Black Bear Hollow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Bear Hollow 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	15% 9% 4 7% 6% 4 5% 5% 5% 7% 34%	78566
	Night	15% 9% 4 6% 6% 3 5% 5% 5% 7% 36%	80954
Transparency	Day	48% 8% 12% 19% 11% 2	78277
	Night	46% 8% 13% 21% 12% 2	80763
Seeing	Day	23% 16% 26% 20% 11% 4	13844
	Night	20% 14% 26% 28% 11% 1	23532

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	15% 14% 6% 10% 7% 3 4 5% 4 5% 28%	2613
	11th to 20th	Day	12% 18% 9% 12% 10% 3 5% 4 4 4 21%	2840
	21st to end	Day	19% 15% 9% 9% 6% 3 5% 4 4 5% 20%	3124
February	1st to 10th	Day	15% 14% 5% 9% 7% 3 6% 4 5% 5% 28%	1710
	11th to 20th	Day	14% 9% 7% 12% 7% 4 4 4 5% 6% 28%	1663
	21st to end	Day	17% 12% 4 9% 5% 3 4 5% 5% 5% 32%	1558
March	1st to 10th	Day	14% 10% 3 7% 6% 3 5% 4 5% 5% 37%	2035
	11th to 20th	Day	18% 10% 4 7% 6% 4 6% 4 4 7% 31%	1980
	21st to end	Day	20% 10% 4 6% 6% 3 3 4 5% 6% 32%	2178
April	1st to 10th	Day	15% 10% 5% 7% 6% 4 5% 5% 5% 7% 33%	2153
	11th to 20th	Day	15% 11% 3 6% 6% 3 4 5% 5% 6% 37%	2134
	21st to end	Day	21% 8% 3 6% 5% 3 4 5% 4 5% 35%	2234
May	1st to 10th	Day	19% 8% 3 6% 6% 4 6% 5% 5% 8% 31%	2340
	11th to 20th	Day	22% 7% 4 5% 5% 4 4 5% 5% 7% 34%	2387
	21st to end	Day	15% 7% 3 5% 5% 4 5% 6% 5% 8% 37%	2725
June	1st to 10th	Day	14% 5% 3 5% 6% 4 6% 6% 7% 8% 35%	2520
	11th to 20th	Day	13% 6% 4 7% 6% 4 5% 5% 7% 9% 34%	2520
	21st to end	Day	12% 4 2 5% 6% 4 5% 6% 6% 10% 38%	2520
July	1st to 10th	Day	10% 5% 3 6% 7% 4 6% 6% 6% 8% 39%	2520
	11th to 20th	Day	7% 5% 3 6% 6% 4 5% 6% 8% 10% 40%	2427
	21st to end	Day	10% 7% 3 7% 6% 5% 6% 6% 7% 8% 35%	2547
August	1st to 10th	Day	10% 5% 3 6% 7% 5% 7% 6% 8% 10% 33%	2327
	11th to 20th	Day	12% 7% 2 5% 7% 5% 6% 5% 7% 10% 34%	2288
	21st to end	Day	14% 5% 2 5% 5% 4 5% 6% 7% 8% 38%	2376
September	1st to 10th	Day	18% 5% 3 4 5% 3 4 5% 5% 7% 41%	2160
	11th to 20th	Day	15% 5% 2 4 5% 3 4 4 5% 7% 46%	2120
	21st to end	Day	18% 7% 3 5% 5% 3 5% 5% 5% 8% 37%	1901
October	1st to 10th	Day	18% 6% 2 5% 5% 3 5% 4 5% 6% 40%	1800
	11th to 20th	Day	19% 7% 3 6% 5% 3 5% 5% 4 6% 38%	1800
	21st to end	Day	18% 8% 3 6% 5% 3 4 3 5% 7% 37%	1980
November	1st to 10th	Day	11% 7% 3 6% 6% 3 4 3 6% 6% 45%	1791
	11th to 20th	Day	16% 9% 5% 6% 5% 3 5% 4 5% 7% 36%	1573
	21st to end	Day	16% 11% 4 6% 6% 3 5% 5% 5% 7% 32%	1520
December	1st to 10th	Day	18% 12% 5% 9% 7% 4 4 5% 6% 7% 24%	1520
	11th to 20th	Day	16% 13% 5% 8% 6% 3 4 5% 4 6% 30%	1910
	21st to end	Day	20% 13% 6% 8% 7% 5% 6% 5% 5% 5% 20%	2772
January	1st to 10th	Night	13% 13% 6% 9% 7% 4 5% 5% 5% 6% 27%	4329
	11th to 20th	Night	15% 14% 6% 11% 8% 4 4 4 4 5% 26%	4120
	21st to end	Night	21% 14% 7% 7% 9% 3 4 4 3 5% 23%	4532
February	1st to 10th	Night	14% 11% 5% 7% 6% 4 5% 5% 6% 6% 31%	2470
	11th to 20th	Night	15% 10% 4 9% 5% 5% 6% 5% 6% 6% 30%	2403
	21st to end	Night	16% 10% 4 9% 6% 3 5% 5% 5% 7% 31%	1892
