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 2024-03-01.

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% 5% 2 5% 5% 3 4 5% 6% 8% 45%	78515
	Night	14% 6% 3 5% 5% 3 4 4 5% 7% 43%	80906
Transparency	Day	38% 4 12% 26% 17% 3	78225
	Night	41% 3 11% 25% 17% 3	80715
Seeing	Day	18% 9% 27% 25% 15% 6%	14115
	Night	17% 9% 27% 31% 14% 2	23701

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% 5% 3 5% 4 2 4 4 4 6% 48%	2517
	11th to 20th	Day	15% 8% 3 6% 5% 3 4 4 5% 6% 40%	2814
	21st to end	Day	16% 9% 3 6% 5% 3 4 4 5% 6% 39%	3124
February	1st to 10th	Day	14% 7% 2 5% 5% 3 5% 4 6% 8% 39%	1710
	11th to 20th	Day	18% 6% 2 5% 4 2 4 4 5% 7% 44%	1787
	21st to end	Day	17% 8% 3 5% 5% 4 4 4 5% 6% 39%	1570
March	1st to 10th	Day	14% 5% 2 4 4 2 3 4 5% 7% 50%	1876
	11th to 20th	Day	17% 6% 2 5% 5% 3 4 3 4 7% 44%	1980
	21st to end	Day	17% 6% 3 6% 5% 3 5% 4 5% 6% 40%	2258
April	1st to 10th	Day	13% 6% 2 5% 5% 2 3 5% 6% 8% 46%	2160
	11th to 20th	Day	12% 5% 2 4 4 3 4 4 4 7% 50%	2134
	21st to end	Day	15% 5% 2 5% 4 3 4 4 5% 8% 45%	2160
May	1st to 10th	Day	14% 7% 2 4 4 3 4 5% 6% 9% 43%	2199
	11th to 20th	Day	15% 6% 2 4 5% 3 4 5% 6% 8% 43%	2473
	21st to end	Day	13% 5% 2 5% 5% 3 3 5% 6% 9% 44%	2725
June	1st to 10th	Day	9% 4 2 4 4 3 5% 7% 5% 10% 46%	2520
	11th to 20th	Day	10% 4 2 4 4 4 5% 6% 6% 10% 46%	2520
	21st to end	Day	8% 4 1 4 4 3 5% 5% 7% 12% 48%	2520
July	1st to 10th	Day	8% 5% 3 5% 5% 3 5% 5% 6% 10% 45%	2520
	11th to 20th	Day	5% 3 2 4 4 4 6% 6% 8% 12% 48%	2516
	21st to end	Day	7% 3 2 4 7% 3 6% 7% 8% 11% 41%	2547
August	1st to 10th	Day	9% 5% 2 5% 5% 3 5% 6% 9% 10% 41%	2327
	11th to 20th	Day	9% 4 3 5% 7% 4 5% 5% 6% 9% 43%	2139
	21st to end	Day	9% 5% 2 5% 5% 3 5% 6% 6% 9% 45%	2376
September	1st to 10th	Day	12% 5% 2 4 4 3 5% 5% 6% 8% 45%	2160
	11th to 20th	Day	11% 6% 2 5% 4 2 4 4 4 7% 50%	2160
	21st to end	Day	19% 8% 3 5% 4 2 4 4 5% 8% 38%	1932
October	1st to 10th	Day	16% 5% 2 5% 4 3 4 4 5% 7% 46%	1800
	11th to 20th	Day	18% 5% 2 3 3 2 3 3 3 6% 52%	1800
	21st to end	Day	15% 4 2 5% 4 2 3 4 5% 6% 49%	1980
November	1st to 10th	Day	13% 5% 2 3 4 2 4 4 5% 6% 52%	1703
	11th to 20th	Day	14% 5% 2 4 4 3 4 4 5% 7% 49%	1710
	21st to end	Day	15% 5% 2 5% 4 2 3 3 5% 7% 49%	1596
December	1st to 10th	Day	17% 6% 3 5% 4 3 4 4 6% 8% 41%	1520
	11th to 20th	Day	16% 7% 3 5% 4 3 3 3 4 5% 47%	1910
