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 2026-10-29.

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%	149407
	Night	11% 7% 3 7% 4 4 4 3 5% 7% 47%	143015
Transparency	Day	38% 5% 12% 26% 16% 2	153016
	Night	37% 4 12% 26% 18% 3	147486
Seeing	Day	14% 10% 30% 28% 15% 3	18462
	Night	14% 9% 33% 32% 11% 1	28214

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	13% 9% 3 9% 5% 4 4 3 5% 7% 39%	5230
	11th to 20th	Day	6% 8% 3 8% 7% 6% 7% 3 5% 6% 41%	5310
	21st to end	Day	11% 13% 6% 11% 5% 5% 4 3 4 5% 35%	5812
February	1st to 10th	Day	13% 10% 5% 7% 5% 5% 4 3 6% 6% 35%	1890
	11th to 20th	Day	12% 11% 5% 7% 5% 3 3 2 5% 7% 40%	1844
	21st to end	Day	10% 9% 3 7% 4 3 4 3 5% 6% 45%	1752
March	1st to 10th	Day	15% 9% 3 6% 3 2 3 2 4 4 49%	5046
	11th to 20th	Day	9% 7% 2 5% 3 4 4 3 5% 6% 51%	5090
	21st to end	Day	13% 11% 5% 8% 5% 5% 5% 4 5% 7% 31%	5583
April	1st to 10th	Day	15% 8% 3 6% 5% 4 3 4 4 6% 42%	2457
	11th to 20th	Day	14% 8% 2 7% 4 4 5% 3 5% 7% 40%	2494
	21st to end	Day	20% 8% 3 8% 4 5% 4 3 5% 7% 34%	2656
May	1st to 10th	Day	14% 7% 2 6% 4 4 4 3 5% 7% 43%	7617
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 8% 46%	7627
	21st to end	Day	18% 8% 2 7% 4 4 4 4 5% 7% 38%	8965
June	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 9% 46%	2940
	11th to 20th	Day	7% 6% 2 6% 5% 4 5% 4 8% 8% 46%	2940
	21st to end	Day	8% 5% 2 5% 4 4 5% 4 6% 9% 48%	2940
July	1st to 10th	Day	8% 6% 2 6% 4 4 5% 4 6% 9% 46%	8103
	11th to 20th	Day	7% 5% 2 5% 4 4 4 4 6% 9% 51%	7680
	21st to end	Day	9% 5% 3 7% 4 5% 5% 5% 7% 10% 41%	8337
August	1st to 10th	Day	6% 5% 2 7% 5% 5% 4 4 7% 9% 46%	6014
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 4 6% 9% 41%	5948
	21st to end	Day	5% 4 2 5% 3 4 5% 4 7% 10% 51%	6182
September	1st to 10th	Day	11% 5% 1 3 3 4 4 3 5% 7% 53%	2520
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 49%	2378
	21st to end	Day	10% 5% 2 5% 4 3 4 3 5% 5% 53%	2268
October	1st to 10th	Day	12% 6% 2 4 3 3 3 2 5% 6% 54%	2100
	11th to 20th	Day	13% 6% 2 5% 3 4 4 2 4 4 54%	2100
	21st to end	Day	14% 8% 3 6% 3 3 4 2 5% 6% 47%	2280
November	1st to 10th	Day	9% 6% 2 5% 3 3 3 3 6% 7% 53%	2058
	11th to 20th	Day	13% 6% 3 5% 5% 3 3 3 5% 6% 48%	1718
	21st to end	Day	16% 11% 3 6% 3 2 4 3 5% 6% 42%	1680
December	1st to 10th	Day	6% 6% 2 7% 4 3 4 3 5% 7% 53%	2690
	11th to 20th	Day	11% 9% 3 8% 4 4 3 3 4 6% 45%	3088
	21st to end	Day	18% 15% 7% 13% 4 4 3 3 4 5% 23%	4070
January	1st to 10th	Night	10% 10% 4 14% 6% 5% 4 3 5% 5% 34%	7675
	11th to 20th	Night	7% 7% 4 8% 4 5% 5% 4 6% 6% 45%	7680
	21st to end	Night	12% 11% 5% 11% 4 5% 4 3 3 4 38%	8402
February	1st to 10th	Night	11% 12% 4 8% 5% 5% 4 3 5% 5% 38%	2730
	11th to 20th	Night	11% 8% 3 8% 5% 4 4 3 6% 6% 41%	2663
	21st to end	Night	12% 8% 3 5% 4 3 3 3 5% 5% 49%	2071
March	1st to 10th	Night	16% 8% 3 5% 3 3 3 3 4 4 48%	5029
