Golden Ears Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden Ears Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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	29% 10% 2 5% 3 3 3 3 4 5% 31%	131099
	Night	33% 11% 2 5% 3 3 3 2 4 5% 30%	128307
Transparency	Day	57% 6% 12% 16% 7% 1	130807
	Night	59% 5% 12% 15% 7% 1	128176
Seeing	Day	32% 11% 21% 23% 10% 2	16665
	Night	37% 7% 19% 23% 13% 1	24868

By Month

Percentage Cloud Cover NW (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	46% 14% 3 5% 4 4 3 3 3 3 12%	3179
	11th to 20th	Day	24% 10% 4 6% 3 4 4 2 4 4 35%	3184
	21st to end	Day	48% 9% 2 4 2 2 2 1 2 2 27%	4021
February	1st to 10th	Day	39% 13% 3 6% 4 3 4 2 4 4 18%	1800
	11th to 20th	Day	37% 12% 2 6% 4 3 3 3 3 4 22%	1755
	21st to end	Day	30% 21% 3 6% 5% 3 4 2 3 3 19%	1516
March	1st to 10th	Day	33% 19% 4 7% 4 4 3 3 3 5% 16%	4623
	11th to 20th	Day	29% 19% 4 7% 4 3 3 2 2 3 24%	5000
	21st to end	Day	37% 15% 3 6% 5% 4 4 3 4 4 15%	5658
April	1st to 10th	Day	36% 13% 3 7% 5% 4 4 3 5% 5% 16%	2400
	11th to 20th	Day	29% 12% 3 6% 5% 5% 4 3 4 5% 23%	2449
	21st to end	Day	33% 11% 3 7% 4 4 3 4 4 5% 22%	2677
May	1st to 10th	Day	22% 10% 3 6% 3 3 4 3 4 4 38%	6320
	11th to 20th	Day	29% 11% 3 7% 4 4 4 4 5% 6% 23%	6277
	21st to end	Day	31% 9% 3 6% 4 4 5% 4 6% 7% 22%	6985
June	1st to 10th	Day	31% 8% 2 6% 4 4 4 4 5% 6% 28%	3000
	11th to 20th	Day	35% 10% 4 7% 5% 4 4 3 4 5% 20%	3000
	21st to end	Day	25% 8% 2 6% 4 4 4 4 5% 6% 33%	3000
July	1st to 10th	Day	13% 4 2 3 3 3 4 3 5% 5% 56%	6780
	11th to 20th	Day	9% 3 1 3 2 2 2 2 4 5% 67%	6780
	21st to end	Day	16% 4 1 3 2 2 3 3 5% 7% 55%	6930
August	1st to 10th	Day	10% 4 1 3 2 2 2 3 4 6% 62%	4541
	11th to 20th	Day	22% 7% 2 5% 3 3 3 3 5% 6% 40%	4159
	21st to end	Day	24% 7% 2 5% 3 4 3 3 4 6% 39%	4537
September	1st to 10th	Day	20% 7% 2 5% 3 3 2 3 3 7% 45%	2400
	11th to 20th	Day	25% 8% 2 5% 4 3 3 2 4 5% 39%	2400
	21st to end	Day	32% 8% 2 5% 3 3 3 3 4 5% 34%	2110
October	1st to 10th	Day	30% 8% 3 6% 4 4 4 3 5% 6% 27%	3280
	11th to 20th	Day	42% 8% 3 5% 3 3 3 3 4 5% 22%	3261
	21st to end	Day	41% 14% 3 7% 3 3 3 3 4 5% 14%	3280
November	1st to 10th	Day	47% 10% 1 6% 4 3 4 2 4 4 16%	1648
	11th to 20th	Day	47% 12% 2 4 3 2 2 2 2 3 20%	1680
	21st to end	Day	45% 11% 3 5% 3 3 2 2 4 3 18%	1680
December	1st to 10th	Day	29% 10% 3 6% 4 3 4 3 4 6% 26%	2636
	11th to 20th	Day	50% 15% 3 5% 3 3 2 2 3 3 11%	2655
	21st to end	Day	49% 15% 3 7% 3 3 3 2 3 3 8%	3498
January	1st to 10th	Night	46% 14% 3 7% 3 3 2 2 3 3 15%	6766
	11th to 20th	Night	26% 8% 2 5% 3 3 3 3 5% 8% 35%	6711
	21st to end	Night	44% 9% 2 4 2 2 2 2 2 3 28%	6935
February	1st to 10th	Night	39% 12% 2 6% 4 3 3 2 3 4 20%	2600
	11th to 20th	Night	35% 15% 2 6% 4 3 2 2 3 4 23%	2532
	21st to end	Night	34% 13% 3 6% 3 3 3 3 4 4 24%	2113
