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 2024-01-13.

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% 11% 5% 8% 7% 4 5% 5% 5% 7% 30%	74603
	Night	13% 10% 5% 9% 7% 4 5% 5% 5% 6% 31%	75122
Transparency	Day	51% 8% 11% 18% 11% 2	74324
	Night	50% 8% 12% 18% 11% 2	74920
Seeing	Day	25% 20% 26% 17% 9% 3	13740
	Night	23% 20% 23% 22% 11% 1	23614

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	12% 12% 7% 12% 11% 5% 6% 5% 4 6% 21%	1706
	11th to 20th	Day	15% 15% 8% 14% 7% 5% 5% 5% 3 5% 18%	1638
	21st to end	Day	13% 13% 10% 13% 10% 4 4 4 3 4 24%	1782
February	1st to 10th	Day	15% 13% 7% 12% 9% 5% 5% 4 4 5% 22%	1620
	11th to 20th	Day	15% 11% 4 14% 9% 6% 7% 4 4 5% 22%	1573
	21st to end	Day	13% 14% 5% 12% 9% 4 5% 4 4 5% 25%	1519
March	1st to 10th	Day	12% 10% 6% 10% 7% 2 4 5% 5% 7% 33%	1980
	11th to 20th	Day	17% 13% 6% 8% 7% 3 4 4 4 7% 28%	1980
	21st to end	Day	17% 16% 7% 7% 7% 2 5% 4 4 5% 26%	2178
April	1st to 10th	Day	14% 12% 6% 9% 5% 3 5% 4 5% 6% 30%	2088
	11th to 20th	Day	16% 10% 5% 5% 6% 4 5% 4 5% 5% 35%	2134
	21st to end	Day	18% 12% 5% 8% 6% 3 4 3 5% 6% 30%	2293
May	1st to 10th	Day	19% 11% 4 8% 6% 4 5% 4 5% 5% 27%	2340
	11th to 20th	Day	22% 9% 4 7% 6% 3 6% 5% 5% 6% 27%	2301
	21st to end	Day	13% 9% 4 6% 7% 4 6% 6% 6% 8% 30%	2625
June	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 5% 6% 9% 33%	2520
	11th to 20th	Day	15% 8% 3 7% 6% 4 7% 6% 6% 9% 29%	2520
	21st to end	Day	13% 8% 3 6% 7% 4 6% 6% 6% 8% 33%	2520
July	1st to 10th	Day	14% 7% 3 6% 7% 4 6% 6% 6% 8% 32%	2378
	11th to 20th	Day	11% 8% 3 6% 8% 4 6% 7% 7% 9% 32%	2340
	21st to end	Day	15% 9% 4 7% 7% 4 6% 6% 6% 7% 29%	2547
August	1st to 10th	Day	13% 8% 4 7% 8% 5% 7% 6% 8% 8% 25%	2327
	11th to 20th	Day	14% 7% 3 8% 7% 5% 6% 6% 7% 9% 27%	2303
	21st to end	Day	13% 7% 3 6% 8% 4 7% 7% 7% 8% 31%	2404
September	1st to 10th	Day	15% 7% 3 7% 5% 4 5% 4 5% 6% 38%	2160
	11th to 20th	Day	12% 8% 3 5% 6% 4 6% 5% 6% 8% 38%	2015
	21st to end	Day	18% 11% 3 6% 5% 3 4 5% 5% 7% 34%	1959
October	1st to 10th	Day	15% 10% 3 6% 3 3 4 5% 4 6% 40%	1800
	11th to 20th	Day	17% 12% 3 7% 5% 4 3 4 4 5% 37%	1800
	21st to end	Day	14% 14% 4 7% 5% 3 4 4 4 5% 35%	1980
November	1st to 10th	Day	12% 11% 4 7% 5% 3 4 3 3 4 44%	1857
	11th to 20th	Day	12% 11% 6% 10% 6% 4 5% 4 5% 6% 31%	1621
	21st to end	Day	13% 12% 6% 9% 8% 3 6% 3 4 6% 28%	1520
December	1st to 10th	Day	16% 16% 8% 12% 8% 4 4 4 3 5% 22%	1520
	11th to 20th	Day	14% 13% 9% 12% 8% 3 3 4 4 5% 25%	1910
	21st to end	Day	15% 13% 9% 11% 8% 4 6% 6% 6% 6% 17%	2845
January	1st to 10th	Night	11% 12% 8% 14% 9% 4 8% 5% 5% 4 21%	2459
	11th to 20th	Night	15% 13% 6% 17% 10% 5% 6% 4 4 3 17%	2367
	21st to end	Night	12% 12% 8% 13% 10% 5% 7% 4 4 4 20%	2574
February	1st to 10th	Night	12% 11% 7% 12% 10% 4 5% 4 6% 5% 24%	2340
	11th to 20th	Night	13% 11% 6% 13% 11% 6% 6% 5% 3 5% 22%	2273
