Stargazer's Field Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargazer's Field Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	14% 7% 3 7% 5% 4 5% 4 6% 7% 39%	119642
	Night	14% 7% 3 6% 4 4 4 3 5% 7% 43%	118617
Transparency	Day	41% 6% 10% 21% 17% 4	123433
	Night	39% 5% 9% 21% 20% 6%	122964
Seeing	Day	18% 11% 23% 22% 18% 8%	15294
	Night	17% 9% 20% 30% 21% 4	25333

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	18% 10% 5% 6% 3 3 3 3 5% 5% 40%	4056
	11th to 20th	Day	16% 6% 6% 9% 3 2 3 2 3 5% 45%	4078
	21st to end	Day	21% 10% 4 6% 3 3 3 3 5% 6% 36%	4972
February	1st to 10th	Day	19% 9% 3 6% 4 3 3 3 5% 5% 38%	2000
	11th to 20th	Day	22% 8% 2 7% 4 4 3 3 4 4 36%	1948
	21st to end	Day	22% 7% 3 6% 4 3 4 3 5% 5% 38%	1650
March	1st to 10th	Day	19% 9% 3 7% 5% 5% 4 4 5% 5% 33%	4480
	11th to 20th	Day	13% 7% 3 6% 4 3 4 3 5% 6% 46%	4814
	21st to end	Day	14% 7% 3 8% 4 5% 4 4 5% 7% 41%	5681
April	1st to 10th	Day	14% 7% 2 6% 4 4 5% 3 6% 7% 43%	2400
	11th to 20th	Day	13% 7% 2 7% 4 3 4 4 5% 7% 46%	2374
	21st to end	Day	10% 6% 2 6% 5% 4 5% 4 5% 8% 44%	2420
May	1st to 10th	Day	17% 7% 3 7% 5% 5% 5% 5% 7% 8% 32%	5862
	11th to 20th	Day	15% 9% 3 9% 6% 5% 6% 5% 6% 8% 28%	5861
	21st to end	Day	15% 7% 3 7% 5% 4 5% 4 6% 7% 39%	6433
June	1st to 10th	Day	9% 6% 2 6% 5% 6% 7% 6% 8% 10% 35%	2587
	11th to 20th	Day	5% 5% 1 5% 5% 4 6% 5% 8% 10% 45%	2470
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 6% 7% 9% 41%	2470
July	1st to 10th	Day	7% 5% 2 8% 6% 7% 7% 6% 10% 12% 29%	4120
	11th to 20th	Day	9% 5% 3 6% 6% 6% 7% 6% 9% 11% 32%	4120
	21st to end	Day	14% 11% 4 10% 7% 6% 6% 5% 7% 8% 22%	4466
August	1st to 10th	Day	4 3 1 5% 5% 5% 5% 4 7% 11% 48%	3831
	11th to 20th	Day	5% 4 2 6% 6% 5% 6% 6% 8% 9% 43%	3729
	21st to end	Day	7% 4 2 5% 4 5% 6% 4 5% 7% 51%	4180
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 6% 5% 6% 10% 39%	2223
	11th to 20th	Day	11% 5% 3 6% 5% 4 5% 4 6% 9% 41%	2090
	21st to end	Day	11% 6% 2 6% 4 4 4 4 5% 7% 48%	2090
October	1st to 10th	Day	10% 5% 1 5% 4 4 4 3 3 5% 56%	2090
	11th to 20th	Day	10% 4 2 5% 3 4 4 3 5% 6% 54%	2090
	21st to end	Day	14% 5% 1 5% 4 4 3 3 4 6% 52%	1926
November	1st to 10th	Day	12% 6% 2 5% 2 3 5% 3 4 6% 52%	1762
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 5% 6% 50%	1800
	21st to end	Day	16% 7% 3 5% 3 4 4 4 5% 7% 44%	1800
December	1st to 10th	Day	17% 8% 2 6% 4 4 3 3 4 5% 43%	2930
	11th to 20th	Day	20% 11% 4 7% 5% 4 4 3 4 5% 34%	3373
	21st to end	Day	19% 9% 5% 7% 5% 4 4 3 5% 7% 33%	4466
January	1st to 10th	Night	16% 11% 3 8% 4 3 3 2 4 4 41%	5889
	11th to 20th	Night	18% 8% 4 8% 3 2 3 2 3 4 44%	5877
	21st to end	Night	20% 10% 2 5% 3 3 3 3 4 5% 41%	5984
February	1st to 10th	Night	19% 9% 3 6% 4 3 3 3 4 6% 41%	2400
	11th to 20th	Night	23% 7% 3 6% 4 4 3 3 4 4 39%	2338
	21st to end	Night	22% 7% 2 6% 4 4 5% 3 5% 5% 38%	1980
