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 2026-09-14.

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	5% 9% 3 8% 5% 4 5% 4 5% 7% 45%	157508
	Night	6% 9% 4 8% 5% 5% 5% 4 5% 7% 43%	150895
Transparency	Day	37% 8% 9% 21% 18% 8%	152223
	Night	40% 8% 10% 21% 15% 5%	147185
Seeing	Day	19% 23% 31% 19% 7% 1	16684
	Night	17% 14% 29% 28% 11% 1	26105

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 13% 8% 19% 10% 7% 7% 5% 5% 5% 16%	4722
	11th to 20th	Day	3 10% 6% 14% 5% 3 4 3 5% 6% 41%	4740
	21st to end	Day	3 9% 3 10% 8% 7% 8% 4 6% 6% 36%	5187
February	1st to 10th	Day	8% 19% 6% 13% 7% 4 5% 3 6% 7% 22%	1738
	11th to 20th	Day	5% 18% 8% 15% 8% 5% 5% 4 5% 6% 21%	2050
	21st to end	Day	5% 19% 8% 18% 8% 5% 5% 4 5% 4 20%	1730
March	1st to 10th	Day	4 14% 5% 14% 7% 7% 6% 5% 6% 7% 26%	4618
	11th to 20th	Day	3 14% 7% 14% 8% 6% 6% 3 4 4 32%	4879
	21st to end	Day	5% 18% 6% 15% 8% 7% 8% 5% 6% 6% 15%	5918
April	1st to 10th	Day	9% 18% 6% 11% 6% 5% 5% 4 6% 6% 23%	2520
	11th to 20th	Day	10% 17% 5% 10% 6% 5% 5% 3 5% 6% 29%	2555
	21st to end	Day	15% 18% 4 8% 7% 4 4 3 5% 6% 27%	2730
May	1st to 10th	Day	6% 11% 2 5% 4 4 3 3 6% 6% 50%	7626
	11th to 20th	Day	9% 11% 3 9% 6% 5% 5% 4 6% 6% 37%	8138
	21st to end	Day	10% 9% 3 6% 5% 4 5% 4 5% 7% 43%	8992
June	1st to 10th	Day	14% 10% 3 8% 5% 4 5% 4 6% 8% 31%	2940
	11th to 20th	Day	14% 8% 3 7% 5% 5% 4 4 5% 5% 39%	2940
	21st to end	Day	7% 4 2 5% 3 3 4 4 5% 7% 56%	2940
July	1st to 10th	Day	2 2 1 3 2 2 3 3 5% 6% 71%	8219
	11th to 20th	Day	1 2 1 2 2 3 4 3 4 5% 71%	8220
	21st to end	Day	2 2 1 2 2 3 3 3 6% 8% 69%	8922
August	1st to 10th	Day	2 2 1 4 3 4 4 3 5% 6% 65%	8022
	11th to 20th	Day	2 2 1 3 3 3 4 3 6% 8% 65%	7565
	21st to end	Day	4 3 1 4 3 3 4 4 6% 9% 59%	7867
September	1st to 10th	Day	5% 3 2 4 3 3 4 3 5% 6% 63%	2520
	11th to 20th	Day	6% 5% 2 6% 5% 4 5% 4 5% 7% 52%	2276
	21st to end	Day	8% 6% 2 5% 4 4 4 4 4 7% 53%	2200
October	1st to 10th	Day	8% 6% 2 5% 4 3 3 2 3 5% 60%	3600
	11th to 20th	Day	10% 7% 2 6% 4 4 4 3 5% 7% 46%	3048
	21st to end	Day	9% 13% 4 9% 6% 5% 5% 4 5% 6% 34%	3200
November	1st to 10th	Day	11% 15% 4 10% 6% 4 5% 4 5% 7% 29%	1854
	11th to 20th	Day	8% 16% 5% 11% 7% 7% 6% 4 6% 7% 23%	1890
	21st to end	Day	5% 15% 6% 10% 6% 5% 5% 4 6% 7% 31%	1741
December	1st to 10th	Day	5% 11% 4 9% 7% 4 4 3 4 5% 43%	2428
	11th to 20th	Day	4 12% 5% 15% 8% 8% 8% 5% 8% 8% 18%	2881
	21st to end	Day	5% 13% 7% 14% 7% 7% 6% 4 6% 8% 24%	4092
January	1st to 10th	Night	5% 15% 8% 16% 8% 6% 6% 4 6% 7% 18%	8172
	11th to 20th	Night	5% 11% 6% 12% 6% 5% 5% 4 6% 6% 35%	8220
	21st to end	Night	2 9% 4 10% 7% 8% 7% 5% 6% 6% 36%	8994
February	1st to 10th	Night	9% 18% 7% 14% 7% 5% 5% 4 5% 5% 21%	2879
	11th to 20th	Night	7% 19% 6% 11% 7% 6% 5% 5% 5% 5% 24%	2458
	21st to end	Night	5% 16% 6% 15% 9% 7% 5% 4 5% 7% 21%	2076
