Coleman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Coleman clear sky chart from 2005-11-06 to 2026-04-02.

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 7% 5% 5% 5% 4 6% 7% 38%	131438
	Night	13% 9% 3 8% 5% 4 4 3 5% 7% 39%	130704
Transparency	Day	43% 6% 12% 25% 13% 1	134900
	Night	44% 5% 12% 24% 13% 1	135317
Seeing	Day	16% 8% 29% 28% 15% 5%	17860
	Night	17% 6% 30% 34% 12% 1	27894

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% 10% 4 10% 5% 5% 6% 5% 6% 6% 33%	4691
	11th to 20th	Day	10% 12% 4 7% 5% 5% 6% 4 6% 7% 35%	4710
	21st to end	Day	10% 10% 5% 9% 5% 4 4 4 5% 7% 36%	5156
February	1st to 10th	Day	10% 10% 4 8% 5% 5% 4 4 5% 6% 37%	1822
	11th to 20th	Day	10% 11% 4 8% 5% 4 6% 4 5% 6% 37%	2001
	21st to end	Day	12% 13% 4 8% 5% 4 4 4 5% 8% 33%	1730
March	1st to 10th	Day	12% 8% 2 5% 3 3 4 4 5% 7% 48%	4580
	11th to 20th	Day	10% 9% 4 7% 5% 5% 5% 4 6% 8% 37%	4784
	21st to end	Day	25% 11% 3 8% 4 4 4 3 4 5% 29%	6099
April	1st to 10th	Day	14% 12% 4 9% 5% 6% 4 5% 6% 6% 29%	2412
	11th to 20th	Day	20% 9% 2 7% 4 5% 4 4 5% 6% 34%	2374
	21st to end	Day	17% 9% 3 8% 5% 4 5% 4 5% 7% 33%	2585
May	1st to 10th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 45%	6042
	11th to 20th	Day	11% 7% 2 6% 4 5% 5% 4 6% 7% 43%	6319
	21st to end	Day	14% 8% 3 7% 4 5% 5% 4 6% 7% 38%	6935
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 4 5% 6% 8% 42%	2800
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 8% 38%	2800
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 4 7% 9% 40%	2800
July	1st to 10th	Day	12% 5% 2 6% 5% 5% 5% 4 7% 9% 41%	6360
	11th to 20th	Day	6% 4 1 5% 4 5% 5% 4 7% 10% 48%	6360
	21st to end	Day	8% 6% 2 7% 4 5% 5% 4 6% 9% 44%	6924
August	1st to 10th	Day	9% 5% 3 7% 6% 6% 6% 4 6% 8% 40%	4563
	11th to 20th	Day	11% 4 2 6% 4 4 5% 4 6% 7% 46%	4123
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 42%	4312
September	1st to 10th	Day	11% 7% 2 6% 5% 4 5% 3 5% 8% 44%	2400
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 7% 9% 45%	2285
	21st to end	Day	11% 6% 3 7% 5% 5% 4 5% 7% 9% 39%	2200
October	1st to 10th	Day	13% 7% 3 7% 4 4 4 3 5% 8% 43%	2112
	11th to 20th	Day	19% 9% 3 7% 6% 5% 4 4 6% 8% 30%	1930
	21st to end	Day	18% 9% 3 8% 5% 5% 5% 4 5% 6% 33%	1980
November	1st to 10th	Day	13% 7% 2 7% 5% 5% 5% 4 5% 7% 40%	1852
	11th to 20th	Day	13% 11% 4 9% 6% 6% 5% 4 5% 7% 30%	1869
	21st to end	Day	15% 10% 3 7% 5% 5% 5% 4 5% 7% 34%	1680
December	1st to 10th	Day	10% 12% 4 8% 6% 5% 6% 5% 7% 6% 32%	2690
	11th to 20th	Day	13% 17% 4 9% 4 4 5% 3 5% 7% 30%	3088
	21st to end	Day	20% 19% 5% 11% 6% 4 4 2 3 5% 21%	4070
January	1st to 10th	Night	12% 12% 5% 9% 5% 4 4 3 4 6% 38%	8232
	11th to 20th	Night	9% 14% 6% 12% 7% 6% 4 3 5% 5% 28%	8280
	21st to end	Night	7% 12% 5% 11% 6% 5% 5% 4 5% 6% 35%	9058
February	1st to 10th	Night	9% 14% 4 11% 7% 5% 4 3 4 6% 34%	2796