	21st to end	Day	16% 6% 2 6% 5% 3 5% 5% 6% 7% 40%	2772
January	1st to 10th	Night	15% 9% 3 5% 4 3 4 4 4 6% 43%	4429
	11th to 20th	Night	17% 7% 3 5% 5% 3 4 3 4 5% 45%	4143
	21st to end	Night	18% 10% 3 6% 4 2 3 4 4 5% 41%	4532
February	1st to 10th	Night	16% 6% 3 5% 6% 3 4 4 4 7% 43%	2470
	11th to 20th	Night	19% 6% 3 4 5% 2 4 3 4 7% 42%	2279
	21st to end	Night	19% 7% 3 4 4 2 4 3 5% 6% 43%	1884
March	1st to 10th	Night	14% 5% 3 4 5% 2 4 4 4 5% 49%	2089
	11th to 20th	Night	17% 6% 2 5% 4 2 4 4 5% 6% 44%	1980
	21st to end	Night	16% 8% 4 5% 4 3 4 4 4 6% 42%	2098
April	1st to 10th	Night	15% 6% 3 6% 5% 2 5% 3 5% 7% 42%	1800
	11th to 20th	Night	11% 6% 3 6% 5% 3 4 4 4 7% 48%	1775
	21st to end	Night	16% 5% 2 5% 4 3 5% 4 5% 8% 43%	1800
May	1st to 10th	Night	14% 6% 2 5% 6% 3 5% 6% 6% 9% 39%	1776
	11th to 20th	Night	14% 6% 3 5% 5% 4 5% 5% 6% 7% 39%	1420
	21st to end	Night	13% 6% 3 5% 5% 3 5% 4 6% 10% 41%	1550
June	1st to 10th	Night	11% 4 2 5% 5% 4 5% 5% 6% 10% 42%	1440
	11th to 20th	Night	9% 6% 3 6% 6% 3 5% 5% 5% 11% 42%	1440
	21st to end	Night	9% 4 3 6% 6% 3 6% 6% 7% 10% 40%	1440
July	1st to 10th	Night	9% 4 2 7% 7% 4 4 6% 6% 10% 42%	1440
	11th to 20th	Night	6% 4 2 5% 5% 4 6% 6% 8% 10% 45%	1440
	21st to end	Night	7% 4 2 6% 6% 3 6% 7% 7% 11% 41%	1771
August	1st to 10th	Night	7% 5% 2 6% 5% 4 5% 6% 8% 9% 43%	1611
	11th to 20th	Night	9% 6% 3 6% 6% 4 5% 6% 8% 8% 39%	1742
	21st to end	Night	8% 5% 3 6% 6% 4 5% 5% 7% 9% 43%	1980
September	1st to 10th	Night	14% 5% 2 5% 4 3 4 5% 5% 8% 46%	1800
	11th to 20th	Night	10% 5% 1 5% 4 2 3 5% 6% 7% 52%	1800
	21st to end	Night	18% 8% 2 6% 5% 3 4 5% 5% 7% 38%	2024
October	1st to 10th	Night	16% 6% 3 5% 6% 2 5% 4 4 5% 45%	2160
	11th to 20th	Night	17% 5% 2 5% 3 2 3 4 4 5% 49%	2160
	21st to end	Night	17% 6% 2 4 4 2 4 4 4 7% 46%	2376
November	1st to 10th	Night	12% 6% 2 6% 4 2 4 4 4 6% 52%	2375
	11th to 20th	Night	16% 7% 3 4 3 2 4 3 4 6% 48%	2470
	21st to end	Night	12% 5% 2 4 4 2 4 4 5% 7% 49%	2583
December	1st to 10th	Night	17% 8% 3 5% 5% 2 4 4 5% 7% 39%	2660
	11th to 20th	Night	17% 6% 3 6% 5% 2 4 4 5% 6% 43%	3285
	21st to end	Night	14% 8% 3 5% 5% 3 5% 5% 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	35% 3 12% 26% 20% 3	1876
	11th to 20th	Day	42% 3 11% 22% 19% 5%	1980
	21st to end	Day	44% 4 9% 22% 18% 4	2258
April	1st to 10th	Day	36% 3 12% 23% 20% 6%	2160
