%	1520
	11th to 20th	Night	1 3 1 5% 4 2 2 3 3 6% 68%	1520
	21st to end	Night	2 4 3 6% 4 3 3 2 3 5% 66%	1520
July	1st to 10th	Night	2 1 4 3 3 2 2 3 4 75%	2540
	11th to 20th	Night	1 2 1 9% 6% 4 4 2 4 6% 60%	2786
	21st to end	Night	1 6% 6% 14% 6% 4 3 3 6% 6% 47%	3109
August	1st to 10th	Night	3 4 3 9% 9% 10% 7% 6% 5% 7% 38%	2848
	11th to 20th	Night	3 3 9% 6% 4 3 2 4 5% 61%	3029
	21st to end	Night	2 6% 2 9% 5% 4 3 2 3 5% 58%	3498
September	1st to 10th	Night	4 2 6% 4 3 2 2 3 6% 68%	1900
	11th to 20th	Night	3 7% 3 9% 5% 3 3 2 5% 7% 54%	1900
	21st to end	Night	2 3 1 5% 4 2 3 2 3 6% 69%	2153
October	1st to 10th	Night	2 3 1 4 3 2 2 2 4 6% 71%	3800
	11th to 20th	Night	3 7% 6% 9% 5% 3 3 2 3 5% 54%	3777
	21st to end	Night	5% 5% 1 5% 3 3 4 3 5% 6% 59%	4121
November	1st to 10th	Night	7% 6% 2 4 3 3 4 3 6% 8% 55%	2395
	11th to 20th	Night	9% 6% 3 5% 4 3 3 3 5% 9% 50%	2600
	21st to end	Night	10% 5% 2 5% 3 3 3 3 5% 7% 54%	2703
December	1st to 10th	Night	12% 8% 2 7% 4 4 4 3 3 6% 48%	2660
	11th to 20th	Night	23% 13% 3 6% 3 2 4 3 6% 6% 31%	3276
	21st to end	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	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	42% 10% 13% 25% 8% 3	2671
	11th to 20th	Day	50% 8% 10% 14% 11% 6%	2860
	21st to end	Day	51% 10% 10% 13% 13% 4	3146
February	1st to 10th	Day	39% 6% 8% 19% 19% 8%	1710
	11th to 20th	Day	39% 7% 9% 18% 20% 7%	1768
	21st to end	Day	36% 7% 9% 23% 19% 6%	1570
March	1st to 10th	Day	49% 13% 9% 12% 14% 2	3367
	11th to 20th	Day	29% 6% 13% 26% 15% 11%	3490
	21st to end	Day	38% 16% 16% 17% 11% 2	3903
April	1st to 10th	Day	36% 8% 14% 20% 19% 4	2280
	11th to 20th	Day	29% 6% 14% 24% 22% 6%	2252
	21st to end	Day	21% 6% 14% 28% 26% 5%	2280
May	1st to 10th	Day	15% 4 11% 30% 25% 15%	3909
	11th to 20th	Day	11% 3 8% 23% 41% 15%	4195
	21st to end	Day	13% 5% 13% 30% 33% 6%	4814
June	1st to 10th	Day	21% 5% 11% 24% 27% 11%	2660
	11th to 20th	Day	10% 4 8% 21% 36% 21%	2660
	21st to end	Day	12% 2 4 13% 29% 40%	2660
July	1st to 10th	Day	6% 1 2 6% 13% 71%	4351
	11th to 20th	Day	10% 2 3 8% 14% 63%	4106
	21st to end	Day	8% 1 2 7% 27% 55%	4315
August	1st to 10th	Day	13% 2 2 9% 26% 47%	4076
	11th to 20th	Day	7% 1 3 11% 39% 40%	3854
	21st to end	Day	11% 2 5% 11% 33% 38%	4179
September	1st to 10th	Day	9% 1 4 10% 30% 46%	2280
	11th to 20th	Day	17% 3 8% 21% 32% 19%	2280
	21st to end	Day	10% 2 7% 22% 34% 25%	2023
October	1st to 10th	Day	13% 2 5% 11% 28% 42%	3180
	11th to 20th	Day	18% 4 8% 21% 28% 21%	3161
	21st to end	Day	20% 4 7% 20% 33% 15%	3448
November	1st to 10th	Day	26% 6% 11% 24% 22% 12%	1903
	11th to 20th	Day	32% 7% 10% 23% 22% 6%	1800
	21st to end	Day	31% 5% 11% 17% 26% 9%	1626