	11th to 20th	Night	10% 10% 4 9% 5% 5% 4 4 5% 6% 38%	2505
	21st to end	Night	13% 11% 4 9% 5% 4 5% 3 5% 6% 34%	2076
March	1st to 10th	Night	13% 7% 3 6% 3 3 3 3 4 7% 48%	5493
	11th to 20th	Night	11% 10% 3 7% 4 4 5% 4 7% 9% 37%	5438
	21st to end	Night	21% 9% 3 8% 5% 5% 4 3 5% 6% 31%	5072
April	1st to 10th	Night	18% 10% 3 7% 5% 4 4 3 5% 7% 35%	2010
	11th to 20th	Night	20% 8% 3 6% 4 4 4 3 5% 6% 37%	1975
	21st to end	Night	17% 8% 2 7% 5% 3 4 4 5% 6% 37%	1814
May	1st to 10th	Night	14% 8% 2 6% 4 3 4 3 5% 7% 44%	3857
	11th to 20th	Night	10% 8% 2 7% 4 4 4 4 6% 6% 44%	3596
	21st to end	Night	17% 8% 3 7% 4 4 4 3 5% 6% 40%	3942
June	1st to 10th	Night	9% 6% 2 5% 5% 4 4 4 6% 8% 46%	1600
	11th to 20th	Night	14% 7% 3 7% 4 6% 4 4 6% 8% 38%	1600
	21st to end	Night	10% 6% 2 5% 4 4 5% 4 6% 9% 45%	1600
July	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 8% 46%	3618
	11th to 20th	Night	8% 4 2 4 3 3 3 3 5% 9% 56%	3617
	21st to end	Night	6% 5% 2 6% 4 4 5% 3 5% 8% 51%	3947
August	1st to 10th	Night	11% 5% 2 6% 6% 5% 4 4 6% 9% 44%	2597
	11th to 20th	Night	11% 5% 1 5% 3 3 5% 4 6% 8% 49%	2924
	21st to end	Night	10% 5% 2 7% 4 4 3 3 5% 6% 50%	3586
September	1st to 10th	Night	8% 5% 2 6% 3 3 3 3 6% 7% 53%	2000
	11th to 20th	Night	11% 5% 2 5% 3 3 3 3 6% 7% 52%	2095
	21st to end	Night	13% 7% 2 5% 3 5% 4 3 5% 7% 46%	2200
October	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 5% 6% 47%	2285
	11th to 20th	Night	16% 8% 3 7% 4 5% 4 3 6% 6% 37%	2470
	21st to end	Night	17% 10% 3 8% 5% 3 4 3 5% 6% 35%	2860
November	1st to 10th	Night	14% 9% 3 6% 4 4 3 3 5% 6% 42%	2666
	11th to 20th	Night	13% 11% 3 7% 6% 5% 4 3 5% 6% 37%	2746
	21st to end	Night	15% 12% 3 8% 5% 4 4 4 6% 6% 34%	2940
December	1st to 10th	Night	13% 11% 3 6% 4 4 3 3 6% 7% 39%	4720
	11th to 20th	Night	12% 15% 6% 11% 7% 5% 4 3 4 5% 28%	5339
	21st to end	Night	23% 16% 4 8% 5% 4 4 3 5% 5% 25%	7150

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% 6% 14% 21% 9% 1	4692
	11th to 20th	Day	48% 4 10% 24% 12% 2	4710
	21st to end	Day	47% 4 13% 21% 16%	5156
February	1st to 10th	Day	46% 5% 13% 23% 12% 1	1822
	11th to 20th	Day	46% 5% 13% 22% 13% 1	2011
	21st to end	Day	49% 5% 11% 22% 11% 1	1730
March	1st to 10th	Day	36% 4 16% 21% 17% 6%	4580
	11th to 20th	Day	42% 7% 15% 23% 12% 2	4784
	21st to end	Day	57% 5% 8% 18% 12%	6101
April	1st to 10th	Day	53% 5% 11% 20% 9% 1	2412
	11th to 20th	Day	49% 5% 9% 23% 13% 2	2374
	21st to end	Day	48% 6% 9% 20% 14% 2	2585
May	1st to 10th	Day	38% 5% 11% 27% 18% 2	6077
	11th to 20th	Day	38% 7% 12% 27% 16% 1	6323
	21st to end	Day	43% 7% 10% 23% 16% 2	6949
June	1st to 10th	Day	38% 6% 13% 27% 15% 2	2800
	11th to 20th	Day	42% 6% 13% 23% 14% 2	2800
	21st to end	Day	39% 6% 15% 26% 13% 2	2800
July	1st to 10th	Day	37% 6% 13% 32% 11% 1	6291
	11th to 20th	Day	28% 7% 14% 37% 13% 1	6285
	21st to end	Day	34% 7% 12% 28% 17% 1	6728
August	1st to 10th	Day	39% 7% 14% 26% 13% 1	4548
