Cameron
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cameron clear sky chart from 2005-11-06 to 2025-07-06.

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% 4 4 4 3 5% 7% 44%	120022
	Night	11% 7% 3 7% 4 4 4 3 5% 6% 46%	118996
Transparency	Day	38% 5% 12% 25% 17% 2	123673
	Night	37% 4 11% 25% 19% 3	123488
Seeing	Day	14% 10% 29% 28% 15% 4	16622
	Night	14% 9% 33% 32% 11% 1	26490

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	14% 9% 3 9% 5% 4 4 4 5% 7% 35%	4031
	11th to 20th	Day	7% 9% 4 9% 6% 6% 7% 3 4 5% 39%	4080
	21st to end	Day	12% 13% 6% 12% 5% 5% 4 3 4 4 32%	4488
February	1st to 10th	Day	13% 10% 5% 7% 5% 5% 5% 3 6% 6% 34%	1800
	11th to 20th	Day	12% 11% 5% 7% 5% 3 4 2 5% 7% 40%	1754
	21st to end	Day	11% 9% 3 7% 4 3 4 3 5% 6% 44%	1671
March	1st to 10th	Day	15% 8% 2 6% 3 2 3 2 4 4 49%	4936
	11th to 20th	Day	9% 7% 2 5% 3 4 4 3 5% 6% 51%	4980
	21st to end	Day	14% 12% 5% 8% 5% 5% 5% 4 5% 7% 31%	5462
April	1st to 10th	Day	14% 8% 3 6% 5% 4 3 4 4 6% 43%	2340
	11th to 20th	Day	14% 9% 2 8% 4 4 4 3 5% 7% 40%	2374
	21st to end	Day	20% 8% 3 8% 4 5% 4 3 5% 6% 34%	2530
May	1st to 10th	Day	13% 8% 3 6% 4 4 4 4 6% 7% 43%	5862
	11th to 20th	Day	15% 6% 2 5% 4 4 3 3 4 7% 46%	5862
	21st to end	Day	16% 7% 2 6% 4 4 4 3 5% 7% 41%	6881
June	1st to 10th	Day	6% 5% 2 5% 5% 5% 5% 5% 7% 9% 47%	2800
	11th to 20th	Day	7% 6% 2 6% 5% 4 5% 4 8% 8% 46%	2800
	21st to end	Day	7% 4 2 5% 5% 4 5% 4 6% 9% 49%	2800
July	1st to 10th	Day	10% 7% 3 7% 4 5% 4 5% 6% 8% 41%	4418
	11th to 20th	Day	7% 4 1 5% 4 3 4 4 6% 8% 54%	4120
	21st to end	Day	5% 3 2 6% 4 5% 5% 5% 7% 11% 47%	4465
August	1st to 10th	Day	5% 4 2 5% 4 4 4 4 7% 9% 50%	4104
	11th to 20th	Day	11% 5% 2 5% 4 4 4 4 6% 8% 46%	4041
	21st to end	Day	6% 4 2 5% 3 4 4 3 7% 9% 53%	4254
September	1st to 10th	Day	11% 5% 1 3 3 4 4 3 5% 7% 54%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 50%	2152
	21st to end	Day	9% 4 2 5% 4 3 4 3 4 5% 56%	2052
October	1st to 10th	Day	12% 7% 2 4 4 4 3 2 5% 6% 52%	1900
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 4 4 54%	1900
	21st to end	Day	14% 8% 3 6% 3 4 4 2 5% 6% 47%	2090
November	1st to 10th	Day	9% 6% 2 5% 3 3 3 4 6% 7% 52%	1958
	11th to 20th	Day	13% 6% 3 5% 4 3 3 3 5% 6% 48%	1637
	21st to end	Day	15% 10% 3 5% 3 2 3 3 5% 6% 43%	1600
December	1st to 10th	Day	6% 6% 2 7% 5% 3 4 3 5% 7% 54%	2610
	11th to 20th	Day	11% 9% 3 8% 4 4 3 3 4 6% 45%	3008
	21st to end	Day	18% 15% 7% 13% 4 4 3 3 4 5% 23%	3982
January	1st to 10th	Night	11% 10% 4 15% 6% 5% 4 3 5% 6% 31%	5916
	11th to 20th	Night	8% 8% 4 9% 5% 5% 6% 4 6% 5% 40%	5900
	21st to end	Night	13% 10% 5% 12% 4 4 4 3 4 4 37%	6490
February	1st to 10th	Night	11% 12% 4 8% 5% 5% 4 4 5% 5% 37%	2600
	11th to 20th	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	2533
	21st to end	Night	12% 8% 3 5% 4 3 3 3 5% 5% 48%	1975
