Bunch Hollow Conservation Area
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bunch Hollow Conservation Area clear sky chart from 2005-11-06 to 2025-12-03.

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	12% 8% 3 7% 4 4 4 3 5% 7% 44%	126980
	Night	12% 7% 3 7% 4 4 4 3 5% 7% 45%	123994
Transparency	Day	39% 5% 12% 25% 16% 2	130586
	Night	38% 5% 11% 25% 18% 3	128464
Seeing	Day	15% 10% 28% 28% 16% 4	17175
	Night	15% 9% 31% 32% 12% 1	27008

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	14% 12% 4 11% 4 5% 5% 2 5% 6% 33%	3916
	11th to 20th	Day	8% 9% 4 9% 6% 6% 7% 3 3 5% 40%	4080
	21st to end	Day	13% 15% 6% 10% 4 4 4 3 3 5% 34%	4488
February	1st to 10th	Day	14% 12% 3 7% 5% 4 4 3 6% 7% 34%	1800
	11th to 20th	Day	14% 11% 5% 6% 5% 3 3 3 5% 7% 39%	1754
	21st to end	Day	12% 10% 3 7% 4 3 3 3 5% 6% 44%	1667
March	1st to 10th	Day	14% 10% 3 5% 3 3 3 2 3 5% 49%	4936
	11th to 20th	Day	9% 6% 2 6% 4 3 4 3 5% 6% 51%	4980
	21st to end	Day	15% 12% 3 8% 5% 5% 4 4 6% 7% 31%	5462
April	1st to 10th	Day	15% 8% 3 7% 4 4 3 3 5% 6% 41%	2370
	11th to 20th	Day	14% 10% 2 7% 4 4 4 3 4 6% 41%	2374
	21st to end	Day	20% 8% 4 6% 5% 5% 4 4 5% 6% 34%	2471
May	1st to 10th	Day	13% 8% 2 6% 4 4 4 4 6% 8% 40%	5862
	11th to 20th	Day	16% 7% 2 6% 4 3 3 3 5% 7% 44%	5943
	21st to end	Day	17% 7% 2 6% 4 4 4 3 5% 6% 41%	6935
June	1st to 10th	Day	7% 5% 2 5% 5% 4 5% 5% 7% 8% 47%	2800
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 5% 6% 9% 45%	2800
	21st to end	Day	7% 5% 2 6% 5% 4 5% 4 6% 9% 48%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 9% 45%	6360
	11th to 20th	Day	9% 6% 2 6% 4 4 4 4 7% 9% 44%	5908
	21st to end	Day	8% 5% 2 6% 4 4 5% 5% 8% 10% 42%	6422
August	1st to 10th	Day	4 3 2 5% 4 4 5% 4 7% 10% 52%	4234
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 5% 7% 46%	4171
	21st to end	Day	5% 5% 2 5% 4 4 4 4 6% 8% 53%	4322
September	1st to 10th	Day	12% 4 1 5% 3 4 4 3 4 7% 54%	2400
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 6% 8% 50%	2320
	21st to end	Day	9% 4 1 5% 4 4 4 3 4 7% 54%	2130
October	1st to 10th	Day	13% 5% 2 5% 3 4 2 3 5% 7% 52%	2000
	11th to 20th	Day	12% 6% 2 5% 3 3 3 3 3 4 54%	2000
	21st to end	Day	16% 8% 2 6% 3 3 3 3 5% 6% 46%	2200
November	1st to 10th	Day	10% 7% 2 5% 3 3 3 3 4 6% 53%	2042
	11th to 20th	Day	14% 7% 2 7% 4 3 3 3 4 6% 48%	1737
	21st to end	Day	17% 11% 3 6% 3 3 4 3 5% 5% 42%	1680
December	1st to 10th	Day	7% 6% 3 7% 4 4 3 3 4 6% 54%	2626
	11th to 20th	Day	11% 8% 3 9% 4 3 4 3 4 5% 45%	3008
	21st to end	Day	19% 18% 9% 10% 5% 4 3 4 4 4 22%	3982
January	1st to 10th	Night	12% 11% 5% 15% 6% 5% 4 3 4 5% 31%	6044
	11th to 20th	Night	10% 9% 4 10% 6% 6% 5% 4 5% 5% 37%	5900
	21st to end	Night	14% 10% 5% 11% 5% 3 3 3 4 4 37%	6490
February	1st to 10th	Night	13% 10% 4 8% 5% 4 4 3 6% 6% 36%	2600
	11th to 20th	Night	13% 9% 3 8% 4 4 4 4 5% 7% 40%	2533
