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 2025-04-26.

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% 44%	113650
	Night	13% 8% 3 6% 4 3 4 3 5% 6% 45%	115146
Transparency	Day	38% 5% 10% 25% 17% 4	117287
	Night	39% 4 10% 24% 19% 4	119652
Seeing	Day	19% 12% 28% 24% 13% 4	16106
	Night	19% 12% 30% 25% 12% 2	26066

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	14% 11% 3 10% 4 4 3 2 4 5% 40%	3732
	11th to 20th	Day	9% 9% 4 7% 4 4 4 3 4 6% 47%	4080
	21st to end	Day	19% 7% 3 7% 3 4 4 3 4 5% 42%	4488
February	1st to 10th	Day	16% 11% 3 9% 4 5% 4 3 4 6% 36%	1800
	11th to 20th	Day	16% 9% 2 7% 4 4 4 4 4 6% 39%	1905
	21st to end	Day	15% 10% 2 6% 5% 5% 4 3 6% 6% 39%	1650
March	1st to 10th	Day	16% 13% 2 5% 3 3 3 3 4 4 44%	4724
	11th to 20th	Day	10% 7% 2 4 3 3 3 3 5% 7% 53%	4980
	21st to end	Day	15% 7% 2 7% 5% 4 5% 4 6% 7% 39%	5660
April	1st to 10th	Day	12% 7% 2 6% 5% 4 4 3 5% 8% 44%	2400
	11th to 20th	Day	16% 9% 2 6% 5% 4 4 3 6% 5% 40%	2374
	21st to end	Day	19% 8% 3 6% 5% 5% 4 3 5% 6% 37%	2340
May	1st to 10th	Day	14% 8% 3 8% 5% 5% 5% 6% 7% 9% 32%	3765
	11th to 20th	Day	17% 8% 2 6% 4 4 4 3 6% 8% 38%	4287
	21st to end	Day	13% 7% 2 7% 5% 4 5% 3 5% 7% 41%	4824
June	1st to 10th	Day	9% 6% 2 6% 5% 4 6% 5% 6% 8% 42%	2660
	11th to 20th	Day	6% 4 2 5% 4 5% 5% 4 7% 9% 49%	2660
	21st to end	Day	5% 3 2 5% 4 6% 4 5% 8% 9% 48%	2660
July	1st to 10th	Day	12% 4 2 6% 5% 5% 5% 4 7% 8% 41%	4440
	11th to 20th	Day	4 3 1 6% 4 5% 5% 4 7% 11% 50%	4297
	21st to end	Day	8% 6% 2 8% 7% 6% 6% 6% 7% 10% 34%	4465
August	1st to 10th	Day	5% 3 2 4 4 4 4 4 7% 9% 54%	4104
	11th to 20th	Day	12% 5% 2 6% 5% 5% 5% 4 5% 8% 44%	3738
	21st to end	Day	8% 4 2 5% 3 4 5% 4 6% 9% 52%	4180
September	1st to 10th	Day	12% 5% 2 5% 3 4 4 4 5% 7% 50%	2280
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 6% 7% 48%	2280
	21st to end	Day	10% 6% 2 5% 4 3 4 3 5% 7% 51%	2036
October	1st to 10th	Day	9% 4 2 5% 4 3 3 3 4 6% 57%	1900
	11th to 20th	Day	14% 6% 2 5% 3 2 3 2 3 5% 54%	1900
	21st to end	Day	18% 8% 2 5% 3 3 4 2 3 4 47%	2090
November	1st to 10th	Day	12% 6% 2 4 3 3 4 3 4 5% 53%	1829
	11th to 20th	Day	12% 8% 3 5% 4 3 3 2 5% 7% 48%	1800
	21st to end	Day	16% 10% 4 6% 4 3 3 3 4 5% 44%	1722
December	1st to 10th	Day	10% 9% 3 6% 4 3 3 3 4 5% 50%	2610
	11th to 20th	Day	13% 11% 4 7% 5% 3 4 3 4 5% 41%	3008
	21st to end	Day	18% 21% 4 8% 4 4 4 3 4 4 28%	3982
January	1st to 10th	Night	15% 10% 5% 10% 5% 4 4 3 4 4 35%	6230
	11th to 20th	Night	11% 9% 3 10% 5% 3 4 3 4 5% 43%	5900
	21st to end	Night	17% 10% 4 6% 4 3 3 3 4 5% 41%	6490
February	1st to 10th	Night	18% 10% 3 7% 4 3 3 3 5% 7% 37%	2600
	11th to 20th	Night	16% 8% 3 8% 4 3 3 3 4 6% 42%	2379
	21st to end	Night	16% 9% 3 7% 4 4 3 3 4 5% 42%	1980
March	1st to 10th	Night	17% 13% 3 6% 4 3 4 2 4 4 41%	5171
