Falling Water Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Falling Water Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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% 6% 2 5% 4 4 4 3 5% 7% 48%	132526
	Night	13% 6% 2 5% 3 3 3 3 5% 6% 52%	130972
Transparency	Day	34% 6% 9% 20% 19% 11%	136344
	Night	32% 5% 10% 19% 20% 13%	135218
Seeing	Day	14% 8% 23% 29% 21% 6%	16850
	Night	15% 7% 25% 36% 15% 1	26842

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% 7% 2 5% 3 3 3 2 4 5% 55%	5289
	11th to 20th	Day	13% 6% 2 4 2 2 3 3 4 4 56%	5310
	21st to end	Day	21% 7% 2 5% 2 2 3 2 4 6% 45%	6450
February	1st to 10th	Day	15% 8% 2 6% 3 3 3 2 4 5% 49%	2100
	11th to 20th	Day	16% 7% 2 5% 3 2 3 3 5% 6% 47%	2049
	21st to end	Day	14% 7% 2 4 2 3 3 3 4 5% 53%	1730
March	1st to 10th	Day	13% 6% 2 5% 3 3 3 2 4 6% 54%	4865
	11th to 20th	Day	14% 7% 2 6% 3 3 3 2 3 4 53%	5090
	21st to end	Day	14% 7% 2 5% 4 3 3 3 5% 6% 48%	5583
April	1st to 10th	Day	14% 8% 3 6% 4 4 3 3 4 6% 46%	2310
	11th to 20th	Day	19% 6% 2 6% 4 4 3 3 5% 5% 43%	2385
	21st to end	Day	14% 8% 2 6% 5% 4 4 3 4 6% 44%	2612
May	1st to 10th	Day	19% 8% 2 6% 4 3 4 3 6% 8% 36%	5992
	11th to 20th	Day	11% 5% 2 5% 4 4 4 3 6% 9% 46%	5992
	21st to end	Day	14% 8% 2 7% 5% 5% 5% 4 7% 8% 36%	6577
June	1st to 10th	Day	6% 5% 2 5% 4 5% 5% 5% 6% 9% 48%	2601
	11th to 20th	Day	7% 6% 2 5% 4 4 5% 4 7% 9% 47%	2600
	21st to end	Day	7% 5% 2 5% 7% 6% 6% 4 7% 9% 41%	2600
July	1st to 10th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	5900
	11th to 20th	Day	6% 4 2 5% 5% 6% 5% 5% 7% 9% 47%	5900
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 10% 44%	6422
August	1st to 10th	Day	1 2 1 3 3 3 3 3 5% 9% 66%	4046
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 10% 59%	3846
	21st to end	Day	4 3 2 6% 4 6% 6% 5% 7% 11% 46%	4221
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 4 5% 6% 43%	2200
	11th to 20th	Day	10% 6% 3 6% 6% 5% 5% 4 6% 8% 43%	2200
	21st to end	Day	9% 4 2 6% 5% 4 5% 3 6% 7% 49%	2200
October	1st to 10th	Day	6% 4 2 4 5% 4 4 3 5% 7% 55%	2200
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 4 6% 54%	2125
	21st to end	Day	11% 4 2 5% 3 3 2 3 4 5% 58%	2200
November	1st to 10th	Day	15% 8% 2 5% 4 4 3 3 4 6% 48%	2053
	11th to 20th	Day	10% 7% 2 5% 3 3 4 4 4 6% 52%	1890
	21st to end	Day	16% 8% 2 5% 4 2 3 2 4 5% 47%	1890
December	1st to 10th	Day	23% 10% 3 6% 3 2 2 2 4 4 41%	3030
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 5% 5% 45%	3481
	21st to end	Day	13% 6% 2 3 3 2 2 2 3 4 60%	4587
January	1st to 10th	Night	13% 5% 2 5% 2 2 3 2 4 5% 56%	7634
	11th to 20th	Night	9% 4 1 3 2 2 2 3 5% 4 65%	7680
	21st to end	Night	27% 6% 2 5% 3 3 2 2 4 5% 42%	7806
February	1st to 10th	Night	15% 8% 2 5% 2 2 3 2 4 4 52%	2520
	11th to 20th	Night	17% 6% 2 4 3 2 2 3 5% 6% 50%	2458
	21st to end	Night	16% 7% 2 5% 4 3 3 3 4 5% 50%	2076
