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 2024-11-28.

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 8% 5% 5% 5% 4 6% 7% 33%	101381
	Night	14% 11% 4 8% 5% 4 4 4 5% 7% 34%	98172
Transparency	Day	47% 7% 12% 21% 12% 1	104983
	Night	47% 7% 12% 21% 13% 1	102685
Seeing	Day	17% 12% 29% 23% 13% 5%	15769
	Night	18% 10% 30% 28% 12% 1	25618

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	16% 15% 7% 11% 7% 6% 4 3 5% 5% 20%	2527
	11th to 20th	Day	15% 16% 7% 14% 7% 6% 6% 6% 6% 5% 12%	2530
	21st to end	Day	26% 21% 6% 13% 6% 4 3 2 2 3 14%	2948
February	1st to 10th	Day	13% 14% 6% 11% 9% 5% 5% 4 5% 6% 20%	1725
	11th to 20th	Day	14% 11% 4 13% 8% 7% 6% 3 5% 4 24%	1848
	21st to end	Day	16% 15% 6% 12% 5% 4 4 4 5% 6% 23%	1570
March	1st to 10th	Day	16% 15% 5% 10% 6% 4 4 4 5% 6% 26%	3120
	11th to 20th	Day	12% 10% 4 10% 6% 6% 5% 3 4 8% 32%	3476
	21st to end	Day	17% 13% 6% 11% 5% 5% 4 4 5% 5% 25%	3815
April	1st to 10th	Day	16% 14% 4 9% 5% 4 4 3 5% 6% 29%	2275
	11th to 20th	Day	16% 10% 3 8% 5% 4 5% 4 5% 6% 35%	2353
	21st to end	Day	16% 10% 3 7% 5% 5% 5% 3 5% 8% 33%	2470
May	1st to 10th	Day	17% 8% 3 6% 5% 4 5% 4 5% 7% 34%	4082
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 5% 6% 9% 35%	4081
	21st to end	Day	9% 6% 2 7% 4 4 5% 4 6% 8% 44%	4570
June	1st to 10th	Day	9% 7% 3 6% 5% 5% 5% 4 7% 9% 40%	2660
	11th to 20th	Day	10% 6% 2 4 5% 5% 5% 4 7% 9% 42%	2660
	21st to end	Day	9% 6% 2 7% 6% 5% 5% 5% 8% 9% 38%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 6% 6% 4 7% 9% 36%	4440
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 6% 11% 47%	4440
	21st to end	Day	5% 7% 2 7% 6% 5% 7% 6% 8% 9% 39%	4638
August	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 6% 9% 43%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 9% 41%	4044
	21st to end	Day	8% 6% 2 6% 5% 5% 5% 4 6% 9% 43%	4345
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 5% 7% 42%	2190
	11th to 20th	Day	9% 4 2 6% 4 4 5% 5% 7% 9% 46%	2090
	21st to end	Day	13% 8% 3 6% 4 4 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	12% 7% 3 6% 4 4 5% 4 4 7% 43%	2089
	11th to 20th	Day	15% 10% 3 8% 5% 5% 5% 3 5% 7% 34%	1899
	21st to end	Day	18% 11% 3 8% 5% 5% 4 4 6% 7% 29%	1881
November	1st to 10th	Day	11% 9% 3 8% 5% 4 4 4 6% 5% 40%	1762
	11th to 20th	Day	14% 15% 4 10% 6% 4 4 4 5% 6% 28%	1800
	21st to end	Day	18% 15% 5% 9% 5% 5% 4 3 4 5% 25%	1773
December	1st to 10th	Day	13% 16% 8% 12% 6% 5% 4 3 4 6% 22%	1710
	11th to 20th	Day	13% 16% 6% 12% 7% 5% 5% 4 6% 6% 19%	1933
	21st to end	Day	19% 21% 8% 15% 7% 5% 3 3 4 5% 11%	2783
January	1st to 10th	Night	15% 16% 8% 11% 6% 5% 4 3 5% 6% 21%	4428
	11th to 20th	Night	13% 17% 8% 14% 7% 5% 5% 5% 7% 5% 13%	4440
	21st to end	Night	23% 17% 8% 13% 6% 4 4 3 4 4 14%	4711
February	1st to 10th	Night	15% 15% 5% 11% 7% 6% 5% 4 5% 5% 22%	2451
