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 2024-11-05.

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	3 5% 2 5% 4 4 5% 4 7% 8% 53%	105062
	Night	2 4 2 5% 3 3 4 4 6% 8% 59%	102689
Transparency	Day	24% 8% 12% 22% 23% 10%	104813
	Night	21% 7% 13% 25% 25% 9%	102529
Seeing	Day	10% 20% 32% 25% 11% 2	15428
	Night	6% 16% 34% 29% 13% 2	25454

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	1 3 2 5% 3 3 3 4 6% 9% 60%	2538
	11th to 20th	Day	3 2 4 4 3 4 4 6% 7% 65%	2778
	21st to end	Day	8% 4 7% 3 3 4 4 6% 7% 55%	3146
February	1st to 10th	Day	5% 3 7% 3 3 3 3 5% 7% 59%	1716
	11th to 20th	Day	1 3 2 5% 4 2 4 4 5% 8% 64%	1849
	21st to end	Day	1 6% 3 7% 4 4 3 4 5% 6% 56%	1570
March	1st to 10th	Day	5% 3 7% 3 3 3 3 5% 7% 61%	3148
	11th to 20th	Day	2 12% 5% 7% 6% 5% 4 4 6% 7% 42%	3490
	21st to end	Day	1 6% 3 7% 4 4 4 4 6% 8% 54%	4031
April	1st to 10th	Day	2 7% 2 5% 4 4 4 4 5% 8% 56%	2280
	11th to 20th	Day	3 8% 4 7% 4 4 4 3 5% 7% 50%	2251
	21st to end	Day	4 9% 3 6% 5% 5% 4 4 7% 7% 46%	2280
May	1st to 10th	Day	5% 11% 3 6% 4 4 4 4 5% 7% 48%	3861
	11th to 20th	Day	5% 7% 2 6% 4 4 5% 5% 7% 9% 44%	4281
	21st to end	Day	3 4 1 3 3 3 4 4 7% 9% 58%	4825
June	1st to 10th	Day	3 4 2 4 4 5% 5% 5% 8% 11% 49%	2660
	11th to 20th	Day	3 3 1 4 3 4 4 5% 7% 7% 58%	2660
	21st to end	Day	3 5% 1 5% 4 5% 7% 6% 9% 8% 47%	2660
July	1st to 10th	Day	3 4 1 4 4 5% 5% 6% 9% 9% 50%	4430
	11th to 20th	Day	3 3 1 7% 6% 8% 8% 7% 9% 9% 39%	4430
	21st to end	Day	5% 4 2 6% 5% 6% 7% 5% 9% 9% 42%	4517
August	1st to 10th	Day	4 4 2 7% 6% 8% 9% 7% 9% 10% 34%	4032
	11th to 20th	Day	3 3 1 4 4 5% 6% 6% 9% 11% 48%	3726
	21st to end	Day	6% 5% 2 6% 5% 6% 6% 6% 9% 10% 39%	4180
September	1st to 10th	Day	5% 5% 2 6% 4 4 6% 5% 7% 8% 49%	2280
	11th to 20th	Day	5% 3 2 4 3 3 3 4 6% 7% 61%	2267
	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 3 3 5% 7% 68%	1709
	11th to 20th	Day	3 1 4 2 2 4 3 5% 7% 68%	1710
	21st to end	Day	1 4 1 4 3 3 3 3 5% 7% 65%	1681
December	1st to 10th	Day	1 3 2 5% 3 3 4 2 5% 7% 66%	1520
	11th to 20th	Day	1 4 2 5% 3 2 3 3 8% 10% 61%	1926
	21st to end	Day	4 3 7% 4 3 3 3 6% 7% 60%	2794
January	1st to 10th	Night	2 2 7% 4 4 4 3 6% 7% 59%	4417
	11th to 20th	Night	2 1 4 3 3 4 4 5% 7% 66%	4206
	21st to end	Night	4 2 7% 5% 4 4 3 5% 8% 57%	4521
February	1st to 10th	Night	1 4 2 7% 4 3 3 3 4 6% 64%	2461
	11th to 20th	Night	1 5% 2 5% 5% 3 3 4 4 7% 62%	2218
	21st to end	Night	4 2 5% 4 3 3 3 5% 7% 64%	1884
March	1st to 10th	Night	1 6% 2 6% 2 3 3 3 4 6% 64%	3713
	11th to 20th	Night	2 10% 3 6% 4 3 4 4 5% 6% 53%	3490
