Blackbird State Forest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackbird State Forest clear sky chart from 2005-11-06 to 2025-11-18.

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	14% 6% 2 6% 4 4 4 4 6% 8% 42%	126856
	Night	15% 7% 2 6% 4 4 4 4 5% 7% 43%	123510
Transparency	Day	38% 7% 12% 24% 17% 3	130416
	Night	39% 6% 11% 23% 18% 4	128020
Seeing	Day	18% 12% 27% 24% 14% 5%	16389
	Night	18% 10% 30% 30% 11% 1	25717

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	13% 6% 2 4 3 4 4 3 5% 6% 52%	3597
	11th to 20th	Day	14% 7% 3 7% 4 4 4 3 4 4 46%	3853
	21st to end	Day	16% 6% 3 6% 4 4 4 3 5% 6% 44%	4466
February	1st to 10th	Day	14% 7% 3 6% 4 4 4 4 6% 7% 41%	1800
	11th to 20th	Day	17% 8% 2 5% 4 4 5% 3 5% 6% 42%	1894
	21st to end	Day	17% 9% 3 6% 3 3 4 3 4 7% 41%	1650
March	1st to 10th	Day	19% 5% 1 4 3 3 4 3 5% 6% 47%	4571
	11th to 20th	Day	10% 7% 2 5% 3 3 4 4 5% 6% 50%	4980
	21st to end	Day	17% 5% 2 6% 4 4 4 3 4 6% 43%	5735
April	1st to 10th	Day	14% 7% 2 5% 4 4 5% 4 5% 7% 43%	2400
	11th to 20th	Day	12% 6% 2 5% 4 3 5% 4 5% 7% 46%	2374
	21st to end	Day	15% 5% 2 6% 5% 3 4 5% 5% 8% 42%	2400
May	1st to 10th	Day	22% 8% 2 6% 4 4 4 4 6% 8% 32%	5667
	11th to 20th	Day	23% 6% 3 6% 4 4 4 4 5% 8% 33%	6318
	21st to end	Day	17% 5% 2 5% 3 4 4 4 6% 9% 39%	6934
June	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 4 8% 10% 40%	2800
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 42%	2800
	21st to end	Day	9% 4 2 5% 4 3 5% 4 7% 11% 46%	2800
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 8% 11% 42%	6360
	11th to 20th	Day	9% 6% 2 7% 5% 6% 6% 5% 9% 12% 33%	6360
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 7% 11% 40%	6619
August	1st to 10th	Day	15% 6% 2 6% 4 5% 5% 5% 7% 11% 35%	4234
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 7% 10% 43%	3859
	21st to end	Day	8% 5% 2 5% 5% 4 5% 4 6% 8% 48%	4312
September	1st to 10th	Day	13% 6% 2 5% 4 5% 4 4 6% 7% 45%	2400
	11th to 20th	Day	12% 5% 2 5% 3 4 4 4 5% 7% 49%	2388
	21st to end	Day	19% 7% 3 6% 4 4 5% 3 5% 6% 37%	2170
October	1st to 10th	Day	16% 6% 1 4 3 4 4 3 5% 7% 47%	2000
	11th to 20th	Day	16% 4 2 4 3 3 4 2 5% 7% 50%	2000
	21st to end	Day	15% 6% 2 6% 4 3 3 2 4 5% 50%	2176
November	1st to 10th	Day	12% 5% 2 4 3 4 3 3 5% 7% 53%	1851
	11th to 20th	Day	13% 6% 2 5% 4 3 3 4 5% 7% 49%	1863
	21st to end	Day	14% 6% 2 5% 3 3 4 3 5% 6% 47%	1675
December	1st to 10th	Day	11% 5% 2 5% 4 4 5% 3 6% 7% 48%	2600
	11th to 20th	Day	19% 9% 2 5% 3 3 3 3 4 7% 41%	2990
	21st to end	Day	13% 6% 2 6% 4 4 4 3 6% 7% 43%	3960
January	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 4 6% 49%	6349
	11th to 20th	Night	14% 7% 2 5% 3 3 4 3 4 5% 51%	6102
	21st to end	Night	16% 7% 3 6% 3 3 4 3 5% 6% 45%	6490
February	1st to 10th	Night	16% 8% 2 6% 4 4 4 4 5% 6% 41%	2600
	11th to 20th	Night	18% 8% 2 5% 4 3 4 3 4 5% 43%	2392
