FoxStar II Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the FoxStar II Observatory clear sky chart from 2005-11-06 to 2026-07-31.

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	12% 8% 3 6% 4 4 4 3 5% 7% 44%	138054
	Night	12% 8% 3 6% 4 4 3 3 5% 6% 46%	135237
Transparency	Day	38% 5% 11% 26% 17% 3	141666
	Night	38% 4 10% 26% 18% 4	139705
Seeing	Day	18% 12% 29% 25% 13% 3	17978
	Night	17% 12% 32% 27% 11% 1	27744

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	13% 10% 4 7% 5% 4 4 3 4 6% 42%	5289
	11th to 20th	Day	6% 11% 4 8% 4 5% 4 3 4 6% 45%	5310
	21st to end	Day	16% 11% 3 7% 3 3 3 3 4 5% 42%	5812
February	1st to 10th	Day	15% 11% 3 9% 5% 5% 3 3 4 6% 36%	1890
	11th to 20th	Day	15% 9% 4 8% 5% 4 3 3 4 5% 40%	1860
	21st to end	Day	15% 10% 3 6% 4 4 4 5% 5% 6% 40%	1793
March	1st to 10th	Day	14% 10% 2 5% 3 3 3 3 4 5% 48%	5046
	11th to 20th	Day	11% 7% 2 5% 3 3 3 3 4 7% 53%	5090
	21st to end	Day	13% 11% 3 7% 5% 4 5% 4 5% 7% 35%	5583
April	1st to 10th	Day	15% 8% 2 6% 5% 4 4 3 4 7% 42%	2494
	11th to 20th	Day	16% 9% 2 6% 4 4 5% 3 5% 5% 41%	2494
	21st to end	Day	20% 8% 3 7% 6% 4 3 3 5% 7% 34%	2520
May	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 6% 7% 39%	7554
	11th to 20th	Day	13% 6% 2 7% 4 5% 4 4 5% 7% 42%	7627
	21st to end	Day	21% 8% 3 6% 5% 4 4 3 5% 7% 33%	8869
June	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	2940
	11th to 20th	Day	8% 5% 2 5% 4 5% 5% 4 7% 9% 45%	2940
	21st to end	Day	6% 4 1 5% 4 4 5% 4 6% 10% 52%	2940
July	1st to 10th	Day	9% 6% 2 7% 4 4 5% 4 5% 9% 45%	6227
	11th to 20th	Day	6% 5% 3 7% 5% 5% 5% 5% 7% 10% 42%	6030
	21st to end	Day	7% 4 2 5% 4 5% 6% 5% 8% 11% 44%	6553
August	1st to 10th	Day	4 4 1 5% 4 4 5% 4 7% 10% 52%	4234
	11th to 20th	Day	8% 6% 3 6% 4 5% 5% 4 6% 8% 46%	4082
	21st to end	Day	6% 4 2 4 3 4 4 3 5% 8% 56%	4312
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 7% 51%	2400
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 5% 7% 48%	2341
	21st to end	Day	9% 6% 2 4 5% 4 4 4 5% 7% 52%	2115
October	1st to 10th	Day	11% 5% 2 5% 3 3 4 2 4 5% 55%	2000
	11th to 20th	Day	15% 5% 2 5% 2 2 3 2 3 6% 54%	2000
	21st to end	Day	19% 8% 2 6% 3 2 2 2 4 4 47%	2200
November	1st to 10th	Day	12% 6% 2 4 3 3 3 3 4 5% 56%	2058
	11th to 20th	Day	14% 8% 2 6% 3 3 3 3 4 7% 48%	1876
	21st to end	Day	17% 9% 2 5% 3 3 3 3 4 6% 45%	1680
December	1st to 10th	Day	11% 10% 3 5% 3 2 3 3 4 5% 51%	2690
	11th to 20th	Day	12% 9% 3 6% 3 3 3 3 4 7% 47%	3088
	21st to end	Day	21% 20% 5% 8% 3 4 3 3 3 4 26%	4117
January	1st to 10th	Night	13% 11% 4 12% 5% 4 3 3 3 4 38%	7634
	11th to 20th	Night	9% 7% 3 10% 6% 5% 4 3 4 4 47%	7680
	21st to end	Night	15% 10% 3 8% 4 5% 3 3 4 5% 41%	8402
February	1st to 10th	Night	14% 12% 3 7% 4 3 3 3 6% 6% 39%	2730
	11th to 20th	Night	15% 10% 4 7% 3 3 3 3 4 6% 42%	2646
	21st to end	Night	15% 8% 3 6% 4 3 4 3 4 6% 43%	2030
