Colton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colton 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	11% 7% 3 7% 5% 4 5% 4 6% 7% 41%	126911
	Night	9% 7% 3 7% 5% 4 4 4 5% 7% 44%	124053
Transparency	Day	39% 7% 14% 24% 14% 2	130476
	Night	37% 7% 14% 25% 15% 2	128545
Seeing	Day	15% 10% 32% 28% 12% 2	17429
	Night	13% 9% 35% 33% 10% 1	27327

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	10% 12% 4 15% 10% 7% 6% 5% 5% 7% 20%	3475
	11th to 20th	Day	5% 10% 4 12% 6% 6% 9% 4 9% 9% 27%	3710
	21st to end	Day	4 9% 6% 14% 6% 6% 5% 4 5% 6% 34%	4488
February	1st to 10th	Day	8% 12% 4 12% 8% 8% 5% 5% 5% 6% 27%	1800
	11th to 20th	Day	7% 9% 4 11% 7% 6% 5% 5% 6% 6% 33%	1777
	21st to end	Day	9% 10% 4 8% 6% 4 4 4 6% 7% 39%	1650
March	1st to 10th	Day	10% 7% 3 8% 4 3 4 3 5% 6% 46%	4737
	11th to 20th	Day	8% 7% 3 7% 4 3 3 3 5% 8% 49%	4980
	21st to end	Day	21% 12% 4 10% 5% 4 4 4 5% 7% 24%	5462
April	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 7% 7% 36%	2275
	11th to 20th	Day	18% 9% 3 6% 5% 4 4 3 4 6% 37%	2572
	21st to end	Day	20% 9% 2 6% 4 4 4 3 4 6% 38%	2600
May	1st to 10th	Day	11% 5% 2 5% 3 3 4 4 6% 7% 50%	5862
	11th to 20th	Day	16% 8% 2 5% 3 3 3 3 4 6% 47%	5862
	21st to end	Day	18% 8% 3 6% 4 4 4 3 5% 7% 36%	6926
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 46%	2946
	11th to 20th	Day	13% 6% 2 5% 4 4 4 4 6% 8% 44%	3000
	21st to end	Day	10% 4 1 5% 4 5% 4 4 7% 8% 47%	3000
July	1st to 10th	Day	7% 4 2 6% 4 5% 5% 5% 8% 10% 44%	6800
	11th to 20th	Day	8% 5% 2 5% 3 4 4 3 5% 8% 54%	6346
	21st to end	Day	6% 5% 2 6% 4 4 5% 5% 7% 10% 46%	6422
August	1st to 10th	Day	8% 6% 2 6% 4 5% 5% 5% 7% 9% 43%	4234
	11th to 20th	Day	15% 7% 2 6% 5% 4 5% 4 7% 8% 37%	4171
	21st to end	Day	8% 4 2 6% 4 4 3 3 5% 7% 52%	4675
September	1st to 10th	Day	13% 5% 1 5% 3 3 3 3 5% 7% 52%	2332
	11th to 20th	Day	10% 5% 2 5% 4 3 4 3 5% 6% 53%	2200
	21st to end	Day	11% 5% 1 5% 3 3 4 3 5% 6% 54%	2200
October	1st to 10th	Day	14% 6% 2 5% 3 3 4 3 5% 7% 48%	2066
	11th to 20th	Day	14% 7% 2 4 3 3 3 3 4 6% 51%	2000
	21st to end	Day	14% 9% 2 7% 3 3 4 3 5% 5% 45%	2097
November	1st to 10th	Day	10% 8% 3 7% 4 4 4 3 6% 8% 44%	1853
	11th to 20th	Day	8% 10% 4 10% 5% 5% 5% 3 6% 5% 40%	1736
	21st to end	Day	11% 10% 3 7% 5% 4 5% 3 7% 7% 39%	1680
December	1st to 10th	Day	4 7% 4 10% 7% 6% 7% 5% 6% 8% 36%	2626
	11th to 20th	Day	8% 12% 6% 12% 7% 7% 5% 5% 6% 7% 25%	2853
	21st to end	Day	15% 10% 3 15% 5% 4 4 4 6% 8% 25%	3498
January	1st to 10th	Night	7% 10% 4 14% 10% 7% 7% 5% 6% 7% 25%	6487
	11th to 20th	Night	3 7% 3 10% 7% 7% 8% 6% 8% 9% 32%	6255
	21st to end	Night	4 8% 5% 11% 4 5% 5% 4 6% 6% 41%	6490
February	1st to 10th	Night	7% 11% 4 9% 7% 5% 5% 4 6% 6% 36%	2600
	11th to 20th	Night	7% 9% 4 9% 6% 5% 4 4 5% 7% 40%	2528
	21st to end	Night	8% 9% 3 8% 5% 6% 5% 4 5% 7% 41%	1980
