Mount Chestnut Oak Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Chestnut Oak Observing Site clear sky chart from 2005-11-06 to 2024-11-04.

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	15% 8% 3 7% 4 4 4 4 5% 7% 37%	100983
	Night	15% 9% 3 6% 4 4 4 3 5% 7% 39%	98009
Transparency	Day	44% 4 10% 23% 15% 2	104727
	Night	43% 4 10% 23% 17% 3	102403
Seeing	Day	20% 11% 23% 22% 16% 7%	14753
	Night	20% 8% 22% 30% 17% 3	24782

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% 16% 6% 9% 4 4 4 4 5% 6% 25%	2836
	11th to 20th	Day	20% 15% 6% 13% 4 5% 3 2 2 3 26%	2840
	21st to end	Day	25% 14% 5% 7% 4 3 3 3 3 5% 27%	3124
February	1st to 10th	Day	18% 12% 5% 9% 4 3 3 3 4 5% 32%	1876
	11th to 20th	Day	23% 9% 4 7% 4 3 4 3 4 6% 32%	1848
	21st to end	Day	21% 13% 3 8% 4 4 4 3 4 5% 32%	1570
March	1st to 10th	Day	25% 13% 3 7% 3 4 3 3 4 6% 30%	3174
	11th to 20th	Day	15% 7% 3 6% 4 3 3 3 4 7% 45%	3480
	21st to end	Day	16% 9% 2 6% 4 4 4 3 5% 7% 38%	3815
April	1st to 10th	Day	14% 7% 3 7% 5% 4 4 3 6% 7% 40%	2207
	11th to 20th	Day	16% 8% 3 7% 5% 3 4 3 5% 6% 42%	2271
	21st to end	Day	16% 7% 3 6% 5% 4 4 4 6% 6% 38%	2470
May	1st to 10th	Day	20% 9% 3 7% 5% 5% 5% 4 6% 7% 30%	4082
	11th to 20th	Day	18% 9% 3 8% 5% 4 4 3 5% 6% 35%	4081
	21st to end	Day	12% 6% 2 7% 5% 5% 6% 5% 7% 10% 37%	4476
June	1st to 10th	Day	12% 6% 2 6% 6% 5% 5% 6% 6% 10% 37%	2470
	11th to 20th	Day	6% 5% 2 6% 6% 5% 5% 5% 7% 9% 43%	2470
	21st to end	Day	9% 5% 2 6% 5% 6% 6% 5% 8% 10% 39%	2470
July	1st to 10th	Day	8% 5% 2 6% 6% 6% 6% 5% 7% 10% 37%	4120
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 40%	4120
	21st to end	Day	21% 10% 4 10% 6% 5% 6% 4 5% 7% 22%	4466
August	1st to 10th	Day	8% 5% 2 7% 4 5% 5% 5% 7% 10% 41%	4104
	11th to 20th	Day	10% 6% 2 6% 5% 5% 6% 5% 8% 11% 36%	3961
	21st to end	Day	6% 3 1 4 3 4 5% 4 7% 10% 53%	4180
September	1st to 10th	Day	14% 6% 2 6% 6% 4 5% 4 6% 6% 41%	2138
	11th to 20th	Day	14% 6% 2 6% 3 4 5% 4 6% 8% 43%	2090
	21st to end	Day	16% 6% 2 5% 3 4 3 3 5% 7% 45%	2090
October	1st to 10th	Day	12% 4 2 4 3 3 3 3 5% 8% 52%	2090
	11th to 20th	Day	13% 6% 2 5% 3 3 3 2 4 6% 51%	1952
	21st to end	Day	18% 7% 2 5% 3 3 3 3 4 7% 45%	2006
November	1st to 10th	Day	12% 6% 2 4 4 3 4 2 4 6% 53%	1699
	11th to 20th	Day	16% 8% 2 5% 3 3 3 4 4 6% 45%	1710
	21st to end	Day	17% 9% 2 6% 3 4 3 3 4 5% 43%	1710
December	1st to 10th	Day	24% 11% 4 6% 5% 3 3 3 4 5% 32%	1710
	11th to 20th	Day	17% 13% 3 6% 4 4 4 4 6% 7% 32%	2153
	21st to end	Day	19% 16% 3 7% 4 4 5% 3 6% 7% 26%	3124
January	1st to 10th	Night	18% 18% 5% 8% 5% 4 3 3 4 4 27%	4109
	11th to 20th	Night	22% 13% 4 8% 7% 3 3 2 3 3 32%	4120
	21st to end	Night	23% 13% 4 7% 4 3 3 3 4 5% 30%	4532
February	1st to 10th	Night	20% 10% 5% 9% 4 3 4 4 5% 5% 31%	2302
	11th to 20th	Night	23% 10% 4 6% 4 4 4 3 4 4 33%	2218
	21st to end	Night	24% 12% 4 7% 5% 4 4 3 4 4 29%	1884
