Heavens Gate Farm Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heavens Gate Farm Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	11% 8% 3 7% 4 4 4 4 6% 8% 40%	131584
	Night	12% 8% 3 7% 4 4 4 3 5% 7% 42%	130532
Transparency	Day	41% 5% 12% 24% 16% 2	135164
	Night	42% 4 11% 24% 17% 3	135029
Seeing	Day	15% 11% 28% 26% 15% 5%	17544
	Night	16% 10% 31% 30% 12% 1	27521

By Month

Percentage Cloud Cover SE (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	12% 11% 5% 13% 6% 4 4 3 5% 6% 31%	4691
	11th to 20th	Day	6% 9% 4 10% 7% 5% 6% 3 6% 6% 38%	5050
	21st to end	Day	12% 16% 8% 10% 4 3 3 2 3 4 34%	5812
February	1st to 10th	Day	14% 11% 4 9% 5% 5% 4 4 5% 7% 33%	1890
	11th to 20th	Day	13% 11% 3 8% 4 5% 5% 4 5% 7% 35%	1962
	21st to end	Day	13% 10% 4 8% 5% 4 4 3 4 6% 39%	1730
March	1st to 10th	Day	15% 11% 3 6% 3 3 3 2 3 4 46%	4720
	11th to 20th	Day	7% 6% 2 5% 4 4 4 4 5% 9% 49%	5090
	21st to end	Day	14% 10% 3 8% 5% 5% 5% 4 6% 8% 33%	5834
April	1st to 10th	Day	14% 9% 3 8% 4 4 4 4 4 7% 39%	2412
	11th to 20th	Day	15% 9% 3 7% 4 4 3 3 5% 7% 38%	2374
	21st to end	Day	19% 6% 3 8% 5% 4 4 4 6% 7% 35%	2400
May	1st to 10th	Day	12% 8% 3 8% 5% 5% 5% 4 7% 9% 34%	5713
	11th to 20th	Day	14% 7% 3 7% 4 4 4 4 5% 7% 40%	6319
	21st to end	Day	13% 8% 3 7% 5% 4 5% 4 5% 7% 39%	6935
June	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 9% 46%	2800
	11th to 20th	Day	8% 5% 2 5% 5% 5% 5% 5% 6% 9% 46%	2800
	21st to end	Day	7% 6% 2 5% 5% 5% 5% 4 8% 8% 44%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 43%	6360
	11th to 20th	Day	7% 7% 3 8% 5% 5% 6% 5% 7% 10% 38%	6360
	21st to end	Day	8% 6% 3 7% 5% 5% 6% 5% 8% 12% 36%	6613
August	1st to 10th	Day	5% 4 1 6% 4 4 6% 5% 7% 10% 48%	4234
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 9% 42%	3942
	21st to end	Day	5% 4 1 4 4 4 5% 5% 7% 10% 50%	4312
September	1st to 10th	Day	12% 5% 2 4 3 4 4 3 5% 8% 52%	2400
	11th to 20th	Day	9% 5% 2 4 4 4 3 3 6% 8% 52%	2400
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 7% 50%	2145
October	1st to 10th	Day	11% 6% 2 5% 3 4 3 3 5% 6% 54%	2000
	11th to 20th	Day	14% 7% 2 6% 4 3 4 3 5% 5% 47%	2000
	21st to end	Day	16% 8% 3 6% 4 4 3 3 4 7% 43%	2185
November	1st to 10th	Day	10% 7% 2 5% 3 4 4 3 4 7% 51%	1852
	11th to 20th	Day	14% 8% 3 6% 4 4 3 3 4 6% 44%	1890
	21st to end	Day	16% 11% 4 8% 4 3 4 3 4 6% 38%	1711
December	1st to 10th	Day	7% 9% 4 6% 4 4 3 2 4 6% 51%	2690
	11th to 20th	Day	13% 9% 6% 10% 5% 5% 5% 4 5% 6% 32%	3088
	21st to end	Day	20% 21% 7% 11% 4 4 4 3 4 5% 19%	4070
January	1st to 10th	Night	12% 11% 5% 13% 5% 4 4 3 4 5% 33%	8232
	11th to 20th	Night	9% 9% 4 11% 6% 5% 6% 4 5% 5% 37%	7938
	21st to end	Night	13% 13% 5% 10% 5% 4 3 3 4 5% 34%	8402
February	1st to 10th	Night	15% 11% 5% 8% 5% 5% 4 4 5% 6% 33%	2730
	11th to 20th	Night	13% 8% 3 8% 6% 4 5% 3 5% 6% 39%	2543
