Golden State Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Golden State Star Party clear sky chart from 2005-11-06 to 2026-02-16.

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	6% 8% 2 5% 3 3 3 3 4 5% 58%	139855
	Night	6% 10% 3 6% 3 3 3 3 4 5% 54%	138348
Transparency	Day	27% 4 8% 19% 23% 17%	134748
	Night	31% 5% 10% 19% 21% 13%	134443
Seeing	Day	11% 14% 27% 27% 16% 5%	16462
	Night	11% 7% 20% 38% 21% 3	25780

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	11% 21% 7% 10% 5% 4 4 3 4 4 27%	4722
	11th to 20th	Day	7% 11% 3 5% 2 3 2 2 3 5% 57%	4818
	21st to end	Day	8% 11% 3 7% 5% 4 4 3 5% 5% 44%	5843
February	1st to 10th	Day	10% 12% 3 7% 4 4 4 4 4 6% 42%	1890
	11th to 20th	Day	8% 15% 4 8% 5% 3 3 3 4 6% 41%	1886
	21st to end	Day	7% 14% 4 7% 4 4 4 4 5% 6% 40%	1650
March	1st to 10th	Day	7% 21% 8% 11% 5% 4 3 3 4 6% 29%	4579
	11th to 20th	Day	8% 14% 5% 8% 4 3 3 2 4 5% 43%	5000
	21st to end	Day	8% 17% 5% 10% 6% 4 4 3 5% 5% 33%	5739
April	1st to 10th	Day	11% 14% 4 8% 6% 4 4 3 5% 7% 35%	2400
	11th to 20th	Day	9% 11% 3 6% 4 4 4 3 5% 6% 46%	2369
	21st to end	Day	7% 10% 2 6% 4 3 3 3 5% 7% 49%	2400
May	1st to 10th	Day	6% 7% 2 4 2 2 3 3 5% 6% 60%	5981
	11th to 20th	Day	4 5% 2 5% 3 3 3 3 5% 6% 62%	6277
	21st to end	Day	5% 3 1 3 3 3 2 2 4 6% 68%	6902
June	1st to 10th	Day	7% 5% 2 5% 4 4 5% 4 6% 7% 52%	2800
	11th to 20th	Day	4 3 2 4 3 3 3 3 5% 5% 67%	2800
	21st to end	Day	3 2 1 2 3 2 3 2 3 4 77%	2800
July	1st to 10th	Day	1 1 1 1 2 2 2 2 4 84%	6319
	11th to 20th	Day	1 1 1 2 2 2 2 2 2 3 82%	6320
	21st to end	Day	2 2 1 2 2 3 4 3 4 5% 73%	6760
August	1st to 10th	Day	2 2 1 2 2 2 3 2 4 5% 76%	5777
	11th to 20th	Day	1 1 1 1 1 1 1 1 2 3 86%	5560
	21st to end	Day	3 2 1 2 2 2 2 2 4 5% 76%	5984
September	1st to 10th	Day	1 1 1 2 2 2 2 2 3 5% 78%	2400
	11th to 20th	Day	4 3 1 4 3 3 3 3 4 6% 67%	2400
	21st to end	Day	3 3 2 3 2 2 2 2 4 6% 71%	2156
October	1st to 10th	Day	4 3 1 3 2 2 3 2 4 5% 72%	3280
	11th to 20th	Day	6% 4 1 5% 3 3 2 4 5% 7% 61%	3261
	21st to end	Day	7% 7% 3 7% 4 3 4 4 6% 7% 48%	3495
November	1st to 10th	Day	11% 10% 3 6% 4 3 4 3 5% 7% 44%	1854
	11th to 20th	Day	12% 11% 3 7% 5% 4 5% 3 6% 8% 37%	1853
	21st to end	Day	8% 12% 4 6% 3 3 3 3 4 9% 45%	1680
December	1st to 10th	Day	6% 7% 3 4 3 3 3 3 5% 7% 56%	2700
	11th to 20th	Day	13% 17% 5% 10% 5% 5% 4 4 6% 6% 25%	3108
	21st to end	Day	14% 14% 4 8% 4 5% 5% 4 6% 8% 27%	4092
January	1st to 10th	Night	8% 20% 6% 10% 5% 4 4 4 5% 6% 28%	8172
	11th to 20th	Night	6% 12% 4 5% 3 2 2 2 3 4 57%	8131
	21st to end	Night	6% 13% 4 8% 5% 5% 4 3 4 5% 43%	8371
February	1st to 10th	Night	9% 13% 4 6% 4 3 4 3 4 6% 43%	2730
	11th to 20th	Night	8% 13% 4 8% 5% 5% 3 3 5% 6% 41%	2511
	21st to end	Night	8% 14% 3 8% 4 3 5% 3 4 6% 41%	1980
March	1st to 10th	Night	8% 23% 7% 9% 3 3 3 3 4 6% 32%	5300
