Heaven's Gate Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heaven's Gate Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	19% 8% 2 5% 3 3 3 3 4 5% 43%	146924
	Night	23% 10% 2 5% 3 3 3 3 4 5% 39%	142470
Transparency	Day	44% 4 11% 20% 14% 6%	141721
	Night	49% 5% 11% 18% 12% 5%	138671
Seeing	Day	24% 10% 24% 26% 12% 4	16743
	Night	27% 5% 14% 30% 21% 2	25776

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	38% 17% 4 8% 5% 4 4 2 3 4 12%	4722
	11th to 20th	Day	22% 9% 2 4 2 3 2 2 3 5% 46%	4777
	21st to end	Day	26% 9% 3 6% 4 4 4 3 4 5% 31%	5843
February	1st to 10th	Day	29% 14% 3 7% 5% 4 5% 3 5% 4 20%	1890
	11th to 20th	Day	31% 14% 3 7% 4 3 4 4 3 5% 21%	1845
	21st to end	Day	31% 19% 2 8% 4 4 3 3 3 5% 19%	1657
March	1st to 10th	Day	23% 17% 4 7% 4 4 4 5% 6% 6% 21%	4884
	11th to 20th	Day	31% 15% 2 6% 4 4 3 2 3 3 27%	5110
	21st to end	Day	29% 14% 4 9% 6% 5% 5% 4 5% 6% 14%	5696
April	1st to 10th	Day	30% 16% 4 8% 5% 4 4 3 5% 5% 17%	2520
	11th to 20th	Day	25% 15% 4 7% 5% 3 4 3 4 5% 26%	2489
	21st to end	Day	25% 10% 3 6% 4 4 3 3 5% 7% 28%	2689
May	1st to 10th	Day	15% 8% 2 6% 4 3 4 3 4 6% 45%	7926
	11th to 20th	Day	17% 7% 2 6% 4 4 4 4 6% 8% 39%	8160
	21st to end	Day	15% 7% 2 6% 4 4 5% 4 6% 7% 42%	8992
June	1st to 10th	Day	24% 9% 2 6% 4 3 4 3 4 5% 36%	2940
	11th to 20th	Day	18% 8% 3 6% 4 4 4 4 5% 7% 37%	2871
	21st to end	Day	10% 5% 2 4 3 3 3 3 4 6% 58%	2800
July	1st to 10th	Day	3 2 1 2 1 1 2 1 2 3 82%	6319
	11th to 20th	Day	3 2 1 2 2 1 2 1 2 3 81%	6320
	21st to end	Day	3 2 1 2 2 2 2 2 2 4 78%	6763
August	1st to 10th	Day	3 3 1 4 2 2 3 2 4 5% 70%	5777
	11th to 20th	Day	6% 4 1 4 3 2 3 3 4 6% 64%	5796
	21st to end	Day	6% 4 1 4 3 3 3 3 5% 7% 62%	6116
September	1st to 10th	Day	7% 4 1 3 2 2 2 2 4 5% 69%	2400
	11th to 20th	Day	12% 6% 3 5% 3 4 3 3 5% 6% 51%	2395
	21st to end	Day	15% 5% 2 5% 3 3 3 3 4 6% 50%	2105
October	1st to 10th	Day	15% 6% 2 5% 3 2 3 2 3 5% 55%	3280
	11th to 20th	Day	19% 7% 2 7% 4 3 4 3 5% 7% 38%	3261
	21st to end	Day	29% 8% 2 6% 4 4 5% 3 5% 7% 26%	3539
November	1st to 10th	Day	35% 10% 3 7% 4 3 3 3 4 5% 22%	1782
	11th to 20th	Day	34% 10% 3 7% 4 4 4 3 5% 5% 21%	1680
	21st to end	Day	30% 10% 3 6% 4 3 4 3 4 6% 26%	1680
December	1st to 10th	Day	23% 8% 2 5% 3 3 4 4 4 5% 40%	2700
	11th to 20th	Day	37% 12% 4 8% 4 4 3 3 4 5% 14%	3108
	21st to end	Day	42% 15% 4 6% 3 3 3 2 3 4 14%	4092
January	1st to 10th	Night	42% 16% 3 6% 3 4 4 2 3 4 13%	8172
	11th to 20th	Night	23% 10% 2 5% 3 3 3 3 4 5% 41%	8180
	21st to end	Night	26% 11% 3 7% 4 3 3 2 3 4 34%	8371
February	1st to 10th	Night	30% 17% 4 7% 4 4 3 3 4 5% 20%	2730
	11th to 20th	Night	31% 15% 3 7% 4 4 3 3 3 3 24%	2662
	21st to end	Night	30% 16% 3 6% 3 3 3 3 5% 5% 23%	2149
March	1st to 10th	Night	23% 18% 4 7% 5% 4 4 4 5% 5% 20%	5226