	21st to end	Night	15% 9% 3 7% 5% 4 3 3 4 5% 42%	2076
March	1st to 10th	Night	18% 11% 4 6% 3 3 3 2 4 5% 41%	5384
	11th to 20th	Night	10% 8% 2 6% 3 4 3 3 4 6% 51%	5090
	21st to end	Night	15% 10% 4 7% 5% 5% 5% 4 6% 7% 32%	5336
April	1st to 10th	Night	13% 6% 2 7% 5% 4 4 3 5% 6% 43%	2010
	11th to 20th	Night	13% 7% 3 6% 4 4 4 4 5% 7% 44%	1975
	21st to end	Night	16% 9% 3 6% 4 3 4 3 5% 6% 40%	2000
May	1st to 10th	Night	17% 9% 3 8% 5% 4 4 4 5% 8% 35%	4172
	11th to 20th	Night	12% 7% 3 6% 4 4 4 3 5% 8% 44%	3596
	21st to end	Night	12% 7% 2 6% 4 4 4 4 5% 8% 44%	3942
June	1st to 10th	Night	7% 5% 2 4 3 5% 3 4 6% 8% 53%	1600
	11th to 20th	Night	7% 6% 2 7% 4 3 4 4 5% 10% 48%	1600
	21st to end	Night	6% 3 2 5% 4 5% 5% 4 7% 9% 49%	1600
July	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 3 6% 10% 44%	3618
	11th to 20th	Night	4 4 2 7% 5% 5% 5% 4 7% 9% 47%	3617
	21st to end	Night	9% 5% 2 7% 4 4 5% 4 8% 11% 40%	4255
August	1st to 10th	Night	4 2 2 4 3 3 3 4 6% 9% 58%	2926
	11th to 20th	Night	8% 5% 2 5% 4 4 4 4 5% 8% 52%	3110
	21st to end	Night	3 3 1 5% 4 4 5% 4 7% 10% 54%	3586
September	1st to 10th	Night	10% 5% 1 4 3 3 3 3 5% 6% 55%	2000
	11th to 20th	Night	7% 5% 2 5% 3 5% 3 3 7% 7% 52%	2000
	21st to end	Night	7% 4 2 5% 3 4 5% 3 5% 8% 54%	2231
October	1st to 10th	Night	8% 5% 2 4 4 3 4 3 4 7% 57%	2400
	11th to 20th	Night	13% 6% 2 5% 4 3 3 3 5% 6% 52%	2400
	21st to end	Night	17% 7% 3 5% 3 3 3 4 4 6% 45%	2655
November	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 5% 7% 53%	2666
	11th to 20th	Night	11% 7% 3 7% 4 4 3 3 5% 6% 47%	2730
	21st to end	Night	17% 9% 3 6% 4 4 3 3 5% 6% 41%	2903
December	1st to 10th	Night	9% 8% 3 7% 5% 4 4 3 5% 5% 46%	4720
	11th to 20th	Night	13% 9% 4 8% 4 4 4 3 5% 6% 39%	5339
	21st to end	Night	21% 17% 6% 11% 6% 4 4 3 4 4 20%	7150

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	54% 4 11% 20% 10% 1	4692
	11th to 20th	Day	47% 4 11% 19% 14% 5%	5050
	21st to end	Day	56% 2 8% 21% 10% 2	5812
February	1st to 10th	Day	51% 5% 12% 21% 10% 2	1890
	11th to 20th	Day	49% 5% 11% 21% 13% 2	1971
	21st to end	Day	47% 4 10% 25% 12% 2	1730
March	1st to 10th	Day	43% 3 7% 23% 22% 2	4720
	11th to 20th	Day	33% 4 10% 29% 22% 3	5090
	21st to end	Day	49% 5% 16% 22% 7% 1	5836
April	1st to 10th	Day	45% 5% 11% 25% 14% 1	2412
	11th to 20th	Day	46% 4 10% 25% 14% 2	2374
	21st to end	Day	48% 6% 13% 19% 13% 1	2400
May	1st to 10th	Day	46% 6% 14% 20% 14% 1	5748
	11th to 20th	Day	43% 5% 10% 26% 13% 3	6323
	21st to end	Day	43% 5% 10% 23% 18% 1	6949
June	1st to 10th	Day	31% 8% 15% 28% 15% 3	2800
	11th to 20th	Day	33% 7% 13% 25% 20% 3	2800
	21st to end	Day	34% 7% 16% 23% 18% 3	2800
July	1st to 10th	Day	36% 5% 13% 28% 17% 2	6291
	11th to 20th	Day	41% 5% 15% 24% 14% 1	6285
	21st to end	Day	39% 4 20% 27% 9% 1	6426
August	1st to 10th	Day	29% 6% 17% 35% 12% 1	4220
	11th to 20th	Day	38% 6% 13% 28% 14% 1	3980