	21st to end	Night	15% 14% 5% 11% 9% 4 5% 3 5% 5% 24%	1733
March	1st to 10th	Night	13% 10% 6% 9% 7% 4 5% 5% 4 6% 32%	1980
	11th to 20th	Night	16% 11% 5% 9% 8% 3 4 4 5% 6% 29%	1980
	21st to end	Night	15% 12% 7% 9% 6% 3 5% 4 4 5% 29%	2178
April	1st to 10th	Night	13% 12% 7% 9% 6% 2 4 4 5% 6% 32%	1872
	11th to 20th	Night	13% 9% 4 7% 5% 3 5% 5% 5% 8% 36%	1775
	21st to end	Night	15% 9% 4 7% 6% 4 5% 5% 6% 6% 33%	1682
May	1st to 10th	Night	18% 10% 3 8% 6% 3 4 4 5% 5% 32%	1620
	11th to 20th	Night	20% 9% 3 5% 5% 4 4 4 6% 8% 31%	1592
	21st to end	Night	11% 6% 2 7% 7% 3 6% 5% 7% 9% 37%	1646
June	1st to 10th	Night	11% 8% 3 6% 6% 3 5% 5% 5% 9% 40%	1440
	11th to 20th	Night	11% 7% 4 8% 7% 3 5% 6% 6% 9% 34%	1440
	21st to end	Night	11% 7% 3 5% 4 3 5% 6% 8% 11% 37%	1440
July	1st to 10th	Night	12% 8% 2 6% 5% 5% 6% 4 6% 8% 37%	1575
	11th to 20th	Night	9% 6% 3 6% 6% 4 4 5% 7% 8% 43%	1620
	21st to end	Night	10% 6% 3 6% 6% 3 6% 7% 7% 8% 37%	1771
August	1st to 10th	Night	9% 6% 2 7% 6% 4 5% 6% 7% 10% 37%	1611
	11th to 20th	Night	11% 8% 3 6% 5% 4 5% 6% 7% 8% 37%	1598
	21st to end	Night	10% 8% 3 6% 6% 3 5% 5% 6% 9% 41%	1932
September	1st to 10th	Night	13% 7% 2 6% 6% 3 4 5% 5% 6% 44%	1800
	11th to 20th	Night	10% 6% 2 5% 5% 4 5% 5% 5% 6% 46%	1942
	21st to end	Night	15% 9% 4 6% 7% 4 5% 6% 5% 5% 36%	2000
October	1st to 10th	Night	14% 9% 3 6% 5% 4 4 4 5% 7% 40%	2160
	11th to 20th	Night	13% 11% 3 6% 4 3 4 5% 6% 6% 38%	2160
	21st to end	Night	16% 14% 4 6% 6% 3 4 3 4 4 36%	2376
November	1st to 10th	Night	11% 11% 4 7% 5% 3 4 4 5% 4 42%	2221
	11th to 20th	Night	13% 10% 6% 12% 7% 4 5% 4 3 4 31%	2554
	21st to end	Night	12% 12% 7% 11% 9% 4 5% 4 4 5% 27%	2660
December	1st to 10th	Night	16% 14% 8% 14% 9% 3 4 3 4 4 20%	2660
	11th to 20th	Night	15% 10% 7% 14% 9% 4 6% 5% 4 5% 22%	3285
	21st to end	Night	13% 15% 8% 12% 8% 5% 6% 5% 4 5% 19%	4806

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	61% 5% 10% 17% 6% 2	1707
	11th to 20th	Day	65% 5% 10% 14% 6% 1	1638
	21st to end	Day	63% 4 9% 14% 9% 2	1782
February	1st to 10th	Day	62% 5% 10% 15% 7% 1	1620
	11th to 20th	Day	62% 5% 10% 14% 9% 1	1582
	21st to end	Day	59% 6% 10% 14% 9% 2	1519
March	1st to 10th	Day	49% 6% 11% 21% 12% 1	1980
	11th to 20th	Day	56% 6% 8% 18% 10% 2	1980
	21st to end	Day	59% 5% 8% 16% 10% 2	2178
April	1st to 10th	Day	53% 6% 11% 15% 12% 3	2088
	11th to 20th	Day	47% 6% 10% 18% 15% 3	2134
	21st to end	Day	53% 6% 9% 20% 9% 2	2293
May	1st to 10th	Day	56% 8% 10% 14% 10% 1	2340
	11th to 20th	Day	54% 9% 12% 16% 7% 2	2305
	21st to end	Day	49% 11% 13% 19% 8% 1	2625
June	1st to 10th	Day	45% 10% 13% 20% 11%	2520
	11th to 20th	Day	48% 10% 13% 19% 9% 1	2520
	21st to end	Day	45% 10% 15% 21% 9% 1	2520
July	1st to 10th	Day	47% 9% 12% 19% 11% 2	2313
	11th to 20th	Day	44% 11% 13% 20% 11% 1	2271
	21st to end	Day	49% 10% 12% 17% 12% 1	2405
August	1st to 10th	Day	50% 10% 15% 17% 7%	2314