March	1st to 10th	Night	17% 11% 3 6% 4 3 3 3 3 4 44%	5029
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 6% 52%	5090
	21st to end	Night	14% 8% 3 6% 5% 5% 4 3 6% 7% 39%	5588
April	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 5% 7% 51%	2124
	11th to 20th	Night	15% 7% 3 5% 3 4 3 3 4 6% 47%	2075
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 4 7% 39%	2100
May	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 5% 7% 42%	5310
	11th to 20th	Night	13% 7% 2 6% 3 4 4 3 5% 9% 45%	5265
	21st to end	Night	18% 9% 3 6% 4 4 4 3 4 7% 37%	5298
June	1st to 10th	Night	8% 4 2 4 4 4 3 3 7% 8% 51%	1680
	11th to 20th	Night	5% 4 1 4 3 4 6% 4 8% 10% 50%	1680
	21st to end	Night	4 3 1 2 4 3 3 3 7% 11% 60%	1680
July	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 7% 9% 46%	3965
	11th to 20th	Night	4 4 2 5% 4 3 5% 4 6% 10% 54%	4167
	21st to end	Night	5% 3 2 5% 4 4 4 4 7% 11% 52%	4539
August	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 9% 64%	2926
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 6% 7% 50%	2974
	21st to end	Night	4 3 1 4 3 3 3 3 6% 9% 62%	3586
September	1st to 10th	Night	11% 4 2 4 4 3 3 3 5% 6% 55%	2000
	11th to 20th	Night	10% 4 2 4 4 3 4 3 5% 8% 53%	2055
	21st to end	Night	8% 5% 2 5% 3 3 3 3 4 7% 57%	2264
October	1st to 10th	Night	8% 4 1 3 3 3 2 3 5% 7% 61%	2400
	11th to 20th	Night	15% 5% 1 4 3 3 3 3 3 6% 55%	2400
	21st to end	Night	17% 7% 2 5% 2 3 2 3 3 6% 49%	2640
November	1st to 10th	Night	12% 5% 2 4 3 3 2 3 4 5% 58%	2460
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 3 6% 52%	2735
	21st to end	Night	16% 10% 2 5% 3 3 2 2 3 5% 47%	2940
December	1st to 10th	Night	10% 8% 2 6% 4 3 3 2 4 5% 50%	4720
	11th to 20th	Night	16% 9% 3 6% 3 3 3 2 4 5% 44%	5339
	21st to end	Night	23% 18% 5% 8% 4 4 3 2 3 4 28%	7086

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% 2 8% 27% 15% 2	5290
	11th to 20th	Day	40% 3 8% 29% 15% 5%	5310
	21st to end	Day	46% 2 8% 19% 17% 8%	5812
February	1st to 10th	Day	51% 4 10% 23% 12% 1	1890
	11th to 20th	Day	46% 3 12% 19% 15% 4	1869
	21st to end	Day	45% 4 7% 23% 17% 5%	1793
March	1st to 10th	Day	40% 3 7% 22% 19% 8%	5046
	11th to 20th	Day	32% 3 8% 24% 23% 9%	5090
	21st to end	Day	47% 5% 15% 25% 7% 1	5585
April	1st to 10th	Day	43% 4 10% 24% 16% 2	2494
	11th to 20th	Day	44% 4 13% 22% 15% 2	2494
	21st to end	Day	50% 4 11% 23% 10% 1	2520
May	1st to 10th	Day	44% 5% 12% 23% 15% 1	7592
	11th to 20th	Day	40% 6% 12% 23% 17% 2	7631
	21st to end	Day	50% 6% 10% 23% 12% 1	8883
June	1st to 10th	Day	34% 6% 17% 25% 17% 1	2940
	11th to 20th	Day	33% 6% 14% 31% 14% 3	2940
	21st to end	Day	27% 6% 17% 31% 16% 4	2940
July	1st to 10th	Day	35% 6% 13% 23% 21% 2	6163
	11th to 20th	Day	34% 8% 15% 30% 12% 2	5961
	21st to end	Day	29% 8% 21% 32% 10% 1	6371
August	1st to 10th	Day	25% 6% 19% 28% 21% 1	4220
