Branched Oak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Branched Oak Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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 4 5% 7% 45%	100968
	Night	10% 6% 2 6% 4 3 4 3 5% 7% 50%	98091
Transparency	Day	39% 3 13% 27% 16% 2	100780
	Night	36% 3 12% 28% 18% 3	97950
Seeing	Day	14% 8% 30% 30% 15% 3	15780
	Night	13% 8% 32% 34% 11% 1	25624

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	10% 12% 4 12% 7% 6% 5% 4 5% 5% 29%	2847
	11th to 20th	Day	9% 11% 4 9% 5% 5% 7% 4 5% 6% 37%	2850
	21st to end	Day	8% 12% 5% 13% 5% 4 5% 3 4 5% 36%	3135
February	1st to 10th	Day	10% 11% 5% 8% 6% 4 4 4 6% 7% 35%	1710
	11th to 20th	Day	8% 10% 2 8% 4 4 4 4 5% 8% 42%	1744
	21st to end	Day	9% 8% 3 6% 5% 4 4 3 5% 6% 46%	1570
March	1st to 10th	Day	11% 8% 3 7% 4 3 3 2 3 5% 51%	3341
	11th to 20th	Day	11% 7% 3 6% 4 4 3 3 4 5% 51%	3480
	21st to end	Day	19% 11% 3 9% 4 4 4 4 6% 7% 30%	3814
April	1st to 10th	Day	14% 8% 2 5% 4 3 4 3 5% 6% 46%	2109
	11th to 20th	Day	15% 7% 3 6% 5% 4 4 4 4 7% 41%	2409
	21st to end	Day	19% 7% 2 7% 4 4 4 3 5% 7% 38%	2470
May	1st to 10th	Day	16% 7% 2 7% 4 5% 4 4 5% 8% 38%	4082
	11th to 20th	Day	13% 7% 3 6% 4 4 4 3 5% 6% 45%	4082
	21st to end	Day	14% 6% 3 6% 5% 4 5% 4 6% 7% 40%	4477
June	1st to 10th	Day	6% 4 1 5% 4 4 5% 4 6% 10% 51%	2589
	11th to 20th	Day	9% 6% 2 5% 4 4 4 4 6% 9% 47%	2660
	21st to end	Day	6% 5% 2 5% 4 5% 5% 5% 6% 9% 48%	2535
July	1st to 10th	Day	13% 5% 2 5% 4 5% 4 4 6% 8% 45%	4120
	11th to 20th	Day	7% 4 2 5% 4 4 4 4 6% 8% 52%	4120
	21st to end	Day	4 3 1 5% 3 4 5% 4 7% 11% 52%	4465
August	1st to 10th	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 10% 45%	4104
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 7% 8% 43%	4041
	21st to end	Day	6% 4 2 6% 4 4 5% 4 6% 7% 53%	4505
September	1st to 10th	Day	12% 4 2 4 4 3 3 3 4 7% 53%	2150
	11th to 20th	Day	9% 5% 2 5% 3 4 4 3 5% 7% 54%	2090
	21st to end	Day	10% 4 1 4 3 3 3 3 5% 6% 59%	2090
October	1st to 10th	Day	12% 6% 2 5% 4 3 4 2 4 5% 53%	1978
	11th to 20th	Day	10% 5% 2 5% 3 2 3 3 4 4 58%	1900
	21st to end	Day	13% 7% 2 6% 4 3 3 2 4 6% 50%	2075
November	1st to 10th	Day	8% 6% 1 6% 3 3 3 2 6% 7% 56%	1682
	11th to 20th	Day	9% 6% 2 8% 4 4 3 3 5% 7% 51%	1710
	21st to end	Day	12% 8% 3 6% 4 3 3 3 5% 7% 45%	1554
December	1st to 10th	Day	8% 9% 2 6% 5% 3 4 4 6% 8% 47%	1520
	11th to 20th	Day	8% 8% 4 8% 5% 4 4 4 6% 8% 41%	1918
	21st to end	Day	15% 11% 3 13% 6% 5% 5% 4 5% 5% 29%	3042
January	1st to 10th	Night	7% 11% 4 15% 6% 5% 5% 4 6% 6% 32%	4108
	11th to 20th	Night	8% 9% 3 6% 5% 4 7% 4 5% 6% 42%	4120
	21st to end	Night	11% 11% 5% 11% 4 3 3 3 4 6% 39%	4532
February	1st to 10th	Night	11% 10% 3 8% 5% 4 5% 4 5% 5% 40%	2470
	11th to 20th	Night	8% 7% 3 7% 5% 5% 5% 4 5% 7% 44%	2340
	21st to end	Night	8% 8% 2 6% 4 3 4 3 4 5% 51%	1884
