Waning Crescent Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waning Crescent Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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	16% 7% 2 6% 4 4 4 4 5% 7% 40%	126365
	Night	17% 8% 2 6% 4 4 4 3 5% 6% 42%	123016
Transparency	Day	27% 38% 8% 15% 11% 2	129892
	Night	28% 37% 7% 15% 11% 2	127576
Seeing	Day	21% 14% 32% 22% 9% 2	16228
	Night	21% 12% 31% 27% 9% 1	25292

By Month

Percentage Cloud Cover NE (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% 6% 1 5% 3 3 3 2 4 6% 52%	3597
	11th to 20th	Day	14% 8% 2 6% 4 4 4 4 4 6% 44%	3570
	21st to end	Day	18% 10% 4 7% 4 4 4 2 4 4 39%	4236
February	1st to 10th	Day	17% 9% 2 6% 4 4 4 3 4 7% 39%	1847
	11th to 20th	Day	15% 7% 2 7% 4 3 3 3 5% 6% 44%	1948
	21st to end	Day	20% 7% 3 6% 4 3 4 3 5% 5% 39%	1650
March	1st to 10th	Day	22% 7% 2 6% 3 3 3 3 4 5% 42%	4476
	11th to 20th	Day	12% 8% 3 6% 4 4 4 4 6% 8% 42%	4711
	21st to end	Day	18% 7% 2 6% 4 3 4 3 5% 6% 42%	5970
April	1st to 10th	Day	19% 8% 2 6% 4 4 4 3 5% 8% 37%	2400
	11th to 20th	Day	18% 6% 2 6% 5% 4 4 3 5% 8% 40%	2374
	21st to end	Day	18% 6% 2 5% 4 3 4 4 6% 8% 40%	2452
May	1st to 10th	Day	28% 9% 2 5% 3 3 4 3 6% 8% 29%	5886
	11th to 20th	Day	24% 9% 3 6% 4 3 3 3 4 6% 35%	6170
	21st to end	Day	21% 7% 2 5% 4 4 4 4 5% 8% 36%	6949
June	1st to 10th	Day	18% 6% 1 5% 4 4 4 4 6% 9% 38%	2800
	11th to 20th	Day	15% 7% 3 5% 4 4 5% 4 6% 8% 39%	2800
	21st to end	Day	11% 5% 2 6% 5% 4 4 4 6% 9% 43%	2800
July	1st to 10th	Day	11% 8% 2 7% 5% 5% 5% 4 7% 10% 36%	6360
	11th to 20th	Day	11% 7% 2 7% 5% 5% 5% 5% 8% 11% 34%	6360
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 6% 9% 39%	6926
August	1st to 10th	Day	17% 7% 3 7% 4 5% 5% 4 7% 9% 34%	4294
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 7% 8% 41%	3850
	21st to end	Day	8% 5% 2 5% 3 4 5% 4 7% 10% 47%	4312
September	1st to 10th	Day	15% 5% 2 5% 4 4 4 3 5% 7% 46%	2400
	11th to 20th	Day	11% 7% 2 4 3 3 3 4 4 8% 51%	2289
	21st to end	Day	19% 7% 3 6% 4 4 3 4 6% 5% 39%	2200
October	1st to 10th	Day	19% 6% 2 6% 4 4 4 3 4 7% 42%	2057
	11th to 20th	Day	15% 5% 2 4 5% 4 4 3 5% 6% 48%	1900
	21st to end	Day	19% 6% 2 6% 4 4 4 3 5% 7% 43%	1913
November	1st to 10th	Day	13% 6% 2 6% 3 3 3 3 4 5% 52%	1761
	11th to 20th	Day	16% 7% 3 4 2 3 3 3 4 6% 49%	1800
	21st to end	Day	15% 6% 2 5% 4 4 3 3 4 7% 45%	1761
December	1st to 10th	Day	15% 7% 2 6% 4 3 3 4 5% 8% 45%	2600
	11th to 20th	Day	23% 8% 2 3 3 2 2 3 3 5% 46%	2986
	21st to end	Day	18% 9% 2 6% 4 4 4 4 5% 6% 39%	3960
January	1st to 10th	Night	14% 6% 2 5% 3 3 3 2 5% 6% 51%	6349
	11th to 20th	Night	14% 8% 2 6% 4 3 4 2 4 5% 48%	6315
	21st to end	Night	17% 10% 3 6% 4 4 4 3 5% 6% 39%	6702
February	1st to 10th	Night	18% 8% 3 5% 4 4 3 3 5% 5% 41%	2551
	11th to 20th	Night	18% 7% 3 6% 5% 3 4 3 4 5% 41%	2338
