Luckey
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Luckey clear sky chart from 2005-11-06 to 2026-05-17.

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% 10% 4 8% 5% 5% 5% 4 5% 7% 33%	131943
	Night	15% 10% 4 8% 5% 4 4 4 5% 6% 34%	131000
Transparency	Day	51% 3 11% 22% 13% 1	135542
	Night	50% 3 11% 22% 13% 1	135458
Seeing	Day	18% 10% 28% 24% 14% 6%	17569
	Night	19% 9% 28% 29% 13% 1	27424

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% 18% 7% 16% 6% 4 4 3 6% 6% 15%	4691
	11th to 20th	Day	12% 17% 7% 14% 9% 6% 6% 3 4 4 18%	4859
	21st to end	Day	19% 15% 7% 13% 6% 6% 6% 4 5% 5% 16%	5780
February	1st to 10th	Day	15% 15% 5% 12% 7% 6% 5% 4 5% 5% 21%	1890
	11th to 20th	Day	15% 12% 5% 12% 8% 5% 5% 4 5% 5% 24%	2022
	21st to end	Day	16% 13% 4 9% 5% 5% 5% 3 6% 7% 26%	1730
March	1st to 10th	Day	18% 12% 6% 11% 5% 4 4 3 4 5% 27%	4708
	11th to 20th	Day	12% 11% 3 7% 4 5% 4 4 5% 6% 39%	5090
	21st to end	Day	18% 13% 5% 10% 5% 5% 5% 3 5% 6% 25%	5586
April	1st to 10th	Day	14% 12% 4 9% 6% 5% 5% 5% 5% 7% 29%	2431
	11th to 20th	Day	16% 8% 3 7% 5% 5% 4 4 6% 7% 34%	2644
	21st to end	Day	18% 9% 3 7% 4 4 4 3 5% 6% 35%	2730
May	1st to 10th	Day	22% 9% 3 7% 5% 4 5% 4 5% 6% 30%	5992
	11th to 20th	Day	17% 8% 2 7% 5% 5% 5% 4 6% 7% 35%	5939
	21st to end	Day	17% 5% 2 6% 5% 4 5% 4 6% 8% 39%	6433
June	1st to 10th	Day	12% 6% 2 6% 5% 5% 6% 5% 6% 8% 40%	2701
	11th to 20th	Day	10% 6% 2 6% 5% 6% 4 4 6% 9% 42%	2800
	21st to end	Day	10% 6% 2 7% 5% 5% 5% 5% 7% 10% 38%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 4 6% 10% 41%	6360
	11th to 20th	Day	8% 5% 2 6% 5% 6% 6% 5% 7% 10% 40%	6314
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	6424
August	1st to 10th	Day	11% 5% 1 6% 4 4 6% 5% 7% 9% 43%	4234
	11th to 20th	Day	9% 5% 2 6% 5% 5% 7% 6% 8% 10% 38%	4174
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 4 7% 10% 43%	4578
September	1st to 10th	Day	13% 6% 2 6% 4 3 5% 4 5% 9% 45%	2252
	11th to 20th	Day	8% 6% 2 5% 4 4 5% 4 5% 9% 48%	2200
	21st to end	Day	17% 7% 3 6% 3 4 5% 3 5% 6% 41%	2200
October	1st to 10th	Day	12% 7% 2 6% 4 5% 5% 3 6% 8% 44%	2159
	11th to 20th	Day	17% 7% 2 7% 5% 4 4 3 5% 7% 39%	2000
	21st to end	Day	18% 9% 3 7% 6% 4 5% 4 6% 7% 32%	2060
November	1st to 10th	Day	12% 10% 3 6% 5% 4 4 4 6% 6% 41%	1852
	11th to 20th	Day	17% 13% 3 7% 5% 4 4 3 4 6% 34%	1890
	21st to end	Day	18% 15% 4 9% 5% 4 4 3 5% 6% 27%	1890
December	1st to 10th	Day	14% 15% 7% 11% 6% 5% 5% 4 4 6% 23%	3020
	11th to 20th	Day	19% 17% 7% 10% 5% 5% 4 3 4 5% 22%	3440
	21st to end	Day	25% 20% 6% 12% 5% 4 3 2 3 4 14%	4070
January	1st to 10th	Night	15% 16% 6% 15% 6% 5% 5% 3 4 4 20%	8232
	11th to 20th	Night	10% 17% 8% 14% 7% 6% 5% 4 4 5% 20%	8119
	21st to end	Night	17% 14% 6% 10% 5% 4 5% 4 5% 6% 24%	8401
February	1st to 10th	Night	17% 14% 5% 10% 6% 5% 4 4 5% 5% 24%	2730
	11th to 20th	Night	14% 14% 4 9% 6% 6% 5% 4 6% 7% 26%	2479