March	1st to 10th	Night	24% 9% 3 7% 4 4 4 3 4 6% 31%	5373
	11th to 20th	Night	11% 6% 2 5% 3 4 4 4 6% 7% 48%	5146
	21st to end	Night	16% 7% 3 8% 5% 5% 4 3 4 4 42%	5289
April	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 6% 8% 46%	2000
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 8% 49%	1975
	21st to end	Night	11% 6% 2 5% 4 4 3 3 6% 6% 49%	1979
May	1st to 10th	Night	13% 8% 3 8% 6% 5% 5% 4 7% 8% 34%	4033
	11th to 20th	Night	18% 9% 4 9% 6% 4 5% 4 5% 7% 29%	4032
	21st to end	Night	12% 7% 2 7% 4 4 5% 4 6% 9% 39%	4421
June	1st to 10th	Night	7% 6% 2 7% 6% 4 5% 5% 6% 11% 40%	1797
	11th to 20th	Night	5% 3 1 3 4 4 5% 5% 7% 12% 52%	1710
	21st to end	Night	6% 5% 2 5% 4 4 5% 5% 7% 11% 46%	1710
July	1st to 10th	Night	7% 6% 3 8% 7% 6% 6% 5% 8% 10% 35%	2840
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 11% 39%	2840
	21st to end	Night	10% 9% 5% 11% 7% 6% 6% 5% 7% 9% 25%	3087
August	1st to 10th	Night	2 3 1 4 3 3 4 4 7% 12% 57%	3080
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 7% 9% 51%	3100
	21st to end	Night	6% 4 1 4 3 3 4 3 6% 7% 59%	3476
September	1st to 10th	Night	8% 6% 2 5% 4 4 4 4 6% 8% 49%	1937
	11th to 20th	Night	10% 6% 3 6% 5% 4 4 3 6% 9% 44%	2090
	21st to end	Night	9% 6% 2 6% 4 3 3 3 5% 7% 52%	2090
October	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 6% 60%	2090
	11th to 20th	Night	12% 6% 2 6% 4 4 3 2 4 5% 53%	2090
	21st to end	Night	14% 6% 1 5% 3 2 3 3 4 5% 53%	2666
November	1st to 10th	Night	12% 5% 2 4 3 4 4 3 5% 6% 52%	2536
	11th to 20th	Night	12% 6% 3 5% 4 4 3 3 5% 6% 51%	2600
	21st to end	Night	15% 8% 2 6% 4 3 3 3 5% 6% 46%	2600
December	1st to 10th	Night	20% 7% 2 5% 3 3 3 3 4 5% 45%	4250
	11th to 20th	Night	22% 9% 3 6% 3 3 3 2 4 5% 40%	4822
	21st to end	Night	19% 10% 4 7% 4 4 4 3 4 6% 34%	6490

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	46% 4 6% 21% 21% 2	4057
	11th to 20th	Day	43% 4 5% 22% 25% 1	4078
	21st to end	Day	49% 4 6% 20% 18% 3	4972
February	1st to 10th	Day	48% 4 7% 20% 18% 3	2000
	11th to 20th	Day	52% 4 5% 18% 16% 4	1958
	21st to end	Day	49% 4 7% 15% 20% 6%	1650
March	1st to 10th	Day	52% 4 7% 12% 17% 8%	4480
	11th to 20th	Day	39% 4 6% 20% 20% 12%	4814
	21st to end	Day	43% 4 10% 24% 17% 2	5683
April	1st to 10th	Day	39% 5% 11% 24% 16% 5%	2400
	11th to 20th	Day	38% 5% 6% 23% 22% 6%	2374
	21st to end	Day	38% 6% 10% 27% 17% 3	2420
May	1st to 10th	Day	46% 9% 13% 21% 10% 2	5897
	11th to 20th	Day	50% 8% 14% 20% 8%	5865
	21st to end	Day	43% 7% 8% 23% 16% 2	6447
June	1st to 10th	Day	40% 9% 13% 21% 14% 1	2587
	11th to 20th	Day	30% 8% 18% 25% 17% 2	2470
	21st to end	Day	35% 10% 18% 20% 14% 3	2470
July	1st to 10th	Day	40% 12% 19% 22% 5% 1	4055
	11th to 20th	Day	39% 11% 21% 22% 6% 1	4051
	21st to end	Day	57% 9% 13% 16% 5%	4324
August	1st to 10th	Day	27% 8% 13% 36% 16% 1	3818
	11th to 20th	Day	32% 9% 15% 26% 15% 3	3765