March	1st to 10th	Night	21% 13% 3 7% 4 4 4 3 4 5% 30%	3679
	11th to 20th	Night	13% 8% 2 4 4 4 3 4 5% 7% 48%	3480
	21st to end	Night	14% 8% 3 6% 5% 5% 5% 4 6% 7% 38%	3817
April	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 7% 44%	1989
	11th to 20th	Night	16% 7% 2 5% 4 4 4 3 5% 5% 44%	1856
	21st to end	Night	17% 7% 2 6% 4 4 4 4 6% 7% 40%	1710
May	1st to 10th	Night	18% 8% 4 8% 6% 5% 4 4 5% 7% 31%	2813
	11th to 20th	Night	19% 8% 3 6% 4 4 4 3 7% 7% 36%	2812
	21st to end	Night	7% 6% 2 6% 5% 4 5% 4 7% 9% 44%	3079
June	1st to 10th	Night	10% 6% 2 5% 4 4 5% 5% 6% 9% 44%	1710
	11th to 20th	Night	5% 3 2 6% 4 6% 4 4 7% 11% 48%	1710
	21st to end	Night	7% 5% 1 6% 5% 5% 6% 4 9% 11% 40%	1710
July	1st to 10th	Night	8% 4 2 7% 5% 5% 5% 5% 9% 9% 41%	2840
	11th to 20th	Night	9% 5% 2 5% 4 3 4 4 7% 10% 47%	2840
	21st to end	Night	14% 9% 3 10% 6% 5% 7% 6% 6% 8% 25%	3087
August	1st to 10th	Night	9% 5% 3 6% 4 4 5% 4 6% 9% 46%	2825
	11th to 20th	Night	10% 7% 2 6% 4 4 5% 4 7% 9% 41%	2865
	21st to end	Night	4 3 1 3 3 3 3 3 6% 9% 62%	3476
September	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 8% 47%	2023
	11th to 20th	Night	13% 6% 2 6% 4 5% 4 3 5% 7% 46%	2090
	21st to end	Night	14% 6% 3 5% 3 3 3 4 5% 6% 50%	2090
October	1st to 10th	Night	10% 5% 1 4 2 4 3 2 4 6% 58%	2090
	11th to 20th	Night	16% 6% 2 5% 3 3 3 2 5% 5% 51%	2228
	21st to end	Night	16% 7% 2 5% 3 3 3 4 4 6% 47%	2589
November	1st to 10th	Night	11% 7% 3 5% 4 3 3 3 4 5% 52%	2452
	11th to 20th	Night	15% 7% 2 5% 3 3 3 3 4 7% 47%	2470
	21st to end	Night	17% 10% 3 5% 4 3 3 3 4 6% 43%	2470
December	1st to 10th	Night	23% 14% 3 7% 4 4 3 3 5% 6% 29%	2470
	11th to 20th	Night	19% 12% 4 8% 3 3 3 3 4 5% 35%	3042
	21st to end	Night	18% 15% 4 9% 5% 6% 6% 4 5% 7% 22%	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	59% 3 7% 19% 11% 1	2837
	11th to 20th	Day	65% 3 5% 16% 9%	2840
	21st to end	Day	61% 3 6% 22% 8% 1	3124
February	1st to 10th	Day	57% 2 7% 19% 14% 2	1876
	11th to 20th	Day	56% 3 7% 21% 11% 2	1858
	21st to end	Day	56% 3 7% 16% 13% 4	1570
March	1st to 10th	Day	56% 3 6% 17% 13% 4	3174
	11th to 20th	Day	40% 3 9% 26% 18% 3	3480
	21st to end	Day	46% 4 9% 28% 12% 1	3815
April	1st to 10th	Day	44% 4 10% 24% 15% 4	2207
	11th to 20th	Day	44% 3 8% 21% 21% 4	2271
	21st to end	Day	46% 3 10% 26% 12% 2	2470
May	1st to 10th	Day	54% 4 10% 22% 9% 1	4120
	11th to 20th	Day	51% 4 11% 22% 12% 1	4085
	21st to end	Day	42% 6% 13% 20% 17% 2	4489
June	1st to 10th	Day	43% 6% 11% 23% 15% 2	2470
	11th to 20th	Day	36% 5% 15% 24% 18% 2	2470
	21st to end	Day	38% 6% 15% 21% 17% 3	2470
July	1st to 10th	Day	39% 8% 20% 21% 11% 1	4055
	11th to 20th	Day	37% 5% 16% 31% 9% 2	4051
	21st to end	Day	61% 5% 11% 15% 8% 1	4324
August	1st to 10th	Day	36% 6% 16% 29% 13%	4091
	11th to 20th	Day	38% 5% 15% 27% 14% 1	4000