	21st to end	Night	19% 13% 5% 9% 5% 4 4 3 5% 5% 29%	2076
March	1st to 10th	Night	18% 11% 4 7% 5% 4 3 2 4 5% 36%	5364
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 4 6% 7% 43%	5090
	21st to end	Night	16% 9% 4 8% 4 4 4 3 4 6% 36%	5588
April	1st to 10th	Night	17% 10% 3 7% 5% 5% 4 4 5% 6% 33%	2205
	11th to 20th	Night	16% 8% 2 7% 5% 5% 4 3 5% 7% 36%	1925
	21st to end	Night	17% 8% 2 6% 4 4 5% 3 6% 7% 38%	1890
May	1st to 10th	Night	21% 10% 3 8% 6% 4 5% 3 5% 6% 28%	4123
	11th to 20th	Night	18% 7% 3 7% 4 3 4 3 5% 7% 38%	4086
	21st to end	Night	14% 6% 2 6% 5% 5% 4 4 5% 8% 42%	4421
June	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 5% 7% 45%	1693
	11th to 20th	Night	10% 5% 2 6% 5% 4 4 4 8% 8% 44%	1600
	21st to end	Night	9% 5% 2 5% 4 4 4 5% 7% 9% 46%	1600
July	1st to 10th	Night	9% 4 2 6% 5% 5% 4 4 6% 10% 46%	3618
	11th to 20th	Night	9% 5% 2 5% 4 5% 5% 4 7% 9% 44%	3657
	21st to end	Night	9% 5% 2 5% 4 4 5% 4 6% 9% 47%	4427
August	1st to 10th	Night	13% 5% 2 7% 4 4 4 4 5% 8% 44%	2915
	11th to 20th	Night	9% 5% 2 5% 4 4 5% 5% 5% 8% 47%	2875
	21st to end	Night	8% 4 2 6% 5% 4 5% 4 6% 7% 48%	3316
September	1st to 10th	Night	10% 6% 2 5% 4 3 4 3 6% 6% 51%	2126
	11th to 20th	Night	8% 5% 2 5% 4 4 3 3 4 7% 56%	2200
	21st to end	Night	14% 6% 3 6% 4 4 4 3 5% 6% 45%	2200
October	1st to 10th	Night	12% 5% 2 6% 4 4 4 3 5% 7% 49%	2240
	11th to 20th	Night	17% 8% 3 7% 4 4 4 3 4 6% 40%	2400
	21st to end	Night	20% 8% 3 6% 4 4 4 3 5% 7% 37%	2778
November	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 5% 6% 43%	2666
	11th to 20th	Night	15% 11% 3 8% 6% 4 5% 4 5% 6% 34%	2730
	21st to end	Night	19% 15% 3 8% 5% 5% 4 4 5% 6% 26%	2730
December	1st to 10th	Night	13% 12% 6% 11% 6% 5% 5% 4 5% 6% 26%	4380
	11th to 20th	Night	16% 18% 7% 11% 5% 4 4 4 4 5% 23%	4970
	21st to end	Night	25% 18% 6% 10% 5% 4 4 3 4 5% 14%	7150

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	71% 2 11% 13% 3	4692
	11th to 20th	Day	72% 2 6% 8% 12%	4859
	21st to end	Day	73% 1 8% 11% 6%	5780
February	1st to 10th	Day	65% 4 10% 15% 6%	1890
	11th to 20th	Day	61% 4 9% 18% 7% 1	2032
	21st to end	Day	57% 3 15% 16% 7% 1	1730
March	1st to 10th	Day	62% 2 9% 19% 8% 1	4708
	11th to 20th	Day	47% 2 13% 26% 10% 1	5090
	21st to end	Day	61% 2 10% 17% 9% 1	5586
April	1st to 10th	Day	54% 4 10% 18% 12% 1	2431
	11th to 20th	Day	49% 4 12% 21% 13% 2	2644
	21st to end	Day	50% 4 11% 23% 11% 2	2730
May	1st to 10th	Day	55% 3 9% 18% 13% 1	6027
	11th to 20th	Day	49% 3 12% 22% 12% 2	5943
	21st to end	Day	44% 3 10% 23% 16% 3	6447
June	1st to 10th	Day	41% 5% 11% 26% 14% 3	2701
	11th to 20th	Day	40% 5% 13% 23% 17% 3	2800
	21st to end	Day	40% 6% 14% 21% 15% 4	2800
July	1st to 10th	Day	40% 2 9% 27% 19% 2	6291
	11th to 20th	Day	39% 3 13% 26% 18% 1	6239
	21st to end	Day	40% 3 12% 22% 20% 2	6240
August	1st to 10th	Day	37% 5% 14% 28% 16% 1	4221
