FoxStar Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the FoxStar Observatory clear sky chart from 2005-11-06 to 2025-12-03.

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% 7% 3 6% 4 4 4 3 5% 7% 45%	126720
	Night	12% 7% 3 6% 4 4 4 3 5% 6% 47%	124233
Transparency	Day	38% 3 12% 26% 17% 3	130332
	Night	37% 3 11% 26% 19% 4	128697
Seeing	Day	15% 10% 29% 27% 15% 4	17133
	Night	14% 9% 32% 31% 12% 1	26968

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% 9% 3 9% 4 5% 4 3 4 5% 37%	4077
	11th to 20th	Day	8% 8% 4 9% 7% 7% 6% 3 3 4 41%	4080
	21st to end	Day	14% 13% 4 8% 5% 4 4 3 4 4 37%	4488
February	1st to 10th	Day	15% 12% 4 8% 5% 3 3 3 5% 7% 36%	1800
	11th to 20th	Day	14% 11% 3 7% 4 4 4 3 4 6% 40%	1754
	21st to end	Day	12% 8% 3 7% 4 3 4 3 5% 6% 45%	1695
March	1st to 10th	Day	13% 10% 3 6% 3 3 2 2 3 4 51%	4936
	11th to 20th	Day	10% 6% 2 5% 3 3 3 3 4 6% 55%	4980
	21st to end	Day	14% 11% 4 7% 5% 4 5% 3 6% 7% 35%	5462
April	1st to 10th	Day	15% 7% 3 6% 4 4 4 3 4 7% 44%	2335
	11th to 20th	Day	15% 9% 2 7% 5% 4 4 3 5% 6% 40%	2374
	21st to end	Day	20% 7% 3 8% 5% 4 5% 4 4 6% 34%	2502
May	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 5% 7% 42%	5862
	11th to 20th	Day	15% 6% 3 6% 4 4 4 3 5% 7% 44%	5862
	21st to end	Day	19% 6% 2 5% 4 4 4 3 5% 7% 41%	6747
June	1st to 10th	Day	8% 5% 2 4 4 4 4 5% 7% 11% 48%	2800
	11th to 20th	Day	8% 5% 2 6% 5% 3 5% 4 6% 9% 47%	2800
	21st to end	Day	7% 3 2 4 4 4 5% 4 7% 9% 52%	2800
July	1st to 10th	Day	9% 6% 2 6% 4 4 5% 3 6% 8% 46%	6048
	11th to 20th	Day	8% 5% 2 5% 4 4 4 4 7% 9% 48%	5900
	21st to end	Day	7% 5% 2 6% 5% 6% 6% 5% 8% 10% 41%	6422
August	1st to 10th	Day	5% 3 2 5% 3 4 4 4 6% 10% 54%	4234
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 5% 8% 49%	4171
	21st to end	Day	5% 4 2 5% 3 4 4 4 6% 9% 55%	4356
September	1st to 10th	Day	12% 5% 2 5% 3 3 3 3 6% 7% 53%	2400
	11th to 20th	Day	9% 5% 1 5% 3 4 4 4 5% 8% 50%	2261
	21st to end	Day	10% 4 2 5% 3 3 4 4 5% 5% 55%	2162
October	1st to 10th	Day	11% 5% 2 5% 3 3 4 2 5% 6% 54%	2000
	11th to 20th	Day	13% 5% 1 5% 3 3 2 2 4 6% 55%	2000
	21st to end	Day	17% 7% 2 6% 3 3 4 2 4 6% 46%	2200
November	1st to 10th	Day	10% 6% 2 5% 3 3 3 3 4 7% 53%	2058
	11th to 20th	Day	14% 6% 2 5% 3 3 4 3 4 6% 50%	1789
	21st to end	Day	16% 9% 3 6% 4 3 3 3 3 4 46%	1680
December	1st to 10th	Day	7% 6% 2 6% 5% 3 3 3 4 6% 55%	2626
	11th to 20th	Day	11% 7% 3 8% 5% 3 3 2 5% 5% 48%	3008
	21st to end	Day	18% 18% 7% 11% 5% 4 4 2 4 4 25%	4051
January	1st to 10th	Night	12% 10% 4 15% 5% 4 4 2 4 4 36%	5888
	11th to 20th	Night	10% 9% 3 9% 5% 6% 4 3 4 4 42%	5900
	21st to end	Night	15% 9% 4 9% 4 4 3 3 4 5% 40%	6490
February	1st to 10th	Night	12% 12% 3 7% 5% 5% 4 3 5% 6% 38%	2600
	11th to 20th	Night	13% 9% 3 8% 5% 4 4 3 4 6% 42%	2533