	11th to 20th	Night	28% 16% 2 6% 3 3 3 2 3 3 29%	5110
	21st to end	Night	32% 17% 3 8% 4 4 4 2 4 5% 17%	5521
April	1st to 10th	Night	30% 16% 3 6% 4 3 4 3 4 5% 22%	2100
	11th to 20th	Night	26% 14% 3 5% 4 3 3 3 4 4 30%	2079
	21st to end	Night	26% 12% 2 6% 4 4 4 3 4 6% 30%	1927
May	1st to 10th	Night	17% 10% 2 5% 3 3 2 2 4 6% 45%	5005
	11th to 20th	Night	19% 11% 2 6% 4 3 4 2 5% 5% 39%	4700
	21st to end	Night	17% 7% 2 6% 3 4 3 3 4 6% 44%	5181
June	1st to 10th	Night	21% 9% 3 5% 3 4 3 3 6% 6% 38%	1680
	11th to 20th	Night	15% 8% 2 6% 3 3 4 3 5% 6% 45%	1640
	21st to end	Night	11% 4 1 3 3 3 3 2 4 4 61%	1600
July	1st to 10th	Night	4 2 1 2 1 1 2 2 4 4 77%	3640
	11th to 20th	Night	2 2 1 1 1 1 1 2 2 85%	3640
	21st to end	Night	5% 1 1 2 2 2 1 1 2 4 78%	4076
August	1st to 10th	Night	5% 3 1 3 2 3 3 3 4 6% 67%	4035
	11th to 20th	Night	7% 4 1 4 3 3 3 2 4 6% 63%	4052
	21st to end	Night	7% 4 1 4 2 2 3 2 4 5% 65%	4877
September	1st to 10th	Night	6% 4 1 3 1 3 3 2 4 5% 69%	2000
	11th to 20th	Night	12% 5% 2 3 3 3 4 3 5% 6% 55%	2001
	21st to end	Night	13% 6% 2 5% 3 2 3 2 4 6% 53%	2295
October	1st to 10th	Night	13% 6% 2 4 3 2 2 2 3 4 59%	3920
	11th to 20th	Night	16% 7% 2 6% 3 3 4 3 5% 8% 43%	3897
	21st to end	Night	31% 11% 3 6% 4 4 4 3 4 4 27%	4269
November	1st to 10th	Night	32% 9% 3 7% 4 3 4 3 5% 5% 25%	2733
	11th to 20th	Night	37% 11% 3 6% 3 3 3 3 4 5% 21%	2940
	21st to end	Night	27% 11% 3 6% 4 3 3 4 4 5% 30%	2940
December	1st to 10th	Night	20% 8% 2 5% 3 3 3 3 4 6% 42%	4700
	11th to 20th	Night	39% 13% 3 7% 4 3 4 3 4 5% 14%	5316
	21st to end	Night	38% 14% 3 7% 4 3 4 3 3 4 17%	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	77% 4 6% 8% 4 1	4723
	11th to 20th	Day	44% 2 5% 20% 17% 13%	4777
	21st to end	Day	55% 5% 6% 14% 13% 7%	5843
February	1st to 10th	Day	65% 7% 10% 11% 6% 1	1890
	11th to 20th	Day	65% 7% 10% 9% 6% 3	1854
	21st to end	Day	69% 5% 8% 9% 7% 2	1657
March	1st to 10th	Day	60% 5% 11% 18% 5%	4884
	11th to 20th	Day	63% 5% 6% 17% 9% 1	5110
	21st to end	Day	68% 8% 11% 10% 3	5696
April	1st to 10th	Day	69% 6% 10% 11% 4	2520
	11th to 20th	Day	60% 7% 10% 13% 7% 2	2492
	21st to end	Day	55% 8% 13% 16% 6% 1	2689
May	1st to 10th	Day	40% 5% 10% 29% 15%	7926
	11th to 20th	Day	42% 4 18% 27% 8%	8163
	21st to end	Day	40% 6% 24% 23% 7%	8994
June	1st to 10th	Day	50% 6% 15% 22% 7% 1	2940
	11th to 20th	Day	45% 7% 16% 22% 9% 1	2871
	21st to end	Day	29% 5% 15% 34% 14% 4	2800
July	1st to 10th	Day	11% 2 7% 26% 27% 26%	6251
	11th to 20th	Day	11% 2 5% 14% 33% 35%	6245
	21st to end	Day	13% 1 10% 36% 30% 9%	6566
August	1st to 10th	Day	17% 3 8% 26% 33% 12%	4206
	11th to 20th	Day	21% 3 12% 39% 20% 5%	4195
	21st to end	Day	23% 2 14% 25% 24% 12%	4407
September	1st to 10th	Day	20% 3 10% 30% 24% 14%	2400
	11th to 20th	Day	34% 6% 11% 25% 17% 8%	2395