March	1st to 10th	Night	4 12% 5% 11% 6% 5% 5% 5% 6% 7% 32%	5496
	11th to 20th	Night	4 12% 6% 12% 7% 6% 7% 4 5% 5% 33%	5340
	21st to end	Night	6% 15% 5% 13% 8% 6% 7% 5% 7% 8% 21%	5296
April	1st to 10th	Night	8% 17% 6% 10% 6% 5% 5% 4 6% 6% 28%	2100
	11th to 20th	Night	13% 13% 3 8% 6% 4 4 4 5% 5% 36%	2012
	21st to end	Night	14% 13% 4 9% 5% 4 4 4 5% 7% 32%	1890
May	1st to 10th	Night	9% 8% 2 4 3 3 3 3 6% 8% 52%	5321
	11th to 20th	Night	8% 9% 3 7% 4 4 4 3 5% 8% 44%	4707
	21st to end	Night	13% 9% 2 6% 3 3 3 2 4 6% 48%	5181
June	1st to 10th	Night	15% 7% 2 6% 5% 5% 4 4 6% 8% 38%	1680
	11th to 20th	Night	15% 6% 2 4 3 4 4 4 6% 8% 45%	1680
	21st to end	Night	6% 4 2 4 3 3 5% 3 5% 7% 57%	1680
July	1st to 10th	Night	1 1 1 2 2 2 3 4 5% 6% 73%	4740
	11th to 20th	Night	1 1 1 2 2 3 3 2 4 5% 76%	4740
	21st to end	Night	1 2 1 2 2 2 3 3 5% 8% 71%	5153
August	1st to 10th	Night	2 2 1 3 2 2 3 2 4 7% 71%	4775
	11th to 20th	Night	1 1 1 2 2 3 3 3 6% 7% 70%	5291
	21st to end	Night	4 4 1 4 3 4 4 3 5% 6% 61%	6372
September	1st to 10th	Night	4 2 1 3 3 3 3 3 6% 7% 65%	2100
	11th to 20th	Night	6% 5% 2 4 3 4 4 4 6% 7% 55%	2191
	21st to end	Night	11% 5% 2 5% 3 3 3 2 5% 6% 56%	2200
October	1st to 10th	Night	7% 5% 2 4 4 3 3 2 4 4 62%	3600
	11th to 20th	Night	6% 9% 2 6% 4 4 5% 5% 5% 7% 46%	4100
	21st to end	Night	8% 12% 4 9% 7% 6% 5% 4 5% 7% 34%	4600
November	1st to 10th	Night	12% 13% 4 9% 6% 5% 6% 4 6% 6% 31%	2665
	11th to 20th	Night	11% 15% 4 10% 6% 5% 6% 4 6% 6% 26%	2730
	21st to end	Night	6% 15% 5% 12% 6% 5% 5% 3 6% 6% 32%	2877
December	1st to 10th	Night	5% 10% 4 8% 5% 4 4 3 5% 7% 46%	4930
	11th to 20th	Night	4 13% 5% 12% 8% 8% 7% 5% 8% 8% 21%	5543
	21st to end	Night	5% 14% 6% 14% 7% 7% 6% 4 5% 7% 24%	7106

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	63% 13% 11% 9% 3	4723
	11th to 20th	Day	44% 6% 9% 24% 13% 4	4740
	21st to end	Day	46% 9% 12% 15% 13% 4	5187
February	1st to 10th	Day	62% 11% 11% 13% 3	1738
	11th to 20th	Day	65% 7% 10% 12% 5%	2060
	21st to end	Day	67% 7% 8% 10% 7% 1	1730
March	1st to 10th	Day	53% 12% 7% 16% 9% 3	4618
	11th to 20th	Day	50% 10% 8% 29% 3	4879
	21st to end	Day	63% 11% 10% 13% 3	5918
April	1st to 10th	Day	60% 9% 12% 16% 3	2520
	11th to 20th	Day	54% 7% 10% 18% 10% 1	2558
	21st to end	Day	57% 7% 10% 17% 9%	2730
May	1st to 10th	Day	31% 7% 7% 32% 22% 1	7626
	11th to 20th	Day	40% 11% 8% 30% 10% 2	8141
	21st to end	Day	38% 8% 13% 27% 13% 1	8994
June	1st to 10th	Day	49% 8% 11% 23% 9%	2940
	11th to 20th	Day	45% 6% 8% 21% 16% 4	2940
	21st to end	Day	27% 6% 8% 28% 26% 5%	2940
July	1st to 10th	Day	13% 5% 5% 20% 33% 25%	8151
	11th to 20th	Day	13% 6% 4 12% 33% 33%	8145
	21st to end	Day	12% 5% 5% 21% 32% 24%	8723
August	1st to 10th	Day	14% 4 4 13% 32% 33%	6358
	11th to 20th	Day	16% 6% 9% 25% 34% 10%	5964
	21st to end	Day	16% 7% 5% 32% 30% 10%	6170