	21st to end	Night	13% 7% 3 7% 4 4 3 3 4 5% 47%	1949
March	1st to 10th	Night	14% 10% 3 6% 3 3 3 3 3 5% 48%	4919
	11th to 20th	Night	9% 7% 2 4 3 3 3 3 5% 7% 56%	4980
	21st to end	Night	14% 9% 4 7% 5% 4 4 3 5% 7% 37%	5467
April	1st to 10th	Night	12% 7% 2 6% 3 4 4 3 5% 7% 49%	2065
	11th to 20th	Night	14% 7% 3 6% 3 3 3 3 5% 7% 47%	1975
	21st to end	Night	18% 7% 3 6% 3 4 4 3 5% 7% 41%	1895
May	1st to 10th	Night	16% 6% 2 6% 4 3 4 3 4 6% 45%	4053
	11th to 20th	Night	15% 6% 2 4 3 3 3 3 5% 6% 49%	4053
	21st to end	Night	16% 5% 2 5% 4 3 4 3 4 5% 50%	4128
June	1st to 10th	Night	7% 3 1 4 3 4 4 4 6% 11% 53%	1600
	11th to 20th	Night	6% 3 2 5% 5% 4 4 3 7% 12% 50%	1600
	21st to end	Night	5% 2 1 4 4 3 4 4 7% 9% 58%	1600
July	1st to 10th	Night	9% 5% 2 5% 4 3 4 4 5% 10% 49%	3910
	11th to 20th	Night	6% 4 2 5% 4 4 4 4 6% 9% 53%	4077
	21st to end	Night	7% 4 2 6% 4 4 5% 4 8% 12% 44%	4449
August	1st to 10th	Night	2 1 1 3 3 3 4 4 6% 10% 63%	2926
	11th to 20th	Night	12% 6% 2 4 3 3 4 3 4 6% 52%	2888
	21st to end	Night	4 3 2 5% 4 3 3 3 5% 8% 60%	3541
September	1st to 10th	Night	11% 4 2 5% 4 3 4 3 4 5% 56%	2000
	11th to 20th	Night	9% 4 1 4 3 4 4 4 5% 8% 54%	2135
	21st to end	Night	7% 4 2 5% 4 3 4 2 5% 6% 57%	2217
October	1st to 10th	Night	10% 4 2 4 3 3 3 3 4 5% 59%	2400
	11th to 20th	Night	13% 4 2 4 3 3 2 2 3 5% 57%	2400
	21st to end	Night	17% 6% 2 5% 3 3 3 2 4 4 51%	2640
November	1st to 10th	Night	9% 5% 2 4 3 3 3 3 4 5% 60%	2460
	11th to 20th	Night	10% 6% 2 5% 4 3 3 3 5% 6% 54%	2825
	21st to end	Night	15% 8% 2 6% 3 3 3 3 4 5% 49%	2940
December	1st to 10th	Night	8% 5% 3 5% 4 3 3 3 5% 6% 55%	4609
	11th to 20th	Night	12% 8% 3 7% 3 4 4 3 5% 6% 45%	5199
	21st to end	Night	19% 16% 5% 10% 4 4 3 3 4 4 29%	6922

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	51% 2 10% 24% 11% 1	4078
	11th to 20th	Day	49% 2 9% 21% 14% 4	4080
	21st to end	Day	52% 2 10% 15% 18% 3	4488
February	1st to 10th	Day	50% 3 12% 22% 11% 2	1800
	11th to 20th	Day	47% 3 12% 21% 15% 2	1763
	21st to end	Day	40% 2 10% 25% 19% 3	1695
March	1st to 10th	Day	40% 1 7% 23% 22% 6%	4936
	11th to 20th	Day	32% 2 9% 23% 28% 6%	4980
	21st to end	Day	49% 3 17% 25% 5% 1	5464
April	1st to 10th	Day	41% 3 12% 25% 16% 2	2335
	11th to 20th	Day	45% 2 12% 24% 15% 1	2374
	21st to end	Day	52% 3 10% 24% 10% 1	2502
May	1st to 10th	Day	43% 3 12% 27% 14% 1	5900
	11th to 20th	Day	40% 3 13% 24% 18% 3	5866
	21st to end	Day	44% 3 9% 30% 13% 1	6761
June	1st to 10th	Day	30% 4 17% 32% 15% 2	2800
	11th to 20th	Day	33% 3 15% 30% 17% 1	2800
	21st to end	Day	28% 5% 18% 30% 16% 4	2800
July	1st to 10th	Day	35% 4 13% 26% 19% 2	5984
	11th to 20th	Day	32% 5% 16% 30% 16% 1	5831
	21st to end	Day	32% 9% 15% 33% 10% 1	6240
August	1st to 10th	Day	26% 5% 16% 30% 21% 1	4220
	11th to 20th	Day	34% 5% 16% 29% 16% 1	4210