	21st to end	Day	26% 5% 13% 40% 15% 2	4179
September	1st to 10th	Day	43% 4 11% 19% 17% 5%	2138
	11th to 20th	Day	41% 3 10% 22% 21% 2	2090
	21st to end	Day	40% 3 9% 24% 22% 3	2090
October	1st to 10th	Day	25% 3 6% 22% 40% 4	3480
	11th to 20th	Day	26% 2 10% 24% 31% 7%	3218
	21st to end	Day	32% 2 8% 29% 21% 10%	3282
November	1st to 10th	Day	34% 2 8% 24% 26% 5%	1699
	11th to 20th	Day	41% 2 6% 26% 20% 5%	1710
	21st to end	Day	45% 2 8% 23% 19% 4	1710
December	1st to 10th	Day	56% 2 7% 22% 11% 1	1710
	11th to 20th	Day	52% 4 10% 19% 14% 2	2150
	21st to end	Day	57% 4 9% 21% 7% 1	3124
January	1st to 10th	Night	60% 4 8% 16% 11% 2	4109
	11th to 20th	Night	59% 2 5% 16% 15% 3	4120
	21st to end	Night	58% 3 7% 19% 12% 1	4532
February	1st to 10th	Night	55% 3 10% 19% 13% 1	2302
	11th to 20th	Night	56% 2 6% 19% 13% 3	2219
	21st to end	Night	60% 3 7% 13% 13% 4	1884
March	1st to 10th	Night	56% 4 7% 17% 13% 2	3679
	11th to 20th	Night	37% 3 9% 30% 13% 8%	3480
	21st to end	Night	45% 4 11% 24% 15% 1	3817
April	1st to 10th	Night	40% 3 10% 24% 20% 3	1989
	11th to 20th	Night	42% 2 8% 20% 21% 6%	1856
	21st to end	Night	44% 3 11% 27% 14% 2	1710
May	1st to 10th	Night	52% 5% 12% 23% 7% 2	2840
	11th to 20th	Night	48% 4 14% 23% 11% 1	2813
	21st to end	Night	34% 6% 13% 27% 18% 2	3087
June	1st to 10th	Night	36% 5% 15% 27% 14% 4	1710
	11th to 20th	Night	30% 6% 18% 25% 19% 2	1710
	21st to end	Night	36% 6% 17% 21% 16% 5%	1710
July	1st to 10th	Night	36% 7% 19% 26% 11% 1	2795
	11th to 20th	Night	31% 5% 17% 32% 12% 3	2786
	21st to end	Night	54% 7% 12% 18% 8% 1	2988
August	1st to 10th	Night	34% 6% 14% 30% 15% 2	2814
	11th to 20th	Night	38% 5% 14% 29% 13% 1	2892
	21st to end	Night	20% 4 14% 39% 21% 3	3476
September	1st to 10th	Night	35% 5% 14% 20% 19% 6%	2023
	11th to 20th	Night	38% 5% 9% 26% 20% 3	2090
	21st to end	Night	36% 3 7% 23% 27% 4	2090
October	1st to 10th	Night	27% 2 8% 21% 36% 6%	3480
	11th to 20th	Night	25% 2 7% 25% 31% 9%	3701
	21st to end	Night	27% 3 7% 25% 28% 10%	4263
November	1st to 10th	Night	36% 2 6% 25% 24% 6%	2452
	11th to 20th	Night	40% 2 6% 21% 24% 6%	2470
	21st to end	Night	44% 2 6% 26% 19% 3	2470
December	1st to 10th	Night	57% 2 9% 19% 10% 2	2470
	11th to 20th	Night	53% 2 7% 21% 15% 2	3044
	21st to end	Night	61% 4 9% 16% 10%	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	29% 21% 32% 14% 4	270
	11th to 20th	Day	39% 24% 23% 10% 4	270
	21st to end	Day	30% 27% 31% 10% 3	297
February	1st to 10th	Day	29% 19% 34% 14% 3	270
	11th to 20th	Day	40% 24% 27% 7% 1	270
	21st to end	Day	38% 20% 35% 5% 1	225
March	1st to 10th	Day	34% 18% 35% 10% 3	298
	11th to 20th	Day	28% 21% 28% 18% 5%	460
	21st to end	Day	29% 17% 30% 16% 6% 1	506
April	1st to 10th	Day	27% 16% 26% 20% 10% 1	460
	11th to 20th	Day	22% 18% 28% 19% 10% 3	452
	21st to end	Day	23% 14% 31% 20% 10% 3	460
May	1st to 10th	Day	22% 15% 29% 17% 12% 4	463