	11th to 20th	Day	50% 10% 13% 18% 9%	2303
	21st to end	Day	44% 11% 14% 19% 10% 2	2404
September	1st to 10th	Day	46% 9% 10% 17% 16% 2	2160
	11th to 20th	Day	42% 8% 11% 22% 15% 3	2015
	21st to end	Day	47% 8% 11% 18% 14% 1	1959
October	1st to 10th	Day	43% 7% 11% 22% 14% 3	1800
	11th to 20th	Day	49% 6% 8% 22% 15%	1800
	21st to end	Day	49% 7% 9% 20% 13% 3	1980
November	1st to 10th	Day	43% 4 9% 21% 17% 6%	1857
	11th to 20th	Day	51% 6% 8% 15% 16% 4	1621
	21st to end	Day	55% 5% 11% 16% 11% 1	1520
December	1st to 10th	Day	66% 5% 9% 14% 5% 2	1520
	11th to 20th	Day	56% 7% 9% 19% 8% 2	1906
	21st to end	Day	55% 12% 12% 14% 7%	2845
January	1st to 10th	Night	60% 6% 9% 14% 8% 2	2459
	11th to 20th	Night	69% 5% 8% 12% 5%	2367
	21st to end	Night	64% 5% 9% 13% 6% 2	2574
February	1st to 10th	Night	57% 6% 12% 16% 8% 1	2340
	11th to 20th	Night	63% 5% 10% 13% 8% 1	2275
	21st to end	Night	60% 6% 8% 14% 9% 3	1733
March	1st to 10th	Night	51% 6% 10% 21% 10% 2	1980
	11th to 20th	Night	53% 8% 11% 18% 9% 1	1980
	21st to end	Night	55% 6% 10% 16% 10% 3	2178
April	1st to 10th	Night	51% 6% 10% 17% 13% 2	1872
	11th to 20th	Night	43% 9% 13% 18% 14% 3	1775
	21st to end	Night	48% 8% 12% 20% 10% 2	1682
May	1st to 10th	Night	50% 8% 12% 17% 10% 3	1620
	11th to 20th	Night	49% 10% 12% 16% 11% 1	1593
	21st to end	Night	40% 10% 18% 23% 8% 1	1647
June	1st to 10th	Night	40% 8% 12% 27% 12% 1	1440
	11th to 20th	Night	44% 9% 15% 21% 10% 1	1440
	21st to end	Night	37% 10% 17% 22% 13% 1	1440
July	1st to 10th	Night	42% 11% 17% 17% 11% 2	1530
	11th to 20th	Night	35% 10% 17% 23% 13% 1	1566
	21st to end	Night	36% 12% 19% 20% 13%	1672
August	1st to 10th	Night	38% 13% 19% 19% 10% 1	1600
	11th to 20th	Night	39% 11% 15% 23% 10%	1598
	21st to end	Night	37% 9% 17% 24% 12% 2	1932
September	1st to 10th	Night	38% 9% 15% 18% 16% 3	1800
	11th to 20th	Night	35% 8% 11% 26% 18% 2	1942
	21st to end	Night	44% 10% 11% 20% 15%	2000
October	1st to 10th	Night	42% 8% 12% 22% 13% 3	2160
	11th to 20th	Night	43% 7% 11% 24% 13% 2	2160
	21st to end	Night	50% 6% 7% 20% 15% 2	2376
November	1st to 10th	Night	43% 8% 9% 17% 17% 7%	2221
	11th to 20th	Night	54% 5% 8% 14% 15% 3	2554
	21st to end	Night	57% 5% 10% 15% 11% 2	2660
December	1st to 10th	Night	65% 6% 8% 14% 4 2	2660
	11th to 20th	Night	59% 7% 8% 16% 9% 1	3288
	21st to end	Night	60% 11% 10% 13% 6%	4806

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	37% 31% 21% 7% 3	270
	11th to 20th	Day	41% 31% 22% 4 1	246
	21st to end	Day	41% 30% 21% 7% 2	264
February	1st to 10th	Day	46% 28% 20% 5% 1	240
	11th to 20th	Day	47% 30% 20% 3	240
	21st to end	Day	41% 32% 22% 6%	271
March	1st to 10th	Day	37% 27% 24% 10% 2	420
	11th to 20th	Day	38% 28% 21% 8% 5% 1	420
	21st to end	Day	33% 26% 26% 11% 4	462
April	1st to 10th	Day	33% 24% 25% 14% 3 1	420
	11th to 20th	Day	25% 25% 28% 11% 8% 2	412
