Lazy J Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lazy J Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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	2 4 2 5% 4 4 5% 4 7% 8% 54%	134820
	Night	2 4 2 5% 3 4 4 4 6% 8% 60%	131683
Transparency	Day	24% 8% 11% 22% 24% 11%	129802
	Night	20% 7% 12% 24% 27% 10%	127706
Seeing	Day	10% 20% 32% 25% 11% 2	16650
	Night	6% 16% 35% 29% 12% 2	26613

By Month

Percentage Cloud Cover SW (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	3 2 7% 3 3 3 3 5% 8% 62%	3638
	11th to 20th	Day	2 1 4 4 4 5% 4 5% 7% 65%	3990
	21st to end	Day	6% 3 6% 3 3 3 3 5% 7% 60%	4510
February	1st to 10th	Day	5% 3 6% 3 3 3 3 6% 7% 60%	1807
	11th to 20th	Day	1 3 2 5% 4 2 4 4 5% 8% 63%	1949
	21st to end	Day	1 6% 2 7% 4 4 3 4 5% 6% 58%	1650
March	1st to 10th	Day	4 3 7% 4 4 4 3 5% 6% 60%	4518
	11th to 20th	Day	1 9% 4 8% 6% 6% 5% 4 7% 7% 43%	5000
	21st to end	Day	1 4 2 6% 4 3 4 4 6% 10% 57%	5783
April	1st to 10th	Day	2 7% 2 5% 4 4 4 4 5% 8% 56%	2400
	11th to 20th	Day	3 8% 4 7% 4 4 4 3 5% 7% 51%	2371
	21st to end	Day	4 8% 3 6% 5% 5% 4 4 7% 8% 47%	2400
May	1st to 10th	Day	5% 10% 3 7% 5% 5% 5% 4 6% 8% 43%	5529
	11th to 20th	Day	3 6% 2 5% 4 4 5% 4 7% 8% 52%	6152
	21st to end	Day	2 3 1 4 3 4 5% 5% 8% 10% 55%	6925
June	1st to 10th	Day	3 4 2 4 4 5% 5% 6% 8% 11% 48%	2800
	11th to 20th	Day	3 3 1 4 3 4 4 5% 7% 7% 58%	2800
	21st to end	Day	3 5% 1 5% 4 5% 7% 6% 9% 8% 48%	2800
July	1st to 10th	Day	2 3 1 4 3 5% 5% 5% 8% 9% 54%	6339
	11th to 20th	Day	2 3 1 6% 6% 8% 9% 7% 9% 9% 40%	6340
	21st to end	Day	4 4 2 7% 6% 7% 8% 6% 9% 9% 38%	6492
August	1st to 10th	Day	3 3 2 6% 5% 7% 9% 7% 10% 12% 37%	5695
	11th to 20th	Day	2 3 1 5% 5% 5% 7% 6% 9% 12% 47%	5366
	21st to end	Day	5% 5% 2 7% 5% 6% 6% 5% 9% 10% 39%	5984
September	1st to 10th	Day	5% 5% 2 6% 4 4 6% 5% 7% 8% 49%	2400
	11th to 20th	Day	4 3 2 4 3 3 3 4 6% 7% 60%	2364
	21st to end	Day	4 3 1 5% 3 3 4 3 4 5% 65%	2090
October	1st to 10th	Day	3 3 1 3 3 3 3 2 3 5% 72%	3179
	11th to 20th	Day	2 3 2 4 3 4 4 4 6% 8% 60%	3150
	21st to end	Day	2 4 1 3 2 2 2 3 4 6% 73%	3417
November	1st to 10th	Day	1 3 2 4 2 3 2 3 5% 7% 68%	1763
	11th to 20th	Day	3 1 4 2 2 3 3 5% 7% 69%	1800
	21st to end	Day	1 4 1 4 3 3 3 3 5% 7% 66%	1769
December	1st to 10th	Day	2 2 4 2 3 3 2 4 5% 73%	2620
	11th to 20th	Day	3 1 3 2 2 3 3 7% 9% 67%	3026
	21st to end	Day	3 2 6% 4 3 3 3 6% 7% 61%	4004
January	1st to 10th	Night	2 2 8% 4 4 4 3 5% 8% 60%	6327
	11th to 20th	Night	2 1 3 3 3 4 4 5% 7% 68%	6018
	21st to end	Night	3 2 5% 4 4 4 3 5% 6% 64%	6468
February	1st to 10th	Night	1 4 2 6% 3 3 3 3 4 6% 65%	2590
	11th to 20th	Night	1 4 2 5% 5% 3 4 4 5% 7% 62%	2338
	21st to end	Night	4 2 5% 4 3 3 3 5% 7% 65%	1980
March	1st to 10th	Night	5% 2 6% 3 3 3 3 4 5% 64%	5340
	11th to 20th	Night	1 7% 2 5% 4 4 4 3 5% 6% 58%	5000
