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 2024-11-10.

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%	101449
	Night	10% 7% 3 7% 5% 4 4 4 5% 7% 44%	97779
Transparency	Day	39% 8% 14% 24% 13% 2	105053
	Night	37% 7% 14% 24% 15% 2	102296
Seeing	Day	15% 10% 32% 29% 12% 2	15969
	Night	13% 9% 35% 33% 10% 1	25851

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% 13% 3 13% 10% 6% 6% 5% 6% 6% 21%	2417
	11th to 20th	Day	4 12% 6% 13% 6% 5% 9% 3 8% 10% 24%	2584
	21st to end	Day	5% 12% 7% 17% 6% 6% 6% 4 5% 6% 23%	3135
February	1st to 10th	Day	8% 11% 3 12% 7% 8% 6% 5% 5% 6% 27%	1710
	11th to 20th	Day	8% 10% 4 10% 7% 6% 5% 5% 6% 7% 33%	1685
	21st to end	Day	9% 10% 4 8% 6% 5% 4 4 6% 7% 37%	1570
March	1st to 10th	Day	10% 9% 4 9% 5% 4 4 3 5% 6% 41%	3302
	11th to 20th	Day	10% 8% 3 8% 5% 4 4 3 4 6% 46%	3480
	21st to end	Day	23% 13% 4 11% 4 4 4 3 5% 6% 23%	3814
April	1st to 10th	Day	16% 8% 2 7% 5% 4 4 4 7% 7% 36%	2161
	11th to 20th	Day	19% 9% 3 6% 5% 4 4 3 4 7% 37%	2442
	21st to end	Day	20% 9% 2 6% 4 4 5% 3 4 6% 37%	2470
May	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 6% 8% 38%	4082
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 4 6% 48%	4082
	21st to end	Day	18% 7% 2 5% 4 4 4 4 5% 8% 40%	4815
June	1st to 10th	Day	11% 5% 2 5% 4 4 5% 4 6% 8% 46%	2798
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 6% 8% 44%	2850
	21st to end	Day	9% 4 1 5% 4 5% 4 4 7% 8% 47%	2850
July	1st to 10th	Day	10% 5% 2 6% 4 5% 5% 5% 7% 10% 41%	4750
	11th to 20th	Day	6% 3 1 4 3 4 3 3 6% 8% 58%	4436
	21st to end	Day	4 4 2 5% 4 4 5% 5% 7% 10% 52%	4465
August	1st to 10th	Day	8% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4104
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 7% 8% 37%	4041
	21st to end	Day	8% 4 2 6% 4 4 3 4 5% 7% 52%	4532
September	1st to 10th	Day	13% 5% 1 5% 3 3 3 3 4 7% 53%	2216
	11th to 20th	Day	9% 5% 2 5% 4 3 4 3 5% 6% 54%	2090
	21st to end	Day	11% 5% 1 5% 3 3 4 3 5% 6% 54%	2090
October	1st to 10th	Day	15% 7% 2 5% 3 3 4 3 5% 7% 48%	1963
	11th to 20th	Day	13% 7% 2 4 3 3 3 3 5% 6% 51%	1900
	21st to end	Day	14% 8% 2 7% 3 3 4 3 5% 5% 45%	1992
November	1st to 10th	Day	10% 8% 2 7% 3 4 4 4 6% 8% 44%	1754
	11th to 20th	Day	8% 10% 3 11% 5% 5% 5% 3 6% 5% 40%	1572
	21st to end	Day	11% 9% 3 6% 4 4 5% 3 7% 7% 41%	1520
December	1st to 10th	Day	7% 10% 3 10% 6% 5% 7% 5% 6% 7% 35%	1520
	11th to 20th	Day	8% 11% 6% 10% 7% 7% 4 4 6% 8% 29%	1815
	21st to end	Day	17% 8% 3 14% 6% 4 4 4 6% 6% 26%	2442
January	1st to 10th	Night	9% 11% 3 13% 10% 6% 6% 4 6% 7% 24%	4535
	11th to 20th	Night	4 9% 4 10% 7% 6% 8% 6% 9% 9% 27%	4371
	21st to end	Night	5% 10% 7% 15% 4 6% 5% 4 6% 7% 29%	4532
February	1st to 10th	Night	7% 11% 4 9% 7% 5% 5% 4 6% 6% 36%	2470
	11th to 20th	Night	8% 9% 4 9% 6% 5% 4 4 5% 7% 40%	2399
	21st to end	Night	8% 9% 3 8% 6% 6% 5% 4 5% 7% 40%	1884