	21st to end	Day	26% 5% 15% 34% 15% 5%	4355
September	1st to 10th	Day	31% 3 12% 27% 20% 6%	2400
	11th to 20th	Day	31% 4 12% 27% 23% 2	2261
	21st to end	Day	32% 3 8% 31% 23% 3	2162
October	1st to 10th	Day	19% 2 7% 23% 40% 9%	3260
	11th to 20th	Day	22% 1 4 25% 39% 9%	3240
	21st to end	Day	35% 3 10% 24% 26% 3	3538
November	1st to 10th	Day	32% 2 13% 28% 20% 4	2058
	11th to 20th	Day	37% 2 9% 27% 21% 3	1789
	21st to end	Day	44% 1 9% 27% 17% 1	1680
December	1st to 10th	Day	31% 3 14% 34% 17% 1	2626
	11th to 20th	Day	39% 2 13% 32% 12% 1	3005
	21st to end	Day	65% 2 11% 15% 6% 1	4051
January	1st to 10th	Night	54% 2 10% 22% 10% 1	5888
	11th to 20th	Night	47% 2 9% 23% 15% 4	5900
	21st to end	Night	49% 2 10% 18% 17% 5%	6490
February	1st to 10th	Night	47% 3 10% 23% 14% 3	2600
	11th to 20th	Night	45% 2 11% 21% 18% 3	2534
	21st to end	Night	41% 2 8% 23% 20% 5%	1949
March	1st to 10th	Night	41% 1 7% 22% 24% 4	4919
	11th to 20th	Night	29% 2 7% 25% 30% 8%	4980
	21st to end	Night	47% 3 15% 24% 9% 2	5467
April	1st to 10th	Night	36% 3 10% 25% 21% 4	2065
	11th to 20th	Night	39% 2 9% 29% 17% 4	1975
	21st to end	Night	44% 3 11% 26% 15% 1	1895
May	1st to 10th	Night	42% 3 14% 25% 16% 1	4080
	11th to 20th	Night	37% 3 13% 24% 18% 5%	4054
	21st to end	Night	38% 3 9% 28% 21% 1	4136
June	1st to 10th	Night	25% 4 17% 34% 17% 3	1600
	11th to 20th	Night	28% 4 13% 32% 21% 2	1600
	21st to end	Night	21% 4 15% 35% 21% 4	1600
July	1st to 10th	Night	31% 5% 14% 25% 23% 3	3867
	11th to 20th	Night	27% 6% 15% 33% 17% 2	4026
	21st to end	Night	29% 7% 18% 36% 10% 1	4320
August	1st to 10th	Night	16% 4 23% 30% 23% 4	2916
	11th to 20th	Night	34% 3 10% 31% 20% 1	2915
	21st to end	Night	23% 5% 12% 38% 17% 5%	3541
September	1st to 10th	Night	31% 3 10% 26% 22% 8%	2000
	11th to 20th	Night	28% 4 10% 29% 24% 5%	2135
	21st to end	Night	29% 3 7% 27% 29% 4	2217
October	1st to 10th	Night	18% 2 6% 21% 45% 7%	3920
	11th to 20th	Night	23% 2 6% 26% 30% 14%	3899
	21st to end	Night	34% 3 7% 29% 24% 3	4252
November	1st to 10th	Night	29% 2 12% 29% 23% 6%	2460
	11th to 20th	Night	32% 2 9% 27% 23% 5%	2825
	21st to end	Night	40% 2 9% 28% 18% 3	2940
December	1st to 10th	Night	30% 4 14% 35% 17% 1	4609
	11th to 20th	Night	40% 3 12% 27% 15% 2	5201
	21st to end	Night	61% 2 10% 18% 7% 1	6922

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% 18% 37% 19% 5%	300
	11th to 20th	Day	28% 17% 40% 14% 1	300
	21st to end	Day	15% 15% 47% 19% 3	330
February	1st to 10th	Day	26% 16% 39% 17% 2	300
	11th to 20th	Day	23% 21% 37% 14% 4	300
	21st to end	Day	16% 27% 40% 12% 4 1	249
March	1st to 10th	Day	19% 16% 44% 17% 3	300
	11th to 20th	Day	29% 12% 35% 20% 4	300
	21st to end	Day	31% 19% 32% 14% 3	330
April	1st to 10th	Day	23% 17% 37% 16% 6%	435
	11th to 20th	Day	20% 17% 36% 20% 6% 1	492
