New Moon Telescopes Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the New Moon Telescopes 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	13% 6% 2 6% 4 4 4 4 6% 8% 43%	113585
	Night	14% 6% 2 6% 4 4 4 3 5% 7% 45%	115042
Transparency	Day	37% 7% 12% 22% 18% 5%	117230
	Night	37% 6% 10% 22% 19% 6%	119536
Seeing	Day	18% 12% 27% 24% 14% 4	15731
	Night	17% 11% 29% 30% 13% 1	25548

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	15% 5% 2 4 3 3 3 3 4 4 56%	4028
	11th to 20th	Day	13% 7% 2 5% 3 3 3 3 4 5% 54%	4060
	21st to end	Day	14% 6% 3 7% 5% 4 3 3 4 6% 45%	4466
February	1st to 10th	Day	13% 7% 2 7% 4 4 6% 4 6% 7% 41%	1800
	11th to 20th	Day	22% 6% 2 4 4 3 3 3 5% 5% 43%	1830
	21st to end	Day	17% 6% 3 6% 4 4 5% 4 5% 7% 39%	1660
March	1st to 10th	Day	17% 8% 3 7% 4 4 4 3 5% 6% 39%	4935
	11th to 20th	Day	10% 6% 2 5% 3 3 4 3 5% 6% 52%	4980
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 6% 44%	5501
April	1st to 10th	Day	12% 5% 2 5% 4 4 3 3 6% 7% 49%	2400
	11th to 20th	Day	12% 5% 2 5% 4 4 4 3 4 7% 49%	2374
	21st to end	Day	15% 6% 2 6% 3 3 4 3 5% 7% 44%	2340
May	1st to 10th	Day	15% 7% 2 7% 5% 5% 6% 5% 7% 9% 32%	3940
	11th to 20th	Day	19% 6% 2 6% 5% 4 4 4 6% 8% 33%	4081
	21st to end	Day	9% 5% 1 5% 4 4 5% 4 6% 10% 48%	4810
June	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 5% 7% 10% 43%	2660
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 5% 7% 10% 42%	2660
	21st to end	Day	8% 4 2 5% 5% 4 6% 5% 8% 11% 41%	2660
July	1st to 10th	Day	6% 4 2 6% 5% 5% 7% 6% 9% 13% 38%	4325
	11th to 20th	Day	11% 6% 2 6% 6% 6% 5% 6% 7% 11% 34%	4120
	21st to end	Day	9% 7% 3 8% 7% 5% 7% 5% 8% 9% 32%	4466
August	1st to 10th	Day	16% 7% 3 8% 6% 5% 6% 5% 7% 11% 27%	4104
	11th to 20th	Day	11% 5% 2 8% 5% 6% 6% 5% 8% 8% 36%	3826
	21st to end	Day	8% 4 2 5% 4 4 4 4 7% 10% 48%	4180
September	1st to 10th	Day	13% 5% 2 5% 4 5% 5% 4 6% 8% 43%	2280
	11th to 20th	Day	13% 6% 2 6% 5% 5% 4 4 5% 7% 42%	2280
	21st to end	Day	19% 8% 3 7% 5% 4 4 3 5% 6% 37%	1987
October	1st to 10th	Day	16% 6% 2 6% 4 4 3 3 4 6% 47%	1900
	11th to 20th	Day	16% 4 2 4 4 3 3 2 3 6% 53%	1900
	21st to end	Day	12% 5% 1 5% 3 3 3 3 4 6% 54%	2090
November	1st to 10th	Day	13% 5% 2 5% 3 3 3 3 4 5% 53%	1952
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 4 6% 50%	1800
	21st to end	Day	14% 4 2 5% 3 3 3 3 5% 6% 52%	1640
December	1st to 10th	Day	10% 5% 2 6% 3 4 3 2 5% 6% 52%	2600
	11th to 20th	Day	18% 7% 2 6% 3 3 3 2 4 5% 47%	2990
	21st to end	Day	13% 6% 3 5% 4 4 3 4 6% 7% 47%	3960
January	1st to 10th	Night	13% 7% 2 5% 3 3 3 2 4 4 54%	5912
	11th to 20th	Night	14% 6% 2 5% 3 2 3 2 4 4 54%	5900
	21st to end	Night	17% 6% 2 5% 3 3 2 2 4 5% 50%	6490
February	1st to 10th	Night	17% 7% 2 5% 4 3 4 3 6% 6% 44%	2600
	11th to 20th	Night	20% 8% 2 6% 4 4 3 3 4 6% 41%	2454
	21st to end	Night	16% 7% 2 5% 3 3 3 3 4 6% 47%	1966
