Heaven's Gate
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heaven's Gate clear sky chart from 2005-11-06 to 2025-05-11.

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% 10% 4 9% 5% 5% 5% 4 5% 6% 41%	117141
	Night	6% 11% 4 9% 6% 5% 5% 4 5% 6% 39%	120562
Transparency	Day	42% 8% 9% 19% 15% 7%	116885
	Night	44% 8% 10% 20% 13% 5%	120407
Seeing	Day	18% 22% 32% 20% 7% 1	14915
	Night	17% 14% 29% 28% 11% 1	24540

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	4 15% 9% 18% 9% 7% 6% 5% 5% 5% 17%	3639
	11th to 20th	Day	4 13% 7% 18% 6% 4 4 3 4 6% 30%	3640
	21st to end	Day	4 12% 4 10% 7% 6% 6% 4 5% 5% 36%	4004
February	1st to 10th	Day	8% 20% 6% 14% 7% 4 5% 3 6% 6% 21%	1655
	11th to 20th	Day	5% 19% 8% 15% 8% 5% 5% 4 5% 5% 21%	1950
	21st to end	Day	5% 19% 8% 18% 8% 6% 5% 4 5% 4 18%	1650
March	1st to 10th	Day	4 13% 5% 14% 7% 7% 6% 5% 6% 7% 26%	4518
	11th to 20th	Day	3 14% 7% 14% 8% 6% 6% 3 4 4 32%	4774
	21st to end	Day	5% 19% 6% 15% 8% 7% 8% 5% 6% 6% 14%	5790
April	1st to 10th	Day	10% 19% 6% 11% 6% 6% 5% 4 6% 5% 22%	2400
	11th to 20th	Day	10% 17% 5% 10% 6% 5% 4 3 5% 6% 30%	2432
	21st to end	Day	15% 18% 4 8% 7% 4 4 3 5% 6% 26%	2600
May	1st to 10th	Day	8% 19% 4 8% 5% 5% 4 3 5% 5% 34%	4240
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 6% 7% 47%	4370
	21st to end	Day	14% 13% 4 8% 5% 5% 5% 4 5% 7% 31%	4813
June	1st to 10th	Day	16% 11% 3 8% 6% 4 5% 4 6% 8% 29%	2660
	11th to 20th	Day	15% 9% 3 7% 6% 5% 4 4 5% 5% 37%	2660
	21st to end	Day	7% 3 2 5% 3 3 4 3 5% 7% 58%	2660
July	1st to 10th	Day	2 2 3 2 3 3 3 4 5% 73%	4420
	11th to 20th	Day	1 2 1 2 2 2 3 3 4 5% 75%	4420
	21st to end	Day	2 2 1 2 3 2 3 3 5% 6% 73%	4790
August	1st to 10th	Day	3 2 1 4 4 4 4 4 6% 8% 60%	4349
	11th to 20th	Day	2 2 1 3 3 3 4 3 5% 7% 65%	4028
	21st to end	Day	3 3 1 3 3 3 3 3 4 6% 68%	4247
September	1st to 10th	Day	5% 3 1 4 3 3 4 2 4 6% 65%	2280
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 5% 7% 52%	2128
	21st to end	Day	8% 6% 2 5% 3 4 4 4 5% 7% 52%	2090
October	1st to 10th	Day	8% 7% 2 5% 4 3 3 2 3 4 61%	3490
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 7% 47%	2954
	21st to end	Day	9% 13% 4 9% 6% 5% 5% 3 5% 6% 33%	3101
November	1st to 10th	Day	12% 16% 4 10% 6% 4 5% 3 5% 7% 28%	1764
	11th to 20th	Day	8% 15% 5% 11% 7% 7% 6% 5% 7% 7% 24%	1800
	21st to end	Day	6% 16% 6% 10% 6% 5% 5% 4 6% 6% 31%	1658
December	1st to 10th	Day	5% 10% 4 9% 6% 4 4 3 4 5% 45%	2356
	11th to 20th	Day	4 12% 5% 15% 8% 8% 8% 5% 8% 8% 17%	2807
	21st to end	Day	5% 13% 7% 14% 7% 6% 6% 4 6% 8% 24%	4004
January	1st to 10th	Night	6% 16% 8% 16% 8% 6% 5% 4 6% 7% 19%	6306
	11th to 20th	Night	6% 15% 8% 16% 7% 6% 5% 4 5% 5% 24%	6320
	21st to end	Night	3 11% 4 10% 7% 7% 5% 4 5% 5% 37%	6952
February	1st to 10th	Night	9% 19% 7% 14% 7% 5% 5% 4 5% 5% 20%	2742
	11th to 20th	Night	7% 19% 6% 12% 7% 6% 5% 4 5% 5% 24%	2338
