Golden Mean Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden Mean Observatory clear sky chart from 2005-11-06 to 2024-11-01.

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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	101141
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 42%	97766
Transparency	Day	40% 3 13% 25% 16% 3	100936
	Night	42% 3 11% 25% 16% 3	97641
Seeing	Day	18% 9% 28% 25% 15% 6%	15095
	Night	17% 9% 27% 31% 14% 2	24515

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	16% 6% 3 6% 3 3 4 3 5% 6% 47%	2517
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 4 5% 6% 40%	2814
	21st to end	Day	16% 9% 3 7% 4 4 4 3 5% 6% 39%	3124
February	1st to 10th	Day	14% 8% 2 6% 5% 5% 5% 4 6% 8% 39%	1710
	11th to 20th	Day	17% 7% 2 6% 3 3 3 3 5% 6% 44%	1787
	21st to end	Day	17% 8% 2 6% 5% 4 4 3 5% 6% 39%	1570
March	1st to 10th	Day	22% 7% 2 5% 4 3 3 4 5% 8% 37%	3265
	11th to 20th	Day	10% 4 2 4 3 4 4 3 6% 8% 54%	3480
	21st to end	Day	20% 7% 2 5% 4 3 4 3 5% 6% 41%	3964
April	1st to 10th	Day	13% 7% 2 5% 4 3 3 4 6% 8% 45%	2280
	11th to 20th	Day	11% 5% 2 4 4 4 4 3 5% 7% 50%	2254
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 7% 46%	2280
May	1st to 10th	Day	20% 9% 3 6% 3 4 4 4 6% 9% 32%	3846
	11th to 20th	Day	18% 8% 3 7% 4 5% 4 4 6% 8% 34%	4393
	21st to end	Day	9% 5% 2 5% 4 4 4 4 6% 10% 48%	4823
June	1st to 10th	Day	9% 5% 2 5% 4 4 6% 5% 6% 10% 45%	2660
	11th to 20th	Day	9% 4 1 5% 3 5% 5% 4 6% 10% 47%	2660
	21st to end	Day	7% 4 1 4 4 4 4 4 7% 11% 48%	2660
July	1st to 10th	Day	6% 4 2 6% 4 4 5% 5% 9% 13% 42%	4440
	11th to 20th	Day	10% 4 2 6% 4 5% 5% 5% 8% 11% 40%	4422
	21st to end	Day	9% 5% 3 7% 6% 5% 6% 6% 8% 10% 36%	4466
August	1st to 10th	Day	15% 6% 2 5% 4 4 5% 4 8% 11% 34%	4104
	11th to 20th	Day	9% 5% 2 7% 5% 5% 5% 4 6% 9% 43%	3743
	21st to end	Day	8% 5% 2 5% 4 3 4 4 6% 9% 50%	4180
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 7% 46%	2280
	11th to 20th	Day	11% 6% 2 6% 3 3 4 3 4 8% 49%	2280
	21st to end	Day	20% 8% 3 6% 3 3 4 3 5% 8% 37%	2038
October	1st to 10th	Day	16% 5% 2 6% 3 4 4 3 5% 6% 47%	1900
	11th to 20th	Day	17% 5% 2 3 3 3 2 3 3 6% 54%	1900
	21st to end	Day	14% 4 2 5% 4 3 3 3 4 6% 51%	2090
November	1st to 10th	Day	13% 5% 1 4 4 3 4 3 5% 6% 52%	1703
	11th to 20th	Day	13% 5% 2 4 3 4 3 4 5% 7% 49%	1710
	21st to end	Day	15% 5% 2 5% 4 3 3 3 5% 6% 49%	1596
December	1st to 10th	Day	17% 6% 2 5% 4 4 4 4 6% 8% 40%	1520
	11th to 20th	Day	15% 8% 3 5% 4 3 3 2 4 5% 47%	1910
	21st to end	Day	15% 6% 2 7% 4 4 5% 4 6% 7% 40%	2772
January	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 4 6% 43%	4429
	11th to 20th	Night	17% 7% 2 6% 5% 4 3 3 4 5% 45%	4143
	21st to end	Night	18% 10% 3 7% 4 3 3 3 4 5% 41%	4532
February	1st to 10th	Night	15% 7% 2 6% 5% 4 4 3 4 7% 43%	2470
	11th to 20th	Night	19% 7% 2 5% 4 4 4 3 5% 6% 42%	2279
