Star Corral Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Star Corral Observatory clear sky chart from 2005-11-06 to 2024-07-08.

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% 6% 2 5% 4 4 4 3 5% 7% 47%	89834
	Night	12% 5% 2 5% 3 3 3 3 5% 6% 52%	89524
Transparency	Day	36% 6% 11% 24% 19% 4	89609
	Night	32% 5% 10% 25% 22% 6%	89354
Seeing	Day	13% 8% 25% 28% 20% 5%	14984
	Night	13% 8% 30% 34% 14% 1	24878

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% 9% 4 6% 4 3 4 3 4 6% 45%	2847
	11th to 20th	Day	9% 6% 2 6% 3 3 3 3 4 7% 53%	2850
	21st to end	Day	22% 10% 2 5% 3 2 2 2 2 4 45%	3135
February	1st to 10th	Day	15% 11% 3 6% 5% 3 2 3 4 5% 42%	1710
	11th to 20th	Day	15% 6% 2 7% 3 4 3 4 5% 6% 45%	1788
	21st to end	Day	17% 8% 3 5% 4 4 4 3 4 5% 45%	1617
March	1st to 10th	Day	15% 7% 2 4 3 3 3 2 4 4 53%	3436
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 6% 7% 51%	3480
	21st to end	Day	15% 10% 3 8% 5% 4 4 4 5% 6% 36%	3814
April	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 6% 6% 46%	2106
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 4 6% 45%	2254
	21st to end	Day	20% 7% 3 6% 4 3 4 3 4 5% 42%	2416
May	1st to 10th	Day	22% 8% 2 6% 4 4 3 3 4 5% 39%	4082
	11th to 20th	Day	12% 6% 2 7% 5% 5% 4 4 5% 7% 43%	4082
	21st to end	Day	15% 7% 2 8% 5% 5% 5% 4 7% 8% 35%	4477
June	1st to 10th	Day	7% 4 2 6% 6% 4 4 3 7% 9% 47%	2470
	11th to 20th	Day	9% 4 1 5% 4 5% 4 5% 6% 8% 48%	2470
	21st to end	Day	6% 3 1 4 4 4 3 4 6% 9% 56%	2470
July	1st to 10th	Day	8% 4 2 5% 4 5% 6% 6% 7% 10% 43%	2433
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 9% 56%	2340
	21st to end	Day	7% 4 1 5% 4 5% 4 5% 7% 10% 48%	2546
August	1st to 10th	Day	5% 3 1 5% 4 4 6% 4 8% 9% 50%	2328
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 7% 9% 47%	2301
	21st to end	Day	5% 4 1 5% 3 4 4 4 6% 9% 54%	2436
September	1st to 10th	Day	10% 5% 2 5% 4 3 3 3 4 6% 54%	2039
	11th to 20th	Day	13% 4 2 5% 3 4 4 5% 6% 8% 46%	1980
	21st to end	Day	8% 4 2 4 3 3 4 3 5% 7% 56%	1980
October	1st to 10th	Day	10% 4 1 4 3 3 3 3 5% 7% 58%	1854
	11th to 20th	Day	12% 5% 1 3 2 2 2 2 3 5% 62%	1800
	21st to end	Day	17% 5% 2 4 3 3 3 2 3 5% 54%	1980
November	1st to 10th	Day	11% 4 2 4 3 2 3 2 5% 7% 57%	1858
	11th to 20th	Day	11% 5% 2 3 3 3 4 2 4 5% 59%	1739
	21st to end	Day	16% 6% 2 4 2 2 2 2 5% 6% 52%	1710
December	1st to 10th	Day	14% 6% 2 6% 4 2 3 3 5% 6% 50%	1710
	11th to 20th	Day	15% 8% 2 6% 5% 4 4 2 4 5% 45%	2161
	21st to end	Day	17% 11% 4 8% 5% 5% 4 3 5% 5% 33%	3135
January	1st to 10th	Night	12% 8% 3 6% 3 3 4 3 5% 5% 48%	4108
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 5% 6% 56%	4120
	21st to end	Night	22% 8% 3 4 2 2 2 2 3 5% 47%	4532
February	1st to 10th	Night	15% 9% 2 6% 4 3 3 3 5% 5% 47%	2470
	11th to 20th	Night	15% 7% 3 5% 3 3 3 2 4 5% 51%	2293
