Waterfall Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waterfall Creek Observatory clear sky chart from 2005-11-06 to 2026-08-30.

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% 7% 2 6% 4 4 4 4 5% 7% 43%	143734
	Night	13% 8% 3 6% 4 4 4 3 5% 6% 45%	138778
Transparency	Day	39% 5% 11% 25% 17% 3	147330
	Night	39% 5% 11% 24% 18% 4	143262
Seeing	Day	19% 12% 28% 24% 13% 3	18070
	Night	18% 12% 30% 25% 12% 2	27781

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% 11% 3 9% 4 4 3 2 4 5% 43%	4848
	11th to 20th	Day	7% 8% 3 7% 3 4 4 3 4 6% 50%	5310
	21st to end	Day	17% 7% 3 7% 4 4 3 2 4 5% 44%	5812
February	1st to 10th	Day	15% 11% 3 8% 4 5% 4 3 4 6% 37%	1890
	11th to 20th	Day	16% 8% 2 7% 4 4 4 4 4 6% 39%	2003
	21st to end	Day	14% 10% 2 6% 5% 5% 4 3 6% 6% 39%	1730
March	1st to 10th	Day	16% 13% 2 6% 3 3 3 3 4 4 43%	4829
	11th to 20th	Day	10% 6% 2 4 3 3 3 3 5% 7% 53%	5090
	21st to end	Day	14% 7% 2 7% 5% 4 4 4 6% 7% 39%	5785
April	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 5% 8% 44%	2520
	11th to 20th	Day	16% 9% 2 6% 5% 4 4 3 6% 5% 39%	2494
	21st to end	Day	18% 8% 3 6% 5% 5% 4 3 6% 6% 36%	2520
May	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 5% 6% 8% 34%	7021
	11th to 20th	Day	15% 7% 3 8% 5% 5% 4 3 6% 7% 37%	8001
	21st to end	Day	21% 9% 3 7% 5% 4 4 3 5% 6% 33%	9047
June	1st to 10th	Day	10% 6% 2 6% 5% 4 6% 5% 6% 9% 42%	2940
	11th to 20th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 47%	2940
	21st to end	Day	6% 4 2 5% 4 6% 4 5% 8% 9% 48%	2940
July	1st to 10th	Day	9% 4 2 6% 5% 5% 5% 4 7% 9% 44%	8280
	11th to 20th	Day	5% 4 2 7% 4 5% 6% 5% 7% 11% 45%	8025
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 7% 11% 42%	8337
August	1st to 10th	Day	5% 3 2 4 4 4 4 4 7% 9% 54%	4364
	11th to 20th	Day	12% 5% 2 6% 5% 5% 4 4 5% 8% 45%	3978
	21st to end	Day	8% 4 2 5% 3 4 5% 4 5% 9% 52%	4420
September	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 5% 7% 50%	2400
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 6% 7% 48%	2400
	21st to end	Day	10% 6% 2 5% 4 3 4 3 5% 7% 51%	2142
October	1st to 10th	Day	9% 4 2 5% 4 3 3 3 4 6% 58%	2000
	11th to 20th	Day	13% 6% 2 5% 3 2 3 2 4 5% 54%	2000
	21st to end	Day	19% 8% 2 5% 3 3 4 2 3 4 47%	2200
November	1st to 10th	Day	12% 6% 2 4 3 3 4 3 4 5% 53%	1922
	11th to 20th	Day	12% 8% 3 6% 4 3 3 3 5% 6% 47%	1890
	21st to end	Day	17% 10% 4 6% 4 3 3 3 4 5% 43%	1808
December	1st to 10th	Day	10% 9% 3 6% 4 3 3 3 4 5% 50%	2690
	11th to 20th	Day	13% 11% 4 7% 5% 3 4 3 4 5% 41%	3088
	21st to end	Day	18% 20% 4 8% 4 4 4 3 4 4 28%	4070
January	1st to 10th	Night	14% 9% 5% 10% 5% 4 4 3 4 4 39%	8072
	11th to 20th	Night	9% 8% 3 9% 5% 3 4 3 4 5% 48%	7680
	21st to end	Night	15% 9% 4 7% 6% 4 4 3 4 5% 40%	8402
February	1st to 10th	Night	17% 10% 3 7% 4 3 3 3 5% 7% 39%	2730
	11th to 20th	Night	16% 7% 3 8% 4 3 3 3 4 6% 43%	2501