March	1st to 10th	Night	30% 19% 3 6% 3 3 3 2 3 4 22%	5256
	11th to 20th	Night	33% 17% 3 6% 3 2 3 2 3 4 25%	4999
	21st to end	Night	45% 13% 3 6% 3 3 3 2 3 3 17%	5317
April	1st to 10th	Night	34% 13% 3 7% 4 4 3 3 4 5% 20%	2000
	11th to 20th	Night	27% 12% 3 6% 5% 4 4 3 5% 5% 27%	1897
	21st to end	Night	32% 10% 3 7% 4 3 4 3 4 5% 24%	1721
May	1st to 10th	Night	20% 11% 3 5% 3 2 2 2 3 4 45%	3640
	11th to 20th	Night	24% 9% 3 7% 3 3 3 3 5% 6% 33%	3616
	21st to end	Night	28% 9% 3 7% 4 4 4 3 5% 6% 27%	3888
June	1st to 10th	Night	28% 8% 2 6% 4 5% 4 3 5% 6% 30%	1400
	11th to 20th	Night	27% 10% 3 7% 5% 4 3 3 5% 7% 26%	1400
	21st to end	Night	22% 6% 2 6% 4 3 4 3 5% 5% 40%	1400
July	1st to 10th	Night	12% 3 1 4 2 2 3 2 4 5% 62%	3180
	11th to 20th	Night	5% 2 1 2 2 2 2 2 3 4 77%	3180
	21st to end	Night	9% 3 1 3 2 3 3 3 4 6% 63%	3911
August	1st to 10th	Night	8% 2 1 2 1 2 2 3 5% 7% 67%	2609
	11th to 20th	Night	17% 4 2 5% 3 3 3 3 5% 6% 49%	2897
	21st to end	Night	20% 6% 2 5% 3 3 3 3 5% 7% 42%	3375
September	1st to 10th	Night	15% 4 2 4 3 3 3 3 4 6% 53%	2000
	11th to 20th	Night	24% 6% 2 5% 3 3 3 2 4 6% 43%	2000
	21st to end	Night	29% 7% 3 5% 3 3 4 3 3 5% 37%	2286
October	1st to 10th	Night	29% 11% 2 7% 4 3 4 3 4 5% 28%	3920
	11th to 20th	Night	40% 8% 2 4 3 3 3 3 4 5% 26%	3897
	21st to end	Night	39% 15% 3 6% 3 3 2 2 3 3 21%	4518
November	1st to 10th	Night	48% 9% 2 5% 4 3 3 2 3 4 17%	2870
	11th to 20th	Night	46% 11% 2 4 3 2 2 2 3 3 21%	2940
	21st to end	Night	43% 11% 3 6% 4 3 3 2 2 3 20%	2940
December	1st to 10th	Night	31% 11% 2 5% 3 3 3 3 5% 5% 28%	4588
	11th to 20th	Night	49% 14% 3 6% 3 3 3 2 3 3 12%	5547
	21st to end	Night	50% 17% 3 6% 3 2 2 2 2 2 11%	7458

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	79% 4 6% 8% 2 1	3179
	11th to 20th	Day	54% 5% 11% 19% 8% 3	3205
	21st to end	Day	68% 2 6% 16% 8%	4021
February	1st to 10th	Day	73% 4 7% 8% 6% 2	1800
	11th to 20th	Day	69% 5% 6% 11% 7% 2	1764
	21st to end	Day	73% 4 8% 10% 4 2	1516
March	1st to 10th	Day	71% 9% 7% 10% 4	4623
	11th to 20th	Day	69% 5% 6% 17% 3	5000
	21st to end	Day	73% 7% 9% 9% 2	5658
April	1st to 10th	Day	73% 7% 11% 7% 2	2400
	11th to 20th	Day	65% 6% 8% 11% 8% 2	2449
	21st to end	Day	66% 7% 10% 10% 6%	2677
May	1st to 10th	Day	50% 6% 14% 23% 7%	6320
	11th to 20th	Day	61% 10% 14% 12% 2	6280
	21st to end	Day	60% 9% 14% 15% 2	6986
June	1st to 10th	Day	60% 7% 14% 13% 5% 2	3000
	11th to 20th	Day	70% 7% 12% 9% 3	3000
	21st to end	Day	54% 7% 14% 16% 7% 1	3000
July	1st to 10th	Day	33% 5% 17% 22% 17% 6%	6706
	11th to 20th	Day	22% 5% 18% 34% 20% 2	6699
	21st to end	Day	31% 6% 27% 25% 9% 1	6735
August	1st to 10th	Day	25% 6% 12% 40% 16% 1	4524
	11th to 20th	Day	46% 8% 19% 18% 8% 1	4198
	21st to end	Day	49% 6% 15% 20% 9% 1	4536
