Blackwater Falls
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackwater Falls 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	14% 11% 4 10% 6% 5% 5% 4 5% 7% 29%	126558
	Night	13% 12% 4 11% 6% 5% 5% 4 5% 6% 29%	124127
Transparency	Day	49% 9% 11% 19% 11% 2	130164
	Night	50% 9% 11% 18% 10% 2	128590
Seeing	Day	26% 20% 26% 16% 9% 3	16267
	Night	24% 20% 23% 22% 10% 1	26056

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	11% 11% 11% 14% 9% 10% 6% 4 4 5% 17%	4056
	11th to 20th	Day	8% 15% 8% 24% 5% 9% 5% 2 3 3 18%	4060
	21st to end	Day	13% 11% 7% 16% 8% 6% 4 3 4 5% 24%	4466
February	1st to 10th	Day	14% 13% 6% 12% 7% 6% 4 3 4 6% 24%	1800
	11th to 20th	Day	15% 12% 4 15% 7% 7% 6% 3 4 5% 22%	1753
	21st to end	Day	12% 15% 5% 13% 7% 5% 4 3 4 5% 26%	1695
March	1st to 10th	Day	12% 11% 7% 13% 5% 3 3 3 4 6% 33%	4935
	11th to 20th	Day	10% 10% 5% 9% 5% 4 4 4 5% 8% 37%	4980
	21st to end	Day	13% 15% 6% 10% 6% 5% 4 3 4 5% 29%	5465
April	1st to 10th	Day	15% 14% 5% 10% 5% 4 4 4 5% 6% 29%	2320
	11th to 20th	Day	15% 12% 4 7% 5% 5% 4 3 5% 5% 35%	2374
	21st to end	Day	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	2549
May	1st to 10th	Day	17% 13% 4 9% 6% 6% 6% 5% 6% 6% 24%	5862
	11th to 20th	Day	19% 11% 3 8% 5% 5% 6% 5% 7% 7% 23%	5861
	21st to end	Day	18% 11% 4 8% 5% 6% 6% 4 6% 7% 26%	6680
June	1st to 10th	Day	15% 8% 2 8% 5% 5% 5% 4 7% 9% 32%	2800
	11th to 20th	Day	14% 9% 3 8% 6% 6% 6% 5% 6% 9% 30%	2800
	21st to end	Day	12% 8% 2 7% 6% 5% 6% 5% 7% 9% 33%	2800
July	1st to 10th	Day	11% 7% 3 7% 5% 5% 5% 4 7% 8% 38%	5994
	11th to 20th	Day	12% 9% 3 9% 7% 5% 7% 5% 7% 9% 28%	5900
	21st to end	Day	15% 9% 3 8% 6% 5% 6% 4 7% 9% 29%	6424
August	1st to 10th	Day	14% 10% 3 9% 6% 6% 6% 5% 8% 8% 26%	4234
	11th to 20th	Day	13% 9% 2 8% 6% 6% 6% 6% 7% 8% 28%	4174
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 10% 42%	4355
September	1st to 10th	Day	14% 7% 3 8% 4 5% 5% 3 5% 6% 41%	2400
	11th to 20th	Day	11% 9% 2 6% 5% 5% 6% 4 6% 8% 39%	2238
	21st to end	Day	19% 11% 3 7% 4 4 4 4 5% 7% 32%	2176
October	1st to 10th	Day	14% 10% 2 6% 3 3 4 4 4 7% 43%	2000
	11th to 20th	Day	16% 13% 3 7% 4 4 3 3 4 5% 39%	2000
	21st to end	Day	13% 16% 4 8% 4 4 4 3 4 6% 35%	2200
November	1st to 10th	Day	11% 11% 4 8% 4 4 4 3 3 4 44%	2057
	11th to 20th	Day	11% 13% 5% 11% 5% 6% 4 3 5% 6% 30%	1789
	21st to end	Day	13% 15% 6% 11% 7% 4 4 3 4 5% 27%	1680
December	1st to 10th	Day	13% 12% 6% 12% 14% 7% 4 3 3 4 22%	2616
	11th to 20th	Day	18% 12% 6% 11% 5% 4 5% 4 5% 5% 24%	2990
	21st to end	Day	14% 14% 8% 13% 6% 5% 5% 4 6% 7% 18%	4075
January	1st to 10th	Night	9% 13% 7% 22% 11% 9% 6% 3 4 3 14%	5889
	11th to 20th	Night	9% 12% 6% 21% 11% 8% 6% 4 4 3 17%	5900
	21st to end	Night	11% 13% 5% 15% 7% 8% 6% 3 3 4 25%	6490
February	1st to 10th	Night	12% 13% 6% 13% 7% 5% 4 3 6% 5% 26%	2600
	11th to 20th	Night	13% 13% 5% 15% 10% 7% 5% 4 3 4 22%	2533