March	1st to 10th	Night	18% 6% 2 5% 4 3 3 3 5% 6% 46%	4918
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 5% 6% 51%	4980
	21st to end	Night	13% 5% 2 6% 4 4 4 3 5% 7% 48%	5430
April	1st to 10th	Night	13% 6% 3 6% 4 5% 4 3 5% 6% 44%	2000
	11th to 20th	Night	12% 5% 2 5% 3 3 3 4 5% 7% 49%	1975
	21st to end	Night	14% 6% 2 5% 4 4 5% 3 5% 7% 46%	1957
May	1st to 10th	Night	16% 7% 3 7% 5% 5% 4 3 5% 8% 36%	2984
	11th to 20th	Night	23% 7% 3 7% 4 3 4 3 5% 6% 35%	2812
	21st to end	Night	11% 5% 2 5% 4 4 5% 4 6% 9% 45%	2741
June	1st to 10th	Night	11% 5% 2 5% 5% 5% 5% 6% 7% 9% 40%	1520
	11th to 20th	Night	9% 6% 3 6% 5% 4 6% 4 7% 10% 40%	1520
	21st to end	Night	7% 5% 2 5% 6% 4 6% 4 6% 12% 42%	1520
July	1st to 10th	Night	7% 4 2 6% 5% 6% 6% 6% 10% 10% 39%	2630
	11th to 20th	Night	10% 5% 3 6% 6% 5% 6% 6% 8% 9% 35%	2840
	21st to end	Night	12% 8% 3 10% 7% 6% 5% 4 6% 8% 29%	3087
August	1st to 10th	Night	17% 7% 3 7% 5% 4 5% 4 7% 10% 29%	2825
	11th to 20th	Night	9% 6% 3 7% 5% 4 5% 4 7% 9% 40%	2969
	21st to end	Night	9% 4 2 5% 4 4 4 4 7% 10% 47%	3476
September	1st to 10th	Night	12% 5% 2 7% 5% 4 4 4 5% 8% 44%	1900
	11th to 20th	Night	13% 5% 2 6% 4 5% 6% 3 6% 7% 44%	1900
	21st to end	Night	22% 7% 3 7% 4 3 4 3 5% 6% 35%	2188
October	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 4 6% 47%	2280
	11th to 20th	Night	15% 6% 2 6% 3 3 3 2 4 6% 50%	2280
	21st to end	Night	14% 4 2 5% 3 3 3 3 3 7% 53%	2508
November	1st to 10th	Night	12% 6% 2 6% 4 3 3 3 4 5% 52%	2342
	11th to 20th	Night	15% 6% 2 4 3 3 4 3 4 6% 49%	2600
	21st to end	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2757
December	1st to 10th	Night	10% 5% 2 4 4 4 4 3 5% 5% 55%	4580
	11th to 20th	Night	18% 7% 3 7% 5% 4 3 3 4 6% 40%	5205
	21st to end	Night	14% 7% 2 6% 4 3 4 3 5% 6% 47%	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	32% 3 6% 24% 24% 11%	4029
	11th to 20th	Day	33% 4 6% 19% 28% 10%	4060
	21st to end	Day	41% 4 8% 26% 17% 4	4466
February	1st to 10th	Day	41% 6% 12% 24% 15% 3	1800
	11th to 20th	Day	43% 5% 7% 20% 20% 5%	1839
	21st to end	Day	45% 5% 12% 15% 18% 5%	1660
March	1st to 10th	Day	45% 4 8% 17% 18% 8%	4935
	11th to 20th	Day	31% 6% 8% 22% 23% 10%	4980
	21st to end	Day	40% 6% 11% 18% 18% 6%	5501
April	1st to 10th	Day	33% 6% 12% 22% 19% 8%	2400
	11th to 20th	Day	35% 5% 11% 22% 20% 6%	2374
	21st to end	Day	39% 6% 13% 21% 16% 5%	2340
May	1st to 10th	Day	44% 11% 15% 18% 10% 2	3975
	11th to 20th	Day	45% 9% 15% 21% 9% 1	4085
	21st to end	Day	29% 9% 17% 24% 18% 2	4824
June	1st to 10th	Day	34% 10% 16% 25% 14% 1	2660
	11th to 20th	Day	35% 11% 15% 22% 16% 1	2660
	21st to end	Day	33% 11% 17% 23% 14% 2	2660
July	1st to 10th	Day	33% 12% 23% 17% 10% 4	4258
	11th to 20th	Day	41% 10% 24% 18% 6% 1	4051
	21st to end	Day	44% 11% 14% 16% 14%	4324
August	1st to 10th	Day	49% 9% 18% 19% 5%	4091
