Belleview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Belleview 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	8% 6% 2 7% 5% 5% 5% 5% 7% 10% 40%	109381
	Night	9% 6% 2 6% 4 4 5% 4 6% 9% 43%	109955
Transparency	Day	37% 9% 16% 19% 14% 5%	113162
	Night	36% 8% 15% 20% 15% 6%	114313
Seeing	Day	9% 5% 17% 25% 24% 20%	15936
	Night	10% 4 18% 34% 27% 7%	26076

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	9% 5% 2 5% 3 4 3 3 5% 7% 54%	4056
	11th to 20th	Day	20% 9% 4 7% 5% 4 4 3 3 6% 34%	4060
	21st to end	Day	12% 5% 2 4 3 3 4 3 6% 9% 48%	4668
February	1st to 10th	Day	13% 6% 2 6% 5% 4 4 4 7% 8% 43%	2000
	11th to 20th	Day	11% 5% 2 4 4 4 4 3 5% 7% 52%	1948
	21st to end	Day	10% 6% 2 6% 4 4 4 3 5% 7% 49%	1715
March	1st to 10th	Day	8% 7% 2 8% 5% 5% 5% 4 7% 10% 38%	3545
	11th to 20th	Day	6% 4 2 5% 4 3 4 4 7% 10% 51%	3590
	21st to end	Day	10% 5% 2 6% 4 4 4 3 5% 7% 49%	3881
April	1st to 10th	Day	8% 4 2 5% 4 5% 4 4 6% 9% 50%	2090
	11th to 20th	Day	9% 5% 1 6% 5% 6% 5% 4 7% 8% 44%	2080
	21st to end	Day	5% 3 1 4 4 4 5% 4 7% 8% 55%	2312
May	1st to 10th	Day	3 2 1 3 3 4 4 4 6% 10% 58%	4082
	11th to 20th	Day	9% 5% 2 7% 5% 7% 6% 5% 7% 9% 38%	4081
	21st to end	Day	4 3 2 5% 4 5% 5% 4 7% 9% 53%	4476
June	1st to 10th	Day	9% 7% 3 8% 8% 7% 8% 6% 9% 9% 26%	2470
	11th to 20th	Day	6% 6% 2 8% 8% 8% 9% 7% 9% 11% 28%	2470
	21st to end	Day	8% 6% 3 8% 8% 7% 7% 7% 8% 10% 28%	2470
July	1st to 10th	Day	7% 6% 2 8% 8% 8% 8% 7% 11% 13% 22%	4120
	11th to 20th	Day	4 5% 2 8% 7% 7% 8% 7% 10% 15% 26%	4120
	21st to end	Day	4 6% 2 8% 7% 7% 8% 7% 11% 15% 25%	4466
August	1st to 10th	Day	7% 6% 2 7% 7% 6% 7% 5% 9% 14% 29%	4104
	11th to 20th	Day	5% 4 2 7% 5% 7% 7% 6% 9% 13% 34%	3849
	21st to end	Day	8% 6% 3 9% 6% 8% 7% 6% 9% 12% 26%	3828
September	1st to 10th	Day	8% 6% 3 10% 8% 8% 8% 7% 9% 10% 23%	2090
	11th to 20th	Day	10% 7% 4 11% 7% 7% 7% 5% 8% 10% 25%	2090
	21st to end	Day	9% 7% 3 7% 6% 6% 7% 5% 7% 8% 34%	2090
October	1st to 10th	Day	11% 6% 2 10% 5% 6% 6% 4 5% 8% 36%	2090
	11th to 20th	Day	6% 5% 1 6% 5% 4 4 4 6% 8% 52%	1902
	21st to end	Day	7% 5% 2 5% 5% 4 4 4 6% 8% 50%	2090
November	1st to 10th	Day	8% 6% 2 6% 4 4 4 4 6% 7% 49%	1957
	11th to 20th	Day	9% 6% 2 7% 4 5% 5% 4 5% 6% 46%	2000
	21st to end	Day	10% 5% 2 5% 4 5% 4 3 6% 8% 48%	1822
December	1st to 10th	Day	5% 4 2 5% 3 3 4 4 6% 8% 56%	2930
	11th to 20th	Day	9% 7% 3 6% 4 4 5% 4 7% 9% 42%	3373
	21st to end	Day	11% 8% 3 7% 4 4 4 3 5% 7% 43%	4466
January	1st to 10th	Night	9% 5% 2 4 3 3 3 3 5% 8% 56%	5889
	11th to 20th	Night	20% 9% 3 8% 4 4 4 4 6% 7% 32%	5900
	21st to end	Night	16% 6% 2 6% 3 4 4 4 6% 8% 42%	6286
February	1st to 10th	Night	12% 8% 2 6% 4 4 3 4 5% 7% 45%	2400
	11th to 20th	Night	10% 5% 2 6% 4 4 4 3 6% 6% 49%	2338
	21st to end	Night	8% 7% 2 7% 4 4 4 4 6% 7% 47%	1912
March	1st to 10th	Night	15% 10% 4 8% 4 4 4 3 5% 5% 39%	3528