	21st to end	Night	19% 7% 2 5% 4 4 3 4 4 5% 42%	1980
March	1st to 10th	Night	20% 9% 2 5% 3 3 3 3 4 5% 44%	5364
	11th to 20th	Night	15% 10% 2 6% 4 3 4 3 4 5% 43%	5247
	21st to end	Night	19% 9% 2 7% 5% 3 4 3 5% 5% 39%	4962
April	1st to 10th	Night	20% 6% 3 7% 4 4 4 3 5% 6% 37%	2000
	11th to 20th	Night	20% 8% 3 5% 3 3 5% 3 6% 6% 39%	1975
	21st to end	Night	18% 8% 3 6% 4 3 4 3 4 6% 42%	1946
May	1st to 10th	Night	26% 10% 3 8% 4 4 3 3 5% 8% 26%	4054
	11th to 20th	Night	23% 10% 3 6% 4 3 4 3 4 5% 34%	3764
	21st to end	Night	23% 8% 2 6% 4 4 3 3 4 7% 35%	3926
June	1st to 10th	Night	17% 7% 2 4 5% 5% 4 3 5% 7% 40%	1600
	11th to 20th	Night	15% 8% 2 5% 4 4 4 5% 6% 9% 39%	1600
	21st to end	Night	10% 6% 2 7% 5% 4 6% 4 8% 9% 39%	1600
July	1st to 10th	Night	12% 9% 3 9% 6% 5% 5% 4 6% 8% 34%	3600
	11th to 20th	Night	15% 10% 3 9% 5% 4 5% 4 6% 8% 31%	3600
	21st to end	Night	13% 7% 2 6% 4 4 4 4 6% 8% 41%	3926
August	1st to 10th	Night	23% 7% 2 6% 4 5% 4 4 6% 8% 32%	2817
	11th to 20th	Night	14% 6% 3 7% 5% 5% 5% 4 6% 7% 39%	3197
	21st to end	Night	8% 5% 2 5% 4 4 4 3 6% 8% 52%	3586
September	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 6% 6% 44%	2000
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 51%	2110
	21st to end	Night	18% 6% 2 7% 5% 4 4 3 4 7% 41%	2200
October	1st to 10th	Night	19% 7% 2 7% 3 4 4 2 4 6% 42%	2187
	11th to 20th	Night	15% 5% 2 6% 3 3 4 3 4 6% 50%	2280
	21st to end	Night	21% 6% 2 6% 3 3 3 3 5% 5% 43%	2684
November	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 4 6% 51%	2537
	11th to 20th	Night	19% 6% 2 5% 3 3 2 3 4 6% 49%	2600
	21st to end	Night	15% 5% 2 4 5% 3 4 4 5% 6% 47%	2635
December	1st to 10th	Night	16% 7% 2 5% 3 3 3 3 4 5% 48%	4580
	11th to 20th	Night	26% 7% 2 5% 2 3 3 3 3 4 43%	5208
	21st to end	Night	19% 8% 2 6% 3 4 4 3 5% 5% 42%	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	24% 27% 3 26% 18% 2	3598
	11th to 20th	Day	29% 27% 6% 19% 14% 5%	3600
	21st to end	Day	39% 28% 6% 16% 10% 1	4236
February	1st to 10th	Day	18% 62% 7% 8% 4	1847
	11th to 20th	Day	18% 61% 2 11% 9% 1	1957
	21st to end	Day	18% 62% 5% 9% 5% 1	1650
March	1st to 10th	Day	33% 30% 7% 12% 10% 8%	4479
	11th to 20th	Day	28% 30% 9% 22% 9% 2	4711
	21st to end	Day	32% 29% 7% 9% 18% 4	5970
April	1st to 10th	Day	21% 62% 3 7% 6% 1	2400
	11th to 20th	Day	16% 62% 4 9% 7% 1	2374
	21st to end	Day	17% 62% 3 10% 7% 1	2452
May	1st to 10th	Day	41% 29% 14% 9% 5%	5897
	11th to 20th	Day	39% 28% 8% 14% 10% 1	6174
	21st to end	Day	36% 30% 7% 17% 10% 1	6949
June	1st to 10th	Day	16% 62% 4 9% 8%	2800
	11th to 20th	Day	16% 62% 5% 9% 7%	2800
	21st to end	Day	14% 61% 5% 10% 8% 1	2800
July	1st to 10th	Day	34% 30% 9% 16% 11%	6290
	11th to 20th	Day	33% 30% 16% 14% 6%	6285
	21st to end	Day	31% 27% 9% 17% 15% 1	6728
August	1st to 10th	Day	32% 37% 10% 15% 5%	4280
	11th to 20th	Day	24% 38% 9% 25% 3	3886