	21st to end	Night	15% 8% 3 7% 4 4 3 3 4 5% 43%	2076
March	1st to 10th	Night	17% 13% 3 6% 4 3 4 2 4 4 41%	5287
	11th to 20th	Night	11% 9% 2 6% 3 3 3 4 4 5% 48%	5090
	21st to end	Night	14% 8% 3 7% 5% 4 4 3 5% 7% 39%	5384
April	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 6% 8% 49%	2100
	11th to 20th	Night	14% 7% 3 5% 5% 4 4 3 4 7% 45%	2075
	21st to end	Night	18% 8% 2 6% 4 4 3 3 5% 6% 41%	2100
May	1st to 10th	Night	16% 7% 2 6% 4 4 4 4 6% 8% 39%	5832
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 5% 8% 43%	4855
	21st to end	Night	20% 11% 3 8% 5% 5% 4 3 5% 6% 30%	5139
June	1st to 10th	Night	9% 5% 1 5% 4 4 5% 4 6% 9% 47%	1680
	11th to 20th	Night	7% 4 2 4 3 3 3 3 6% 10% 55%	1680
	21st to end	Night	4 3 1 4 3 4 4 4 6% 10% 58%	1680
July	1st to 10th	Night	9% 4 2 6% 4 5% 4 4 6% 9% 48%	4708
	11th to 20th	Night	4 4 2 5% 4 4 5% 4 7% 9% 52%	4943
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 9% 48%	5770
August	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 7% 61%	3016
	11th to 20th	Night	9% 6% 2 5% 4 4 4 3 6% 8% 49%	3290
	21st to end	Night	5% 4 1 4 3 3 3 4 6% 8% 59%	3676
September	1st to 10th	Night	10% 5% 2 4 4 3 4 3 5% 7% 53%	2000
	11th to 20th	Night	9% 6% 2 5% 3 3 3 4 5% 7% 52%	2000
	21st to end	Night	10% 5% 2 4 3 4 3 3 5% 6% 55%	2232
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 4 6% 63%	2400
	11th to 20th	Night	12% 6% 2 3 4 3 3 2 4 4 55%	2400
	21st to end	Night	20% 7% 2 4 3 3 3 2 3 5% 48%	2640
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 6% 56%	2592
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 4 6% 50%	2730
	21st to end	Night	18% 10% 3 6% 3 3 2 2 4 5% 44%	2809
December	1st to 10th	Night	12% 9% 2 5% 4 3 4 3 5% 6% 47%	4720
	11th to 20th	Night	15% 9% 4 6% 4 4 4 3 4 5% 44%	5339
	21st to end	Night	22% 17% 5% 8% 4 4 3 3 3 5% 27%	7150

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	45% 3 10% 26% 14% 3	4849
	11th to 20th	Day	37% 3 7% 29% 20% 6%	5310
	21st to end	Day	45% 3 9% 18% 16% 10%	5812
February	1st to 10th	Day	49% 3 11% 22% 13% 1	1890
	11th to 20th	Day	45% 5% 11% 20% 15% 5%	2013
	21st to end	Day	45% 4 8% 23% 14% 7%	1730
March	1st to 10th	Day	45% 3 6% 21% 15% 10%	4829
	11th to 20th	Day	32% 3 7% 26% 22% 9%	5090
	21st to end	Day	42% 6% 13% 28% 11% 1	5787
April	1st to 10th	Day	39% 4 12% 24% 20% 2	2520
	11th to 20th	Day	45% 4 10% 20% 17% 3	2494
	21st to end	Day	48% 5% 10% 22% 13% 1	2520
May	1st to 10th	Day	45% 7% 11% 23% 14% 1	7056
	11th to 20th	Day	46% 6% 11% 20% 16% 1	8005
	21st to end	Day	52% 5% 8% 20% 13% 1	9061
June	1st to 10th	Day	38% 7% 13% 26% 15% 2	2940
	11th to 20th	Day	31% 6% 12% 30% 19% 3	2940
	21st to end	Day	29% 7% 19% 25% 16% 4	2940
July	1st to 10th	Day	36% 7% 13% 26% 17% 2	8211
	11th to 20th	Day	32% 9% 16% 27% 14% 1	7950
	21st to end	Day	33% 8% 19% 30% 9% 1	8155
August	1st to 10th	Day	24% 6% 16% 32% 21%	4350