	11th to 20th	Night	12% 13% 4 12% 7% 6% 4 4 5% 5% 28%	2218
	21st to end	Night	19% 10% 4 11% 5% 5% 5% 4 4 6% 27%	1884
March	1st to 10th	Night	15% 12% 5% 8% 5% 3 3 3 5% 6% 35%	3733
	11th to 20th	Night	9% 9% 2 5% 4 4 5% 4 6% 7% 45%	3481
	21st to end	Night	17% 10% 4 9% 6% 4 4 3 5% 6% 33%	3817
April	1st to 10th	Night	14% 10% 3 7% 5% 4 4 4 5% 6% 36%	1922
	11th to 20th	Night	18% 8% 3 7% 4 4 4 4 5% 6% 37%	1775
	21st to end	Night	16% 10% 3 6% 5% 4 4 4 6% 7% 36%	1710
May	1st to 10th	Night	15% 10% 3 7% 5% 5% 5% 4 6% 9% 31%	2813
	11th to 20th	Night	17% 7% 2 7% 4 4 4 3 5% 7% 40%	2812
	21st to end	Night	10% 6% 2 5% 4 4 4 4 5% 8% 46%	2972
June	1st to 10th	Night	10% 4 2 5% 5% 3 5% 4 6% 10% 47%	1520
	11th to 20th	Night	10% 6% 2 7% 5% 5% 4 4 7% 9% 43%	1520
	21st to end	Night	7% 6% 2 5% 4 4 4 5% 6% 10% 47%	1520
July	1st to 10th	Night	9% 3 2 6% 4 5% 4 4 6% 10% 47%	2530
	11th to 20th	Night	8% 4 1 4 3 3 3 3 6% 7% 56%	2530
	21st to end	Night	5% 5% 2 5% 4 6% 6% 5% 7% 9% 47%	2919
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 4 6% 8% 47%	2825
	11th to 20th	Night	9% 6% 2 6% 4 4 5% 3 6% 8% 47%	2785
	21st to end	Night	8% 6% 3 6% 5% 4 5% 4 5% 7% 46%	3307
September	1st to 10th	Night	9% 6% 3 5% 4 4 4 3 5% 6% 50%	1971
	11th to 20th	Night	9% 5% 1 4 3 4 4 3 5% 7% 55%	2090
	21st to end	Night	13% 7% 2 7% 5% 4 4 3 5% 7% 43%	2090
October	1st to 10th	Night	12% 7% 2 5% 4 4 4 3 5% 6% 47%	2090
	11th to 20th	Night	17% 10% 3 8% 4 4 4 3 4 6% 37%	2280
	21st to end	Night	20% 10% 3 7% 4 4 4 3 6% 6% 34%	2716
November	1st to 10th	Night	11% 11% 4 6% 5% 4 5% 3 4 6% 41%	2536
	11th to 20th	Night	15% 11% 4 9% 5% 5% 5% 4 6% 6% 29%	2600
	21st to end	Night	16% 15% 5% 9% 5% 5% 4 3 5% 6% 27%	2562
December	1st to 10th	Night	16% 15% 5% 12% 7% 5% 5% 4 5% 5% 20%	2470
	11th to 20th	Night	15% 13% 6% 13% 6% 5% 5% 4 6% 6% 22%	3260
	21st to end	Night	25% 22% 6% 11% 5% 4 4 3 4 5% 12%	4884

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	64% 7% 12% 13% 3	2528
	11th to 20th	Day	71% 8% 10% 7% 4	2530
	21st to end	Day	77% 5% 7% 7% 3	2948
February	1st to 10th	Day	62% 7% 10% 13% 7% 1	1725
	11th to 20th	Day	60% 7% 9% 15% 9% 1	1858
	21st to end	Day	60% 7% 12% 14% 5% 2	1570
March	1st to 10th	Day	57% 8% 10% 18% 6%	3120
	11th to 20th	Day	48% 8% 13% 22% 8% 1	3476
	21st to end	Day	58% 8% 10% 15% 8% 1	3815
April	1st to 10th	Day	54% 7% 9% 20% 10%	2275
	11th to 20th	Day	48% 7% 11% 20% 12% 2	2353
	21st to end	Day	49% 7% 13% 16% 14% 1	2470
May	1st to 10th	Day	46% 9% 12% 21% 12% 1	4120
	11th to 20th	Day	43% 9% 15% 23% 9% 1	4085
	21st to end	Day	35% 9% 11% 19% 22% 3	4583
June	1st to 10th	Day	37% 8% 13% 25% 14% 2	2660
	11th to 20th	Day	36% 8% 14% 22% 18% 2	2660
	21st to end	Day	40% 9% 13% 21% 15% 2	2660
July	1st to 10th	Day	41% 7% 14% 20% 15% 3	4371
	11th to 20th	Day	29% 7% 13% 33% 17% 1	4365
	21st to end	Day	36% 10% 14% 19% 20% 2	4491