	11th to 20th	Day	39% 4 11% 32% 12% 1	4213
	21st to end	Day	37% 3 11% 34% 13% 2	4577
September	1st to 10th	Day	37% 5% 11% 26% 18% 3	2252
	11th to 20th	Day	33% 4 11% 31% 20% 2	2200
	21st to end	Day	43% 4 11% 24% 18% 1	2200
October	1st to 10th	Day	30% 3 12% 34% 21% 1	3510
	11th to 20th	Day	40% 2 9% 28% 20% 1	3240
	21st to end	Day	42% 3 11% 25% 19% 1	3310
November	1st to 10th	Day	42% 4 10% 26% 16% 1	1852
	11th to 20th	Day	53% 4 10% 20% 12% 1	1890
	21st to end	Day	58% 4 11% 20% 7%	1890
December	1st to 10th	Day	64% 2 14% 15% 4	3020
	11th to 20th	Day	66% 2 10% 17% 5%	3437
	21st to end	Day	77% 2 7% 9% 4	4070
January	1st to 10th	Night	69% 2 8% 16% 5%	8233
	11th to 20th	Night	68% 1 9% 11% 9% 1	8119
	21st to end	Night	63% 1 12% 14% 9%	8401
February	1st to 10th	Night	61% 4 11% 16% 6% 1	2730
	11th to 20th	Night	58% 4 9% 20% 8% 1	2480
	21st to end	Night	58% 3 11% 17% 9% 1	2076
March	1st to 10th	Night	52% 2 10% 25% 9% 1	5364
	11th to 20th	Night	41% 3 13% 27% 15% 1	5090
	21st to end	Night	51% 3 8% 22% 15% 1	5588
April	1st to 10th	Night	51% 4 10% 19% 13% 2	2205
	11th to 20th	Night	48% 4 10% 20% 17% 2	1925
	21st to end	Night	46% 4 10% 23% 14% 2	1890
May	1st to 10th	Night	58% 3 8% 15% 13% 2	4150
	11th to 20th	Night	47% 3 10% 25% 13% 1	4087
	21st to end	Night	41% 3 10% 26% 17% 2	4429
June	1st to 10th	Night	38% 4 10% 26% 18% 3	1693
	11th to 20th	Night	35% 6% 12% 27% 16% 3	1600
	21st to end	Night	33% 6% 14% 26% 18% 2	1600
July	1st to 10th	Night	36% 3 13% 25% 18% 5%	3580
	11th to 20th	Night	37% 3 15% 28% 16% 1	3612
	21st to end	Night	35% 3 14% 23% 20% 4	4297
August	1st to 10th	Night	39% 4 12% 28% 15% 2	2904
	11th to 20th	Night	35% 4 12% 30% 18% 1	2902
	21st to end	Night	35% 4 12% 30% 17% 2	3316
September	1st to 10th	Night	34% 5% 11% 28% 18% 4	2126
	11th to 20th	Night	29% 4 9% 30% 26% 2	2200
	21st to end	Night	41% 4 10% 23% 20% 2	2200
October	1st to 10th	Night	26% 2 8% 31% 32% 1	3656
	11th to 20th	Night	38% 2 9% 29% 21% 1	3899
	21st to end	Night	37% 2 8% 34% 16% 3	4478
November	1st to 10th	Night	42% 3 11% 26% 17% 2	2666
	11th to 20th	Night	50% 4 11% 23% 11% 2	2730
	21st to end	Night	60% 3 12% 19% 6%	2730
December	1st to 10th	Night	60% 3 12% 19% 7% 1	4380
	11th to 20th	Night	65% 3 11% 14% 7% 1	4972
	21st to end	Night	74% 2 10% 9% 5%	7150

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	23% 19% 33% 19% 5% 1	330
	11th to 20th	Day	23% 22% 38% 12% 5% 1	330
	21st to end	Day	25% 17% 33% 21% 4 1	363
February	1st to 10th	Day	25% 14% 41% 15% 4 1	330
	11th to 20th	Day	23% 18% 35% 22% 2	330
	21st to end	Day	25% 19% 43% 11% 2	273
March	1st to 10th	Day	22% 16% 39% 18% 5% 1	380
	11th to 20th	Day	24% 13% 37% 19% 5% 1	540
	21st to end	Day	28% 15% 32% 18% 6%	594
April	1st to 10th	Day	23% 15% 32% 18% 11% 1	540
	11th to 20th	Day	21% 18% 30% 19% 8% 3	532
	21st to end	Day	24% 11% 30% 24% 9% 2	540