December	1st to 10th	Day	36% 8% 12% 19% 17% 9%	1520
	11th to 20th	Day	53% 7% 10% 13% 13% 5%	1928
	21st to end	Day	46% 10% 13% 18% 11% 3	2794
January	1st to 10th	Night	38% 11% 16% 22% 10% 3	4274
	11th to 20th	Night	50% 11% 12% 11% 9% 7%	4110
	21st to end	Night	53% 9% 9% 12% 12% 6%	4521
February	1st to 10th	Night	37% 5% 9% 19% 19% 11%	2470
	11th to 20th	Night	37% 6% 10% 18% 20% 8%	2309
	21st to end	Night	32% 7% 12% 26% 18% 4	1884
March	1st to 10th	Night	46% 15% 11% 12% 14% 3	3504
	11th to 20th	Night	30% 6% 12% 24% 17% 11%	3490
	21st to end	Night	40% 15% 16% 16% 10% 4	3750
April	1st to 10th	Night	33% 8% 15% 20% 18% 6%	1900
	11th to 20th	Night	29% 7% 12% 25% 19% 9%	1879
	21st to end	Night	21% 6% 13% 29% 25% 6%	1900
May	1st to 10th	Night	17% 8% 12% 22% 26% 14%	3064
	11th to 20th	Night	14% 3 14% 19% 32% 19%	2689
	21st to end	Night	14% 5% 15% 29% 30% 7%	2762
June	1st to 10th	Night	22% 5% 10% 23% 27% 13%	1520
	11th to 20th	Night	13% 3 8% 17% 33% 26%	1520
	21st to end	Night	11% 4 5% 15% 30% 36%	1520
July	1st to 10th	Night	7% 1 2 8% 14% 68%	2500
	11th to 20th	Night	15% 2 3 9% 19% 53%	2735
	21st to end	Night	25% 2 3 10% 25% 36%	3011
August	1st to 10th	Night	29% 3 2 12% 26% 28%	2839
	11th to 20th	Night	12% 1 4 11% 39% 32%	3057
	21st to end	Night	23% 2 4 11% 29% 31%	3498
September	1st to 10th	Night	14% 2 4 9% 24% 46%	1900
	11th to 20th	Night	22% 2 7% 22% 28% 20%	1900
	21st to end	Night	12% 2 7% 19% 31% 28%	2153
October	1st to 10th	Night	13% 3 6% 11% 21% 46%	3800
	11th to 20th	Night	28% 3 8% 19% 21% 22%	3777
	21st to end	Night	23% 3 6% 21% 27% 20%	4121
November	1st to 10th	Night	26% 6% 11% 25% 18% 15%	2395
	11th to 20th	Night	30% 6% 12% 23% 22% 8%	2600
	21st to end	Night	30% 5% 11% 19% 23% 12%	2703
December	1st to 10th	Night	36% 6% 12% 17% 16% 12%	2660
	11th to 20th	Night	52% 6% 11% 13% 15% 4	3276
	21st to end	Night	46% 12% 13% 14% 11% 4	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	24% 14% 28% 20% 13% 1	260
	11th to 20th	Day	19% 10% 24% 30% 16% 2	370
	21st to end	Day	20% 7% 24% 31% 16% 3	407
February	1st to 10th	Day	19% 13% 21% 28% 16% 2	370
	11th to 20th	Day	20% 17% 26% 23% 12% 1	410
	21st to end	Day	14% 15% 30% 29% 11% 1	382
March	1st to 10th	Day	22% 19% 28% 20% 10% 2	460
	11th to 20th	Day	21% 18% 23% 22% 14% 3	460
	21st to end	Day	16% 20% 34% 21% 9% 1	506
April	1st to 10th	Day	17% 18% 30% 21% 11% 3	460
	11th to 20th	Day	14% 20% 30% 23% 9% 4	452
	21st to end	Day	8% 20% 29% 27% 10% 5%	460
May	1st to 10th	Day	10% 17% 33% 27% 12% 1	463
	11th to 20th	Day	9% 13% 33% 31% 12% 2	488
	21st to end	Day	8% 14% 29% 32% 14% 3	529
June	1st to 10th	Day	6% 12% 33% 32% 13% 3	490