	11th to 20th	Day	37% 6% 13% 25% 17% 2	4014
	21st to end	Day	29% 6% 14% 36% 12% 3	4419
September	1st to 10th	Day	34% 6% 11% 27% 17% 5%	2400
	11th to 20th	Day	35% 5% 8% 26% 25% 2	2400
	21st to end	Day	33% 5% 6% 27% 26% 3	2142
October	1st to 10th	Day	17% 3 6% 19% 43% 13%	3260
	11th to 20th	Day	23% 3 5% 22% 38% 9%	3240
	21st to end	Day	32% 2 6% 32% 24% 4	3538
November	1st to 10th	Day	34% 4 9% 25% 21% 6%	1922
	11th to 20th	Day	38% 3 7% 24% 21% 7%	1890
	21st to end	Day	45% 3 8% 25% 18% 2	1808
December	1st to 10th	Day	37% 3 7% 37% 14% 1	2690
	11th to 20th	Day	45% 3 7% 23% 20% 1	3085
	21st to end	Day	60% 5% 10% 14% 11% 1	4070
January	1st to 10th	Night	49% 4 10% 23% 13% 1	8073
	11th to 20th	Night	38% 4 5% 24% 24% 4	7680
	21st to end	Night	48% 3 7% 20% 18% 4	8402
February	1st to 10th	Night	46% 4 10% 22% 15% 2	2730
	11th to 20th	Night	44% 3 11% 22% 17% 3	2502
	21st to end	Night	44% 3 7% 23% 18% 5%	2076
March	1st to 10th	Night	48% 3 6% 21% 16% 6%	5287
	11th to 20th	Night	38% 5% 8% 22% 18% 9%	5090
	21st to end	Night	43% 6% 13% 25% 12% 1	5384
April	1st to 10th	Night	34% 4 13% 25% 21% 3	2100
	11th to 20th	Night	40% 4 11% 23% 17% 5%	2075
	21st to end	Night	46% 3 9% 25% 16% 1	2100
May	1st to 10th	Night	42% 7% 15% 24% 11% 1	5862
	11th to 20th	Night	39% 6% 12% 26% 14% 3	4856
	21st to end	Night	55% 6% 9% 18% 10% 2	5149
June	1st to 10th	Night	32% 7% 15% 24% 20% 2	1680
	11th to 20th	Night	24% 5% 13% 34% 20% 4	1680
	21st to end	Night	21% 7% 17% 31% 18% 6%	1680
July	1st to 10th	Night	32% 7% 16% 24% 19% 2	4670
	11th to 20th	Night	28% 9% 17% 29% 16% 1	4898
	21st to end	Night	31% 7% 18% 33% 10% 1	5641
August	1st to 10th	Night	21% 6% 18% 32% 22% 1	3006
	11th to 20th	Night	34% 6% 17% 25% 16% 3	3320
	21st to end	Night	23% 5% 15% 38% 16% 3	3676
September	1st to 10th	Night	31% 5% 10% 28% 21% 5%	2000
	11th to 20th	Night	31% 5% 10% 27% 25% 2	2000
	21st to end	Night	30% 5% 9% 25% 28% 4	2232
October	1st to 10th	Night	14% 2 6% 17% 47% 14%	3920
	11th to 20th	Night	24% 2 6% 21% 33% 14%	3899
	21st to end	Night	32% 3 7% 26% 27% 5%	4252
November	1st to 10th	Night	31% 4 11% 27% 22% 5%	2592
	11th to 20th	Night	36% 3 7% 24% 23% 7%	2730
	21st to end	Night	44% 2 6% 25% 20% 2	2809
December	1st to 10th	Night	39% 4 9% 31% 17% 1	4720
	11th to 20th	Night	44% 3 9% 23% 20% 2	5341
	21st to end	Night	61% 4 9% 17% 7% 2	7150

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	29% 23% 35% 10% 3	330
	11th to 20th	Day	31% 27% 35% 7% 1	330
	21st to end	Day	24% 29% 35% 10% 1	363
February	1st to 10th	Day	27% 27% 33% 11% 2	330
	11th to 20th	Day	35% 24% 32% 7% 1 1	330
	21st to end	Day	35% 24% 31% 9% 1	273
March	1st to 10th	Day	29% 21% 37% 11% 1	330
	11th to 20th	Day	35% 19% 35% 9% 2	330
	21st to end	Day	33% 21% 36% 9% 2	449
April	1st to 10th	Day	25% 19% 36% 16% 4 1	540
	11th to 20th	Day	28% 24% 28% 16% 4 1	532