	11th to 20th	Day	35% 6% 15% 29% 14% 1	4121
	21st to end	Day	26% 6% 13% 37% 14% 4	4311
September	1st to 10th	Day	33% 4 12% 27% 18% 6%	2400
	11th to 20th	Day	35% 5% 8% 26% 24% 2	2341
	21st to end	Day	31% 5% 8% 26% 24% 4	2115
October	1st to 10th	Day	19% 2 5% 20% 39% 14%	3260
	11th to 20th	Day	22% 2 5% 25% 36% 10%	3240
	21st to end	Day	32% 3 7% 28% 25% 4	3538
November	1st to 10th	Day	32% 3 10% 28% 23% 4	2058
	11th to 20th	Day	38% 3 9% 23% 23% 5%	1876
	21st to end	Day	42% 4 8% 28% 17% 2	1680
December	1st to 10th	Day	35% 3 9% 37% 15% 1	2690
	11th to 20th	Day	39% 3 8% 29% 19% 2	3085
	21st to end	Day	63% 3 9% 17% 7% 1	4117
January	1st to 10th	Night	52% 3 9% 24% 11% 1	7635
	11th to 20th	Night	41% 4 6% 27% 19% 3	7680
	21st to end	Night	48% 3 9% 21% 16% 4	8402
February	1st to 10th	Night	45% 3 11% 24% 14% 2	2730
	11th to 20th	Night	44% 3 10% 25% 16% 3	2647
	21st to end	Night	42% 3 8% 23% 19% 6%	2030
March	1st to 10th	Night	46% 3 7% 18% 22% 5%	5029
	11th to 20th	Night	34% 3 8% 22% 24% 8%	5090
	21st to end	Night	43% 5% 14% 25% 12% 1	5588
April	1st to 10th	Night	34% 3 14% 24% 21% 4	2124
	11th to 20th	Night	39% 3 11% 23% 19% 5%	2075
	21st to end	Night	44% 5% 11% 25% 14% 1	2100
May	1st to 10th	Night	42% 6% 12% 25% 14% 2	5337
	11th to 20th	Night	37% 5% 11% 24% 17% 5%	5266
	21st to end	Night	48% 6% 10% 22% 12% 2	5309
June	1st to 10th	Night	28% 5% 17% 29% 18% 3	1680
	11th to 20th	Night	27% 6% 15% 29% 21% 3	1680
	21st to end	Night	18% 5% 18% 33% 21% 5%	1680
July	1st to 10th	Night	33% 6% 13% 24% 20% 3	3922
	11th to 20th	Night	25% 8% 13% 37% 16% 2	4116
	21st to end	Night	24% 7% 19% 38% 12% 1	4410
August	1st to 10th	Night	17% 6% 18% 34% 24% 2	2916
	11th to 20th	Night	33% 6% 13% 29% 17% 2	3001
	21st to end	Night	20% 4 15% 39% 18% 4	3586
September	1st to 10th	Night	30% 4 10% 28% 21% 7%	2000
	11th to 20th	Night	30% 5% 10% 25% 25% 5%	2055
	21st to end	Night	28% 4 9% 27% 28% 4	2264
October	1st to 10th	Night	14% 2 6% 21% 43% 14%	3920
	11th to 20th	Night	22% 3 6% 22% 28% 18%	3899
	21st to end	Night	31% 3 6% 31% 25% 4	4252
November	1st to 10th	Night	31% 2 10% 28% 23% 6%	2460
	11th to 20th	Night	36% 3 7% 26% 23% 6%	2735
	21st to end	Night	42% 2 8% 26% 19% 3	2940
December	1st to 10th	Night	38% 3 9% 34% 15% 1	4720
	11th to 20th	Night	43% 2 9% 25% 19% 2	5341
	21st to end	Night	62% 3 10% 17% 6% 1	7086

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	21% 19% 43% 16% 1	330
	11th to 20th	Day	27% 24% 41% 8% 1	330
	21st to end	Day	20% 24% 44% 10% 2	363
February	1st to 10th	Day	26% 24% 37% 12% 2	330
	11th to 20th	Day	28% 25% 33% 12% 1	330
	21st to end	Day	28% 25% 37% 8% 2	273
March	1st to 10th	Day	28% 22% 36% 12% 2	330
	11th to 20th	Day	33% 18% 36% 12% 1	330
	21st to end	Day	31% 23% 35% 8% 2	363
April	1st to 10th	Day	26% 21% 34% 15% 4	514
	11th to 20th	Day	28% 22% 34% 14% 3	532