	11th to 20th	Day	2 13% 32% 39% 12% 2	490
	21st to end	Day	2 8% 31% 39% 17% 3	490
July	1st to 10th	Day	2 5% 27% 44% 18% 3	486
	11th to 20th	Day	2 25% 48% 21% 3	484
	21st to end	Day	2 2 26% 45% 20% 6%	531
August	1st to 10th	Day	3 7% 27% 42% 17% 4	487
	11th to 20th	Day	1 4 29% 39% 19% 7%	477
	21st to end	Day	1 3 23% 43% 22% 6%	539
September	1st to 10th	Day	3 3 21% 42% 23% 8%	490
	11th to 20th	Day	5% 11% 25% 36% 17% 6%	490
	21st to end	Day	3 8% 24% 33% 25% 7%	490
October	1st to 10th	Day	4 8% 27% 31% 22% 8%	490
	11th to 20th	Day	7% 10% 21% 31% 24% 8%	490
	21st to end	Day	6% 11% 24% 30% 23% 5%	539
November	1st to 10th	Day	9% 11% 22% 25% 27% 6%	439
	11th to 20th	Day	7% 12% 16% 35% 22% 7%	300
	21st to end	Day	16% 8% 26% 27% 23% 1	219
December	1st to 10th	Day	16% 14% 22% 22% 21% 4	180
	11th to 20th	Day	17% 13% 23% 22% 22% 3	180
	21st to end	Day	23% 10% 29% 21% 15% 2	198
January	1st to 10th	Night	19% 7% 13% 33% 22% 7%	760
	11th to 20th	Night	16% 5% 14% 34% 25% 5%	760
	21st to end	Night	19% 5% 14% 36% 23% 5%	836
February	1st to 10th	Night	19% 7% 13% 35% 23% 4	760
	11th to 20th	Night	13% 8% 18% 35% 20% 6%	744
	21st to end	Night	14% 10% 17% 37% 20% 3	628
March	1st to 10th	Night	19% 10% 17% 31% 21% 3	760
	11th to 20th	Night	17% 9% 15% 33% 22% 4	760
	21st to end	Night	15% 10% 21% 36% 17% 2	836
April	1st to 10th	Night	12% 8% 20% 37% 20% 2	760
	11th to 20th	Night	11% 10% 22% 32% 20% 4	751
	21st to end	Night	7% 7% 22% 37% 22% 5%	760
May	1st to 10th	Night	7% 6% 20% 40% 23% 4	696
	11th to 20th	Night	8% 3 13% 42% 29% 4	482
	21st to end	Night	8% 8% 20% 38% 24% 3	411
June	1st to 10th	Night	6% 4 17% 44% 26% 2	380
	11th to 20th	Night	2 3 16% 53% 24% 2	380
	21st to end	Night	3 4 13% 41% 37% 2	380
July	1st to 10th	Night	2 3 10% 41% 41% 3	370
	11th to 20th	Night	2 9% 41% 39% 9%	507
	21st to end	Night	2 1 10% 35% 42% 9%	624
August	1st to 10th	Night	4 4 14% 34% 36% 8%	567
	11th to 20th	Night	2 2 12% 40% 37% 7%	691
	21st to end	Night	2 1 11% 40% 39% 7%	836
September	1st to 10th	Night	2 2 9% 36% 41% 10%	760
	11th to 20th	Night	5% 5% 13% 36% 35% 6%	760
	21st to end	Night	3 3 11% 32% 40% 11%	760
October	1st to 10th	Night	5% 3 10% 38% 35% 9%	760
	11th to 20th	Night	8% 4 11% 33% 36% 8%	760
	21st to end	Night	7% 5% 11% 34% 32% 12%	836
November	1st to 10th	Night	8% 4 15% 31% 32% 9%	780
	11th to 20th	Night	13% 3 12% 36% 29% 7%	800
	21st to end	Night	14% 4 14% 35% 26% 6%	788
December	1st to 10th	Night	16% 6% 13% 34% 25% 5%	760
	11th to 20th	Night	22% 6% 13% 34% 21% 4	760
	21st to end	Night	19% 9% 20% 31% 19% 2	836

Page generated at 2024-11-24 21:22:21. Version ac07

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