	21st to end	Day	35% 6% 11% 22% 16% 9%	2105
October	1st to 10th	Day	34% 4 8% 20% 21% 14%	3280
	11th to 20th	Day	46% 3 14% 22% 12% 2	3261
	21st to end	Day	57% 4 9% 17% 12% 2	3539
November	1st to 10th	Day	65% 6% 10% 13% 6% 1	1782
	11th to 20th	Day	64% 6% 10% 9% 7% 3	1680
	21st to end	Day	59% 5% 12% 10% 11% 4	1680
December	1st to 10th	Day	47% 4 8% 15% 22% 4	2700
	11th to 20th	Day	72% 6% 8% 10% 4 1	3108
	21st to end	Day	76% 4 10% 8% 2 1	4092
January	1st to 10th	Night	76% 4 7% 9% 3 1	8172
	11th to 20th	Night	47% 3 6% 18% 15% 11%	8180
	21st to end	Night	57% 3 4 12% 16% 9%	8371
February	1st to 10th	Night	67% 5% 9% 11% 6% 2	2730
	11th to 20th	Night	65% 6% 9% 12% 5% 3	2664
	21st to end	Night	62% 6% 10% 12% 7% 2	2149
March	1st to 10th	Night	62% 6% 13% 12% 6% 1	5226
	11th to 20th	Night	60% 5% 9% 16% 9% 1	5110
	21st to end	Night	69% 7% 12% 10% 2	5521
April	1st to 10th	Night	66% 6% 12% 11% 5%	2100
	11th to 20th	Night	57% 7% 14% 13% 6% 3	2079
	21st to end	Night	55% 9% 13% 15% 6% 2	1927
May	1st to 10th	Night	40% 5% 13% 30% 12%	5003
	11th to 20th	Night	48% 5% 12% 29% 5% 1	4700
	21st to end	Night	40% 7% 25% 25% 3	5182
June	1st to 10th	Night	46% 9% 12% 27% 6%	1680
	11th to 20th	Night	39% 9% 17% 25% 8% 1	1640
	21st to end	Night	27% 5% 18% 32% 13% 4	1600
July	1st to 10th	Night	13% 2 9% 27% 26% 24%	3600
	11th to 20th	Night	9% 1 6% 16% 39% 27%	3592
	21st to end	Night	14% 1 15% 33% 30% 6%	3961
August	1st to 10th	Night	14% 3 8% 34% 29% 12%	2929
	11th to 20th	Night	22% 2 17% 36% 19% 4	2929
	21st to end	Night	22% 3 12% 28% 28% 8%	3509
September	1st to 10th	Night	19% 4 10% 30% 25% 13%	2000
	11th to 20th	Night	31% 6% 12% 27% 15% 9%	2001
	21st to end	Night	33% 4 12% 24% 16% 10%	2295
October	1st to 10th	Night	31% 3 8% 22% 27% 9%	3920
	11th to 20th	Night	41% 4 22% 20% 11% 2	3897
	21st to end	Night	60% 4 8% 15% 9% 3	4269
November	1st to 10th	Night	60% 7% 10% 13% 9% 1	2733
	11th to 20th	Night	65% 7% 9% 10% 6% 3	2940
	21st to end	Night	56% 5% 9% 13% 11% 5%	2940
December	1st to 10th	Night	44% 4 9% 18% 22% 3	4700
	11th to 20th	Night	73% 6% 8% 8% 5%	5316
	21st to end	Night	69% 6% 14% 8% 2 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	50% 9% 15% 16% 10% 1	220
	11th to 20th	Day	38% 5% 14% 23% 14% 5%	231
	21st to end	Day	33% 10% 19% 21% 14% 3	473
February	1st to 10th	Day	36% 9% 21% 23% 9% 2	430
	11th to 20th	Day	37% 14% 24% 17% 6% 2	425
	21st to end	Day	40% 14% 18% 22% 4 1	408
March	1st to 10th	Day	39% 13% 21% 19% 7% 1	540
	11th to 20th	Day	35% 10% 26% 19% 8% 2	540
	21st to end	Day	37% 17% 23% 17% 5% 1	594
April	1st to 10th	Day	35% 13% 21% 19% 9% 3	540
	11th to 20th	Day	32% 15% 24% 18% 8% 3	532
	21st to end	Day	29% 14% 22% 23% 9% 2	540
May	1st to 10th	Day	21% 14% 26% 27% 8% 4	543
	11th to 20th	Day	29% 13% 23% 22% 11% 3	568