	21st to end	Day	17% 37% 10% 21% 14% 1	4312
September	1st to 10th	Day	16% 57% 7% 11% 8% 1	2400
	11th to 20th	Day	16% 57% 4 11% 12%	2289
	21st to end	Day	24% 57% 5% 8% 6%	2200
October	1st to 10th	Day	20% 38% 9% 11% 17% 5%	3395
	11th to 20th	Day	11% 37% 6% 13% 28% 4	3140
	21st to end	Day	13% 38% 11% 19% 17% 2	3125
November	1st to 10th	Day	18% 55% 7% 9% 10% 1	1761
	11th to 20th	Day	14% 56% 3 12% 14% 2	1800
	21st to end	Day	15% 57% 7% 15% 5% 2	1761
December	1st to 10th	Day	26% 35% 10% 20% 9% 1	2600
	11th to 20th	Day	30% 31% 7% 16% 14% 2	2986
	21st to end	Day	35% 27% 4 17% 13% 2	3960
January	1st to 10th	Night	25% 25% 5% 20% 21% 3	6349
	11th to 20th	Night	28% 26% 9% 17% 15% 5%	6360
	21st to end	Night	38% 27% 6% 14% 12% 3	6702
February	1st to 10th	Night	18% 61% 6% 11% 3 1	2551
	11th to 20th	Night	18% 60% 2 9% 10% 2	2340
	21st to end	Night	18% 61% 4 7% 7% 3	1980
March	1st to 10th	Night	35% 29% 6% 14% 9% 8%	5374
	11th to 20th	Night	31% 29% 10% 18% 9% 3	5248
	21st to end	Night	37% 29% 4 8% 19% 4	4962
April	1st to 10th	Night	20% 61% 3 8% 6% 1	2000
	11th to 20th	Night	15% 63% 5% 9% 8% 1	1975
	21st to end	Night	18% 62% 3 9% 8% 1	1946
May	1st to 10th	Night	45% 29% 10% 10% 6% 1	4060
	11th to 20th	Night	40% 28% 11% 10% 8% 1	3765
	21st to end	Night	39% 28% 8% 16% 8% 1	3927
June	1st to 10th	Night	18% 61% 2 9% 10%	1600
	11th to 20th	Night	17% 63% 5% 10% 6%	1600
	21st to end	Night	15% 62% 5% 10% 7% 1	1600
July	1st to 10th	Night	38% 29% 8% 17% 8% 1	3560
	11th to 20th	Night	41% 28% 11% 14% 6%	3552
	21st to end	Night	31% 27% 11% 18% 12% 1	3809
August	1st to 10th	Night	38% 37% 10% 10% 4	2807
	11th to 20th	Night	27% 37% 10% 20% 6%	3227
	21st to end	Night	15% 37% 8% 26% 13% 1	3586
September	1st to 10th	Night	16% 57% 5% 13% 8% 1	2000
	11th to 20th	Night	17% 57% 4 10% 11% 2	2110
	21st to end	Night	23% 57% 4 9% 6% 1	2200
October	1st to 10th	Night	24% 37% 7% 16% 14% 2	3629
	11th to 20th	Night	10% 37% 5% 18% 27% 4	3779
	21st to end	Night	15% 36% 9% 22% 16% 2	4422
November	1st to 10th	Night	17% 56% 5% 11% 9% 2	2537
	11th to 20th	Night	16% 56% 3 10% 12% 3	2600
	21st to end	Night	15% 57% 6% 14% 7% 1	2635
December	1st to 10th	Night	25% 35% 7% 22% 9% 2	4580
	11th to 20th	Night	33% 31% 4 17% 12% 2	5208
	21st to end	Night	35% 26% 6% 15% 15% 4	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	28% 24% 33% 13% 4	200
	11th to 20th	Day	24% 28% 32% 14% 3	200
	21st to end	Day	23% 20% 39% 12% 5% 1	280
February	1st to 10th	Day	28% 20% 37% 13% 2	347
	11th to 20th	Day	27% 21% 38% 14% 2	496
	21st to end	Day	28% 19% 36% 13% 4	414
March	1st to 10th	Day	24% 22% 33% 18% 3	500
	11th to 20th	Day	22% 21% 38% 16% 4 1	500
	21st to end	Day	28% 19% 34% 13% 5% 1	550
April	1st to 10th	Day	27% 22% 33% 13% 6% 1	500
	11th to 20th	Day	27% 18% 31% 18% 5% 1	492
	21st to end	Day	28% 16% 35% 16% 4 1	500