	21st to end	Day	29% 8% 13% 25% 23% 2	4179
September	1st to 10th	Day	38% 8% 15% 18% 17% 5%	2223
	11th to 20th	Day	38% 8% 11% 20% 21% 3	2090
	21st to end	Day	35% 5% 11% 22% 20% 7%	2090
October	1st to 10th	Day	22% 4 4 15% 39% 16%	3480
	11th to 20th	Day	21% 3 5% 19% 31% 21%	3458
	21st to end	Day	27% 4 6% 23% 30% 10%	3150
November	1st to 10th	Day	34% 4 8% 19% 28% 7%	1762
	11th to 20th	Day	36% 4 6% 21% 26% 8%	1800
	21st to end	Day	40% 5% 5% 21% 24% 5%	1800
December	1st to 10th	Day	44% 4 4 20% 24% 4	2930
	11th to 20th	Day	54% 4 5% 20% 13% 3	3370
	21st to end	Day	51% 5% 8% 23% 12% 2	4466
January	1st to 10th	Night	47% 3 6% 20% 21% 3	5889
	11th to 20th	Night	45% 4 5% 18% 23% 5%	5877
	21st to end	Night	46% 3 4 20% 21% 6%	5984
February	1st to 10th	Night	46% 3 7% 20% 20% 4	2400
	11th to 20th	Night	49% 4 6% 18% 16% 7%	2339
	21st to end	Night	48% 5% 6% 16% 18% 7%	1980
March	1st to 10th	Night	54% 4 5% 14% 18% 5%	5373
	11th to 20th	Night	35% 4 7% 17% 22% 14%	5146
	21st to end	Night	46% 3 7% 21% 19% 4	5289
April	1st to 10th	Night	34% 6% 12% 23% 20% 5%	2000
	11th to 20th	Night	34% 4 7% 22% 22% 10%	1975
	21st to end	Night	35% 5% 11% 27% 18% 4	1979
May	1st to 10th	Night	45% 9% 13% 19% 13% 1	4060
	11th to 20th	Night	52% 8% 13% 18% 9%	4033
	21st to end	Night	39% 9% 13% 23% 16% 1	4429
June	1st to 10th	Night	37% 8% 14% 22% 18% 2	1797
	11th to 20th	Night	24% 8% 18% 29% 20% 2	1710
	21st to end	Night	29% 9% 18% 23% 17% 5%	1710
July	1st to 10th	Night	41% 9% 21% 21% 7% 2	2795
	11th to 20th	Night	34% 10% 24% 23% 7% 2	2786
	21st to end	Night	54% 10% 14% 15% 7% 1	2988
August	1st to 10th	Night	18% 8% 14% 37% 21% 1	3069
	11th to 20th	Night	27% 8% 19% 28% 16% 2	3130
	21st to end	Night	24% 6% 14% 25% 28% 3	3476
September	1st to 10th	Night	31% 8% 18% 21% 17% 6%	1937
	11th to 20th	Night	35% 8% 14% 17% 23% 3	2090
	21st to end	Night	32% 5% 9% 22% 22% 9%	2090
October	1st to 10th	Night	20% 4 5% 18% 35% 19%	3480
	11th to 20th	Night	22% 2 4 17% 32% 23%	3461
	21st to end	Night	24% 3 4 27% 29% 14%	4392
November	1st to 10th	Night	34% 5% 7% 21% 23% 10%	2536
	11th to 20th	Night	34% 4 5% 19% 28% 10%	2600
	21st to end	Night	40% 3 6% 21% 23% 6%	2600
December	1st to 10th	Night	42% 3 5% 21% 25% 3	4250
	11th to 20th	Night	48% 3 5% 19% 22% 4	4824
	21st to end	Night	51% 5% 7% 24% 13% 1	6490

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	32% 25% 27% 14% 2	300
	11th to 20th	Day	31% 24% 28% 11% 5%	300
	21st to end	Day	24% 28% 30% 15% 2	330
February	1st to 10th	Day	28% 24% 32% 13% 4	300
	11th to 20th	Day	40% 20% 30% 8% 1 1	300
	21st to end	Day	39% 19% 33% 9% 1	249
March	1st to 10th	Day	31% 23% 29% 13% 3 1	300
	11th to 20th	Day	26% 20% 29% 19% 4 1	425
	21st to end	Day	25% 19% 32% 18% 6% 1	550
April	1st to 10th	Day	26% 16% 27% 19% 11% 1	500
	11th to 20th	Day	22% 15% 30% 22% 10% 1	492
