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 2025-03-27.

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%	109044
	Night	13% 8% 3 6% 4 3 3 3 4 6% 46%	110456
Transparency	Day	38% 4 11% 26% 17% 3	112695
	Night	38% 4 10% 26% 18% 4	114945
Seeing	Day	18% 12% 29% 26% 13% 3	16017
	Night	17% 12% 32% 27% 11% 1	26028

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	15% 11% 4 7% 5% 4 4 3 4 6% 39%	4077
	11th to 20th	Day	8% 12% 4 7% 4 5% 4 3 4 5% 42%	4080
	21st to end	Day	17% 11% 3 8% 3 3 3 3 4 5% 40%	4488
February	1st to 10th	Day	16% 12% 4 9% 5% 5% 3 3 4 6% 34%	1800
	11th to 20th	Day	15% 10% 4 8% 5% 4 3 3 5% 5% 39%	1769
	21st to end	Day	15% 10% 3 6% 4 4 4 5% 5% 6% 40%	1710
March	1st to 10th	Day	17% 10% 2 6% 3 3 3 3 4 6% 46%	3546
	11th to 20th	Day	13% 8% 2 5% 3 3 2 3 4 7% 50%	3590
	21st to end	Day	16% 12% 3 7% 4 4 5% 4 5% 6% 35%	3880
April	1st to 10th	Day	13% 8% 2 7% 5% 4 4 3 4 7% 43%	2256
	11th to 20th	Day	17% 9% 2 6% 4 4 5% 3 5% 5% 41%	2254
	21st to end	Day	20% 8% 3 7% 5% 4 3 3 5% 6% 35%	2280
May	1st to 10th	Day	18% 8% 3 7% 5% 4 5% 4 6% 6% 34%	4047
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 7% 41%	4082
	21st to end	Day	13% 7% 3 6% 5% 5% 5% 4 6% 8% 40%	4730
June	1st to 10th	Day	8% 5% 2 5% 4 4 5% 4 6% 10% 46%	2660
	11th to 20th	Day	7% 5% 2 5% 5% 6% 5% 4 6% 9% 46%	2660
	21st to end	Day	5% 3 1 4 4 4 5% 4 6% 9% 53%	2660
July	1st to 10th	Day	12% 6% 3 7% 4 4 5% 4 5% 9% 41%	4257
	11th to 20th	Day	5% 5% 2 5% 4 5% 5% 5% 7% 10% 48%	4120
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 39%	4465
August	1st to 10th	Day	4 4 1 5% 4 4 5% 4 7% 10% 52%	4104
	11th to 20th	Day	9% 6% 3 6% 5% 5% 5% 4 6% 8% 45%	3955
	21st to end	Day	6% 4 2 4 3 4 4 3 5% 8% 57%	4180
September	1st to 10th	Day	11% 5% 2 5% 4 4 3 3 5% 7% 51%	2280
	11th to 20th	Day	10% 6% 2 5% 4 4 4 4 5% 7% 49%	2224
	21st to end	Day	8% 6% 2 5% 5% 4 4 4 5% 7% 52%	2009
October	1st to 10th	Day	11% 5% 2 5% 3 2 4 2 4 5% 56%	1900
	11th to 20th	Day	15% 5% 2 5% 2 2 3 2 3 6% 54%	1900
	21st to end	Day	19% 8% 2 6% 3 3 3 2 4 4 48%	2090
November	1st to 10th	Day	13% 6% 2 4 3 3 3 3 4 4 56%	1958
	11th to 20th	Day	14% 8% 2 6% 3 3 3 3 4 7% 48%	1787
	21st to end	Day	17% 8% 3 5% 3 3 3 3 4 6% 46%	1600
December	1st to 10th	Day	11% 10% 3 5% 3 2 3 3 4 5% 52%	2610
	11th to 20th	Day	12% 9% 3 7% 3 3 3 3 4 7% 47%	3008
	21st to end	Day	21% 20% 5% 8% 3 4 3 2 3 4 25%	4028
January	1st to 10th	Night	14% 11% 5% 13% 6% 5% 4 3 3 4 33%	5888
	11th to 20th	Night	10% 7% 3 11% 6% 5% 4 3 4 4 41%	5900
	21st to end	Night	17% 11% 3 8% 3 3 3 2 3 4 42%	6490
February	1st to 10th	Night	14% 13% 3 7% 4 3 3 3 5% 7% 38%	2600
	11th to 20th	Night	15% 10% 4 7% 3 3 3 3 4 7% 42%	2517
	21st to end	Night	15% 9% 3 6% 4 3 3 3 5% 6% 43%	1936
March	1st to 10th	Night	17% 10% 3 6% 4 3 3 2 3 4 45%	3529