	11th to 20th	Night	8% 16% 4 7% 4 3 3 3 4 5% 43%	5000
	21st to end	Night	7% 18% 5% 9% 5% 4 4 3 4 6% 34%	5234
April	1st to 10th	Night	8% 12% 4 7% 6% 5% 4 3 5% 8% 37%	2000
	11th to 20th	Night	9% 12% 3 5% 4 3 4 3 4 6% 47%	1979
	21st to end	Night	10% 9% 2 5% 3 3 3 3 5% 6% 51%	2000
May	1st to 10th	Night	5% 7% 2 3 2 2 3 2 4 6% 65%	3973
	11th to 20th	Night	5% 5% 2 5% 3 3 3 2 4 5% 63%	3616
	21st to end	Night	6% 4 2 3 2 2 2 2 4 5% 66%	3972
June	1st to 10th	Night	9% 6% 2 5% 4 3 4 4 5% 8% 53%	1600
	11th to 20th	Night	6% 3 1 3 3 2 3 3 3 6% 67%	1600
	21st to end	Night	3 2 1 2 3 2 3 2 3 5% 74%	1600
July	1st to 10th	Night	1 1 1 1 2 2 2 4 85%	3640
	11th to 20th	Night	1 1 1 1 1 2 1 1 2 3 85%	3640
	21st to end	Night	1 1 1 3 2 3 3 3 4 5% 74%	4093
August	1st to 10th	Night	2 2 1 3 2 2 2 2 4 7% 74%	4035
	11th to 20th	Night	2 1 1 2 1 1 1 1 2 3 86%	4299
	21st to end	Night	2 3 1 2 2 2 2 2 3 4 76%	5015
September	1st to 10th	Night	1 2 1 2 2 1 2 2 3 4 81%	2000
	11th to 20th	Night	5% 4 1 3 2 3 2 2 3 5% 71%	2000
	21st to end	Night	4 3 1 3 2 3 2 2 5% 6% 70%	2239
October	1st to 10th	Night	3 3 2 4 2 2 2 1 2 3 76%	3920
	11th to 20th	Night	6% 4 1 4 2 3 3 2 4 5% 66%	3897
	21st to end	Night	6% 6% 2 5% 3 3 3 4 6% 7% 54%	4312
November	1st to 10th	Night	11% 11% 3 6% 4 4 4 3 4 6% 44%	2665
	11th to 20th	Night	11% 10% 2 7% 5% 5% 4 4 5% 7% 39%	2762
	21st to end	Night	7% 10% 2 6% 4 4 4 3 6% 7% 47%	2940
December	1st to 10th	Night	7% 6% 1 4 3 3 3 3 4 7% 59%	4700
	11th to 20th	Night	10% 19% 6% 10% 5% 5% 6% 4 6% 7% 24%	5316
	21st to end	Night	15% 17% 5% 8% 5% 4 4 3 4 5% 29%	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	55% 7% 10% 18% 9%	4723
	11th to 20th	Day	31% 4 6% 18% 20% 21%	4818
	21st to end	Day	38% 5% 10% 15% 20% 12%	5843
February	1st to 10th	Day	42% 5% 12% 21% 15% 6%	1890
	11th to 20th	Day	43% 4 13% 21% 16% 2	1895
	21st to end	Day	42% 6% 14% 19% 13% 5%	1650
March	1st to 10th	Day	54% 6% 6% 16% 13% 3	4579
	11th to 20th	Day	39% 5% 12% 26% 18% 1	5000
	21st to end	Day	48% 7% 14% 20% 9% 2	5739
April	1st to 10th	Day	47% 6% 12% 19% 14% 3	2400
	11th to 20th	Day	37% 6% 12% 23% 17% 6%	2372
	21st to end	Day	34% 5% 15% 23% 19% 3	2400
May	1st to 10th	Day	22% 5% 7% 24% 36% 6%	5981
	11th to 20th	Day	20% 5% 9% 22% 33% 11%	6280
	21st to end	Day	17% 4 9% 31% 35% 3	6904
June	1st to 10th	Day	28% 7% 12% 24% 24% 6%	2800
	11th to 20th	Day	18% 3 9% 22% 34% 13%	2800
	21st to end	Day	13% 2 6% 19% 34% 26%	2800
July	1st to 10th	Day	6% 2 4 11% 23% 54%	6251
	11th to 20th	Day	8% 2 2 8% 21% 60%	6245
	21st to end	Day	13% 3 6% 19% 26% 33%	6563
August	1st to 10th	Day	13% 3 4 11% 26% 44%	4206
	11th to 20th	Day	5% 1 3 12% 43% 36%	4019
	21st to end	Day	9% 2 3 18% 36% 32%	4311
September	1st to 10th	Day	11% 2 4 12% 30% 42%	2400
	11th to 20th	Day	18% 3 8% 20% 31% 20%	2400