	11th to 20th	Night	11% 9% 2 6% 3 3 3 4 4 5% 49%	4980
	21st to end	Night	14% 8% 3 7% 5% 4 4 4 5% 7% 38%	5267
April	1st to 10th	Night	11% 6% 2 5% 4 3 3 3 6% 7% 49%	2000
	11th to 20th	Night	14% 7% 3 5% 5% 3 4 2 4 7% 46%	1975
	21st to end	Night	19% 7% 2 6% 4 4 3 2 5% 7% 41%	1956
May	1st to 10th	Night	18% 7% 2 4 3 3 3 3 5% 7% 43%	3130
	11th to 20th	Night	15% 8% 2 6% 4 4 3 3 5% 8% 43%	2597
	21st to end	Night	13% 8% 3 7% 5% 5% 5% 3 6% 7% 38%	2743
June	1st to 10th	Night	8% 4 2 5% 4 4 5% 4 7% 10% 47%	1520
	11th to 20th	Night	6% 3 2 4 3 2 3 3 6% 11% 57%	1520
	21st to end	Night	3 3 1 4 3 4 4 4 7% 10% 58%	1520
July	1st to 10th	Night	11% 4 2 5% 4 5% 4 4 6% 9% 48%	2530
	11th to 20th	Night	5% 3 1 4 3 3 4 2 5% 8% 62%	2654
	21st to end	Night	9% 6% 2 8% 5% 5% 5% 4 7% 8% 41%	3098
August	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 7% 62%	2836
	11th to 20th	Night	9% 7% 2 5% 4 5% 4 3 6% 8% 48%	3091
	21st to end	Night	5% 4 1 4 3 3 3 4 6% 8% 58%	3476
September	1st to 10th	Night	10% 5% 2 4 4 3 3 3 5% 7% 54%	1900
	11th to 20th	Night	9% 6% 2 5% 3 3 3 4 6% 7% 53%	1900
	21st to end	Night	9% 5% 2 4 3 4 4 3 5% 6% 55%	2120
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 4 6% 63%	2280
	11th to 20th	Night	13% 6% 2 3 4 3 3 2 4 4 55%	2280
	21st to end	Night	19% 6% 2 4 3 3 3 2 4 5% 48%	2508
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 4 6% 56%	2465
	11th to 20th	Night	13% 6% 2 6% 4 3 4 3 4 6% 49%	2600
	21st to end	Night	17% 9% 3 5% 4 3 2 2 4 5% 45%	2675
December	1st to 10th	Night	13% 9% 2 5% 4 3 4 3 5% 6% 47%	4580
	11th to 20th	Night	15% 9% 4 6% 4 4 4 3 4 5% 43%	5199
	21st to end	Night	22% 17% 5% 8% 4 4 3 3 3 4 26%	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	48% 4 9% 22% 15% 3	3733
	11th to 20th	Day	40% 3 7% 27% 17% 6%	4080
	21st to end	Day	45% 3 9% 15% 16% 11%	4488
February	1st to 10th	Day	50% 3 10% 22% 12% 2	1800
	11th to 20th	Day	45% 5% 11% 19% 15% 5%	1915
	21st to end	Day	45% 4 8% 23% 13% 7%	1650
March	1st to 10th	Day	45% 3 5% 21% 15% 10%	4724
	11th to 20th	Day	32% 4 7% 25% 23% 9%	4980
	21st to end	Day	43% 6% 13% 27% 11% 1	5662
April	1st to 10th	Day	38% 4 12% 24% 20% 2	2400
	11th to 20th	Day	45% 4 10% 21% 17% 4	2374
	21st to end	Day	48% 5% 10% 22% 14% 1	2340
May	1st to 10th	Day	45% 10% 12% 21% 12% 1	3800
	11th to 20th	Day	44% 7% 11% 24% 13% 1	4291
	21st to end	Day	42% 6% 9% 23% 19% 1	4837
June	1st to 10th	Day	37% 7% 13% 25% 15% 2	2660
	11th to 20th	Day	29% 6% 13% 29% 19% 3	2660
	21st to end	Day	28% 7% 19% 25% 16% 5%	2660
July	1st to 10th	Day	39% 6% 12% 29% 11% 2	4371
	11th to 20th	Day	28% 7% 13% 35% 16% 2	4222
	21st to end	Day	40% 10% 15% 26% 7% 1	4325
August	1st to 10th	Day	25% 6% 16% 31% 21%	4090
	11th to 20th	Day	39% 6% 13% 24% 17% 2	3774
	21st to end	Day	29% 6% 14% 36% 12% 3	4179