	11th to 20th	Day	40% 10% 15% 23% 11% 1	3865
	21st to end	Day	29% 8% 15% 29% 18% 1	4180
September	1st to 10th	Day	38% 9% 14% 15% 20% 4	2280
	11th to 20th	Day	39% 7% 11% 21% 18% 3	2280
	21st to end	Day	48% 6% 9% 20% 14% 3	1987
October	1st to 10th	Day	37% 4 8% 19% 26% 6%	3160
	11th to 20th	Day	23% 3 5% 21% 34% 13%	3140
	21st to end	Day	21% 3 8% 28% 26% 14%	3428
November	1st to 10th	Day	33% 5% 9% 23% 26% 4	1952
	11th to 20th	Day	36% 5% 9% 21% 22% 7%	1800
	21st to end	Day	33% 4 8% 25% 24% 5%	1640
December	1st to 10th	Day	33% 4 8% 27% 21% 7%	2600
	11th to 20th	Day	41% 3 12% 23% 17% 5%	2986
	21st to end	Day	35% 6% 13% 27% 18% 2	3960
January	1st to 10th	Night	34% 4 6% 19% 25% 11%	5912
	11th to 20th	Night	34% 4 5% 20% 30% 7%	5900
	21st to end	Night	38% 3 6% 27% 21% 5%	6490
February	1st to 10th	Night	40% 5% 12% 22% 17% 4	2600
	11th to 20th	Night	45% 4 7% 19% 18% 7%	2456
	21st to end	Night	38% 5% 8% 22% 18% 8%	1966
March	1st to 10th	Night	39% 5% 8% 18% 21% 8%	4918
	11th to 20th	Night	33% 5% 8% 18% 26% 11%	4980
	21st to end	Night	37% 5% 9% 22% 21% 6%	5430
April	1st to 10th	Night	39% 6% 10% 17% 21% 6%	2000
	11th to 20th	Night	33% 6% 11% 23% 21% 7%	1975
	21st to end	Night	37% 7% 13% 22% 16% 5%	1957
May	1st to 10th	Night	44% 9% 15% 19% 11% 2	3014
	11th to 20th	Night	47% 10% 11% 22% 8% 1	2813
	21st to end	Night	31% 11% 17% 24% 16% 1	2748
June	1st to 10th	Night	36% 10% 17% 23% 13% 2	1520
	11th to 20th	Night	37% 11% 16% 21% 14% 1	1520
	21st to end	Night	34% 10% 13% 22% 18% 3	1520
July	1st to 10th	Night	35% 15% 18% 18% 11% 3	2587
	11th to 20th	Night	41% 12% 22% 19% 5% 1	2786
	21st to end	Night	52% 9% 12% 17% 11%	2988
August	1st to 10th	Night	48% 9% 19% 18% 6%	2814
	11th to 20th	Night	39% 8% 18% 22% 12%	2996
	21st to end	Night	31% 8% 13% 27% 20% 1	3476
September	1st to 10th	Night	37% 9% 14% 18% 17% 5%	1900
	11th to 20th	Night	37% 8% 10% 21% 21% 2	1900
	21st to end	Night	48% 7% 10% 17% 14% 4	2188
October	1st to 10th	Night	40% 4 11% 17% 23% 4	3800
	11th to 20th	Night	25% 3 7% 20% 30% 14%	3779
	21st to end	Night	21% 3 5% 31% 25% 14%	4120
November	1st to 10th	Night	35% 5% 10% 21% 24% 5%	2342
	11th to 20th	Night	37% 5% 9% 18% 22% 10%	2600
	21st to end	Night	33% 5% 9% 23% 24% 6%	2757
December	1st to 10th	Night	32% 4 7% 27% 24% 6%	4580
	11th to 20th	Night	47% 4 10% 18% 15% 6%	5208
	21st to end	Night	37% 5% 12% 28% 17% 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	27% 26% 29% 13% 4	293
	11th to 20th	Day	28% 31% 29% 10% 2	300
	21st to end	Day	24% 23% 39% 12% 1	330
February	1st to 10th	Day	20% 28% 39% 11% 2	300
	11th to 20th	Day	36% 26% 28% 10% 1	377
	21st to end	Day	27% 19% 33% 18% 3	414
March	1st to 10th	Day	25% 21% 32% 18% 5%	500
	11th to 20th	Day	23% 22% 35% 15% 4 1	500
	21st to end	Day	22% 20% 39% 14% 5% 1	550
April	1st to 10th	Day	24% 20% 32% 17% 7%	500