	21st to end	Night	16% 8% 2 6% 3 4 5% 4 5% 5% 43%	1980
March	1st to 10th	Night	16% 7% 2 5% 3 3 3 3 3 6% 47%	5268
	11th to 20th	Night	11% 8% 2 5% 3 3 4 4 5% 6% 50%	4980
	21st to end	Night	14% 8% 3 6% 4 3 4 3 5% 5% 45%	5195
April	1st to 10th	Night	16% 8% 3 6% 4 4 3 4 5% 6% 41%	2000
	11th to 20th	Night	14% 6% 2 7% 5% 4 5% 3 5% 6% 43%	1975
	21st to end	Night	18% 5% 2 5% 4 4 4 3 6% 6% 44%	2000
May	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 5% 5% 8% 29%	4255
	11th to 20th	Night	22% 9% 2 6% 4 4 4 4 6% 7% 32%	3575
	21st to end	Night	19% 6% 2 6% 4 4 4 4 6% 8% 36%	3920
June	1st to 10th	Night	12% 7% 2 6% 4 3 4 4 6% 8% 44%	1600
	11th to 20th	Night	10% 6% 3 6% 6% 4 5% 4 6% 9% 41%	1600
	21st to end	Night	9% 6% 2 6% 5% 4 5% 3 8% 11% 43%	1600
July	1st to 10th	Night	7% 6% 3 7% 5% 6% 6% 5% 8% 10% 37%	3598
	11th to 20th	Night	10% 7% 3 8% 5% 6% 5% 5% 8% 11% 32%	3597
	21st to end	Night	10% 7% 2 6% 5% 4 4 5% 7% 9% 41%	4215
August	1st to 10th	Night	16% 7% 2 6% 4 5% 6% 4 6% 10% 32%	2915
	11th to 20th	Night	12% 7% 2 7% 5% 5% 4 4 6% 8% 40%	3157
	21st to end	Night	11% 5% 2 5% 4 4 4 4 6% 8% 49%	3586
September	1st to 10th	Night	13% 7% 3 6% 3 4 4 4 4 7% 46%	2000
	11th to 20th	Night	11% 6% 2 4 3 3 3 2 5% 8% 54%	2011
	21st to end	Night	19% 7% 2 7% 3 5% 4 3 6% 7% 38%	2225
October	1st to 10th	Night	16% 7% 2 6% 4 3 3 3 5% 6% 45%	2400
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 5% 6% 51%	2400
	21st to end	Night	15% 5% 2 5% 3 3 4 3 5% 6% 50%	2662
November	1st to 10th	Night	10% 5% 2 5% 3 3 3 3 6% 6% 54%	2667
	11th to 20th	Night	14% 8% 2 5% 4 3 4 3 4 4 49%	2692
	21st to end	Night	12% 6% 1 5% 4 4 4 4 5% 7% 48%	2723
December	1st to 10th	Night	12% 6% 2 5% 3 4 4 3 5% 7% 50%	4580
	11th to 20th	Night	21% 6% 2 5% 3 3 3 3 5% 7% 40%	5205
	21st to end	Night	16% 7% 3 6% 4 4 5% 4 5% 7% 39%	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	33% 3 8% 26% 26% 4	3598
	11th to 20th	Day	42% 4 8% 22% 17% 6%	3853
	21st to end	Day	40% 5% 11% 27% 14% 3	4466
February	1st to 10th	Day	41% 6% 14% 24% 13% 2	1800
	11th to 20th	Day	42% 5% 10% 24% 16% 3	1903
	21st to end	Day	44% 5% 10% 22% 15% 4	1650
March	1st to 10th	Day	37% 4 9% 25% 19% 7%	4571
	11th to 20th	Day	33% 6% 9% 27% 19% 6%	4980
	21st to end	Day	42% 5% 9% 18% 21% 6%	5735
April	1st to 10th	Day	40% 6% 12% 20% 17% 6%	2400
	11th to 20th	Day	37% 6% 11% 23% 18% 6%	2374
	21st to end	Day	38% 7% 11% 19% 20% 4	2400
May	1st to 10th	Day	48% 7% 14% 18% 11% 1	5699
	11th to 20th	Day	48% 7% 11% 23% 11% 1	6322
	21st to end	Day	40% 7% 12% 23% 16% 1	6949
June	1st to 10th	Day	36% 9% 13% 24% 16% 2	2800
	11th to 20th	Day	37% 9% 13% 25% 14% 2	2800
	21st to end	Day	30% 9% 15% 24% 19% 2	2800
July	1st to 10th	Day	34% 11% 18% 20% 14% 2	6290
	11th to 20th	Day	39% 10% 20% 21% 8% 1	6285
	21st to end	Day	35% 9% 12% 23% 20% 1	6430
August	1st to 10th	Day	41% 8% 16% 25% 8%	4221