March	1st to 10th	Night	8% 7% 2 7% 4 4 4 4 4 7% 49%	3556
	11th to 20th	Night	9% 7% 3 6% 4 3 3 4 5% 8% 49%	3480
	21st to end	Night	22% 13% 4 7% 7% 4 3 3 4 6% 26%	3817
April	1st to 10th	Night	14% 9% 3 5% 5% 4 4 4 5% 7% 39%	2014
	11th to 20th	Night	16% 9% 3 6% 4 3 3 3 4 6% 44%	1689
	21st to end	Night	16% 9% 3 5% 3 5% 3 3 6% 6% 40%	1710
May	1st to 10th	Night	18% 6% 2 4 3 3 4 3 5% 6% 46%	2823
	11th to 20th	Night	9% 5% 2 6% 3 4 4 3 5% 8% 51%	2823
	21st to end	Night	16% 5% 2 5% 4 3 5% 4 5% 8% 44%	2748
June	1st to 10th	Night	6% 6% 1 4 3 3 5% 3 7% 9% 52%	1378
	11th to 20th	Night	8% 5% 1 4 3 4 4 4 5% 9% 52%	1330
	21st to end	Night	6% 4 2 4 3 2 3 4 5% 9% 57%	1330
July	1st to 10th	Night	9% 6% 2 5% 3 4 4 4 6% 8% 49%	2220
	11th to 20th	Night	3 3 1 3 2 3 4 3 5% 6% 66%	2530
	21st to end	Night	3 3 1 3 3 3 4 3 7% 10% 59%	3097
August	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 4 6% 8% 48%	2836
	11th to 20th	Night	11% 5% 3 5% 4 4 3 4 5% 7% 49%	2798
	21st to end	Night	8% 4 1 4 3 3 4 4 6% 8% 56%	3135
September	1st to 10th	Night	9% 4 2 4 3 3 4 3 4 6% 59%	1958
	11th to 20th	Night	7% 5% 2 5% 4 3 3 3 5% 7% 57%	2090
	21st to end	Night	9% 5% 2 3 3 3 3 3 5% 6% 59%	2090
October	1st to 10th	Night	14% 5% 2 4 3 3 3 3 4 6% 54%	2197
	11th to 20th	Night	12% 6% 2 5% 3 3 4 2 6% 6% 51%	2280
	21st to end	Night	13% 8% 2 7% 3 3 3 3 4 7% 48%	2603
November	1st to 10th	Night	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2529
	11th to 20th	Night	7% 9% 2 8% 4 4 5% 4 6% 7% 43%	2607
	21st to end	Night	8% 7% 2 7% 4 4 4 4 5% 7% 46%	2660
December	1st to 10th	Night	7% 9% 3 11% 5% 6% 5% 4 5% 7% 38%	2660
	11th to 20th	Night	9% 9% 3 8% 5% 4 5% 4 7% 8% 38%	3375
	21st to end	Night	17% 11% 4 14% 5% 4 4 4 4 6% 27%	5225

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	61% 8% 12% 13% 5%	2418
	11th to 20th	Day	54% 5% 9% 23% 7%	2584
	21st to end	Day	57% 9% 15% 12% 7%	3135
February	1st to 10th	Day	55% 8% 12% 16% 9%	1710
	11th to 20th	Day	48% 8% 14% 19% 9% 2	1694
	21st to end	Day	46% 8% 16% 19% 11% 1	1570
March	1st to 10th	Day	40% 9% 12% 28% 9% 1	3302
	11th to 20th	Day	37% 6% 10% 28% 14% 3	3480
	21st to end	Day	61% 8% 13% 13% 4 1	3814
April	1st to 10th	Day	44% 6% 15% 23% 11% 1	2161
	11th to 20th	Day	47% 6% 12% 21% 11% 2	2442
	21st to end	Day	46% 6% 14% 23% 10%	2470
May	1st to 10th	Day	40% 9% 14% 22% 15%	4120
	11th to 20th	Day	35% 8% 12% 27% 15% 3	4086
	21st to end	Day	40% 8% 13% 24% 14% 1	4828
June	1st to 10th	Day	33% 9% 17% 28% 12% 2	2798
	11th to 20th	Day	38% 7% 15% 24% 14% 2	2850
	21st to end	Day	30% 9% 16% 27% 14% 2	2850
July	1st to 10th	Day	33% 11% 20% 23% 11% 2	4676
	11th to 20th	Day	23% 6% 15% 33% 20% 3	4360
	21st to end	Day	24% 10% 18% 26% 20% 2	4325
August	1st to 10th	Day	34% 9% 15% 27% 14% 2	4090
	11th to 20th	Day	43% 8% 15% 25% 8% 1	4080