March	1st to 10th	Night	13% 8% 3 6% 5% 3 5% 5% 5% 7% 40%	2042
	11th to 20th	Night	18% 8% 5% 6% 5% 3 3 4 5% 6% 38%	1980
	21st to end	Night	16% 9% 4 6% 6% 3 4 4 5% 6% 37%	2178
April	1st to 10th	Night	16% 11% 5% 8% 5% 3 5% 4 5% 6% 33%	1806
	11th to 20th	Night	12% 8% 2 6% 5% 3 5% 5% 5% 9% 40%	1775
	21st to end	Night	19% 5% 2 4 5% 3 5% 4 5% 8% 40%	1742
May	1st to 10th	Night	19% 8% 4 6% 6% 3 4 4 4 8% 34%	1620
	11th to 20th	Night	19% 8% 2 5% 6% 3 5% 5% 5% 6% 36%	1505
	21st to end	Night	12% 6% 2 5% 5% 3 5% 4 7% 9% 43%	1550
June	1st to 10th	Night	11% 6% 3 5% 4 3 5% 4 5% 8% 46%	1440
	11th to 20th	Night	12% 6% 2 5% 6% 4 5% 5% 7% 8% 39%	1440
	21st to end	Night	10% 4 1 4 5% 3 5% 5% 7% 11% 45%	1440
July	1st to 10th	Night	10% 6% 3 4 5% 3 5% 5% 8% 8% 44%	1440
	11th to 20th	Night	7% 3 2 4 4 3 4 6% 6% 9% 51%	1529
	21st to end	Night	9% 4 3 6% 5% 3 5% 5% 7% 9% 42%	1771
August	1st to 10th	Night	7% 5% 3 6% 6% 3 4 6% 6% 10% 45%	1611
	11th to 20th	Night	10% 6% 3 5% 5% 3 4 4 5% 7% 47%	1598
	21st to end	Night	12% 6% 2 5% 4 3 5% 4 5% 9% 45%	1975
September	1st to 10th	Night	16% 5% 2 5% 4 3 4 4 5% 7% 45%	1800
	11th to 20th	Night	12% 6% 2 4 4 3 4 4 4 7% 51%	1836
	21st to end	Night	16% 7% 2 5% 5% 3 3 5% 5% 7% 43%	2058
October	1st to 10th	Night	16% 7% 2 5% 5% 3 4 4 5% 6% 43%	2160
	11th to 20th	Night	16% 6% 2 5% 4 3 4 4 5% 8% 42%	2160
	21st to end	Night	19% 7% 2 5% 4 2 4 5% 5% 7% 39%	2376
November	1st to 10th	Night	10% 8% 3 5% 5% 2 4 4 4 6% 49%	2284
	11th to 20th	Night	15% 9% 3 6% 5% 3 5% 5% 4 7% 37%	2603
	21st to end	Night	15% 8% 4 6% 6% 4 6% 5% 5% 6% 35%	2660
December	1st to 10th	Night	17% 12% 4 7% 8% 3 5% 5% 6% 8% 26%	2660
	11th to 20th	Night	17% 9% 4 7% 7% 3 6% 5% 5% 5% 31%	3285
	21st to end	Night	18% 13% 5% 7% 7% 4 6% 5% 6% 7% 22%	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	55% 8% 11% 19% 5% 2	2614
	11th to 20th	Day	64% 8% 9% 10% 9% 1	2840
	21st to end	Day	65% 6% 10% 14% 4 1	3124
February	1st to 10th	Day	57% 6% 13% 17% 7% 1	1710
	11th to 20th	Day	55% 6% 11% 19% 8% 1	1672
	21st to end	Day	53% 7% 12% 17% 8% 3	1558
March	1st to 10th	Day	47% 7% 13% 21% 11% 1	2035
	11th to 20th	Day	52% 6% 11% 17% 10% 3	1980
	21st to end	Day	53% 6% 9% 20% 11% 2	2178
April	1st to 10th	Day	49% 6% 12% 18% 12% 2	2153
	11th to 20th	Day	46% 7% 10% 18% 16% 3	2134
	21st to end	Day	50% 6% 9% 20% 12% 3	2234
May	1st to 10th	Day	50% 9% 10% 18% 12% 1	2340
	11th to 20th	Day	50% 7% 12% 16% 12% 3	2391
	21st to end	Day	43% 9% 16% 19% 11% 2	2725
June	1st to 10th	Day	43% 9% 13% 21% 14% 1	2520
	11th to 20th	Day	44% 10% 14% 18% 13% 1	2520
	21st to end	Day	38% 9% 14% 25% 12% 1	2520
July	1st to 10th	Day	41% 10% 13% 20% 14% 3	2450
	11th to 20th	Day	35% 9% 15% 22% 17% 1	2353
	21st to end	Day	41% 10% 12% 20% 14% 2	2405
August	1st to 10th	Day	42% 11% 16% 20% 10%	2314
	11th to 20th	Day	43% 9% 12% 23% 12% 1	2288