	21st to end	Night	1 4 2 5% 3 4 4 3 5% 6% 64%	5177
April	1st to 10th	Night	1 4 2 5% 3 2 3 3 6% 7% 64%	2000
	11th to 20th	Night	3 7% 1 6% 3 3 3 3 5% 7% 58%	1977
	21st to end	Night	3 7% 2 5% 4 4 3 4 5% 8% 55%	2000
May	1st to 10th	Night	3 6% 2 8% 5% 5% 5% 4 6% 7% 50%	4448
	11th to 20th	Night	5% 5% 2 5% 3 2 3 3 4 8% 60%	3759
	21st to end	Night	3 4 2 5% 3 4 4 3 5% 7% 60%	3972
June	1st to 10th	Night	3 4 2 5% 3 4 4 5% 6% 9% 56%	1600
	11th to 20th	Night	1 2 2 4 3 3 3 4 6% 8% 65%	1600
	21st to end	Night	2 4 2 5% 4 5% 5% 6% 7% 8% 52%	1600
July	1st to 10th	Night	2 2 1 4 4 5% 5% 5% 8% 9% 55%	3640
	11th to 20th	Night	2 3 1 4 4 5% 8% 8% 11% 12% 43%	3640
	21st to end	Night	2 4 1 6% 5% 6% 7% 6% 9% 11% 42%	4376
August	1st to 10th	Night	3 3 2 6% 5% 6% 7% 6% 8% 10% 44%	4114
	11th to 20th	Night	2 2 1 4 4 4 6% 5% 10% 14% 48%	4483
	21st to end	Night	4 6% 2 7% 5% 5% 7% 6% 9% 12% 37%	4993
September	1st to 10th	Night	5% 4 2 5% 4 4 4 4 6% 9% 53%	2000
	11th to 20th	Night	5% 4 1 4 2 3 4 4 5% 7% 61%	1991
	21st to end	Night	4 4 2 4 3 3 3 3 6% 5% 65%	2090
October	1st to 10th	Night	3 2 1 2 2 2 3 2 3 4 75%	3789
	11th to 20th	Night	2 3 1 5% 3 4 3 3 5% 7% 64%	3778
	21st to end	Night	2 3 1 3 1 2 2 2 3 5% 75%	4120
November	1st to 10th	Night	1 2 1 4 2 2 3 3 5% 7% 70%	2522
	11th to 20th	Night	2 1 3 2 3 3 2 3 6% 75%	2600
	21st to end	Night	1 5% 2 3 2 3 3 3 5% 7% 67%	2628
December	1st to 10th	Night	2 1 4 2 2 2 2 4 6% 76%	4570
	11th to 20th	Night	1 3 2 3 2 2 2 3 4 8% 71%	5181
	21st to end	Night	3 2 6% 4 4 3 4 6% 8% 61%	6974

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	20% 4 11% 29% 28% 9%	3639
	11th to 20th	Day	16% 6% 11% 24% 25% 18%	3990
	21st to end	Day	22% 6% 8% 25% 25% 13%	4510
February	1st to 10th	Day	22% 5% 14% 29% 20% 11%	1807
	11th to 20th	Day	19% 6% 12% 26% 29% 8%	1959
	21st to end	Day	24% 5% 10% 20% 25% 16%	1650
March	1st to 10th	Day	19% 6% 8% 14% 34% 20%	4518
	11th to 20th	Day	33% 9% 8% 22% 23% 5%	5000
	21st to end	Day	19% 7% 10% 43% 18% 3	5783
April	1st to 10th	Day	25% 7% 11% 22% 23% 12%	2400
	11th to 20th	Day	31% 5% 11% 23% 20% 11%	2374
	21st to end	Day	31% 8% 12% 23% 21% 6%	2400
May	1st to 10th	Day	32% 10% 11% 20% 18% 9%	5529
	11th to 20th	Day	25% 8% 11% 21% 24% 11%	6156
	21st to end	Day	19% 9% 10% 20% 28% 15%	6926
June	1st to 10th	Day	25% 10% 15% 20% 20% 9%	2800
	11th to 20th	Day	19% 8% 11% 16% 24% 22%	2800
	21st to end	Day	27% 10% 12% 20% 20% 12%	2800
July	1st to 10th	Day	21% 9% 11% 15% 20% 24%	6271
	11th to 20th	Day	31% 12% 16% 23% 12% 5%	6265
	21st to end	Day	35% 11% 16% 16% 14% 8%	6306
August	1st to 10th	Day	36% 14% 19% 17% 9% 4	4146
	11th to 20th	Day	26% 11% 17% 17% 17% 11%	3882
	21st to end	Day	34% 11% 17% 17% 18% 4	4311
September	1st to 10th	Day	28% 8% 12% 22% 20% 10%	2400
	11th to 20th	Day	21% 7% 11% 17% 30% 14%	2364