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 8% 11% 48%	3590
	21st to end	Night	10% 6% 2 6% 4 4 3 3 5% 8% 49%	3890
April	1st to 10th	Night	8% 4 2 5% 3 3 4 4 6% 9% 52%	2090
	11th to 20th	Night	7% 5% 2 5% 4 3 3 4 7% 9% 51%	2049
	21st to end	Night	6% 4 2 4 4 3 4 4 5% 8% 56%	1881
May	1st to 10th	Night	4 3 1 4 4 4 5% 4 6% 8% 57%	2813
	11th to 20th	Night	7% 5% 2 5% 4 4 5% 5% 7% 10% 45%	2812
	21st to end	Night	3 2 1 4 3 4 3 3 5% 8% 63%	3079
June	1st to 10th	Night	10% 5% 2 7% 5% 5% 7% 5% 8% 10% 36%	1710
	11th to 20th	Night	5% 5% 3 6% 6% 5% 7% 5% 10% 13% 35%	1710
	21st to end	Night	6% 7% 3 8% 6% 6% 5% 5% 9% 12% 34%	1710
July	1st to 10th	Night	7% 8% 4 11% 7% 7% 8% 6% 8% 11% 24%	2840
	11th to 20th	Night	3 5% 2 8% 7% 8% 7% 7% 12% 12% 28%	2840
	21st to end	Night	7% 8% 4 11% 7% 8% 8% 7% 9% 12% 21%	3087
August	1st to 10th	Night	6% 5% 3 7% 6% 6% 8% 5% 9% 11% 33%	2825
	11th to 20th	Night	4 4 1 5% 5% 5% 6% 5% 8% 16% 40%	2941
	21st to end	Night	7% 6% 3 9% 6% 6% 6% 5% 9% 12% 31%	3814
September	1st to 10th	Night	8% 7% 3 8% 7% 6% 6% 5% 8% 11% 30%	2090
	11th to 20th	Night	11% 8% 3 7% 6% 6% 6% 6% 8% 11% 28%	2090
	21st to end	Night	8% 6% 3 8% 5% 6% 7% 4 7% 9% 38%	2090
October	1st to 10th	Night	9% 8% 3 7% 5% 5% 5% 4 6% 7% 41%	2090
	11th to 20th	Night	5% 4 1 5% 4 3 4 3 5% 8% 56%	2275
	21st to end	Night	8% 5% 3 5% 4 5% 4 3 6% 7% 51%	2508
November	1st to 10th	Night	9% 4 2 6% 3 4 4 4 6% 8% 50%	2341
	11th to 20th	Night	9% 7% 3 6% 5% 5% 4 4 5% 6% 47%	2400
	21st to end	Night	8% 6% 3 5% 5% 4 4 4 6% 8% 47%	2575
December	1st to 10th	Night	6% 4 2 4 4 3 4 3 5% 7% 58%	4250
	11th to 20th	Night	10% 7% 2 6% 4 4 4 3 5% 6% 49%	4822
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 3 5% 7% 39%	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	30% 4 8% 15% 28% 15%	4057
	11th to 20th	Day	53% 3 5% 13% 17% 9%	4060
	21st to end	Day	33% 5% 9% 27% 18% 9%	4668
February	1st to 10th	Day	38% 7% 9% 15% 21% 11%	2000
	11th to 20th	Day	33% 4 8% 19% 24% 12%	1958
	21st to end	Day	34% 5% 10% 18% 22% 11%	1715
March	1st to 10th	Day	39% 8% 14% 19% 15% 6%	3545
	11th to 20th	Day	28% 6% 13% 24% 21% 8%	3590
	21st to end	Day	34% 5% 10% 28% 16% 7%	3881
April	1st to 10th	Day	29% 6% 15% 20% 20% 10%	2090
	11th to 20th	Day	35% 8% 11% 18% 21% 6%	2080
	21st to end	Day	24% 8% 13% 23% 24% 8%	2312
May	1st to 10th	Day	19% 8% 17% 32% 18% 6%	4120
	11th to 20th	Day	39% 10% 15% 24% 11% 2	4085
	21st to end	Day	24% 8% 14% 34% 18% 1	4489
June	1st to 10th	Day	47% 14% 16% 17% 6% 1	2470
	11th to 20th	Day	43% 13% 20% 20% 3	2470
	21st to end	Day	46% 14% 22% 15% 4	2470
July	1st to 10th	Day	46% 16% 29% 9% 1	4055
	11th to 20th	Day	41% 17% 36% 6%	4051
	21st to end	Day	39% 19% 32% 9% 1	4324
August	1st to 10th	Day	42% 13% 29% 13% 3	4091
	11th to 20th	Day	36% 13% 24% 23% 4	3888