	21st to end	Day	22% 16% 35% 17% 8% 1	602
May	1st to 10th	Day	19% 12% 36% 23% 8% 1	703
	11th to 20th	Day	19% 10% 30% 26% 12% 3	725
	21st to end	Day	17% 8% 29% 29% 14% 4	789
June	1st to 10th	Day	7% 6% 22% 34% 25% 7%	730
	11th to 20th	Day	9% 3 27% 38% 20% 4	730
	21st to end	Day	8% 5% 32% 35% 17% 2	730
July	1st to 10th	Day	12% 3 14% 29% 28% 13%	721
	11th to 20th	Day	5% 3 21% 37% 26% 9%	718
	21st to end	Day	8% 3 15% 34% 31% 8%	794
August	1st to 10th	Day	5% 3 19% 40% 27% 6%	726
	11th to 20th	Day	8% 4 17% 36% 29% 6%	715
	21st to end	Day	8% 1 16% 34% 30% 10%	614
September	1st to 10th	Day	12% 3 14% 38% 27% 6%	530
	11th to 20th	Day	5% 5% 18% 40% 26% 6%	391
	21st to end	Day	13% 4 26% 32% 17% 7%	330
October	1st to 10th	Day	13% 6% 28% 29% 18% 5%	330
	11th to 20th	Day	12% 18% 37% 25% 8%	330
	21st to end	Day	24% 18% 32% 22% 4 1	363
November	1st to 10th	Day	16% 13% 41% 21% 6% 4	330
	11th to 20th	Day	17% 18% 33% 24% 8% 1	330
	21st to end	Day	24% 14% 33% 23% 6%	330
December	1st to 10th	Day	12% 17% 41% 21% 5% 3	306
	11th to 20th	Day	22% 15% 39% 18% 5% 1	300
	21st to end	Day	21% 25% 37% 16% 1	330
January	1st to 10th	Night	15% 14% 39% 26% 6%	1000
	11th to 20th	Night	16% 16% 38% 23% 6% 1	1000
	21st to end	Night	15% 13% 43% 26% 3	1100
February	1st to 10th	Night	18% 14% 43% 22% 4	1000
	11th to 20th	Night	19% 14% 38% 26% 4	979
	21st to end	Night	18% 13% 45% 19% 4	629
March	1st to 10th	Night	17% 12% 42% 24% 5%	600
	11th to 20th	Night	21% 12% 34% 27% 6%	600
	21st to end	Night	26% 11% 38% 22% 3	660
April	1st to 10th	Night	15% 12% 41% 26% 6%	600
	11th to 20th	Night	20% 14% 32% 27% 6%	593
	21st to end	Night	21% 10% 35% 27% 7%	600
May	1st to 10th	Night	18% 9% 33% 33% 7% 1	600
	11th to 20th	Night	16% 6% 28% 35% 14% 1	591
	21st to end	Night	13% 5% 29% 36% 15% 2	650
June	1st to 10th	Night	7% 4 19% 44% 23% 3	600
	11th to 20th	Night	6% 3 24% 45% 20% 2	600
	21st to end	Night	5% 2 31% 47% 14% 1	600
July	1st to 10th	Night	9% 3 11% 40% 33% 4	585
	11th to 20th	Night	4 2 16% 43% 31% 3	582
	21st to end	Night	7% 2 14% 42% 33% 2	657
August	1st to 10th	Night	4 2 13% 49% 32% 1	597
	11th to 20th	Night	8% 3 13% 41% 30% 5%	594
	21st to end	Night	6% 1 13% 43% 35% 2	660
September	1st to 10th	Night	11% 2 18% 41% 24% 4	600
	11th to 20th	Night	10% 2 20% 39% 25% 4	600
	21st to end	Night	7% 4 23% 41% 21% 4	617
October	1st to 10th	Night	11% 4 27% 37% 19% 2	800
	11th to 20th	Night	15% 8% 37% 31% 8%	800
	21st to end	Night	21% 11% 34% 26% 9%	880
November	1st to 10th	Night	12% 10% 36% 32% 10% 1	820
	11th to 20th	Night	13% 13% 39% 27% 8%	1013
	21st to end	Night	21% 10% 38% 27% 5%	1050
December	1st to 10th	Night	17% 11% 38% 28% 6% 1	1011
	11th to 20th	Night	18% 11% 39% 27% 5%	1000
	21st to end	Night	21% 15% 36% 24% 4	1100

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