	21st to end	Night	1 5% 2 6% 4 4 4 3 5% 7% 60%	3614
April	1st to 10th	Night	1 4 2 5% 3 2 3 3 6% 7% 65%	1900
	11th to 20th	Night	3 7% 1 6% 3 3 4 4 5% 7% 57%	1877
	21st to end	Night	4 7% 2 5% 4 4 3 4 5% 8% 54%	1900
May	1st to 10th	Night	4 7% 2 6% 4 4 4 3 4 5% 57%	3106
	11th to 20th	Night	7% 7% 2 6% 4 3 3 4 5% 8% 50%	2620
	21st to end	Night	4 3 1 4 3 3 4 3 5% 7% 64%	2762
June	1st to 10th	Night	3 4 2 5% 3 4 3 5% 6% 9% 56%	1520
	11th to 20th	Night	1 3 2 4 3 2 3 4 6% 7% 65%	1520
	21st to end	Night	2 4 2 5% 4 5% 5% 6% 7% 8% 52%	1520
July	1st to 10th	Night	3 3 1 5% 4 6% 5% 6% 8% 8% 50%	2540
	11th to 20th	Night	2 3 1 4 4 5% 7% 7% 11% 12% 44%	2540
	21st to end	Night	3 4 1 5% 5% 6% 6% 5% 8% 11% 46%	3041
August	1st to 10th	Night	4 5% 2 8% 6% 7% 7% 6% 10% 12% 33%	2904
	11th to 20th	Night	3 2 1 4 4 4 6% 5% 10% 14% 46%	3113
	21st to end	Night	3 6% 2 6% 5% 5% 6% 6% 9% 13% 39%	3487
September	1st to 10th	Night	5% 4 2 5% 4 4 4 4 6% 9% 52%	1900
	11th to 20th	Night	5% 4 1 3 2 3 4 4 5% 7% 61%	1911
	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 3 2 2 3 3 4 7% 72%	2457
	11th to 20th	Night	2 1 3 2 2 3 2 3 6% 74%	2470
	21st to end	Night	2 5% 2 3 2 3 3 3 5% 7% 66%	2496
December	1st to 10th	Night	1 3 1 4 3 3 3 2 6% 8% 67%	2660
	11th to 20th	Night	1 4 3 4 3 3 3 3 6% 9% 61%	3271
	21st to end	Night	4 2 5% 4 3 3 4 6% 8% 61%	4873

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	19% 5% 15% 30% 27% 5%	2539
	11th to 20th	Day	15% 7% 15% 33% 24% 6%	2778
	21st to end	Day	25% 7% 11% 29% 22% 6%	3146
February	1st to 10th	Day	22% 4 14% 30% 20% 9%	1716
	11th to 20th	Day	19% 6% 12% 26% 29% 9%	1859
	21st to end	Day	25% 5% 11% 21% 25% 13%	1570
March	1st to 10th	Day	20% 6% 9% 17% 36% 12%	3148
	11th to 20th	Day	34% 9% 10% 27% 17% 3	3490
	21st to end	Day	23% 7% 11% 34% 21% 3	4031
April	1st to 10th	Day	25% 7% 12% 21% 23% 12%	2280
	11th to 20th	Day	32% 5% 11% 23% 19% 10%	2254
	21st to end	Day	32% 8% 11% 22% 21% 6%	2280
May	1st to 10th	Day	30% 9% 10% 18% 21% 12%	3861
	11th to 20th	Day	31% 9% 13% 23% 17% 7%	4285
	21st to end	Day	19% 8% 8% 20% 26% 19%	4825
June	1st to 10th	Day	24% 10% 15% 20% 20% 10%	2660
	11th to 20th	Day	20% 8% 11% 17% 24% 21%	2660
	21st to end	Day	27% 10% 12% 21% 20% 11%	2660
July	1st to 10th	Day	24% 10% 12% 15% 18% 21%	4361
	11th to 20th	Day	32% 11% 14% 25% 12% 6%	4355
	21st to end	Day	30% 11% 16% 19% 13% 11%	4375
August	1st to 10th	Day	37% 14% 20% 16% 9% 4	4018
	11th to 20th	Day	26% 11% 17% 17% 17% 12%	3762
	21st to end	Day	34% 11% 17% 17% 18% 4	4179