September	1st to 10th	Day	34% 5% 11% 28% 17% 6%	2280
	11th to 20th	Day	35% 5% 8% 26% 25% 2	2280
	21st to end	Day	33% 5% 6% 28% 25% 2	2036
October	1st to 10th	Day	17% 3 6% 18% 43% 13%	3160
	11th to 20th	Day	23% 2 5% 22% 39% 9%	3140
	21st to end	Day	31% 3 6% 32% 25% 4	3428
November	1st to 10th	Day	34% 4 9% 24% 22% 7%	1829
	11th to 20th	Day	38% 3 7% 23% 21% 8%	1800
	21st to end	Day	44% 3 8% 25% 18% 2	1722
December	1st to 10th	Day	37% 3 7% 37% 15% 1	2610
	11th to 20th	Day	46% 3 7% 23% 20% 1	3005
	21st to end	Day	60% 5% 10% 13% 11% 2	3982
January	1st to 10th	Night	52% 4 8% 19% 15% 1	6230
	11th to 20th	Night	43% 5% 6% 24% 20% 3	5900
	21st to end	Night	47% 3 6% 20% 19% 5%	6490
February	1st to 10th	Night	48% 4 10% 22% 14% 2	2600
	11th to 20th	Night	45% 3 11% 21% 17% 3	2380
	21st to end	Night	45% 3 7% 23% 18% 5%	1980
March	1st to 10th	Night	48% 3 6% 21% 16% 6%	5171
	11th to 20th	Night	38% 5% 8% 22% 19% 9%	4980
	21st to end	Night	44% 6% 13% 24% 12% 1	5267
April	1st to 10th	Night	34% 4 12% 26% 21% 3	2000
	11th to 20th	Night	40% 4 11% 24% 17% 5%	1975
	21st to end	Night	45% 3 10% 25% 16% 2	1956
May	1st to 10th	Night	38% 8% 16% 22% 14% 2	3160
	11th to 20th	Night	39% 7% 13% 24% 15% 1	2598
	21st to end	Night	43% 7% 11% 23% 14% 1	2751
June	1st to 10th	Night	32% 7% 15% 24% 19% 2	1520
	11th to 20th	Night	22% 5% 13% 36% 21% 4	1520
	21st to end	Night	20% 7% 16% 31% 18% 7%	1520
July	1st to 10th	Night	34% 6% 15% 27% 15% 3	2490
	11th to 20th	Night	21% 5% 12% 39% 20% 2	2606
	21st to end	Night	38% 8% 16% 26% 12% 1	2999
August	1st to 10th	Night	20% 6% 18% 33% 22% 1	2826
	11th to 20th	Night	35% 6% 16% 24% 16% 3	3121
	21st to end	Night	24% 5% 15% 38% 15% 3	3476
September	1st to 10th	Night	31% 5% 10% 29% 21% 5%	1900
	11th to 20th	Night	31% 5% 11% 26% 25% 2	1900
	21st to end	Night	30% 5% 9% 26% 27% 3	2120
October	1st to 10th	Night	14% 2 6% 17% 47% 14%	3800
	11th to 20th	Night	24% 2 5% 21% 33% 15%	3779
	21st to end	Night	31% 3 7% 27% 28% 5%	4120
November	1st to 10th	Night	31% 4 11% 26% 23% 6%	2465
	11th to 20th	Night	37% 3 6% 23% 24% 7%	2600
	21st to end	Night	43% 3 6% 25% 21% 2	2675
December	1st to 10th	Night	38% 4 8% 31% 17% 1	4580
	11th to 20th	Night	45% 2 9% 23% 20% 2	5201
	21st to end	Night	62% 4 9% 16% 7% 2	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	29% 24% 34% 10% 3	300
	11th to 20th	Day	31% 25% 36% 7% 1	300
	21st to end	Day	23% 30% 35% 11% 1	330
February	1st to 10th	Day	29% 26% 33% 10% 2	300
	11th to 20th	Day	35% 25% 30% 8% 1 1	300
	21st to end	Day	35% 23% 32% 9% 1	249
March	1st to 10th	Day	29% 20% 38% 12% 1	300
	11th to 20th	Day	36% 18% 35% 10% 2	300
	21st to end	Day	35% 21% 33% 9% 2	412
April	1st to 10th	Day	26% 19% 34% 16% 4 1	500
	11th to 20th	Day	28% 23% 27% 17% 4 1	492
	21st to end	Day	27% 18% 32% 18% 4 1	480
