Luckie's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Luckie's Observatory clear sky chart from 2005-11-06 to 2025-05-26.

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	15% 6% 2 6% 4 4 5% 4 6% 7% 42%	114365
	Night	16% 6% 2 5% 4 4 4 3 5% 7% 45%	114923
Transparency	Day	38% 7% 10% 19% 19% 7%	118172
	Night	37% 6% 10% 19% 21% 7%	119255
Seeing	Day	21% 9% 22% 23% 17% 8%	15633
	Night	19% 8% 21% 29% 19% 4	25732

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	17% 6% 2 4 3 3 4 2 4 5% 51%	4056
	11th to 20th	Day	13% 6% 2 4 3 3 3 2 3 3 59%	4060
	21st to end	Day	23% 6% 2 6% 3 3 3 2 3 5% 42%	4483
February	1st to 10th	Day	18% 7% 2 5% 4 3 4 3 5% 6% 43%	2000
	11th to 20th	Day	23% 6% 2 5% 3 3 3 4 5% 5% 42%	1948
	21st to end	Day	21% 6% 2 5% 4 4 3 3 4 6% 42%	1650
March	1st to 10th	Day	22% 7% 3 6% 4 3 4 3 4 5% 40%	4701
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 4 6% 54%	4980
	21st to end	Day	19% 6% 2 6% 4 4 4 3 3 5% 45%	5465
April	1st to 10th	Day	14% 4 2 4 4 5% 4 5% 7% 7% 43%	2202
	11th to 20th	Day	13% 5% 2 5% 5% 4 4 4 5% 6% 47%	2391
	21st to end	Day	14% 4 2 4 4 4 4 4 5% 8% 47%	2600
May	1st to 10th	Day	14% 7% 3 7% 4 4 4 3 6% 8% 39%	4212
	11th to 20th	Day	19% 7% 3 7% 4 4 5% 4 6% 7% 33%	4211
	21st to end	Day	10% 5% 2 5% 5% 5% 6% 5% 7% 10% 41%	4541
June	1st to 10th	Day	12% 6% 3 7% 6% 5% 7% 5% 8% 8% 33%	2470
	11th to 20th	Day	7% 5% 2 5% 6% 7% 6% 6% 9% 11% 38%	2470
	21st to end	Day	8% 4 2 6% 6% 6% 6% 6% 8% 11% 36%	2470
July	1st to 10th	Day	7% 6% 3 8% 6% 6% 7% 6% 9% 12% 29%	4120
	11th to 20th	Day	9% 5% 2 7% 6% 7% 8% 6% 9% 10% 31%	4120
	21st to end	Day	11% 8% 3 12% 9% 8% 9% 7% 9% 8% 18%	4466
August	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 8% 12% 35%	4104
	11th to 20th	Day	8% 5% 2 6% 5% 5% 6% 5% 8% 13% 36%	3948
	21st to end	Day	8% 4 2 6% 4 5% 6% 4 6% 7% 48%	4130
September	1st to 10th	Day	11% 5% 2 8% 6% 5% 6% 5% 7% 8% 38%	2090
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 4 6% 7% 38%	2090
	21st to end	Day	16% 5% 2 6% 4 4 4 3 6% 6% 45%	2090
October	1st to 10th	Day	14% 5% 1 4 3 3 3 3 4 6% 54%	2090
	11th to 20th	Day	13% 5% 1 3 3 2 3 2 4 6% 56%	1938
	21st to end	Day	15% 5% 1 4 3 3 3 3 3 4 57%	2090
November	1st to 10th	Day	14% 5% 2 4 3 2 3 3 4 5% 56%	1810
	11th to 20th	Day	17% 4 2 3 3 3 3 3 4 7% 52%	1800
	21st to end	Day	16% 5% 2 3 4 3 4 3 5% 6% 50%	1800
December	1st to 10th	Day	21% 4 1 3 3 3 3 3 4 5% 49%	2930
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 4 5% 42%	3373
	21st to end	Day	25% 5% 1 4 2 3 3 2 5% 7% 43%	4466
January	1st to 10th	Night	16% 5% 1 4 3 3 3 3 4 5% 53%	5889
	11th to 20th	Night	15% 7% 2 4 3 2 2 3 4 5% 52%	5900
	21st to end	Night	20% 7% 2 5% 3 3 3 2 4 5% 47%	6471
February	1st to 10th	Night	16% 5% 2 4 3 4 4 3 5% 6% 47%	2400
	11th to 20th	Night	22% 7% 2 5% 4 4 3 3 4 4 42%	2338
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 41%	1980