September	1st to 10th	Day	29% 8% 12% 21% 20% 10%	2280
	11th to 20th	Day	21% 7% 11% 17% 29% 14%	2267
	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	14% 5% 10% 21% 38% 12%	1709
	11th to 20th	Day	14% 5% 9% 33% 30% 8%	1710
	21st to end	Day	19% 6% 9% 22% 30% 14%	1681
December	1st to 10th	Day	18% 6% 16% 28% 23% 8%	1520
	11th to 20th	Day	16% 7% 15% 26% 28% 8%	1924
	21st to end	Day	21% 7% 12% 24% 22% 14%	2794
January	1st to 10th	Night	22% 6% 12% 27% 28% 6%	4417
	11th to 20th	Night	16% 4 13% 34% 27% 5%	4206
	21st to end	Night	20% 9% 15% 29% 22% 5%	4521
February	1st to 10th	Night	22% 4 13% 30% 22% 9%	2461
	11th to 20th	Night	23% 5% 12% 27% 27% 7%	2218
	21st to end	Night	20% 4 9% 24% 31% 12%	1884
March	1st to 10th	Night	19% 5% 9% 20% 37% 10%	3713
	11th to 20th	Night	28% 7% 11% 29% 21% 4	3490
	21st to end	Night	22% 6% 15% 33% 22% 2	3614
April	1st to 10th	Night	18% 6% 14% 26% 26% 9%	1900
	11th to 20th	Night	26% 5% 11% 26% 25% 7%	1877
	21st to end	Night	27% 6% 14% 28% 21% 5%	1900
May	1st to 10th	Night	25% 6% 11% 22% 24% 12%	3106
	11th to 20th	Night	30% 6% 15% 27% 15% 7%	2621
	21st to end	Night	19% 7% 10% 21% 31% 12%	2762
June	1st to 10th	Night	22% 9% 16% 23% 17% 14%	1520
	11th to 20th	Night	16% 7% 10% 22% 24% 20%	1520
	21st to end	Night	25% 10% 13% 19% 20% 12%	1520
July	1st to 10th	Night	25% 10% 12% 18% 19% 16%	2500
	11th to 20th	Night	24% 10% 23% 28% 10% 4	2492
	21st to end	Night	26% 13% 17% 22% 17% 5%	2946
August	1st to 10th	Night	37% 14% 21% 16% 8% 4	2895
	11th to 20th	Night	26% 11% 24% 15% 16% 6%	3143
	21st to end	Night	33% 12% 17% 22% 14% 3	3487
September	1st to 10th	Night	25% 8% 16% 23% 20% 8%	1900
	11th to 20th	Night	20% 6% 12% 21% 27% 14%	1911
	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	12% 5% 10% 27% 33% 14%	2457
	11th to 20th	Night	12% 5% 9% 33% 31% 10%	2470
	21st to end	Night	17% 5% 10% 23% 33% 12%	2496
December	1st to 10th	Night	16% 6% 16% 29% 24% 9%	2660
	11th to 20th	Night	17% 8% 14% 24% 30% 7%	3272
	21st to end	Night	19% 7% 14% 25% 23% 12%	4873

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% 26% 28% 21% 7% 1	270
	11th to 20th	Day	17% 30% 35% 16% 2	270
	21st to end	Day	5% 26% 42% 19% 8% 1	297
February	1st to 10th	Day	12% 37% 37% 11% 1 1	270
	11th to 20th	Day	15% 36% 37% 9% 3 1	270
	21st to end	Day	23% 33% 32% 11%	225
March	1st to 10th	Day	15% 33% 29% 19% 4	275
	11th to 20th	Day	14% 31% 36% 15% 4	460
	21st to end	Day	18% 39% 32% 9% 2	506
April	1st to 10th	Day	18% 35% 33% 11% 3 1	460
	11th to 20th	Day	20% 36% 33% 10% 2	452