	21st to end	Night	14% 8% 2 5% 3 3 3 3 4 4 49%	1835
March	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 5% 49%	3419
	11th to 20th	Night	11% 4 2 4 3 3 3 3 4 6% 58%	3480
	21st to end	Night	15% 5% 2 6% 3 4 4 3 5% 7% 46%	3817
April	1st to 10th	Night	12% 5% 2 4 3 3 3 3 5% 6% 54%	2072
	11th to 20th	Night	14% 5% 3 5% 4 3 4 2 4 6% 51%	1875
	21st to end	Night	16% 7% 2 5% 4 3 3 2 5% 6% 47%	1761
May	1st to 10th	Night	16% 7% 2 5% 4 3 3 3 5% 6% 45%	2823
	11th to 20th	Night	14% 6% 2 7% 4 4 3 4 5% 7% 45%	2823
	21st to end	Night	12% 6% 2 4 3 4 5% 4 6% 9% 46%	3090
June	1st to 10th	Night	5% 3 2 5% 4 4 4 5% 6% 7% 56%	1710
	11th to 20th	Night	4 4 1 3 3 4 4 4 6% 10% 56%	1710
	21st to end	Night	3 3 1 3 3 3 3 3 6% 9% 64%	1710
July	1st to 10th	Night	5% 4 1 5% 4 4 4 3 7% 12% 51%	1692
	11th to 20th	Night	3 2 2 4 3 3 3 4 6% 9% 62%	1620
	21st to end	Night	5% 3 1 4 3 3 5% 4 7% 9% 56%	1772
August	1st to 10th	Night	3 2 1 4 2 5% 4 5% 6% 11% 57%	1611
	11th to 20th	Night	5% 4 2 5% 4 5% 5% 4 6% 8% 53%	1600
	21st to end	Night	3 3 2 4 4 3 4 3 6% 8% 60%	1917
September	1st to 10th	Night	8% 4 1 5% 4 2 2 3 4 7% 59%	1916
	11th to 20th	Night	10% 5% 2 6% 4 3 4 3 5% 7% 51%	1980
	21st to end	Night	8% 3 1 4 4 3 4 4 3 6% 60%	1980
October	1st to 10th	Night	8% 3 1 4 3 3 3 3 3 7% 61%	2088
	11th to 20th	Night	12% 4 2 4 2 3 3 2 4 6% 59%	2160
	21st to end	Night	15% 5% 2 4 2 2 3 2 4 4 56%	2376
November	1st to 10th	Night	11% 4 2 3 2 2 2 2 3 5% 64%	2220
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 3 5% 60%	2436
	21st to end	Night	15% 5% 1 4 2 3 3 2 3 5% 56%	2470
December	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 3 6% 52%	2470
	11th to 20th	Night	13% 6% 2 7% 3 4 4 3 4 4 50%	3036
	21st to end	Night	17% 9% 3 6% 4 3 4 3 5% 5% 42%	4532

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	42% 3 8% 24% 21% 2	2848
	11th to 20th	Day	31% 4 15% 28% 18% 5%	2850
	21st to end	Day	46% 2 7% 21% 22% 2	3135
February	1st to 10th	Day	45% 3 11% 21% 15% 4	1710
	11th to 20th	Day	40% 4 9% 24% 18% 4	1798
	21st to end	Day	42% 3 7% 22% 17% 9%	1617
March	1st to 10th	Day	36% 4 6% 22% 22% 11%	3436
	11th to 20th	Day	33% 6% 12% 25% 19% 4	3480
	21st to end	Day	48% 5% 9% 25% 11% 1	3814
April	1st to 10th	Day	37% 6% 10% 23% 18% 6%	2106
	11th to 20th	Day	39% 5% 12% 22% 16% 6%	2254
	21st to end	Day	45% 5% 8% 22% 17% 2	2416
May	1st to 10th	Day	47% 5% 8% 21% 16% 3	4120
	11th to 20th	Day	38% 9% 12% 23% 18% 1	4086
	21st to end	Day	45% 9% 12% 19% 12% 3	4489
June	1st to 10th	Day	32% 8% 15% 27% 16% 3	2470
	11th to 20th	Day	31% 7% 13% 28% 17% 2	2470
	21st to end	Day	24% 7% 14% 30% 20% 5%	2470
July	1st to 10th	Day	32% 10% 15% 27% 15% 1	2369
	11th to 20th	Day	21% 8% 14% 29% 25% 3	2271
	21st to end	Day	28% 8% 16% 31% 16% 1	2405
August	1st to 10th	Day	26% 9% 15% 28% 18% 3	2314
	11th to 20th	Day	32% 8% 14% 24% 20% 3	2301