March	1st to 10th	Night	10% 8% 2 6% 3 3 3 3 4 6% 51%	5126
	11th to 20th	Night	9% 6% 2 5% 3 3 3 4 5% 9% 50%	4980
	21st to end	Night	18% 11% 3 7% 6% 4 4 3 4 6% 33%	5467
April	1st to 10th	Night	14% 10% 3 5% 5% 4 4 4 5% 7% 39%	2119
	11th to 20th	Night	16% 8% 3 5% 4 3 3 3 4 6% 44%	1779
	21st to end	Night	17% 9% 3 5% 4 5% 3 3 6% 6% 40%	1800
May	1st to 10th	Night	13% 4 2 4 3 2 3 3 5% 6% 56%	4053
	11th to 20th	Night	12% 7% 2 5% 3 3 3 2 4 6% 50%	4053
	21st to end	Night	18% 6% 2 6% 4 3 5% 4 5% 7% 41%	3947
June	1st to 10th	Night	6% 6% 2 5% 3 3 5% 3 7% 8% 52%	1450
	11th to 20th	Night	7% 5% 1 4 4 4 4 4 6% 9% 52%	1400
	21st to end	Night	8% 4 2 4 3 3 4 4 5% 9% 56%	1400
July	1st to 10th	Night	8% 5% 2 5% 3 4 4 4 7% 9% 50%	3178
	11th to 20th	Night	7% 5% 2 5% 3 3 4 3 5% 6% 58%	3627
	21st to end	Night	7% 4 1 4 3 3 4 3 6% 9% 53%	4448
August	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 3 6% 8% 47%	2926
	11th to 20th	Night	11% 5% 3 5% 4 4 4 3 5% 7% 49%	2888
	21st to end	Night	8% 4 1 4 3 3 4 4 6% 8% 56%	3234
September	1st to 10th	Night	8% 4 2 4 3 3 4 3 5% 6% 59%	2062
	11th to 20th	Night	7% 5% 2 5% 4 3 3 3 5% 7% 56%	2200
	21st to end	Night	8% 5% 2 3 3 3 3 3 5% 6% 60%	2200
October	1st to 10th	Night	13% 5% 2 4 3 3 3 3 4 6% 54%	2313
	11th to 20th	Night	13% 6% 2 5% 3 3 4 2 5% 6% 50%	2400
	21st to end	Night	13% 8% 2 6% 3 3 3 3 4 7% 48%	2740
November	1st to 10th	Night	9% 5% 3 6% 4 4 5% 3 5% 7% 49%	2665
	11th to 20th	Night	7% 9% 3 8% 4 4 5% 4 6% 7% 44%	2882
	21st to end	Night	8% 7% 3 8% 4 4 4 4 5% 7% 45%	2940
December	1st to 10th	Night	4 7% 3 12% 5% 6% 4 4 5% 7% 42%	4609
	11th to 20th	Night	9% 9% 4 8% 6% 7% 6% 4 7% 8% 34%	5347
	21st to end	Night	14% 13% 4 14% 6% 5% 4 4 5% 5% 26%	7480

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	62% 7% 14% 12% 5%	3476
	11th to 20th	Day	52% 4 11% 18% 14%	3710
	21st to end	Day	47% 8% 17% 17% 11%	4488
February	1st to 10th	Day	55% 8% 12% 15% 9%	1800
	11th to 20th	Day	48% 8% 13% 19% 10% 2	1786
	21st to end	Day	44% 7% 16% 20% 11% 1	1650
March	1st to 10th	Day	37% 7% 12% 31% 11% 2	4737
	11th to 20th	Day	32% 6% 10% 31% 19% 2	4980
	21st to end	Day	58% 7% 12% 16% 5% 1	5464
April	1st to 10th	Day	45% 6% 15% 23% 11% 1	2275
	11th to 20th	Day	47% 6% 12% 22% 12% 2	2572
	21st to end	Day	46% 6% 14% 24% 10%	2600
May	1st to 10th	Day	30% 7% 12% 26% 24%	5900
	11th to 20th	Day	38% 6% 11% 21% 15% 9%	5866
	21st to end	Day	45% 8% 12% 22% 13% 1	6940
June	1st to 10th	Day	33% 9% 17% 28% 12% 2	2946
	11th to 20th	Day	37% 8% 16% 24% 13% 2	3000
	21st to end	Day	31% 9% 16% 27% 15% 2	3000
July	1st to 10th	Day	30% 10% 20% 28% 11% 2	6726
	11th to 20th	Day	29% 6% 14% 32% 18% 2	6270
	21st to end	Day	30% 9% 19% 25% 16% 1	6240
August	1st to 10th	Day	34% 9% 15% 27% 14% 2	4220
	11th to 20th	Day	43% 8% 15% 25% 8% 1	4210
	21st to end	Day	30% 8% 18% 26% 15% 2	4674