	11th to 20th	Day	18% 15% 33% 22% 10% 3	492
	21st to end	Day	21% 13% 33% 25% 8% 2	480
May	1st to 10th	Day	18% 16% 33% 23% 9% 2	463
	11th to 20th	Day	21% 9% 28% 28% 11% 3	487
	21st to end	Day	19% 4 25% 28% 17% 6%	529
June	1st to 10th	Day	13% 4 28% 29% 21% 4	490
	11th to 20th	Day	10% 7% 23% 33% 20% 7%	490
	21st to end	Day	9% 5% 26% 35% 20% 4	490
July	1st to 10th	Day	9% 3 18% 33% 29% 8%	485
	11th to 20th	Day	7% 2 16% 36% 30% 10%	484
	21st to end	Day	10% 2 21% 35% 23% 8%	532
August	1st to 10th	Day	14% 3 19% 30% 27% 7%	486
	11th to 20th	Day	12% 4 16% 30% 28% 9%	479
	21st to end	Day	8% 2 19% 31% 25% 14%	539
September	1st to 10th	Day	15% 4 18% 26% 22% 15%	490
	11th to 20th	Day	16% 4 17% 30% 22% 12%	490
	21st to end	Day	26% 9% 25% 23% 13% 3	490
October	1st to 10th	Day	21% 6% 20% 26% 19% 8%	490
	11th to 20th	Day	17% 12% 23% 28% 17% 2	490
	21st to end	Day	15% 11% 33% 26% 11% 4	539
November	1st to 10th	Day	16% 11% 32% 23% 15% 3	492
	11th to 20th	Day	20% 15% 30% 23% 11% 1	400
	21st to end	Day	21% 19% 27% 23% 9% 2	240
December	1st to 10th	Day	21% 21% 37% 15% 6%	200
	11th to 20th	Day	23% 14% 38% 19% 6% 1	200
	21st to end	Day	24% 15% 31% 21% 8% 1	220
January	1st to 10th	Night	20% 19% 38% 20% 3	800
	11th to 20th	Night	20% 19% 32% 25% 4	800
	21st to end	Night	20% 16% 38% 24% 1	880
February	1st to 10th	Night	20% 14% 39% 24% 3	800
	11th to 20th	Night	26% 19% 36% 17% 1	783
	21st to end	Night	22% 16% 38% 21% 3	660
March	1st to 10th	Night	19% 18% 36% 24% 3	800
	11th to 20th	Night	21% 18% 35% 21% 5%	800
	21st to end	Night	19% 15% 42% 20% 4	880
April	1st to 10th	Night	18% 19% 37% 22% 4	800
	11th to 20th	Night	14% 15% 37% 25% 8%	791
	21st to end	Night	16% 11% 36% 30% 8%	783
May	1st to 10th	Night	18% 10% 34% 29% 8%	679
	11th to 20th	Night	17% 7% 29% 37% 10% 1	561
	21st to end	Night	16% 3 19% 40% 21% 1	421
June	1st to 10th	Night	11% 4 21% 44% 20%	380
	11th to 20th	Night	8% 5% 19% 46% 19% 3	380
	21st to end	Night	7% 2 22% 48% 19% 1	380
July	1st to 10th	Night	11% 2 17% 42% 27% 2	425
	11th to 20th	Night	6% 14% 41% 36% 3	552
	21st to end	Night	8% 2 18% 43% 24% 5%	624
August	1st to 10th	Night	11% 2 16% 41% 27% 3	567
	11th to 20th	Night	12% 3 13% 42% 26% 4	670
	21st to end	Night	11% 3 14% 34% 33% 5%	836
September	1st to 10th	Night	13% 3 13% 39% 27% 5%	760
	11th to 20th	Night	15% 3 17% 31% 30% 4	760
	21st to end	Night	25% 6% 20% 31% 17% 1	760
October	1st to 10th	Night	17% 6% 21% 29% 23% 4	760
	11th to 20th	Night	18% 8% 26% 31% 16% 1	760
	21st to end	Night	17% 9% 28% 29% 15% 2	836
November	1st to 10th	Night	16% 9% 30% 29% 14% 2	780
	11th to 20th	Night	18% 13% 30% 29% 10%	800
	21st to end	Night	15% 14% 30% 30% 10% 1	800
December	1st to 10th	Night	22% 13% 34% 23% 7%	800
	11th to 20th	Night	18% 12% 36% 28% 6%	800
	21st to end	Night	19% 16% 27% 32% 4	880

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