	11th to 20th	Day	34% 6% 14% 32% 12% 1	4163
	21st to end	Day	39% 7% 14% 23% 16% 1	4311
September	1st to 10th	Day	38% 5% 15% 28% 13%	2400
	11th to 20th	Day	35% 6% 18% 31% 10%	2285
	21st to end	Day	40% 6% 14% 28% 11%	2200
October	1st to 10th	Day	27% 4 12% 32% 24% 1	3437
	11th to 20th	Day	48% 4 9% 26% 13% 1	3120
	21st to end	Day	45% 5% 13% 28% 8%	3180
November	1st to 10th	Day	44% 5% 12% 26% 13% 1	1852
	11th to 20th	Day	53% 5% 14% 19% 10% 1	1869
	21st to end	Day	49% 6% 16% 22% 5% 1	1680
December	1st to 10th	Day	50% 7% 15% 22% 6%	2690
	11th to 20th	Day	54% 4 12% 15% 13% 2	3085
	21st to end	Day	68% 3 6% 17% 6%	4070
January	1st to 10th	Night	49% 3 10% 26% 11% 1	8233
	11th to 20th	Night	57% 4 9% 16% 13% 1	8280
	21st to end	Night	49% 5% 11% 20% 15%	9058
February	1st to 10th	Night	52% 3 9% 22% 11% 2	2796
	11th to 20th	Night	46% 5% 11% 24% 12% 2	2506
	21st to end	Night	51% 4 11% 23% 10% 2	2076
March	1st to 10th	Night	38% 3 16% 25% 15% 2	5493
	11th to 20th	Night	42% 6% 17% 21% 12% 2	5438
	21st to end	Night	53% 5% 11% 18% 12% 1	5072
April	1st to 10th	Night	50% 5% 8% 19% 17% 2	2010
	11th to 20th	Night	47% 4 9% 22% 14% 4	1975
	21st to end	Night	47% 4 11% 24% 14% 1	1814
May	1st to 10th	Night	40% 4 12% 24% 16% 4	3884
	11th to 20th	Night	37% 7% 13% 25% 16% 2	3597
	21st to end	Night	45% 4 11% 23% 13% 4	3950
June	1st to 10th	Night	34% 6% 13% 30% 15% 2	1600
	11th to 20th	Night	43% 5% 11% 23% 17% 1	1600
	21st to end	Night	35% 7% 15% 29% 13% 2	1600
July	1st to 10th	Night	36% 6% 14% 32% 9% 3	3580
	11th to 20th	Night	26% 4 16% 37% 14% 2	3572
	21st to end	Night	30% 6% 14% 26% 22% 1	3832
August	1st to 10th	Night	37% 5% 13% 26% 17% 1	2588
	11th to 20th	Night	33% 7% 13% 31% 14% 2	2950
	21st to end	Night	34% 5% 13% 26% 19% 2	3586
September	1st to 10th	Night	30% 5% 13% 33% 18% 1	2000
	11th to 20th	Night	32% 4 15% 36% 13% 1	2095
	21st to end	Night	37% 4 15% 30% 13% 1	2200
October	1st to 10th	Night	30% 4 10% 37% 17% 2	3740
	11th to 20th	Night	37% 5% 13% 28% 17% 1	4019
	21st to end	Night	48% 4 10% 25% 13%	4610
November	1st to 10th	Night	43% 4 12% 26% 14% 1	2666
	11th to 20th	Night	48% 5% 13% 21% 12% 1	2746
	21st to end	Night	50% 4 14% 24% 7% 1	2940
December	1st to 10th	Night	44% 4 23% 22% 6% 1	4720
	11th to 20th	Night	58% 5% 11% 15% 10% 1	5341
	21st to end	Night	61% 5% 9% 16% 9%	7150

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% 8% 32% 32% 12% 2	330
	11th to 20th	Day	20% 8% 35% 27% 8% 2	330
	21st to end	Day	19% 9% 34% 29% 7% 1	363
February	1st to 10th	Day	14% 9% 44% 25% 7% 2	330
	11th to 20th	Day	12% 11% 44% 24% 8%	330
	21st to end	Day	19% 14% 41% 21% 5%	273
March	1st to 10th	Day	16% 12% 43% 24% 5%	330
	11th to 20th	Day	19% 12% 32% 24% 9% 3	359
	21st to end	Day	24% 9% 30% 26% 9% 2	594
April	1st to 10th	Day	21% 12% 32% 27% 8% 1	504
	11th to 20th	Day	25% 15% 24% 24% 10% 2	492