	21st to end	Day	16% 2 8% 22% 28% 24%	2156
October	1st to 10th	Day	16% 2 6% 17% 25% 34%	3280
	11th to 20th	Day	22% 3 7% 31% 29% 8%	3261
	21st to end	Day	30% 5% 11% 25% 21% 9%	3495
November	1st to 10th	Day	38% 5% 11% 19% 21% 6%	1854
	11th to 20th	Day	41% 7% 13% 21% 14% 3	1853
	21st to end	Day	35% 5% 13% 21% 19% 7%	1680
December	1st to 10th	Day	27% 5% 8% 23% 27% 9%	2700
	11th to 20th	Day	57% 8% 11% 14% 9% 2	3108
	21st to end	Day	50% 9% 14% 19% 8% 1	4092
January	1st to 10th	Night	51% 8% 14% 19% 7% 1	8172
	11th to 20th	Night	31% 4 7% 16% 18% 23%	8131
	21st to end	Night	43% 4 8% 12% 23% 10%	8371
February	1st to 10th	Night	41% 6% 12% 20% 16% 5%	2730
	11th to 20th	Night	42% 5% 14% 21% 15% 3	2513
	21st to end	Night	42% 5% 16% 19% 13% 5%	1980
March	1st to 10th	Night	51% 6% 9% 19% 11% 4	5300
	11th to 20th	Night	38% 6% 12% 23% 20% 1	5000
	21st to end	Night	46% 8% 17% 19% 9% 1	5234
April	1st to 10th	Night	42% 8% 14% 22% 11% 3	2000
	11th to 20th	Night	37% 7% 15% 20% 16% 5%	1979
	21st to end	Night	32% 7% 16% 27% 15% 2	2000
May	1st to 10th	Night	20% 6% 9% 26% 31% 8%	3970
	11th to 20th	Night	23% 5% 9% 27% 29% 7%	3616
	21st to end	Night	19% 4 13% 32% 29% 2	3972
June	1st to 10th	Night	30% 5% 15% 29% 19% 3	1600
	11th to 20th	Night	18% 5% 11% 23% 34% 9%	1600
	21st to end	Night	14% 4 5% 21% 34% 22%	1600
July	1st to 10th	Night	6% 2 4 13% 27% 49%	3600
	11th to 20th	Night	7% 1 2 9% 26% 55%	3592
	21st to end	Night	12% 3 8% 20% 26% 32%	3978
August	1st to 10th	Night	13% 2 4 13% 26% 42%	2929
	11th to 20th	Night	7% 2 3 15% 41% 32%	3111
	21st to end	Night	10% 1 3 20% 40% 25%	3608
September	1st to 10th	Night	9% 3 5% 12% 29% 43%	2000
	11th to 20th	Night	18% 3 7% 19% 32% 21%	2000
	21st to end	Night	16% 3 7% 21% 28% 25%	2239
October	1st to 10th	Night	17% 2 5% 13% 32% 31%	3920
	11th to 20th	Night	20% 4 7% 30% 29% 9%	3897
	21st to end	Night	25% 5% 10% 25% 24% 10%	4312
November	1st to 10th	Night	39% 6% 12% 19% 18% 6%	2665
	11th to 20th	Night	42% 7% 12% 20% 15% 4	2762
	21st to end	Night	34% 6% 15% 18% 20% 7%	2940
December	1st to 10th	Night	25% 5% 9% 20% 30% 12%	4700
	11th to 20th	Night	55% 8% 9% 15% 11% 1	5316
	21st to end	Night	52% 9% 13% 15% 10% 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	24% 23% 28% 20% 4	220
	11th to 20th	Day	16% 16% 26% 26% 13% 2	246
	21st to end	Day	17% 14% 26% 26% 14% 2	473
February	1st to 10th	Day	17% 19% 28% 26% 10%	430
	11th to 20th	Day	19% 24% 26% 25% 6%	454
	21st to end	Day	18% 16% 31% 27% 7%	414
March	1st to 10th	Day	21% 27% 28% 17% 7%	500
	11th to 20th	Day	22% 19% 27% 23% 9% 1	500
	21st to end	Day	20% 24% 29% 19% 7% 1	550
April	1st to 10th	Day	19% 21% 28% 22% 8% 1	500
	11th to 20th	Day	19% 19% 28% 21% 10% 2	492
	21st to end	Day	12% 22% 27% 22% 15% 2	500
May	1st to 10th	Day	12% 17% 34% 23% 11% 3	503
	11th to 20th	Day	16% 17% 30% 20% 13% 5%	528