	11th to 20th	Day	20% 11% 24% 26% 14% 6%	487
	21st to end	Day	15% 7% 21% 26% 19% 11%	529
June	1st to 10th	Day	14% 6% 20% 30% 19% 11%	490
	11th to 20th	Day	8% 6% 20% 32% 24% 11%	490
	21st to end	Day	10% 5% 25% 28% 20% 12%	490
July	1st to 10th	Day	12% 4 18% 23% 24% 20%	485
	11th to 20th	Day	10% 5% 16% 28% 24% 16%	484
	21st to end	Day	13% 4 15% 30% 26% 12%	532
August	1st to 10th	Day	14% 5% 15% 24% 26% 15%	486
	11th to 20th	Day	14% 4 14% 32% 25% 11%	479
	21st to end	Day	12% 3 8% 27% 32% 19%	539
September	1st to 10th	Day	14% 3 13% 24% 30% 15%	490
	11th to 20th	Day	16% 3 13% 25% 29% 14%	490
	21st to end	Day	18% 9% 17% 25% 22% 9%	490
October	1st to 10th	Day	13% 5% 20% 30% 24% 8%	490
	11th to 20th	Day	17% 12% 26% 26% 14% 5%	490
	21st to end	Day	22% 11% 27% 26% 11% 2	455
November	1st to 10th	Day	18% 9% 32% 24% 14% 4	279
	11th to 20th	Day	25% 15% 35% 20% 5% 1	270
	21st to end	Day	23% 16% 33% 19% 9% 1	270
December	1st to 10th	Day	31% 20% 26% 16% 6%	270
	11th to 20th	Day	25% 16% 32% 20% 6% 1	270
	21st to end	Day	29% 20% 31% 15% 5%	297
January	1st to 10th	Night	28% 17% 30% 22% 4	760
	11th to 20th	Night	33% 15% 27% 21% 4	760
	21st to end	Night	24% 17% 35% 23% 2	836
February	1st to 10th	Night	27% 11% 35% 24% 3	760
	11th to 20th	Night	32% 16% 32% 18% 2	743
	21st to end	Night	35% 15% 31% 17% 2	628
March	1st to 10th	Night	26% 14% 30% 25% 5%	760
	11th to 20th	Night	24% 14% 31% 24% 6% 1	760
	21st to end	Night	22% 13% 30% 28% 7%	836
April	1st to 10th	Night	18% 12% 32% 29% 9%	659
	11th to 20th	Night	20% 10% 29% 29% 11%	563
	21st to end	Night	19% 8% 33% 29% 9% 1	570
May	1st to 10th	Night	18% 6% 28% 29% 15% 3	570
	11th to 20th	Night	18% 5% 20% 34% 20% 4	561
	21st to end	Night	7% 4 18% 36% 30% 5%	617
June	1st to 10th	Night	10% 4 14% 42% 26% 5%	570
	11th to 20th	Night	6% 2 15% 38% 33% 6%	570
	21st to end	Night	9% 1 14% 41% 29% 6%	570
July	1st to 10th	Night	13% 3 9% 32% 36% 8%	555
	11th to 20th	Night	7% 2 9% 30% 44% 7%	552
	21st to end	Night	11% 2 9% 35% 36% 7%	624
August	1st to 10th	Night	12% 3 8% 31% 41% 7%	567
	11th to 20th	Night	10% 2 8% 38% 35% 7%	564
	21st to end	Night	8% 1 6% 34% 40% 11%	627
September	1st to 10th	Night	14% 2 10% 31% 38% 6%	693
	11th to 20th	Night	15% 2 13% 30% 34% 6%	760
	21st to end	Night	16% 4 17% 31% 29% 4	760
October	1st to 10th	Night	13% 5% 16% 31% 30% 4	760
	11th to 20th	Night	18% 6% 22% 35% 17% 3	760
	21st to end	Night	19% 9% 25% 31% 14% 2	836
November	1st to 10th	Night	15% 7% 23% 36% 16% 2	755
	11th to 20th	Night	19% 11% 28% 32% 9% 1	760
	21st to end	Night	24% 11% 23% 32% 9% 1	760
December	1st to 10th	Night	32% 12% 24% 27% 4	760
	11th to 20th	Night	26% 13% 27% 28% 6% 1	760
	21st to end	Night	31% 12% 24% 28% 4	836

Page generated at 2024-11-01 22:47:38. Version ac07

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