August	1st to 10th	Day	36% 8% 14% 24% 17% 1	4091
	11th to 20th	Day	37% 8% 11% 30% 13% 1	4083
	21st to end	Day	36% 6% 13% 32% 12% 2	4344
September	1st to 10th	Day	39% 8% 15% 20% 16% 2	2190
	11th to 20th	Day	31% 8% 12% 30% 18% 1	2090
	21st to end	Day	42% 8% 14% 20% 17%	2090
October	1st to 10th	Day	30% 5% 11% 34% 20% 1	3466
	11th to 20th	Day	41% 5% 10% 24% 20%	3127
	21st to end	Day	46% 4 12% 24% 11% 2	3081
November	1st to 10th	Day	43% 7% 11% 25% 14% 1	1762
	11th to 20th	Day	56% 6% 11% 17% 8% 1	1800
	21st to end	Day	60% 5% 14% 15% 6% 1	1773
December	1st to 10th	Day	63% 8% 11% 13% 5%	1710
	11th to 20th	Day	62% 9% 14% 13% 3	1930
	21st to end	Day	76% 6% 8% 6% 3	2783
January	1st to 10th	Night	63% 8% 10% 13% 5% 1	4428
	11th to 20th	Night	70% 6% 11% 9% 4	4440
	21st to end	Night	73% 7% 9% 9% 3	4711
February	1st to 10th	Night	63% 7% 10% 12% 6% 2	2451
	11th to 20th	Night	56% 6% 10% 19% 8% 1	2219
	21st to end	Night	58% 5% 13% 16% 7% 2	1884
March	1st to 10th	Night	48% 7% 12% 25% 7%	3733
	11th to 20th	Night	35% 8% 14% 22% 19% 2	3481
	21st to end	Night	50% 7% 12% 20% 9% 1	3817
April	1st to 10th	Night	46% 7% 11% 22% 14% 1	1922
	11th to 20th	Night	46% 6% 11% 18% 17% 2	1775
	21st to end	Night	46% 5% 13% 19% 14% 3	1710
May	1st to 10th	Night	46% 9% 11% 20% 12% 2	2840
	11th to 20th	Night	41% 9% 11% 25% 14% 1	2813
	21st to end	Night	33% 9% 15% 20% 21% 2	2980
June	1st to 10th	Night	32% 6% 14% 28% 18% 2	1520
	11th to 20th	Night	36% 7% 13% 25% 16% 2	1520
	21st to end	Night	31% 8% 15% 26% 18% 2	1520
July	1st to 10th	Night	32% 6% 13% 27% 15% 6%	2490
	11th to 20th	Night	27% 6% 14% 30% 22% 2	2482
	21st to end	Night	31% 8% 17% 18% 25% 2	2826
August	1st to 10th	Night	34% 7% 14% 29% 15% 1	2814
	11th to 20th	Night	33% 7% 11% 33% 15% 2	2812
	21st to end	Night	36% 7% 10% 30% 16% 2	3307
September	1st to 10th	Night	33% 8% 11% 26% 19% 3	1971
	11th to 20th	Night	28% 6% 10% 30% 23% 3	2090
	21st to end	Night	39% 7% 12% 26% 15% 1	2090
October	1st to 10th	Night	25% 4 10% 34% 26% 1	3480
	11th to 20th	Night	42% 4 10% 22% 21%	3779
	21st to end	Night	39% 4 10% 32% 15% 1	4466
November	1st to 10th	Night	45% 6% 11% 23% 15% 1	2536
	11th to 20th	Night	53% 7% 13% 17% 9% 2	2600
	21st to end	Night	56% 6% 13% 18% 7%	2562
December	1st to 10th	Night	64% 8% 10% 12% 6%	2470
	11th to 20th	Night	61% 8% 12% 13% 5%	3262
	21st to end	Night	74% 7% 10% 7% 2	4884

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% 38% 19% 4 1	270
	11th to 20th	Day	23% 17% 43% 14% 3 1	270
	21st to end	Day	28% 18% 34% 17% 4	297
February	1st to 10th	Day	24% 20% 36% 16% 3 1	270
	11th to 20th	Day	27% 19% 36% 17% 2	270
	21st to end	Day	27% 25% 34% 13% 1	225
March	1st to 10th	Day	21% 21% 42% 12% 3	270
	11th to 20th	Day	24% 13% 35% 21% 7% 1	456
	21st to end	Day	25% 18% 35% 16% 5% 1	506
April	1st to 10th	Day	20% 16% 37% 19% 8%	460
	11th to 20th	Day	23% 20% 31% 15% 6% 4	452