September	1st to 10th	Day	22% 4 9% 23% 28% 15%	2520
	11th to 20th	Day	30% 6% 10% 22% 23% 8%	2276
	21st to end	Day	32% 4 10% 29% 20% 5%	2200
October	1st to 10th	Day	29% 4 6% 26% 31% 5%	3600
	11th to 20th	Day	36% 6% 15% 26% 15% 1	3048
	21st to end	Day	47% 10% 8% 23% 12%	3200
November	1st to 10th	Day	54% 9% 13% 19% 5%	1854
	11th to 20th	Day	58% 10% 15% 14% 3	1890
	21st to end	Day	53% 8% 15% 15% 9% 1	1741
December	1st to 10th	Day	43% 10% 14% 21% 12% 1	2428
	11th to 20th	Day	60% 14% 13% 11% 2	2881
	21st to end	Day	54% 13% 14% 14% 4 1	4092
January	1st to 10th	Night	61% 12% 13% 12% 2	8172
	11th to 20th	Night	47% 6% 11% 21% 11% 3	8220
	21st to end	Night	45% 12% 9% 16% 12% 5%	8994
February	1st to 10th	Night	65% 10% 10% 13% 3 1	2879
	11th to 20th	Night	61% 8% 11% 13% 6% 1	2459
	21st to end	Night	64% 7% 8% 14% 6% 2	2076
March	1st to 10th	Night	47% 14% 7% 16% 10% 6%	5496
	11th to 20th	Night	48% 10% 9% 28% 6%	5340
	21st to end	Night	55% 11% 14% 16% 4	5296
April	1st to 10th	Night	53% 8% 14% 20% 5%	2100
	11th to 20th	Night	49% 7% 11% 21% 10% 2	2012
	21st to end	Night	51% 6% 11% 22% 10%	1890
May	1st to 10th	Night	28% 7% 8% 31% 23% 1	5319
	11th to 20th	Night	34% 7% 13% 31% 15%	4707
	21st to end	Night	37% 4 15% 32% 12% 1	5182
June	1st to 10th	Night	42% 8% 17% 24% 7% 1	1680
	11th to 20th	Night	36% 7% 13% 26% 15% 2	1680
	21st to end	Night	26% 5% 11% 31% 22% 4	1680
July	1st to 10th	Night	11% 5% 7% 25% 27% 24%	4700
	11th to 20th	Night	11% 5% 5% 17% 33% 29%	4692
	21st to end	Night	12% 3 5% 30% 34% 16%	5040
August	1st to 10th	Night	12% 4 4 16% 39% 25%	3770
	11th to 20th	Night	12% 5% 11% 27% 34% 11%	4168
	21st to end	Night	18% 7% 5% 34% 28% 8%	4991
September	1st to 10th	Night	18% 5% 9% 25% 30% 13%	2100
	11th to 20th	Night	27% 6% 10% 24% 23% 9%	2191
	21st to end	Night	30% 4 10% 28% 20% 8%	2200
October	1st to 10th	Night	27% 4 6% 23% 32% 7%	3600
	11th to 20th	Night	35% 7% 15% 22% 18% 3	4100
	21st to end	Night	47% 9% 8% 22% 14%	4600
November	1st to 10th	Night	51% 10% 11% 20% 7% 2	2665
	11th to 20th	Night	56% 10% 13% 17% 4	2730
	21st to end	Night	52% 7% 11% 18% 10% 1	2877
December	1st to 10th	Night	39% 9% 16% 24% 12% 1	4930
	11th to 20th	Night	58% 14% 10% 14% 3 1	5543
	21st to end	Night	57% 10% 15% 13% 4 1	7106

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	28% 22% 36% 10% 3	220
	11th to 20th	Day	23% 26% 32% 10% 9%	220
	21st to end	Day	19% 24% 36% 19% 3	242
February	1st to 10th	Day	24% 32% 33% 10% 2	263
	11th to 20th	Day	22% 33% 30% 12% 3	535
	21st to end	Day	28% 29% 32% 10% 2	446
March	1st to 10th	Day	24% 35% 29% 11% 1	540
	11th to 20th	Day	24% 28% 29% 12% 4 1	540
	21st to end	Day	29% 31% 25% 11% 3	594
April	1st to 10th	Day	24% 24% 29% 16% 6% 1	540
	11th to 20th	Day	27% 26% 27% 16% 3 1	532
	21st to end	Day	27% 26% 25% 16% 5% 1	540