	21st to end	Night	5% 16% 7% 15% 10% 7% 5% 4 5% 7% 20%	1980
March	1st to 10th	Night	4 12% 5% 11% 6% 5% 6% 5% 6% 7% 32%	5376
	11th to 20th	Night	4 12% 6% 12% 7% 6% 7% 4 5% 5% 33%	5225
	21st to end	Night	6% 15% 6% 13% 8% 6% 7% 5% 7% 8% 20%	5182
April	1st to 10th	Night	9% 17% 6% 10% 6% 5% 5% 4 6% 6% 27%	2000
	11th to 20th	Night	13% 13% 3 7% 5% 4 4 4 4 5% 36%	1915
	21st to end	Night	14% 12% 4 9% 5% 4 4 4 5% 7% 31%	1800
May	1st to 10th	Night	12% 13% 3 6% 5% 4 3 3 5% 6% 40%	2950
	11th to 20th	Night	7% 6% 2 5% 4 3 4 4 5% 7% 53%	2526
	21st to end	Night	17% 13% 3 6% 4 3 4 2 4 7% 38%	2762
June	1st to 10th	Night	16% 8% 2 6% 6% 5% 4 4 6% 7% 35%	1520
	11th to 20th	Night	16% 7% 2 4 3 4 4 3 5% 8% 44%	1520
	21st to end	Night	6% 4 2 4 3 3 5% 3 5% 8% 58%	1520
July	1st to 10th	Night	1 1 2 2 2 2 3 4 5% 79%	2540
	11th to 20th	Night	1 1 1 1 2 2 2 4 5% 81%	2540
	21st to end	Night	2 2 1 2 2 2 3 3 5% 7% 70%	2761
August	1st to 10th	Night	2 3 1 4 3 2 4 3 5% 9% 64%	2582
	11th to 20th	Night	1 1 2 2 3 3 3 6% 8% 71%	2811
	21st to end	Night	4 4 1 3 2 3 3 3 4 4 69%	3425
September	1st to 10th	Night	4 2 1 3 3 3 3 3 6% 7% 66%	1900
	11th to 20th	Night	6% 5% 2 4 3 4 4 4 6% 7% 55%	2052
	21st to end	Night	11% 5% 2 5% 3 3 3 2 5% 6% 55%	2090
October	1st to 10th	Night	7% 5% 2 4 4 3 3 2 4 4 62%	3490
	11th to 20th	Night	6% 9% 2 6% 4 4 5% 5% 5% 7% 47%	3974
	21st to end	Night	9% 12% 4 9% 7% 6% 5% 4 5% 7% 33%	4457
November	1st to 10th	Night	12% 13% 4 8% 5% 5% 6% 4 6% 6% 31%	2535
	11th to 20th	Night	11% 15% 4 10% 6% 5% 6% 4 6% 6% 27%	2600
	21st to end	Night	6% 15% 5% 11% 6% 5% 5% 3 6% 6% 32%	2740
December	1st to 10th	Night	5% 10% 3 8% 5% 4 4 3 5% 7% 47%	4783
	11th to 20th	Night	4 13% 5% 13% 8% 8% 7% 5% 7% 8% 21%	5396
	21st to end	Night	5% 15% 6% 14% 7% 7% 6% 4 5% 7% 24%	6952

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	65% 12% 10% 10% 3	3639
	11th to 20th	Day	56% 5% 10% 20% 7% 1	3640
	21st to end	Day	48% 9% 10% 13% 14% 5%	4004
February	1st to 10th	Day	64% 11% 11% 12% 2	1655
	11th to 20th	Day	66% 7% 10% 11% 5%	1960
	21st to end	Day	68% 8% 8% 9% 6% 1	1650
March	1st to 10th	Day	53% 12% 7% 16% 10% 3	4518
	11th to 20th	Day	50% 10% 8% 29% 3	4774
	21st to end	Day	63% 11% 10% 13% 2	5790
April	1st to 10th	Day	61% 9% 12% 15% 3	2400
	11th to 20th	Day	54% 7% 10% 18% 10% 1	2435
	21st to end	Day	58% 7% 10% 17% 8%	2600
May	1st to 10th	Day	48% 7% 8% 24% 12% 1	4240
	11th to 20th	Day	33% 7% 9% 35% 12% 4	4373
	21st to end	Day	49% 9% 13% 23% 5%	4814
June	1st to 10th	Day	51% 8% 12% 22% 7%	2660
	11th to 20th	Day	47% 6% 9% 20% 14% 3	2660
	21st to end	Day	26% 5% 8% 29% 27% 6%	2660
July	1st to 10th	Day	13% 4 5% 13% 26% 38%	4351
	11th to 20th	Day	11% 4 4 11% 25% 45%	4345
	21st to end	Day	12% 4 4 16% 40% 25%	4639
August	1st to 10th	Day	20% 6% 6% 17% 34% 18%	4333
	11th to 20th	Day	16% 5% 6% 23% 36% 14%	4067