March	1st to 10th	Night	23% 6% 2 6% 4 4 4 3 5% 6% 38%	5150
	11th to 20th	Night	11% 4 1 3 3 3 4 3 5% 8% 54%	4980
	21st to end	Night	17% 6% 2 6% 4 4 4 3 4 6% 45%	5467
April	1st to 10th	Night	15% 4 1 5% 3 3 4 4 6% 6% 49%	2200
	11th to 20th	Night	13% 6% 2 5% 4 3 4 3 4 6% 50%	1968
	21st to end	Night	12% 5% 2 6% 4 4 3 4 5% 7% 50%	1800
May	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 6% 9% 39%	2903
	11th to 20th	Night	20% 6% 2 5% 5% 4 3 3 5% 8% 38%	2902
	21st to end	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 45%	3130
June	1st to 10th	Night	11% 6% 2 6% 6% 6% 6% 5% 8% 9% 34%	1710
	11th to 20th	Night	7% 5% 2 5% 4 4 6% 5% 8% 11% 42%	1710
	21st to end	Night	8% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	1710
July	1st to 10th	Night	11% 8% 4 9% 6% 7% 6% 5% 7% 9% 28%	2840
	11th to 20th	Night	8% 5% 3 7% 6% 6% 7% 6% 9% 12% 33%	2840
	21st to end	Night	14% 9% 4 10% 6% 7% 6% 5% 8% 9% 22%	3087
August	1st to 10th	Night	9% 6% 3 6% 5% 5% 6% 5% 8% 11% 35%	2825
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 4 7% 9% 39%	2876
	21st to end	Night	8% 5% 2 6% 4 4 5% 4 6% 8% 47%	3492
September	1st to 10th	Night	11% 6% 2 6% 5% 4 6% 4 6% 8% 41%	2090
	11th to 20th	Night	17% 6% 3 5% 4 5% 4 4 6% 8% 39%	2090
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 6% 47%	2090
October	1st to 10th	Night	15% 5% 1 4 3 4 2 2 4 5% 54%	2090
	11th to 20th	Night	13% 4 2 4 3 3 3 3 4 5% 55%	2241
	21st to end	Night	14% 4 1 3 3 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	15% 5% 2 4 2 3 2 3 3 5% 56%	2484
	11th to 20th	Night	17% 4 2 4 3 3 3 2 4 5% 53%	2600
	21st to end	Night	18% 5% 1 4 4 3 4 3 6% 6% 47%	2600
December	1st to 10th	Night	19% 5% 2 4 3 2 3 3 4 5% 51%	4250
	11th to 20th	Night	20% 6% 3 6% 3 3 3 4 4 5% 43%	4822
	21st to end	Night	24% 6% 2 4 2 3 3 3 5% 6% 42%	6490

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	35% 4 5% 20% 26% 9%	4057
	11th to 20th	Day	31% 3 5% 15% 32% 13%	4060
	21st to end	Day	45% 3 4 17% 21% 10%	4483
February	1st to 10th	Day	42% 5% 7% 20% 20% 6%	2000
	11th to 20th	Day	43% 4 6% 18% 20% 7%	1958
	21st to end	Day	44% 5% 7% 14% 21% 9%	1650
March	1st to 10th	Day	47% 4 6% 14% 19% 10%	4701
	11th to 20th	Day	31% 4 6% 14% 24% 21%	4980
	21st to end	Day	42% 4 6% 22% 20% 6%	5465
April	1st to 10th	Day	37% 7% 10% 19% 21% 6%	2202
	11th to 20th	Day	37% 5% 8% 18% 23% 9%	2391
	21st to end	Day	34% 6% 11% 27% 18% 3	2600
May	1st to 10th	Day	41% 9% 12% 18% 18% 3	4250
	11th to 20th	Day	46% 10% 10% 20% 13% 1	4215
	21st to end	Day	34% 11% 14% 21% 19% 1	4554
June	1st to 10th	Day	43% 11% 16% 20% 8% 2	2470
	11th to 20th	Day	34% 11% 19% 21% 13% 1	2470
	21st to end	Day	37% 12% 17% 18% 13% 3	2470
July	1st to 10th	Day	41% 15% 19% 19% 5% 1	4055
	11th to 20th	Day	42% 12% 24% 17% 4 2	4051
	21st to end	Day	57% 14% 13% 11% 4	4324
August	1st to 10th	Day	38% 10% 15% 30% 6%	4091