	21st to end	Night	14% 15% 4 12% 8% 6% 4 2 5% 5% 25%	1931
March	1st to 10th	Night	15% 13% 5% 10% 6% 5% 5% 3 4 5% 30%	4918
	11th to 20th	Night	9% 9% 4 13% 5% 3 4 3 6% 7% 37%	4980
	21st to end	Night	11% 13% 6% 10% 4 5% 4 3 4 5% 34%	5467
April	1st to 10th	Night	13% 14% 6% 10% 6% 3 4 3 5% 6% 31%	2079
	11th to 20th	Night	13% 11% 3 7% 5% 5% 5% 4 5% 7% 35%	1975
	21st to end	Night	15% 9% 4 8% 5% 5% 5% 4 6% 6% 33%	1868
May	1st to 10th	Night	21% 14% 4 10% 5% 4 3 3 5% 6% 24%	4033
	11th to 20th	Night	18% 14% 3 9% 6% 6% 5% 4 6% 7% 23%	4032
	21st to end	Night	20% 14% 4 8% 4 4 4 3 6% 6% 26%	4156
June	1st to 10th	Night	11% 10% 2 8% 5% 4 4 4 5% 8% 39%	1600
	11th to 20th	Night	12% 8% 4 9% 6% 4 4 5% 6% 9% 34%	1600
	21st to end	Night	11% 8% 2 6% 4 4 5% 4 8% 11% 37%	1600
July	1st to 10th	Night	13% 10% 2 7% 5% 6% 5% 4 6% 8% 36%	3957
	11th to 20th	Night	15% 9% 3 8% 5% 5% 4 4 7% 8% 31%	4057
	21st to end	Night	15% 9% 2 7% 5% 4 5% 4 6% 8% 34%	4427
August	1st to 10th	Night	13% 10% 3 8% 5% 5% 5% 4 7% 10% 31%	2915
	11th to 20th	Night	15% 11% 2 6% 4 5% 4 4 6% 6% 36%	2875
	21st to end	Night	6% 6% 2 6% 4 4 5% 5% 7% 8% 46%	3508
September	1st to 10th	Night	13% 7% 2 7% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	10% 7% 2 6% 4 5% 5% 4 5% 7% 46%	2158
	21st to end	Night	15% 10% 4 8% 5% 5% 4 5% 5% 5% 34%	2223
October	1st to 10th	Night	14% 9% 2 6% 4 4 4 3 5% 6% 43%	2400
	11th to 20th	Night	12% 12% 3 7% 4 4 4 4 5% 6% 39%	2400
	21st to end	Night	15% 15% 3 7% 4 5% 3 3 4 4 36%	2640
November	1st to 10th	Night	10% 12% 4 7% 5% 4 4 3 5% 4 42%	2461
	11th to 20th	Night	13% 13% 5% 13% 5% 5% 4 4 3 4 30%	2825
	21st to end	Night	12% 13% 6% 14% 8% 5% 4 3 4 5% 26%	2940
December	1st to 10th	Night	12% 14% 6% 14% 15% 7% 3 2 3 4 20%	4609
	11th to 20th	Night	16% 12% 5% 16% 6% 5% 5% 4 4 4 22%	5205
	21st to end	Night	12% 15% 8% 15% 6% 6% 6% 4 4 5% 18%	6876

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	56% 14% 9% 14% 6% 1	4057
	11th to 20th	Day	62% 11% 7% 9% 9% 1	4060
	21st to end	Day	54% 9% 9% 15% 11% 2	4466
February	1st to 10th	Day	59% 5% 10% 15% 9% 1	1800
	11th to 20th	Day	61% 5% 10% 13% 10% 1	1762
	21st to end	Day	57% 6% 10% 14% 11% 2	1695
March	1st to 10th	Day	47% 9% 8% 21% 11% 4	4935
	11th to 20th	Day	41% 8% 9% 27% 12% 4	4980
	21st to end	Day	51% 11% 7% 16% 13% 2	5465
April	1st to 10th	Day	54% 7% 10% 14% 12% 3	2320
	11th to 20th	Day	46% 7% 11% 18% 15% 3	2374
	21st to end	Day	51% 7% 10% 21% 10% 2	2549
May	1st to 10th	Day	55% 10% 9% 17% 7% 2	5897
	11th to 20th	Day	53% 12% 10% 21% 4 1	5865
	21st to end	Day	49% 13% 12% 16% 8% 2	6695
June	1st to 10th	Day	44% 10% 13% 20% 12% 1	2800
	11th to 20th	Day	47% 9% 13% 20% 9% 1	2800
	21st to end	Day	43% 10% 15% 21% 9% 1	2800
July	1st to 10th	Day	41% 8% 12% 25% 11% 2	5929
	11th to 20th	Day	49% 10% 14% 21% 5%	5831
	21st to end	Day	48% 8% 11% 21% 10% 1	6240
August	1st to 10th	Day	50% 10% 15% 19% 6%	4221