	21st to end	Day	17% 5% 5% 27% 33% 12%	4246
September	1st to 10th	Day	21% 3 9% 23% 28% 16%	2280
	11th to 20th	Day	30% 6% 11% 22% 23% 9%	2128
	21st to end	Day	32% 4 10% 29% 20% 4	2090
October	1st to 10th	Day	29% 4 6% 26% 31% 5%	3490
	11th to 20th	Day	36% 6% 15% 27% 16% 1	2954
	21st to end	Day	48% 10% 7% 23% 11%	3101
November	1st to 10th	Day	55% 9% 13% 17% 5% 1	1764
	11th to 20th	Day	58% 10% 14% 14% 4	1800
	21st to end	Day	53% 8% 14% 16% 9% 1	1658
December	1st to 10th	Day	42% 10% 14% 21% 12% 1	2356
	11th to 20th	Day	60% 14% 13% 11% 2	2807
	21st to end	Day	55% 14% 14% 13% 4 1	4004
January	1st to 10th	Night	64% 9% 12% 12% 3 1	6306
	11th to 20th	Night	59% 6% 11% 18% 5% 1	6320
	21st to end	Night	47% 13% 8% 15% 12% 5%	6952
February	1st to 10th	Night	66% 9% 10% 12% 2 1	2742
	11th to 20th	Night	62% 7% 11% 13% 6% 1	2339
	21st to end	Night	65% 7% 8% 14% 5% 2	1980
March	1st to 10th	Night	46% 14% 8% 16% 10% 6%	5376
	11th to 20th	Night	48% 10% 9% 28% 6%	5225
	21st to end	Night	56% 11% 14% 16% 3	5182
April	1st to 10th	Night	55% 8% 14% 19% 5%	2000
	11th to 20th	Night	49% 6% 11% 21% 11% 2	1915
	21st to end	Night	52% 6% 12% 22% 9%	1800
May	1st to 10th	Night	43% 7% 9% 25% 14% 2	2950
	11th to 20th	Night	27% 6% 12% 37% 17%	2526
	21st to end	Night	45% 4 18% 27% 5%	2762
June	1st to 10th	Night	45% 9% 18% 22% 6%	1520
	11th to 20th	Night	38% 6% 14% 26% 13% 2	1520
	21st to end	Night	24% 5% 13% 30% 22% 5%	1520
July	1st to 10th	Night	9% 3 6% 16% 30% 36%	2500
	11th to 20th	Night	8% 3 5% 16% 26% 42%	2492
	21st to end	Night	13% 4 4 22% 38% 20%	2674
August	1st to 10th	Night	17% 6% 5% 20% 40% 13%	2574
	11th to 20th	Night	11% 5% 6% 27% 36% 14%	2838
	21st to end	Night	18% 5% 5% 29% 32% 11%	3425
September	1st to 10th	Night	18% 5% 9% 25% 29% 15%	1900
	11th to 20th	Night	27% 6% 10% 24% 23% 10%	2052
	21st to end	Night	30% 4 10% 28% 19% 8%	2090
October	1st to 10th	Night	27% 4 6% 22% 32% 8%	3490
	11th to 20th	Night	34% 7% 15% 22% 19% 3	3974
	21st to end	Night	48% 9% 8% 21% 14%	4457
November	1st to 10th	Night	52% 10% 10% 19% 7% 2	2535
	11th to 20th	Night	56% 10% 13% 17% 4	2600
	21st to end	Night	52% 7% 11% 18% 11% 1	2740
December	1st to 10th	Night	38% 9% 16% 24% 12% 1	4783
	11th to 20th	Night	59% 14% 10% 14% 2 1	5396
	21st to end	Night	57% 10% 14% 13% 5% 1	6952

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	25% 22% 38% 12% 4 1	200
	11th to 20th	Day	25% 26% 32% 8% 9% 1	200
	21st to end	Day	20% 23% 36% 18% 3	220
February	1st to 10th	Day	25% 33% 33% 8% 1	240
	11th to 20th	Day	21% 34% 30% 12% 3	495
	21st to end	Day	26% 29% 33% 11% 2	414
March	1st to 10th	Day	22% 36% 29% 11% 1	500
	11th to 20th	Day	21% 29% 30% 13% 5% 2	500
	21st to end	Day	28% 31% 26% 12% 3	550
April	1st to 10th	Day	24% 25% 29% 15% 6% 1	500
	11th to 20th	Day	26% 26% 27% 17% 4 1	492
	21st to end	Day	27% 26% 25% 16% 5% 1	500