	21st to end	Day	30% 8% 19% 25% 15% 2	4531
September	1st to 10th	Day	32% 6% 12% 30% 18% 2	2216
	11th to 20th	Day	30% 7% 17% 31% 15% 1	2090
	21st to end	Day	30% 7% 11% 31% 19% 2	2090
October	1st to 10th	Day	26% 4 9% 27% 30% 4	3262
	11th to 20th	Day	31% 5% 13% 27% 20% 4	3140
	21st to end	Day	40% 5% 14% 22% 18% 1	3261
November	1st to 10th	Day	37% 7% 16% 24% 13% 3	1754
	11th to 20th	Day	44% 7% 14% 22% 12% 1	1572
	21st to end	Day	41% 6% 16% 23% 12% 1	1520
December	1st to 10th	Day	45% 8% 17% 19% 9% 2	1520
	11th to 20th	Day	51% 8% 17% 18% 5%	1812
	21st to end	Day	55% 7% 13% 17% 7% 1	2442
January	1st to 10th	Night	57% 8% 11% 17% 7%	4535
	11th to 20th	Night	48% 8% 14% 21% 9% 1	4371
	21st to end	Night	49% 9% 18% 14% 9%	4532
February	1st to 10th	Night	47% 7% 12% 22% 11% 1	2470
	11th to 20th	Night	42% 7% 12% 23% 13% 3	2400
	21st to end	Night	41% 7% 13% 21% 14% 3	1884
March	1st to 10th	Night	33% 7% 14% 27% 18% 2	3556
	11th to 20th	Night	32% 7% 13% 29% 17% 2	3480
	21st to end	Night	58% 8% 13% 16% 5% 1	3817
April	1st to 10th	Night	42% 8% 14% 23% 12% 1	2014
	11th to 20th	Night	42% 6% 11% 22% 17% 2	1689
	21st to end	Night	42% 7% 11% 25% 13% 2	1710
May	1st to 10th	Night	37% 7% 15% 22% 17% 3	2850
	11th to 20th	Night	29% 8% 14% 26% 21% 3	2824
	21st to end	Night	37% 9% 13% 26% 14% 1	2756
June	1st to 10th	Night	26% 9% 17% 29% 16% 4	1378
	11th to 20th	Night	28% 7% 18% 24% 19% 4	1330
	21st to end	Night	23% 7% 17% 29% 22% 2	1330
July	1st to 10th	Night	31% 8% 21% 23% 14% 2	2185
	11th to 20th	Night	17% 6% 15% 37% 21% 4	2483
	21st to end	Night	18% 10% 18% 31% 20% 3	2999
August	1st to 10th	Night	33% 8% 15% 27% 16% 2	2826
	11th to 20th	Night	33% 8% 16% 29% 12% 1	2825
	21st to end	Night	25% 8% 19% 23% 20% 3	3135
September	1st to 10th	Night	25% 7% 14% 29% 23% 3	1958
	11th to 20th	Night	27% 6% 15% 33% 18% 2	2090
	21st to end	Night	26% 6% 11% 32% 23% 2	2090
October	1st to 10th	Night	20% 3 7% 25% 41% 3	3665
	11th to 20th	Night	26% 4 14% 29% 25% 2	3779
	21st to end	Night	37% 5% 13% 29% 16% 1	4277
November	1st to 10th	Night	34% 6% 14% 23% 20% 4	2529
	11th to 20th	Night	37% 8% 14% 25% 15% 2	2607
	21st to end	Night	37% 5% 16% 27% 15% 1	2660
December	1st to 10th	Night	44% 7% 17% 22% 9%	2660
	11th to 20th	Night	42% 8% 21% 22% 7%	3377
	21st to end	Night	57% 6% 11% 18% 7% 1	5225

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	16% 10% 34% 27% 10% 2	270
	11th to 20th	Day	15% 15% 36% 27% 6%	270
	21st to end	Day	18% 11% 37% 24% 10%	297
February	1st to 10th	Day	12% 16% 44% 26% 2	270
	11th to 20th	Day	13% 18% 39% 23% 7% 1	270
	21st to end	Day	16% 14% 44% 24% 2	225
March	1st to 10th	Day	17% 16% 43% 19% 5%	270
	11th to 20th	Day	19% 11% 40% 19% 10% 1	270
	21st to end	Day	25% 12% 34% 21% 8% 1	297
April	1st to 10th	Day	23% 19% 34% 20% 3	341
	11th to 20th	Day	24% 17% 31% 22% 5% 1	640