	21st to end	Night	19% 8% 2 5% 3 3 3 2 5% 6% 44%	1884
March	1st to 10th	Night	21% 9% 3 6% 4 3 4 3 4 5% 38%	3586
	11th to 20th	Night	13% 5% 2 5% 4 3 3 4 5% 7% 49%	3480
	21st to end	Night	17% 8% 3 6% 3 4 3 2 4 5% 46%	3668
April	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 5% 6% 42%	1900
	11th to 20th	Night	11% 6% 2 7% 3 4 4 3 4 7% 48%	1875
	21st to end	Night	15% 6% 2 6% 4 4 4 3 6% 8% 43%	1900
May	1st to 10th	Night	18% 9% 3 7% 5% 4 5% 4 5% 7% 33%	3078
	11th to 20th	Night	19% 9% 3 7% 5% 4 4 4 6% 6% 33%	2500
	21st to end	Night	10% 5% 2 6% 4 5% 4 4 7% 10% 43%	2732
June	1st to 10th	Night	11% 5% 2 6% 6% 5% 5% 4 7% 9% 41%	1520
	11th to 20th	Night	8% 6% 2 7% 5% 4 5% 4 5% 10% 42%	1520
	21st to end	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	1520
July	1st to 10th	Night	8% 4 2 7% 6% 5% 6% 5% 7% 9% 41%	2520
	11th to 20th	Night	10% 5% 2 6% 5% 4 5% 5% 8% 10% 40%	2520
	21st to end	Night	11% 7% 3 9% 5% 5% 5% 5% 7% 8% 35%	3087
August	1st to 10th	Night	15% 7% 3 7% 4 5% 4 4 6% 8% 35%	2825
	11th to 20th	Night	11% 6% 3 7% 5% 5% 5% 4 7% 8% 38%	3052
	21st to end	Night	7% 6% 2 6% 4 4 4 3 5% 8% 51%	3476
September	1st to 10th	Night	13% 5% 2 6% 4 4 4 4 5% 7% 46%	1900
	11th to 20th	Night	10% 5% 1 5% 3 3 3 4 7% 7% 51%	1900
	21st to end	Night	18% 9% 2 7% 3 4 4 3 5% 6% 37%	2138
October	1st to 10th	Night	16% 6% 3 6% 5% 3 4 3 4 5% 45%	2280
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 4 6% 50%	2280
	21st to end	Night	16% 5% 2 4 3 3 3 3 4 7% 48%	2508
November	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 4 5% 52%	2382
	11th to 20th	Night	16% 8% 3 5% 3 3 3 3 4 6% 47%	2470
	21st to end	Night	12% 5% 2 4 4 3 4 3 5% 7% 49%	2583
December	1st to 10th	Night	17% 8% 3 6% 4 3 3 4 6% 7% 39%	2660
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 6% 43%	3285
	21st to end	Night	14% 8% 3 6% 5% 4 4 4 6% 8% 38%	4884

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	39% 2 7% 32% 17% 4	2518
	11th to 20th	Day	44% 3 9% 21% 18% 5%	2814
	21st to end	Day	48% 2 10% 25% 13% 2	3124
February	1st to 10th	Day	44% 4 11% 26% 13% 2	1710
	11th to 20th	Day	41% 3 8% 26% 18% 3	1796
	21st to end	Day	46% 2 12% 19% 17% 4	1570
March	1st to 10th	Day	47% 3 8% 23% 15% 4	3265
	11th to 20th	Day	30% 2 8% 32% 24% 4	3480
	21st to end	Day	45% 2 9% 20% 18% 4	3964
April	1st to 10th	Day	37% 3 12% 23% 20% 5%	2280
	11th to 20th	Day	35% 3 11% 25% 21% 6%	2254
	21st to end	Day	38% 3 11% 24% 19% 5%	2280
May	1st to 10th	Day	51% 4 12% 22% 10% 2	3881
	11th to 20th	Day	51% 3 13% 23% 9% 1	4397
	21st to end	Day	33% 4 13% 29% 18% 2	4837
June	1st to 10th	Day	34% 5% 16% 28% 15% 2	2660
	11th to 20th	Day	32% 5% 16% 26% 18% 2	2660
	21st to end	Day	30% 6% 16% 28% 19% 2	2660
July	1st to 10th	Day	34% 5% 27% 17% 13% 4	4370
	11th to 20th	Day	38% 4 20% 28% 9% 2	4347
	21st to end	Day	42% 5% 15% 21% 15% 1	4324
August	1st to 10th	Day	43% 3 17% 28% 7% 1	4091