	11th to 20th	Night	9% 7% 2 5% 3 3 3 3 5% 6% 54%	5090
	21st to end	Night	14% 9% 4 9% 5% 4 5% 4 6% 7% 35%	5588
April	1st to 10th	Night	12% 6% 2 7% 3 3 4 3 4 7% 48%	2163
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 5% 7% 45%	2075
	21st to end	Night	15% 9% 3 6% 4 3 4 3 5% 6% 41%	1961
May	1st to 10th	Night	12% 6% 3 6% 4 4 4 3 5% 8% 45%	5266
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 8% 49%	5265
	21st to end	Night	15% 7% 2 7% 4 3 4 3 5% 7% 43%	5201
June	1st to 10th	Night	6% 3 1 4 4 4 5% 4 7% 9% 54%	1680
	11th to 20th	Night	4 4 1 5% 4 5% 5% 4 7% 9% 51%	1680
	21st to end	Night	5% 4 1 4 3 3 3 3 5% 10% 58%	1680
July	1st to 10th	Night	7% 5% 2 5% 3 4 4 4 6% 10% 52%	4879
	11th to 20th	Night	3 4 2 5% 3 4 4 4 6% 8% 56%	5307
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 7% 12% 42%	5770
August	1st to 10th	Night	5% 4 2 3 3 3 4 4 6% 9% 58%	4156
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 5% 9% 49%	4118
	21st to end	Night	5% 3 2 5% 4 4 4 3 5% 8% 59%	4936
September	1st to 10th	Night	9% 4 1 4 3 3 4 3 4 6% 57%	2100
	11th to 20th	Night	9% 4 1 5% 3 4 4 4 5% 7% 53%	2237
	21st to end	Night	8% 5% 2 5% 4 3 3 3 4 7% 55%	2329
October	1st to 10th	Night	11% 6% 2 4 2 3 2 3 4 6% 57%	2520
	11th to 20th	Night	13% 5% 1 4 4 3 3 3 4 6% 55%	2520
	21st to end	Night	16% 7% 2 5% 4 3 3 2 4 5% 49%	2737
November	1st to 10th	Night	8% 4 2 4 2 3 3 3 4 6% 61%	2460
	11th to 20th	Night	11% 7% 2 5% 4 4 3 3 4 5% 52%	2898
	21st to end	Night	14% 9% 2 6% 4 3 3 3 4 5% 48%	2940
December	1st to 10th	Night	7% 7% 2 5% 4 3 4 4 5% 6% 53%	4720
	11th to 20th	Night	11% 8% 3 8% 3 4 4 3 5% 7% 44%	5339
	21st to end	Night	19% 16% 6% 10% 5% 3 3 3 4 4 28%	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	46% 4 12% 24% 12% 2	5231
	11th to 20th	Day	45% 3 12% 21% 14% 5%	5310
	21st to end	Day	53% 4 11% 18% 13% 1	5812
February	1st to 10th	Day	48% 5% 13% 22% 9% 2	1890
	11th to 20th	Day	45% 4 12% 23% 14% 2	1853
	21st to end	Day	40% 5% 11% 24% 19% 2	1752
March	1st to 10th	Day	40% 3 8% 23% 22% 4	5046
	11th to 20th	Day	33% 4 9% 24% 25% 4	5090
	21st to end	Day	50% 7% 16% 21% 5% 1	5585
April	1st to 10th	Day	43% 5% 11% 25% 14% 2	2457
	11th to 20th	Day	43% 5% 13% 23% 15% 1	2494
	21st to end	Day	49% 5% 12% 22% 11% 1	2656
May	1st to 10th	Day	40% 6% 11% 26% 17% 1	7655
	11th to 20th	Day	36% 5% 12% 27% 18% 2	7631
	21st to end	Day	46% 5% 9% 24% 15% 1	8979
June	1st to 10th	Day	31% 9% 15% 30% 13% 2	2940
	11th to 20th	Day	32% 7% 14% 27% 19% 1	2940
	21st to end	Day	31% 7% 17% 28% 14% 3	2940
July	1st to 10th	Day	35% 5% 14% 30% 14% 2	8036
	11th to 20th	Day	30% 5% 14% 27% 19% 4	7611
	21st to end	Day	37% 6% 16% 31% 8% 1	8155
August	1st to 10th	Day	33% 5% 14% 28% 19% 1	6000
	11th to 20th	Day	39% 5% 16% 28% 11%	5987
	21st to end	Day	27% 7% 16% 35% 12% 4	6181