May	1st to 10th	Day	19% 23% 32% 19% 6% 1	503
	11th to 20th	Day	28% 18% 27% 17% 7% 2	489
	21st to end	Day	25% 14% 26% 26% 7% 3	529
June	1st to 10th	Day	19% 18% 32% 23% 7% 2	490
	11th to 20th	Day	21% 26% 30% 17% 4 1	490
	21st to end	Day	8% 18% 37% 26% 8% 2	490
July	1st to 10th	Day	5% 16% 43% 26% 9% 2	486
	11th to 20th	Day	4 21% 38% 27% 8% 1	484
	21st to end	Day	3 16% 41% 27% 12% 2	531
August	1st to 10th	Day	6% 14% 37% 30% 11% 2	487
	11th to 20th	Day	5% 12% 31% 34% 14% 3	477
	21st to end	Day	6% 16% 36% 27% 12% 3	539
September	1st to 10th	Day	8% 14% 31% 30% 12% 4	490
	11th to 20th	Day	10% 18% 31% 28% 10% 2	490
	21st to end	Day	13% 18% 35% 22% 10% 2	490
October	1st to 10th	Day	19% 21% 29% 21% 9% 2	490
	11th to 20th	Day	16% 22% 33% 17% 10% 2	371
	21st to end	Day	26% 24% 26% 18% 5% 1	330
November	1st to 10th	Day	29% 20% 29% 18% 4	300
	11th to 20th	Day	25% 25% 25% 21% 4 1	300
	21st to end	Day	20% 23% 36% 19% 2	228
December	1st to 10th	Day	23% 21% 26% 18% 12% 1	200
	11th to 20th	Day	27% 36% 26% 8% 3	200
	21st to end	Day	28% 30% 29% 7% 4 1	220
January	1st to 10th	Night	25% 20% 34% 16% 5%	800
	11th to 20th	Night	23% 19% 31% 21% 5% 1	800
	21st to end	Night	17% 20% 32% 25% 6% 1	880
February	1st to 10th	Night	22% 20% 39% 16% 3 1	800
	11th to 20th	Night	20% 19% 34% 24% 3	784
	21st to end	Night	19% 23% 35% 17% 5%	660
March	1st to 10th	Night	18% 22% 34% 19% 5% 1	800
	11th to 20th	Night	18% 18% 32% 22% 10% 1	800
	21st to end	Night	20% 15% 36% 24% 5%	880
April	1st to 10th	Night	19% 16% 27% 26% 11% 1	800
	11th to 20th	Night	20% 14% 32% 26% 9% 1	727
	21st to end	Night	21% 10% 28% 31% 9% 1	600
May	1st to 10th	Night	19% 10% 26% 35% 10% 1	600
	11th to 20th	Night	14% 9% 23% 32% 21% 1	382
	21st to end	Night	23% 8% 18% 31% 19% 2	411
June	1st to 10th	Night	18% 6% 22% 34% 17% 2	380
	11th to 20th	Night	20% 6% 27% 33% 13%	380
	21st to end	Night	8% 5% 24% 42% 21%	380
July	1st to 10th	Night	5% 3 18% 52% 21% 1	370
	11th to 20th	Night	3 1 23% 58% 15%	368
	21st to end	Night	3 3 19% 51% 22%	416
August	1st to 10th	Night	5% 3 20% 45% 27%	405
	11th to 20th	Night	3 2 20% 46% 27% 2	564
	21st to end	Night	6% 4 24% 39% 25% 2	789
September	1st to 10th	Night	5% 3 18% 47% 24% 3	760
	11th to 20th	Night	7% 6% 21% 36% 25% 5%	760
	21st to end	Night	14% 6% 23% 31% 22% 3	760
October	1st to 10th	Night	16% 7% 25% 34% 17% 1	760
	11th to 20th	Night	16% 11% 26% 32% 13% 3	760
	21st to end	Night	23% 11% 31% 24% 8% 3	836
November	1st to 10th	Night	21% 15% 35% 24% 4	780
	11th to 20th	Night	25% 18% 33% 19% 4 1	800
	21st to end	Night	18% 19% 33% 21% 8% 1	800
December	1st to 10th	Night	19% 18% 35% 23% 6%	932
	11th to 20th	Night	21% 24% 35% 17% 3	936
	21st to end	Night	24% 24% 36% 14% 2 1	880

Page generated at 2025-05-08 07:33:55. Version ac07

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