May	1st to 10th	Day	22% 19% 35% 19% 5% 1	463
	11th to 20th	Day	20% 12% 31% 23% 11% 3	659
	21st to end	Day	15% 8% 35% 26% 12% 4	734
June	1st to 10th	Day	11% 6% 25% 30% 23% 5%	680
	11th to 20th	Day	8% 3 25% 39% 21% 4	680
	21st to end	Day	5% 7% 34% 32% 18% 4	680
July	1st to 10th	Day	13% 3 18% 31% 28% 8%	671
	11th to 20th	Day	5% 3 21% 37% 28% 6%	668
	21st to end	Day	9% 2 19% 36% 27% 7%	739
August	1st to 10th	Day	10% 3 17% 40% 24% 7%	676
	11th to 20th	Day	15% 3 20% 30% 25% 7%	488
	21st to end	Day	14% 2 14% 30% 29% 11%	539
September	1st to 10th	Day	13% 4 18% 34% 23% 8%	490
	11th to 20th	Day	11% 3 21% 32% 23% 10%	490
	21st to end	Day	13% 10% 24% 29% 18% 7%	426
October	1st to 10th	Day	12% 11% 30% 33% 11% 3	300
	11th to 20th	Day	23% 12% 38% 21% 5% 1	300
	21st to end	Day	32% 19% 28% 18% 3	330
November	1st to 10th	Day	17% 15% 38% 24% 4 2	300
	11th to 20th	Day	25% 17% 34% 16% 7%	300
	21st to end	Day	29% 17% 33% 15% 5% 1	300
December	1st to 10th	Day	22% 24% 34% 14% 4 2	300
	11th to 20th	Day	28% 21% 35% 13% 3	300
	21st to end	Day	33% 22% 33% 9% 2 1	330
January	1st to 10th	Night	22% 23% 36% 16% 3	1000
	11th to 20th	Night	25% 25% 34% 13% 3	1000
	21st to end	Night	22% 22% 39% 16% 2	1100
February	1st to 10th	Night	26% 20% 36% 17% 1	1000
	11th to 20th	Night	25% 21% 39% 14% 1	824
	21st to end	Night	26% 22% 36% 15% 2	660
March	1st to 10th	Night	27% 15% 36% 19% 2	715
	11th to 20th	Night	27% 13% 36% 21% 3	600
	21st to end	Night	25% 18% 34% 19% 4	660
April	1st to 10th	Night	18% 18% 39% 22% 3	600
	11th to 20th	Night	21% 16% 34% 24% 5%	593
	21st to end	Night	21% 13% 37% 21% 7%	587
May	1st to 10th	Night	18% 8% 37% 29% 8%	570
	11th to 20th	Night	19% 6% 33% 26% 14% 1	561
	21st to end	Night	13% 5% 29% 33% 16% 3	617
June	1st to 10th	Night	9% 4 21% 35% 29% 3	570
	11th to 20th	Night	6% 2 24% 44% 23% 2	570
	21st to end	Night	4 2 26% 39% 26% 3	570
July	1st to 10th	Night	9% 3 13% 36% 30% 10%	555
	11th to 20th	Night	6% 2 14% 42% 31% 5%	552
	21st to end	Night	8% 2 14% 41% 32% 4	624
August	1st to 10th	Night	7% 1 13% 41% 34% 4	567
	11th to 20th	Night	9% 2 15% 39% 30% 4	564
	21st to end	Night	8% 13% 35% 36% 7%	627
September	1st to 10th	Night	12% 3 15% 36% 29% 5%	570
	11th to 20th	Night	12% 2 14% 37% 30% 5%	570
	21st to end	Night	13% 6% 24% 27% 25% 4	729
October	1st to 10th	Night	9% 4 29% 31% 23% 3	760
	11th to 20th	Night	17% 12% 34% 27% 10% 1	760
	21st to end	Night	25% 12% 34% 23% 6%	836
November	1st to 10th	Night	14% 13% 40% 24% 8% 1	780
	11th to 20th	Night	20% 16% 32% 26% 7% 1	800
	21st to end	Night	24% 17% 34% 20% 5%	875
December	1st to 10th	Night	25% 15% 37% 19% 4	1000
	11th to 20th	Night	26% 14% 36% 21% 3	1000
	21st to end	Night	29% 19% 33% 17% 2	1100

Page generated at 2025-04-23 08:25:02. Version ac07

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