	11th to 20th	Night	14% 7% 1 5% 3 3 3 3 4 6% 51%	3590
	21st to end	Night	16% 9% 3 8% 5% 5% 4 3 6% 6% 35%	3889
April	1st to 10th	Night	10% 7% 2 5% 3 3 3 2 5% 7% 52%	1922
	11th to 20th	Night	14% 7% 3 5% 4 4 3 3 4 6% 48%	1875
	21st to end	Night	18% 7% 2 6% 4 4 5% 4 4 7% 39%	1900
May	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 6% 7% 41%	2841
	11th to 20th	Night	13% 9% 3 7% 4 4 4 3 4 7% 43%	2823
	21st to end	Night	11% 6% 2 6% 4 3 5% 4 5% 9% 45%	2819
June	1st to 10th	Night	7% 4 2 4 4 4 3 4 8% 9% 52%	1520
	11th to 20th	Night	4 3 1 4 3 4 6% 4 8% 10% 52%	1520
	21st to end	Night	3 2 1 2 3 3 3 3 7% 11% 61%	1520
July	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 6% 8% 46%	2708
	11th to 20th	Night	4 3 1 4 3 3 4 3 6% 10% 59%	2850
	21st to end	Night	5% 4 2 4 4 3 4 4 6% 10% 54%	3098
August	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 8% 64%	2836
	11th to 20th	Night	9% 5% 2 6% 4 4 4 4 6% 6% 50%	2881
	21st to end	Night	3 3 1 4 3 3 3 3 6% 9% 62%	3476
September	1st to 10th	Night	11% 4 1 4 3 3 3 3 5% 7% 56%	1900
	11th to 20th	Night	10% 4 2 4 4 3 4 3 5% 7% 54%	1952
	21st to end	Night	8% 5% 2 5% 3 3 3 3 4 7% 58%	2151
October	1st to 10th	Night	8% 4 1 3 2 3 2 3 5% 7% 61%	2280
	11th to 20th	Night	15% 5% 1 3 3 3 3 3 3 6% 55%	2280
	21st to end	Night	17% 7% 2 5% 2 3 3 3 3 6% 50%	2508
November	1st to 10th	Night	12% 5% 2 4 3 3 2 3 4 5% 58%	2340
	11th to 20th	Night	13% 8% 2 5% 4 3 3 3 3 6% 51%	2605
	21st to end	Night	16% 10% 2 5% 3 3 2 2 3 5% 48%	2800
December	1st to 10th	Night	11% 8% 2 6% 4 3 3 2 4 5% 50%	4580
	11th to 20th	Night	17% 9% 3 6% 3 3 3 2 4 5% 44%	5199
	21st to end	Night	23% 18% 5% 8% 4 4 3 2 3 4 27%	6933

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	49% 2 8% 24% 16% 1	4078
	11th to 20th	Day	44% 3 8% 26% 16% 4	4080
	21st to end	Day	47% 3 8% 18% 16% 9%	4488
February	1st to 10th	Day	53% 4 9% 22% 12% 1	1800
	11th to 20th	Day	47% 3 13% 19% 15% 3	1778
	21st to end	Day	45% 4 7% 24% 15% 5%	1710
March	1st to 10th	Day	42% 3 8% 22% 19% 6%	3546
	11th to 20th	Day	35% 3 10% 29% 17% 6%	3590
	21st to end	Day	50% 4 16% 20% 8% 1	3880
April	1st to 10th	Day	42% 4 10% 25% 17% 2	2256
	11th to 20th	Day	44% 4 13% 22% 15% 2	2254
	21st to end	Day	50% 4 10% 23% 11% 1	2280
May	1st to 10th	Day	49% 6% 11% 20% 13% 1	4085
	11th to 20th	Day	42% 6% 14% 24% 14%	4086
	21st to end	Day	42% 5% 11% 27% 14% 1	4743
June	1st to 10th	Day	33% 6% 17% 26% 16% 2	2660
	11th to 20th	Day	32% 6% 14% 31% 14% 3	2660
	21st to end	Day	25% 6% 17% 32% 16% 4	2660
July	1st to 10th	Day	40% 6% 14% 24% 14% 3	4193
	11th to 20th	Day	29% 7% 14% 32% 17% 2	4051
	21st to end	Day	32% 9% 23% 26% 9% 1	4325
August	1st to 10th	Day	26% 6% 19% 28% 21% 1	4090
	11th to 20th	Day	36% 6% 15% 28% 14% 1	3994
	21st to end	Day	25% 6% 14% 37% 14% 4	4179