May	1st to 10th	Day	32% 17% 30% 16% 5% 1	503
	11th to 20th	Day	22% 15% 36% 20% 6% 1	527
	21st to end	Day	20% 8% 32% 24% 13% 2	573
June	1st to 10th	Day	21% 8% 31% 28% 10% 2	530
	11th to 20th	Day	18% 10% 35% 26% 9% 1	530
	21st to end	Day	14% 7% 36% 29% 11% 3	530
July	1st to 10th	Day	13% 7% 27% 34% 15% 4	525
	11th to 20th	Day	10% 6% 29% 36% 16% 3	524
	21st to end	Day	14% 9% 31% 30% 13% 2	576
August	1st to 10th	Day	14% 6% 29% 30% 16% 5%	526
	11th to 20th	Day	13% 7% 25% 36% 16% 3	519
	21st to end	Day	12% 7% 31% 31% 13% 6%	583
September	1st to 10th	Day	19% 8% 29% 23% 17% 4	530
	11th to 20th	Day	15% 7% 29% 26% 14% 9%	530
	21st to end	Day	22% 8% 29% 23% 13% 4	530
October	1st to 10th	Day	25% 8% 26% 22% 15% 4	502
	11th to 20th	Day	16% 15% 33% 23% 11% 2	490
	21st to end	Day	21% 12% 37% 19% 9% 2	445
November	1st to 10th	Day	15% 16% 30% 26% 10% 2	395
	11th to 20th	Day	22% 23% 29% 20% 6% 1	400
	21st to end	Day	21% 17% 33% 22% 7% 1	361
December	1st to 10th	Day	24% 22% 34% 16% 4 1	200
	11th to 20th	Day	35% 18% 34% 10% 4	200
	21st to end	Day	25% 16% 37% 15% 7%	220
January	1st to 10th	Night	21% 21% 36% 19% 3	800
	11th to 20th	Night	25% 20% 29% 24% 3	800
	21st to end	Night	21% 18% 38% 21% 2	880
February	1st to 10th	Night	22% 17% 37% 22% 2	800
	11th to 20th	Night	25% 20% 37% 16% 1	783
	21st to end	Night	24% 19% 36% 17% 4	660
March	1st to 10th	Night	23% 19% 33% 19% 5%	800
	11th to 20th	Night	22% 15% 39% 19% 5% 1	800
	21st to end	Night	23% 16% 36% 19% 4	880
April	1st to 10th	Night	24% 18% 35% 19% 5%	800
	11th to 20th	Night	25% 11% 35% 24% 5%	791
	21st to end	Night	22% 13% 36% 24% 5% 1	746
May	1st to 10th	Night	24% 11% 33% 24% 7% 1	600
	11th to 20th	Night	24% 12% 33% 28% 4	479
	21st to end	Night	23% 5% 24% 33% 14% 2	433
June	1st to 10th	Night	21% 6% 26% 35% 13%	400
	11th to 20th	Night	17% 4 25% 41% 14% 1	400
	21st to end	Night	13% 5% 26% 44% 12% 1	400
July	1st to 10th	Night	14% 2 23% 45% 15% 1	390
	11th to 20th	Night	14% 5% 22% 40% 17% 2	388
	21st to end	Night	14% 3 23% 42% 17%	438
August	1st to 10th	Night	12% 2 24% 43% 18% 1	525
	11th to 20th	Night	15% 3 22% 37% 22% 2	790
	21st to end	Night	14% 4 20% 38% 22% 3	880
September	1st to 10th	Night	16% 4 26% 35% 16% 3	800
	11th to 20th	Night	15% 5% 20% 36% 19% 6%	800
	21st to end	Night	21% 4 26% 30% 17% 2	800
October	1st to 10th	Night	24% 7% 24% 27% 16% 3	773
	11th to 20th	Night	17% 11% 29% 30% 12% 1	760
	21st to end	Night	24% 10% 32% 24% 9%	836
November	1st to 10th	Night	14% 12% 34% 27% 11% 2	780
	11th to 20th	Night	22% 15% 33% 22% 8%	800
	21st to end	Night	18% 18% 32% 24% 7% 1	800
December	1st to 10th	Night	25% 17% 33% 19% 5% 1	800
	11th to 20th	Night	25% 16% 34% 21% 4	800
	21st to end	Night	23% 15% 36% 22% 3	880

Page generated at 2025-10-01 01:39:05. Version ac07

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