May	1st to 10th	Day	18% 22% 33% 20% 6% 1	543
	11th to 20th	Day	30% 20% 26% 16% 6% 2	568
	21st to end	Day	23% 16% 27% 25% 7% 3	617
June	1st to 10th	Day	19% 20% 31% 22% 6% 2	570
	11th to 20th	Day	21% 28% 29% 17% 4 1	570
	21st to end	Day	10% 21% 35% 25% 7% 2	570
July	1st to 10th	Day	6% 16% 42% 26% 8% 2	566
	11th to 20th	Day	5% 22% 38% 26% 8% 1	564
	21st to end	Day	4 17% 40% 27% 11% 2	619
August	1st to 10th	Day	8% 16% 36% 28% 10% 2	567
	11th to 20th	Day	5% 14% 32% 32% 13% 3	557
	21st to end	Day	7% 17% 36% 27% 11% 3	627
September	1st to 10th	Day	10% 14% 31% 30% 12% 4	570
	11th to 20th	Day	12% 18% 30% 28% 11% 2	543
	21st to end	Day	13% 18% 35% 23% 10% 2	530
October	1st to 10th	Day	19% 23% 28% 20% 8% 2	530
	11th to 20th	Day	18% 22% 33% 16% 9% 2	405
	21st to end	Day	26% 24% 26% 17% 5% 1	363
November	1st to 10th	Day	31% 21% 28% 16% 4	330
	11th to 20th	Day	26% 25% 25% 19% 4 1	330
	21st to end	Day	22% 24% 35% 17% 2	251
December	1st to 10th	Day	27% 19% 25% 17% 10% 1	220
	11th to 20th	Day	29% 36% 25% 7% 3	220
	21st to end	Day	30% 29% 28% 8% 4 1	242
January	1st to 10th	Night	25% 21% 34% 15% 5%	840
	11th to 20th	Night	22% 20% 32% 21% 5% 1	840
	21st to end	Night	16% 20% 33% 24% 5% 1	924
February	1st to 10th	Night	22% 20% 38% 17% 2	840
	11th to 20th	Night	20% 19% 33% 24% 3	824
	21st to end	Night	20% 24% 35% 16% 5%	692
March	1st to 10th	Night	18% 23% 34% 19% 5%	840
	11th to 20th	Night	19% 20% 31% 21% 9% 1	840
	21st to end	Night	20% 16% 36% 23% 5%	924
April	1st to 10th	Night	18% 15% 28% 27% 10% 1	840
	11th to 20th	Night	20% 14% 32% 25% 8% 1	764
	21st to end	Night	21% 10% 28% 31% 10% 1	630
May	1st to 10th	Night	18% 11% 26% 34% 10% 1	630
	11th to 20th	Night	14% 10% 24% 30% 20% 1	421
	21st to end	Night	22% 8% 19% 31% 18% 2	455
June	1st to 10th	Night	17% 7% 22% 34% 18% 1	420
	11th to 20th	Night	19% 7% 29% 33% 13%	420
	21st to end	Night	9% 5% 24% 41% 21%	420
July	1st to 10th	Night	4 3 18% 52% 22% 1	410
	11th to 20th	Night	2 1 25% 57% 15%	408
	21st to end	Night	3 4 20% 50% 23% 1	460
August	1st to 10th	Night	4 4 21% 45% 26%	448
	11th to 20th	Night	3 2 22% 46% 26% 1	624
	21st to end	Night	6% 5% 25% 39% 24% 2	873
September	1st to 10th	Night	6% 3 19% 46% 24% 3	840
	11th to 20th	Night	8% 6% 21% 37% 24% 4	812
	21st to end	Night	14% 5% 24% 32% 22% 3	800
October	1st to 10th	Night	16% 8% 25% 33% 17% 1	800
	11th to 20th	Night	16% 12% 27% 30% 12% 3	800
	21st to end	Night	23% 12% 31% 24% 8% 3	880
November	1st to 10th	Night	22% 15% 35% 24% 4	820
	11th to 20th	Night	25% 19% 33% 18% 4 1	840
	21st to end	Night	18% 20% 33% 21% 8% 1	840
December	1st to 10th	Night	20% 19% 34% 22% 5%	979
	11th to 20th	Night	22% 25% 34% 16% 3	983
	21st to end	Night	26% 23% 35% 14% 2 1	924

Page generated at 2026-09-11 02:11:52. Version ac07

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