	21st to end	Night	13% 8% 3 6% 3 3 3 3 4 6% 47%	1978
March	1st to 10th	Night	16% 10% 3 5% 3 3 3 2 3 5% 47%	4919
	11th to 20th	Night	9% 7% 2 5% 3 2 3 3 5% 7% 54%	4980
	21st to end	Night	15% 10% 4 9% 5% 4 4 4 6% 7% 33%	5467
April	1st to 10th	Night	11% 7% 2 5% 3 4 4 3 4 7% 48%	2028
	11th to 20th	Night	13% 7% 3 7% 4 5% 3 3 4 7% 45%	1975
	21st to end	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	1925
May	1st to 10th	Night	14% 7% 3 6% 4 4 4 4 6% 8% 41%	4053
	11th to 20th	Night	14% 6% 2 5% 3 4 4 3 5% 9% 47%	3972
	21st to end	Night	15% 6% 2 6% 4 4 4 3 4 6% 46%	3942
June	1st to 10th	Night	6% 3 2 4 4 3 5% 5% 7% 10% 53%	1600
	11th to 20th	Night	6% 3 2 6% 4 4 5% 5% 6% 10% 50%	1600
	21st to end	Night	5% 4 2 5% 3 3 4 4 5% 9% 57%	1600
July	1st to 10th	Night	10% 6% 2 4 3 3 3 3 6% 10% 49%	3618
	11th to 20th	Night	6% 4 2 5% 4 4 5% 4 6% 9% 50%	4065
	21st to end	Night	8% 4 2 6% 5% 4 5% 4 7% 10% 46%	4449
August	1st to 10th	Night	3 2 2 3 3 3 4 4 7% 11% 58%	2926
	11th to 20th	Night	11% 6% 2 5% 3 3 3 3 3 8% 53%	2888
	21st to end	Night	4 3 1 5% 3 3 4 4 5% 8% 59%	3576
September	1st to 10th	Night	10% 4 2 4 2 2 4 3 4 5% 57%	2000
	11th to 20th	Night	10% 5% 1 4 2 3 4 4 7% 8% 53%	2076
	21st to end	Night	7% 4 2 5% 4 3 3 3 4 6% 57%	2250
October	1st to 10th	Night	11% 4 2 5% 3 2 3 2 4 6% 58%	2400
	11th to 20th	Night	14% 4 2 5% 3 3 3 2 4 4 54%	2400
	21st to end	Night	17% 7% 2 5% 3 2 2 2 3 5% 50%	2640
November	1st to 10th	Night	11% 4 2 4 2 3 3 3 5% 6% 58%	2475
	11th to 20th	Night	12% 6% 3 5% 4 3 3 3 4 6% 51%	2881
	21st to end	Night	17% 8% 2 6% 4 3 3 2 4 5% 46%	2940
December	1st to 10th	Night	8% 7% 2 6% 4 4 4 3 5% 6% 52%	4609
	11th to 20th	Night	12% 8% 3 8% 4 4 4 4 5% 7% 43%	5199
	21st to end	Night	22% 16% 5% 9% 4 4 3 2 3 4 27%	6996

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	51% 5% 12% 21% 10% 1	3917
	11th to 20th	Day	48% 4 11% 19% 14% 4	4080
	21st to end	Day	55% 4 9% 15% 14% 2	4488
February	1st to 10th	Day	49% 5% 14% 20% 10% 2	1800
	11th to 20th	Day	46% 4 13% 21% 14% 2	1763
	21st to end	Day	42% 4 11% 24% 17% 2	1667
March	1st to 10th	Day	40% 3 8% 25% 22% 3	4936
	11th to 20th	Day	33% 5% 8% 25% 24% 5%	4980
	21st to end	Day	50% 7% 16% 22% 5% 1	5464
April	1st to 10th	Day	44% 4 12% 25% 14% 2	2370
	11th to 20th	Day	45% 4 12% 24% 14% 1	2374
	21st to end	Day	51% 5% 11% 21% 11% 1	2471
May	1st to 10th	Day	41% 7% 14% 24% 14% 1	5900
	11th to 20th	Day	40% 6% 13% 25% 15% 2	5947
	21st to end	Day	43% 5% 10% 25% 16% 1	6949
June	1st to 10th	Day	31% 9% 15% 29% 14% 2	2800
	11th to 20th	Day	33% 8% 14% 27% 17% 2	2800
	21st to end	Day	31% 7% 17% 27% 15% 3	2800
July	1st to 10th	Day	36% 6% 12% 29% 16% 2	6291
	11th to 20th	Day	36% 6% 15% 28% 15% 1	5838
	21st to end	Day	34% 8% 15% 32% 10% 1	6240
August	1st to 10th	Day	27% 7% 16% 31% 18% 1	4220
	11th to 20th	Day	36% 6% 13% 28% 17% 1	4210
