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 2026-09-29.

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	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	148689
	Night	15% 6% 2 6% 4 4 4 4 5% 7% 43%	142713
Transparency	Day	39% 8% 12% 19% 17% 6%	152452
	Night	38% 6% 12% 19% 19% 6%	147022
Seeing	Day	20% 9% 23% 23% 17% 8%	17474
	Night	18% 8% 21% 30% 19% 4	27455

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	19% 7% 2 6% 4 3 4 2 3 5% 46%	5258
	11th to 20th	Day	11% 5% 1 4 3 3 2 2 3 3 63%	5280
	21st to end	Day	23% 7% 3 7% 3 3 3 3 4 5% 39%	5797
February	1st to 10th	Day	17% 7% 2 5% 4 3 4 3 5% 5% 44%	2100
	11th to 20th	Day	22% 6% 2 5% 3 3 3 4 5% 5% 42%	2048
	21st to end	Day	21% 6% 2 5% 4 4 3 4 4 6% 42%	1730
March	1st to 10th	Day	22% 7% 2 6% 4 4 4 3 4 5% 40%	4806
	11th to 20th	Day	11% 5% 2 5% 4 3 3 3 4 6% 54%	5090
	21st to end	Day	18% 6% 2 5% 4 4 3 3 4 5% 46%	5586
April	1st to 10th	Day	14% 4 2 4 5% 5% 5% 4 7% 7% 42%	2312
	11th to 20th	Day	13% 5% 2 5% 5% 4 4 3 5% 6% 48%	2512
	21st to end	Day	14% 4 2 5% 4 4 4 4 5% 8% 47%	2730
May	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 4 6% 8% 37%	7616
	11th to 20th	Day	16% 7% 3 7% 5% 5% 6% 4 7% 8% 33%	7626
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 6% 7% 31%	8391
June	1st to 10th	Day	12% 7% 3 7% 6% 5% 6% 5% 8% 9% 33%	2730
	11th to 20th	Day	7% 5% 2 5% 6% 6% 6% 6% 9% 12% 37%	2730
	21st to end	Day	7% 4 2 6% 6% 6% 5% 6% 9% 12% 37%	2730
July	1st to 10th	Day	5% 4 2 7% 6% 6% 7% 6% 9% 13% 36%	7680
	11th to 20th	Day	7% 5% 2 7% 6% 7% 8% 7% 10% 13% 28%	7680
	21st to end	Day	9% 6% 3 9% 7% 7% 8% 6% 9% 11% 26%	8340
August	1st to 10th	Day	10% 7% 3 8% 6% 6% 7% 6% 8% 12% 27%	6014
	11th to 20th	Day	6% 4 2 5% 4 5% 6% 5% 7% 13% 44%	5810
	21st to end	Day	7% 4 2 6% 4 5% 6% 4 7% 8% 47%	6015
September	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 9% 39%	2310
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 7% 40%	2310
	21st to end	Day	16% 6% 2 6% 4 4 4 3 6% 7% 44%	2288
October	1st to 10th	Day	14% 5% 1 4 3 3 3 3 4 6% 53%	2200
	11th to 20th	Day	13% 5% 2 3 2 2 3 2 4 6% 58%	2040
	21st to end	Day	15% 5% 1 4 3 2 3 3 3 4 57%	2200
November	1st to 10th	Day	13% 5% 2 4 3 2 3 3 4 5% 56%	1902
	11th to 20th	Day	16% 4 2 3 3 3 3 2 4 7% 53%	1890
	21st to end	Day	17% 5% 2 3 4 3 3 3 5% 6% 50%	1890
December	1st to 10th	Day	21% 5% 1 3 3 3 4 3 4 5% 48%	3020
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 4 4 43%	3463
	21st to end	Day	24% 5% 1 4 2 3 3 2 5% 7% 44%	4565
January	1st to 10th	Night	18% 5% 1 4 3 3 3 3 4 6% 49%	7635
	11th to 20th	Night	13% 6% 2 5% 3 3 2 3 4 5% 54%	7680
	21st to end	Night	21% 8% 2 5% 3 3 3 2 4 4 45%	8368
February	1st to 10th	Night	16% 5% 2 5% 3 4 4 3 5% 6% 48%	2520
	11th to 20th	Night	22% 7% 3 5% 4 4 3 3 4 4 42%	2458
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 40%	2076