	21st to end	Day	28% 5% 17% 30% 14% 4	4311
September	1st to 10th	Day	31% 6% 11% 27% 21% 5%	2400
	11th to 20th	Day	30% 4 10% 30% 22% 4	2400
	21st to end	Day	31% 5% 10% 28% 24% 2	2145
October	1st to 10th	Day	22% 3 6% 17% 47% 5%	3260
	11th to 20th	Day	26% 3 7% 21% 36% 7%	3240
	21st to end	Day	40% 3 7% 23% 24% 2	3511
November	1st to 10th	Day	35% 4 12% 26% 20% 4	1852
	11th to 20th	Day	42% 3 10% 24% 18% 3	1890
	21st to end	Day	49% 5% 10% 24% 12%	1711
December	1st to 10th	Day	36% 3 17% 30% 14%	2690
	11th to 20th	Day	51% 4 11% 22% 10% 1	3085
	21st to end	Day	69% 3 12% 11% 4	4070
January	1st to 10th	Night	54% 4 13% 21% 8%	8233
	11th to 20th	Night	49% 3 8% 21% 16% 3	7938
	21st to end	Night	54% 2 11% 20% 11% 2	8402
February	1st to 10th	Night	51% 5% 11% 21% 10% 2	2730
	11th to 20th	Night	46% 5% 11% 22% 15% 2	2544
	21st to end	Night	43% 4 11% 23% 15% 3	2076
March	1st to 10th	Night	47% 3 7% 22% 19% 2	5384
	11th to 20th	Night	36% 3 6% 28% 21% 6%	5090
	21st to end	Night	50% 6% 11% 23% 8% 2	5336
April	1st to 10th	Night	40% 5% 13% 23% 16% 3	2010
	11th to 20th	Night	40% 4 11% 24% 18% 4	1975
	21st to end	Night	46% 5% 9% 22% 16% 2	2000
May	1st to 10th	Night	47% 5% 12% 23% 10% 1	4202
	11th to 20th	Night	39% 6% 12% 27% 13% 4	3597
	21st to end	Night	38% 5% 12% 22% 20% 2	3950
June	1st to 10th	Night	28% 6% 16% 29% 19% 3	1600
	11th to 20th	Night	32% 7% 11% 22% 25% 4	1600
	21st to end	Night	29% 7% 17% 22% 21% 4	1600
July	1st to 10th	Night	37% 3 12% 30% 16% 2	3580
	11th to 20th	Night	33% 4 15% 29% 17% 1	3572
	21st to end	Night	37% 4 19% 27% 12% 1	4131
August	1st to 10th	Night	22% 5% 19% 35% 18% 2	2916
	11th to 20th	Night	31% 5% 13% 30% 20% 1	3138
	21st to end	Night	25% 5% 19% 30% 16% 4	3586
September	1st to 10th	Night	28% 5% 10% 24% 26% 7%	2000
	11th to 20th	Night	30% 5% 10% 25% 26% 4	2000
	21st to end	Night	30% 4 9% 25% 28% 4	2231
October	1st to 10th	Night	20% 3 6% 22% 45% 4	3920
	11th to 20th	Night	26% 3 9% 22% 35% 7%	3899
	21st to end	Night	36% 3 9% 23% 25% 4	4279
November	1st to 10th	Night	32% 4 11% 27% 20% 5%	2666
	11th to 20th	Night	39% 3 10% 26% 19% 3	2730
	21st to end	Night	45% 4 11% 25% 14% 1	2903
December	1st to 10th	Night	40% 4 11% 32% 13% 1	4720
	11th to 20th	Night	46% 4 11% 23% 14% 1	5341
	21st to end	Night	69% 3 11% 11% 5% 1	7150

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	19% 20% 35% 21% 5% 1	330
	11th to 20th	Day	25% 24% 38% 11% 2	330
	21st to end	Day	17% 22% 40% 18% 3	363
February	1st to 10th	Day	23% 16% 42% 15% 4	330
	11th to 20th	Day	24% 24% 35% 13% 4	330
	21st to end	Day	22% 21% 39% 16% 1	273
March	1st to 10th	Day	18% 23% 45% 12% 2	330
	11th to 20th	Day	26% 18% 34% 19% 2 1	330
	21st to end	Day	29% 18% 35% 14% 4	472
April	1st to 10th	Day	22% 17% 32% 22% 6% 1	504
	11th to 20th	Day	21% 18% 31% 19% 9% 1	492
	21st to end	Day	21% 16% 34% 23% 6% 1	500