	11th to 20th	Day	35% 3 11% 25% 21% 6%	2134
	21st to end	Day	38% 3 12% 23% 19% 5%	2160
May	1st to 10th	Day	38% 4 14% 23% 17% 3	2199
	11th to 20th	Day	40% 4 15% 24% 14% 3	2477
	21st to end	Day	37% 5% 15% 30% 12% 1	2725
June	1st to 10th	Day	34% 5% 16% 27% 15% 2	2520
	11th to 20th	Day	34% 5% 17% 24% 17% 2	2520
	21st to end	Day	30% 6% 16% 28% 19% 2	2520
July	1st to 10th	Day	36% 5% 15% 24% 17% 3	2450
	11th to 20th	Day	28% 6% 19% 30% 14% 3	2441
	21st to end	Day	35% 6% 15% 25% 17% 2	2405
August	1st to 10th	Day	35% 5% 15% 31% 13% 1	2314
	11th to 20th	Day	38% 5% 16% 23% 16% 1	2139
	21st to end	Day	36% 5% 15% 24% 16% 4	2376
September	1st to 10th	Day	37% 5% 15% 22% 18% 4	2160
	11th to 20th	Day	35% 3 9% 27% 23% 3	2160
	21st to end	Day	45% 4 8% 21% 18% 3	1932
October	1st to 10th	Day	39% 3 10% 26% 19% 3	1800
	11th to 20th	Day	36% 2 8% 28% 22% 4	1800
	21st to end	Day	37% 3 7% 28% 21% 4	1980
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% 4	1884
March	1st to 10th	Night	38% 2 9% 28% 19% 4	2089
	11th to 20th	Night	42% 3 9% 24% 19% 3	1980
	21st to end	Night	45% 3 9% 20% 18% 6%	2098
April	1st to 10th	Night	43% 2 11% 19% 20% 5%	1800
	11th to 20th	Night	38% 2 11% 22% 20% 7%	1775
	21st to end	Night	41% 4 10% 25% 17% 4	1800
May	1st to 10th	Night	42% 5% 11% 24% 16% 3	1776
	11th to 20th	Night	43% 5% 14% 18% 18% 2	1421
	21st to end	Night	40% 5% 16% 25% 13% 1	1551
June	1st to 10th	Night	38% 6% 11% 28% 17% 1	1440
	11th to 20th	Night	38% 6% 15% 25% 14% 2	1440
	21st to end	Night	37% 5% 15% 22% 18% 2	1440
July	1st to 10th	Night	39% 5% 18% 21% 13% 4	1400
	11th to 20th	Night	32% 6% 19% 29% 12% 2	1392
	21st to end	Night	34% 6% 15% 30% 15% 1	1672
August	1st to 10th	Night	37% 4 19% 25% 14%	1600
	11th to 20th	Night	40% 6% 16% 24% 14% 1	1742
	21st to end	Night	38% 4 17% 22% 17% 3	1980
September	1st to 10th	Night	37% 5% 15% 22% 17% 5%	1800
	11th to 20th	Night	30% 5% 10% 27% 24% 4	1800
	21st to end	Night	46% 4 8% 21% 19% 3	2024
October	1st to 10th	Night	43% 3 8% 24% 19% 3	2160
	11th to 20th	Night	39% 3 8% 26% 21% 4	2160
	21st to end	Night	39% 2 7% 28% 20% 3	2376
November	1st to 10th	Night	36% 3 9% 28% 19% 5%	2375
	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% 17% 35% 19% 3	382
March	1st to 10th	Day	20% 18% 34% 24% 3 1	420
	11th to 20th	Day	23% 16% 34% 20% 4 2	420