	11th to 20th	Day	35% 8% 14% 29% 14% 1	3895
	21st to end	Day	31% 7% 12% 29% 18% 3	4312
September	1st to 10th	Day	37% 8% 11% 21% 20% 4	2400
	11th to 20th	Day	32% 7% 11% 24% 23% 3	2388
	21st to end	Day	47% 6% 8% 18% 19% 2	2170
October	1st to 10th	Day	32% 5% 10% 20% 28% 5%	3260
	11th to 20th	Day	25% 4 9% 25% 28% 9%	3240
	21st to end	Day	24% 3 10% 29% 28% 6%	3490
November	1st to 10th	Day	32% 4 13% 28% 20% 4	1851
	11th to 20th	Day	35% 6% 10% 24% 23% 3	1863
	21st to end	Day	37% 4 11% 30% 15% 3	1675
December	1st to 10th	Day	34% 6% 17% 26% 13% 3	2600
	11th to 20th	Day	43% 4 12% 28% 11% 2	2986
	21st to end	Day	39% 6% 14% 22% 18% 1	3960
January	1st to 10th	Night	37% 3 7% 24% 23% 6%	6349
	11th to 20th	Night	37% 4 8% 25% 19% 7%	6102
	21st to end	Night	41% 3 8% 27% 18% 2	6490
February	1st to 10th	Night	43% 5% 13% 23% 14% 1	2600
	11th to 20th	Night	44% 4 8% 21% 18% 4	2394
	21st to end	Night	42% 5% 10% 20% 17% 6%	1980
March	1st to 10th	Night	40% 4 8% 25% 13% 10%	5268
	11th to 20th	Night	34% 6% 12% 25% 17% 6%	4980
	21st to end	Night	41% 4 9% 17% 24% 4	5195
April	1st to 10th	Night	43% 5% 9% 19% 20% 5%	2000
	11th to 20th	Night	40% 5% 11% 19% 19% 6%	1975
	21st to end	Night	39% 6% 10% 20% 19% 6%	2000
May	1st to 10th	Night	51% 7% 11% 17% 10% 3	4285
	11th to 20th	Night	51% 7% 10% 20% 11% 1	3576
	21st to end	Night	44% 7% 13% 20% 13% 3	3927
June	1st to 10th	Night	37% 7% 12% 23% 20% 2	1600
	11th to 20th	Night	39% 8% 14% 24% 14% 2	1600
	21st to end	Night	34% 8% 15% 23% 17% 3	1600
July	1st to 10th	Night	40% 10% 17% 18% 13% 2	3560
	11th to 20th	Night	42% 11% 20% 20% 6% 1	3552
	21st to end	Night	37% 8% 13% 23% 19%	4091
August	1st to 10th	Night	45% 9% 17% 20% 8%	2904
	11th to 20th	Night	40% 8% 12% 26% 13% 1	3187
	21st to end	Night	32% 7% 10% 28% 20% 2	3586
September	1st to 10th	Night	39% 6% 10% 23% 20% 4	2000
	11th to 20th	Night	30% 5% 11% 26% 24% 4	2011
	21st to end	Night	45% 7% 9% 18% 17% 3	2225
October	1st to 10th	Night	39% 6% 9% 22% 20% 4	3920
	11th to 20th	Night	25% 3 12% 23% 30% 7%	3899
	21st to end	Night	24% 3 11% 31% 25% 6%	4298
November	1st to 10th	Night	31% 5% 11% 25% 22% 6%	2667
	11th to 20th	Night	38% 4 9% 22% 21% 6%	2692
	21st to end	Night	35% 5% 12% 26% 20% 2	2723
December	1st to 10th	Night	34% 4 13% 29% 16% 3	4580
	11th to 20th	Night	43% 4 13% 19% 16% 4	5208
	21st to end	Night	42% 6% 12% 21% 18% 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	23% 24% 34% 14% 5% 1	200
	11th to 20th	Day	25% 32% 25% 14% 3	255
	21st to end	Day	22% 22% 38% 12% 5% 1	330
February	1st to 10th	Day	22% 26% 34% 14% 3	300
	11th to 20th	Day	27% 23% 38% 10% 2	442
	21st to end	Day	24% 22% 32% 16% 4	414
March	1st to 10th	Day	20% 23% 33% 19% 5%	500
	11th to 20th	Day	22% 22% 33% 17% 5% 1	500
	21st to end	Day	23% 19% 34% 18% 6% 1	550
April	1st to 10th	Day	22% 21% 36% 14% 5% 2	500
	11th to 20th	Day	20% 18% 30% 21% 8% 3	492