	21st to end	Day	19% 13% 30% 25% 12% 1	500
May	1st to 10th	Day	18% 11% 31% 24% 12% 5%	503
	11th to 20th	Day	12% 10% 28% 27% 15% 8%	527
	21st to end	Day	15% 8% 20% 30% 16% 12%	573
June	1st to 10th	Day	13% 7% 18% 26% 26% 10%	526
	11th to 20th	Day	6% 4 18% 26% 26% 21%	490
	21st to end	Day	11% 4 16% 24% 29% 15%	490
July	1st to 10th	Day	12% 2 12% 23% 31% 20%	485
	11th to 20th	Day	9% 2 11% 23% 30% 25%	484
	21st to end	Day	12% 2 9% 25% 31% 21%	532
August	1st to 10th	Day	12% 2 9% 25% 33% 19%	486
	11th to 20th	Day	11% 3 11% 28% 34% 12%	479
	21st to end	Day	14% 3 10% 22% 34% 17%	539
September	1st to 10th	Day	11% 3 12% 31% 31% 12%	490
	11th to 20th	Day	11% 4 15% 26% 30% 14%	490
	21st to end	Day	17% 4 15% 28% 31% 6%	490
October	1st to 10th	Day	12% 4 25% 29% 21% 9%	490
	11th to 20th	Day	13% 10% 28% 30% 18% 2	490
	21st to end	Day	20% 11% 23% 30% 14% 2	354
November	1st to 10th	Day	18% 9% 35% 24% 12% 2	300
	11th to 20th	Day	17% 17% 39% 21% 6%	300
	21st to end	Day	21% 20% 30% 18% 11% 1	300
December	1st to 10th	Day	32% 17% 29% 16% 5%	300
	11th to 20th	Day	26% 23% 30% 13% 8%	300
	21st to end	Day	31% 17% 31% 16% 5%	330
January	1st to 10th	Night	28% 16% 29% 22% 5%	800
	11th to 20th	Night	27% 18% 27% 22% 7%	800
	21st to end	Night	22% 14% 32% 28% 4	880
February	1st to 10th	Night	23% 14% 29% 30% 5%	800
	11th to 20th	Night	29% 17% 27% 25% 2	783
	21st to end	Night	29% 16% 28% 25% 2	660
March	1st to 10th	Night	23% 16% 26% 31% 5%	800
	11th to 20th	Night	20% 12% 30% 30% 8% 1	800
	21st to end	Night	21% 12% 29% 29% 10%	805
April	1st to 10th	Night	15% 12% 29% 31% 13%	600
	11th to 20th	Night	16% 10% 30% 29% 13% 1	593
	21st to end	Night	16% 9% 23% 37% 15% 1	600
May	1st to 10th	Night	15% 6% 24% 34% 20% 3	600
	11th to 20th	Night	15% 5% 20% 32% 25% 4	591
	21st to end	Night	9% 2 14% 39% 31% 6%	650
June	1st to 10th	Night	9% 3 15% 32% 36% 6%	599
	11th to 20th	Night	5% 2 8% 33% 42% 11%	570
	21st to end	Night	8% 1 8% 32% 43% 9%	570
July	1st to 10th	Night	10% 2 8% 27% 39% 15%	555
	11th to 20th	Night	10% 1 6% 25% 41% 18%	552
	21st to end	Night	10% 1 6% 24% 46% 13%	624
August	1st to 10th	Night	5% 1 4 25% 54% 11%	567
	11th to 20th	Night	10% 3 7% 29% 43% 7%	564
	21st to end	Night	11% 2 7% 27% 43% 9%	627
September	1st to 10th	Night	11% 3 9% 26% 43% 8%	607
	11th to 20th	Night	12% 3 14% 29% 36% 6%	760
	21st to end	Night	11% 3 13% 31% 39% 2	760
October	1st to 10th	Night	11% 5% 18% 32% 29% 6%	760
	11th to 20th	Night	16% 6% 24% 32% 21% 1	760
	21st to end	Night	18% 8% 18% 35% 19% 2	836
November	1st to 10th	Night	15% 9% 19% 35% 19% 3	780
	11th to 20th	Night	16% 10% 27% 32% 14% 1	800
	21st to end	Night	21% 12% 24% 30% 13% 1	800
December	1st to 10th	Night	25% 14% 25% 29% 7%	800
	11th to 20th	Night	24% 12% 26% 29% 9%	800
	21st to end	Night	29% 11% 25% 29% 5%	880

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