	21st to end	Day	22% 5% 7% 23% 33% 10%	2090
October	1st to 10th	Day	16% 5% 6% 15% 37% 21%	3179
	11th to 20th	Day	18% 7% 9% 28% 28% 9%	3150
	21st to end	Day	13% 4 6% 22% 40% 15%	3417
November	1st to 10th	Day	15% 5% 10% 21% 37% 12%	1763
	11th to 20th	Day	13% 5% 9% 32% 31% 10%	1800
	21st to end	Day	19% 6% 9% 22% 30% 14%	1769
December	1st to 10th	Day	13% 5% 10% 25% 36% 10%	2620
	11th to 20th	Day	13% 6% 11% 30% 32% 10%	3024
	21st to end	Day	18% 7% 9% 27% 25% 13%	4004
January	1st to 10th	Night	20% 5% 10% 29% 28% 8%	6327
	11th to 20th	Night	14% 4 10% 27% 30% 15%	6018
	21st to end	Night	17% 7% 11% 25% 24% 16%	6468
February	1st to 10th	Night	21% 4 13% 29% 23% 10%	2590
	11th to 20th	Night	22% 5% 12% 27% 27% 7%	2338
	21st to end	Night	19% 4 9% 24% 31% 13%	1980
March	1st to 10th	Night	19% 6% 7% 15% 37% 16%	5340
	11th to 20th	Night	24% 7% 8% 22% 32% 7%	5000
	21st to end	Night	18% 6% 13% 41% 19% 2	5177
April	1st to 10th	Night	19% 6% 14% 27% 26% 8%	2000
	11th to 20th	Night	25% 5% 11% 25% 26% 7%	1977
	21st to end	Night	26% 6% 14% 28% 21% 5%	2000
May	1st to 10th	Night	28% 8% 13% 26% 18% 8%	4445
	11th to 20th	Night	23% 5% 11% 29% 25% 8%	3760
	21st to end	Night	21% 8% 12% 18% 30% 11%	3972
June	1st to 10th	Night	22% 9% 16% 24% 17% 13%	1600
	11th to 20th	Night	16% 7% 10% 22% 24% 21%	1600
	21st to end	Night	25% 10% 13% 19% 21% 13%	1600
July	1st to 10th	Night	21% 8% 12% 18% 26% 15%	3600
	11th to 20th	Night	26% 11% 25% 25% 9% 3	3592
	21st to end	Night	31% 12% 17% 18% 16% 6%	4251
August	1st to 10th	Night	36% 14% 20% 17% 9% 4	2987
	11th to 20th	Night	26% 11% 24% 16% 16% 6%	3243
	21st to end	Night	33% 12% 17% 22% 14% 2	3597
September	1st to 10th	Night	25% 8% 16% 25% 20% 7%	2000
	11th to 20th	Night	21% 6% 12% 21% 27% 13%	1991
	21st to end	Night	20% 6% 9% 24% 34% 7%	2090
October	1st to 10th	Night	13% 5% 9% 22% 37% 14%	3789
	11th to 20th	Night	19% 7% 10% 25% 30% 9%	3778
	21st to end	Night	14% 4 5% 25% 38% 14%	4120
November	1st to 10th	Night	14% 5% 10% 27% 32% 13%	2522
	11th to 20th	Night	12% 5% 8% 32% 32% 11%	2600
	21st to end	Night	17% 5% 10% 23% 33% 12%	2628
December	1st to 10th	Night	12% 4 9% 29% 36% 9%	4570
	11th to 20th	Night	12% 6% 9% 26% 37% 9%	5182
	21st to end	Night	19% 6% 13% 22% 28% 12%	6974

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	17% 25% 29% 21% 6% 1	300
	11th to 20th	Day	16% 29% 36% 16% 2	300
	21st to end	Day	5% 27% 42% 18% 7% 1	330
February	1st to 10th	Day	12% 38% 35% 13% 1 1	300
	11th to 20th	Day	15% 36% 37% 8% 3 1	300
	21st to end	Day	20% 33% 33% 12% 1	249
March	1st to 10th	Day	15% 33% 27% 22% 3	305
	11th to 20th	Day	16% 31% 35% 15% 3	500
	21st to end	Day	18% 38% 33% 9% 2	550
April	1st to 10th	Day	17% 35% 33% 11% 2 1	500
	11th to 20th	Day	21% 35% 32% 9% 1	492
	21st to end	Day	17% 34% 33% 13% 3	500