September	1st to 10th	Day	33% 4 12% 27% 18% 6%	2280
	11th to 20th	Day	35% 5% 7% 26% 25% 2	2224
	21st to end	Day	31% 5% 9% 27% 24% 4	2009
October	1st to 10th	Day	19% 2 5% 21% 39% 14%	3160
	11th to 20th	Day	22% 2 5% 25% 36% 11%	3140
	21st to end	Day	32% 3 8% 28% 26% 4	3428
November	1st to 10th	Day	33% 3 10% 27% 23% 4	1958
	11th to 20th	Day	38% 3 9% 22% 23% 5%	1787
	21st to end	Day	41% 4 8% 28% 18% 2	1600
December	1st to 10th	Day	35% 3 9% 37% 15% 1	2610
	11th to 20th	Day	40% 3 8% 28% 19% 2	3005
	21st to end	Day	64% 3 9% 17% 7% 1	4028
January	1st to 10th	Night	56% 3 9% 19% 12% 1	5888
	11th to 20th	Night	46% 4 7% 25% 15% 2	5900
	21st to end	Night	48% 3 7% 20% 17% 5%	6490
February	1st to 10th	Night	46% 3 11% 24% 13% 2	2600
	11th to 20th	Night	44% 3 10% 24% 16% 3	2518
	21st to end	Night	43% 3 8% 23% 18% 6%	1936
March	1st to 10th	Night	45% 3 8% 20% 19% 5%	3529
	11th to 20th	Night	36% 4 10% 25% 23% 3	3590
	21st to end	Night	48% 5% 13% 23% 9% 1	3889
April	1st to 10th	Night	33% 3 13% 26% 21% 4	1922
	11th to 20th	Night	38% 3 10% 24% 19% 5%	1875
	21st to end	Night	45% 4 11% 24% 15% 1	1900
May	1st to 10th	Night	41% 6% 12% 23% 15% 3	2868
	11th to 20th	Night	43% 4 12% 28% 12% 1	2824
	21st to end	Night	36% 6% 12% 29% 15% 1	2827
June	1st to 10th	Night	27% 5% 17% 30% 18% 3	1520
	11th to 20th	Night	25% 6% 14% 30% 22% 3	1520
	21st to end	Night	17% 5% 18% 34% 21% 6%	1520
July	1st to 10th	Night	36% 5% 13% 26% 16% 4	2663
	11th to 20th	Night	20% 6% 10% 40% 22% 2	2796
	21st to end	Night	25% 6% 21% 36% 12% 1	2999
August	1st to 10th	Night	17% 6% 18% 33% 24% 2	2826
	11th to 20th	Night	33% 6% 13% 29% 17% 2	2908
	21st to end	Night	20% 4 16% 39% 18% 4	3476
September	1st to 10th	Night	29% 4 10% 28% 22% 7%	1900
	11th to 20th	Night	30% 5% 10% 25% 26% 5%	1952
	21st to end	Night	28% 4 9% 28% 29% 4	2151
October	1st to 10th	Night	14% 2 6% 21% 43% 14%	3800
	11th to 20th	Night	22% 3 6% 22% 29% 18%	3779
	21st to end	Night	31% 3 6% 31% 25% 4	4120
November	1st to 10th	Night	31% 2 10% 28% 23% 7%	2340
	11th to 20th	Night	36% 3 6% 25% 24% 6%	2605
	21st to end	Night	41% 2 8% 27% 19% 3	2800
December	1st to 10th	Night	38% 3 9% 34% 15% 1	4580
	11th to 20th	Night	44% 2 9% 25% 19% 2	5201
	21st to end	Night	62% 3 10% 17% 6% 1	6933

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	22% 19% 42% 16% 1	300
	11th to 20th	Day	28% 22% 40% 9% 1	300
	21st to end	Day	20% 24% 44% 10% 2	330
February	1st to 10th	Day	28% 23% 37% 11% 1	300
	11th to 20th	Day	29% 27% 32% 12% 1	300
	21st to end	Day	28% 26% 37% 8% 2	249
March	1st to 10th	Day	26% 22% 37% 13% 2	300
	11th to 20th	Day	32% 20% 34% 13% 1	300
	21st to end	Day	32% 25% 33% 8% 2	315
April	1st to 10th	Day	23% 22% 35% 16% 4	436
	11th to 20th	Day	27% 19% 34% 15% 4	452
