Camp McGregor Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp McGregor Observatory clear sky chart from 2005-11-06 to 2026-02-01.

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	13% 10% 4 9% 5% 5% 5% 4 6% 7% 33%	127216
	Night	13% 11% 4 9% 5% 5% 4 4 5% 7% 33%	124940
Transparency	Day	48% 7% 12% 21% 12% 1	130772
	Night	49% 6% 11% 20% 12% 1	129429
Seeing	Day	17% 13% 29% 23% 13% 5%	17342
	Night	18% 11% 30% 28% 12% 1	27270

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	12% 14% 8% 19% 7% 5% 4 3 4 5% 18%	3697
	11th to 20th	Day	13% 14% 7% 15% 11% 7% 7% 5% 5% 5% 10%	3700
	21st to end	Day	20% 18% 6% 14% 6% 4 4 3 3 4 17%	4319
February	1st to 10th	Day	13% 14% 6% 12% 9% 5% 5% 4 5% 6% 20%	1816
	11th to 20th	Day	14% 11% 5% 14% 9% 6% 5% 3 5% 4 23%	1948
	21st to end	Day	16% 14% 6% 12% 4 4 4 4 5% 6% 23%	1650
March	1st to 10th	Day	14% 12% 5% 12% 6% 5% 4 4 4 5% 29%	4480
	11th to 20th	Day	10% 11% 4 9% 5% 5% 4 3 5% 8% 36%	4976
	21st to end	Day	14% 15% 6% 11% 5% 5% 5% 4 5% 6% 25%	5465
April	1st to 10th	Day	16% 14% 4 9% 5% 4 4 3 5% 6% 29%	2395
	11th to 20th	Day	15% 10% 3 8% 5% 4 5% 4 5% 6% 35%	2479
	21st to end	Day	15% 10% 3 7% 5% 5% 5% 3 5% 8% 34%	2600
May	1st to 10th	Day	20% 9% 3 7% 4 4 4 4 5% 6% 33%	5862
	11th to 20th	Day	15% 7% 3 7% 5% 5% 5% 4 6% 9% 35%	5861
	21st to end	Day	14% 7% 2 7% 4 4 5% 4 5% 7% 40%	6569
June	1st to 10th	Day	10% 7% 2 6% 5% 5% 5% 4 6% 9% 41%	2800
	11th to 20th	Day	11% 6% 2 5% 5% 5% 5% 4 7% 9% 41%	2800
	21st to end	Day	8% 6% 2 7% 6% 5% 5% 5% 8% 9% 38%	2800
July	1st to 10th	Day	10% 5% 2 7% 4 5% 6% 4 8% 11% 39%	6360
	11th to 20th	Day	6% 5% 2 7% 5% 4 6% 4 6% 11% 44%	6360
	21st to end	Day	7% 6% 3 6% 5% 5% 6% 5% 7% 10% 42%	6680
August	1st to 10th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 44%	4234
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 41%	4174
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4482
September	1st to 10th	Day	11% 6% 3 6% 5% 5% 5% 5% 5% 8% 43%	2305
	11th to 20th	Day	9% 4 2 6% 4 4 5% 5% 7% 9% 47%	2200
	21st to end	Day	12% 8% 3 7% 4 4 5% 4 6% 7% 39%	2200
October	1st to 10th	Day	12% 7% 3 6% 4 4 5% 4 4 7% 44%	2199
	11th to 20th	Day	15% 10% 3 8% 5% 5% 5% 3 5% 7% 35%	1999
	21st to end	Day	17% 11% 3 8% 5% 5% 4 4 6% 7% 30%	1980
November	1st to 10th	Day	11% 9% 3 8% 5% 4 4 4 6% 5% 40%	1852
	11th to 20th	Day	14% 15% 4 10% 6% 4 4 4 5% 6% 29%	1890
	21st to end	Day	17% 15% 5% 9% 5% 5% 4 3 4 6% 25%	1890
December	1st to 10th	Day	10% 15% 9% 15% 6% 6% 5% 4 5% 6% 20%	3020
	11th to 20th	Day	16% 19% 8% 13% 9% 5% 4 3 5% 4 15%	3104
	21st to end	Day	22% 20% 8% 14% 6% 4 3 3 4 5% 12%	4070
January	1st to 10th	Night	13% 15% 7% 17% 7% 6% 5% 3 5% 5% 18%	6488
	11th to 20th	Night	10% 15% 8% 16% 9% 7% 6% 5% 6% 5% 12%	6500
	21st to end	Night	17% 14% 7% 12% 6% 5% 5% 4 5% 5% 20%	6887
February	1st to 10th	Night	14% 15% 5% 12% 7% 6% 5% 4 5% 5% 22%	2581