	11th to 20th	Day	35% 11% 23% 16% 13% 2	3987
	21st to end	Day	32% 8% 14% 24% 20% 2	4130
September	1st to 10th	Day	40% 9% 14% 17% 17% 3	2090
	11th to 20th	Day	42% 9% 11% 16% 20% 2	2090
	21st to end	Day	39% 6% 11% 18% 20% 7%	2090
October	1st to 10th	Day	25% 4 7% 16% 38% 10%	3480
	11th to 20th	Day	21% 3 5% 15% 28% 28%	3204
	21st to end	Day	29% 4 5% 21% 27% 15%	3428
November	1st to 10th	Day	32% 4 7% 16% 29% 11%	1810
	11th to 20th	Day	34% 3 6% 19% 28% 10%	1800
	21st to end	Day	35% 5% 7% 18% 28% 7%	1800
December	1st to 10th	Day	38% 4 5% 17% 27% 10%	2930
	11th to 20th	Day	44% 4 6% 16% 21% 8%	3370
	21st to end	Day	40% 4 9% 25% 20% 2	4466
January	1st to 10th	Night	33% 4 7% 16% 30% 9%	5889
	11th to 20th	Night	34% 4 5% 16% 29% 12%	5900
	21st to end	Night	40% 3 5% 15% 28% 9%	6471
February	1st to 10th	Night	37% 5% 9% 21% 22% 6%	2400
	11th to 20th	Night	46% 3 5% 17% 21% 7%	2339
	21st to end	Night	43% 5% 8% 15% 21% 8%	1980
March	1st to 10th	Night	45% 5% 8% 14% 22% 7%	5150
	11th to 20th	Night	27% 4 8% 16% 27% 17%	4980
	21st to end	Night	40% 4 7% 22% 19% 8%	5467
April	1st to 10th	Night	34% 5% 11% 19% 24% 7%	2200
	11th to 20th	Night	34% 4 7% 23% 22% 10%	1968
	21st to end	Night	34% 7% 10% 27% 19% 3	1800
May	1st to 10th	Night	39% 10% 14% 21% 14% 2	2930
	11th to 20th	Night	44% 8% 14% 22% 13% 1	2903
	21st to end	Night	31% 10% 16% 27% 16% 2	3138
June	1st to 10th	Night	41% 11% 16% 19% 10% 2	1710
	11th to 20th	Night	31% 11% 20% 24% 13% 1	1710
	21st to end	Night	33% 11% 18% 21% 14% 3	1710
July	1st to 10th	Night	48% 12% 18% 16% 5% 1	2795
	11th to 20th	Night	38% 14% 24% 18% 4 1	2786
	21st to end	Night	55% 12% 16% 12% 4 1	2988
August	1st to 10th	Night	38% 10% 24% 22% 5%	2814
	11th to 20th	Night	39% 11% 18% 18% 13% 1	2903
	21st to end	Night	32% 8% 14% 25% 19% 2	3492
September	1st to 10th	Night	39% 10% 13% 18% 16% 4	2090
	11th to 20th	Night	42% 8% 13% 18% 17% 2	2090
	21st to end	Night	38% 6% 11% 19% 19% 6%	2090
October	1st to 10th	Night	25% 6% 10% 15% 36% 9%	3480
	11th to 20th	Night	19% 3 5% 17% 31% 24%	3714
	21st to end	Night	26% 4 6% 21% 27% 17%	4120
November	1st to 10th	Night	32% 4 8% 19% 25% 11%	2484
	11th to 20th	Night	34% 3 6% 17% 28% 11%	2600
	21st to end	Night	37% 4 7% 20% 24% 7%	2600
December	1st to 10th	Night	36% 4 5% 17% 29% 8%	4250
	11th to 20th	Night	43% 4 8% 16% 21% 7%	4824
	21st to end	Night	42% 4 8% 25% 18% 2	6490

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	31% 20% 36% 11% 2	300
	11th to 20th	Day	32% 20% 28% 14% 5% 1	300
	21st to end	Day	31% 20% 34% 12% 2 1	330
February	1st to 10th	Day	29% 15% 37% 15% 3	300
	11th to 20th	Day	45% 18% 29% 8%	300
	21st to end	Day	37% 15% 34% 12% 2	249
March	1st to 10th	Day	29% 15% 28% 20% 7%	391
	11th to 20th	Day	27% 15% 33% 19% 5% 1	500
	21st to end	Day	29% 15% 30% 19% 6% 1	550
April	1st to 10th	Day	24% 14% 28% 22% 10% 1	500
	11th to 20th	Day	18% 15% 33% 21% 10% 3	492