September	1st to 10th	Day	43% 7% 13% 22% 11% 4	2400
	11th to 20th	Day	51% 6% 10% 18% 13% 2	2400
	21st to end	Day	55% 7% 13% 15% 9% 2	2110
October	1st to 10th	Day	60% 5% 13% 15% 7%	3280
	11th to 20th	Day	67% 4 10% 12% 7% 1	3261
	21st to end	Day	74% 5% 6% 10% 5% 1	3280
November	1st to 10th	Day	75% 5% 7% 9% 3 1	1648
	11th to 20th	Day	74% 4 7% 8% 6% 2	1680
	21st to end	Day	72% 4 5% 9% 8% 1	1680
December	1st to 10th	Day	61% 5% 8% 16% 10%	2636
	11th to 20th	Day	81% 5% 5% 7% 1 1	2658
	21st to end	Day	83% 6% 5% 5% 2	3498
January	1st to 10th	Night	77% 4 6% 9% 4 1	6766
	11th to 20th	Night	49% 6% 14% 18% 9% 3	6752
	21st to end	Night	65% 3 8% 16% 8% 1	6935
February	1st to 10th	Night	70% 5% 8% 8% 5% 3	2600
	11th to 20th	Night	69% 5% 6% 11% 7% 2	2534
	21st to end	Night	67% 4 8% 14% 6% 2	2113
March	1st to 10th	Night	67% 5% 9% 11% 7%	5256
	11th to 20th	Night	66% 5% 9% 15% 5%	5000
	21st to end	Night	74% 5% 12% 7% 2	5317
April	1st to 10th	Night	68% 7% 13% 10% 2	2000
	11th to 20th	Night	60% 6% 10% 15% 7% 2	1897
	21st to end	Night	63% 7% 12% 12% 5% 1	1721
May	1st to 10th	Night	46% 4 15% 24% 11% 1	3637
	11th to 20th	Night	53% 10% 19% 15% 3	3616
	21st to end	Night	58% 8% 16% 16% 2	3888
June	1st to 10th	Night	57% 5% 17% 13% 6% 3	1400
	11th to 20th	Night	60% 8% 15% 13% 3	1400
	21st to end	Night	47% 7% 19% 17% 7% 3	1400
July	1st to 10th	Night	27% 5% 18% 29% 14% 7%	3145
	11th to 20th	Night	15% 4 22% 35% 24% 1	3138
	21st to end	Night	25% 5% 23% 30% 15% 2	3801
August	1st to 10th	Night	19% 4 16% 38% 21% 2	2601
	11th to 20th	Night	36% 7% 27% 19% 8% 4	2924
	21st to end	Night	44% 7% 17% 21% 10% 1	3375
September	1st to 10th	Night	35% 8% 15% 23% 14% 5%	2000
	11th to 20th	Night	46% 5% 13% 17% 15% 4	2000
	21st to end	Night	52% 6% 14% 18% 8% 2	2286
October	1st to 10th	Night	60% 6% 14% 14% 6%	3920
	11th to 20th	Night	63% 4 9% 14% 9% 1	3897
	21st to end	Night	71% 4 6% 12% 6%	4518
November	1st to 10th	Night	74% 5% 7% 10% 3 1	2870
	11th to 20th	Night	72% 4 8% 8% 6% 2	2940
	21st to end	Night	72% 4 7% 7% 8% 1	2940
December	1st to 10th	Night	59% 5% 11% 17% 6% 1	4588
	11th to 20th	Night	80% 4 5% 7% 2 1	5543
	21st to end	Night	82% 4 4 6% 3 1	7458

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	48% 10% 20% 13% 8% 3	200
	11th to 20th	Day	49% 9% 15% 19% 8%	200
	21st to end	Day	49% 7% 19% 17% 8%	224
February	1st to 10th	Day	46% 12% 19% 17% 5% 1	400
	11th to 20th	Day	43% 13% 18% 22% 3 1	395
	21st to end	Day	41% 15% 23% 15% 6%	348
March	1st to 10th	Day	41% 14% 20% 18% 6% 1	500
	11th to 20th	Day	42% 13% 17% 19% 9% 1	500
	21st to end	Day	47% 14% 18% 15% 6% 1	550
April	1st to 10th	Day	41% 15% 18% 19% 6% 1	500
	11th to 20th	Day	32% 14% 26% 17% 9% 1	492
	21st to end	Day	34% 15% 23% 17% 11% 1	500
May	1st to 10th	Day	27% 14% 24% 25% 10% 1	503