March	1st to 10th	Night	23% 6% 2 6% 4 4 4 3 5% 6% 38%	5265
	11th to 20th	Night	11% 4 1 3 3 3 4 4 5% 8% 54%	5090
	21st to end	Night	17% 6% 2 6% 4 3 4 3 4 6% 45%	5588
April	1st to 10th	Night	14% 4 1 5% 4 4 4 4 6% 6% 48%	2310
	11th to 20th	Night	12% 5% 2 4 4 3 4 3 4 6% 51%	2068
	21st to end	Night	11% 5% 2 6% 3 4 3 4 5% 7% 49%	1890
May	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 4 6% 8% 35%	5237
	11th to 20th	Night	19% 7% 2 6% 5% 4 4 4 5% 8% 36%	5234
	21st to end	Night	19% 8% 3 6% 5% 4 5% 4 6% 7% 33%	5761
June	1st to 10th	Night	11% 6% 3 6% 6% 6% 6% 5% 8% 9% 35%	1890
	11th to 20th	Night	8% 5% 2 5% 4 5% 6% 4 8% 11% 41%	1890
	21st to end	Night	8% 4 2 6% 5% 4 5% 5% 7% 10% 44%	1890
July	1st to 10th	Night	7% 6% 3 8% 5% 6% 7% 5% 8% 11% 32%	5278
	11th to 20th	Night	7% 6% 3 8% 6% 6% 7% 6% 9% 13% 30%	5277
	21st to end	Night	13% 8% 3 9% 5% 6% 5% 4 7% 10% 30%	5736
August	1st to 10th	Night	12% 8% 3 7% 5% 5% 6% 5% 8% 11% 29%	4135
	11th to 20th	Night	8% 5% 2 6% 4 4 4 4 9% 12% 42%	4231
	21st to end	Night	8% 5% 3 6% 5% 4 5% 5% 6% 9% 45%	5062
September	1st to 10th	Night	11% 6% 2 6% 5% 4 6% 4 6% 9% 41%	2310
	11th to 20th	Night	16% 7% 3 5% 4 5% 4 4 6% 8% 39%	2310
	21st to end	Night	14% 6% 2 6% 4 4 4 3 5% 6% 46%	2289
October	1st to 10th	Night	14% 5% 2 4 4 4 3 2 4 5% 53%	2200
	11th to 20th	Night	13% 4 2 4 3 3 3 3 4 5% 56%	2359
	21st to end	Night	15% 4 1 4 3 3 3 3 4 5% 57%	2640
November	1st to 10th	Night	15% 5% 2 4 2 3 2 3 3 5% 56%	2611
	11th to 20th	Night	16% 4 2 4 3 3 3 2 4 5% 54%	2730
	21st to end	Night	18% 5% 1 4 4 3 3 3 6% 6% 47%	2730
December	1st to 10th	Night	19% 5% 2 4 3 2 3 3 4 4 51%	4380
	11th to 20th	Night	20% 6% 3 6% 3 3 3 3 4 5% 44%	4952
	21st to end	Night	23% 6% 2 4 2 3 3 3 5% 6% 42%	6633

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% 4 6% 21% 21% 7%	5259
	11th to 20th	Day	28% 3 4 13% 34% 18%	5280
	21st to end	Day	49% 3 4 15% 18% 11%	5797
February	1st to 10th	Day	42% 4 7% 21% 20% 6%	2100
	11th to 20th	Day	43% 5% 7% 19% 20% 7%	2058
	21st to end	Day	44% 5% 7% 14% 20% 9%	1730
March	1st to 10th	Day	47% 4 6% 14% 19% 10%	4806
	11th to 20th	Day	31% 4 6% 14% 23% 20%	5090
	21st to end	Day	42% 4 7% 22% 20% 5%	5586
April	1st to 10th	Day	37% 7% 11% 19% 21% 6%	2312
	11th to 20th	Day	36% 5% 8% 18% 25% 8%	2512
	21st to end	Day	34% 6% 11% 27% 18% 3	2730
May	1st to 10th	Day	44% 7% 12% 21% 14% 2	7651
	11th to 20th	Day	45% 9% 15% 19% 10% 2	7630
	21st to end	Day	51% 9% 10% 15% 13% 2	8405
June	1st to 10th	Day	43% 11% 16% 20% 9% 2	2730
	11th to 20th	Day	35% 11% 19% 21% 12% 1	2730
	21st to end	Day	35% 12% 18% 19% 13% 3	2730
July	1st to 10th	Day	34% 13% 23% 24% 5% 1	7615
	11th to 20th	Day	40% 15% 28% 15% 2 1	7611
	21st to end	Day	46% 12% 17% 18% 7% 1	8156
August	1st to 10th	Day	44% 13% 17% 22% 4	6001
	11th to 20th	Day	28% 9% 27% 22% 11% 2	5849
	21st to end	Day	31% 9% 15% 25% 18% 2	6015