	21st to end	Day	26% 18% 33% 18% 4 1	540
May	1st to 10th	Day	21% 20% 35% 18% 5% 1	543
	11th to 20th	Day	21% 14% 32% 22% 10% 2	757
	21st to end	Day	19% 8% 33% 26% 11% 3	844
June	1st to 10th	Day	13% 6% 26% 29% 21% 5%	780
	11th to 20th	Day	8% 4 26% 37% 19% 4	780
	21st to end	Day	6% 8% 32% 33% 18% 3	780
July	1st to 10th	Day	12% 3 18% 32% 27% 8%	771
	11th to 20th	Day	6% 3 21% 38% 27% 5%	768
	21st to end	Day	9% 2 20% 35% 27% 6%	849
August	1st to 10th	Day	10% 3 18% 39% 23% 7%	776
	11th to 20th	Day	14% 3 18% 32% 26% 6%	568
	21st to end	Day	12% 2 16% 31% 28% 10%	619
September	1st to 10th	Day	13% 4 18% 35% 22% 7%	530
	11th to 20th	Day	10% 3 20% 32% 25% 10%	530
	21st to end	Day	13% 10% 24% 28% 18% 7%	462
October	1st to 10th	Day	11% 10% 31% 34% 10% 3	330
	11th to 20th	Day	22% 13% 36% 22% 6% 1	330
	21st to end	Day	34% 18% 29% 16% 2	363
November	1st to 10th	Day	17% 18% 37% 22% 4 2	330
	11th to 20th	Day	24% 17% 37% 15% 6%	330
	21st to end	Day	30% 17% 32% 14% 5% 1	330
December	1st to 10th	Day	22% 23% 35% 14% 4 2	330
	11th to 20th	Day	27% 22% 36% 13% 2	330
	21st to end	Day	31% 22% 35% 9% 2 1	363
January	1st to 10th	Night	22% 23% 37% 16% 3	1050
	11th to 20th	Night	25% 26% 34% 12% 3	1050
	21st to end	Night	22% 22% 39% 15% 2	1155
February	1st to 10th	Night	24% 20% 37% 17% 1	1050
	11th to 20th	Night	25% 21% 38% 15% 1	866
	21st to end	Night	25% 22% 36% 15% 2	692
March	1st to 10th	Night	27% 16% 37% 18% 2	751
	11th to 20th	Night	27% 14% 36% 20% 3	630
	21st to end	Night	24% 19% 34% 19% 4	693
April	1st to 10th	Night	17% 19% 40% 21% 3	630
	11th to 20th	Night	22% 16% 34% 23% 5%	623
	21st to end	Night	22% 13% 37% 21% 6%	630
May	1st to 10th	Night	18% 9% 37% 29% 7%	630
	11th to 20th	Night	19% 8% 33% 25% 13% 1	621
	21st to end	Night	14% 6% 28% 33% 16% 3	683
June	1st to 10th	Night	10% 4 22% 34% 28% 2	630
	11th to 20th	Night	8% 3 23% 42% 22% 2	630
	21st to end	Night	5% 2 26% 40% 25% 2	630
July	1st to 10th	Night	9% 3 12% 37% 30% 9%	615
	11th to 20th	Night	6% 2 14% 42% 32% 5%	612
	21st to end	Night	7% 2 13% 42% 31% 4	690
August	1st to 10th	Night	7% 2 15% 41% 32% 3	627
	11th to 20th	Night	8% 2 15% 40% 31% 4	624
	21st to end	Night	8% 1 14% 37% 35% 7%	687
September	1st to 10th	Night	12% 3 15% 36% 30% 5%	600
	11th to 20th	Night	12% 2 13% 37% 31% 5%	600
	21st to end	Night	13% 6% 24% 28% 25% 5%	768
October	1st to 10th	Night	9% 4 29% 32% 23% 3	800
	11th to 20th	Night	17% 11% 33% 27% 11% 1	800
	21st to end	Night	26% 12% 34% 22% 5%	880
November	1st to 10th	Night	14% 14% 40% 25% 8% 1	820
	11th to 20th	Night	19% 15% 33% 26% 6%	840
	21st to end	Night	25% 17% 34% 19% 5%	919
December	1st to 10th	Night	24% 16% 37% 19% 4	1050
	11th to 20th	Night	25% 15% 36% 21% 3	1050
	21st to end	Night	28% 19% 33% 17% 2	1155

Page generated at 2026-08-27 03:07:12. Version ac07

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