May	1st to 10th	Day	25% 10% 32% 20% 11% 2	543
	11th to 20th	Day	19% 11% 29% 23% 12% 7%	551
	21st to end	Day	15% 7% 25% 26% 17% 10%	573
June	1st to 10th	Day	13% 6% 27% 32% 16% 5%	631
	11th to 20th	Day	13% 7% 28% 28% 18% 5%	730
	21st to end	Day	12% 6% 27% 31% 18% 6%	730
July	1st to 10th	Day	10% 4 20% 34% 19% 13%	721
	11th to 20th	Day	9% 4 23% 31% 21% 11%	698
	21st to end	Day	11% 4 18% 27% 27% 13%	576
August	1st to 10th	Day	12% 2 14% 29% 29% 15%	526
	11th to 20th	Day	13% 3 15% 31% 24% 14%	519
	21st to end	Day	10% 2 18% 28% 28% 14%	583
September	1st to 10th	Day	15% 5% 16% 27% 25% 13%	530
	11th to 20th	Day	8% 3 13% 26% 31% 19%	530
	21st to end	Day	21% 7% 21% 23% 18% 11%	530
October	1st to 10th	Day	13% 7% 24% 27% 21% 9%	530
	11th to 20th	Day	17% 14% 30% 26% 11% 2	530
	21st to end	Day	24% 10% 35% 23% 7% 1	443
November	1st to 10th	Day	15% 15% 32% 23% 12% 3	330
	11th to 20th	Day	27% 17% 30% 18% 7% 1	330
	21st to end	Day	27% 14% 35% 22% 2	330
December	1st to 10th	Day	22% 18% 33% 18% 8%	330
	11th to 20th	Day	22% 21% 34% 18% 5%	330
	21st to end	Day	28% 17% 33% 18% 4	363
January	1st to 10th	Night	24% 13% 35% 21% 6%	1050
	11th to 20th	Night	26% 15% 36% 18% 4 1	993
	21st to end	Night	24% 14% 36% 21% 4	924
February	1st to 10th	Night	25% 12% 34% 25% 4	840
	11th to 20th	Night	22% 13% 36% 26% 3	823
	21st to end	Night	26% 16% 37% 19% 2	692
March	1st to 10th	Night	21% 12% 34% 26% 6%	840
	11th to 20th	Night	19% 15% 35% 24% 6% 1	840
	21st to end	Night	23% 12% 31% 26% 7%	924
April	1st to 10th	Night	22% 14% 35% 25% 4 1	735
	11th to 20th	Night	21% 11% 33% 27% 8% 1	623
	21st to end	Night	21% 7% 33% 28% 9% 1	630
May	1st to 10th	Night	21% 6% 29% 33% 9% 1	630
	11th to 20th	Night	20% 6% 27% 30% 15% 1	609
	21st to end	Night	12% 3 25% 39% 20% 2	650
June	1st to 10th	Night	13% 5% 23% 43% 17%	600
	11th to 20th	Night	12% 4 21% 45% 17% 1	600
	21st to end	Night	12% 1 23% 40% 21% 2	600
July	1st to 10th	Night	11% 1 15% 41% 28% 3	585
	11th to 20th	Night	9% 3 18% 41% 25% 4	582
	21st to end	Night	8% 2 13% 42% 33% 2	657
August	1st to 10th	Night	8% 1 12% 43% 32% 4	597
	11th to 20th	Night	10% 1 15% 36% 34% 4	594
	21st to end	Night	9% 2 13% 38% 34% 4	660
September	1st to 10th	Night	14% 5% 15% 33% 28% 5%	726
	11th to 20th	Night	10% 3 13% 34% 35% 5%	800
	21st to end	Night	16% 5% 20% 33% 22% 3	800
October	1st to 10th	Night	14% 6% 23% 33% 22% 2	800
	11th to 20th	Night	20% 12% 29% 28% 10% 2	800
	21st to end	Night	23% 12% 29% 29% 8%	880
November	1st to 10th	Night	16% 11% 32% 29% 10% 2	820
	11th to 20th	Night	22% 15% 31% 23% 7% 1	840
	21st to end	Night	27% 12% 32% 23% 6%	840
December	1st to 10th	Night	24% 14% 35% 22% 5%	840
	11th to 20th	Night	26% 12% 36% 22% 4	845
	21st to end	Night	30% 13% 32% 22% 3	1155

Page generated at 2026-05-14 01:58:53. Version ac07

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