March	1st to 10th	Night	11% 6% 2 5% 3 3 3 3 4 5% 55%	3515
	11th to 20th	Night	11% 6% 2 5% 3 2 3 2 4 6% 57%	3480
	21st to end	Night	18% 8% 2 7% 4 4 4 4 6% 7% 35%	3817
April	1st to 10th	Night	12% 7% 2 6% 4 3 3 3 5% 7% 48%	2069
	11th to 20th	Night	11% 7% 3 6% 4 3 4 3 5% 7% 47%	1718
	21st to end	Night	15% 7% 2 5% 4 3 4 2 5% 6% 46%	1710
May	1st to 10th	Night	19% 7% 2 5% 4 3 3 2 4 6% 45%	2823
	11th to 20th	Night	11% 5% 2 5% 4 3 4 3 5% 7% 50%	2823
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 7% 44%	3090
June	1st to 10th	Night	6% 3 1 4 4 3 5% 4 7% 10% 54%	1587
	11th to 20th	Night	6% 4 2 5% 4 4 3 4 6% 10% 51%	1520
	21st to end	Night	3 3 2 4 4 4 4 4 7% 8% 59%	1636
July	1st to 10th	Night	8% 4 2 5% 4 3 4 3 5% 7% 54%	2850
	11th to 20th	Night	5% 3 1 3 3 3 4 3 6% 8% 61%	2850
	21st to end	Night	3 2 1 3 3 3 4 4 6% 10% 61%	3098
August	1st to 10th	Night	4 3 1 3 4 3 4 3 6% 10% 58%	2836
	11th to 20th	Night	12% 6% 1 4 3 3 3 3 5% 8% 51%	2798
	21st to end	Night	6% 4 2 5% 4 3 4 3 5% 8% 57%	3160
September	1st to 10th	Night	8% 4 1 4 3 3 3 2 4 7% 62%	2026
	11th to 20th	Night	8% 3 1 4 2 3 3 3 5% 7% 59%	2090
	21st to end	Night	8% 5% 1 3 3 3 3 3 4 5% 60%	2090
October	1st to 10th	Night	12% 5% 2 4 3 3 5% 3 5% 5% 52%	2181
	11th to 20th	Night	11% 6% 2 5% 3 2 2 3 3 5% 59%	2280
	21st to end	Night	13% 5% 2 4 3 3 3 3 4 5% 55%	2521
November	1st to 10th	Night	6% 4 1 4 4 4 3 3 4 8% 59%	2419
	11th to 20th	Night	8% 6% 2 5% 4 3 3 3 4 6% 54%	2470
	21st to end	Night	11% 6% 2 5% 3 3 3 3 5% 6% 53%	2622
December	1st to 10th	Night	7% 8% 2 6% 4 4 4 3 5% 7% 49%	2660
	11th to 20th	Night	9% 7% 3 7% 4 3 3 3 5% 7% 51%	3279
	21st to end	Night	17% 12% 4 11% 4 3 3 3 4 5% 34%	4619

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	57% 1 12% 21% 8% 1	2848
	11th to 20th	Day	50% 1 17% 21% 11% 1	2850
	21st to end	Day	51% 3 12% 21% 13% 1	3135
February	1st to 10th	Day	48% 4 15% 21% 11% 1	1710
	11th to 20th	Day	41% 3 13% 24% 16% 3	1753
	21st to end	Day	39% 3 13% 26% 16% 3	1570
March	1st to 10th	Day	38% 1 9% 28% 20% 3	3341
	11th to 20th	Day	38% 2 10% 30% 19% 1	3480
	21st to end	Day	55% 2 23% 16% 4 1	3814
April	1st to 10th	Day	40% 2 13% 26% 16% 2	2109
	11th to 20th	Day	44% 2 12% 23% 15% 3	2409
	21st to end	Day	45% 3 10% 28% 13% 1	2470
May	1st to 10th	Day	45% 3 9% 26% 14% 3	4120
	11th to 20th	Day	41% 2 10% 25% 20% 1	4086
	21st to end	Day	43% 3 12% 27% 14% 1	4489
June	1st to 10th	Day	29% 4 17% 34% 14% 2	2589
	11th to 20th	Day	33% 4 13% 32% 15% 2	2660
	21st to end	Day	31% 5% 14% 31% 14% 4	2535
July	1st to 10th	Day	37% 3 13% 29% 17% 1	4056
	11th to 20th	Day	31% 4 12% 32% 19% 3	4051
	21st to end	Day	24% 6% 17% 29% 22% 3	4325
August	1st to 10th	Day	32% 5% 16% 29% 15% 3	4090
	11th to 20th	Day	39% 4 14% 24% 17% 1	4080
	21st to end	Day	30% 5% 14% 25% 19% 6%	4504
