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 2024-03-06.

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 6% 5% 3 5% 4 5% 7% 44%	78621
	Night	10% 6% 3 6% 5% 3 4 4 5% 7% 48%	80939
Transparency	Day	40% 3 13% 27% 15% 2	78344
	Night	37% 3 12% 28% 18% 3	80736
Seeing	Day	14% 8% 30% 30% 15% 3	14769
	Night	13% 8% 32% 34% 11% 1	24873

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% 11% 5% 10% 9% 5% 5% 5% 5% 6% 29%	2847
	11th to 20th	Day	9% 10% 4 8% 6% 3 8% 5% 5% 6% 37%	2850
	21st to end	Day	8% 12% 5% 11% 7% 3 5% 4 4 5% 37%	3135
February	1st to 10th	Day	10% 10% 5% 7% 7% 3 4 5% 6% 8% 35%	1710
	11th to 20th	Day	8% 9% 3 8% 5% 3 4 5% 5% 8% 42%	1744
	21st to end	Day	9% 7% 4 5% 5% 3 4 5% 5% 7% 47%	1570
March	1st to 10th	Day	9% 8% 4 7% 5% 2 4 3 4 7% 47%	1972
	11th to 20th	Day	15% 8% 3 5% 5% 3 4 4 4 6% 43%	1980
	21st to end	Day	17% 12% 4 6% 5% 3 4 5% 5% 6% 33%	2178
April	1st to 10th	Day	14% 7% 3 5% 5% 2 5% 4 5% 6% 45%	1998
	11th to 20th	Day	15% 7% 3 6% 5% 3 4 4 4 7% 40%	2280
	21st to end	Day	19% 7% 2 6% 5% 3 4 4 5% 8% 38%	2340
May	1st to 10th	Day	16% 6% 4 6% 5% 3 5% 5% 5% 7% 38%	2340
	11th to 20th	Day	14% 6% 3 6% 5% 3 5% 4 5% 8% 41%	2302
	21st to end	Day	15% 7% 3 5% 6% 3 6% 5% 6% 8% 35%	2531
June	1st to 10th	Day	6% 4 2 4 5% 3 5% 5% 5% 10% 51%	2452
	11th to 20th	Day	9% 5% 2 4 4 3 4 5% 6% 9% 47%	2520
	21st to end	Day	6% 4 2 5% 5% 3 6% 6% 6% 9% 48%	2402
July	1st to 10th	Day	9% 3 2 3 4 3 5% 5% 6% 10% 50%	2340
	11th to 20th	Day	5% 4 2 3 5% 3 4 4 6% 8% 56%	2340
	21st to end	Day	5% 4 2 5% 5% 3 5% 6% 7% 11% 48%	2546
August	1st to 10th	Day	8% 5% 2 5% 5% 4 6% 6% 7% 10% 42%	2328
	11th to 20th	Day	7% 3 2 5% 5% 3 4 4 7% 9% 51%	2301
	21st to end	Day	9% 4 2 5% 5% 3 3 4 5% 7% 53%	2561
September	1st to 10th	Day	13% 4 2 4 4 2 3 4 4 6% 53%	2037
	11th to 20th	Day	10% 5% 2 4 3 3 4 4 5% 7% 53%	1980
	21st to end	Day	10% 4 2 4 3 2 3 3 4 6% 58%	1980
October	1st to 10th	Day	13% 6% 2 5% 4 2 4 3 4 5% 51%	1874
	11th to 20th	Day	11% 4 3 5% 4 2 3 3 4 4 57%	1800
	21st to end	Day	13% 7% 2 6% 5% 2 3 3 4 6% 49%	1966
November	1st to 10th	Day	8% 5% 2 5% 3 2 3 3 5% 7% 56%	1673
	11th to 20th	Day	9% 5% 2 6% 5% 3 4 4 4 7% 51%	1710
	21st to end	Day	13% 7% 3 5% 4 2 4 4 5% 8% 46%	1554
December	1st to 10th	Day	8% 8% 2 4 6% 3 4 4 6% 8% 47%	1520
	11th to 20th	Day	8% 7% 3 7% 6% 3 4 5% 5% 9% 41%	1918
	21st to end	Day	15% 10% 4 12% 7% 4 5% 5% 5% 6% 29%	3042
January	1st to 10th	Night	7% 10% 4 13% 8% 4 5% 4 6% 6% 33%	4108
	11th to 20th	Night	8% 9% 3 5% 5% 3 8% 5% 5% 6% 42%	4120
	21st to end	Night	11% 11% 6% 10% 5% 2 3 3 4 6% 39%	4532
February	1st to 10th	Night	11% 9% 4 7% 6% 3 5% 5% 5% 5% 40%	2470
	11th to 20th	Night	9% 6% 4 6% 6% 4 5% 5% 5% 7% 44%	2340
	21st to end	Night	8% 7% 3 5% 5% 2 4 4 4 6% 51%	1884
March	1st to 10th	Night	10% 7% 3 5% 4 2 4 4 4 6% 51%	2103
	11th to 20th	Night	16% 8% 3 5% 4 2 3 2 4 5% 47%	1980
	21st to end	Night	17% 9% 4 6% 6% 3 5% 4 6% 7% 33%	2178
April	1st to 10th	Night	12% 6% 2 5% 5% 2 4 4 5% 7% 48%	1961
	11th to 20th	Night	11% 7% 3 5% 5% 2 4 4 5% 7% 46%	1627
	21st to end	Night	15% 6% 3 4 5% 3 4 3 5% 7% 46%	1620