September	1st to 10th	Day	31% 5% 12% 28% 20% 5%	2520
	11th to 20th	Day	33% 6% 13% 27% 20% 2	2378
	21st to end	Day	32% 5% 9% 30% 22% 3	2268
October	1st to 10th	Day	20% 3 7% 22% 44% 4	3360
	11th to 20th	Day	23% 3 5% 25% 36% 9%	3340
	21st to end	Day	35% 3 11% 25% 23% 3	3618
November	1st to 10th	Day	31% 5% 14% 28% 20% 3	2058
	11th to 20th	Day	36% 5% 11% 28% 18% 2	1718
	21st to end	Day	43% 4 10% 26% 16%	1680
December	1st to 10th	Day	32% 5% 17% 29% 17%	2690
	11th to 20th	Day	41% 4 14% 29% 10% 1	3085
	21st to end	Day	64% 3 13% 13% 5% 1	4070
January	1st to 10th	Night	52% 5% 12% 20% 10% 1	7676
	11th to 20th	Night	39% 3 10% 25% 19% 4	7680
	21st to end	Night	51% 3 11% 17% 15% 3	8402
February	1st to 10th	Night	48% 4 12% 21% 13% 3	2730
	11th to 20th	Night	43% 4 12% 23% 15% 3	2664
	21st to end	Night	37% 4 10% 24% 20% 5%	2071
March	1st to 10th	Night	40% 3 8% 22% 23% 3	5029
	11th to 20th	Night	31% 4 7% 26% 26% 7%	5090
	21st to end	Night	47% 7% 14% 23% 8% 2	5588
April	1st to 10th	Night	37% 4 10% 27% 18% 4	2163
	11th to 20th	Night	38% 5% 11% 27% 15% 3	2075
	21st to end	Night	43% 5% 11% 25% 15% 1	1961
May	1st to 10th	Night	38% 5% 10% 27% 18% 2	5293
	11th to 20th	Night	34% 5% 11% 25% 20% 5%	5266
	21st to end	Night	42% 6% 10% 24% 18% 1	5212
June	1st to 10th	Night	25% 7% 17% 32% 15% 3	1680
	11th to 20th	Night	27% 8% 15% 28% 19% 3	1680
	21st to end	Night	23% 5% 16% 34% 19% 4	1680
July	1st to 10th	Night	28% 5% 16% 26% 22% 3	4839
	11th to 20th	Night	25% 7% 15% 29% 20% 5%	5256
	21st to end	Night	34% 6% 19% 33% 8% 1	5641
August	1st to 10th	Night	23% 5% 17% 28% 26% 1	4146
	11th to 20th	Night	34% 4 15% 29% 17% 1	4145
	21st to end	Night	24% 4 14% 39% 15% 4	4936
September	1st to 10th	Night	28% 5% 10% 26% 23% 7%	2100
	11th to 20th	Night	28% 5% 12% 30% 22% 3	2237
	21st to end	Night	30% 4 9% 27% 26% 4	2329
October	1st to 10th	Night	19% 3 6% 19% 49% 5%	4040
	11th to 20th	Night	22% 2 6% 25% 33% 11%	4019
	21st to end	Night	37% 3 7% 27% 24% 2	4349
November	1st to 10th	Night	26% 4 14% 29% 22% 6%	2460
	11th to 20th	Night	34% 4 9% 29% 20% 4	2898
	21st to end	Night	40% 4 10% 27% 17% 2	2940
December	1st to 10th	Night	32% 5% 13% 35% 15% 1	4720
	11th to 20th	Night	40% 3 14% 27% 14% 1	5341
	21st to end	Night	61% 4 10% 19% 6% 1	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	20% 16% 37% 22% 5%	330
	11th to 20th	Day	22% 15% 47% 15% 1	330
	21st to end	Day	14% 16% 45% 22% 3	363
February	1st to 10th	Day	18% 20% 42% 17% 2	330
	11th to 20th	Day	18% 19% 43% 13% 5% 1	330
	21st to end	Day	14% 23% 42% 19% 2	273
March	1st to 10th	Day	19% 15% 48% 15% 2	330
	11th to 20th	Day	28% 13% 34% 21% 4	330
	21st to end	Day	32% 20% 31% 15% 2	363
April	1st to 10th	Day	24% 14% 37% 19% 5%	477
	11th to 20th	Day	18% 17% 39% 20% 5% 1	532
	21st to end	Day	24% 15% 35% 18% 7% 1	676