	11th to 20th	Day	31% 10% 21% 24% 11% 4	528
	21st to end	Day	27% 15% 25% 21% 9% 3	603
June	1st to 10th	Day	28% 13% 25% 24% 8% 2	730
	11th to 20th	Day	32% 14% 23% 22% 8% 2	730
	21st to end	Day	25% 11% 22% 28% 12% 2	730
July	1st to 10th	Day	20% 9% 27% 31% 10% 3	721
	11th to 20th	Day	15% 9% 28% 32% 12% 3	718
	21st to end	Day	13% 7% 25% 36% 12% 6%	605
August	1st to 10th	Day	18% 9% 19% 33% 14% 7%	527
	11th to 20th	Day	15% 5% 25% 34% 16% 5%	517
	21st to end	Day	19% 12% 23% 29% 14% 3	583
September	1st to 10th	Day	23% 9% 23% 28% 14% 3	530
	11th to 20th	Day	29% 8% 19% 28% 13% 2	530
	21st to end	Day	30% 13% 20% 25% 10% 2	530
October	1st to 10th	Day	33% 9% 22% 22% 13% 2	530
	11th to 20th	Day	43% 9% 14% 20% 12% 2	530
	21st to end	Day	45% 11% 18% 17% 7% 2	427
November	1st to 10th	Day	48% 10% 18% 19% 5%	220
	11th to 20th	Day	57% 7% 10% 11% 12% 3	220
	21st to end	Day	51% 9% 18% 9% 7% 5%	220
December	1st to 10th	Day	48% 10% 12% 8% 18% 4	204
	11th to 20th	Day	57% 9% 13% 16% 4 3	200
	21st to end	Day	52% 10% 17% 16% 4	220
January	1st to 10th	Night	54% 10% 19% 13% 4	900
	11th to 20th	Night	46% 6% 22% 23% 3	893
	21st to end	Night	46% 10% 19% 21% 4	880
February	1st to 10th	Night	44% 9% 25% 18% 4	800
	11th to 20th	Night	41% 9% 22% 21% 5%	784
	21st to end	Night	40% 11% 24% 18% 7%	660
March	1st to 10th	Night	40% 9% 21% 21% 8% 1	800
	11th to 20th	Night	45% 9% 18% 21% 5%	800
	21st to end	Night	46% 9% 17% 20% 8% 1	880
April	1st to 10th	Night	39% 8% 21% 24% 9% 1	800
	11th to 20th	Night	31% 10% 26% 24% 9% 1	709
	21st to end	Night	37% 7% 21% 26% 9%	521
May	1st to 10th	Night	23% 7% 22% 31% 17% 1	400
	11th to 20th	Night	24% 4 13% 34% 22% 2	394
	21st to end	Night	25% 5% 17% 32% 20%	433
June	1st to 10th	Night	29% 5% 16% 33% 16% 2	400
	11th to 20th	Night	25% 10% 17% 27% 19% 2	400
	21st to end	Night	23% 5% 16% 31% 23% 3	400
July	1st to 10th	Night	13% 6% 10% 36% 33% 3	390
	11th to 20th	Night	11% 4 10% 35% 36% 4	388
	21st to end	Night	8% 3 8% 32% 46% 3	438
August	1st to 10th	Night	12% 2 6% 29% 45% 5%	398
	11th to 20th	Night	11% 3 8% 35% 38% 5%	589
	21st to end	Night	18% 3 13% 36% 29% 2	738
September	1st to 10th	Night	15% 3 16% 37% 27% 1	800
	11th to 20th	Night	26% 4 15% 26% 26% 3	800
	21st to end	Night	33% 6% 14% 32% 15% 1	800
October	1st to 10th	Night	32% 5% 19% 27% 15% 1	800
	11th to 20th	Night	44% 5% 19% 21% 11% 1	800
	21st to end	Night	44% 8% 22% 19% 6% 1	880
November	1st to 10th	Night	51% 10% 21% 17% 1	820
	11th to 20th	Night	52% 8% 20% 14% 5%	840
	21st to end	Night	48% 10% 19% 16% 6%	840
December	1st to 10th	Night	39% 9% 22% 24% 6%	808
	11th to 20th	Night	55% 11% 19% 13% 2	895
	21st to end	Night	52% 11% 24% 12% 1	990

Page generated at 2025-11-29 22:00:53. Version ac07

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