May	1st to 10th	Night	15% 6% 2 6% 5% 3 4 4 6% 8% 40%	1620
	11th to 20th	Night	12% 6% 2 5% 4 3 4 4 6% 8% 46%	1593
	21st to end	Night	12% 8% 2 6% 4 3 4 4 6% 9% 42%	1745
June	1st to 10th	Night	6% 3 1 4 5% 2 4 5% 7% 10% 55%	1504
	11th to 20th	Night	6% 3 2 4 5% 3 4 5% 5% 11% 52%	1440
	21st to end	Night	3 3 2 3 3 3 4 5% 6% 8% 60%	1549
July	1st to 10th	Night	6% 4 2 5% 5% 3 3 4 5% 9% 55%	1620
	11th to 20th	Night	3 2 1 3 4 3 4 5% 6% 8% 60%	1620
	21st to end	Night	3 2 1 2 4 3 5% 6% 5% 11% 57%	1772
August	1st to 10th	Night	5% 3 1 4 5% 3 4 5% 7% 9% 53%	1611
	11th to 20th	Night	5% 3 2 3 4 3 4 3 6% 9% 58%	1600
	21st to end	Night	6% 4 2 3 5% 2 4 4 4 7% 59%	1794
September	1st to 10th	Night	9% 4 1 4 3 2 3 3 4 7% 60%	1919
	11th to 20th	Night	9% 3 1 4 3 2 3 4 5% 7% 59%	1980
	21st to end	Night	8% 4 2 3 3 2 4 4 4 5% 60%	1980
October	1st to 10th	Night	13% 5% 2 4 4 2 5% 4 5% 6% 51%	2066
	11th to 20th	Night	12% 5% 2 5% 3 2 2 3 3 5% 58%	2160
	21st to end	Night	13% 5% 2 4 3 2 3 4 4 5% 55%	2388
November	1st to 10th	Night	6% 3 2 3 4 2 4 4 4 8% 59%	2405
	11th to 20th	Night	9% 5% 3 5% 4 2 4 4 4 7% 54%	2470
	21st to end	Night	11% 5% 3 4 3 2 4 3 5% 6% 54%	2622
December	1st to 10th	Night	7% 7% 3 5% 5% 3 5% 4 5% 7% 49%	2660
	11th to 20th	Night	9% 6% 3 6% 4 2 3 3 4 7% 52%	3279
	21st to end	Night	17% 11% 4 10% 5% 2 3 3 4 5% 35%	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	39% 2 12% 28% 15% 2	1972
	11th to 20th	Day	45% 3 10% 25% 15% 2	1980
	21st to end	Day	53% 3 15% 21% 7% 1	2178
April	1st to 10th	Day	41% 2 14% 26% 16% 2	1998
	11th to 20th	Day	45% 3 12% 24% 14% 3	2280
	21st to end	Day	46% 3 10% 28% 13%	2340
May	1st to 10th	Day	46% 4 13% 22% 14% 1	2340
	11th to 20th	Day	42% 3 15% 26% 13%	2306
	21st to end	Day	46% 4 16% 21% 11% 1	2531
June	1st to 10th	Day	29% 4 17% 34% 14% 2	2452
	11th to 20th	Day	33% 4 13% 32% 16% 2	2520
	21st to end	Day	32% 5% 15% 30% 14% 4	2402
July	1st to 10th	Day	30% 3 15% 32% 17% 2	2276
	11th to 20th	Day	27% 4 13% 31% 21% 5%	2271
	21st to end	Day	29% 4 16% 33% 17% 1	2405
August	1st to 10th	Day	36% 6% 20% 28% 9% 2	2314
	11th to 20th	Day	29% 4 14% 33% 19% 1	2301
	21st to end	Day	30% 4 11% 27% 22% 6%	2561
September	1st to 10th	Day	33% 3 9% 31% 19% 6%	2037
	11th to 20th	Day	32% 3 11% 32% 21% 2	1980
	21st to end	Day	29% 2 9% 33% 26% 1	1980
October	1st to 10th	Day	37% 3 9% 27% 23% 1	1874
	11th to 20th	Day	32% 2 8% 29% 23% 7%	1800
	21st to end	Day	38% 2 12% 23% 20% 4	1966
November	1st to 10th	Day	29% 2 14% 31% 22% 3	1673
	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	35% 3 10% 31% 17% 3	2103
	11th to 20th	Night	41% 3 9% 26% 18% 3	1980
	21st to end	Night	50% 3 15% 22% 10% 1	2178
April	1st to 10th	Night	37% 3 11% 28% 18% 3	1961
	11th to 20th	Night	38% 3 11% 28% 17% 3	1627
	21st to end	Night	39% 3 12% 25% 19% 1	1620
May	1st to 10th	Night	42% 3 15% 23% 15% 2	1620
	11th to 20th	Night	37% 4 15% 27% 17%	1594
	21st to end	Night	39% 4 20% 21% 14% 2	1746
June	1st to 10th	Night	25% 5% 17% 34% 17% 2	1504
	11th to 20th	Night	28% 4 14% 29% 20% 5%	1440
	21st to end	Night	22% 4 14% 35% 21% 4	1549