March	1st to 10th	Night	15% 8% 3 5% 3 3 3 3 4 4 48%	4919
	11th to 20th	Night	9% 7% 2 5% 3 3 3 3 5% 6% 55%	4980
	21st to end	Night	14% 9% 4 9% 5% 4 5% 4 6% 6% 34%	5467
April	1st to 10th	Night	11% 6% 2 7% 3 3 4 3 5% 7% 49%	2060
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 5% 7% 45%	1975
	21st to end	Night	15% 9% 3 6% 4 3 4 4 5% 6% 41%	1868
May	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 9% 45%	4053
	11th to 20th	Night	14% 7% 2 5% 3 3 3 3 5% 7% 49%	4053
	21st to end	Night	15% 6% 2 6% 4 3 4 3 4 6% 47%	3991
June	1st to 10th	Night	5% 3 1 4 3 4 5% 4 7% 9% 54%	1600
	11th to 20th	Night	4 4 1 5% 4 5% 5% 4 8% 10% 51%	1600
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 10% 59%	1600
July	1st to 10th	Night	10% 7% 3 6% 3 4 3 3 4 7% 48%	2657
	11th to 20th	Night	3 3 1 4 3 4 4 3 6% 8% 62%	2850
	21st to end	Night	5% 4 1 5% 4 4 5% 4 8% 11% 48%	3098
August	1st to 10th	Night	3 2 1 2 3 3 4 4 6% 10% 61%	2836
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 4 7% 53%	2798
	21st to end	Night	5% 3 2 5% 4 3 4 3 5% 8% 58%	3404
September	1st to 10th	Night	9% 4 1 4 3 3 4 3 5% 7% 57%	1900
	11th to 20th	Night	9% 4 1 5% 3 4 4 4 5% 7% 55%	2023
	21st to end	Night	7% 4 2 4 4 3 3 3 4 7% 58%	2107
October	1st to 10th	Night	10% 6% 2 4 3 3 2 3 4 6% 56%	2280
	11th to 20th	Night	13% 5% 1 4 4 3 3 3 4 6% 56%	2280
	21st to end	Night	16% 7% 2 5% 4 3 3 2 3 5% 51%	2508
November	1st to 10th	Night	9% 4 2 4 2 3 3 3 4 6% 61%	2340
	11th to 20th	Night	11% 7% 2 5% 4 4 3 3 4 5% 52%	2760
	21st to end	Night	14% 9% 2 6% 4 3 3 3 5% 5% 48%	2800
December	1st to 10th	Night	7% 7% 2 5% 4 3 4 4 4 6% 54%	4580
	11th to 20th	Night	12% 8% 3 8% 3 3 4 3 5% 8% 43%	5199
	21st to end	Night	20% 16% 6% 10% 5% 3 3 3 4 4 28%	6996

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	48% 5% 12% 24% 11% 1	4032
	11th to 20th	Day	48% 3 12% 18% 14% 5%	4080
	21st to end	Day	55% 4 10% 16% 13% 1	4488
February	1st to 10th	Day	50% 5% 12% 20% 10% 2	1800
	11th to 20th	Day	45% 4 12% 23% 14% 2	1763
	21st to end	Day	41% 5% 11% 23% 19% 2	1671
March	1st to 10th	Day	39% 3 9% 23% 22% 4	4936
	11th to 20th	Day	33% 5% 8% 24% 25% 4	4980
	21st to end	Day	50% 7% 16% 21% 5% 1	5464
April	1st to 10th	Day	42% 5% 11% 25% 14% 2	2340
	11th to 20th	Day	43% 5% 13% 23% 15% 1	2374
	21st to end	Day	49% 6% 12% 22% 11% 1	2530
May	1st to 10th	Day	39% 7% 12% 25% 16% 1	5900
	11th to 20th	Day	38% 5% 11% 26% 17% 3	5866
	21st to end	Day	42% 5% 10% 26% 16% 1	6895
June	1st to 10th	Day	30% 9% 15% 30% 14% 2	2800
	11th to 20th	Day	32% 7% 14% 27% 18% 1	2800
	21st to end	Day	30% 7% 17% 28% 15% 3	2800
July	1st to 10th	Day	40% 6% 14% 25% 12% 3	4351
	11th to 20th	Day	28% 5% 11% 35% 19% 2	4051
	21st to end	Day	28% 7% 17% 31% 14% 2	4325
August	1st to 10th	Day	28% 6% 16% 30% 19% 1	4090
	11th to 20th	Day	35% 6% 15% 28% 16% 1	4080