	21st to end	Day	45% 13% 22% 17% 2	3828
September	1st to 10th	Day	50% 17% 17% 11% 4	2090
	11th to 20th	Day	51% 12% 20% 12% 5%	2090
	21st to end	Day	45% 10% 13% 17% 11% 4	2090
October	1st to 10th	Day	56% 8% 12% 12% 7% 6%	3480
	11th to 20th	Day	25% 4 6% 23% 32% 9%	3142
	21st to end	Day	27% 4 6% 24% 32% 7%	3428
November	1st to 10th	Day	33% 6% 11% 20% 18% 12%	1957
	11th to 20th	Day	38% 5% 10% 17% 20% 10%	2000
	21st to end	Day	34% 6% 9% 22% 21% 8%	1822
December	1st to 10th	Day	25% 5% 15% 24% 21% 10%	2930
	11th to 20th	Day	38% 6% 11% 19% 16% 11%	3370
	21st to end	Day	40% 6% 9% 22% 19% 5%	4466
January	1st to 10th	Night	28% 3 7% 17% 31% 14%	5889
	11th to 20th	Night	51% 4 8% 16% 17% 4	5900
	21st to end	Night	39% 5% 10% 20% 16% 9%	6286
February	1st to 10th	Night	37% 5% 10% 17% 18% 13%	2400
	11th to 20th	Night	35% 5% 11% 18% 20% 11%	2339
	21st to end	Night	34% 6% 12% 18% 22% 9%	1912
March	1st to 10th	Night	46% 6% 11% 16% 15% 6%	3528
	11th to 20th	Night	28% 7% 19% 22% 17% 7%	3590
	21st to end	Night	34% 6% 9% 23% 21% 7%	3890
April	1st to 10th	Night	28% 8% 15% 24% 16% 9%	2090
	11th to 20th	Night	29% 7% 11% 26% 19% 7%	2049
	21st to end	Night	26% 6% 14% 26% 21% 8%	1881
May	1st to 10th	Night	21% 11% 19% 30% 15% 4	2840
	11th to 20th	Night	31% 11% 21% 26% 10% 2	2813
	21st to end	Night	18% 7% 15% 38% 21% 1	3087
June	1st to 10th	Night	38% 13% 22% 21% 6%	1710
	11th to 20th	Night	37% 15% 25% 21% 2	1710
	21st to end	Night	41% 13% 25% 16% 5% 1	1710
July	1st to 10th	Night	48% 16% 25% 9% 1	2795
	11th to 20th	Night	41% 19% 32% 7% 1	2786
	21st to end	Night	50% 17% 24% 9% 1	2988
August	1st to 10th	Night	40% 13% 32% 12% 2	2814
	11th to 20th	Night	29% 13% 31% 22% 5%	2968
	21st to end	Night	42% 15% 25% 16% 2	3814
September	1st to 10th	Night	43% 17% 21% 14% 5%	2090
	11th to 20th	Night	44% 16% 21% 14% 4 1	2090
	21st to end	Night	40% 11% 17% 19% 12% 2	2090
October	1st to 10th	Night	53% 10% 12% 14% 7% 5%	3480
	11th to 20th	Night	24% 4 7% 22% 36% 6%	3774
	21st to end	Night	29% 5% 7% 20% 32% 7%	4120
November	1st to 10th	Night	31% 6% 11% 23% 19% 11%	2341
	11th to 20th	Night	37% 5% 9% 19% 19% 10%	2400
	21st to end	Night	34% 5% 11% 21% 20% 9%	2575
December	1st to 10th	Night	27% 4 14% 25% 16% 14%	4250
	11th to 20th	Night	35% 6% 10% 22% 17% 10%	4824
	21st to end	Night	43% 6% 11% 21% 15% 5%	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	12% 7% 41% 28% 9% 2	300
	11th to 20th	Day	9% 13% 33% 28% 13% 3	300
	21st to end	Day	13% 15% 43% 22% 7%	330
February	1st to 10th	Day	13% 9% 28% 29% 19% 2	300
	11th to 20th	Day	14% 8% 30% 33% 11% 4	300
	21st to end	Day	9% 8% 31% 30% 19% 4	314
March	1st to 10th	Day	8% 7% 33% 35% 15% 1	500
	11th to 20th	Day	11% 7% 26% 33% 19% 4	500
	21st to end	Day	8% 7% 25% 32% 23% 3	530
April	1st to 10th	Day	10% 6% 27% 32% 23% 2	460
	11th to 20th	Day	11% 8% 22% 30% 25% 5%	452