	21st to end	Day	17% 35% 32% 13% 3	460
May	1st to 10th	Day	15% 32% 33% 15% 4 1	498
	11th to 20th	Day	10% 16% 39% 23% 10% 1	675
	21st to end	Day	10% 21% 31% 27% 10% 2	734
June	1st to 10th	Day	4 14% 31% 32% 16% 2	680
	11th to 20th	Day	5% 16% 35% 28% 12% 3	680
	21st to end	Day	5% 13% 35% 27% 16% 3	680
July	1st to 10th	Day	7% 5% 27% 37% 19% 5%	671
	11th to 20th	Day	5% 3 20% 39% 26% 6%	668
	21st to end	Day	6% 3 18% 41% 26% 5%	568
August	1st to 10th	Day	8% 5% 25% 38% 19% 5%	487
	11th to 20th	Day	6% 5% 30% 40% 16% 4	477
	21st to end	Day	9% 6% 27% 38% 16% 3	539
September	1st to 10th	Day	7% 9% 29% 34% 16% 4	490
	11th to 20th	Day	6% 13% 37% 29% 12% 2	477
	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	282
	11th to 20th	Day	8% 27% 35% 20% 9% 1	270
	21st to end	Day	6% 26% 36% 27% 4 1	270
December	1st to 10th	Day	16% 26% 34% 18% 6% 1	270
	11th to 20th	Day	7% 39% 34% 14% 6%	270
	21st to end	Day	14% 34% 35% 14% 2	297
January	1st to 10th	Night	5% 26% 34% 25% 8% 1	950
	11th to 20th	Night	6% 27% 39% 20% 6% 2	817
	21st to end	Night	3 20% 44% 26% 7%	836
February	1st to 10th	Night	4 24% 51% 18% 4	760
	11th to 20th	Night	5% 28% 44% 17% 5%	744
	21st to end	Night	5% 25% 52% 17% 2	628
March	1st to 10th	Night	5% 28% 42% 20% 5% 1	760
	11th to 20th	Night	7% 16% 40% 28% 9% 1	760
	21st to end	Night	7% 24% 42% 23% 4	712
April	1st to 10th	Night	9% 20% 47% 22% 2	570
	11th to 20th	Night	12% 17% 40% 25% 6%	563
	21st to end	Night	10% 21% 34% 28% 7%	570
May	1st to 10th	Night	10% 13% 40% 29% 7% 1	570
	11th to 20th	Night	11% 10% 33% 32% 12% 2	561
	21st to end	Night	9% 16% 31% 29% 13% 1	617
June	1st to 10th	Night	4 9% 27% 39% 18% 2	570
	11th to 20th	Night	2 11% 34% 39% 13% 1	570
	21st to end	Night	3 5% 29% 38% 23% 2	570
July	1st to 10th	Night	7% 2 17% 40% 30% 3	555
	11th to 20th	Night	5% 1 12% 41% 34% 7%	552
	21st to end	Night	7% 2 10% 36% 39% 6%	624
August	1st to 10th	Night	5% 4 13% 39% 35% 4	567
	11th to 20th	Night	5% 3 15% 43% 30% 3	564
	21st to end	Night	7% 2 15% 41% 31% 4	627
September	1st to 10th	Night	5% 4 17% 44% 25% 5%	570
	11th to 20th	Night	6% 7% 25% 37% 21% 4	570
	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% 37% 30% 10% 1	937
	11th to 20th	Night	5% 20% 40% 25% 9% 2	950
	21st to end	Night	6% 17% 40% 28% 8% 1	950
December	1st to 10th	Night	6% 23% 39% 25% 6% 1	950
	11th to 20th	Night	5% 25% 41% 20% 8%	950
	21st to end	Night	7% 27% 42% 20% 4 1	1045

Page generated at 2024-11-03 00:11:21. Version ac07

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