September	1st to 10th	Day	38% 9% 14% 19% 17% 3	2310
	11th to 20th	Day	40% 9% 12% 19% 19% 2	2310
	21st to end	Day	39% 6% 12% 18% 19% 6%	2288
October	1st to 10th	Day	26% 5% 7% 16% 37% 10%	3590
	11th to 20th	Day	21% 3 5% 15% 28% 28%	3306
	21st to end	Day	29% 4 5% 20% 28% 14%	3538
November	1st to 10th	Day	31% 4 7% 17% 29% 11%	1902
	11th to 20th	Day	33% 3 7% 21% 27% 10%	1890
	21st to end	Day	35% 5% 7% 18% 28% 7%	1890
December	1st to 10th	Day	39% 4 5% 17% 26% 10%	3020
	11th to 20th	Day	43% 4 7% 16% 21% 9%	3460
	21st to end	Day	39% 4 9% 26% 19% 2	4565
January	1st to 10th	Night	36% 4 11% 19% 23% 7%	7636
	11th to 20th	Night	33% 3 5% 16% 29% 13%	7680
	21st to end	Night	43% 3 5% 15% 24% 11%	8368
February	1st to 10th	Night	37% 4 8% 21% 22% 6%	2520
	11th to 20th	Night	46% 3 5% 17% 22% 7%	2459
	21st to end	Night	43% 5% 8% 15% 20% 8%	2076
March	1st to 10th	Night	45% 5% 8% 14% 22% 6%	5265
	11th to 20th	Night	27% 5% 8% 16% 27% 16%	5090
	21st to end	Night	40% 4 7% 22% 19% 8%	5588
April	1st to 10th	Night	34% 5% 11% 19% 24% 6%	2310
	11th to 20th	Night	33% 4 7% 24% 22% 10%	2068
	21st to end	Night	34% 7% 10% 27% 20% 3	1890
May	1st to 10th	Night	44% 8% 13% 20% 12% 2	5264
	11th to 20th	Night	46% 7% 15% 20% 11% 1	5235
	21st to end	Night	48% 9% 12% 19% 11% 1	5771
June	1st to 10th	Night	41% 11% 16% 19% 11% 2	1890
	11th to 20th	Night	33% 11% 20% 23% 12% 1	1890
	21st to end	Night	32% 11% 19% 21% 14% 3	1890
July	1st to 10th	Night	40% 13% 23% 19% 4	5235
	11th to 20th	Night	41% 15% 27% 15% 2 1	5226
	21st to end	Night	48% 10% 19% 16% 5% 2	5606
August	1st to 10th	Night	46% 12% 20% 18% 4	4124
	11th to 20th	Night	31% 10% 26% 21% 12% 1	4258
	21st to end	Night	34% 8% 16% 24% 17% 1	5062
September	1st to 10th	Night	38% 10% 14% 19% 15% 4	2310
	11th to 20th	Night	41% 8% 13% 20% 16% 2	2310
	21st to end	Night	39% 6% 12% 19% 18% 6%	2289
October	1st to 10th	Night	26% 6% 10% 15% 35% 8%	3590
	11th to 20th	Night	19% 3 6% 18% 31% 23%	3832
	21st to end	Night	27% 4 6% 20% 27% 16%	4252
November	1st to 10th	Night	32% 4 8% 19% 26% 11%	2611
	11th to 20th	Night	33% 3 7% 17% 29% 11%	2730
	21st to end	Night	37% 4 7% 20% 24% 8%	2730
December	1st to 10th	Night	37% 4 5% 17% 29% 8%	4380
	11th to 20th	Night	42% 4 8% 16% 22% 7%	4954
	21st to end	Night	42% 4 8% 25% 18% 2	6633

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	32% 20% 35% 11% 2	330
	11th to 20th	Day	32% 22% 27% 14% 5% 1	330
	21st to end	Day	32% 20% 34% 11% 2 1	363
February	1st to 10th	Day	27% 17% 38% 15% 3	330
	11th to 20th	Day	43% 19% 28% 9%	330
	21st to end	Day	36% 16% 34% 11% 2	273
March	1st to 10th	Day	27% 15% 29% 21% 7%	426
	11th to 20th	Day	27% 15% 33% 19% 5% 1	540
	21st to end	Day	27% 15% 32% 19% 6% 1	594
April	1st to 10th	Day	24% 13% 29% 23% 11% 1	540
	11th to 20th	Day	17% 15% 33% 23% 10% 3	532
	21st to end	Day	20% 10% 26% 25% 14% 4	540