	21st to end	Day	27% 7% 17% 30% 14% 5%	4253
September	1st to 10th	Day	30% 6% 11% 28% 20% 5%	2280
	11th to 20th	Day	32% 6% 13% 27% 21% 2	2152
	21st to end	Day	30% 5% 8% 32% 22% 3	2052
October	1st to 10th	Day	20% 3 7% 22% 44% 4	3160
	11th to 20th	Day	22% 2 5% 25% 36% 10%	3140
	21st to end	Day	34% 4 10% 25% 24% 3	3428
November	1st to 10th	Day	31% 5% 14% 27% 19% 4	1958
	11th to 20th	Day	36% 4 11% 27% 19% 2	1637
	21st to end	Day	42% 4 10% 27% 16%	1600
December	1st to 10th	Day	31% 5% 17% 30% 17%	2610
	11th to 20th	Day	41% 4 14% 29% 10% 1	3005
	21st to end	Day	65% 4 13% 13% 6% 1	3982
January	1st to 10th	Night	54% 5% 10% 20% 10% 1	5916
	11th to 20th	Night	44% 4 11% 21% 15% 4	5900
	21st to end	Night	50% 4 11% 16% 15% 4	6490
February	1st to 10th	Night	48% 4 12% 19% 14% 3	2600
	11th to 20th	Night	43% 4 12% 22% 16% 3	2534
	21st to end	Night	37% 4 10% 23% 19% 6%	1975
March	1st to 10th	Night	39% 3 8% 22% 23% 3	4919
	11th to 20th	Night	30% 4 7% 26% 26% 7%	4980
	21st to end	Night	48% 7% 14% 23% 7% 2	5467
April	1st to 10th	Night	36% 5% 10% 27% 18% 4	2060
	11th to 20th	Night	39% 5% 11% 27% 15% 3	1975
	21st to end	Night	43% 5% 11% 25% 15% 1	1868
May	1st to 10th	Night	37% 6% 12% 27% 17% 1	4080
	11th to 20th	Night	35% 5% 11% 27% 18% 5%	4054
	21st to end	Night	38% 5% 10% 25% 20% 1	3999
June	1st to 10th	Night	24% 8% 17% 32% 16% 3	1600
	11th to 20th	Night	27% 8% 15% 28% 19% 3	1600
	21st to end	Night	21% 5% 17% 34% 20% 4	1600
July	1st to 10th	Night	35% 4 13% 24% 20% 4	2615
	11th to 20th	Night	18% 6% 16% 36% 21% 2	2796
	21st to end	Night	27% 7% 19% 33% 13% 1	2999
August	1st to 10th	Night	18% 5% 20% 29% 26% 2	2826
	11th to 20th	Night	33% 4 12% 28% 22% 1	2825
	21st to end	Night	25% 5% 15% 33% 17% 5%	3404
September	1st to 10th	Night	28% 5% 11% 26% 23% 8%	1900
	11th to 20th	Night	27% 5% 12% 29% 24% 3	2023
	21st to end	Night	28% 4 8% 30% 27% 4	2107
October	1st to 10th	Night	18% 3 7% 19% 49% 5%	3800
	11th to 20th	Night	21% 2 6% 26% 33% 11%	3779
	21st to end	Night	36% 3 7% 27% 25% 2	4120
November	1st to 10th	Night	26% 4 14% 28% 22% 6%	2340
	11th to 20th	Night	34% 4 9% 28% 20% 5%	2760
	21st to end	Night	39% 4 11% 27% 17% 2	2800
December	1st to 10th	Night	32% 5% 13% 36% 15% 1	4580
	11th to 20th	Night	40% 3 15% 27% 14% 1	5201
	21st to end	Night	61% 4 10% 18% 6% 1	6996

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	20% 16% 36% 22% 5%	300
	11th to 20th	Day	23% 14% 46% 15% 1	300
	21st to end	Day	14% 16% 43% 24% 3	330
February	1st to 10th	Day	20% 20% 41% 16% 2	300
	11th to 20th	Day	19% 19% 44% 12% 6% 1	300
	21st to end	Day	14% 23% 41% 19% 2	249
March	1st to 10th	Day	19% 15% 48% 16% 2	300
	11th to 20th	Day	27% 13% 34% 21% 4	300
	21st to end	Day	34% 19% 30% 15% 2	330
April	1st to 10th	Day	23% 15% 37% 20% 6%	440
	11th to 20th	Day	17% 16% 38% 21% 6% 1	492
	21st to end	Day	24% 15% 34% 18% 7% 1	630