	21st to end	Day	26% 8% 14% 29% 18% 6%	2436
September	1st to 10th	Day	31% 5% 9% 23% 23% 8%	2039
	11th to 20th	Day	33% 8% 12% 19% 22% 6%	1980
	21st to end	Day	27% 6% 9% 23% 28% 7%	1980
October	1st to 10th	Day	27% 6% 11% 24% 25% 7%	1854
	11th to 20th	Day	27% 4 6% 23% 31% 9%	1800
	21st to end	Day	35% 4 8% 25% 19% 8%	1980
November	1st to 10th	Day	28% 4 8% 26% 26% 8%	1858
	11th to 20th	Day	29% 3 9% 26% 26% 8%	1739
	21st to end	Day	34% 4 8% 23% 25% 6%	1710
December	1st to 10th	Day	36% 3 10% 28% 21% 2	1710
	11th to 20th	Day	42% 3 6% 22% 23% 4	2159
	21st to end	Day	51% 6% 8% 20% 12% 3	3135
January	1st to 10th	Night	38% 5% 8% 25% 21% 3	4108
	11th to 20th	Night	28% 6% 17% 22% 25% 3	4120
	21st to end	Night	42% 3 8% 21% 21% 4	4532
February	1st to 10th	Night	40% 4 10% 23% 18% 5%	2470
	11th to 20th	Night	37% 4 7% 26% 21% 5%	2293
	21st to end	Night	39% 3 8% 19% 23% 9%	1835
March	1st to 10th	Night	37% 5% 7% 20% 18% 11%	3419
	11th to 20th	Night	29% 5% 9% 32% 20% 5%	3480
	21st to end	Night	36% 5% 11% 31% 14% 2	3817
April	1st to 10th	Night	32% 5% 9% 22% 22% 10%	2072
	11th to 20th	Night	34% 4 11% 23% 19% 9%	1875
	21st to end	Night	38% 4 9% 25% 22% 3	1761
May	1st to 10th	Night	39% 7% 10% 20% 19% 5%	2850
	11th to 20th	Night	38% 7% 12% 24% 16% 2	2824
	21st to end	Night	33% 9% 14% 24% 17% 2	3099
June	1st to 10th	Night	24% 9% 15% 31% 18% 3	1710
	11th to 20th	Night	23% 6% 14% 33% 20% 4	1710
	21st to end	Night	18% 5% 13% 32% 25% 7%	1710
July	1st to 10th	Night	26% 8% 14% 30% 19% 4	1647
	11th to 20th	Night	19% 6% 12% 30% 28% 5%	1566
	21st to end	Night	21% 6% 13% 34% 24% 2	1673
August	1st to 10th	Night	20% 6% 15% 35% 21% 3	1601
	11th to 20th	Night	27% 8% 12% 22% 26% 7%	1600
	21st to end	Night	21% 7% 13% 29% 22% 8%	1917
September	1st to 10th	Night	26% 4 10% 26% 25% 10%	1916
	11th to 20th	Night	32% 6% 10% 21% 24% 7%	1980
	21st to end	Night	25% 4 8% 25% 30% 8%	1980
October	1st to 10th	Night	25% 4 11% 24% 27% 9%	2088
	11th to 20th	Night	29% 3 6% 19% 31% 12%	2160
	21st to end	Night	32% 4 6% 23% 25% 10%	2376
November	1st to 10th	Night	26% 3 8% 24% 31% 9%	2220
	11th to 20th	Night	28% 3 7% 25% 27% 9%	2436
	21st to end	Night	33% 4 7% 21% 29% 7%	2470
December	1st to 10th	Night	34% 4 11% 25% 20% 5%	2470
	11th to 20th	Night	39% 3 7% 22% 25% 5%	3037
	21st to end	Night	43% 4 8% 23% 18% 4	4532

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	17% 13% 37% 26% 6%	270
	11th to 20th	Day	19% 21% 35% 20% 4	270
	21st to end	Day	17% 11% 42% 21% 8% 1	297
February	1st to 10th	Day	24% 16% 36% 20% 4	270
	11th to 20th	Day	20% 16% 40% 21% 3	270
	21st to end	Day	26% 19% 39% 15% 2	225
March	1st to 10th	Day	21% 17% 33% 21% 6%	270
	11th to 20th	Day	17% 22% 37% 19% 4	270
	21st to end	Day	22% 19% 37% 17% 4 1	297
April	1st to 10th	Day	13% 21% 38% 20% 7% 1	286
	11th to 20th	Day	19% 16% 37% 23% 5%	452