	21st to end	Day	22% 15% 32% 21% 8% 2	500
May	1st to 10th	Day	26% 17% 27% 18% 9% 2	503
	11th to 20th	Day	21% 11% 31% 24% 11% 2	527
	21st to end	Day	18% 7% 23% 26% 19% 6%	573
June	1st to 10th	Day	11% 9% 30% 27% 16% 7%	530
	11th to 20th	Day	14% 9% 24% 30% 16% 6%	530
	21st to end	Day	10% 5% 23% 33% 22% 7%	530
July	1st to 10th	Day	10% 3 20% 34% 26% 9%	525
	11th to 20th	Day	7% 2 17% 35% 30% 9%	524
	21st to end	Day	8% 3 20% 35% 26% 8%	576
August	1st to 10th	Day	13% 2 19% 33% 23% 10%	526
	11th to 20th	Day	14% 3 13% 34% 25% 10%	519
	21st to end	Day	10% 3 20% 33% 22% 12%	583
September	1st to 10th	Day	17% 5% 22% 25% 19% 12%	530
	11th to 20th	Day	14% 3 20% 30% 21% 11%	530
	21st to end	Day	24% 8% 23% 29% 12% 5%	530
October	1st to 10th	Day	21% 7% 23% 24% 17% 8%	530
	11th to 20th	Day	18% 13% 26% 25% 15% 3	530
	21st to end	Day	17% 13% 33% 23% 11% 3	569
November	1st to 10th	Day	14% 13% 33% 24% 12% 3	425
	11th to 20th	Day	18% 19% 31% 21% 10%	421
	21st to end	Day	18% 21% 30% 20% 11%	275
December	1st to 10th	Day	18% 22% 37% 17% 6% 1	200
	11th to 20th	Day	29% 20% 32% 15% 5% 1	200
	21st to end	Day	22% 19% 30% 20% 8%	220
January	1st to 10th	Night	19% 19% 38% 21% 4	800
	11th to 20th	Night	21% 17% 32% 25% 4	800
	21st to end	Night	19% 15% 38% 26% 2	880
February	1st to 10th	Night	21% 13% 40% 25% 2	800
	11th to 20th	Night	23% 20% 39% 16% 1	783
	21st to end	Night	23% 17% 37% 21% 3	660
March	1st to 10th	Night	19% 15% 40% 22% 4	800
	11th to 20th	Night	20% 15% 38% 21% 5% 1	800
	21st to end	Night	21% 10% 40% 23% 5%	880
April	1st to 10th	Night	22% 15% 37% 20% 5%	800
	11th to 20th	Night	17% 14% 35% 29% 6%	791
	21st to end	Night	21% 11% 33% 27% 8%	800
May	1st to 10th	Night	20% 7% 33% 31% 7%	708
	11th to 20th	Night	20% 8% 31% 33% 7%	394
	21st to end	Night	16% 3 23% 39% 18% 1	433
June	1st to 10th	Night	15% 5% 25% 41% 14% 1	400
	11th to 20th	Night	12% 3 25% 44% 17%	400
	21st to end	Night	10% 4 21% 48% 17%	400
July	1st to 10th	Night	11% 2 18% 44% 24% 2	390
	11th to 20th	Night	7% 1 15% 44% 30% 2	388
	21st to end	Night	8% 3 15% 46% 25% 2	562
August	1st to 10th	Night	12% 2 13% 45% 27% 2	597
	11th to 20th	Night	14% 2 14% 40% 28% 3	762
	21st to end	Night	13% 3 16% 40% 25% 4	880
September	1st to 10th	Night	17% 2 18% 36% 23% 3	800
	11th to 20th	Night	14% 4 16% 36% 27% 4	800
	21st to end	Night	23% 4 20% 34% 18% 1	800
October	1st to 10th	Night	21% 4 20% 32% 19% 4	800
	11th to 20th	Night	18% 7% 28% 33% 13% 1	800
	21st to end	Night	18% 8% 34% 28% 11% 1	880
November	1st to 10th	Night	13% 8% 35% 32% 11% 1	820
	11th to 20th	Night	20% 13% 31% 28% 7% 1	829
	21st to end	Night	15% 14% 36% 27% 9% 1	800
December	1st to 10th	Night	23% 13% 33% 21% 8% 1	800
	11th to 20th	Night	20% 13% 37% 25% 5%	800
	21st to end	Night	20% 10% 37% 30% 3	880

Page generated at 2025-11-15 00:55:57. Version ac07

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