May	1st to 10th	Day	18% 12% 36% 24% 8% 2	703
	11th to 20th	Day	20% 11% 30% 25% 13% 2	725
	21st to end	Day	18% 9% 29% 26% 17% 2	789
June	1st to 10th	Day	6% 5% 23% 35% 23% 8%	730
	11th to 20th	Day	8% 5% 25% 39% 18% 4	730
	21st to end	Day	7% 6% 35% 37% 14% 2	730
July	1st to 10th	Day	9% 5% 15% 32% 30% 9%	697
	11th to 20th	Day	7% 4 23% 34% 24% 8%	668
	21st to end	Day	7% 2 16% 40% 29% 6%	739
August	1st to 10th	Day	7% 2 18% 39% 27% 6%	676
	11th to 20th	Day	9% 4 19% 35% 26% 7%	665
	21st to end	Day	10% 2 15% 36% 27% 11%	587
September	1st to 10th	Day	12% 2 17% 32% 30% 7%	490
	11th to 20th	Day	10% 2 18% 37% 27% 6%	362
	21st to end	Day	13% 9% 26% 31% 16% 5%	300
October	1st to 10th	Day	17% 6% 26% 30% 15% 6%	300
	11th to 20th	Day	13% 23% 34% 22% 7% 1	300
	21st to end	Day	18% 17% 36% 22% 7% 1	330
November	1st to 10th	Day	15% 10% 40% 26% 6% 3	300
	11th to 20th	Day	18% 18% 35% 21% 5% 3	300
	21st to end	Day	20% 16% 35% 22% 6% 1	300
December	1st to 10th	Day	10% 18% 38% 26% 6% 2	300
	11th to 20th	Day	20% 16% 36% 21% 6% 1	300
	21st to end	Day	22% 20% 37% 19% 1	330
January	1st to 10th	Night	14% 13% 41% 26% 6%	1000
	11th to 20th	Night	15% 15% 41% 23% 6% 1	1000
	21st to end	Night	15% 13% 42% 27% 4	1100
February	1st to 10th	Night	16% 14% 41% 25% 3	1000
	11th to 20th	Night	16% 15% 38% 27% 4	979
	21st to end	Night	17% 15% 44% 19% 4	655
March	1st to 10th	Night	15% 15% 41% 25% 6%	600
	11th to 20th	Night	19% 11% 38% 25% 6% 1	600
	21st to end	Night	26% 11% 39% 20% 4	660
April	1st to 10th	Night	13% 15% 40% 28% 4	600
	11th to 20th	Night	18% 13% 38% 25% 6%	593
	21st to end	Night	20% 10% 37% 26% 6% 1	600
May	1st to 10th	Night	18% 10% 35% 30% 7% 1	600
	11th to 20th	Night	17% 7% 29% 33% 12% 1	591
	21st to end	Night	13% 5% 30% 36% 14% 2	650
June	1st to 10th	Night	7% 4 22% 46% 20% 3	600
	11th to 20th	Night	6% 3 26% 46% 17% 2	600
	21st to end	Night	6% 4 28% 49% 13%	600
July	1st to 10th	Night	7% 2 13% 43% 32% 3	570
	11th to 20th	Night	4 3 16% 49% 26% 2	552
	21st to end	Night	7% 1 13% 45% 32% 2	624
August	1st to 10th	Night	5% 2 17% 49% 26% 1	567
	11th to 20th	Night	7% 2 16% 44% 29% 2	564
	21st to end	Night	7% 2 13% 45% 30% 3	627
September	1st to 10th	Night	10% 3 18% 40% 25% 4	570
	11th to 20th	Night	11% 2 20% 43% 22% 2	570
	21st to end	Night	8% 5% 25% 41% 20% 2	587
October	1st to 10th	Night	13% 5% 30% 33% 17% 2	760
	11th to 20th	Night	15% 9% 36% 31% 9%	760
	21st to end	Night	20% 11% 34% 27% 7%	836
November	1st to 10th	Night	11% 11% 34% 34% 9% 1	780
	11th to 20th	Night	15% 15% 38% 24% 7%	995
	21st to end	Night	18% 12% 35% 29% 6%	1000
December	1st to 10th	Night	16% 12% 38% 27% 6% 1	1000
	11th to 20th	Night	20% 8% 40% 26% 6%	1000
	21st to end	Night	20% 15% 36% 25% 3	1100

Page generated at 2025-07-03 00:30:11. Version ac07

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