	21st to end	Day	31% 28% 24% 12% 5% 1	420
May	1st to 10th	Day	30% 24% 24% 12% 6% 3	423
	11th to 20th	Day	26% 20% 32% 13% 6% 3	447
	21st to end	Day	18% 14% 28% 21% 13% 6%	485
June	1st to 10th	Day	16% 19% 30% 21% 10% 4	450
	11th to 20th	Day	20% 18% 27% 19% 12% 4	450
	21st to end	Day	13% 19% 31% 22% 13% 2	450
July	1st to 10th	Day	15% 11% 27% 21% 18% 8%	445
	11th to 20th	Day	9% 10% 32% 27% 14% 7%	444
	21st to end	Day	15% 10% 28% 26% 15% 6%	488
August	1st to 10th	Day	14% 12% 25% 24% 16% 9%	446
	11th to 20th	Day	15% 9% 28% 23% 15% 9%	439
	21st to end	Day	13% 9% 28% 25% 15% 10%	495
September	1st to 10th	Day	16% 12% 22% 25% 16% 9%	450
	11th to 20th	Day	11% 10% 26% 27% 19% 8%	450
	21st to end	Day	25% 15% 24% 21% 12% 3	450
October	1st to 10th	Day	19% 15% 25% 22% 15% 4	450
	11th to 20th	Day	24% 22% 25% 18% 10% 1	450
	21st to end	Day	29% 23% 26% 14% 7% 1	495
November	1st to 10th	Day	23% 20% 27% 20% 8% 2	455
	11th to 20th	Day	32% 26% 24% 12% 6%	233
	21st to end	Day	34% 24% 29% 9% 4 1	180
December	1st to 10th	Day	37% 29% 21% 9% 2 2	180
	11th to 20th	Day	43% 24% 21% 11% 2	180
	21st to end	Day	40% 25% 22% 9% 4	220
January	1st to 10th	Night	35% 31% 22% 10% 3	760
	11th to 20th	Night	34% 29% 26% 11% 1	729
	21st to end	Night	34% 32% 21% 12% 1	792
February	1st to 10th	Night	31% 29% 25% 15% 1	720
	11th to 20th	Night	34% 35% 23% 8%	703
	21st to end	Night	34% 31% 24% 9% 1	592
March	1st to 10th	Night	29% 26% 26% 16% 2	720
	11th to 20th	Night	32% 27% 21% 13% 5% 1	720
	21st to end	Night	26% 25% 27% 16% 6% 1	792
April	1st to 10th	Night	25% 28% 27% 16% 4	720
	11th to 20th	Night	23% 20% 26% 21% 9%	711
	21st to end	Night	24% 22% 23% 24% 6%	602
May	1st to 10th	Night	26% 16% 23% 26% 9% 1	540
	11th to 20th	Night	22% 17% 23% 27% 10% 1	531
	21st to end	Night	12% 9% 23% 28% 26% 2	486
June	1st to 10th	Night	11% 9% 26% 32% 20% 1	360
	11th to 20th	Night	15% 11% 24% 30% 19% 1	360
	21st to end	Night	12% 9% 27% 39% 14% 1	360
July	1st to 10th	Night	13% 6% 21% 32% 22% 5%	480
	11th to 20th	Night	8% 7% 21% 33% 27% 4	522
	21st to end	Night	10% 8% 20% 38% 23% 2	591
August	1st to 10th	Night	11% 6% 17% 37% 27% 2	537
	11th to 20th	Night	11% 7% 18% 37% 24% 4	534
	21st to end	Night	12% 8% 19% 35% 25% 3	744
September	1st to 10th	Night	14% 8% 23% 28% 22% 5%	720
	11th to 20th	Night	13% 8% 17% 32% 27% 3	720
	21st to end	Night	21% 13% 18% 29% 18% 2	720
October	1st to 10th	Night	18% 16% 20% 24% 19% 3	720
	11th to 20th	Night	22% 19% 24% 23% 11% 1	720
	21st to end	Night	27% 21% 23% 20% 8% 1	792
November	1st to 10th	Night	19% 18% 23% 28% 10% 1	740
	11th to 20th	Night	28% 19% 25% 19% 7% 1	760
	21st to end	Night	25% 27% 25% 17% 4 1	760
December	1st to 10th	Night	32% 29% 21% 14% 5%	760
	11th to 20th	Night	29% 30% 22% 16% 3	760
	21st to end	Night	28% 28% 25% 16% 2	836

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