	21st to end	Day	21% 15% 33% 18% 9% 2	460
May	1st to 10th	Day	23% 14% 30% 20% 10% 2	463
	11th to 20th	Day	20% 10% 29% 22% 12% 7%	487
	21st to end	Day	14% 9% 23% 27% 20% 8%	584
June	1st to 10th	Day	12% 8% 29% 31% 16% 4	680
	11th to 20th	Day	13% 7% 29% 28% 17% 5%	680
	21st to end	Day	10% 10% 31% 29% 15% 5%	680
July	1st to 10th	Day	8% 5% 20% 31% 24% 11%	671
	11th to 20th	Day	10% 6% 25% 27% 21% 11%	668
	21st to end	Day	8% 3 27% 31% 23% 9%	639
August	1st to 10th	Day	9% 4 19% 29% 21% 18%	486
	11th to 20th	Day	12% 5% 20% 26% 28% 10%	479
	21st to end	Day	9% 4 20% 31% 24% 12%	539
September	1st to 10th	Day	14% 6% 23% 23% 22% 12%	490
	11th to 20th	Day	9% 3 21% 23% 28% 15%	490
	21st to end	Day	17% 11% 23% 25% 16% 8%	490
October	1st to 10th	Day	13% 9% 29% 25% 18% 6%	490
	11th to 20th	Day	19% 16% 29% 26% 7% 2	489
	21st to end	Day	28% 17% 34% 15% 4 1	330
November	1st to 10th	Day	13% 19% 35% 24% 7% 2	300
	11th to 20th	Day	21% 25% 30% 18% 5% 1	300
	21st to end	Day	27% 19% 37% 14% 2	291
December	1st to 10th	Day	22% 28% 31% 12% 7% 1	270
	11th to 20th	Day	23% 24% 34% 16% 4	270
	21st to end	Day	24% 26% 33% 17% 1	297
January	1st to 10th	Night	21% 17% 38% 19% 5%	950
	11th to 20th	Night	23% 16% 36% 20% 4 1	950
	21st to end	Night	19% 13% 38% 24% 5%	937
February	1st to 10th	Night	24% 14% 38% 21% 3	760
	11th to 20th	Night	21% 15% 37% 23% 3	743
	21st to end	Night	24% 16% 38% 19% 3	628
March	1st to 10th	Night	20% 13% 36% 24% 6%	760
	11th to 20th	Night	17% 15% 39% 23% 6% 1	760
	21st to end	Night	24% 12% 31% 25% 8%	836
April	1st to 10th	Night	18% 15% 36% 26% 4 1	592
	11th to 20th	Night	21% 12% 36% 22% 9% 1	563
	21st to end	Night	19% 10% 35% 27% 8% 1	570
May	1st to 10th	Night	19% 10% 29% 33% 7% 2	570
	11th to 20th	Night	23% 5% 30% 28% 14% 1	561
	21st to end	Night	12% 4 26% 37% 18% 2	617
June	1st to 10th	Night	11% 3 27% 43% 16%	570
	11th to 20th	Night	12% 4 24% 42% 17% 1	570
	21st to end	Night	9% 3 24% 41% 20% 3	570
July	1st to 10th	Night	8% 2 18% 42% 26% 4	555
	11th to 20th	Night	9% 2 18% 43% 25% 3	552
	21st to end	Night	6% 2 19% 43% 29% 1	624
August	1st to 10th	Night	8% 2 14% 45% 28% 3	567
	11th to 20th	Night	8% 1 17% 42% 27% 4	564
	21st to end	Night	11% 2 15% 38% 30% 4	627
September	1st to 10th	Night	12% 3 20% 35% 25% 5%	641
	11th to 20th	Night	11% 4 16% 34% 32% 4	760
	21st to end	Night	16% 7% 23% 30% 20% 4	760
October	1st to 10th	Night	15% 7% 26% 32% 18% 2	760
	11th to 20th	Night	20% 14% 30% 25% 9% 1	760
	21st to end	Night	24% 14% 33% 23% 6%	836
November	1st to 10th	Night	19% 13% 31% 27% 11% 1	780
	11th to 20th	Night	21% 17% 35% 22% 6% 1	800
	21st to end	Night	24% 13% 36% 23% 4	789
December	1st to 10th	Night	23% 16% 37% 19% 5%	760
	11th to 20th	Night	23% 15% 39% 20% 3	931
	21st to end	Night	30% 15% 35% 19% 2	1045

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