March	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 5% 7% 47%	5216
	11th to 20th	Night	14% 7% 2 4 3 3 3 2 3 5% 53%	5090
	21st to end	Night	16% 10% 2 4 3 3 3 3 4 6% 47%	5588
April	1st to 10th	Night	13% 7% 2 5% 4 2 3 3 5% 6% 49%	2310
	11th to 20th	Night	18% 7% 2 5% 3 3 2 3 4 5% 46%	2179
	21st to end	Night	19% 8% 2 5% 4 3 2 2 4 5% 46%	2006
May	1st to 10th	Night	22% 9% 2 5% 4 2 3 3 4 6% 39%	4143
	11th to 20th	Night	8% 5% 2 5% 5% 4 5% 4 6% 7% 50%	4143
	21st to end	Night	15% 6% 2 6% 4 3 4 3 6% 10% 40%	4542
June	1st to 10th	Night	6% 3 1 3 3 3 3 4 7% 8% 60%	1800
	11th to 20th	Night	5% 4 2 4 4 4 3 3 5% 8% 60%	1800
	21st to end	Night	7% 5% 1 4 3 3 4 4 6% 8% 54%	1800
July	1st to 10th	Night	11% 6% 3 6% 4 4 4 4 6% 10% 42%	4078
	11th to 20th	Night	5% 3 2 5% 3 4 4 4 7% 10% 53%	4077
	21st to end	Night	7% 6% 2 5% 4 4 4 4 6% 9% 48%	4449
August	1st to 10th	Night	1 1 1 3 2 3 3 2 3 8% 74%	3109
	11th to 20th	Night	3 2 1 3 3 3 3 4 6% 11% 61%	3213
	21st to end	Night	4 5% 2 5% 3 4 5% 4 6% 10% 54%	3683
September	1st to 10th	Night	8% 5% 2 6% 5% 4 4 4 5% 7% 49%	2200
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 3 6% 8% 47%	2200
	21st to end	Night	7% 5% 2 5% 4 5% 5% 3 6% 7% 52%	2200
October	1st to 10th	Night	6% 4 2 3 3 3 3 3 4 6% 63%	2200
	11th to 20th	Night	12% 4 1 4 3 3 3 3 5% 5% 58%	2253
	21st to end	Night	14% 4 2 4 2 2 1 2 3 4 62%	2640
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 3 6% 55%	2460
	11th to 20th	Night	10% 6% 1 4 2 2 3 2 4 6% 57%	2730
	21st to end	Night	18% 7% 1 4 3 3 3 3 4 7% 49%	2730
December	1st to 10th	Night	22% 8% 2 6% 3 3 3 3 4 5% 41%	4380
	11th to 20th	Night	19% 9% 2 5% 3 3 2 2 3 5% 48%	4946
	21st to end	Night	16% 6% 2 3 2 2 2 2 3 4 58%	6633

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 5% 21% 26% 12%	5290
	11th to 20th	Day	33% 2 4 15% 26% 22%	5310
	21st to end	Day	42% 3 5% 14% 24% 12%	6450
February	1st to 10th	Day	38% 4 6% 12% 22% 18%	2100
	11th to 20th	Day	38% 4 7% 19% 19% 14%	2059
	21st to end	Day	34% 4 5% 17% 23% 16%	1730
March	1st to 10th	Day	32% 4 5% 16% 18% 25%	4865
	11th to 20th	Day	36% 4 5% 9% 15% 32%	5090
	21st to end	Day	36% 5% 8% 18% 20% 13%	5585
April	1st to 10th	Day	41% 4 8% 17% 17% 13%	2310
	11th to 20th	Day	43% 5% 7% 16% 18% 11%	2385
	21st to end	Day	41% 5% 9% 18% 17% 10%	2612
May	1st to 10th	Day	44% 7% 9% 18% 17% 6%	6030
	11th to 20th	Day	34% 6% 12% 17% 21% 10%	5996
	21st to end	Day	42% 8% 11% 24% 12% 2	6590
June	1st to 10th	Day	29% 8% 14% 27% 19% 3	2601
	11th to 20th	Day	32% 6% 13% 24% 19% 5%	2600
	21st to end	Day	37% 9% 12% 24% 15% 4	2600
July	1st to 10th	Day	43% 8% 16% 28% 5%	5836
	11th to 20th	Day	30% 9% 16% 31% 13% 2	5831
	21st to end	Day	30% 10% 16% 26% 18% 1	6240
August	1st to 10th	Day	14% 6% 12% 40% 28% 1	4032
	11th to 20th	Day	20% 6% 23% 37% 12% 2	3882
	21st to end	Day	28% 11% 18% 24% 18% 2	4220
