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 2024-11-02.

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% 5% 4 5% 4 6% 7% 41%	100979
	Night	16% 6% 2 5% 4 4 4 4 5% 7% 43%	97940
Transparency	Day	40% 8% 11% 19% 18% 5%	100792
	Night	39% 7% 11% 19% 19% 6%	97797
Seeing	Day	20% 8% 22% 23% 17% 9%	14936
	Night	19% 8% 20% 29% 19% 4	24956

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	18% 7% 2 5% 4 3 4 3 5% 6% 42%	2836
	11th to 20th	Day	17% 5% 2 5% 4 3 3 2 3 3 52%	2840
	21st to end	Day	27% 6% 2 4 2 2 3 2 3 5% 44%	3127
February	1st to 10th	Day	19% 7% 2 5% 3 3 4 3 5% 6% 42%	1900
	11th to 20th	Day	22% 6% 2 5% 3 3 3 4 5% 5% 43%	1848
	21st to end	Day	23% 6% 2 5% 4 4 3 4 4 6% 40%	1570
March	1st to 10th	Day	27% 6% 2 5% 3 3 3 2 4 5% 40%	3271
	11th to 20th	Day	14% 5% 2 4 4 3 4 3 4 5% 52%	3480
	21st to end	Day	20% 6% 2 6% 5% 4 4 3 4 6% 42%	3815
April	1st to 10th	Day	14% 4 2 4 5% 5% 5% 4 7% 7% 43%	2092
	11th to 20th	Day	14% 5% 2 5% 5% 4 4 4 5% 6% 46%	2270
	21st to end	Day	13% 4 2 4 4 4 4 4 5% 8% 48%	2470
May	1st to 10th	Day	13% 7% 3 7% 5% 4 4 3 6% 8% 40%	4082
	11th to 20th	Day	19% 6% 3 7% 4 4 5% 4 6% 7% 34%	4081
	21st to end	Day	9% 5% 2 5% 5% 5% 6% 5% 7% 10% 41%	4476
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	14% 5% 1 4 3 3 3 3 3 4 57%	2090
November	1st to 10th	Day	13% 4 2 4 3 2 3 3 4 5% 57%	1728
	11th to 20th	Day	17% 4 2 3 3 3 3 3 4 6% 52%	1710
	21st to end	Day	17% 5% 2 3 4 3 4 3 5% 6% 49%	1710
December	1st to 10th	Day	24% 6% 2 5% 4 4 4 3 5% 5% 38%	1710
	11th to 20th	Day	18% 5% 2 5% 3 3 4 3 4 5% 47%	2153
	21st to end	Day	24% 6% 1 4 2 3 4 2 5% 7% 40%	3124
January	1st to 10th	Night	19% 6% 2 5% 3 4 4 3 4 5% 46%	4109
	11th to 20th	Night	15% 7% 2 5% 4 3 3 3 5% 5% 48%	4120
	21st to end	Night	27% 7% 2 5% 3 3 3 2 4 4 42%	4527
February	1st to 10th	Night	16% 5% 2 4 3 4 4 3 5% 6% 47%	2280
	11th to 20th	Night	22% 6% 2 5% 4 4 3 3 4 4 43%	2218
	21st to end	Night	21% 6% 2 6% 4 4 4 3 5% 5% 39%	1884
March	1st to 10th	Night	27% 6% 2 5% 3 3 3 3 4 5% 38%	3580
	11th to 20th	Night	11% 4 2 4 3 3 4 4 6% 8% 51%	3480
	21st to end	Night	20% 6% 2 5% 4 3 3 4 4 5% 43%	3817
April	1st to 10th	Night	14% 4 1 5% 3 4 4 4 6% 6% 49%	2090
	11th to 20th	Night	14% 6% 2 5% 4 4 4 3 5% 6% 49%	1869
	21st to end	Night	11% 5% 2 6% 4 4 3 3 5% 7% 51%	1710
May	1st to 10th	Night	14% 7% 3 6% 5% 4 4 4 6% 9% 40%	2813
	11th to 20th	Night	20% 6% 2 5% 5% 4 3 3 5% 8% 39%	2812
	21st to end	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 45%	3079
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 4 2 3 3 3 4 5% 57%	2508
November	1st to 10th	Night	15% 4 2 4 2 3 2 3 3 5% 58%	2369
	11th to 20th	Night	16% 4 1 4 3 3 3 2 4 5% 53%	2470
	21st to end	Night	19% 5% 1 4 4 3 4 3 6% 6% 45%	2470
December	1st to 10th	Night	22% 6% 2 6% 3 3 3 3 4 5% 42%	2470
	11th to 20th	Night	17% 6% 2 4 2 2 3 3 4 6% 51%	3042
	21st to end	Night	23% 7% 2 5% 3 4 4 4 6% 7% 35%	4532