	21st to end	Day	23% 15% 33% 21% 7% 1	462
April	1st to 10th	Day	20% 13% 39% 19% 7% 2	420
	11th to 20th	Day	14% 13% 34% 22% 15% 2	412
	21st to end	Day	23% 12% 31% 22% 10% 2	420
May	1st to 10th	Day	23% 13% 27% 22% 11% 4	423
	11th to 20th	Day	19% 8% 31% 29% 10% 3	447
	21st to end	Day	20% 3 21% 28% 19% 9%	485
June	1st to 10th	Day	13% 4 27% 32% 17% 7%	450
	11th to 20th	Day	12% 5% 24% 29% 21% 9%	450
	21st to end	Day	10% 2 26% 35% 20% 7%	450
July	1st to 10th	Day	11% 2 19% 31% 25% 13%	445
	11th to 20th	Day	5% 13% 35% 33% 14%	444
	21st to end	Day	10% 1 18% 33% 26% 11%	488
August	1st to 10th	Day	12% 2 18% 32% 26% 10%	446
	11th to 20th	Day	12% 2 14% 30% 28% 13%	439
	21st to end	Day	10% 2 17% 31% 25% 15%	495
September	1st to 10th	Day	16% 3 18% 25% 20% 18%	450
	11th to 20th	Day	14% 2 20% 29% 20% 14%	450
	21st to end	Day	27% 7% 22% 24% 14% 6%	450
October	1st to 10th	Day	19% 5% 24% 24% 19% 9%	450
	11th to 20th	Day	19% 9% 26% 25% 17% 4	450
	21st to end	Day	19% 9% 33% 24% 12% 3	495
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	19% 15% 36% 24% 6%	723
	11th to 20th	Night	22% 13% 35% 23% 7% 1	720
	21st to end	Night	20% 11% 34% 29% 6% 1	792
April	1st to 10th	Night	19% 14% 39% 22% 6%	720
	11th to 20th	Night	14% 11% 34% 33% 9%	711
	21st to end	Night	20% 9% 31% 32% 9%	720
May	1st to 10th	Night	18% 7% 31% 33% 11% 1	696
	11th to 20th	Night	17% 6% 27% 39% 11%	359
	21st to end	Night	14% 2 19% 41% 22% 2	389
June	1st to 10th	Night	13% 4 20% 42% 20% 1	360
	11th to 20th	Night	10% 3 19% 45% 22% 2	360
	21st to end	Night	11% 1 18% 47% 21% 2	360
July	1st to 10th	Night	13% 1 12% 43% 30% 3	350
	11th to 20th	Night	5% 1 7% 44% 39% 3	348
	21st to end	Night	7% 2 15% 40% 32% 4	591
August	1st to 10th	Night	10% 1 10% 41% 34% 4	537
	11th to 20th	Night	13% 2 12% 38% 31% 4	678
	21st to end	Night	11% 2 9% 38% 33% 6%	792
September	1st to 10th	Night	16% 2 13% 35% 29% 6%	720
	11th to 20th	Night	12% 2 14% 35% 31% 6%	720
	21st to end	Night	22% 4 18% 32% 21% 3	720
October	1st to 10th	Night	19% 5% 17% 31% 22% 5%	720
	11th to 20th	Night	19% 9% 23% 30% 18% 1	720
	21st to end	Night	20% 10% 27% 28% 14% 2	792
November	1st to 10th	Night	14% 7% 31% 31% 14% 3	740
	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 2024-02-27 06:30:12. Version ac07

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