May	1st to 10th	Day	15% 31% 32% 16% 5% 1	540
	11th to 20th	Day	12% 17% 38% 22% 10% 1	725
	21st to end	Day	10% 21% 31% 27% 10% 2	789
June	1st to 10th	Day	4 14% 31% 32% 16% 2	730
	11th to 20th	Day	5% 16% 35% 28% 13% 3	730
	21st to end	Day	5% 14% 34% 27% 17% 3	730
July	1st to 10th	Day	7% 6% 28% 36% 19% 5%	721
	11th to 20th	Day	4 3 21% 40% 26% 6%	718
	21st to end	Day	6% 4 19% 40% 26% 5%	614
August	1st to 10th	Day	8% 5% 28% 36% 18% 5%	527
	11th to 20th	Day	6% 5% 28% 41% 17% 3	517
	21st to end	Day	9% 7% 27% 37% 16% 3	583
September	1st to 10th	Day	7% 9% 30% 35% 15% 4	530
	11th to 20th	Day	6% 14% 38% 29% 11% 2	510
	21st to end	Day	7% 14% 27% 31% 18% 3	300
October	1st to 10th	Day	10% 17% 25% 29% 16% 3	300
	11th to 20th	Day	9% 26% 30% 21% 10% 3	300
	21st to end	Day	13% 23% 34% 20% 9% 1	330
November	1st to 10th	Day	8% 29% 34% 21% 7% 1	300
	11th to 20th	Day	8% 26% 36% 20% 8% 1	300
	21st to end	Day	7% 25% 36% 27% 4 1	300
December	1st to 10th	Day	14% 24% 34% 20% 6% 1	300
	11th to 20th	Day	7% 36% 37% 15% 5%	300
	21st to end	Day	14% 32% 37% 14% 2	330
January	1st to 10th	Night	5% 26% 36% 24% 8% 1	1000
	11th to 20th	Night	5% 26% 41% 20% 6% 2	860
	21st to end	Night	3 20% 45% 25% 6%	880
February	1st to 10th	Night	4 22% 53% 18% 3	800
	11th to 20th	Night	5% 27% 47% 17% 5%	784
	21st to end	Night	5% 24% 52% 17% 2	660
March	1st to 10th	Night	5% 27% 43% 20% 5% 1	800
	11th to 20th	Night	7% 17% 41% 27% 8% 1	800
	21st to end	Night	6% 23% 44% 23% 3	749
April	1st to 10th	Night	9% 20% 48% 22% 2	600
	11th to 20th	Night	11% 18% 41% 25% 5%	593
	21st to end	Night	9% 20% 36% 27% 7%	600
May	1st to 10th	Night	9% 14% 40% 29% 7% 1	600
	11th to 20th	Night	10% 11% 35% 31% 12% 2	591
	21st to end	Night	8% 16% 32% 30% 13% 1	650
June	1st to 10th	Night	5% 9% 27% 39% 18% 2	600
	11th to 20th	Night	2 10% 34% 39% 13% 1	600
	21st to end	Night	4 5% 30% 38% 22% 2	600
July	1st to 10th	Night	7% 2 18% 41% 29% 3	585
	11th to 20th	Night	4 1 13% 42% 34% 7%	582
	21st to end	Night	7% 2 11% 36% 38% 6%	657
August	1st to 10th	Night	5% 3 15% 40% 34% 4	597
	11th to 20th	Night	5% 3 15% 44% 29% 3	594
	21st to end	Night	8% 3 15% 41% 30% 4	660
September	1st to 10th	Night	5% 4 18% 45% 24% 5%	600
	11th to 20th	Night	6% 7% 26% 37% 20% 4	594
	21st to end	Night	5% 10% 27% 38% 17% 3	570
October	1st to 10th	Night	6% 10% 33% 35% 13% 3	749
	11th to 20th	Night	3 13% 36% 33% 12% 3	760
	21st to end	Night	7% 15% 36% 28% 13% 2	836
November	1st to 10th	Night	3 19% 38% 29% 10% 1	962
	11th to 20th	Night	5% 20% 41% 24% 8% 2	1000
	21st to end	Night	6% 17% 41% 27% 8% 1	1000
December	1st to 10th	Night	6% 22% 39% 25% 7% 1	1000
	11th to 20th	Night	5% 24% 43% 20% 7%	1000
	21st to end	Night	7% 26% 42% 19% 4 1	1100

Page generated at 2025-09-15 23:49:13. Version ac07

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