	21st to end	Day	22% 16% 32% 21% 7% 2	596
May	1st to 10th	Day	16% 11% 38% 27% 7% 1	653
	11th to 20th	Day	16% 10% 29% 29% 12% 4	675
	21st to end	Day	14% 8% 31% 23% 17% 6%	734
June	1st to 10th	Day	6% 4 20% 35% 28% 6%	680
	11th to 20th	Day	9% 2 20% 39% 23% 6%	680
	21st to end	Day	3 2 20% 41% 29% 5%	680
July	1st to 10th	Day	8% 1 12% 32% 33% 14%	658
	11th to 20th	Day	3 2 11% 34% 40% 10%	618
	21st to end	Day	7% 1 6% 30% 40% 16%	684
August	1st to 10th	Day	6% 1 9% 40% 37% 7%	626
	11th to 20th	Day	10% 2 11% 30% 37% 9%	615
	21st to end	Day	7% 1 8% 30% 41% 14%	555
September	1st to 10th	Day	7% 1 10% 28% 40% 15%	329
	11th to 20th	Day	7% 1 12% 35% 33% 12%	270
	21st to end	Day	11% 3 19% 32% 26% 10%	270
October	1st to 10th	Day	9% 4 30% 29% 19% 10%	270
	11th to 20th	Day	9% 12% 35% 32% 11% 1	270
	21st to end	Day	24% 9% 29% 26% 11% 2	297
November	1st to 10th	Day	13% 8% 40% 25% 13% 2	270
	11th to 20th	Day	16% 9% 36% 26% 12% 2	270
	21st to end	Day	22% 12% 34% 23% 7% 1	270
December	1st to 10th	Day	15% 14% 37% 22% 11% 1	270
	11th to 20th	Day	21% 12% 35% 24% 7%	270
	21st to end	Day	16% 19% 38% 22% 5%	297
January	1st to 10th	Night	14% 13% 36% 32% 5%	950
	11th to 20th	Night	16% 14% 37% 28% 5%	950
	21st to end	Night	15% 12% 36% 32% 5%	1045
February	1st to 10th	Night	20% 12% 36% 27% 4	950
	11th to 20th	Night	18% 15% 34% 28% 3	818
	21st to end	Night	17% 14% 41% 25% 3	579
March	1st to 10th	Night	17% 11% 36% 32% 4	570
	11th to 20th	Night	17% 11% 37% 30% 5%	570
	21st to end	Night	18% 11% 40% 26% 6%	627
April	1st to 10th	Night	13% 12% 43% 27% 4	570
	11th to 20th	Night	17% 10% 40% 28% 6%	563
	21st to end	Night	18% 10% 39% 26% 6% 1	570
May	1st to 10th	Night	14% 8% 37% 34% 7%	570
	11th to 20th	Night	14% 5% 29% 38% 15% 1	561
	21st to end	Night	10% 5% 30% 33% 19% 2	617
June	1st to 10th	Night	6% 2 18% 42% 29% 2	570
	11th to 20th	Night	4 2 22% 49% 21% 1	570
	21st to end	Night	2 3 19% 51% 22% 2	570
July	1st to 10th	Night	6% 1 10% 45% 35% 3	549
	11th to 20th	Night	3 1 10% 45% 39% 3	522
	21st to end	Night	4 1 8% 42% 42% 3	591
August	1st to 10th	Night	3 1 10% 48% 35% 2	537
	11th to 20th	Night	6% 2 11% 42% 37% 3	534
	21st to end	Night	3 1 11% 38% 44% 3	594
September	1st to 10th	Night	9% 1 12% 42% 34% 1	540
	11th to 20th	Night	13% 1 15% 42% 25% 4	540
	21st to end	Night	9% 2 18% 41% 26% 3	540
October	1st to 10th	Night	9% 1 27% 37% 22% 4	648
	11th to 20th	Night	13% 8% 34% 34% 11%	720
	21st to end	Night	17% 10% 29% 31% 12% 1	792
November	1st to 10th	Night	11% 7% 36% 33% 13% 1	740
	11th to 20th	Night	11% 11% 34% 34% 9%	916
	21st to end	Night	17% 12% 34% 28% 9%	950
December	1st to 10th	Night	16% 11% 34% 31% 7%	950
	11th to 20th	Night	19% 10% 35% 30% 6%	950
	21st to end	Night	18% 11% 36% 29% 5%	1045

Page generated at 2024-07-05 10:05:41. Version ac07

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