September	1st to 10th	Day	32% 3 9% 31% 19% 6%	2150
	11th to 20th	Day	31% 3 11% 32% 22% 2	2090
	21st to end	Day	28% 2 9% 33% 27% 2	2090
October	1st to 10th	Day	35% 2 9% 27% 26% 2	1978
	11th to 20th	Day	31% 2 8% 29% 23% 7%	1900
	21st to end	Day	38% 2 12% 23% 21% 4	2075
November	1st to 10th	Day	28% 2 14% 31% 22% 3	1682
	11th to 20th	Day	35% 3 12% 29% 20% 1	1710
	21st to end	Day	39% 2 10% 30% 16% 2	1554
December	1st to 10th	Day	35% 3 16% 29% 14% 2	1520
	11th to 20th	Day	41% 2 17% 32% 8%	1915
	21st to end	Day	58% 2 10% 20% 10% 1	3042
January	1st to 10th	Night	52% 1 11% 22% 13%	4108
	11th to 20th	Night	44% 1 14% 29% 12% 1	4120
	21st to end	Night	48% 2 13% 20% 15% 1	4532
February	1st to 10th	Night	46% 3 13% 21% 14% 3	2470
	11th to 20th	Night	40% 3 14% 25% 15% 3	2341
	21st to end	Night	35% 3 9% 26% 22% 5%	1884
March	1st to 10th	Night	33% 2 8% 29% 25% 3	3515
	11th to 20th	Night	32% 2 8% 30% 24% 5%	3480
	21st to end	Night	49% 2 22% 21% 6% 1	3817
April	1st to 10th	Night	37% 3 10% 28% 18% 3	2069
	11th to 20th	Night	37% 3 11% 27% 19% 3	1718
	21st to end	Night	39% 3 12% 26% 18% 1	1710
May	1st to 10th	Night	42% 2 10% 25% 18% 2	2850
	11th to 20th	Night	35% 3 12% 27% 23% 1	2824
	21st to end	Night	40% 2 14% 22% 20% 2	3099
June	1st to 10th	Night	26% 5% 17% 33% 17% 3	1587
	11th to 20th	Night	28% 4 14% 29% 20% 5%	1520
	21st to end	Night	23% 4 14% 35% 21% 3	1636
July	1st to 10th	Night	30% 4 13% 32% 18% 3	2805
	11th to 20th	Night	22% 4 14% 36% 21% 3	2796
	21st to end	Night	18% 5% 17% 32% 26% 2	2999
August	1st to 10th	Night	23% 4 18% 34% 19% 4	2826
	11th to 20th	Night	33% 3 16% 29% 17% 2	2825
	21st to end	Night	27% 4 15% 29% 17% 9%	3160
September	1st to 10th	Night	24% 3 11% 30% 24% 8%	2026
	11th to 20th	Night	25% 2 12% 35% 21% 4	2090
	21st to end	Night	28% 2 6% 31% 28% 5%	2090
October	1st to 10th	Night	33% 3 9% 26% 26% 3	2181
	11th to 20th	Night	30% 2 7% 27% 27% 7%	2280
	21st to end	Night	33% 2 11% 25% 26% 3	2521
November	1st to 10th	Night	25% 2 13% 29% 26% 5%	2419
	11th to 20th	Night	32% 2 11% 31% 21% 4	2470
	21st to end	Night	33% 2 12% 28% 21% 3	2622
December	1st to 10th	Night	36% 3 13% 31% 15% 1	2660
	11th to 20th	Night	34% 2 13% 37% 13% 1	3281
	21st to end	Night	54% 2 9% 25% 9% 1	4619

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	18% 14% 37% 20% 9% 2	270
	11th to 20th	Day	21% 13% 33% 23% 8% 1	270
	21st to end	Day	14% 8% 44% 23% 9% 1	297
February	1st to 10th	Day	16% 17% 41% 22% 4	270
	11th to 20th	Day	13% 13% 39% 26% 9% 1	270
	21st to end	Day	14% 18% 44% 19% 4 1	225
March	1st to 10th	Day	17% 10% 42% 24% 6% 1	270
	11th to 20th	Day	24% 9% 36% 21% 10% 1	270
	21st to end	Day	30% 12% 38% 16% 4	297
April	1st to 10th	Day	21% 16% 41% 19% 3	289
	11th to 20th	Day	20% 15% 35% 22% 7%	607
	21st to end	Day	22% 14% 32% 20% 10% 2	650