July	1st to 10th	Night	27% 4 14% 30% 19% 5%	1575
	11th to 20th	Night	21% 4 15% 32% 21% 6%	1566
	21st to end	Night	21% 4 17% 37% 19% 2	1673
August	1st to 10th	Night	27% 4 20% 32% 15% 2	1601
	11th to 20th	Night	25% 3 15% 34% 20% 3	1600
	21st to end	Night	27% 3 11% 28% 22% 9%	1794
September	1st to 10th	Night	25% 3 11% 30% 22% 8%	1919
	11th to 20th	Night	26% 2 11% 35% 21% 4	1980
	21st to end	Night	27% 2 6% 32% 28% 4	1980
October	1st to 10th	Night	34% 3 9% 27% 24% 2	2066
	11th to 20th	Night	31% 2 6% 26% 27% 7%	2160
	21st to end	Night	33% 2 11% 25% 26% 4	2388
November	1st to 10th	Night	26% 2 13% 28% 26% 5%	2405
	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	16% 12% 43% 23% 5% 1	255
	11th to 20th	Day	26% 8% 36% 20% 10%	240
	21st to end	Day	30% 12% 37% 16% 5%	264
April	1st to 10th	Day	21% 14% 41% 21% 3	258
	11th to 20th	Day	20% 15% 35% 22% 8%	558
	21st to end	Day	22% 14% 32% 21% 10% 2	600
May	1st to 10th	Day	19% 11% 33% 25% 10% 2	603
	11th to 20th	Day	19% 8% 32% 25% 13% 4	625
	21st to end	Day	20% 5% 27% 30% 15% 3	679
June	1st to 10th	Day	7% 5% 22% 37% 23% 6%	630
	11th to 20th	Day	9% 5% 30% 32% 19% 4	630
	21st to end	Day	8% 4 31% 36% 18% 3	630
July	1st to 10th	Day	9% 2 16% 36% 28% 8%	621
	11th to 20th	Day	6% 2 22% 38% 24% 8%	618
	21st to end	Day	7% 2 18% 41% 29% 4	684
August	1st to 10th	Day	8% 3 19% 39% 25% 6%	626
	11th to 20th	Day	7% 3 18% 41% 27% 3	615
	21st to end	Day	11% 3 18% 37% 26% 6%	680
September	1st to 10th	Day	15% 3 23% 36% 19% 4	327
	11th to 20th	Day	10% 1 25% 38% 20% 6%	270
	21st to end	Day	15% 5% 33% 31% 13% 3	270
October	1st to 10th	Day	22% 5% 26% 26% 14% 6%	270
	11th to 20th	Day	12% 13% 43% 20% 10% 1	270
	21st to end	Day	21% 12% 38% 18% 9% 2	297
November	1st to 10th	Day	18% 10% 36% 24% 9% 3	270
	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% 39% 26% 7%	619
	11th to 20th	Night	21% 7% 36% 28% 6% 1	540
	21st to end	Night	22% 10% 35% 28% 5%	594
April	1st to 10th	Night	16% 13% 40% 26% 6%	540
	11th to 20th	Night	16% 14% 37% 28% 5%	533
	21st to end	Night	19% 9% 33% 30% 8% 1	540
May	1st to 10th	Night	16% 9% 34% 30% 10%	540
	11th to 20th	Night	14% 10% 32% 32% 12% 1	531
	21st to end	Night	17% 6% 29% 33% 14% 1	584
June	1st to 10th	Night	7% 4 23% 48% 17% 1	540
	11th to 20th	Night	7% 5% 29% 45% 13% 1	540
	21st to end	Night	4 4 32% 42% 17% 1	540
July	1st to 10th	Night	7% 2 17% 44% 30% 1	525
	11th to 20th	Night	4 1 15% 52% 26% 1	522
	21st to end	Night	4 1 15% 53% 27% 1	591
August	1st to 10th	Night	7% 2 15% 49% 24% 2	537
	11th to 20th	Night	6% 2 17% 50% 24% 1	534
	21st to end	Night	8% 2 20% 42% 26% 3	594
September	1st to 10th	Night	9% 1 28% 39% 22% 1	540
	11th to 20th	Night	10% 2 29% 40% 18% 1	540
	21st to end	Night	11% 5% 31% 35% 17% 1	540
October	1st to 10th	Night	17% 6% 30% 33% 12% 2	626
	11th to 20th	Night	14% 10% 36% 30% 9%	720
	21st to end	Night	18% 10% 30% 32% 10%	804
November	1st to 10th	Night	10% 10% 34% 36% 10% 1	925
	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 2024-03-03 05:28:58. Version ac07

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