	21st to end	Day	40% 8% 14% 22% 12% 3	2376
September	1st to 10th	Day	42% 8% 11% 21% 16% 3	2160
	11th to 20th	Day	37% 6% 11% 26% 18% 3	2120
	21st to end	Day	45% 6% 13% 17% 17% 2	1901
October	1st to 10th	Day	45% 7% 12% 21% 14% 2	1800
	11th to 20th	Day	45% 7% 12% 23% 12%	1800
	21st to end	Day	45% 6% 13% 21% 14% 1	1980
November	1st to 10th	Day	38% 6% 14% 21% 16% 4	1791
	11th to 20th	Day	46% 6% 12% 22% 11% 3	1573
	21st to end	Day	50% 7% 13% 22% 8% 1	1520
December	1st to 10th	Day	57% 8% 14% 14% 5%	1520
	11th to 20th	Day	54% 6% 12% 22% 5%	1906
	21st to end	Day	62% 9% 11% 12% 5%	2772
January	1st to 10th	Night	54% 8% 12% 18% 8% 1	4329
	11th to 20th	Night	56% 9% 13% 14% 7% 1	4120
	21st to end	Night	62% 7% 9% 17% 5% 1	4532
February	1st to 10th	Night	51% 7% 12% 21% 8% 1	2470
	11th to 20th	Night	52% 6% 10% 18% 12% 1	2405
	21st to end	Night	51% 7% 11% 18% 10% 2	1892
March	1st to 10th	Night	41% 6% 13% 25% 13% 1	2042
	11th to 20th	Night	45% 7% 13% 20% 14% 2	1980
	21st to end	Night	47% 6% 12% 18% 14% 3	2178
April	1st to 10th	Night	51% 7% 11% 17% 13% 1	1806
	11th to 20th	Night	40% 7% 12% 21% 16% 3	1775
	21st to end	Night	42% 8% 11% 23% 13% 4	1742
May	1st to 10th	Night	48% 8% 8% 20% 12% 4	1620
	11th to 20th	Night	46% 8% 11% 18% 14% 2	1506
	21st to end	Night	36% 10% 16% 26% 12% 2	1551
June	1st to 10th	Night	36% 8% 12% 28% 14% 2	1440
	11th to 20th	Night	40% 10% 13% 24% 12% 2	1440
	21st to end	Night	31% 10% 17% 26% 15% 1	1440
July	1st to 10th	Night	34% 12% 14% 23% 14% 3	1400
	11th to 20th	Night	28% 11% 15% 26% 18% 2	1481
	21st to end	Night	33% 11% 18% 21% 15% 2	1672
August	1st to 10th	Night	32% 11% 18% 25% 13% 1	1600
	11th to 20th	Night	35% 8% 16% 24% 16% 2	1598
	21st to end	Night	35% 7% 15% 25% 15% 3	1975
September	1st to 10th	Night	39% 7% 12% 22% 17% 4	1800
	11th to 20th	Night	32% 7% 11% 29% 20% 2	1836
	21st to end	Night	39% 6% 12% 24% 17% 2	2058
October	1st to 10th	Night	41% 7% 13% 23% 14% 1	2160
	11th to 20th	Night	39% 7% 12% 26% 14% 1	2160
	21st to end	Night	43% 7% 10% 25% 14% 1	2376
November	1st to 10th	Night	36% 5% 13% 24% 18% 4	2284
	11th to 20th	Night	45% 7% 11% 21% 14% 3	2603
	21st to end	Night	47% 7% 13% 22% 10% 1	2660
December	1st to 10th	Night	54% 7% 15% 16% 7%	2660
	11th to 20th	Night	51% 7% 12% 21% 9% 1	3288
	21st to end	Night	57% 10% 15% 14% 4	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	36% 25% 25% 11% 2	207
	11th to 20th	Day	34% 27% 28% 9% 1	270
	21st to end	Day	28% 31% 29% 8% 3	297
February	1st to 10th	Day	33% 27% 29% 10% 1	270
	11th to 20th	Day	40% 28% 29% 3	270
	21st to end	Day	36% 25% 25% 12% 2	354
March	1st to 10th	Day	30% 23% 26% 18% 3	440
	11th to 20th	Day	31% 25% 25% 15% 4 1	420
	21st to end	Day	32% 21% 27% 13% 5% 2	462
April	1st to 10th	Day	29% 25% 25% 15% 5% 1	420
	11th to 20th	Day	23% 22% 26% 16% 9% 4	412
	21st to end	Day	34% 18% 27% 11% 8% 1	420