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	41% 5% 7% 18% 21% 8%	2837
	11th to 20th	Day	37% 4 6% 17% 27% 9%	2840
	21st to end	Day	45% 4 5% 17% 22% 8%	3127
February	1st to 10th	Day	43% 4 7% 19% 20% 6%	1900
	11th to 20th	Day	43% 5% 7% 18% 21% 7%	1858
	21st to end	Day	46% 5% 7% 14% 19% 9%	1570
March	1st to 10th	Day	48% 4 8% 15% 15% 10%	3271
	11th to 20th	Day	34% 5% 7% 16% 25% 13%	3480
	21st to end	Day	44% 5% 8% 19% 21% 4	3815
April	1st to 10th	Day	36% 7% 10% 19% 22% 6%	2092
	11th to 20th	Day	38% 6% 8% 16% 23% 9%	2270
	21st to end	Day	33% 6% 11% 27% 19% 4	2470
May	1st to 10th	Day	41% 9% 12% 17% 18% 3	4120
	11th to 20th	Day	46% 10% 10% 20% 13% 1	4085
	21st to end	Day	34% 11% 14% 21% 19% 1	4489
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	32% 5% 9% 18% 28% 8%	2090
	11th to 20th	Day	30% 5% 8% 21% 23% 13%	1938
	21st to end	Day	32% 3 5% 19% 28% 13%	2090
November	1st to 10th	Day	31% 4 7% 16% 31% 12%	1728
	11th to 20th	Day	34% 3 7% 19% 27% 10%	1710
	21st to end	Day	36% 5% 6% 18% 27% 7%	1710
December	1st to 10th	Day	47% 5% 5% 18% 18% 7%	1710
	11th to 20th	Day	38% 4 6% 16% 25% 10%	2150
	21st to end	Day	42% 4 9% 19% 23% 3	3124
January	1st to 10th	Night	39% 5% 8% 14% 27% 7%	4109
	11th to 20th	Night	38% 5% 7% 17% 23% 11%	4120
	21st to end	Night	47% 3 5% 13% 24% 8%	4527
February	1st to 10th	Night	38% 5% 8% 20% 22% 7%	2280
	11th to 20th	Night	45% 4 5% 17% 22% 7%	2219
	21st to end	Night	45% 5% 8% 15% 19% 7%	1884
March	1st to 10th	Night	47% 5% 9% 15% 16% 7%	3580
	11th to 20th	Night	30% 5% 10% 18% 26% 11%	3480
	21st to end	Night	43% 4 8% 19% 18% 8%	3817
April	1st to 10th	Night	33% 5% 11% 19% 24% 7%	2090
	11th to 20th	Night	35% 4 7% 22% 21% 10%	1869
	21st to end	Night	32% 7% 9% 28% 20% 3	1710
May	1st to 10th	Night	39% 10% 14% 21% 14% 2	2840
	11th to 20th	Night	43% 8% 13% 22% 13% 1	2813
	21st to end	Night	31% 10% 16% 27% 16% 2	3087
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	32% 5% 10% 18% 28% 6%	2090
	11th to 20th	Night	32% 5% 8% 20% 23% 12%	2241
	21st to end	Night	29% 4 6% 21% 27% 12%	2508
November	1st to 10th	Night	31% 4 8% 20% 26% 12%	2369
	11th to 20th	Night	34% 3 6% 17% 27% 12%	2470
	21st to end	Night	38% 4 7% 19% 24% 7%	2470
December	1st to 10th	Night	45% 5% 6% 18% 19% 6%	2470
	11th to 20th	Night	35% 4 8% 17% 28% 8%	3044
	21st to end	Night	45% 5% 9% 19% 19% 4	4532

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	30% 19% 38% 11% 2	270
	11th to 20th	Day	33% 18% 29% 15% 5% 1	270
	21st to end	Day	32% 20% 34% 11% 3 1	297
February	1st to 10th	Day	30% 16% 36% 15% 3	270
	11th to 20th	Day	43% 18% 30% 9%	270
	21st to end	Day	40% 15% 33% 11% 1	225
March	1st to 10th	Day	28% 14% 29% 20% 8%	356
	11th to 20th	Day	27% 15% 33% 20% 5% 1	460
	21st to end	Day	28% 14% 30% 20% 7% 1	506
April	1st to 10th	Day	24% 13% 28% 22% 11% 2	460
	11th to 20th	Day	18% 16% 31% 21% 10% 3	452
	21st to end	Day	20% 10% 27% 25% 14% 4	460
May	1st to 10th	Day	16% 13% 29% 22% 13% 6%	463
	11th to 20th	Day	20% 6% 17% 29% 18% 10%	487
	21st to end	Day	17% 7% 19% 25% 20% 12%	529
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% 31% 16% 2	539
November	1st to 10th	Day	22% 6% 30% 25% 14% 3	320
	11th to 20th	Day	24% 17% 32% 21% 5%	270
	21st to end	Day	19% 13% 36% 22% 7% 2	270
December	1st to 10th	Day	33% 16% 29% 18% 4	270
	11th to 20th	Day	26% 14% 35% 18% 5% 1	270
	21st to end	Day	38% 12% 27% 16% 6% 1	297
January	1st to 10th	Night	25% 16% 29% 23% 6%	760
	11th to 20th	Night	23% 16% 28% 26% 7%	760
	21st to end	Night	24% 15% 33% 24% 3	836
February	1st to 10th	Night	21% 13% 31% 30% 6%	760
	11th to 20th	Night	26% 18% 29% 25% 2	743
	21st to end	Night	26% 14% 32% 25% 3	628
March	1st to 10th	Night	22% 13% 30% 30% 4	760
	11th to 20th	Night	20% 14% 29% 29% 7% 1	760
	21st to end	Night	22% 13% 27% 30% 8%	836
April	1st to 10th	Night	19% 13% 29% 28% 10%	760
	11th to 20th	Night	18% 12% 23% 32% 14% 1	576
	21st to end	Night	14% 6% 23% 34% 21% 2	570
May	1st to 10th	Night	15% 8% 21% 33% 22% 2	570
	11th to 20th	Night	19% 3 17% 31% 25% 4	561
	21st to end	Night	16% 2 12% 31% 34% 6%	617
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% 20% 34% 19% 3	836
November	1st to 10th	Night	18% 7% 21% 33% 19% 3	745
	11th to 20th	Night	19% 10% 25% 32% 13% 1	760
	21st to end	Night	21% 10% 25% 31% 12% 1	760
December	1st to 10th	Night	27% 12% 22% 30% 8% 1	760
	11th to 20th	Night	22% 11% 26% 31% 10%	760
	21st to end	Night	30% 10% 25% 29% 5%	836

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