	11th to 20th	Day	48% 9% 11% 24% 8%	4213
	21st to end	Day	34% 10% 16% 26% 13% 1	4355
September	1st to 10th	Day	43% 8% 9% 18% 19% 3	2400
	11th to 20th	Day	41% 7% 10% 23% 15% 3	2238
	21st to end	Day	49% 8% 11% 17% 13% 1	2176
October	1st to 10th	Day	32% 5% 8% 26% 23% 6%	3260
	11th to 20th	Day	40% 6% 10% 19% 15% 10%	3240
	21st to end	Day	35% 5% 9% 25% 22% 4	3538
November	1st to 10th	Day	43% 4 9% 21% 18% 5%	2057
	11th to 20th	Day	50% 7% 8% 16% 16% 4	1789
	21st to end	Day	57% 5% 11% 15% 11% 1	1680
December	1st to 10th	Day	58% 12% 11% 15% 3 1	2616
	11th to 20th	Day	55% 7% 12% 16% 8% 1	2986
	21st to end	Day	56% 10% 11% 15% 8%	4075
January	1st to 10th	Night	62% 14% 6% 10% 7% 1	5889
	11th to 20th	Night	61% 10% 8% 12% 7% 1	5900
	21st to end	Night	54% 11% 11% 13% 10% 1	6490
February	1st to 10th	Night	56% 7% 11% 16% 9% 1	2600
	11th to 20th	Night	63% 5% 10% 13% 9% 1	2535
	21st to end	Night	58% 7% 9% 14% 9% 3	1931
March	1st to 10th	Night	47% 12% 9% 20% 10% 2	4918
	11th to 20th	Night	41% 8% 11% 26% 10% 4	4980
	21st to end	Night	45% 10% 12% 18% 13% 2	5467
April	1st to 10th	Night	53% 7% 10% 16% 13% 2	2079
	11th to 20th	Night	44% 9% 12% 19% 13% 3	1975
	21st to end	Night	47% 8% 12% 21% 10% 2	1868
May	1st to 10th	Night	57% 10% 12% 12% 8% 2	4060
	11th to 20th	Night	53% 14% 10% 17% 5%	4033
	21st to end	Night	52% 13% 13% 16% 5% 2	4163
June	1st to 10th	Night	41% 9% 12% 25% 13% 1	1600
	11th to 20th	Night	44% 9% 15% 22% 10% 1	1600
	21st to end	Night	38% 10% 16% 22% 13% 1	1600
July	1st to 10th	Night	44% 9% 15% 22% 9% 1	3914
	11th to 20th	Night	47% 11% 16% 20% 6% 1	4006
	21st to end	Night	44% 8% 13% 22% 12%	4297
August	1st to 10th	Night	46% 11% 19% 18% 6%	2904
	11th to 20th	Night	45% 8% 11% 24% 12%	2902
	21st to end	Night	32% 9% 16% 32% 10% 1	3508
September	1st to 10th	Night	38% 8% 14% 18% 19% 3	2000
	11th to 20th	Night	35% 8% 11% 27% 17% 2	2158
	21st to end	Night	47% 9% 11% 19% 14% 1	2223
October	1st to 10th	Night	36% 6% 10% 25% 20% 3	3920
	11th to 20th	Night	40% 5% 9% 20% 14% 12%	3899
	21st to end	Night	35% 6% 6% 26% 19% 7%	4252
November	1st to 10th	Night	42% 8% 9% 17% 17% 6%	2461
	11th to 20th	Night	55% 6% 8% 15% 14% 3	2825
	21st to end	Night	59% 5% 9% 14% 10% 2	2940
December	1st to 10th	Night	60% 13% 9% 13% 4 1	4609
	11th to 20th	Night	60% 6% 11% 15% 8%	5208
	21st to end	Night	61% 9% 10% 11% 7% 1	6876

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	39% 31% 19% 7% 3	300
	11th to 20th	Day	47% 27% 21% 4 1	300
	21st to end	Day	40% 29% 22% 7% 2	330
February	1st to 10th	Day	46% 27% 20% 7% 1	300
	11th to 20th	Day	51% 27% 18% 3 1	300
	21st to end	Day	40% 32% 23% 5%	331
March	1st to 10th	Day	38% 26% 23% 10% 3	500
	11th to 20th	Day	37% 28% 22% 8% 4 1	500
	21st to end	Day	35% 27% 25% 10% 4	550
April	1st to 10th	Day	35% 26% 24% 12% 3 1	500
	11th to 20th	Day	27% 25% 28% 11% 7% 2	492
	21st to end	Day	30% 27% 25% 13% 5% 1	500