	21st to end	Day	23% 9% 28% 24% 14% 2	500
May	1st to 10th	Day	19% 8% 32% 29% 9% 3	579
	11th to 20th	Day	16% 9% 32% 29% 10% 4	725
	21st to end	Day	16% 7% 29% 27% 15% 6%	789
June	1st to 10th	Day	12% 7% 30% 29% 17% 5%	730
	11th to 20th	Day	16% 9% 27% 29% 15% 4	730
	21st to end	Day	14% 7% 26% 33% 15% 5%	730
July	1st to 10th	Day	8% 3 22% 34% 25% 8%	721
	11th to 20th	Day	8% 4 27% 32% 22% 7%	718
	21st to end	Day	7% 3 21% 38% 23% 9%	794
August	1st to 10th	Day	10% 4 19% 35% 22% 11%	726
	11th to 20th	Day	11% 4 16% 30% 25% 13%	562
	21st to end	Day	12% 7% 19% 29% 22% 11%	583
September	1st to 10th	Day	15% 6% 22% 30% 18% 8%	530
	11th to 20th	Day	12% 5% 16% 32% 29% 7%	530
	21st to end	Day	14% 7% 25% 27% 20% 6%	530
October	1st to 10th	Day	15% 12% 27% 25% 17% 4	442
	11th to 20th	Day	18% 15% 36% 23% 8%	330
	21st to end	Day	21% 11% 35% 24% 8% 1	363
November	1st to 10th	Day	14% 12% 37% 24% 11% 2	330
	11th to 20th	Day	15% 17% 34% 23% 9% 2	330
	21st to end	Day	21% 10% 38% 23% 7% 1	330
December	1st to 10th	Day	15% 8% 42% 25% 8% 1	330
	11th to 20th	Day	21% 11% 39% 21% 6% 2	330
	21st to end	Day	26% 12% 34% 21% 7% 1	363
January	1st to 10th	Night	18% 7% 37% 30% 7%	1050
	11th to 20th	Night	19% 8% 37% 27% 9% 1	1050
	21st to end	Night	17% 6% 35% 33% 8% 1	1155
February	1st to 10th	Night	14% 7% 37% 32% 8% 1	1050
	11th to 20th	Night	15% 8% 38% 30% 9%	870
	21st to end	Night	19% 9% 35% 32% 5%	692
March	1st to 10th	Night	17% 6% 32% 36% 8% 1	840
	11th to 20th	Night	16% 8% 38% 29% 8%	826
	21st to end	Night	21% 5% 32% 32% 8% 1	693
April	1st to 10th	Night	22% 6% 35% 31% 5%	603
	11th to 20th	Night	24% 6% 30% 29% 10%	593
	21st to end	Night	21% 6% 30% 33% 10% 1	600
May	1st to 10th	Night	19% 4 30% 36% 10%	600
	11th to 20th	Night	17% 5% 32% 35% 9% 1	591
	21st to end	Night	15% 5% 23% 39% 17% 1	650
June	1st to 10th	Night	11% 5% 26% 43% 15% 1	600
	11th to 20th	Night	16% 5% 25% 40% 13% 2	600
	21st to end	Night	13% 4 21% 43% 19% 1	600
July	1st to 10th	Night	8% 2 17% 47% 25% 1	585
	11th to 20th	Night	10% 4 18% 41% 26% 1	582
	21st to end	Night	7% 2 19% 48% 20% 3	657
August	1st to 10th	Night	9% 1 18% 45% 25% 3	597
	11th to 20th	Night	10% 2 14% 42% 27% 4	594
	21st to end	Night	11% 2 18% 42% 26% 2	660
September	1st to 10th	Night	9% 3 25% 34% 24% 4	600
	11th to 20th	Night	13% 4 22% 33% 25% 4	695
	21st to end	Night	14% 7% 23% 34% 20% 2	800
October	1st to 10th	Night	16% 8% 25% 34% 17% 1	800
	11th to 20th	Night	19% 9% 31% 33% 9%	800
	21st to end	Night	23% 6% 30% 30% 10% 1	880
November	1st to 10th	Night	19% 8% 34% 31% 8% 1	820
	11th to 20th	Night	17% 12% 36% 28% 8%	856
	21st to end	Night	19% 10% 35% 28% 7%	1050
December	1st to 10th	Night	19% 10% 37% 26% 7% 1	1050
	11th to 20th	Night	20% 8% 35% 28% 7% 2	1050
	21st to end	Night	25% 7% 32% 30% 5%	1155

Page generated at 2026-03-30 01:18:43. Version ac07

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