	21st to end	Day	27% 15% 37% 16% 5%	460
May	1st to 10th	Day	25% 15% 36% 19% 5%	631
	11th to 20th	Day	20% 12% 31% 25% 10% 1	675
	21st to end	Day	16% 10% 34% 25% 12% 3	734
June	1st to 10th	Day	10% 5% 25% 34% 20% 5%	680
	11th to 20th	Day	8% 5% 27% 38% 20% 3	680
	21st to end	Day	7% 6% 33% 36% 15% 3	680
July	1st to 10th	Day	11% 4 18% 32% 28% 6%	671
	11th to 20th	Day	5% 3 21% 40% 25% 5%	668
	21st to end	Day	10% 2 17% 38% 27% 6%	739
August	1st to 10th	Day	9% 3 19% 41% 25% 4	676
	11th to 20th	Day	11% 3 20% 38% 23% 5%	618
	21st to end	Day	10% 3 15% 34% 29% 9%	539
September	1st to 10th	Day	11% 4 15% 38% 26% 5%	490
	11th to 20th	Day	10% 2 23% 38% 22% 6%	434
	21st to end	Day	12% 8% 30% 31% 14% 4	300
October	1st to 10th	Day	14% 10% 28% 28% 16% 4	300
	11th to 20th	Day	17% 17% 39% 21% 6%	300
	21st to end	Day	32% 16% 32% 17% 3	330
November	1st to 10th	Day	20% 12% 44% 17% 6% 2	300
	11th to 20th	Day	20% 21% 33% 19% 5% 1	300
	21st to end	Day	30% 17% 28% 20% 5%	300
December	1st to 10th	Day	21% 21% 35% 15% 6% 2	300
	11th to 20th	Day	26% 20% 35% 15% 4 1	300
	21st to end	Day	29% 27% 33% 9% 2	330
January	1st to 10th	Night	20% 19% 37% 20% 4	1000
	11th to 20th	Night	20% 23% 37% 17% 3	1000
	21st to end	Night	18% 20% 38% 21% 2	1100
February	1st to 10th	Night	21% 20% 40% 16% 3	1000
	11th to 20th	Night	23% 20% 37% 18% 2	963
	21st to end	Night	23% 21% 38% 15% 2	616
March	1st to 10th	Night	21% 18% 38% 21% 3	600
	11th to 20th	Night	25% 13% 36% 21% 4	600
	21st to end	Night	26% 16% 36% 18% 4	647
April	1st to 10th	Night	15% 18% 40% 22% 5%	570
	11th to 20th	Night	19% 15% 36% 24% 6%	563
	21st to end	Night	22% 10% 38% 24% 6%	570
May	1st to 10th	Night	16% 8% 39% 30% 7%	570
	11th to 20th	Night	18% 7% 28% 32% 13% 1	561
	21st to end	Night	16% 7% 31% 28% 16% 2	617
June	1st to 10th	Night	9% 4 20% 41% 24% 2	570
	11th to 20th	Night	6% 2 28% 41% 20% 2	570
	21st to end	Night	4 2 31% 43% 18% 2	570
July	1st to 10th	Night	12% 2 15% 39% 28% 4	555
	11th to 20th	Night	3 2 20% 45% 28% 2	552
	21st to end	Night	7% 1 16% 40% 34% 2	624
August	1st to 10th	Night	7% 1 16% 44% 30% 2	567
	11th to 20th	Night	7% 2 16% 46% 25% 3	564
	21st to end	Night	5% 2 16% 38% 36% 4	627
September	1st to 10th	Night	12% 2 16% 41% 26% 3	570
	11th to 20th	Night	13% 2 17% 37% 26% 4	570
	21st to end	Night	11% 5% 23% 38% 20% 3	631
October	1st to 10th	Night	10% 6% 28% 31% 22% 3	760
	11th to 20th	Night	19% 9% 38% 27% 8%	760
	21st to end	Night	21% 13% 35% 23% 7%	836
November	1st to 10th	Night	14% 12% 41% 24% 9% 1	780
	11th to 20th	Night	18% 16% 35% 24% 7%	845
	21st to end	Night	23% 14% 37% 20% 6%	1000
December	1st to 10th	Night	21% 14% 39% 21% 5%	1000
	11th to 20th	Night	24% 15% 36% 22% 4	1000
	21st to end	Night	24% 19% 36% 19% 2	1100

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