May	1st to 10th	Day	20% 11% 34% 25% 9% 2	653
	11th to 20th	Day	19% 8% 32% 25% 13% 4	675
	21st to end	Day	19% 5% 29% 30% 14% 3	734
June	1st to 10th	Day	7% 5% 22% 38% 23% 5%	680
	11th to 20th	Day	10% 6% 32% 32% 18% 4	680
	21st to end	Day	8% 4 32% 36% 18% 2	680
July	1st to 10th	Day	9% 3 17% 36% 27% 8%	671
	11th to 20th	Day	6% 2 22% 39% 25% 8%	668
	21st to end	Day	7% 2 18% 40% 29% 5%	739
August	1st to 10th	Day	8% 3 20% 38% 25% 6%	676
	11th to 20th	Day	8% 3 18% 42% 25% 3	665
	21st to end	Day	11% 3 18% 37% 25% 6%	734
September	1st to 10th	Day	13% 3 24% 36% 19% 4	360
	11th to 20th	Day	10% 2 25% 38% 20% 5%	300
	21st to end	Day	15% 5% 32% 31% 13% 4	300
October	1st to 10th	Day	20% 5% 26% 28% 16% 5%	300
	11th to 20th	Day	11% 13% 42% 23% 10% 1	300
	21st to end	Day	20% 12% 39% 19% 9% 2	330
November	1st to 10th	Day	18% 10% 37% 24% 8% 3	273
	11th to 20th	Day	13% 11% 47% 21% 7% 1	270
	21st to end	Day	21% 11% 31% 26% 9% 1	270
December	1st to 10th	Day	10% 11% 42% 28% 7% 1	270
	11th to 20th	Day	16% 9% 40% 26% 8%	270
	21st to end	Day	21% 14% 41% 21% 3	297
January	1st to 10th	Night	11% 12% 36% 32% 8% 1	950
	11th to 20th	Night	15% 12% 35% 31% 7% 1	950
	21st to end	Night	15% 9% 40% 30% 5% 1	1045
February	1st to 10th	Night	16% 10% 41% 29% 5%	950
	11th to 20th	Night	12% 10% 41% 33% 4	866
	21st to end	Night	14% 14% 41% 26% 5%	628
March	1st to 10th	Night	15% 13% 38% 27% 7%	632
	11th to 20th	Night	21% 8% 38% 27% 6% 1	570
	21st to end	Night	22% 10% 35% 28% 5%	627
April	1st to 10th	Night	16% 13% 40% 25% 6%	570
	11th to 20th	Night	15% 15% 38% 27% 4	563
	21st to end	Night	20% 9% 33% 30% 8% 1	570
May	1st to 10th	Night	17% 8% 34% 30% 10%	570
	11th to 20th	Night	14% 9% 32% 33% 12% 1	561
	21st to end	Night	17% 5% 30% 34% 13% 1	617
June	1st to 10th	Night	7% 4 24% 47% 17% 1	570
	11th to 20th	Night	7% 5% 30% 44% 13% 1	570
	21st to end	Night	4 4 32% 43% 16% 1	570
July	1st to 10th	Night	7% 2 17% 43% 30% 1	555
	11th to 20th	Night	4 1 15% 52% 26% 1	552
	21st to end	Night	4 1 15% 51% 28% 1	624
August	1st to 10th	Night	7% 2 16% 49% 24% 2	567
	11th to 20th	Night	7% 2 17% 50% 23% 1	564
	21st to end	Night	9% 1 20% 42% 25% 3	627
September	1st to 10th	Night	9% 1 27% 39% 23% 1	570
	11th to 20th	Night	10% 2 29% 40% 18% 1	570
	21st to end	Night	12% 5% 30% 36% 18% 1	570
October	1st to 10th	Night	16% 7% 29% 33% 14% 2	661
	11th to 20th	Night	13% 10% 37% 31% 9%	760
	21st to end	Night	18% 10% 30% 32% 10%	849
November	1st to 10th	Night	10% 10% 34% 36% 10% 1	931
	11th to 20th	Night	13% 10% 39% 30% 7%	950
	21st to end	Night	15% 10% 35% 31% 9% 1	950
December	1st to 10th	Night	13% 10% 40% 30% 6% 1	950
	11th to 20th	Night	15% 11% 34% 34% 6%	950
	21st to end	Night	18% 12% 33% 32% 5%	1045

Page generated at 2024-10-30 00:23:00. Version ac07

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