September	1st to 10th	Day	31% 6% 13% 30% 17% 2	2332
	11th to 20th	Day	31% 7% 17% 30% 15% 1	2200
	21st to end	Day	29% 7% 10% 31% 21% 2	2200
October	1st to 10th	Day	25% 4 9% 28% 30% 4	3365
	11th to 20th	Day	31% 5% 13% 26% 21% 3	3240
	21st to end	Day	40% 5% 14% 22% 18% 1	3366
November	1st to 10th	Day	37% 7% 16% 24% 13% 3	1853
	11th to 20th	Day	43% 7% 14% 23% 12% 1	1736
	21st to end	Day	43% 6% 15% 23% 11% 1	1680
December	1st to 10th	Day	43% 7% 17% 23% 8% 1	2626
	11th to 20th	Day	55% 7% 17% 15% 5%	2850
	21st to end	Day	54% 6% 14% 18% 7% 1	3498
January	1st to 10th	Night	56% 7% 12% 16% 8%	6487
	11th to 20th	Night	44% 7% 16% 17% 15% 1	6255
	21st to end	Night	39% 7% 17% 22% 14%	6490
February	1st to 10th	Night	47% 7% 12% 22% 12% 2	2600
	11th to 20th	Night	43% 7% 12% 23% 13% 3	2529
	21st to end	Night	40% 7% 13% 22% 14% 3	1980
March	1st to 10th	Night	33% 5% 11% 32% 17% 2	5126
	11th to 20th	Night	30% 5% 12% 32% 19% 2	4980
	21st to end	Night	51% 7% 12% 22% 6% 1	5467
April	1st to 10th	Night	43% 7% 14% 23% 12% 1	2119
	11th to 20th	Night	40% 6% 11% 24% 17% 2	1779
	21st to end	Night	43% 7% 11% 25% 12% 2	1800
May	1st to 10th	Night	28% 6% 13% 29% 22% 2	4080
	11th to 20th	Night	33% 7% 11% 20% 20% 8%	4054
	21st to end	Night	40% 8% 12% 27% 12% 1	3955
June	1st to 10th	Night	27% 8% 16% 30% 15% 4	1450
	11th to 20th	Night	29% 7% 18% 25% 18% 4	1400
	21st to end	Night	25% 7% 17% 28% 21% 2	1400
July	1st to 10th	Night	28% 8% 19% 29% 15% 1	3145
	11th to 20th	Night	26% 6% 13% 36% 16% 3	3583
	21st to end	Night	26% 9% 20% 28% 15% 2	4320
August	1st to 10th	Night	33% 8% 15% 26% 16% 2	2916
	11th to 20th	Night	33% 8% 16% 29% 12% 1	2915
	21st to end	Night	25% 8% 19% 24% 20% 3	3234
September	1st to 10th	Night	25% 7% 14% 29% 22% 3	2062
	11th to 20th	Night	27% 6% 15% 32% 17% 2	2200
	21st to end	Night	25% 5% 11% 33% 24% 3	2200
October	1st to 10th	Night	20% 3 7% 26% 41% 3	3781
	11th to 20th	Night	27% 4 14% 29% 25% 3	3899
	21st to end	Night	37% 5% 12% 29% 16% 1	4414
November	1st to 10th	Night	34% 6% 14% 24% 19% 4	2665
	11th to 20th	Night	37% 7% 15% 24% 15% 2	2882
	21st to end	Night	38% 5% 15% 27% 13% 1	2940
December	1st to 10th	Night	40% 6% 17% 28% 8%	4609
	11th to 20th	Night	46% 8% 19% 21% 6%	5349
	21st to end	Night	58% 6% 11% 19% 6%	7480

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	15% 10% 35% 27% 10% 3	300
	11th to 20th	Day	15% 15% 37% 27% 6% 1	300
	21st to end	Day	16% 12% 38% 24% 10%	330
February	1st to 10th	Day	13% 18% 43% 24% 2	300
	11th to 20th	Day	12% 18% 38% 25% 7% 1	300
	21st to end	Day	17% 13% 44% 23% 3	249
March	1st to 10th	Day	16% 15% 43% 21% 4	300
	11th to 20th	Day	18% 12% 41% 19% 10% 1	300
	21st to end	Day	26% 12% 34% 20% 7% 1	330
April	1st to 10th	Day	23% 18% 34% 21% 3	375
	11th to 20th	Day	23% 18% 31% 22% 4 1	690
	21st to end	Day	24% 17% 28% 20% 10% 2	700