May	1st to 10th	Day	17% 15% 29% 21% 13% 6%	543
	11th to 20th	Day	18% 7% 19% 29% 17% 9%	567
	21st to end	Day	20% 8% 19% 24% 18% 11%	617
June	1st to 10th	Day	16% 5% 17% 28% 23% 11%	570
	11th to 20th	Day	10% 4 19% 26% 24% 16%	570
	21st to end	Day	10% 2 19% 31% 25% 13%	570
July	1st to 10th	Day	10% 2 11% 25% 30% 23%	565
	11th to 20th	Day	10% 2 10% 23% 33% 22%	564
	21st to end	Day	6% 2 10% 27% 33% 21%	620
August	1st to 10th	Day	17% 2 12% 27% 24% 18%	566
	11th to 20th	Day	13% 2 8% 28% 32% 18%	559
	21st to end	Day	15% 2 11% 25% 31% 16%	627
September	1st to 10th	Day	12% 3 14% 28% 30% 14%	570
	11th to 20th	Day	18% 3 12% 24% 33% 11%	570
	21st to end	Day	19% 4 18% 28% 22% 9%	562
October	1st to 10th	Day	19% 4 21% 30% 18% 7%	530
	11th to 20th	Day	16% 7% 22% 33% 18% 4	530
	21st to end	Day	21% 8% 25% 28% 15% 2	583
November	1st to 10th	Day	22% 7% 31% 24% 13% 3	380
	11th to 20th	Day	22% 17% 35% 21% 5%	330
	21st to end	Day	21% 15% 35% 21% 7% 2	330
December	1st to 10th	Day	32% 19% 30% 16% 3	330
	11th to 20th	Day	27% 15% 34% 19% 5% 1	330
	21st to end	Day	36% 12% 28% 19% 5% 1	363
January	1st to 10th	Night	26% 16% 30% 23% 6%	840
	11th to 20th	Night	23% 16% 30% 25% 6%	840
	21st to end	Night	24% 15% 35% 23% 3	924
February	1st to 10th	Night	21% 13% 31% 30% 5%	840
	11th to 20th	Night	26% 18% 30% 24% 2	823
	21st to end	Night	26% 14% 33% 25% 3	692
March	1st to 10th	Night	22% 13% 30% 31% 4	840
	11th to 20th	Night	19% 13% 30% 30% 7% 1	840
	21st to end	Night	21% 13% 28% 30% 8%	924
April	1st to 10th	Night	19% 14% 28% 29% 10%	840
	11th to 20th	Night	16% 11% 23% 34% 14% 1	637
	21st to end	Night	15% 7% 22% 35% 20% 2	630
May	1st to 10th	Night	15% 8% 22% 34% 20% 1	630
	11th to 20th	Night	19% 4 17% 31% 24% 4	621
	21st to end	Night	18% 2 13% 30% 31% 6%	683
June	1st to 10th	Night	13% 2 13% 34% 34% 5%	630
	11th to 20th	Night	10% 2 11% 32% 31% 13%	630
	21st to end	Night	9% 2 9% 37% 35% 9%	630
July	1st to 10th	Night	12% 2 7% 23% 45% 11%	615
	11th to 20th	Night	11% 2 5% 22% 46% 14%	612
	21st to end	Night	9% 3 6% 26% 43% 12%	690
August	1st to 10th	Night	16% 3 4 24% 38% 14%	627
	11th to 20th	Night	16% 2 6% 26% 39% 11%	624
	21st to end	Night	15% 2 6% 28% 40% 10%	696
September	1st to 10th	Night	13% 2 10% 31% 35% 9%	840
	11th to 20th	Night	18% 4 11% 28% 34% 5%	840
	21st to end	Night	17% 4 13% 35% 28% 3	833
October	1st to 10th	Night	17% 4 18% 32% 23% 6%	800
	11th to 20th	Night	14% 7% 22% 36% 18% 3	800
	21st to end	Night	17% 8% 22% 33% 18% 3	880
November	1st to 10th	Night	18% 6% 21% 34% 18% 3	820
	11th to 20th	Night	19% 9% 25% 33% 12% 1	840
	21st to end	Night	20% 11% 27% 30% 11% 1	840
December	1st to 10th	Night	26% 12% 25% 29% 7% 1	840
	11th to 20th	Night	22% 12% 26% 30% 9%	840
	21st to end	Night	29% 11% 25% 30% 5%	924

Page generated at 2026-09-26 04:18:44. Version ac07

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