	21st to end	Day	28% 6% 16% 31% 13% 6%	4321
September	1st to 10th	Day	30% 6% 13% 26% 20% 6%	2400
	11th to 20th	Day	31% 6% 12% 28% 20% 3	2320
	21st to end	Day	31% 4 9% 30% 22% 3	2130
October	1st to 10th	Day	20% 3 7% 21% 40% 9%	3260
	11th to 20th	Day	23% 3 5% 22% 39% 8%	3240
	21st to end	Day	36% 4 8% 25% 25% 2	3538
November	1st to 10th	Day	33% 4 14% 27% 19% 4	2042
	11th to 20th	Day	38% 3 10% 28% 19% 2	1737
	21st to end	Day	45% 4 10% 28% 14%	1680
December	1st to 10th	Day	32% 4 16% 31% 17%	2626
	11th to 20th	Day	42% 4 15% 29% 9% 1	3005
	21st to end	Day	66% 4 12% 12% 5% 1	3982
January	1st to 10th	Night	55% 5% 10% 21% 9% 1	6044
	11th to 20th	Night	48% 4 11% 20% 14% 3	5900
	21st to end	Night	52% 4 10% 17% 16% 3	6490
February	1st to 10th	Night	48% 5% 12% 20% 13% 3	2600
	11th to 20th	Night	44% 5% 11% 21% 16% 2	2534
	21st to end	Night	39% 4 9% 24% 20% 4	1978
March	1st to 10th	Night	41% 3 8% 22% 22% 4	4919
	11th to 20th	Night	31% 4 7% 28% 25% 6%	4980
	21st to end	Night	48% 6% 14% 22% 7% 2	5467
April	1st to 10th	Night	36% 5% 10% 27% 18% 4	2028
	11th to 20th	Night	40% 5% 9% 27% 15% 4	1975
	21st to end	Night	45% 5% 11% 23% 15% 1	1925
May	1st to 10th	Night	39% 7% 13% 25% 14% 1	4080
	11th to 20th	Night	35% 6% 11% 28% 15% 5%	3973
	21st to end	Night	40% 6% 8% 24% 21% 1	3950
June	1st to 10th	Night	24% 8% 18% 31% 16% 3	1600
	11th to 20th	Night	28% 8% 13% 27% 20% 5%	1600
	21st to end	Night	24% 6% 16% 30% 20% 4	1600
July	1st to 10th	Night	31% 5% 11% 27% 23% 3	3580
	11th to 20th	Night	30% 7% 16% 28% 19% 2	4015
	21st to end	Night	31% 7% 18% 33% 10% 1	4320
August	1st to 10th	Night	19% 6% 19% 32% 22% 2	2916
	11th to 20th	Night	33% 4 11% 30% 22% 1	2915
	21st to end	Night	24% 5% 16% 34% 17% 4	3576
September	1st to 10th	Night	29% 4 11% 25% 24% 7%	2000
	11th to 20th	Night	28% 6% 12% 28% 23% 4	2076
	21st to end	Night	28% 5% 9% 28% 27% 4	2250
October	1st to 10th	Night	18% 2 7% 19% 47% 7%	3920
	11th to 20th	Night	24% 3 6% 23% 33% 12%	3899
	21st to end	Night	36% 3 7% 26% 25% 3	4252
November	1st to 10th	Night	29% 4 14% 27% 22% 5%	2475
	11th to 20th	Night	34% 4 9% 29% 20% 4	2881
	21st to end	Night	42% 4 10% 27% 16% 2	2940
December	1st to 10th	Night	34% 3 12% 37% 14%	4609
	11th to 20th	Night	40% 5% 15% 26% 14% 1	5201
	21st to end	Night	62% 4 11% 16% 5% 1	6996

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	21% 17% 35% 23% 5%	300
	11th to 20th	Day	25% 19% 38% 17% 1	300
	21st to end	Day	15% 17% 46% 19% 2	330
February	1st to 10th	Day	22% 19% 41% 16% 3	300
	11th to 20th	Day	22% 20% 38% 13% 7%	300
	21st to end	Day	20% 20% 42% 14% 3	249
March	1st to 10th	Day	19% 16% 45% 18% 2	300
	11th to 20th	Day	27% 12% 34% 22% 4	300
	21st to end	Day	38% 15% 31% 14% 3	330
April	1st to 10th	Day	23% 15% 35% 22% 6%	470
	11th to 20th	Day	21% 15% 36% 21% 7% 1	492
	21st to end	Day	22% 16% 32% 22% 7% 1	571