May	1st to 10th	Day	16% 14% 36% 24% 9% 1	569
	11th to 20th	Day	19% 11% 29% 26% 13% 3	725
	21st to end	Day	14% 9% 28% 28% 14% 6%	789
June	1st to 10th	Day	8% 6% 24% 33% 22% 7%	730
	11th to 20th	Day	9% 3 25% 36% 21% 6%	730
	21st to end	Day	8% 7% 28% 34% 18% 5%	730
July	1st to 10th	Day	9% 3 16% 36% 23% 13%	721
	11th to 20th	Day	8% 3 21% 37% 25% 7%	718
	21st to end	Day	9% 3 17% 33% 31% 7%	794
August	1st to 10th	Day	6% 3 17% 42% 25% 7%	726
	11th to 20th	Day	7% 3 18% 31% 31% 10%	576
	21st to end	Day	9% 2 15% 34% 30% 10%	583
September	1st to 10th	Day	12% 3 16% 32% 28% 9%	530
	11th to 20th	Day	8% 3 15% 33% 28% 12%	530
	21st to end	Day	9% 10% 22% 30% 19% 9%	473
October	1st to 10th	Day	11% 7% 29% 31% 15% 7%	330
	11th to 20th	Day	12% 22% 34% 22% 9%	330
	21st to end	Day	25% 19% 33% 20% 4	363
November	1st to 10th	Day	12% 14% 38% 25% 8% 3	330
	11th to 20th	Day	20% 18% 36% 18% 7% 1	330
	21st to end	Day	27% 13% 34% 19% 6% 1	330
December	1st to 10th	Day	13% 21% 43% 15% 5% 3	330
	11th to 20th	Day	23% 15% 40% 16% 5%	330
	21st to end	Day	26% 21% 37% 13% 2	363
January	1st to 10th	Night	16% 17% 40% 22% 5%	1050
	11th to 20th	Night	19% 19% 36% 21% 4	1050
	21st to end	Night	19% 16% 38% 24% 2	1155
February	1st to 10th	Night	20% 14% 40% 22% 4	1050
	11th to 20th	Night	19% 16% 38% 24% 3	908
	21st to end	Night	21% 16% 39% 22% 2	692
March	1st to 10th	Night	21% 15% 40% 21% 4	796
	11th to 20th	Night	20% 13% 36% 25% 5%	630
	21st to end	Night	24% 13% 35% 24% 4	693
April	1st to 10th	Night	17% 15% 37% 26% 5%	603
	11th to 20th	Night	17% 12% 33% 29% 8%	593
	21st to end	Night	21% 9% 35% 30% 5%	600
May	1st to 10th	Night	16% 7% 36% 33% 8% 1	600
	11th to 20th	Night	16% 6% 27% 38% 13% 1	591
	21st to end	Night	14% 5% 26% 33% 20% 3	650
June	1st to 10th	Night	8% 6% 20% 45% 21% 1	600
	11th to 20th	Night	9% 3 23% 43% 20% 2	600
	21st to end	Night	7% 3 25% 43% 22% 2	600
July	1st to 10th	Night	10% 2 10% 38% 36% 4	585
	11th to 20th	Night	6% 2 16% 44% 29% 3	582
	21st to end	Night	9% 1 12% 43% 33% 1	657
August	1st to 10th	Night	7% 2 12% 45% 32% 3	597
	11th to 20th	Night	7% 1 14% 40% 33% 5%	594
	21st to end	Night	5% 1 13% 38% 40% 3	660
September	1st to 10th	Night	13% 3 15% 37% 28% 4	600
	11th to 20th	Night	9% 2 17% 35% 31% 6%	600
	21st to end	Night	9% 7% 22% 34% 24% 5%	777
October	1st to 10th	Night	10% 5% 27% 33% 23% 2	800
	11th to 20th	Night	15% 11% 33% 30% 11% 1	800
	21st to end	Night	23% 11% 34% 26% 6%	880
November	1st to 10th	Night	14% 9% 38% 30% 8% 1	820
	11th to 20th	Night	15% 14% 40% 26% 5% 1	840
	21st to end	Night	22% 14% 36% 23% 5%	1013
December	1st to 10th	Night	18% 13% 39% 25% 4 1	1050
	11th to 20th	Night	22% 12% 34% 27% 5%	1050
	21st to end	Night	25% 15% 35% 22% 3	1155

Page generated at 2026-03-30 01:18:43. Version ac07

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