	11th to 20th	Night	12% 13% 4 12% 7% 6% 4 4 5% 5% 27%	2338
	21st to end	Night	19% 10% 4 11% 5% 4 5% 4 4 6% 28%	1980
March	1st to 10th	Night	14% 10% 5% 8% 5% 3 4 3 5% 7% 35%	5373
	11th to 20th	Night	9% 8% 3 5% 4 4 4 4 6% 7% 44%	4981
	21st to end	Night	15% 10% 4 9% 5% 4 4 3 5% 6% 35%	5467
April	1st to 10th	Night	15% 10% 3 7% 5% 4 4 4 5% 6% 36%	2023
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 5% 6% 37%	1869
	21st to end	Night	15% 9% 3 7% 5% 4 4 3 6% 7% 37%	1800
May	1st to 10th	Night	19% 12% 3 8% 5% 5% 4 3 5% 7% 29%	4033
	11th to 20th	Night	17% 8% 2 7% 4 4 4 3 5% 6% 40%	4032
	21st to end	Night	15% 6% 2 6% 4 4 4 4 5% 8% 43%	4275
June	1st to 10th	Night	10% 4 2 5% 5% 3 5% 4 6% 10% 47%	1600
	11th to 20th	Night	10% 6% 2 7% 5% 5% 4 4 7% 9% 42%	1600
	21st to end	Night	7% 6% 2 5% 4 4 4 5% 6% 10% 47%	1600
July	1st to 10th	Night	7% 4 2 6% 4 5% 4 4 6% 10% 47%	3618
	11th to 20th	Night	7% 5% 2 5% 4 4 3 4 6% 8% 51%	3617
	21st to end	Night	8% 6% 2 5% 3 5% 4 4 6% 8% 48%	4181
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 5% 8% 48%	2915
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 3 6% 8% 47%	2875
	21st to end	Night	8% 6% 3 6% 5% 4 5% 4 5% 7% 47%	3412
September	1st to 10th	Night	8% 6% 3 5% 4 4 4 3 4 7% 51%	2075
	11th to 20th	Night	8% 5% 1 4 3 4 4 3 5% 7% 56%	2200
	21st to end	Night	13% 7% 2 7% 5% 4 4 3 5% 7% 43%	2200
October	1st to 10th	Night	11% 7% 2 5% 4 4 4 3 5% 6% 48%	2200
	11th to 20th	Night	16% 10% 3 8% 4 4 4 3 4 6% 37%	2400
	21st to end	Night	19% 9% 3 7% 4 4 4 3 5% 6% 35%	2859
November	1st to 10th	Night	11% 11% 3 7% 4 4 5% 3 4 6% 41%	2666
	11th to 20th	Night	15% 11% 4 8% 5% 5% 5% 4 6% 7% 30%	2730
	21st to end	Night	16% 15% 5% 9% 5% 5% 4 3 5% 6% 26%	2730
December	1st to 10th	Night	11% 13% 6% 15% 7% 5% 6% 4 6% 6% 22%	4380
	11th to 20th	Night	14% 18% 7% 14% 7% 5% 5% 4 5% 5% 17%	5305
	21st to end	Night	22% 22% 6% 12% 5% 4 4 3 4 5% 13%	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	68% 6% 10% 13% 3	3698
	11th to 20th	Day	73% 6% 10% 6% 5%	3700
	21st to end	Day	72% 4 8% 10% 6%	4319
February	1st to 10th	Day	63% 7% 10% 13% 7% 1	1816
	11th to 20th	Day	62% 6% 8% 15% 8% 1	1958
	21st to end	Day	60% 7% 12% 14% 6% 2	1650
March	1st to 10th	Day	56% 6% 11% 17% 8% 1	4480
	11th to 20th	Day	45% 6% 15% 24% 8% 2	4976
	21st to end	Day	58% 7% 9% 15% 10% 1	5465
April	1st to 10th	Day	54% 6% 9% 19% 10%	2395
	11th to 20th	Day	48% 7% 11% 20% 12% 2	2479
	21st to end	Day	48% 7% 13% 18% 14% 1	2600
May	1st to 10th	Day	50% 7% 10% 18% 14% 1	5897
	11th to 20th	Day	44% 8% 14% 21% 12% 1	5865
	21st to end	Day	41% 7% 10% 22% 18% 3	6583
June	1st to 10th	Day	37% 8% 13% 25% 15% 2	2800
	11th to 20th	Day	37% 8% 14% 23% 17% 2	2800
	21st to end	Day	39% 9% 13% 22% 15% 2	2800
July	1st to 10th	Day	37% 7% 13% 26% 15% 2	6291
	11th to 20th	Day	33% 7% 13% 29% 17% 1	6285
	21st to end	Day	35% 8% 13% 23% 20% 1	6489