	21st to end	Day	21% 10% 26% 25% 14% 4	500
May	1st to 10th	Day	17% 14% 29% 21% 12% 6%	503
	11th to 20th	Day	19% 7% 19% 28% 17% 9%	527
	21st to end	Day	18% 8% 19% 24% 20% 11%	549
June	1st to 10th	Day	17% 4 17% 28% 22% 12%	490
	11th to 20th	Day	11% 3 16% 28% 25% 18%	490
	21st to end	Day	11% 3 19% 29% 25% 13%	490
July	1st to 10th	Day	12% 1 11% 23% 29% 24%	485
	11th to 20th	Day	11% 1 10% 23% 33% 22%	484
	21st to end	Day	6% 2 8% 27% 34% 23%	532
August	1st to 10th	Day	15% 2 12% 26% 25% 20%	486
	11th to 20th	Day	15% 1 9% 27% 31% 17%	479
	21st to end	Day	17% 2 8% 24% 32% 18%	539
September	1st to 10th	Day	13% 3 15% 26% 30% 13%	490
	11th to 20th	Day	21% 3 12% 22% 32% 10%	490
	21st to end	Day	20% 4 16% 28% 23% 9%	490
October	1st to 10th	Day	20% 4 21% 29% 19% 8%	490
	11th to 20th	Day	16% 8% 23% 32% 17% 4	490
	21st to end	Day	20% 8% 24% 30% 16% 2	539
November	1st to 10th	Day	23% 6% 30% 25% 13% 3	348
	11th to 20th	Day	24% 17% 33% 20% 5%	300
	21st to end	Day	20% 13% 36% 21% 7% 2	300
December	1st to 10th	Day	32% 18% 29% 18% 4	300
	11th to 20th	Day	27% 15% 34% 18% 5% 1	300
	21st to end	Day	38% 12% 27% 18% 5% 1	330
January	1st to 10th	Night	25% 17% 30% 22% 6%	800
	11th to 20th	Night	23% 16% 30% 25% 6%	800
	21st to end	Night	23% 15% 35% 24% 3	880
February	1st to 10th	Night	21% 12% 31% 31% 6%	800
	11th to 20th	Night	27% 18% 29% 24% 2	783
	21st to end	Night	25% 14% 32% 26% 3	660
March	1st to 10th	Night	23% 13% 30% 30% 4	800
	11th to 20th	Night	20% 14% 30% 29% 7% 1	800
	21st to end	Night	21% 13% 28% 30% 8%	880
April	1st to 10th	Night	19% 14% 29% 28% 10%	800
	11th to 20th	Night	17% 12% 23% 33% 14% 1	606
	21st to end	Night	15% 7% 22% 34% 20% 2	600
May	1st to 10th	Night	15% 8% 21% 34% 21% 2	600
	11th to 20th	Night	20% 4 17% 31% 24% 4	591
	21st to end	Night	15% 2 14% 30% 33% 6%	634
June	1st to 10th	Night	14% 2 12% 33% 34% 5%	570
	11th to 20th	Night	9% 2 11% 32% 32% 14%	570
	21st to end	Night	9% 2 10% 37% 33% 9%	570
July	1st to 10th	Night	13% 2 7% 23% 43% 11%	555
	11th to 20th	Night	11% 1 5% 23% 45% 15%	552
	21st to end	Night	9% 3 5% 25% 45% 13%	624
August	1st to 10th	Night	15% 3 4 25% 39% 16%	567
	11th to 20th	Night	16% 2 6% 28% 38% 11%	564
	21st to end	Night	15% 1 5% 26% 42% 11%	630
September	1st to 10th	Night	13% 1 11% 29% 35% 10%	760
	11th to 20th	Night	20% 3 12% 26% 33% 6%	760
	21st to end	Night	18% 4 12% 35% 28% 3	760
October	1st to 10th	Night	17% 4 18% 31% 23% 6%	760
	11th to 20th	Night	15% 8% 22% 35% 18% 3	760
	21st to end	Night	17% 8% 21% 34% 19% 3	836
November	1st to 10th	Night	18% 7% 21% 33% 18% 3	780
	11th to 20th	Night	19% 10% 25% 32% 13% 1	800
	21st to end	Night	21% 11% 26% 31% 11% 1	800
December	1st to 10th	Night	26% 12% 24% 29% 8% 1	800
	11th to 20th	Night	22% 12% 26% 31% 10%	800
	21st to end	Night	30% 10% 25% 30% 5%	880

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