	21st to end	Day	24% 17% 27% 20% 10% 2	650
May	1st to 10th	Day	20% 12% 32% 26% 8% 1	653
	11th to 20th	Day	20% 10% 31% 23% 14% 2	675
	21st to end	Day	18% 9% 31% 30% 11% 1	734
June	1st to 10th	Day	10% 8% 24% 35% 19% 4	680
	11th to 20th	Day	14% 7% 36% 27% 12% 3	680
	21st to end	Day	10% 7% 32% 36% 13% 2	680
July	1st to 10th	Day	7% 4 24% 36% 24% 5%	671
	11th to 20th	Day	6% 5% 32% 36% 19% 3	668
	21st to end	Day	5% 3 26% 41% 21% 4	739
August	1st to 10th	Day	9% 3 24% 41% 20% 4	676
	11th to 20th	Day	11% 4 25% 34% 22% 4	665
	21st to end	Day	7% 6% 29% 36% 19% 4	748
September	1st to 10th	Day	15% 7% 31% 30% 15% 3	426
	11th to 20th	Day	8% 6% 38% 30% 16% 2	300
	21st to end	Day	16% 15% 30% 26% 10% 4	300
October	1st to 10th	Day	19% 11% 30% 24% 12% 4	300
	11th to 20th	Day	15% 16% 38% 22% 8% 1	300
	21st to end	Day	19% 18% 35% 23% 5% 1	330
November	1st to 10th	Day	20% 13% 34% 23% 7% 2	297
	11th to 20th	Day	13% 18% 41% 22% 6%	270
	21st to end	Day	20% 16% 33% 24% 7%	270
December	1st to 10th	Day	11% 14% 40% 24% 9% 1	270
	11th to 20th	Day	14% 14% 44% 23% 5%	270
	21st to end	Day	25% 12% 39% 21% 3	297
January	1st to 10th	Night	11% 11% 38% 29% 9% 1	950
	11th to 20th	Night	11% 13% 37% 32% 5% 1	950
	21st to end	Night	14% 12% 38% 29% 7%	1045
February	1st to 10th	Night	13% 11% 40% 30% 5% 1	950
	11th to 20th	Night	13% 11% 39% 30% 6% 1	925
	21st to end	Night	13% 9% 38% 31% 7% 1	628
March	1st to 10th	Night	12% 10% 44% 28% 5% 1	660
	11th to 20th	Night	15% 12% 37% 31% 5%	570
	21st to end	Night	18% 9% 37% 28% 8% 1	627
April	1st to 10th	Night	19% 14% 37% 27% 3	570
	11th to 20th	Night	20% 15% 32% 26% 7% 1	563
	21st to end	Night	18% 13% 34% 26% 9% 1	570
May	1st to 10th	Night	17% 10% 34% 29% 9%	570
	11th to 20th	Night	16% 9% 32% 30% 11% 1	561
	21st to end	Night	16% 7% 34% 33% 10%	617
June	1st to 10th	Night	9% 6% 29% 37% 18% 1	570
	11th to 20th	Night	9% 5% 35% 42% 9% 1	570
	21st to end	Night	8% 4 25% 49% 14%	570
July	1st to 10th	Night	5% 4 24% 42% 24% 1	555
	11th to 20th	Night	3 3 27% 51% 16% 1	552
	21st to end	Night	4 2 25% 52% 16% 1	624
August	1st to 10th	Night	6% 3 24% 46% 20% 1	567
	11th to 20th	Night	9% 2 26% 38% 24% 1	564
	21st to end	Night	6% 4 28% 43% 18% 2	627
September	1st to 10th	Night	10% 3 29% 41% 15% 2	570
	11th to 20th	Night	8% 6% 35% 35% 14% 3	570
	21st to end	Night	11% 7% 36% 32% 12% 1	570
October	1st to 10th	Night	15% 10% 34% 31% 10%	677
	11th to 20th	Night	14% 11% 39% 29% 7%	760
	21st to end	Night	18% 12% 34% 27% 8%	931
November	1st to 10th	Night	12% 9% 39% 30% 9% 1	973
	11th to 20th	Night	12% 12% 39% 28% 8% 1	950
	21st to end	Night	12% 11% 39% 31% 7%	950
December	1st to 10th	Night	11% 12% 40% 30% 6%	950
	11th to 20th	Night	16% 9% 38% 30% 7% 1	950
	21st to end	Night	21% 12% 36% 26% 5%	1045

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