September	1st to 10th	Day	40% 6% 10% 18% 18% 8%	2200
	11th to 20th	Day	36% 9% 12% 20% 18% 5%	2200
	21st to end	Day	33% 6% 9% 21% 17% 13%	2200
October	1st to 10th	Day	17% 4 7% 12% 26% 34%	3590
	11th to 20th	Day	25% 4 8% 19% 24% 21%	3443
	21st to end	Day	27% 4 5% 17% 34% 13%	3538
November	1st to 10th	Day	38% 5% 8% 18% 20% 12%	2053
	11th to 20th	Day	34% 4 7% 16% 20% 18%	1890
	21st to end	Day	40% 4 6% 16% 21% 14%	1890
December	1st to 10th	Day	48% 3 5% 17% 17% 11%	3030
	11th to 20th	Day	40% 6% 7% 11% 21% 15%	3479
	21st to end	Day	30% 3 4 15% 28% 19%	4587
January	1st to 10th	Night	32% 3 6% 17% 27% 15%	7635
	11th to 20th	Night	24% 2 4 17% 29% 25%	7680
	21st to end	Night	46% 3 4 10% 23% 15%	7806
February	1st to 10th	Night	36% 4 6% 12% 23% 19%	2520
	11th to 20th	Night	36% 4 7% 18% 19% 16%	2458
	21st to end	Night	37% 4 7% 13% 21% 18%	2076
March	1st to 10th	Night	36% 5% 6% 19% 18% 17%	5216
	11th to 20th	Night	35% 5% 6% 11% 16% 28%	5090
	21st to end	Night	38% 5% 8% 18% 18% 13%	5588
April	1st to 10th	Night	36% 6% 10% 17% 15% 16%	2310
	11th to 20th	Night	41% 5% 9% 14% 16% 16%	2179
	21st to end	Night	42% 5% 8% 18% 17% 10%	2006
May	1st to 10th	Night	47% 5% 8% 17% 14% 9%	4170
	11th to 20th	Night	32% 7% 11% 19% 18% 13%	4144
	21st to end	Night	38% 8% 14% 26% 11% 3	4551
June	1st to 10th	Night	20% 9% 16% 33% 19% 3	1800
	11th to 20th	Night	23% 6% 15% 30% 21% 5%	1800
	21st to end	Night	26% 9% 18% 28% 16% 3	1800
July	1st to 10th	Night	36% 10% 23% 26% 4	4035
	11th to 20th	Night	24% 9% 22% 31% 12% 1	4026
	21st to end	Night	30% 9% 20% 26% 12% 3	4320
August	1st to 10th	Night	11% 5% 15% 45% 23%	3099
	11th to 20th	Night	17% 7% 30% 35% 9% 2	3243
	21st to end	Night	25% 12% 20% 24% 17% 2	3683
September	1st to 10th	Night	33% 7% 14% 20% 18% 8%	2200
	11th to 20th	Night	33% 9% 15% 22% 15% 5%	2200
	21st to end	Night	30% 7% 12% 21% 18% 13%	2200
October	1st to 10th	Night	14% 4 8% 15% 23% 36%	3590
	11th to 20th	Night	22% 4 9% 17% 29% 19%	3661
	21st to end	Night	25% 3 5% 18% 33% 15%	4252
November	1st to 10th	Night	32% 4 7% 19% 23% 14%	2460
	11th to 20th	Night	29% 4 9% 21% 20% 18%	2730
	21st to end	Night	37% 4 9% 16% 20% 15%	2730
December	1st to 10th	Night	46% 4 7% 15% 16% 12%	4380
	11th to 20th	Night	41% 3 5% 11% 20% 19%	4947
	21st to end	Night	32% 3 4 15% 28% 18%	6633

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	19% 14% 37% 22% 6% 1	330
	11th to 20th	Day	22% 15% 32% 22% 7% 1	330
	21st to end	Day	20% 15% 38% 20% 7%	363
February	1st to 10th	Day	23% 13% 31% 24% 8%	330
	11th to 20th	Day	24% 16% 34% 23% 2 1	330
	21st to end	Day	24% 14% 41% 18% 4	273
March	1st to 10th	Day	24% 16% 36% 22% 3	330
	11th to 20th	Day	16% 18% 39% 22% 5%	330
	21st to end	Day	18% 15% 38% 22% 6% 1	363
April	1st to 10th	Day	21% 16% 38% 22% 4	330
	11th to 20th	Day	22% 17% 36% 22% 4	423