May	1st to 10th	Day	17% 12% 38% 23% 9% 1	703
	11th to 20th	Day	21% 10% 27% 28% 11% 3	725
	21st to end	Day	16% 7% 31% 25% 17% 3	789
June	1st to 10th	Day	8% 5% 21% 35% 23% 8%	730
	11th to 20th	Day	10% 4 25% 36% 21% 4	730
	21st to end	Day	8% 5% 34% 34% 17% 2	730
July	1st to 10th	Day	10% 3 14% 32% 29% 12%	721
	11th to 20th	Day	7% 3 21% 35% 26% 9%	718
	21st to end	Day	7% 2 16% 35% 32% 7%	794
August	1st to 10th	Day	6% 3 18% 40% 26% 6%	726
	11th to 20th	Day	9% 3 16% 35% 30% 7%	715
	21st to end	Day	9% 2 15% 32% 31% 11%	593
September	1st to 10th	Day	12% 4 16% 34% 28% 6%	530
	11th to 20th	Day	8% 2 19% 36% 26% 8%	450
	21st to end	Day	13% 7% 23% 30% 20% 7%	330
October	1st to 10th	Day	15% 5% 30% 30% 14% 6%	330
	11th to 20th	Day	12% 24% 34% 21% 8% 1	330
	21st to end	Day	23% 15% 35% 21% 6% 1	363
November	1st to 10th	Day	15% 14% 39% 22% 7% 3	330
	11th to 20th	Day	17% 18% 36% 22% 5% 2	330
	21st to end	Day	22% 19% 29% 25% 4 1	330
December	1st to 10th	Day	11% 16% 41% 23% 7% 2	306
	11th to 20th	Day	21% 16% 35% 21% 5% 1	300
	21st to end	Day	24% 21% 36% 18% 1	330
January	1st to 10th	Night	14% 14% 39% 26% 7%	1000
	11th to 20th	Night	17% 16% 37% 24% 5% 1	1000
	21st to end	Night	17% 12% 39% 29% 3	1100
February	1st to 10th	Night	18% 14% 42% 23% 4	1000
	11th to 20th	Night	18% 13% 37% 27% 4	979
	21st to end	Night	19% 14% 43% 20% 4 1	658
March	1st to 10th	Night	18% 13% 39% 25% 5%	600
	11th to 20th	Night	21% 11% 35% 29% 5% 1	600
	21st to end	Night	27% 10% 36% 22% 5%	660
April	1st to 10th	Night	15% 11% 41% 29% 3	600
	11th to 20th	Night	19% 12% 34% 27% 7%	593
	21st to end	Night	22% 10% 34% 28% 6% 1	600
May	1st to 10th	Night	16% 8% 36% 31% 8% 1	600
	11th to 20th	Night	17% 6% 27% 36% 15% 1	591
	21st to end	Night	12% 6% 26% 38% 17% 2	650
June	1st to 10th	Night	6% 3 21% 44% 23% 3	600
	11th to 20th	Night	7% 4 25% 45% 18% 2	600
	21st to end	Night	6% 3 27% 46% 17% 1	600
July	1st to 10th	Night	9% 2 12% 38% 34% 4	585
	11th to 20th	Night	5% 2 18% 44% 28% 2	582
	21st to end	Night	7% 1 13% 44% 33% 2	657
August	1st to 10th	Night	6% 1 17% 48% 27% 1	597
	11th to 20th	Night	8% 2 12% 42% 33% 3	594
	21st to end	Night	6% 2 12% 42% 35% 3	660
September	1st to 10th	Night	11% 2 17% 40% 27% 4	600
	11th to 20th	Night	12% 2 17% 40% 26% 4	600
	21st to end	Night	8% 4 23% 40% 21% 3	650
October	1st to 10th	Night	12% 5% 30% 33% 18% 2	800
	11th to 20th	Night	15% 9% 34% 33% 9%	800
	21st to end	Night	22% 10% 33% 26% 8%	880
November	1st to 10th	Night	12% 11% 34% 34% 9%	820
	11th to 20th	Night	15% 13% 39% 26% 8%	991
	21st to end	Night	22% 10% 36% 26% 6%	1050
December	1st to 10th	Night	17% 12% 37% 27% 6% 1	1011
	11th to 20th	Night	20% 9% 36% 30% 5%	1000
	21st to end	Night	23% 15% 34% 25% 3	1100

Page generated at 2025-11-30 00:00:57. Version ac07

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