August	1st to 10th	Day	35% 8% 14% 25% 17% 1	4221
	11th to 20th	Day	37% 8% 12% 30% 13% 1	4213
	21st to end	Day	35% 6% 13% 32% 12% 2	4481
September	1st to 10th	Day	38% 8% 15% 22% 15% 2	2305
	11th to 20th	Day	30% 8% 12% 31% 18% 1	2200
	21st to end	Day	42% 8% 13% 20% 17%	2200
October	1st to 10th	Day	30% 5% 10% 34% 20% 1	3576
	11th to 20th	Day	41% 5% 10% 25% 20%	3227
	21st to end	Day	46% 4 12% 24% 12% 2	3180
November	1st to 10th	Day	43% 7% 10% 25% 14% 1	1852
	11th to 20th	Day	56% 6% 11% 18% 8% 2	1890
	21st to end	Day	61% 5% 13% 15% 6%	1890
December	1st to 10th	Day	64% 7% 14% 10% 4	3020
	11th to 20th	Day	71% 6% 10% 11% 2	3101
	21st to end	Day	75% 5% 7% 9% 3	4070
January	1st to 10th	Night	65% 6% 8% 14% 5% 1	6488
	11th to 20th	Night	70% 5% 10% 9% 5%	6500
	21st to end	Night	64% 6% 12% 11% 7%	6887
February	1st to 10th	Night	63% 7% 10% 13% 6% 1	2581
	11th to 20th	Night	58% 6% 10% 18% 7% 1	2339
	21st to end	Night	57% 5% 13% 16% 8% 2	1980
March	1st to 10th	Night	47% 5% 13% 24% 10% 1	5373
	11th to 20th	Night	37% 6% 14% 27% 15% 1	4981
	21st to end	Night	50% 6% 11% 18% 14% 1	5467
April	1st to 10th	Night	47% 6% 10% 21% 14% 1	2023
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1869
	21st to end	Night	46% 6% 12% 20% 14% 3	1800
May	1st to 10th	Night	53% 7% 9% 15% 13% 2	4060
	11th to 20th	Night	43% 7% 11% 25% 12% 2	4033
	21st to end	Night	38% 7% 13% 21% 19% 2	4283
June	1st to 10th	Night	32% 6% 14% 27% 19% 2	1600
	11th to 20th	Night	37% 7% 13% 25% 16% 2	1600
	21st to end	Night	31% 9% 16% 26% 18% 2	1600
July	1st to 10th	Night	31% 6% 14% 27% 17% 5%	3580
	11th to 20th	Night	30% 6% 15% 28% 19% 2	3572
	21st to end	Night	32% 7% 13% 21% 24% 2	4059
August	1st to 10th	Night	33% 7% 14% 30% 15% 1	2904
	11th to 20th	Night	33% 7% 12% 33% 14% 2	2902
	21st to end	Night	35% 7% 10% 30% 16% 1	3412
September	1st to 10th	Night	32% 7% 10% 28% 19% 3	2075
	11th to 20th	Night	27% 6% 11% 31% 23% 2	2200
	21st to end	Night	39% 7% 12% 25% 16% 1	2200
October	1st to 10th	Night	25% 4 10% 33% 27% 1	3590
	11th to 20th	Night	41% 4 10% 23% 21%	3899
	21st to end	Night	39% 4 9% 32% 15% 1	4609
November	1st to 10th	Night	45% 6% 11% 23% 15% 1	2666
	11th to 20th	Night	52% 6% 13% 18% 8% 2	2730
	21st to end	Night	58% 6% 12% 18% 6%	2730
December	1st to 10th	Night	61% 6% 14% 14% 4	4380
	11th to 20th	Night	68% 6% 10% 12% 4	5307
	21st to end	Night	74% 6% 8% 8% 4	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% 18% 40% 18% 4 1	330
	11th to 20th	Day	22% 21% 42% 12% 2 1	330
	21st to end	Day	27% 19% 35% 16% 3	363
February	1st to 10th	Day	25% 20% 36% 15% 2 1	300
	11th to 20th	Day	27% 19% 36% 16% 2	300
	21st to end	Day	27% 25% 33% 12% 2	249
March	1st to 10th	Day	22% 21% 42% 12% 2	300
	11th to 20th	Day	23% 14% 35% 21% 6% 1	496
	21st to end	Day	25% 18% 34% 16% 5% 1	550
April	1st to 10th	Day	22% 16% 36% 18% 7%	500
	11th to 20th	Day	23% 20% 31% 15% 7% 3	492