	21st to end	Day	19% 15% 40% 21% 5%	632
May	1st to 10th	Day	19% 11% 38% 25% 6%	753
	11th to 20th	Day	18% 10% 32% 30% 8% 2	775
	21st to end	Day	16% 8% 30% 31% 14% 1	844
June	1st to 10th	Day	8% 4 18% 44% 24% 4	731
	11th to 20th	Day	11% 2 17% 48% 21% 3	730
	21st to end	Day	7% 2 15% 35% 32% 9%	730
July	1st to 10th	Day	13% 2 10% 34% 32% 10%	721
	11th to 20th	Day	6% 1 5% 35% 45% 8%	718
	21st to end	Day	5% 2 5% 33% 42% 12%	794
August	1st to 10th	Day	2 1 4 34% 46% 13%	616
	11th to 20th	Day	8% 1 4 33% 39% 15%	517
	21st to end	Day	5% 1 6% 26% 40% 21%	531
September	1st to 10th	Day	11% 1 7% 27% 33% 20%	330
	11th to 20th	Day	6% 1 3 29% 45% 16%	330
	21st to end	Day	9% 2 6% 29% 40% 14%	330
October	1st to 10th	Day	5% 2 13% 32% 38% 10%	330
	11th to 20th	Day	10% 3 20% 38% 24% 5%	330
	21st to end	Day	18% 14% 23% 28% 14% 3	363
November	1st to 10th	Day	16% 8% 27% 33% 11% 4	330
	11th to 20th	Day	20% 10% 25% 28% 12% 4	330
	21st to end	Day	22% 16% 31% 19% 10% 2	330
December	1st to 10th	Day	18% 10% 32% 28% 10% 2	330
	11th to 20th	Day	17% 17% 32% 23% 9% 1	330
	21st to end	Day	19% 10% 34% 26% 10% 1	363
January	1st to 10th	Night	18% 9% 31% 34% 8%	1050
	11th to 20th	Night	19% 11% 32% 31% 7%	1050
	21st to end	Night	22% 11% 29% 31% 7%	945
February	1st to 10th	Night	21% 12% 30% 30% 7%	840
	11th to 20th	Night	21% 13% 34% 28% 4	824
	21st to end	Night	21% 10% 43% 23% 2	692
March	1st to 10th	Night	22% 12% 34% 29% 3	718
	11th to 20th	Night	20% 10% 36% 30% 5%	630
	21st to end	Night	16% 11% 38% 30% 4	693
April	1st to 10th	Night	16% 10% 44% 28% 3	630
	11th to 20th	Night	20% 13% 40% 25% 2	623
	21st to end	Night	20% 12% 39% 22% 6%	630
May	1st to 10th	Night	19% 8% 40% 29% 4	630
	11th to 20th	Night	14% 8% 34% 37% 7% 1	621
	21st to end	Night	15% 5% 31% 35% 13%	683
June	1st to 10th	Night	5% 2 23% 48% 21% 1	600
	11th to 20th	Night	7% 3 26% 51% 14% 1	600
	21st to end	Night	7% 2 17% 46% 26% 2	600
July	1st to 10th	Night	10% 3 9% 45% 30% 3	585
	11th to 20th	Night	5% 1 8% 50% 34% 2	582
	21st to end	Night	5% 1 9% 48% 34% 3	657
August	1st to 10th	Night	2 1 4 49% 41% 3	597
	11th to 20th	Night	5% 1 5% 49% 38% 3	594
	21st to end	Night	6% 1 6% 39% 42% 6%	660
September	1st to 10th	Night	9% 2 6% 43% 35% 5%	600
	11th to 20th	Night	10% 2 8% 41% 37% 3	600
	21st to end	Night	9% 2 12% 41% 32% 4	600
October	1st to 10th	Night	7% 2 11% 46% 32% 3	600
	11th to 20th	Night	13% 3 20% 42% 20% 2	653
	21st to end	Night	16% 7% 24% 30% 20% 2	880
November	1st to 10th	Night	15% 7% 19% 41% 17% 1	820
	11th to 20th	Night	14% 7% 24% 38% 15% 1	1050
	21st to end	Night	21% 9% 26% 32% 11% 1	1050
December	1st to 10th	Night	19% 7% 28% 37% 9% 1	1050
	11th to 20th	Night	23% 9% 29% 31% 8%	1050
	21st to end	Night	18% 10% 29% 34% 9%	1155

Page generated at 2026-05-29 00:53:27. Version ac07

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