	11th to 20th	Day	39% 3 13% 30% 14% 1	3779
	21st to end	Day	32% 3 13% 30% 19% 3	4180
September	1st to 10th	Day	37% 5% 14% 21% 19% 4	2280
	11th to 20th	Day	35% 3 9% 27% 23% 3	2280
	21st to end	Day	47% 4 8% 21% 17% 4	2038
October	1st to 10th	Day	39% 3 10% 25% 20% 3	1900
	11th to 20th	Day	35% 2 7% 28% 22% 5%	1900
	21st to end	Day	36% 3 7% 28% 22% 5%	2090
November	1st to 10th	Day	33% 2 9% 30% 21% 4	1703
	11th to 20th	Day	36% 3 11% 24% 22% 4	1710
	21st to end	Day	38% 2 9% 29% 19% 3	1596
December	1st to 10th	Day	43% 4 13% 25% 13% 3	1520
	11th to 20th	Day	41% 3 8% 31% 13% 4	1906
	21st to end	Day	44% 2 14% 26% 14%	2772
January	1st to 10th	Night	43% 2 7% 27% 17% 4	4429
	11th to 20th	Night	44% 2 8% 26% 17% 3	4143
	21st to end	Night	48% 2 6% 27% 16% 1	4532
February	1st to 10th	Night	43% 2 12% 25% 16% 2	2470
	11th to 20th	Night	44% 2 8% 22% 19% 5%	2281
	21st to end	Night	43% 2 9% 23% 18% 5%	1884
March	1st to 10th	Night	51% 2 7% 24% 15% 2	3586
	11th to 20th	Night	35% 3 9% 29% 21% 4	3480
	21st to end	Night	44% 2 7% 22% 20% 6%	3668
April	1st to 10th	Night	43% 2 10% 19% 21% 5%	1900
	11th to 20th	Night	38% 3 11% 23% 20% 6%	1875
	21st to end	Night	40% 4 10% 25% 17% 4	1900
May	1st to 10th	Night	52% 3 11% 23% 10% 2	3108
	11th to 20th	Night	52% 4 12% 22% 10% 1	2501
	21st to end	Night	37% 4 16% 25% 16% 3	2739
June	1st to 10th	Night	39% 5% 11% 27% 17% 1	1520
	11th to 20th	Night	37% 5% 14% 27% 14% 2	1520
	21st to end	Night	37% 5% 15% 23% 17% 3	1520
July	1st to 10th	Night	40% 7% 21% 19% 12% 2	2480
	11th to 20th	Night	38% 4 24% 26% 7% 1	2472
	21st to end	Night	46% 5% 14% 22% 13%	2988
August	1st to 10th	Night	47% 3 17% 23% 8%	2814
	11th to 20th	Night	43% 3 14% 28% 11% 1	3082
	21st to end	Night	34% 3 11% 29% 22% 2	3476
September	1st to 10th	Night	37% 5% 14% 21% 18% 5%	1900
	11th to 20th	Night	31% 5% 10% 28% 23% 3	1900
	21st to end	Night	48% 4 8% 20% 18% 3	2138
October	1st to 10th	Night	43% 3 8% 24% 19% 3	2280
	11th to 20th	Night	37% 3 8% 26% 22% 5%	2280
	21st to end	Night	37% 2 7% 29% 21% 4	2508
November	1st to 10th	Night	36% 3 9% 29% 19% 5%	2382
	11th to 20th	Night	40% 2 9% 21% 23% 5%	2470
	21st to end	Night	35% 3 11% 28% 20% 4	2583
December	1st to 10th	Night	45% 3 11% 25% 13% 3	2660
	11th to 20th	Night	43% 2 9% 23% 19% 4	3288
	21st to end	Night	45% 2 14% 26% 11% 1	4884

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	23% 19% 33% 18% 4 2	180
	11th to 20th	Day	26% 25% 32% 11% 5%	265
	21st to end	Day	20% 19% 42% 13% 5%	297
February	1st to 10th	Day	21% 19% 39% 15% 7%	270
	11th to 20th	Day	27% 20% 37% 14% 2	395
	21st to end	Day	25% 18% 36% 19% 3	382
March	1st to 10th	Day	22% 18% 33% 23% 3 1	460
	11th to 20th	Day	22% 17% 35% 19% 4 2	460
	21st to end	Day	23% 14% 35% 20% 6% 1	506
April	1st to 10th	Day	21% 15% 37% 18% 7% 2	460
	11th to 20th	Day	15% 13% 34% 22% 13% 2	452
	21st to end	Day	23% 12% 32% 22% 10% 2	460