May	1st to 10th	Day	28% 19% 27% 13% 9% 4	423
	11th to 20th	Day	26% 17% 28% 17% 9% 3	447
	21st to end	Day	19% 14% 26% 21% 14% 7%	485
June	1st to 10th	Day	19% 16% 27% 21% 14% 2	450
	11th to 20th	Day	19% 12% 31% 23% 12% 3	450
	21st to end	Day	13% 13% 30% 26% 15% 3	450
July	1st to 10th	Day	12% 7% 22% 30% 21% 9%	445
	11th to 20th	Day	7% 7% 29% 31% 19% 8%	444
	21st to end	Day	15% 8% 26% 30% 15% 6%	488
August	1st to 10th	Day	11% 7% 23% 28% 22% 9%	446
	11th to 20th	Day	15% 5% 25% 25% 19% 10%	439
	21st to end	Day	14% 7% 23% 29% 16% 11%	495
September	1st to 10th	Day	20% 8% 19% 25% 18% 10%	450
	11th to 20th	Day	17% 5% 21% 29% 20% 8%	450
	21st to end	Day	25% 13% 23% 20% 13% 6%	450
October	1st to 10th	Day	23% 10% 21% 26% 17% 3	450
	11th to 20th	Day	23% 17% 26% 22% 12% 1	450
	21st to end	Day	23% 18% 32% 19% 7% 1	495
November	1st to 10th	Day	18% 15% 32% 21% 11% 2	424
	11th to 20th	Day	26% 23% 28% 15% 6% 1	233
	21st to end	Day	27% 23% 35% 12% 3 1	180
December	1st to 10th	Day	32% 28% 26% 10% 4 1	180
	11th to 20th	Day	30% 26% 28% 15% 2	180
	21st to end	Day	28% 24% 26% 18% 3	198
January	1st to 10th	Night	22% 23% 34% 18% 3	760
	11th to 20th	Night	27% 19% 30% 21% 3	760
	21st to end	Night	22% 23% 32% 20% 2	836
February	1st to 10th	Night	24% 19% 30% 24% 3	760
	11th to 20th	Night	25% 28% 30% 17% 1	743
	21st to end	Night	27% 21% 32% 19% 2	628
March	1st to 10th	Night	23% 20% 34% 21% 3	743
	11th to 20th	Night	27% 20% 27% 21% 5% 1	720
	21st to end	Night	22% 18% 34% 21% 5% 1	792
April	1st to 10th	Night	25% 22% 29% 21% 4	720
	11th to 20th	Night	18% 17% 30% 27% 9%	711
	21st to end	Night	23% 15% 26% 29% 8%	662
May	1st to 10th	Night	22% 10% 24% 30% 14%	540
	11th to 20th	Night	22% 9% 26% 31% 11%	444
	21st to end	Night	16% 6% 21% 36% 18% 2	389
June	1st to 10th	Night	14% 5% 25% 36% 19% 1	360
	11th to 20th	Night	14% 6% 22% 38% 19% 1	360
	21st to end	Night	9% 4 24% 47% 16%	360
July	1st to 10th	Night	11% 4 17% 40% 24% 3	350
	11th to 20th	Night	8% 2 17% 39% 31% 3	437
	21st to end	Night	9% 2 19% 42% 26% 2	591
August	1st to 10th	Night	9% 2 16% 44% 28% 2	537
	11th to 20th	Night	12% 3 14% 41% 26% 5%	534
	21st to end	Night	14% 4 16% 36% 27% 4	787
September	1st to 10th	Night	17% 3 17% 35% 23% 4	720
	11th to 20th	Night	13% 6% 18% 30% 28% 5%	720
	21st to end	Night	19% 7% 24% 26% 22% 3	720
October	1st to 10th	Night	18% 8% 20% 31% 20% 2	720
	11th to 20th	Night	19% 14% 27% 29% 10% 1	720
	21st to end	Night	24% 13% 27% 27% 8%	792
November	1st to 10th	Night	15% 12% 29% 33% 10% 1	740
	11th to 20th	Night	22% 19% 26% 25% 7% 1	760
	21st to end	Night	22% 20% 27% 25% 6%	760
December	1st to 10th	Night	27% 19% 27% 21% 5%	760
	11th to 20th	Night	22% 18% 31% 26% 3	760
	21st to end	Night	23% 20% 28% 28% 2	836

Page generated at 2024-03-03 06:28:53. Version ac07

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