	21st to end	Day	20% 13% 25% 25% 12% 5%	617
June	1st to 10th	Day	24% 11% 22% 28% 11% 4	570
	11th to 20th	Day	19% 15% 30% 26% 10% 1	551
	21st to end	Day	9% 6% 30% 35% 14% 5%	530
July	1st to 10th	Day	7% 6% 32% 37% 14% 6%	526
	11th to 20th	Day	4 6% 32% 36% 15% 6%	524
	21st to end	Day	3 5% 29% 37% 20% 7%	575
August	1st to 10th	Day	3 3 28% 43% 16% 7%	527
	11th to 20th	Day	5% 4 24% 40% 18% 8%	517
	21st to end	Day	7% 7% 29% 34% 17% 6%	583
September	1st to 10th	Day	8% 6% 29% 32% 20% 5%	530
	11th to 20th	Day	16% 5% 24% 35% 17% 3	530
	21st to end	Day	17% 10% 26% 28% 15% 3	530
October	1st to 10th	Day	20% 8% 27% 24% 16% 4	530
	11th to 20th	Day	25% 6% 21% 27% 17% 4	530
	21st to end	Day	30% 12% 22% 21% 13% 3	576
November	1st to 10th	Day	36% 9% 21% 20% 12% 2	291
	11th to 20th	Day	36% 9% 17% 21% 12% 5%	220
	21st to end	Day	35% 8% 15% 23% 16% 3	220
December	1st to 10th	Day	34% 10% 18% 21% 10% 8%	220
	11th to 20th	Day	44% 7% 17% 20% 10% 2	220
	21st to end	Day	43% 10% 18% 18% 7% 3	242
January	1st to 10th	Night	46% 8% 15% 21% 9% 2	840
	11th to 20th	Night	35% 7% 15% 23% 17% 3	840
	21st to end	Night	33% 5% 16% 29% 14% 2	924
February	1st to 10th	Night	37% 7% 16% 30% 11% 1	840
	11th to 20th	Night	38% 7% 15% 29% 12% 1	824
	21st to end	Night	37% 9% 17% 27% 11%	692
March	1st to 10th	Night	36% 9% 15% 29% 10% 1	840
	11th to 20th	Night	30% 8% 17% 30% 14% 1	840
	21st to end	Night	38% 9% 15% 25% 13% 1	924
April	1st to 10th	Night	37% 7% 15% 25% 15% 1	840
	11th to 20th	Night	30% 9% 17% 26% 16% 2	831
	21st to end	Night	30% 6% 15% 30% 16% 2	667
May	1st to 10th	Night	24% 7% 15% 29% 23% 3	520
	11th to 20th	Night	25% 4 12% 31% 26% 2	414
	21st to end	Night	24% 4 15% 28% 27% 2	455
June	1st to 10th	Night	22% 6% 12% 32% 27% 2	420
	11th to 20th	Night	16% 7% 17% 35% 24% 1	410
	21st to end	Night	14% 1 11% 39% 36% 1	400
July	1st to 10th	Night	6% 2 9% 41% 42% 1	390
	11th to 20th	Night	6% 1 15% 47% 31% 1	388
	21st to end	Night	4 9% 40% 44% 3	482
August	1st to 10th	Night	5% 2 6% 34% 46% 8%	597
	11th to 20th	Night	6% 1 5% 36% 47% 7%	594
	21st to end	Night	7% 2 11% 39% 36% 5%	820
September	1st to 10th	Night	9% 2 12% 34% 39% 4	800
	11th to 20th	Night	14% 2 9% 31% 39% 6%	800
	21st to end	Night	15% 4 11% 36% 31% 3	800
October	1st to 10th	Night	19% 2 15% 36% 25% 4	800
	11th to 20th	Night	23% 4 10% 34% 25% 4	800
	21st to end	Night	30% 5% 15% 30% 16% 4	880
November	1st to 10th	Night	35% 6% 14% 30% 14% 1	820
	11th to 20th	Night	40% 7% 14% 28% 9% 2	840
	21st to end	Night	32% 6% 15% 32% 14% 1	840
December	1st to 10th	Night	33% 5% 17% 28% 16% 2	840
	11th to 20th	Night	43% 6% 15% 23% 13% 1	840
	21st to end	Night	45% 8% 17% 23% 7% 1	924

Page generated at 2026-06-12 23:31:39. Version ac07

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