May	1st to 10th	Day	18% 12% 36% 24% 8% 1	753
	11th to 20th	Day	19% 11% 32% 25% 12% 2	775
	21st to end	Day	18% 9% 29% 26% 16% 2	844
June	1st to 10th	Day	7% 5% 23% 36% 22% 7%	780
	11th to 20th	Day	9% 6% 26% 38% 18% 4	780
	21st to end	Day	9% 6% 34% 35% 13% 2	780
July	1st to 10th	Day	9% 5% 16% 32% 31% 9%	771
	11th to 20th	Day	7% 4 21% 34% 26% 9%	768
	21st to end	Day	8% 2 17% 40% 28% 5%	849
August	1st to 10th	Day	8% 2 20% 38% 26% 6%	776
	11th to 20th	Day	8% 4 18% 36% 26% 7%	765
	21st to end	Day	9% 2 16% 37% 27% 10%	679
September	1st to 10th	Day	12% 2 18% 33% 28% 6%	570
	11th to 20th	Day	10% 2 20% 36% 27% 5%	428
	21st to end	Day	14% 9% 24% 31% 16% 6%	360
October	1st to 10th	Day	16% 6% 25% 33% 15% 5%	360
	11th to 20th	Day	14% 21% 34% 21% 9% 1	360
	21st to end	Day	19% 15% 34% 22% 8% 1	387
November	1st to 10th	Day	14% 12% 42% 25% 6% 2	330
	11th to 20th	Day	17% 17% 37% 22% 6% 2	330
	21st to end	Day	21% 17% 34% 22% 5% 1	330
December	1st to 10th	Day	11% 18% 38% 26% 5% 2	330
	11th to 20th	Day	20% 16% 37% 20% 6% 1	330
	21st to end	Day	22% 19% 39% 20% 1	363
January	1st to 10th	Night	14% 13% 42% 26% 5%	1050
	11th to 20th	Night	15% 15% 41% 22% 5% 1	1050
	21st to end	Night	15% 13% 42% 26% 3	1155
February	1st to 10th	Night	16% 14% 41% 25% 4	1050
	11th to 20th	Night	16% 15% 38% 27% 4	1029
	21st to end	Night	17% 16% 45% 19% 4	687
March	1st to 10th	Night	16% 15% 40% 24% 5%	630
	11th to 20th	Night	19% 11% 40% 24% 5% 1	630
	21st to end	Night	25% 11% 40% 20% 4	693
April	1st to 10th	Night	15% 15% 40% 27% 3	630
	11th to 20th	Night	17% 14% 39% 24% 6%	623
	21st to end	Night	20% 10% 38% 25% 6% 1	630
May	1st to 10th	Night	17% 10% 36% 30% 7% 1	630
	11th to 20th	Night	17% 7% 30% 33% 12% 1	621
	21st to end	Night	13% 5% 29% 37% 14% 2	683
June	1st to 10th	Night	7% 4 22% 46% 19% 3	630
	11th to 20th	Night	6% 3 28% 45% 16% 2	630
	21st to end	Night	7% 4 29% 48% 12%	630
July	1st to 10th	Night	7% 2 13% 42% 32% 3	615
	11th to 20th	Night	5% 2 16% 47% 28% 2	612
	21st to end	Night	8% 2 14% 45% 31% 1	690
August	1st to 10th	Night	6% 2 17% 49% 26% 1	627
	11th to 20th	Night	6% 2 16% 43% 30% 2	624
	21st to end	Night	6% 2 13% 47% 29% 3	693
September	1st to 10th	Night	11% 3 17% 41% 24% 3	630
	11th to 20th	Night	11% 2 19% 44% 21% 3	630
	21st to end	Night	10% 5% 24% 40% 20% 1	649
October	1st to 10th	Night	13% 5% 29% 35% 17% 2	840
	11th to 20th	Night	15% 9% 35% 31% 9%	840
	21st to end	Night	20% 11% 34% 28% 7%	913
November	1st to 10th	Night	10% 12% 36% 33% 8% 1	820
	11th to 20th	Night	14% 15% 39% 25% 7%	1045
	21st to end	Night	19% 11% 35% 29% 6%	1050
December	1st to 10th	Night	16% 12% 38% 27% 6% 1	1050
	11th to 20th	Night	20% 8% 41% 26% 5%	1050
	21st to end	Night	20% 15% 37% 25% 3	1155

Page generated at 2026-10-26 03:37:48. Version ac07

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