	21st to end	Day	5% 3 20% 31% 26% 14%	460
May	1st to 10th	Day	4 4 17% 30% 28% 17%	463
	11th to 20th	Day	8% 2 12% 28% 27% 22%	487
	21st to end	Day	7% 1 8% 20% 33% 31%	529
June	1st to 10th	Day	12% 3 7% 20% 30% 29%	490
	11th to 20th	Day	7% 3 7% 20% 26% 36%	490
	21st to end	Day	6% 2 6% 15% 23% 49%	490
July	1st to 10th	Day	6% 3 3 10% 26% 53%	485
	11th to 20th	Day	7% 1 3 9% 26% 54%	484
	21st to end	Day	9% 2 3 12% 29% 45%	532
August	1st to 10th	Day	7% 3 6% 16% 24% 43%	486
	11th to 20th	Day	6% 1 3 12% 25% 53%	479
	21st to end	Day	10% 3 4 16% 28% 39%	539
September	1st to 10th	Day	10% 3 6% 13% 28% 39%	490
	11th to 20th	Day	10% 3 4 22% 35% 26%	490
	21st to end	Day	12% 2 6% 21% 33% 27%	490
October	1st to 10th	Day	14% 5% 13% 32% 27% 9%	490
	11th to 20th	Day	6% 4 17% 30% 31% 12%	490
	21st to end	Day	9% 3 18% 36% 28% 6%	539
November	1st to 10th	Day	11% 3 21% 31% 29% 6%	495
	11th to 20th	Day	14% 4 21% 35% 22% 4	500
	21st to end	Day	9% 7% 28% 35% 17% 3	322
December	1st to 10th	Day	6% 8% 35% 28% 18% 5%	300
	11th to 20th	Day	15% 7% 30% 32% 15% 1	300
	21st to end	Day	11% 6% 29% 36% 15% 3	330
January	1st to 10th	Night	13% 7% 33% 34% 13% 1	800
	11th to 20th	Night	12% 6% 28% 38% 15% 1	800
	21st to end	Night	18% 8% 32% 35% 7%	880
February	1st to 10th	Night	15% 6% 27% 38% 13% 1	800
	11th to 20th	Night	12% 5% 31% 40% 11% 1	783
	21st to end	Night	12% 6% 30% 44% 8%	660
March	1st to 10th	Night	8% 7% 33% 40% 12%	800
	11th to 20th	Night	10% 6% 29% 40% 14% 1	800
	21st to end	Night	8% 6% 28% 43% 15% 1	863
April	1st to 10th	Night	8% 5% 28% 43% 15% 1	760
	11th to 20th	Night	9% 4 30% 40% 16% 1	751
	21st to end	Night	7% 3 21% 47% 22%	741
May	1st to 10th	Night	5% 2 13% 51% 26% 2	570
	11th to 20th	Night	7% 2 13% 41% 32% 5%	561
	21st to end	Night	6% 2 7% 35% 43% 7%	617
June	1st to 10th	Night	11% 2 6% 31% 42% 8%	570
	11th to 20th	Night	6% 2 4 24% 41% 22%	570
	21st to end	Night	9% 1 3 17% 46% 23%	570
July	1st to 10th	Night	7% 2 2 12% 47% 30%	555
	11th to 20th	Night	5% 1 2 9% 51% 32%	552
	21st to end	Night	7% 1 3 13% 52% 25%	624
August	1st to 10th	Night	7% 2 3 14% 50% 24%	567
	11th to 20th	Night	7% 1 2 10% 47% 34%	564
	21st to end	Night	12% 2 4 19% 43% 21%	822
September	1st to 10th	Night	11% 2 5% 23% 40% 19%	760
	11th to 20th	Night	12% 4 6% 25% 41% 11%	760
	21st to end	Night	11% 2 8% 28% 42% 8%	760
October	1st to 10th	Night	13% 3 13% 38% 29% 4	760
	11th to 20th	Night	6% 2 14% 41% 34% 3	760
	21st to end	Night	11% 3 17% 40% 28% 2	836
November	1st to 10th	Night	11% 4 19% 39% 25% 2	780
	11th to 20th	Night	12% 5% 19% 41% 21% 2	800
	21st to end	Night	11% 5% 25% 42% 17% 1	800
December	1st to 10th	Night	11% 3 24% 39% 22% 1	800
	11th to 20th	Night	12% 4 24% 41% 18% 1	800
	21st to end	Night	12% 6% 25% 39% 17% 1	880

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