May	1st to 10th	Day	29% 24% 26% 12% 6% 3	503
	11th to 20th	Day	26% 21% 30% 14% 6% 3	527
	21st to end	Day	21% 15% 28% 19% 11% 5%	573
June	1st to 10th	Day	17% 19% 30% 19% 11% 4	530
	11th to 20th	Day	18% 18% 28% 21% 12% 4	530
	21st to end	Day	12% 19% 31% 23% 13% 3	530
July	1st to 10th	Day	14% 13% 28% 21% 17% 7%	525
	11th to 20th	Day	10% 12% 31% 26% 14% 7%	524
	21st to end	Day	16% 11% 28% 25% 16% 6%	576
August	1st to 10th	Day	15% 13% 26% 23% 15% 8%	526
	11th to 20th	Day	15% 11% 28% 23% 14% 9%	519
	21st to end	Day	12% 10% 28% 25% 16% 10%	583
September	1st to 10th	Day	17% 12% 24% 25% 15% 8%	530
	11th to 20th	Day	10% 11% 27% 26% 19% 8%	530
	21st to end	Day	26% 16% 26% 19% 10% 3	530
October	1st to 10th	Day	18% 15% 25% 23% 15% 4	530
	11th to 20th	Day	24% 22% 25% 18% 10% 2	530
	21st to end	Day	28% 23% 26% 14% 7% 1	583
November	1st to 10th	Day	26% 22% 25% 19% 7% 1	535
	11th to 20th	Day	35% 27% 23% 10% 5%	281
	21st to end	Day	40% 22% 26% 8% 4	220
December	1st to 10th	Day	37% 30% 22% 8% 1 1	204
	11th to 20th	Day	42% 26% 21% 10% 2	200
	21st to end	Day	40% 24% 22% 9% 4	245
January	1st to 10th	Night	36% 31% 21% 9% 3	800
	11th to 20th	Night	36% 28% 25% 10% 1	800
	21st to end	Night	35% 32% 20% 11% 1	880
February	1st to 10th	Night	31% 28% 24% 16% 1	800
	11th to 20th	Night	37% 34% 22% 7% 1	783
	21st to end	Night	34% 30% 26% 9% 1	660
March	1st to 10th	Night	31% 25% 25% 16% 2	800
	11th to 20th	Night	32% 27% 21% 14% 5% 1	800
	21st to end	Night	28% 25% 27% 14% 5% 1	880
April	1st to 10th	Night	26% 28% 27% 15% 4	800
	11th to 20th	Night	24% 20% 26% 21% 9%	791
	21st to end	Night	24% 21% 23% 25% 6%	668
May	1st to 10th	Night	27% 16% 23% 26% 8% 1	600
	11th to 20th	Night	22% 16% 23% 26% 11% 1	591
	21st to end	Night	15% 9% 23% 27% 24% 2	540
June	1st to 10th	Night	12% 11% 26% 32% 19% 1	400
	11th to 20th	Night	15% 11% 24% 31% 19% 1	400
	21st to end	Night	12% 8% 25% 38% 15% 2	400
July	1st to 10th	Night	13% 7% 21% 34% 21% 5%	536
	11th to 20th	Night	9% 7% 21% 32% 27% 4	582
	21st to end	Night	11% 8% 18% 37% 23% 2	657
August	1st to 10th	Night	12% 6% 17% 37% 25% 2	597
	11th to 20th	Night	12% 7% 18% 37% 23% 4	594
	21st to end	Night	11% 7% 20% 35% 24% 3	828
September	1st to 10th	Night	14% 7% 24% 30% 21% 5%	800
	11th to 20th	Night	12% 8% 19% 31% 27% 3	800
	21st to end	Night	21% 13% 19% 30% 16% 2	800
October	1st to 10th	Night	17% 16% 20% 25% 19% 3	800
	11th to 20th	Night	22% 19% 24% 23% 11% 1	800
	21st to end	Night	26% 21% 22% 22% 8% 1	880
November	1st to 10th	Night	21% 18% 25% 26% 9% 1	820
	11th to 20th	Night	31% 20% 24% 18% 7% 1	840
	21st to end	Night	28% 27% 24% 16% 4 1	840
December	1st to 10th	Night	33% 29% 20% 13% 5%	809
	11th to 20th	Night	30% 29% 22% 16% 3	800
	21st to end	Night	28% 27% 26% 17% 2	880

Page generated at 2025-11-30 01:00:51. Version ac07

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