May	1st to 10th	Day	19% 12% 31% 26% 11% 2	703
	11th to 20th	Day	21% 10% 30% 23% 13% 2	725
	21st to end	Day	19% 9% 30% 29% 12% 2	789
June	1st to 10th	Day	10% 8% 24% 34% 19% 4	730
	11th to 20th	Day	14% 7% 37% 28% 12% 3	730
	21st to end	Day	11% 7% 33% 35% 12% 2	730
July	1st to 10th	Day	7% 4 25% 36% 23% 5%	721
	11th to 20th	Day	6% 5% 32% 36% 18% 3	718
	21st to end	Day	5% 3 27% 40% 20% 4	794
August	1st to 10th	Day	9% 3 25% 40% 19% 3	726
	11th to 20th	Day	10% 4 26% 35% 21% 5%	715
	21st to end	Day	7% 5% 28% 36% 20% 4	803
September	1st to 10th	Day	14% 7% 30% 30% 16% 3	462
	11th to 20th	Day	9% 6% 39% 29% 15% 2	330
	21st to end	Day	15% 14% 28% 26% 12% 4	330
October	1st to 10th	Day	17% 12% 30% 25% 12% 3	330
	11th to 20th	Day	17% 16% 38% 21% 7% 1	330
	21st to end	Day	20% 17% 35% 22% 5% 1	363
November	1st to 10th	Day	19% 14% 38% 21% 7% 2	330
	11th to 20th	Day	15% 18% 41% 21% 5%	330
	21st to end	Day	18% 17% 35% 22% 7% 1	330
December	1st to 10th	Day	12% 14% 40% 24% 9% 1	306
	11th to 20th	Day	15% 15% 44% 22% 4	300
	21st to end	Day	25% 11% 39% 22% 3 1	330
January	1st to 10th	Night	11% 11% 38% 30% 9% 1	1000
	11th to 20th	Night	11% 13% 38% 32% 5% 1	1000
	21st to end	Night	13% 12% 40% 28% 6%	1100
February	1st to 10th	Night	13% 11% 41% 29% 5% 1	1000
	11th to 20th	Night	12% 11% 40% 30% 6% 1	974
	21st to end	Night	13% 10% 38% 31% 7% 1	660
March	1st to 10th	Night	13% 10% 44% 28% 5% 1	695
	11th to 20th	Night	16% 13% 37% 30% 5%	600
	21st to end	Night	18% 9% 38% 26% 8% 1	660
April	1st to 10th	Night	19% 14% 37% 27% 3	600
	11th to 20th	Night	20% 15% 33% 26% 6% 1	593
	21st to end	Night	19% 13% 34% 26% 8% 1	600
May	1st to 10th	Night	17% 9% 34% 30% 10%	600
	11th to 20th	Night	17% 9% 31% 31% 10% 1	591
	21st to end	Night	16% 7% 33% 33% 10% 1	650
June	1st to 10th	Night	10% 6% 28% 37% 18% 1	600
	11th to 20th	Night	8% 5% 36% 42% 9% 1	600
	21st to end	Night	9% 5% 25% 48% 13%	600
July	1st to 10th	Night	5% 4 23% 43% 23% 1	585
	11th to 20th	Night	4 3 27% 50% 15% 1	582
	21st to end	Night	4 2 26% 52% 15% 1	657
August	1st to 10th	Night	7% 4 24% 47% 19% 1	597
	11th to 20th	Night	9% 3 26% 38% 24% 1	594
	21st to end	Night	6% 4 27% 43% 18% 2	660
September	1st to 10th	Night	9% 4 29% 41% 15% 2	600
	11th to 20th	Night	8% 6% 34% 36% 14% 3	600
	21st to end	Night	11% 7% 35% 33% 13% 1	600
October	1st to 10th	Night	14% 11% 34% 31% 10%	713
	11th to 20th	Night	15% 12% 38% 28% 7%	800
	21st to end	Night	18% 13% 35% 27% 8%	980
November	1st to 10th	Night	12% 10% 40% 29% 9% 1	1025
	11th to 20th	Night	12% 12% 41% 28% 7% 1	1050
	21st to end	Night	12% 10% 39% 32% 7%	1050
December	1st to 10th	Night	11% 12% 39% 31% 6%	1011
	11th to 20th	Night	16% 9% 39% 29% 7% 1	1000
	21st to end	Night	20% 12% 36% 26% 5% 1	1100

Page generated at 2025-11-30 00:00:50. Version ac07

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