May	1st to 10th	Day	24% 13% 26% 22% 11% 4	463
	11th to 20th	Day	19% 7% 31% 29% 10% 3	487
	21st to end	Day	19% 4 23% 28% 18% 8%	529
June	1st to 10th	Day	13% 5% 28% 31% 17% 7%	490
	11th to 20th	Day	11% 6% 24% 30% 21% 9%	490
	21st to end	Day	11% 3 26% 35% 20% 6%	490
July	1st to 10th	Day	11% 2 19% 33% 24% 12%	485
	11th to 20th	Day	5% 16% 34% 32% 12%	484
	21st to end	Day	11% 1 20% 33% 25% 10%	532
August	1st to 10th	Day	12% 2 20% 31% 25% 10%	486
	11th to 20th	Day	11% 2 17% 30% 27% 12%	479
	21st to end	Day	9% 3 17% 32% 24% 15%	539
September	1st to 10th	Day	15% 4 19% 25% 20% 16%	490
	11th to 20th	Day	14% 2 22% 29% 20% 13%	490
	21st to end	Day	29% 6% 22% 23% 14% 6%	490
October	1st to 10th	Day	18% 6% 24% 24% 18% 9%	490
	11th to 20th	Day	19% 10% 25% 25% 17% 4	490
	21st to end	Day	17% 9% 33% 24% 13% 4	539
November	1st to 10th	Day	18% 10% 27% 25% 15% 5%	381
	11th to 20th	Day	19% 14% 33% 21% 12% 2	370
	21st to end	Day	21% 14% 32% 20% 10% 3	256
December	1st to 10th	Day	18% 19% 38% 17% 6% 2	180
	11th to 20th	Day	24% 18% 33% 17% 8%	180
	21st to end	Day	23% 14% 27% 27% 8% 1	198
January	1st to 10th	Night	19% 18% 35% 23% 5%	760
	11th to 20th	Night	21% 13% 33% 27% 6%	760
	21st to end	Night	20% 16% 36% 25% 2	836
February	1st to 10th	Night	20% 12% 36% 28% 3	760
	11th to 20th	Night	23% 19% 34% 21% 1	743
	21st to end	Night	22% 17% 35% 23% 3	628
March	1st to 10th	Night	20% 15% 35% 24% 6%	760
	11th to 20th	Night	21% 14% 34% 22% 6% 1	760
	21st to end	Night	21% 12% 33% 28% 6%	836
April	1st to 10th	Night	19% 14% 40% 22% 6%	760
	11th to 20th	Night	14% 11% 35% 32% 8%	751
	21st to end	Night	19% 9% 31% 32% 9%	760
May	1st to 10th	Night	18% 7% 31% 33% 10% 1	734
	11th to 20th	Night	17% 6% 27% 40% 11%	379
	21st to end	Night	13% 2 19% 41% 21% 2	411
June	1st to 10th	Night	13% 3 21% 42% 20% 1	380
	11th to 20th	Night	9% 2 19% 45% 22% 2	380
	21st to end	Night	11% 1 18% 47% 20% 2	380
July	1st to 10th	Night	12% 1 12% 43% 30% 2	370
	11th to 20th	Night	6% 1 8% 44% 37% 3	368
	21st to end	Night	8% 2 16% 40% 31% 4	624
August	1st to 10th	Night	11% 1 11% 40% 33% 4	567
	11th to 20th	Night	13% 2 12% 39% 30% 4	717
	21st to end	Night	11% 2 10% 39% 32% 6%	836
September	1st to 10th	Night	16% 2 14% 35% 28% 5%	760
	11th to 20th	Night	13% 2 14% 36% 30% 6%	760
	21st to end	Night	23% 4 19% 31% 21% 3	760
October	1st to 10th	Night	19% 5% 17% 31% 22% 5%	760
	11th to 20th	Night	18% 9% 24% 30% 18% 1	760
	21st to end	Night	19% 9% 26% 29% 15% 2	836
November	1st to 10th	Night	14% 7% 31% 31% 14% 3	743
	11th to 20th	Night	21% 14% 27% 28% 10% 1	760
	21st to end	Night	15% 15% 29% 32% 9% 1	760
December	1st to 10th	Night	22% 14% 31% 23% 9% 1	760
	11th to 20th	Night	20% 12% 36% 26% 7%	760
	21st to end	Night	20% 11% 32% 33% 5%	836

Page generated at 2024-10-29 11:20:45. Version ac07

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