	21st to end	Day	21% 15% 33% 19% 10% 2	500
May	1st to 10th	Day	24% 14% 31% 20% 10% 2	503
	11th to 20th	Day	20% 11% 29% 22% 12% 6%	527
	21st to end	Day	14% 10% 24% 26% 18% 7%	631
June	1st to 10th	Day	13% 9% 29% 30% 15% 4	730
	11th to 20th	Day	14% 7% 30% 28% 17% 5%	730
	21st to end	Day	9% 9% 31% 31% 15% 5%	730
July	1st to 10th	Day	8% 5% 21% 31% 23% 11%	721
	11th to 20th	Day	10% 6% 25% 27% 21% 10%	718
	21st to end	Day	8% 3 26% 31% 24% 9%	689
August	1st to 10th	Day	8% 4 18% 30% 22% 18%	526
	11th to 20th	Day	12% 4 20% 26% 28% 10%	519
	21st to end	Day	9% 3 21% 31% 24% 12%	583
September	1st to 10th	Day	13% 7% 23% 23% 22% 13%	530
	11th to 20th	Day	8% 3 19% 23% 29% 17%	530
	21st to end	Day	18% 11% 22% 24% 17% 8%	530
October	1st to 10th	Day	12% 9% 28% 25% 19% 7%	530
	11th to 20th	Day	19% 16% 29% 27% 8% 2	529
	21st to end	Day	26% 17% 35% 16% 4 1	363
November	1st to 10th	Day	15% 19% 35% 22% 7% 2	330
	11th to 20th	Day	22% 25% 30% 18% 4 1	330
	21st to end	Day	27% 20% 36% 14% 2	330
December	1st to 10th	Day	21% 28% 31% 13% 7% 1	330
	11th to 20th	Day	25% 25% 33% 15% 3	330
	21st to end	Day	25% 26% 32% 16% 1	363
January	1st to 10th	Night	20% 17% 38% 19% 5%	1050
	11th to 20th	Night	22% 18% 37% 19% 4	1050
	21st to end	Night	19% 15% 38% 24% 5%	1035
February	1st to 10th	Night	24% 15% 38% 21% 3	801
	11th to 20th	Night	21% 16% 37% 22% 3	783
	21st to end	Night	24% 16% 39% 19% 2	660
March	1st to 10th	Night	20% 13% 37% 24% 6%	800
	11th to 20th	Night	17% 16% 39% 23% 5% 1	800
	21st to end	Night	24% 12% 31% 25% 7%	880
April	1st to 10th	Night	19% 15% 36% 26% 4 1	623
	11th to 20th	Night	20% 13% 35% 22% 9% 1	593
	21st to end	Night	19% 10% 35% 28% 8% 1	600
May	1st to 10th	Night	20% 11% 29% 32% 7% 2	600
	11th to 20th	Night	23% 6% 30% 27% 14% 1	591
	21st to end	Night	12% 4 26% 38% 17% 2	650
June	1st to 10th	Night	11% 3 27% 43% 15%	600
	11th to 20th	Night	12% 4 24% 42% 17% 1	600
	21st to end	Night	9% 3 24% 42% 20% 3	600
July	1st to 10th	Night	8% 2 18% 42% 26% 4	585
	11th to 20th	Night	9% 2 18% 43% 25% 3	582
	21st to end	Night	7% 2 19% 44% 28% 1	657
August	1st to 10th	Night	8% 2 14% 44% 30% 3	597
	11th to 20th	Night	8% 2 17% 41% 28% 4	594
	21st to end	Night	11% 2 16% 38% 29% 4	660
September	1st to 10th	Night	11% 3 21% 35% 26% 5%	675
	11th to 20th	Night	11% 3 16% 33% 33% 4	800
	21st to end	Night	16% 7% 22% 31% 21% 5%	800
October	1st to 10th	Night	14% 7% 25% 33% 19% 2	800
	11th to 20th	Night	20% 14% 30% 26% 9% 1	800
	21st to end	Night	23% 14% 34% 24% 6%	880
November	1st to 10th	Night	19% 13% 31% 26% 10% 1	820
	11th to 20th	Night	20% 17% 35% 22% 6% 1	840
	21st to end	Night	25% 13% 36% 22% 4	840
December	1st to 10th	Night	23% 16% 37% 20% 5%	840
	11th to 20th	Night	23% 16% 38% 20% 3	1029
	21st to end	Night	29% 15% 35% 18% 2	1155

Page generated at 2026-01-29 01:21:42. Version ac07

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