	21st to end	Day	26% 15% 37% 16% 5%	540
May	1st to 10th	Day	23% 16% 36% 20% 5%	729
	11th to 20th	Day	20% 13% 32% 25% 9% 1	775
	21st to end	Day	18% 9% 33% 25% 11% 3	844
June	1st to 10th	Day	11% 6% 26% 32% 19% 5%	780
	11th to 20th	Day	9% 6% 27% 36% 19% 2	780
	21st to end	Day	8% 6% 34% 36% 15% 2	780
July	1st to 10th	Day	10% 4 17% 34% 28% 7%	771
	11th to 20th	Day	6% 3 21% 39% 25% 5%	768
	21st to end	Day	10% 2 16% 39% 27% 6%	845
August	1st to 10th	Day	8% 2 19% 42% 24% 4	726
	11th to 20th	Day	10% 3 18% 38% 25% 5%	665
	21st to end	Day	11% 3 16% 33% 28% 9%	583
September	1st to 10th	Day	11% 4 16% 38% 25% 5%	530
	11th to 20th	Day	9% 2 22% 37% 24% 6%	471
	21st to end	Day	12% 7% 29% 30% 16% 5%	330
October	1st to 10th	Day	13% 9% 30% 29% 15% 4	330
	11th to 20th	Day	17% 17% 38% 22% 6% 1	330
	21st to end	Day	33% 16% 32% 17% 3	363
November	1st to 10th	Day	19% 13% 45% 16% 5% 2	330
	11th to 20th	Day	20% 21% 34% 18% 5% 1	330
	21st to end	Day	31% 17% 28% 18% 5%	330
December	1st to 10th	Day	21% 22% 35% 15% 6% 2	330
	11th to 20th	Day	24% 20% 37% 15% 4 1	330
	21st to end	Day	28% 26% 34% 10% 1	363
January	1st to 10th	Night	20% 19% 37% 20% 4	1050
	11th to 20th	Night	20% 24% 37% 16% 3	1050
	21st to end	Night	18% 21% 39% 21% 2	1155
February	1st to 10th	Night	20% 19% 41% 17% 3	1050
	11th to 20th	Night	23% 19% 38% 18% 2	1012
	21st to end	Night	23% 21% 38% 15% 2	646
March	1st to 10th	Night	22% 17% 38% 20% 3	630
	11th to 20th	Night	25% 14% 36% 21% 4	630
	21st to end	Night	26% 16% 37% 18% 3	693
April	1st to 10th	Night	17% 18% 40% 21% 4	630
	11th to 20th	Night	20% 15% 37% 23% 5%	623
	21st to end	Night	23% 10% 38% 23% 6%	630
May	1st to 10th	Night	16% 8% 39% 30% 7%	630
	11th to 20th	Night	18% 8% 29% 32% 13% 1	621
	21st to end	Night	16% 8% 29% 30% 16% 2	683
June	1st to 10th	Night	10% 4 21% 39% 23% 2	630
	11th to 20th	Night	8% 2 27% 42% 20% 2	630
	21st to end	Night	5% 3 31% 43% 17% 1	630
July	1st to 10th	Night	11% 2 15% 40% 30% 3	615
	11th to 20th	Night	3 2 19% 45% 28% 2	612
	21st to end	Night	8% 1 16% 40% 33% 2	687
August	1st to 10th	Night	7% 1 16% 45% 29% 2	597
	11th to 20th	Night	7% 2 16% 45% 27% 3	594
	21st to end	Night	5% 2 15% 39% 35% 4	660
September	1st to 10th	Night	12% 2 16% 41% 26% 3	600
	11th to 20th	Night	13% 2 17% 37% 28% 4	600
	21st to end	Night	11% 5% 22% 38% 20% 3	664
October	1st to 10th	Night	10% 6% 28% 32% 22% 3	800
	11th to 20th	Night	19% 9% 37% 27% 9%	800
	21st to end	Night	21% 13% 35% 23% 7%	880
November	1st to 10th	Night	14% 12% 40% 24% 8%	820
	11th to 20th	Night	18% 15% 36% 24% 6%	887
	21st to end	Night	24% 14% 36% 20% 5%	1050
December	1st to 10th	Night	21% 14% 40% 21% 5%	1050
	11th to 20th	Night	24% 15% 36% 22% 4	1050
	21st to end	Night	23% 19% 36% 19% 2	1155

Page generated at 2026-07-28 02:25:25. Version ac07

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