	21st to end	Day	13% 11% 25% 27% 18% 6%	573
June	1st to 10th	Day	8% 15% 25% 25% 21% 7%	530
	11th to 20th	Day	8% 16% 33% 24% 15% 4	530
	21st to end	Day	3 10% 24% 31% 24% 8%	530
July	1st to 10th	Day	2 7% 27% 36% 21% 7%	526
	11th to 20th	Day	1 7% 27% 32% 25% 9%	524
	21st to end	Day	1 6% 26% 34% 22% 10%	575
August	1st to 10th	Day	3 6% 27% 29% 22% 13%	527
	11th to 20th	Day	2 10% 19% 32% 24% 13%	517
	21st to end	Day	2 7% 26% 31% 25% 8%	583
September	1st to 10th	Day	2 5% 29% 32% 26% 6%	530
	11th to 20th	Day	7% 9% 25% 29% 24% 7%	530
	21st to end	Day	5% 10% 27% 33% 20% 5%	530
October	1st to 10th	Day	7% 11% 28% 28% 21% 5%	530
	11th to 20th	Day	10% 12% 21% 31% 23% 5%	530
	21st to end	Day	12% 12% 25% 30% 16% 5%	544
November	1st to 10th	Day	16% 11% 20% 32% 19% 2	330
	11th to 20th	Day	11% 10% 32% 26% 17% 4	311
	21st to end	Day	13% 11% 27% 33% 15% 1	220
December	1st to 10th	Day	13% 12% 24% 30% 17% 3	220
	11th to 20th	Day	18% 17% 23% 25% 13% 4	220
	21st to end	Day	20% 18% 24% 28% 10%	242
January	1st to 10th	Night	16% 8% 28% 31% 14% 2	840
	11th to 20th	Night	14% 9% 24% 34% 18% 2	840
	21st to end	Night	16% 7% 24% 35% 16% 2	924
February	1st to 10th	Night	14% 9% 25% 37% 14% 1	840
	11th to 20th	Night	14% 10% 22% 39% 13% 1	804
	21st to end	Night	13% 12% 26% 37% 11% 1	660
March	1st to 10th	Night	22% 12% 24% 30% 11% 2	800
	11th to 20th	Night	15% 10% 23% 33% 18% 2	800
	21st to end	Night	17% 13% 26% 32% 12% 1	880
April	1st to 10th	Night	11% 11% 28% 37% 12% 1	800
	11th to 20th	Night	14% 12% 26% 28% 17% 3	791
	21st to end	Night	13% 10% 24% 34% 18% 2	800
May	1st to 10th	Night	10% 9% 29% 34% 18% 1	551
	11th to 20th	Night	10% 6% 20% 38% 21% 4	394
	21st to end	Night	13% 8% 18% 36% 24% 2	433
June	1st to 10th	Night	10% 5% 17% 43% 24% 2	400
	11th to 20th	Night	6% 6% 24% 44% 19% 1	400
	21st to end	Night	4 1 14% 52% 29% 1	400
July	1st to 10th	Night	1 1 10% 56% 32% 1	390
	11th to 20th	Night	1 1 9% 61% 28% 1	388
	21st to end	Night	1 4 53% 39% 3	486
August	1st to 10th	Night	3 1 5% 49% 40% 4	597
	11th to 20th	Night	2 1 10% 44% 38% 5%	698
	21st to end	Night	1 1 12% 46% 36% 3	880
September	1st to 10th	Night	1 2 13% 47% 33% 4	800
	11th to 20th	Night	5% 2 14% 34% 39% 6%	800
	21st to end	Night	5% 3 15% 38% 32% 7%	800
October	1st to 10th	Night	7% 4 18% 38% 29% 4	800
	11th to 20th	Night	7% 6% 14% 41% 28% 4	800
	21st to end	Night	10% 5% 17% 38% 23% 6%	880
November	1st to 10th	Night	14% 8% 18% 36% 20% 4	820
	11th to 20th	Night	13% 7% 25% 39% 14% 2	840
	21st to end	Night	12% 7% 23% 38% 18% 2	840
December	1st to 10th	Night	13% 8% 23% 36% 17% 2	840
	11th to 20th	Night	21% 8% 21% 32% 16% 1	840
	21st to end	Night	22% 14% 25% 32% 8% 1	924

Page generated at 2026-02-12 22:42:14. Version ac07

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